Biologically Active Isoquinoline Alkaloids covering 2014-2018

Abstract

Isoquinoline alkaloids, an important class of N-based heterocyclic compounds, have attracted considerable attention from researchers worldwide since the early 19^th century. Over the past 200 years, many compounds from this class were isolated, and most of them and their analogs possess various bioactivities. In this review, we survey the updated literature on bioactive alkaloids and highlight research achievements of this alkaloid class during the period of 2014–2018. We reviewed over 400 molecules with a broad range of bioactivities, including antitumor, antidiabetic and its complications, antibacterial, antifungal, antiviral, antiparasitic, insecticidal, anti-inflammatory, antioxidant, neuroprotective, and other activities. This review should provide new indications or directions for the discovery of new and better drugs from the original naturally occurring isoquinoline alkaloids.

1. Introduction

Isoquinoline alkaloids, an important class of N-heterocyclic bioactive natural products, are common throughout the plant kingdom¹. They are likely derived from tyrosine or phenylalanine building blocks and show a wide range of structural diversity². Since the first bioactive isoquinoline alkaloid, morphine, was isolated from the opium plant in the early 19th century³, this compound class has attracted considerable scientific attention. Increasing numbers of isoquinoline alkaloids have been isolated and identified from natural sources, and various studies have reported their antitumor, antimalarial, antibacterial, antifungal, antiparasitic and insecticidal, antiviral, anti-inflammatory, antiplatelet and other activities^4-12. As lead compounds in the drug discovery and development process, isoquinoline alkaloids have high probabilities of success,¹³ as reflected by several revolutionary drugs, such as the analgesic morphine, the antibacterial berberine, the antitussive codeine¹⁴, the antirheumatic sinomenine¹⁵, and the acetylcholinesterase inhibitor galanthamine¹⁶ (Figure 1). Therefore, the search for novel isoquinolines as promising drug leads remains an active area of study in natural product chemistry.

Figure 1.

The chemical structures of five major isoquinoline molecules

In view of the importance and significant biological activities of isoquinoline alkaloid natural products, several thousand publications (journal articles, books and patents) on isoquinoline alkaloids have been recorded over the past 200 years. The increasing numbers of publications reflect the research intensity and importance of this field, as well as the bright prospect for drug development from these compounds. Some excellent earlier reviews on the chemical structures and biological properties of isolated isoquinoline alkaloids have contributed significantly to the general scientific understanding of this kind of compounds^{5,6,8,9,10,11,12,17-21}. However, during the past five years, significant studies and novel technologies, such as metabolomics, were widely reported and used to identify alkaloids from plants. Many new compounds were isolated, and novel pharmacological activities and comprehensive mechanism of actions were investigated by researchers worldwide. Hence, a more comprehensive and up-to-date review is merited. Therefore, this review combines newer literature reports as well as presents the developments in this field particularly from the perspective of biological activities. It covers not only the chemical structures of isolated isoquinoline alkaloids (Table 1), but also their biological activities and mechanism of actions. We hope that this review will provide new indications or directions for the development of these compounds as new clinically useful therapeutic agents.

Table 1.

Isolated isoquinoline alkaloids between 2014 to 2018

No.	Names	Species	Year	Ref.
Simple isoquinoline alkaloids
1	3,8-Diolisoquinoline	Scolopendra subspinipes mutilans		22
2	1-Methoxy-4,5-diolisoquinoline	Scolopendra subspinipes mutilans		22
3	1,5-Dihydroxy-4-methoxyisoquinoline	Centipede species		23
4	Carnegine	Hammada scoparia		24
5	N-Methylisosalsoline	Hammada scoparia		24
6	N-Methylcorydaldine	Fumaria officinalis Michelia champaca		25 27
7	6,7-Dimethoxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid	Mucuna pruriens		26
8	7-Methoxy-1,2,3,4-tetrahydroisoquinolin-1-one, thalifoline	Michelia champaca		27
9	Thalifoline	Corydalis tomentella Plumula nelumbinis		27-30
10	Corydaldine	Corydalis tomentella Corydalis hendersonii		27-30
11	Oxohydrastinine	Corydalis tomentella		28
12	6,7-Methylenedioxy-1(2H)-isoquinolinone	Corydalis tomentella		28
		Corydalis hendersonii		29
13	Oxyhydrastinine	Corydalis hendersonii		29
14	6,7-Dihydroxy-1-methyl-3,4-dihydroisoquinolone,	Portulaca oleracea		31
15	(S)-(−)-Salsolinol	Portulaca oleracea		31
16	6,7-Dihydroxy-3,4-dihydroisoquinolone	Portulaca oleracea		31
17	(R)-(+)-1-Isobutyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline	Portulaca oleracea		31
18	Ealaine A	Ancistrocladus ealaensis		32
19	Ealaine B	Ancistrocladus ealaensis		32
20	Ealaine C	Ancistrocladus ealaensis		32
21	Ealaine D	Ancistrocladus ealaensis		32
22	Noroxyhydrastinine	Phellodendron amurense		33
Benzylisoquinoline alkaloids
23	Reticuline	Litsea cubeba Cryptocarya densiflora, Cryptocarya infectoria, Cryptocarya griffithiana Unonopsis floribunda Dehaasia longipedicellata Bocageopsis pleiosperma		34 35 36 37 38 39
24	(+)-N-Methylisococlaurine	Cryptocarya species Plumula nelumbinis		37 30
25	(−)-N-Methylcoclaurine	Sinomenium acutum Plumula nelumbinis		40 30
26	Berbithine	Coptis chinensis		41
27	6-([1,3]Dioxolo[4,5-g]isoquinoline-5-carbonyl)-2,3-dimethoxybenzoic acid methyl ester	Coptis chinensis		41
28	Norcolaurine-4′-O-glucoside	Plumula nelumbinis		30
29	N-Methylhigenamine	Plumula nelumbinis		30
30	Norcoclaurine-6-O-glucoside	Plumula nelumbinis		30
31	Norcoclaurine	Plumula nelumbinis		30
32	Argemexirine	Plumula nelumbinis		30
33	Lotusine	Plumula nelumbinis		30
34	Isococlaurine	Plumula nelumbinis		30
35	Armepavine	Plumula nelumbinis		30
36	6-Demethy-4′-methyl-N-methylcoclaurine	Plumula nelumbinis		30
37	Coclaurine	Plumula nelumbinis		30
38	N-Nor-O-methylarmepavine	Plumula nelumbinis		30
39	Isococlaurine-5′-O-pentoside	Plumula nelumbinis		30
40	Coclaurine-5′-O-pentoside	Plumula nelumbinis		30
41	Juzirine	Leonurus japonicus		42
42	(R)-(+)-1-Benzyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline	Portulaca oleracea		31
43	Laudanosine	Thalictrum cirrhosum		31
44	Pseudolaudanine	Thalictrum cirrhosum		43
45	Rugosinone	Thalictrum cirrhosum		43
46	Hendersine B methyl ester	Corydalis tomentella		28
47	Bicucullinine	Corydalis tomentella		28
48	Hendersine B	Corydalis tomentella		28
49	6,6′,7′,12-Tetramethoxy-5′-hydroxy-2,2′-dimethyloxycanthan	Thalictrum foliolosum		44
50	6,5′,6′,7′,12-Pentamethoxy-2,2′-dimethoxyethane	Thalictrum foliolosum		44
51	Hernandezine	Thalictrum flavum		45
52	6,7,12-Trimethoxy-2-methyl-13-hydroxy-11-(4′-formylphenoxy) benzylisoquinoline	Thalictrum wangii		46
53	5,6-(Methylenedioxy)-7,12-dimethoxy-2-methyl-10-(4′-formylphenoxy) benzylisoquinoline	Thalictrum wangii		46
54	Tiliamosine	Thalictrum racemosa		47
55	(−)-Pseudocurine	Stephania abyssinica		48
56	(−)-Pseudoisocurine	Stephania abyssinica		48
57	Tetrandrine	Stephania tetrandra		49
58	Tangchinoline	Stephania tetrandra		49
59	(−)-O-O-Dimethylgrisabine	Dehaasia longipedicellata		38
60	Berbamine	Mahonia aquifolium		50
61	Neferine	Nelumbo nucifera Plumula nelumbinis		59 30
62	Liensinine	Plumula nelumbinis		30
63	Isoliensinine	Plumula nelumbinis		30
64	Norisoliensinine	Plumula nelumbinis		30
65	6-Hydroxynorisoliensinine	Plumula nelumbinis		30
66	(−)-Gyrolidine	Alseodaphne corneri		60
67	(+)-O-Methyllimacusine	Alseodaphne corneri		60
68	(+)-2-Norobaberine	Alseodaphne corneri		60
69	Norstephasubine	Alseodaphne corneri		60
70	(+)-Stephasubine	Alseodaphne corneri		60
71	Coptichic aldehyde	Coptidis Rhizoma- Euodiae Fructus couple		61
72	Fumaranine	Fumaria officinalis		24
73	(−)-Fumaricine	Fumaria officinalis		24
74	(+)-Dihydrofumariline	Fumaria officinalis		24
75	(−)-Fumaritine	Fumaria officinalis		24
76	(−)-O-Methylfumarophycine	Fumaria officinalis		24
77	(−)-Fumarophycine	Fumaria officinalis		24
78	(+)-Fumariline	Fumaria officinalis		24
79	(+)-Parfumidine	Fumaria officinalis		24
80	(+)-Parfumine	Fumaria officinalis		24
81	Hendersine C	Corydalis hendersonii		29
82	Hendersine D	Corydalis hendersonii		29
83	Hendersine E	Corydalis hendersonii		29
84	Hendersine F	Corydalis hendersonii		29
Aporphine alkaloids
85	Boldine	Litsea cubeba Dehaasia longipedicellata		67 60, 38
86	(−)-Norboldine	Dehaasia longipedicellata		38
87	(+)-Laurotetanine	Alseodaphne corneri		68
		Cryptocarya densiflora, Cryptocarya infectoria Cryptocarya griffithiana Bocageopsis pleiosperma		37 39
88	(+)-Nornantenine	Cryptocarya densiflora, Cryptocarya infectoria Cryptocarya griffithiana		37
89	(+)-N-Methyllaurotetanine	Cryptocarya densiflora, Cryptocarya infectoria Cryptocarya griffithiana Thalictrum cirrhosum Bocageopsis pleiosperma		37 43 39
90	Corydine	Croton echinocarpus		69
91	Norisoboldine	Croton echinocarpus		69
92	Isocorydine	Alseodaphne corneri		60
93	Norisocorydine	Alseodaphne corneri		60
		Unonopsis floribunda		35, 36
94	1,2-Methylenedioxy-3-methoxyaporphine	Aconitum carmichaelii		70
95	N-Formyl-asimilobine-2-O-β-D-glucoside	Stephania succifera		71
96	Isoboldine	Annona hypoglauca		72
		Bocageopsis pleiosperma		39
97	Anonaine	Annona hypoglauca		72
		Plumula nelumbinis		30
		Unonopsis floribunda		35, 36
		Unonopsis duckei		75
		Bocageopsis pleiosperma		39
98	Nornuciferine	Annona hypoglauca		72
		Plumula nelumbinis		30
		Unonopsis floribunda		35, 36
		Unonopsis duckei		75
99	Actinodaphnine	Annona hypoglauca		72
100	Magnoflorine	Mahonia aquifolium Coptis japonica Sinomenium acutum		50 73 40
101	Norpurpureine	Annona purpurea		74
102	Purpureine	Annona purpurea		74
103	Nornuciferidine	Plumula nelumbinis		30
104	N-Nornuciferine	Plumula nelumbinis		30
105	O-Nornuciferine	Plumula nelumbinis		30
106	Nuciferine	Plumula nelumbinis		30
107	Roemerine	Plumula nelumbinis		30
108	Oxidation-nuciferine	Plumula nelumbinis		30
109	Asimilobine	Unonopsis floribunda		35, 36
		Unonopsis duckei		75
		Bocageopsis pleiosperma		39
110	Isopiline	Unonopsis floribunda		35, 36
111	O-Methylisopiline	Unonopsis floribunda		35, 36
112	Glaucine	Unonopsis floribunda		35, 36
		Unonopsis duckei		75
113	Norglaucine	Unonopsis floribunda		35, 36
114	(+)-N-Formylnorglaucine	Unonopsis stipitata		76
115	6aR-2′-Methoxycarbonyl-thaliadin	Thalictrum cirrhosum		43
116	6aR-2′-Carboxylthaliadin	Thalictrum cirrhosum		43
117	6aR-3-Methoxy-hernandalinol	Thalictrum cirrhosum		43
118	6aS-1,3,10-Trimethoxy-natalamine	Thalictrum cirrhosum		43
119	Predicentrine	Thalictrum cirrhosum		43
120	Thaliadine	Thalictrum cirrhosum Thalictrum wangii		43
121	Glaucine	Corydalis turtschaninovii		77
122	(+)-8-(4′-Formylphenoxy)glaucine	Thalictrum wangii		46
123	(+)-8-(4′-Hydroxymethylphenoxy) glaucine	Thalictrum wangii		46
124	(+)-3-Methoxy-8-(4′-formylphenoxy) glaucine	Thalictrum wangii		46
125	4-Methoxyoxohernandaline	Thalictrum wangii		46
126	Dactyllactone A	Dactylicapnos scandens		78
127	Sallisonine E	Sinomenium acutum		39
128	Dauriporphine	Sinomenium acutum		81
129	Isomoschaltoline	Guatteria blepharophylla		237
130	O-Methylmoschatoline	Guatteria blepharophylla		237
131	Liriodenine	Guatteria blepharophylla Unonopsis floribunda Unonopsis duckei		237 35 75
132	Subsessiline	Guatteria blepharophylla		237
133	Lysicamine	Guatteria blepharophylla Unonopsis floribunda Unonopsis duckei		237 35 75
134	7-Hydroxyguatteriopsiscine	Guatteria friesiana		82
135	(R)-Dihydroguatteriscine	Guatteria friesiana		82
136	Guatterfriesidine	Guatteria friesiana		82
137	Iso-9-methoxyguatterfriesine	Guatteria friesiana		82
138	Norushinsunine	Unonopsis floribunda		35
139	Oxoglaucine	Unonopsis floribunda		35
140	Lanuginosine	Unonopsis floribunda		35
141	3-Methoxy-2′-methoxycarbonyl-oxohernandalincin	Thalictrum cirrhosum		43
142	3-Methoxy-oxohernandaline	Thalictrum cirrhosum		43
143	Oxopurpureine	Thalictrum cirrhosum		43
144	Oxophoebine	Thalictrum cirrhosum		43
145	1,2,3,9,10-Pentamethoxy-11-(4′-formylphenoxy)-7-oxoaporphine	Thalictrum wangii		46
146	1,2,9,10-Tetramethoxy-11-(4′-formylphenoxy)-7-oxoaporphine	Thalictrum wangii		46
147	Dehydrocrebanine	Stephania venosa		85
148	Crebanine	Stephania venosa		85
149	Stephanine	Stephania venosa		85
150	O-Methylbulbocapnine	Stephania venosa		85
151	6-Formyl-1,2,9,10-tetramethoxy-6α,7-dehydroaporphine	Annona crassiflora		70
152	Glaziovine	Unonopsis duckei		75
153	(+)-Oridine	Cryptocarya densiflora, Cryptocarya infectoria Cryptocarya griffithiana		37
154	(−)-10-O-Acetyl prodensiflorin A	Thalictrum wangii		46
155	(−)-10-O-Acetyl prodensiflorin B	Thalictrum wangii		46
156	Prodensiflorin B	Thalictrum wangii		46
157	Dihydroglaziovine	Thalictrum cirrhosum		43
158	Linearisine	Thalictrum cirrhosum		43
159	Pronuciferine	Plumula nelumbinis		30
160	Stepharine	Unonopsis genus Bocageopsis pleiosperma		35, 36 39
Berberines and tetrahydroberberines isoquinoline alkaloids
161	Berberine	Berberis sp. Thalictrum foliolosum Chelidonium majus Mahonia aquifolium Mahonia bealei Coptis chinensis Corydalis turtschaninovii Ancistrocladus tectorius		33 44 123 50 87 41 89 77 127
162	Jatrorrhizine	Corydalis turtschaninovii		77
163	Epiberberine	Chelidonium majus Mahonia aquifolium Mahonia bealei		50 87
164	Demethyleneberberine	Chelidonium majus Mahonia aquifolium Mahonia bealei		50 87
165	Coptisine	Corydalis turtschaninovii		77
166	Palmatine	Corydalis turtschaninovii		77
167	Pseudodehydrocorydaline	Corydalis turtschaninovii		77
168	Dehydrocorybulbine	Corydalis turtschaninovii		77
169	Pseudocoptisine	Corydalis turtschaninovii		77
170	Dehydroisoapocavidine	Corydalis tomentella		28
171	Dehydrocheilanthifoline	Corydalis tomentella		28
172	Corydamine	Fumaria officinalis		24
173	5-Hydroxyl-8-oxyberberine	Coptis chinensis		41, 89
174	8,13-Dioxocoptisine hydroxide	Coptis chinensis		41, 89
175	8-Oxyberberine	Coptis chinensis		41, 89
176	8-Oxo-epiberberine	Coptis chinensis		41, 89
177	8-Oxocoptisine	Coptis chinensis Coptis pallida Coptidis Rhizoma-Euodiae Fructus couple		41, 89 90 61
178	8-Oxyberberrubine	Coptis chinensis		41, 89
179	Tetrahydroberberine	Coptis chinensis		41, 89
180	Corydaline	Coptis chinensis Corydalis turtschaninovii		41, 89 77
181	Orydalidzine	Coptis pallida		90
182	(−)-Corybulbine	Coptis pallida		90
183	(−)-Yuanhunine	Coptis pallida		90
184	(−)-Ophiocarpine	Coptis pallida		90
185	Dehydrocorydaline	Coptis pallida		90
186	Dihydrocoptisine	Corydalis tomentella		28
187	Trans-Protopinium	Corydalis tomentella Fumaria parviflora		28 91
188	Cis-Protopinium	Corydalis tomentella Fumaria parviflora		28 91
189	Thalictrifoline	Corydalis tomentella		28
190	Tetrahydrocoptisine	Corydalis turtschaninovii		77
191	13-Carboxaldehyde-8-oxocoptisine	Coptidis Rhizoma-Euodiae Fructus couple		61
192	Tetrahydropalmatine	Corydalis hendersonii		29
193	8-Hydroxy-7, 8-dihydrocoptisine	Coptis japonica		73
194	Cavidine	Corydalis impatiens		92
195	(−)-Stylopine	Fumaria officinalis Corydalis rupestris		24 98
196	(−)-Sinactine	Fumaria officinalis		24
197	Cheilanthifoline	Fumaria officinalis Sinomenium acutum		24 81
198	Phellodendrine	Phellodendri chinensis		93
199	(−)-1-O-β-D-Glucoside-8-oxotetrahydropalmatine	Stephania succifera		71
200	N-Methylcanadine	Zanthoxylum tingoassuiba		94
201	Demethylalangiside	Ophiorrhiza nutans		95
202	Alangiside	Ophiorrhiza nutans		95
203	Isoalangiside	Ophiorrhiza nutans Alangium longiflorum		95 97
204	Scoulerine	Corydalis dubia		96
205	2′-O-Trans-Sinapoylisoalangiside	Alangium longiflorum		97
206	Rupestrine A	Corydalis rupestris		98
207	Rupestrine B	Corydalis rupestris		98
208	Rupestrine C	Corydalis rupestris		98
209	Rupestrine D	Corydalis rupestris		98
Protopine isoquinoline alkaloids
210	Protopine	Fumaria officinalis Corydalis mucronifera		24 99
211	Cryptopine	Fumaria officinalis		24
Naphthylisoquinoline alkaloids
212	Ancistectorine D	Ancistrocladus tectorius		105, 107
213	6-O-Demethyl ancistectorine D	Ancistrocladus tectorius		105
214	Ancistrotectoriline A	Ancistrocladus tectorius Unidentified Ancistrocladus plant Ancistrocladus ealaensis		105 109 113
215	Ancistrotanzanine B	Ancistrocladus tectorius		105
216	Ancistroealaine A	Ancistrocladus tectorius		105
217	6-O-Methylancistectorine B1	Ancistrocladus tectorius		105
218	Ancistectorine B2	Ancistrocladus tectorius		105
219	6-O-Demethyl-8-O-methyl-7-epi-ancistrobrevine D	Ancistrocladus tectorius		105
220	Ancistrobenomine B	Ancistrocladus tectorius		106
221	Ancistrobenomine C	Ancistrocladus tectorius		106
222	6-O-Methylancistectorine A3	Ancistrocladus tectorius		106
223	4′-O-Demethylancistectorine A2	Ancistrocladus tectorius		106
224	Ancistectorine A3	Ancistrocladus tectorius		106
225	Ancistrocladine	Ancistrocladus tectorius Ancistrocladus ileboensis		106 108
226	Hamatine	Ancistrocladus tectorius		106
		Ancistrocladus congolensis		110
227	5′-O-Demethylhamatine	Ancistrocladus tectorius		106
228	Ancistrocline	Ancistrocladus tectorius		106
229	Ancistrocladinine	Ancistrocladus tectorius		106
230	Hamatinine	Ancistrocladus tectorius		106
231	Ancistectorine A2	Ancistrocladus tectorius		106
232	5-Epi-ancistectorine A2	Ancistrocladus tectorius		106
233	Ancistrobenomine A	Ancistrocladus tectorius		106
234	6-O-Methylancistrocladine	Ancistrocladus tectorius		106
235	6-O-Methylhamatine	Ancistrocladus tectorius Unidentified Ancistrocladus plant		106 109
		Ancistrocladus congolensis		110
236	4′-O-Demethylancistrocladine	Ancistrocladus tectorius Unidentified Ancistrocladus plant		106 109
237	5′-O-Demethylhamatine	Ancistrocladus tectorius Ancistrocladus congolensis		106 110
238	6-O-Methylhamatinine	Ancistrocladus tectorius Ancistrocladus congolensis		106 110
239	5′-O-Demethylhamatinine	Ancistrocladus tectorius		106
240	Korupensamine D	Ancistrocladus congolensis		110
241	Ancistrocyclinone A	Ancistrocladus tectorius		107
242	Ancistrocyclinone B	Ancistrocladus tectorius		107
243	Ancistrocladinium A (a/b)	Ancistrocladus tectorius Unidentified Ancistrocladus plant Ancistrocladus ealaensis		107 109 113
244	4′-O-Demethylancistrocladinium A (a/b)	Ancistrocladus tectorius		107
245	6,4′-O,O-Didemethylancistrocladinium A (a/b)	Ancistrocladus tectorius Ancistrocladus ealaensis		107 113
246	Ancistrotectorine B1	Ancistrocladus tectorius		107
247	Shuangancistrotectorine C	Ancistrocladus tectorius		107
248	Ancistrotectoquinone B (a/b)	Ancistrocladus tectorius		107
249	Dioncophylline F	Ancistrocladus ileboensis		108
250	Dioncophylline C2	Ancistrocladus ileboensis		108
251	Dioncophylline D2	Ancistrocladus ileboensis		108
252	5′-O-Methyldioncophylline D	Ancistrocladus ileboensis		108
253	Dioncophylline A	Ancistrocladus ileboensis		108
254	4′-O-Demethyldioncophylline A	Ancistrocladus ileboensis		108
255	Ancistrocladisine B	Ancistrocladus ileboensis		108
256	Ancistrobrevine C	Ancistrocladus ileboensis		108
257	Ancistrocladisine A	Ancistrocladus ileboensis		108
258	Ancistrobertsonine D	Ancistrocladus ileboensis		108
259	Ancistroyafungine A	Unidentified Ancistrocladus plant		109
260	Ancistroyafungine B	Unidentified Ancistrocladus plant		109
261	Ancistroyafungine C	Unidentified Ancistrocladus plant		109
262	Ancistroyafungine D	Unidentified Ancistrocladus plant		109
263	Ancistroguineine A	Unidentified Ancistrocladus plant		109
264	Ancistrobertsonine A	Unidentified Ancistrocladus plant		109
265	Ancistrobrevine B	Unidentified Ancistrocladus plant Ancistrocladus congolensis		109 110
266	6,5′-O,O-Didemethylancistroealaine A	Unidentified Ancistrocladus plant		109
267	6-O-Demethylancistroealaine A	Unidentified Ancistrocladus plant		109
268	7-Epi-ancistrobrevine D	Unidentified Ancistrocladus plant		109
269	Ancistrocladinium B	Unidentified Ancistrocladus plant		109
270	Michellamine A2	Ancistrocladus congolensis Unidentified Ancistrocladus plant		110 111
271	Michellamine A3	Ancistrocladus congolensis		110
272	Michellamine A4	Ancistrocladus congolensis		110
273	Michellamine B2	Ancistrocladus congolensis		110
274	Michellamine B3	Ancistrocladus congolensis		110
275	Michellamine A	Ancistrocladus congolensis		110
276	Michellamine B	Ancistrocladus congolensis		110
277	Michellamine A6	Unidentified Ancistrocladus plant		111
278	Michellamine A7	Unidentified Ancistrocladus plant		111
279	Michellamine B4	Unidentified Ancistrocladus plant		111
280	Michellamine B5	Unidentified Ancistrocladus plant		111
281	Ancistrobonsoline A1	Unidentified Ancistrocladus plant		111
282	Ancistrobonsoline A2	Unidentified Ancistrocladus plant		111
283	Ancistroealaine C	Unidentified Ancistrocladus plant Ancistrocladus ealaensis		111 113
284	Korupensamine A	Unidentified Ancistrocladus plant		111
		Ancistrocladus ealaensis		113
285	Korupensamine B	Unidentified Ancistrocladus plant		111
286	Michellamine E	Unidentified Ancistrocladus plant		111
287	Ealapasamine A	Ancistrocladus ealaensis		112
288	Ealapasamine B	Ancistrocladus ealaensis		112
289	Ealapasamine C	Ancistrocladus ealaensis		112
290	Mbandakamine A	Ancistrocladus ealaensis		107
291	Mbandakamine C	Ancistrocladus ealaensis		113
292	Mbandakamine D	Ancistrocladus ealaensis		113
293	Mbandakamine E	Ancistrocladus ealaensis		113
294	Mbandakamine A	Ancistrocladus ealaensis		113
295	Ancistroealaine D	Ancistrocladus ealaensis		113
296	Ancistroealaine E	Ancistrocladus ealaensis		113
297	Ancistroealaine F	Ancistrocladus ealaensis		113
298	Ancistrolikokine B	Ancistrocladus ealaensis		113
Phenanthridine alkaloids
299	Sanguinarine	Chelidonium majus		124
300	Chelidonine	Chelidonium majus		125
301	Homochelidonine	Chelidonium majus		125
302	(1′R,6R/1′S,6S)-1-(Dihydrochelerythrine-6-yl) ethanol	Chelidonium majus		126
303	(1′S,6R/1′R,6S)-1-(Dihydrochelerythrine-6-yl) ethanol	Chelidonium majus		126
304	(1′R,6R)/(1′S,6S)-1-(Dihydrosanguinarine-6-yl)ethanol	Chelidonium majus		126
305	(1′S,6R)/(1′R,6S)-1-(Dihydrosanguinarine-6-yl)ethanol	Chelidonium majus		126
306	(±)-Ethyl 2-(dihydrosanguinarine-6-yl) acetate	Chelidonium majus		126
307	(±)-Ethyl dihydrosanguinarine-6- carboxylate	Chelidonium majus		126
308	Heitziquinone	Zanthoxylum heitzii		127
309	Dihydronitidine	Zanthoxylum heitzii		127
310	Isoarnottianamide	Zanthoxylum heitzii		127
311	Rhoifoline B	Zanthoxylum heitzii		127
312	Dihydrocheleryhtrine	Zanthoxylum tingoassuiba		94
313	Decarine	Zanthoxylum myriacanthum var. pubescens		128
314	Corynoline	Corydalis bungeana		129
315	Ambinine	Corydalis ambigua var. amurensis		130
316	Norsanguinarine	Corydalis tomentella		28
317	(−)-6-Acetonyldihydrisanguinarine	Corydalis tomentella Corydali pallida		28 90
318	Cavidilinine	Corydalis tomentella		28
319	8-Methoxydihydrosanguinarine	Corydalis mucronifera		99
320	Dihydrosanguinarine	Corydalis mucronifera		99
321	Lycorine	Amaryllidaceae family		136
322	Acetycaranine	Amaryllidaceae family		136
323	Caranine	Amaryllidaceae family		136
324	Galanthine	Amaryllidaceae family		136
325	9-O-Demthylgalanthine	Amaryllidaceae family		136
326	Haemanthamine	Amaryllidaceae family		136
		Narcissus poeticus cv. Pink Parasol		138
327	Haemanthidine	Amaryllidaceae family		136
328	Ambelline	Amaryllidaceae family		136
329	11-O-Acetylambelline	Amaryllidaceae family		136
330	1-O-Acetylbulbisine	Amaryllidaceae family		136
331	Undulatine	Amaryllidaceae family		136
332	Crinamidine	Amaryllidaceae family		136
333	Buphanamine	Amaryllidaceae family		136
334	Crinine	Amaryllidaceae family		136
335	6,7,11b,11c-Didehydrolycorinium salt	Crinum firmifolium Crinum hardyi		137
336	Seco-isopowellaminone	Narcissus poeticus cv. Pink Parasol		138
337	Incartine	Narcissus poeticus cv. Pink Parasol		138
Manzamine alkaloids
338	Manzamine A	Acanthostrongylophora sp. sponge		146
339	Kepulauamine A	Acanthostrongylophora sp. sponge		146
340	Manzamine B N-oxide	Acanthostrongylophora sp. sponge		146
341	3,4-Dihydromanzamine B N-oxide	Acanthostrongylophora sp. sponge		146
342	11-Hydroxymanzamine J	Acanthostrongylophora sp. sponge		146
343	31-Hydroxymanzamine A	Acanthostrongylophora sp. sponge		146
344	32,33-Dihydro-31-hydroxymanzamine A	Acanthostrongylophora sp. sponge		146
345	6-Deoxymanzamine X	Acanthostrongylophora sp. sponge		146
346	Manzamine B	Acanthostrongylophora sp. sponge		146
347	neo-Kauluamine	Acanthostrongylophora sp. sponge		146
Emetine isoquinoline alkaloids
348	Emetine	Alangiaceae, Icacinaceae, and Rubiaceae		149
349	7′,10-Dide-O-methylcephaeline	Ophiorrhiza nutans		95
350	10-O-Demethylprotoemetine	Ophiorrhiza nutans		95
351	8-Hydroxytubulosine	Alangium longiflorum		97
352	9-Demethyltubulosine	Alangium longiflorum		97
353	(+)-Sebiferine	Dehaasia longipedicellata		38
354	(−)-Milonine	Dehaasia longipedicellata		38
355	Sinomacutine A	Sinomenium acutum		40
356	Sinomacutine B	Sinomenium acutum		40
357	Sinomacutine C	Sinomenium acutum		40
358	Cephalonine-2-O-β-D-glucopyranoside	Sinomenium acutum		40
359	Sinomenine	Sinomenium acutum		40
		Sinomenium acutum		81
360	Sinoacutine	Sinomenium acutum		40
361	8-Demethoxycephatonine	Sinomenium acutum		81
362	7(R)-7,8-dihydrosinomenine	Sinomenium acutum		81
363	8-Demethoxyrunanine	Sinomenium acutum		81
364	14-Episinomenine	Sinomenium acutum		81
365	Sinomenine N-oxide	Sinomenium acutum		81
366	Salutaridine	Sinomenium acutum		81
367	Acutumine	Sinomenium acutum		81
368	Acutumidine	Sinomenium acutum		81
369	Dauricumine	Sinomenium acutum		81
370	Pallidine	Unonopsis floribunda		36
371	O-Methylflavinantine	Thalictrum cirrhosum		43
Phthalideisoquinoline alkaloids
372	(+)-Bicuculline	Fumaria officinalis		24
373	(+)-Corlumine	Viola tianschanica		150
374	(9S, 7′S) Tomentelline A	Corydalis tomentella		28
375	(9S, 7′R) Tomentelline A	Corydalis tomentella		28
376	(9R, 7′S) Tomentelline B	Corydalis tomentella		28
377	Adlumidine	Corydalis tomentella Corydalis mucronifera		28 99
378	(+)-Capnoidine	Corydalis tomentella		28
379	Mucroniferanine A	Corydalis mucronifera		99
380	Mucroniferanine B	Corydalis mucronifera		99
381	Mucroniferanine C	Corydalis mucronifera		99
382	Mucroniferanine D	Corydalis mucronifera		99
383	Mucroniferanine E	Corydalis mucronifera		99
384	Mucroniferanine F	Corydalis mucronifera		99
385	Mucroniferanine G	Corydalis mucronifera		99
386	(±)-Hypecorinine	Corydalis mucronifera		99
387	(−)-7′-O-Methylegenine	Corydalis mucronifera		99
388	Sibiricine	Corydalis mucronifera		99
389	(+)-Humosine A	Corydalis mucronifera		99
390	Capnoidine	Corydalis dubia		151
Benzopyrroloisoquinoline Alkaloids
391	Tengerensine	Ficus fistulosa var. tengerensis		152
Phenylethyl tetrahydroisoquinoline alkaloids
392	Fumarostrejdine	Fumaria officinalis		24
393	(±)-O-Methylfumarofine	Fumaria officinalis		24
Others
394	Coptichine	Coptidis Rhizoma–Euodiae Fructus couple		61
395	Coptisonine	Coptis chinensis		89
396	Sallisonine D	Sinomenium acutum		40
397	Alternamine A	Alternanthera littoralis		153
398	(±)-7-Benzyloxy-1-(3-benzyloxy-4-methoxyphenethyl)-1,2,3,4-tetrahydro-6-methoxy-2-methylisoquinoline oxalate	Chemical library		154
399	Tomentelline C	Corydalis tomentella		28
400	Tomentelline D	Corydalis tomentella		28
401	6,7-Methylenedioxy-2-(6-acetyl-2,3-methylenedioxybenzyl)-1(2H)-isoquinolinone	Corydalis tomentella		28
402	Oleracein E	Portulaca oleracea		31
403	Pipermullesine B	Piper mullesua		155
404	Pipermullesine C	Piper mullesua		155
405	Delavatine A	Incarvillea delavayi		156
406	Neotatarine	Acorus calamus		158

2. Structure and classification of isolated isoquinoline alkaloids

2.1. Simple isoquinoline alkaloids

The alkaloids in this classification have the simplest structures and are distributed mainly in the genera Papaver, Corydalis, Thalictrum and others. Eighteen isoquinoline alkaloids were identified and isolated from plants and animals between 2014 and 2018 (Figure 2).

Figure 2.

The Chemical Structures of Compounds 1-22

In 2016, two new isoquinoline alkaloids 3,8-diolisoquinoline (1) and 1-methoxy-4,5-diolisoquinoline (2) were isolated from an ethanol extract of the Chinese redheaded centipede Scolopendra subspinipes mutilans²². In another study in the following year, the new isoquinoline alkaloid 1,5-dihydroxy-4-methoxyisoquinoline (3), also isolated from this centipede species, showed moderate cytotoxicity against five cancer cells²³.

Carnegine (4) and N-methylisosalsoline (5), isolated from the plant Hammada scoparia, exhibited antibacterial and antioxidant activities²⁴. Also, in 2016, N-methylcorydaldine (6) was isolated from Fumaria officinalis²⁵ and 6,7-dimethoxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid (7) from Mucuna pruriens seeds²⁶.

In 2018, the previously reported N-methylcorydaldine (6) together with two more isoquinoline alkaloids 7-methoxy-1,2,3,4-tetrahydroisoquinolin-1-one (8) and thalifoline (9) were isolated from Michelia champaca²⁷. Other studies in same year described the isolation as well as hepatoprotective activities of the latter compound (9), N-methylisosalsoline (5), corydaldine (10), oxohydrastinine (11), 6,7-methylenedioxy-1(2H)-isoquinolinone (12) and oxyhydrastinine (13) from Corydalis tomentella, C. hendersonii and Plumula nelumbinis^28-30.

6,7-Dihydroxy-1-methyl-3,4-dihydroisoquinolone (14), (S)-(−)-salsolinol (15), 6,7-dihydroxy-3,4-dihydroisoquinolone (16) and (R)-(+)-1-isobutyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (17), were isolated from the medicinal plant Portulaca oleracea³¹. These four simple isoquinoline alkaloids contained 6,7-dihydroxy substitution but different saturation or substituents at C-1. Four “naphthalene-devoid” tetra- and dihydroisoquinolines, named ealaines A–D (18-21), were isolated from the Congolese plant Ancistrocladus ealaensis³². Akihisa et al.³³ isolated noroxyhydrastinine (22) from the bark of Phellodendron amurense (Figure 2).

2.2. Benzylisoquinoline alkaloids

2.2.1. Simple benzylisoquinoline alkaloids

Reticuline (23) exhibits significant pharmacological activities, leading to the search for and identification of alternate natural sources, such as Litsea cubeba, Unonopsis genus, Cryptocarya densiflora, C. infectoria, C. griffithiana and Dehaasia longipedicellata, over the past five years^34-39. (+)-N-Methylisococlaurine (24) also was found in Cryptocarya species³⁷ and (−)-N-methylcoclaurine (25) was identified in the rhizomes of Sinomenium acutum in 2014⁴⁰. Berbithine (26) and 6-([1,3]dioxolo[4,5-g]isoquinoline-5-carbonyl)-2,3-dimethoxybenzoic acid methyl ester (27) were isolated from the rhizome of Coptis chinensis⁴¹.

In 2018, several benzylisoquinoline alkaloids, including 24, 25, norcolaurine-4′-O-glucoside (28), N-methylhigenamine (29), norcoclaurine-6-O-glucoside (30), norcoclaurine (31), argemexirine (32), lotusine (33), isococlaurine (34), armepavine (35), 6-demethy-4′-methyl-N-methylcoclaurine (36), coclaurine (37), N-nor-O-methylarmepavine (38), isococlaurine-5′-O-pentoside (39), and coclaurine-5′-O-pentoside (40) were identified from Plumula nelumbinis through UPLC-ESI-QTOF-MS³⁰. Subsequently, juzirine (41) was identified from the aerial parts of Leonurus japonicus⁴². (R)-(+)-1-Benzyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (42) from Portulaca oleracea showed anti-inflammatory and β2-adrenergic receptor agonist activities²⁶. Laudanosine (43), pseudolaudanine (44) and rugosinone (45)were isolated from the whole herb of Thalictrum cirrhosum⁴³ (Figure 3). Hendersine B methyl ester (46), bicucullinine (47) and hendersine B (48) were isolated from Corydalis tomentella²⁸.

Figure 3.

The Chemical Structures of Compounds 23-56

2.2.2. Bisbenzylisoquinoline alkaloids

Bisbenzyl isoquinoline alkaloids are one of the major phytochemicals reported from members of the plant families Menispermacea, Berberidaceae, Lauraceae, and Ranunculaceae, which grow in tropical and subtropical regions. They contain two benzylisoquinolines linked through diphenyl ether, benzyl phenyl ether, or biphenyl bonds^5,19. In 2016, two new bisbenzylisoquinolines, 6,6′,7′,12-tetramethoxy-5′-hydroxy-2,2′-dimethyloxycanthan (49) and 6,5′,6′,7′,12-pentamethoxy-2,2′-dimethoxyethane (50), were isolated from the stems of Thalictrum foliolosum⁴⁴. Meanwhile, hernandezine (51), a known alkaloid, was identified from T. flavum⁴⁵. In 2018, two seco-bisbenzylisoquinolines, 6,7,12-trimethoxy-2-methyl-13-hydroxy-11-(4′-formylphenoxy)benzylisoquinoline (52) and 5,6-(methylenedioxy)-7,12-dimethoxy-2-methyl-10-(4′-formylphenoxy)benzylisoquinoline (53), were isolated from T. wangii⁴⁶. Tiliamosine (54) was found from T. racemosa⁴⁷ (Figure 3).

Bisbenzylisoquinoline alkaloids are also found in the genus Stephania. In 2014, two new compounds, (−)-pseudocurine (55) and (−)-pseudoisocurine (56), were isolated from a leaf extract of Stephania abyssinica⁴⁸. Tetrandrine (57) and fangchinoline (58) were isolated from S. tetrandra, which has been used for 2,000 years as an antirheumatic herbal medicine in China⁴⁹. In addition, (−)-O-O-dimethylgrisabine (59) from Dehaasia longipedicellata exhibited significant antiparasitic and antioxidant activities³⁸. Using a ¹H NMR-based metabolomics approach, berbamine (60), a bisbenzylisoquinoline-type compound, was identified from Mahonia aquifolium⁵⁰ (Figure 4).

Figure 4.

The Chemical Structures of Compounds 57-84

Neferine (61) is a well-known bisbenzylisoquinoline-type alkaloid due to its wide range of pharmacological activities, including antiarrhythmic, antihypertensive^51,52, relaxant⁵³, antidiabetic⁵⁴, cholinesterase inhibitory⁵⁵, antioxidant, anti-inflammatory, anti-amnesic⁵⁶ and sedative^57,58 effects. In addition to M. aquifolium, it is found in lotus (Nelumbo nucifera) seed embryos⁵⁹. In 2018, compound 61 as well as four other bisbenzylisoquinoline alkaloids, liensinine (62), isoliensinine (63), norisoliensinine (64) and 6-hydroxynorisoliensinine (65) were found in Plumula nelumbinis³⁰. Five alkaloids also were isolated from Alseodaphne corneri, including (−)-gyrolidine (66), (+)-O-methyllimacusine (67), (+)-2-norobaberine (68), (+)-norstephasubine (69) and (+)-stephasubine (70)⁶⁰ (Figure 4).

2.2.3. Spirobenzylisoquinoline alkaloids

Spirobenzylisoquinoline alkaloids are isoquinoline alkaloids with a unique ‘spiro’ structure as shown in Figure 6. They have been found only within the plant family Fumariaceae, and more specifically within the genera Fumaria and Corydalis. In 2014, coptichic aldehyde (71) was isolated from the traditional Chinese medicine preparation Coptidis Rhizoma–Euodiae Fructus couple; it showed growth inhibitory activity against NCI-N87 cells with an IC₅₀ value of 8.92 μM⁶¹. In 2016, the new isoquinoline alkaloid fumaranine (72) together with seven other alkaloids, (−)-fumaricine (73), (+)-dihydrofumariline (74), (−)-fumaritine (75), (−)-O-methylfumarophycine (76), (−)-fumarophycine (77), (+)-fumariline (78), (+)-parfumidine (79), and (+)-parfumine (80) were found from the aerial parts of F. officinalis²⁴. Also, four new spirobenzylisoquinoline N-oxide alkaloids hendersines C-F (81-84) were identified from Corydalis hendersonii²⁷ (Figure 4).

Figure 6.

The Chemical Structures of Compounds 127-160

2.3. Aporphine isoquinoline alkaloids

Aporphine alkaloids are a large group of isoquinolines that generally possess a characteristic tetracyclic ring system (rings A-D) with a nitrogen in ring B⁶². The structures of the aporphine alkaloids can be classified into subtypes, including simple aporphines, their dehydro derivatives, oxoaporphines, miscellaneous aporphinoids, and dimeric aporphinoid alkaloids^63-66.

2.3.1. Simple aporphines

Simple aporphines have a 5,6,6a,7-tetrahydro-4H-dibenzo[de,g]quinoline core substituted primarily with different numbers of hydroxy, methoxy, and methylenedioxy groups at various positions. The nitrogen is substituted most frequently with hydrogen or methyl, although other groups (e.g., formyl, acetyl, and others) are sometimes present. They are 1-benzylisoquinolines with one additional ring closure between the 2′-carbon in the pendant phenyl ring and the 1a-carbon in the isoquinoline ring junction, forming a non-linear tetracyclic (6-6-6-6) system.

Boldine (85), isolated from Litsea cubeba and Dehaasia longipedicellata, showed anti-inflammatory activity and potential synergistic effects in vivo^67,60. Compound 85 and (−)-norboldine (86), also found in D. longipedicellata,³⁸ showed moderate antioxidant and antiplasmodial activities³⁸. In 2016, (+)-laurotetanine (87), isolated from Alseodaphne corneri⁶⁸ and Bocageopsis pleiosperma³⁹, was found to exhibit strong antiplasmodial activity (Figure 5).

Figure 5.

The Chemical Structures of Compounds 85-126

Compound 87, (+)-nornantenine (88) and (+)-N-methyllaurotetanine (89) were isolated from Cryptocarya densiflora, C. infectoria and C. griffithiana³⁷. Corydine (90) and norisoboldine (91) were isolated from Croton echinocarpus leaves⁶⁹, while isocorydine (92) and norisocorydine (93) were identified from Alseodaphne corneri⁶⁰ (Figure 5).

The aporphine stephalagine (1,2-methylenedioxy-3-methoxyaporphine) (94) was isolated from the fruit peel of Annona crassiflora⁷⁰. In 2017, N-formyl-asimilobine-2-O-β-d-glucoside (95), an amidic aporphine, was obtained from the tubers of Stephania succifera⁷¹. Four aporphine alkaloids, isoboldine (96), anonaine (97), nornuciferine (98) and actinodaphnine (99), were isolated from Annona hypoglauca⁷². Magnoflorine (100) was found in the rhizomes of Mahonia aquifolium, Coptis japonica and Sinomenium acutum^40,50,73 (Figure 5).

Both norpurpureine (101) and purpureine (102) were isolated from Annona purpurea leaves⁷⁴. In 2018, eight aporphine alkaloids [anonaine (97), N-nornuciferine (98), nornuciferidine (103), zenkerine (104), O-nornuciferine (105), nuciferine (106), roemerine (107) and oxidation-nuciferine (5-hydroxynuciferine) (108)] were identified from Plumula nelumbinis³⁰. Compounds 93, 97 and 98 as well as asimilobine (109), isopiline (110), O-methylisopiline (111), glaucine (112), and norglaucine (113) were reported for the first time from Unonopsis floribunda^35,36 (Figure 5). Compounds 97, 98, 109 and 112 also were found from Unonopsis duckei⁷⁵, and compounds 89, 96, 97 and 109 also were reported from Bocageopsis pleiosperma⁴⁰. (+)-N-Formylnorglaucine (114) was reported from Unonopsis stipitata⁷⁶.

Four new phenyl-C₁ substituted aporphine alkaloids, 6aR-2′-methoxycarbonylthaliadine (115), 6aR-2′-carboxylthaliadine (116), 6aR-3-methoxyhernandalinol (117), 6aS-1,3,10-trimethoxynatalamine (118), together with three known isoquinoline alkaloids 89, predicentrine (119), and thaliadine (120) were isolated from the whole herb of Thalictrum cirrhosum⁴³.

Glaucine (121) from Corydalis turtschaninovii⁷⁷, as well as three new analogs, (+)-8-(4′-formylphenoxy)glaucine (122), (+)-8-(4′-hydroxymethylphenoxy)glaucine (123), (+)-3-methoxy-8-(4′-formylphenoxy)glaucine (124), and two known alkaloids, 120 and its oxidized derivative 125, were isolated from the whole plant of Thalictrum wangii⁴⁶ (Figure 5).

An unprecedented alkaloid, dactyllactone A (126), which contains a rearranged benzofuran lactone with a gemdimethoxycarbonyl unit and is derived from an 8,9;11,11a-bis-seco-aporphine skeleton, was isolated from Dactylicapnos scandens. It exhibited anti-inflammatory activity⁷⁸ (Figure 5).

2.3.2. 7-Substituted Aporphines and Oxoaporphines

7-Oxygenated aporphines have a hydroxyl or methoxy group at C-7 or two such groups at C-4 and C-7^66,79. The oxoaporphines (7H-dibenzo[de,g]quinoline-7-one skeleton) and oxoisoaporphines (7H-dibenzo[de,h]quinoline-7-one skeleton) have an aromatic isoquinoline (aromatic ring B in the tetracyclic structure) and a carbonyl group at C-7⁸⁰.

Two oxoisoaporphines sallisonine E (127) and dauriporphine (128) were isolated from the rhizomes of Sinomenium acutum, in 2014 and 2016, respectively^40,81. Five oxoaporphines isomoschatoline (129), O-methylmoschatoline (130), liriodenine (131), subsessiline (132) and lysicamine (133) were identified from Guatteria blepharophylla also in 2016⁷⁴ and compounds 131, 133 were reported from Unonopsis duckei in 2014⁷⁵.

One new 4,7-dihydroxy-7-methylaporphine alkaloid (7-hydroxyguatteriopsiscine (134)) and three new 7,7-dimethylaporphinoids [(R)-dihydroguatteriscine (135), guatterfriesidine (136), and iso-9-methoxyguatterfriesine (137)] were isolated from the stem bark of G. friesiana in 2018.⁷⁵ Compound 136 exhibited antiglycation activity as determined by inhibiting the formation of advanced glycation end-products in both bovine serum albumin (BSA)/methylglyoxal and BSA/fructose assay systems⁸². In 2018, one 7-hydroxyaporphine [norushinsunine (138)] and four oxoaporphines [131, 133, oxoglaucine (139), and lanuginosine (140)] were reported for the first time from Unonopsis floribunda³⁵ (Figure 6).

Another new oxoaporphine alkaloid 3-methoxy-2′-methoxycarbonyl-oxohernandalincin (141) as well as the known 3-methoxy-oxohernandaline (142), oxopurpureine (143), and oxophoebine (144) were isolated from the whole herb of Thalictrum cirrhosum⁴³. 1,2,3,9,10-Pentamethoxy-11-(4′-formylphenoxy)-7-oxoaporphine (145) and 1,2,9,10-tetramethoxy-11-(4′-formylphenoxy)-7-oxoaporphine (146), two new oxoaporphines that, like 142, contain an ether-linked formylphenyl moiety were identified from T. wangii⁴⁶ (Figure 6).

2.3.3. Dehydroaporphines

Dehydroaporphines are 5,6-dihydro-4H-dibenzo[de,g]quinolines with a double, rather than single, between C-6a and C-7. In the preceding subtypes, this bond is saturated or C-7 is substituted with hydroxy, methoxy, or methyl groups or part of a carbonyl unit^19,83,84. Based on bioassay-guided fractionation against numerous cancer cells, Le et al.⁸⁵ isolated one dehydroaporphine [dehydrocrebanine (147)] and three simple aporphines [crebanine (148), stephanine (149) and O-methylbulbocapnine (150)] from the tubers of Stephania venosa growing in Vietnam. Compound 149 was the most active among the four compounds with IC₅₀ values of 3.33 μM, 5.66 μM and 6.49 μM against HeLa, MDA-MB231 and MCF-7 cells, respectively. In 2017, an amidic dehydroapophine (151, 6-formyl-1,2,9,10-tetramethoxy-6α,7-dehydroaporphine) was isolated from the aerial parts of Aconitum carmichaelii⁷⁰ (Figure 6).

2.3.4. Proaporphine alkaloids

Proaporphine alkaloids are biogenetic precursors to certain aporphine alkaloids. The tetracyclic system (2’,3’,8’,8a’-tetrahydro-1’H-spiro[cyclohexane-1,7’-cyclopenta[ij]isoquinoline) is composed of a bicyclic isoquinoline fused to a five-membered ring that is also connected to a six-membered ring through a spiro carbon.

In 2014, glaziovine (152) was reported from Unonopsis duckei⁷⁵. In 2016, the proaporpine (+)-oridine (153) was obtained from leaves of Cryptocarya densiflora³⁷. In 2018, several proaporphines were identified from various plant species: two new [(−)-10-O-acetylprodensiflorins A (154) and B (155)] and one known [prodensiflorin B (156)] and from the whole plant of Thalictrum wangii⁴⁶, dihydroglaziovine (157) and linearisine (158) from T. cirrhosum,⁴³ pronuciferine (159) from Plumula nelumbinis³⁰ and stepharine (160) from Unonopsis floribunda for the first time^35,36, and compound 160 also was found Bocageopsis pleiosperma³⁹. (Figure 6).

2.4. Berberine and protoberberine isoquinoline alkaloids

2.4.1. Berberine (quaternary protoberberine) alkaloids

Berberine (161) is a famous isoquinoline alkaloid from the rhizome, roots and stem bark of Berberis sp.; it exhibits various pharmacological effects, such as antitumor, antibacterial, antiviral, antiinflammatory, antidiabetic and myocardial protective activities. Berberine is a quaternary protoberberine alkaloid with a tetracyclic skeleton [5,6-dihydrobenzo[a,g]quinolizinium (C₁₇H₁₄N⁺) salt] with the nitrogen at the junction of the two middle rings (position 7). Structurally, it is a benzylisoquinoline with an additional ring formed between the 2′-carbon of the pendant phenyl ring and a methyl on the isoquinoline nitrogen. Various oxygenated substituents (hydroxy, methoxy, methylenedioxy) are present on the two outer rings, most often, although not exclusively, at positions 2,3,9,10 or 2,3,10,11, which is often designated as ‘pseudo’. Methylation at position 13 is commonly seen as well. Besides the genus Berberis, it has also been isolated from plants of the genera Coptis, Corydalis and Mahonia together with other known structurally related alkaloids, including jatrorrhizine (162), epiberberine (163), demethyleneberberine (164), coptisine (165) and palmatine (166)^50,73,86-88.

Compounds 161, 162, 165, 166, pseudodehydrocorydaline (167), dehydrocorybulbine (168) and pseudocoptisine (169) were isolated from the roots of Corydalis turtschaninovii. They showed strong neuraminidase inhibitory activity (IC₅₀, 12.8–65.2 μM)⁷⁷. Dehydroisoapocavidine (170), dehydrocheilanthifoline (171), isolated from the related species C. tomentella, showed hepatoprotective activity²⁸. Corydamine (172), a B-ring opened 3-phenyl isoquinoline analog of 159, was isolated from the aerial parts of Fumaria officinalis¹⁹ (Figure 7).

Figure 7.

The Chemical Structures of Compounds 161-189

2.4.2. Protoberberine isoquinoline alkaloids

Other protoberberines include tetrahydroprotoberberines and dihydroprotoberberines. In 2014, several 8-oxo-protoberberines, including a pair of new enantiomeric isoquinoline alkaloids, (+)- and (−)-5-hydroxyl-8-oxyberberine (173), 8,13-dioxocoptisine hydroxide (174), 8-oxyberberine (175), 8-oxo-epiberberine (176), 8-oxocoptisine (177), and 8-oxoberberrubine (178), together with tetrahydroberberine (179) and corydaline (180) as well as the benzylisoquinoline alkaloid 26 were isolated from the rhizoma of Coptis chinensis. C2C12 cells exposed to 176 and 178 showed reduced glucose uptake^41,89. The whole plant of Corydalis pallida also yielded 177 together with four tetrahydroprotoberberines, (−)-corydalidzine (181), (−)-corybulbine (182), (−)-yuanhunine (183) and (−)-ophiocarpine (184), as well as the quaternary protoberberine alkaloid dehydrocorydaline (185)⁹⁰. Dihydrocoptisine (186), trans-protopinium (187), cis-protopinium (188), and thalictrifoline (189) from Corydalis tomentella displayed moderate hepatoprotective activities; the values of relative survival rates were 34.25–47.51% at a concentration of 10 μM²⁸. The isomeric 187 and 188 obtained from roots of Fumaria parviflora also showed nematocidal activity⁹¹ (Figure 7).

In 2014, compound 180 and tetrahydrocoptisine (190) were isolated from the roots of Corydalis turtschaninovii⁷⁷. A new compound 13-carboxaldehyde-8-oxocoptisine (191) together with 177 were isolated from the traditional Chinese preparation Coptidis Rhizoma-Euodiae Fructus couple, used to treat gastrointestinal disorders⁶¹. Corydalis hendersonii and Coptis japonica were found to contain tetrahydropalmatine (192) and 8-hydroxy-7,8-dihydrocoptisine (1 93), respectively^27,73. Cavidine (194) was isolated from Corydalis impatiens⁹². In 2016, (−)-stylopine (195), (−)-sinactine (196) and (−)-cheilanthifoline (197) were isolated from aerial parts of Fumaria officinalis²⁴. The latter compound also was found in Sinomenium acutum⁸¹. Phellodendrine (198) was identified from Phellodendri chinensis cortex⁹³. In 2017, a new glycoalkaloid, (−)-1-O-β-d-glucoside-8-oxotetrahydropalmatine (199), isolated from tubers of Stephania succifera, exhibited antimicrobial activity against Staphylococcus aureus⁷¹. N-Methylcanadine (200) was isolated from Zanthoxylum tingoassuiba⁹⁴, and demethylalangiside (201), alangiside (202) and isoalangiside (203) were identified and isolated from Ophiorrhiza nutans⁹⁵. Subsequently, in 2018, it was shown that scoulerine (204) from Corydalis dubia exhibited promising suppression of cancer cell growth⁹⁶. (Figure 8).

Figure 8.

The Chemical Structures of Compounds 190-209

2′-O-trans-Sinapoylisoalangiside (205) was identified from Alangium longiflorum⁹⁷. Four new isoquinoline alkaloids rupestrines A-D (206-209) and the known 195 were identified from Corydalis rupestris⁹⁸ (Figure 8).

2.5. Protopine isoquinoline alkaloids

Compounds from this classification have a 5,6,7,8,13,14-hexahydrodibenzo[c,g]azecine skeleton. They lack the B/C bond and, thus, are tricyclic (6-10-6) with a 10-membered ring between two phenyl rings. Only two compounds of this type were identified during the past five years. Protopine (210) and cryptopine (211) were isolated from Fumaria officinalis²⁴, and the former compound also was found in Corydalis mucronifera⁹⁹ (Figure 9).

Figure 9.

The Chemical Structures of Compounds 210-211

2.6. Naphthylisoquinoline alkaloids

Naphthylisoquinolines are a group of structurally diverse secondary metabolites containing both naphthalene and isoquinoline bicyclic systems connected by a C,C or C,N biaryl axis. These chiral compounds are mostly found only in two palaeotropic families, Dioncophyllaceae and Ancistrocladaceae. Dioncophyllaceae-type alkaloids have a R-configuration at C-3 and always lack an oxygen function at C-6. The structurally similar Ancistrocladaceae-type alkaloids are found in the closely related Ancistrocladaceae plant family. Among the studies over the past two decades on the isolation and bioactivity evaluation of naphthylisoquinoline alkaloids, extensive work has been published by Bringmann et al.^{21, 100-113}.

From 2014 to the present, numerous new compounds were isolated in investigations by several research groups on Asian lianas. The approximately 60 structurally divergent monomeric and dimeric naphthylisoquinoline alkaloids exhibit all seven known C,C-coupling types (5,1′, 5,3′, 5,8′, 7,1′, 7,3′, 7,6′, and 7,8′). The twigs and stems of the Chinese liana Ancistrocladus tectorius contained five new 5,8′-coupled naphthylisoquinolines, ancistectorine D (212), its 6-O-demethyl derivative (213), ancistrotectoriline A (214), ancistrotanzanine B (215), and ancistroealaine A (216), three new 7,1′-linked alkaloids, 6-O-methylancistectorine B₁ (217), ancistectorine B₂ (218), and 6-O-demethyl-8-O-methyl-7-epi-ancistrobrevine D (219), and twenty 5,1′-linked naphthylisoquinoline alkaloids ancistrobenomines B (220) and C (221), 6-O-methylancistectorine A₃ (222), 4′-O-demethylancistectorine A₂ (223), ancistectorine A₃ (224), ancistrocladine (225), hamatine (226), 5′-O-demethylhamatine (227), ancistrocline (228), ancistrocladinine (229), hamatinine (230), ancistectorine A₂ (231) and its atropo-diastereomer 5-epi-ancistectorine A₂ (232), ancistrobenomine A (233), 6-O-methylancistrocladine (234), 6-O-methylhamatine (235), 4′-O-demethylancistrocladine (236), 5′-O-demethylhamatine (237), 6-O-methylhamatinine (238) and 5′-O-demethylhamatinine (239)^105,106. Although some compounds were already known from related Asian and African Ancistrocladus species, they were discovered from A. tectorius for the first time, such as a monomeric alkaloid, korupensamine D (240)¹¹⁰. From this species, two unique pentacyclic N,C-coupled naphthylisoquinolines, ancistrocyclinones A (241) and B (242), also were discovered, as well as six known N,C-coupled alkaloids, viz., ancistrocladinium A (a/b) (243), 4′-O-demethylancistrocladinium A (a/b) (244), 6,4′-O,O-didemethylancistrocladinium A (a/b) (245), ancistrotectorine B₁ (246), shuangancistrotectorine C (247), ancistrotectoquinone B (a/b) (248) and compounds 161 and 222¹⁰⁷ (Figures 10, 11).

Figure 10.

The Chemical Structures of Compounds 212-235

Figure 11.

The Chemical Structures of Compounds 236-248

In 2017, the first 5,8′-coupled Dioncophyllaceous alkaloid, dioncophylline F (249), together with dioncophyllines C₂ (250), D₂ (251), and three known compounds, 5′-O-methyldioncophylline D (252), dioncophylline A (253) and 4′-O-demethyldioncophylline A (254) were isolated from the Congolese liana Ancistrocladus ileboensis¹⁰⁸. Moreover, the Ancistrocladaceae-type compound ancistrocladisine B (255) (oxygenated at C-6 and S-configured at C-3), together with four known alkaloids, 225, ancistrobrevine C (256), ancistrocladisine A (257) and ancistrobertsonine D (258) also were identified. Four new C,C-coupled compounds, ancistroyafungines A-D (259-262), and eleven known C,C- and N,C-linked analogs, including compounds 214, 235, 236 and 243, ancistroguineine A (263), ancistrobertsonine A (264), ancistrobrevine B (265), 6,5′-O,O-didemethylancistroealaine A (266), 6-O-demethylancistroealaine A (267), 7-epi-ancistrobrevine D (268) and ancistrocladinium B (269), were isolated from an unidentified Ancistrocladus plant¹⁰⁹ (Figure 12).

Figure 12.

The Chemical Structures of Compounds 249-269

In 2016, five new michellamine-type dimeric naphthylisoquinoline alkaloids, named michellamines A₂, A₃, A₄, B₂, and B₃ (270-274), were isolated from the root bark of the Central African liana Ancistrocladus congolensis, along with their two known parent compounds, michellamines A (275) and B (276)¹¹⁰. More recently in 2018, michellamines A₆ (277) and A₇ (278), the first dimeric 5,8′-coupled naphthylisoquinoline alkaloids with cis-configured stereocenters in both tetrahydroisoquinoline subunits, were isolated from the leaves of an unidentified Congolese Ancistrocladus liana together with two new dimeric analogs, michellamines B₄ (279) and B₅ (280)¹¹¹ (Figure 13). In addition, ancistrobonsolines A₁ (281) and A₂ (282), unique naphthyldihydroisoquinolines with an M-configured biaryl axis and R-configuration at C-3, together with five known compounds, ancistroealaine C (283), korupensamines A (284) and B (285), 270 and michellamine E (286) were reported¹¹¹ (Figure 14).

Figure 13.

The Chemical Structures of Compounds 270-280

Figure 14.

The Chemical Structures of Compounds 281-298

In 2017, ealapasamines A-C (287-289), three unusual new heterodimeric naphthylisoquinoline alkaloids, were obtained from the leaves of the Congolese Ancistrocladus ealaensis¹¹² (Figure 14). These ‘mixed’, constitutionally unsymmetrical dimers are the first cross-coupled products of a 5,8′- and a 7,8′-coupled naphthylisoquinoline linked via C-6′ in both naphthalene segments. Previously, dimers with a central 6,6″-axis were found only from two African Ancistrocladus species¹¹². The following year, four new [(michellamine A₅ (290), mbandakamines C-E (291-293)] and one known [mbandakamine A (294)] dimeric naphthylisoquinoline alkaloids were isolated in another study on A. ealaensis^32,113. Four new 5,8′-coupled monomeric naphthylisoquinolines, ancistroealaines C-F (283, 295-297) as well as five known compounds 214, 243, 245, 284 and ancistrolikokine B (298) were isolated from the same plant¹¹³ (Figure 14).

2.7. Phenanthridine alkaloid

2.7.1. Benzophenanthridine alkaloid

Benzophenanthridine isoquinoline compounds occur only in higher plants and show a wide spectrum of non-specific biological activities as well as multiple pharmacological properties. Sanguinarine (299) (Figure 15), the most extensively studied alkaloid of this group, exhibits many biological effects, such as antibacterial¹¹⁴, antifungal^115,116, anti-inflammatory¹¹⁷, antioxidant¹¹⁸, antiviral¹¹⁹, nematicidal¹²⁰, antitumor¹²¹, immunomodulatory¹²², and insecticidal^123,124 activities.

Figure 15.

The Chemical Structures of Compounds 299-320

Chelidonine (300) and homochelidonine (301), two B/C-cis-11-hydroxyhexahydrobenzo[c]phenanthridine alkaloids classified as partially hydrogenated-type congeners, were isolated and described as the main natural constituents of Chelidonium majus¹²⁵. From the same plant, six pairs of 6-monosubstituted dihydrobenzophenanthridine alkaloids were separated as corresponding six scalemic mixtures from the aerial parts. Two scalemic mixtures were assigned as (1′R,6R/1′S,6S)- and (1′S,6R/ 1′R,6S)-1-(dihydrochelerythrine-6-yl) ethanol (302, 303), two as (1′R,6R)/(1′S,6S)- and (1′S,6R)/ (1′R,6S)-1-(dihydrosanguinarine-6-yl)ethanol (304, 305), one as (±)-ethyl 2-(dihydrosanguinarine-6-yl) acetate (306), and one as (±)-ethyl dihydrosanguinarine-6-carboxylate (307) (Figure 15)¹²⁶.

Heitziquinone (308), a new benzophenanthridine alkaloid, together with dihydronitidine (309), isoarnottianamide (310), rhoifoline B (311) were found as minor compounds from a hexane extract of Zanthoxylum heitzii stem bark¹²⁷. Furthermore, dihydrocheleryhtrine (312) was isolated from Z. tingoassuiba⁹⁴ and decarine (313) was identified from Z. myriacanthum var. pubescens bark¹²⁸.

The genus Corydalis contains many benzophenanthridine alkaloids. Corynoline (314) from Corydalis bungeana possesses anti-inflammatory and antibacterial activities¹²⁹. Ambinine (315), the major alkaloid of tuber C. ambigua var. amurensis tuber, produces protective effects on H9C2 myocardial cells¹³⁰. Norsanguinarine (316), (−)-6-acetonyldihydrisanguinarine (317) and cavidilinine (318) were isolated from C. tomentella²⁸, and compound 317 also was found in the whole plant of C. pallida⁹⁰. 8-Methoxydihydrosanguinarine (319) and dihydrosanguinarine (320) were obtained from C. mucronifera⁹⁹ (Figure 15).

2.7.2. Pyrrolophenanthridine alkaloids

The pyrrolephenanthridines have a non-linear tetracyclic structure (6-6-6-5) containing three six-membered rings (“phenanthridine”) and one five-membered ring (“pyrrole”). The N-atom and two carbons are common to the phenanthrene and pyrrole, while the points of fusion result in either a pyrrolo[3,2,1-de]phenanthridine (e.g., 321) or a 5,10b-ethanophenanthridine (e.g., 326, 328).

Lycorine-type alkaloids, including lycorine (321), acetycaranine (322), caranine (323), galanthine (324), 9-O-demethylgalanthine (325), as well as α-crinane types, haemanthamine (326), haemanthidine (327), and β-crinane types, ambelline (328), 11-O-acetylambelline (329), 1-O-acetylbulbisine (330), undulatine (331), crinamidine (332), buphanamine (333) and srinine (334), were isolated from Zephyranthes robusta, Chlidanthus fragrans, Nerine bowdenii and Narcissus poeticus cv. Brackenhurst by Cahlíková and collegaues, these compounds show moderate antitumor activities^131-136. In 2018, a novel lycorine-related iminium salt, 6,7,11b,11c-didehydrolycorinium salt (335), as well as the above compounds were isolated from bulbs of both Crinum firmifolium and C. hardyi¹³⁷. Seco-isopowellaminone (336), 326 and incartine (337) also were isolated from Narcissus poeticus cv. Pink Parasol¹³⁸ (Figure 16).

Figure 16.

The Chemical Structures of Compounds 321-337

2.8. Manzamine alkaloids

The isoquinoline ring in manzamine alkaloids is both attached to a β-carboline (9H-pyrido[3,4-b]indole) heterocycle and fused with two polycyclic N-containing systems. Since manzamine A hydrochloride (keramamine A, 338) was initially isolated from an Okinawan sponge in 1986, almost 100 natural manzamines have been isolated from Indian and Pacific sponges^9,139-145. In 2017, five new manzamine alkaloids, kepulauamine A (339), manzamine B N-oxide (340), 3,4-dihydromanzamine B N-oxide (341), 11-hydroxymanzamine J (342), and 31-hydroxymanzamine A (343), together with new hydrogen chloride salts of the known manzamine J N-oxide and 3,4-dihydromanzamine J N-oxide, as well as five known manzamine alkaloids, 32,33-dihydro-31-hydroxymanzamine A (344), 338, 6-deoxymanzamine X (345), manzamine B (346), and neo-kauluamine (347), a manzamine dimer, were isolated from an Indonesian Acanthostrongylophora sp. sponge¹⁴⁶ (Figure 17).

Figure 17.

The Chemical Structures of Compounds 338-347

2.9. Emetine isoquinoline alkaloids

Emetine (348) as well as its analogs are present in three plant families, Alangiaceae, Icacinaceae, and Rubiaceae. Structurally, 348 contains both pyridoisoquinoline and isoquinoline heterocycles linked through a methylene bridge. Another heterocycle found in compounds from this classification is a 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole. Previous studies showed that 348 can be used as an emetic and expectorant,¹⁴⁷ and recently, its antiviral and anti-trypanosomes activities were proved^148,149. In 2017, a new emetine isoquinoline alkaloid, 7′,10-dide-O-methylcephaeline (349), as well as the known 10-O-demethylprotoemetine (350) were identified and isolated from Ophiorrhiza nutans⁹⁵. In 2018, two new alkaloids of this type, 8-hydroxytubulosine (351) and 9-demethyltubulosine (352), were isolated from Alangium longiflorum⁹⁷ (Figure 18).

Figure 18.

The Chemical Structures of Compounds 348-352

2.10. Morphine isoquinoline alkaloids

Like aporphine alkaloids, morphine alkaloids have a 1-benzylisoquinoline skeleton with one additional ring closure. However, the added bond is between the 2′-carbon in the pendant phenyl ring and carbon 4a, rather than 1a, at the isoquinoline ring junction. Morphinan or 1,3,4,9,10,10a-hexahydro-2H-10,4a-(azanoethano)phenanthrene is the prototype chemical skeleton of this alkaloid classification. However, compounds with several structural variations, including rearranged (e.g., spiro) or additional rings, are found as well.

In 2014, two morphinandienones, (+)-sebiferine (353) and (−)-milonine (354), were isolated from Dehaasia longipedicellata³⁸. Also, new bistetrahydroisoquinolines with morphinane-proaporphine and morphinane-benzyltetrahydroisoquinoline types, sinomacutines A–C (355-357), and cephalonine-2-O-β-d-glucopyranoside (358), together with sinomenine (359) and sinoacutine (360) were isolated from the rhizomes of Sinomenium acutum⁴⁰.

Subsequently, two new compounds, 8-demethoxycephatonine (361) and 7(R)-7,8-dihydrosinomenine (362), along with eight morphine alkaloids, 359, 8-demethoxyrunanine (363), 14-episinomenine (364), sinomenine N-oxide (365), salutaridine (366), acutumine (367), acutumidine (368) and dauricumine (369) were isolated from a rhizome extract of Sinomenium acutum⁸¹. Then in 2018, the morphinadienone pallidine (370) was found for the first time in Unonopsis floribunda³⁶ and O-methylflavinantine (371) was isolated from Thalictrum cirrhosum⁴³ (Figure 19).

Figure 19.

The Chemical Structures of Compounds 353-371

2.11. Phthalideisoquinoline alkaloids

As indicated by the classification’s name, tetracyclic phthalideisoquinoline alkaloids contain both bicyclic isoquinoline and bicyclic phthalide (fused benzene and gamma-lactone ring) systems. From the basic structure of a 1-benzylisoquinoline, the ester functionality (O-C=O) forming the lactone is inserted between the benzyl linking carbon and an alpha-carbon on the pendant phenyl ring.

Two phthalideisoquinoline alkaloids, (+)-bicuculline (372) and (+)-corlumine (373), were isolated from Fumaria officinalis and Viola tianschanica in 2016 and 2017, respectively^24,150. Three undescribed isoquinolines, (9S,7′S) tomentelline A (374), (9S,7′R) tomentelline A (375), (9R,7′S) tomentelline B (376) together with adlumidine (377) and (+)-capnoidine (378) were isolated for the first time from Corydalis tomentella²⁸. Five pairs of isoquinoline alkaloid enantiomers, mucroniferanines A–E (379-383), two inseparable epimeric pairs, mucroniferanines F (384) and G (385), and five known isoquinoline alkaloids, 377, (±)-hypecorinine (386), (−)-7′-O-methylegenine (387), sibiricine (388) and (+)-humosine A (389) were obtained from C. mucronifera⁹⁹. Capnoidine (390) was isolated from a third related species, C. dubia¹⁵¹ (Figure 20).

Figure 20.

The Chemical Structures of Compounds 372-390

2.12. Benzopyrroloisoquinoline alkaloids

Seldom found in nature, the benzopyrroloisoquinolines have a linear tetracyclic structure (6-6-6-5) containing two aromatic six-membered rings, one non-aromatic six-membered heterocyclic ring and one five-membered heterocyclic ring. Thus, the alkaloid N-atom and one adjacent carbon are shared by benzopyrrole and isoquinoline systems. In 2017, a dimeric benzopyrroloisoquinoline alkaloid, tengerensine (391) with a rare unsymmetrical cyclobutane adduct was isolated from Ficus fistulosa var. tengerensis¹⁵² (Figure 21).

Figure 21.

The Chemical Structure of Compound 391

2.13. Phenylethyltetrahydroisoquinoline alkaloids

The simplest compounds are 1-phenylethylisoquinolines (-CH₂CH₂C₆H₅) rather than 1-benzylisoquinolines (-CH₂C₆H₅). However, more complex rearranged compounds, including those with a tetracyclic 6-7-5-6 system, also belong to this classification. In 2016, the new compound fumarostrejdine (392) and its known oxo-derivative (±)-O-methylfumarofine (393) were isolated from Fumaria officinalis²⁴ (Figure 22).

Figure 22.

The Chemical Structures of Compounds 392-393

2.14. Various isoquinoline alkaloids

In 2014, a new alkaloid, coptichine (394), from the Coptidis Rhizoma-Euodiae Fructus couple showed significant cytotoxicity against NCI-N87 cells⁶¹. Coptisonine (395) from Coptis chinensis showed significant stimulation of glucose uptake⁸⁹. Sallisonine D (396) was isolated from the rhizomes of Sinomenium acutum⁴⁰.

A new compound, alternamine A (397) was isolated from the aerial parts of Alternanthera littoralis¹⁵³. The phenethylisoquinoline alkaloid (±)-7-benzyloxy-1-(3-benzyloxy-4-methoxyphenethyl)-1,2,3,4-tetrahydro-6-methoxy-2-methylisoquinoline oxalate (398) was targeted as a novel ABCB1 inhibitor based on high-throughput screening of a chemical library¹⁵⁴ (Figure 23).

Figure 23.

The Chemical Structures of Compounds 394-406

Tomentelline C (399), tomentelline D (400), and 6,7-methylenedioxy-2-(6-acetyl-2,3-methylenedioxybenzyl)-1(2H)-isoquinolinone (401) were obtained for the first time from Corydalis tomentella. They exhibited hepatoprotective activities²⁸. Oleracein E (402) was isolated from the medicinal plant Portulaca oleracea³¹. Two undescribed isoquinoline alkaloids, pipermullesines B (403) and C (404), were isolated from the aerial parts of Piper mullesua¹⁵⁵.

Zhang et al.¹⁵⁶ isolated a structurally unusual cyclopenta[de]isoquinoline alkaloid, delavatine A (405), from Incarvillea delavayi. It exhibited substantial cytotoxicity and anti-inflammatory activities¹⁵⁷. A novel tropoloisoquinoline alkaloid, neotatarine (406), was isolated from a 95% ethanol extract of the rhizome parts of Acorus calamus L in 2017¹⁵⁸ (Figure 23).

3. Bioactivities

3.1. Antitumor activities

3.1.1. Cytotoxic activity

In the search to find potential antitumor agents from isoquinoline alkaloids, the most commonly studied bioactivity is the cytotoxicity of new isolated and known compounds from plants. In this review, we list in Table 2 the inhibitory rates and the IC₅₀ values of compounds against various cancer cell lines corresponding to different human tumors, such as HL-60 (acute promyelocytic leukemia), Jurkat (acute T cell leukemia), MOLT-4 (acute lymphoblastic leukemia), A549 (lung carcinoma), H1299 (non-small cell lung cancer), COLO-201 (colorectal adenocarcinoma), AGS (gastric adenocarcinoma), PANC-1 (pancreas epithelioid carcinoma), A2780 (ovarian carcinoma), HeLa (cervix adenocarcinoma), MCF-7 (breast adenocarcinoma) and SAOS-2 (osteosarcoma). From this table, we found that most compounds exhibited moderate cytotoxicity with IC₅₀ values ranging from 10 to 50 μM^{22, 25, 26, 33, 38, 40, 45, 46, 61, 85, 97, 105-109, 111, 113, 125, 136, 146, 152,156,159}.

Table 2.

The cytotoxic activity of isoquinoline alkaloids

Compound	Cell lines or organism	Biological results	Positive drug	Ref.
3,8-Diolisoquinoline (1)	HT-29 U87 A549 Bel-7402 MGC-803 Hela cells	4.40 μM (IC50) 3.46 μM (IC50) 6.20 μM (IC50) 8.05 μM (IC50) 25.75 μM (IC50) >30.00μM (IC50)	Paclitaxel 0.77 μM (IC50), 2.74 μM (IC50), 2.67 μM (IC50), 1.98 μM (IC50), 3.87 μM (IC50), 0.90 μM (IC50)	22
1-Methoxy-4,5-diolisoquinoline (2)	HT-29 U87 A549 Bel-7402 MGC-803 Hela cells	1.19 μM (IC50) 2.14 μM (IC50) 2.46 μM (IC50) 4.10 μM (IC50) 9.73 μM (IC50) 16.15 μM (IC50)	Paclitaxel 0.77 μM (IC50), 2.74 μM (IC50), 2.67 μM (IC50), 1.98 μM (IC50), 3.87 μM (IC50), 0.90 μM (IC50)	22
4-Methoxy-1,5-dihydroisoquinoline (3)	HT29 A549 Bel7402 MGC803 U87	18.63 μM (IC50) 29.25 μM (IC50) 29.92 μM (IC50) 35.26 μM (IC50) 41.20 μM (IC50)	--	23
6,7-Dimethoxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid (7)	Huh-7	13.97 μM (EC50)		26
(−)-Reticuline (19)	A549 A375 BxPC-3	>200.00 μM (IC50) 97.60 μM (IC50) 82.57 μM (IC50)	Cisplatin 17.52 μM, 35.9 μM, 26.86 μM (IC50)	38
Hernandezine (43)	pcDNA-HEK 293 (parental) MDR19-HEK293 (resistant) KB-3-1(parental) KB-V-1 (resistant)	3.85, 27.25 nM (IC50, 500 nm + Doxorubicine); 0.11 and 0.10 μM (IC50, 500 nM + Doxorubicine)	5.28 and 504.65 nM (IC50, Doxorubicine only) 0.15 and 5.07 μM (IC50, doxorubicine only)	45
6,7,12-Trimethoxy-2-methyl-13-hydroxy-11-(4′-formylphenoxy) benzylisoquin oline (44)	GSC-3#	43.15 μM (IC50)	Taxol IC50 15.92 μM; Temozolomide IC50 > 257.53 μM.	46
(−)-O-O-Dimethylgrisabine (51)	A549 A375 BxPC-3	>200.00 μM (IC50) 82.85 μM (IC50) >200.00 μM (IC50)	Cisplatin 17.52 μM, 35.90 μM, 26.86 μM (IC50)	38
Coptichic aldehyde (63)	NCI-N87 Caco-2	30.14 μM (IC50) >100.00 μM (IC50)	Vinorelbine 12.19 μM (IC50), 21.64 μM (IC50)	61
(−)-Boldine (77)	A549 A375 BxPC-3	117.57 μM (IC50) 112.53 μM (IC50) 45.50 μM (IC50)	Cisplatin 17.52 μM, 35.90 μM, 26.86 μM (IC50)	38
(−)-Norboldine (78)	A549 A375 BxPC-3	>200.00 μM (IC50) 82.89 μM (IC50) 27.06 μM (IC50)	Cisplatin 17.52 μM, 35.90 μM, 26.86 μM (IC50)	38
(+)-8-(4′-Formylphenoxy) glaucine (113)	GSC-3#	40.48 μM (IC50)	Taxol IC50 15.92 μM; Temozolomide IC50 > 257.53 μM.	46
(+)-3-Methoxy-8-(4′-formylphenoxy) glaucine (115)	GSC-3#	30.12 μM (IC50)	Taxol IC50 15.92 μM; Temozolomide IC50 > 257.53 μM.	46
1,2,3,9,10-Pentamethoxy-11-(4′-formylphenoxy)-7-oxoaporphine (136)	GSC-3#	32.52 μM (IC50)	Taxol IC50 15.92 μM; Temozolomide IC50 > 257.53 μM.	46
1,2,9,10-Tetramethoxy-11-(4′-formylphenoxy)-7-oxoaporphine (137)	GSC-3#	32.81 μM (IC50)	Taxol IC50 15.92 μM; Temozolomide IC50 > 257.53 μM.	46
Dehydrocrebanine (138)	HeLa MDA-MB231 MCF-7	18.73 μM (IC50) 14.52 μM (IC50) 10.64 μM (IC50)	Paclitaxel 2.29 μM (IC50), 2.56 μM (IC50), 3.99 μM (IC50)	85
Crebanine (139)	HeLa MDA-MB231 MCF-7	48.13 μM (IC50) 38.94 μM (IC50) 30.50 μM (IC50)	Paclitaxel 2.29 μM (IC50), 2.56 μM (IC50), 3.99 μM (IC50)	85
Stephanine (140)	HeLa MDA-MB231 MCF-7	3.33 μM (IC50) 5.66 μM (IC50) 6.49 μM (IC50)	Paclitaxel 2.29 μM (IC50), 2.56 μM (IC50), 3.99 μM (IC50)	85
O-Methylbulbocapnine (141)	HeLa MDA-MB231 MCF-7	70.37 μM (IC50) 56.59 μM (IC50) 39.36 μM (IC50)	Paclitaxel 2.29 μM (IC50), 2.56 μM (IC50), 3.99 μM (IC50)	85
Berberine (151)	HL60 AZ521 SK-BR-3 B16 melanoma	29.40 μM (IC50) 2.60 μM (IC50) 21.00 μM (IC50) Melanin content 8.9% at 10 μM	Cisplatin 4.20 μM (IC50), 9.50 μM (IC50), 18.80 μM (IC50) Melanin content 92.7% for arbutin at 10 μM	33
8-Oxocoptisine (168)	NCI-N87 Caco-2	20.31 μM (IC50) >100.00 μM (IC50)	Vinorelbine 12.19 μM (IC50), 21.64 μM (IC50)	61
13-Carboxaldehyde-8-oxocoptisine (182)	NCI-N87 Caco-2	35.98 μM (IC50) >100.00 μM (IC50)	Vinorelbine 12.19 μM (IC50), 21.64 μM (IC50)	61
Ancistectorine D (203)	CCRF-CEM CEM/ADR5000	4.50 μM (IC50) 25.83 μM (IC50)	Doxorubicin 0.02 μM (IC50), 30.07 μM (IC50)	105
Ancistrotectoriline A (205)	PANC-1	67.80 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistrobenomine B (211)	CCRF-CEM CEM/ADR5000	3.50 μM (IC50) 21.38 μM (IC50)	Doxorubicin 0.02 μM (IC50), 30.07 μM (IC50)	106
6-O-Methylhamatine (226)	PANC-1	31.90 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
4′-O-Demethylancistrocladine (227)	PANC-1	11.20 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistrocyclinone A (231)	CCRF-CEM CEM/ADR5000	16.21 μM (IC50) 25.32 μM (IC50)	Doxorubicin 0.02 μM, 30.07 (IC50)	107
Ancistrocladinium A (233)	CCRF-CEM CEM/ADR5000	1.40 μM (IC50) >100.00 μM (IC50)	Doxorubicin 0.02 μM, 30.07 (IC50)	107
4′-O-Demethylancistrocladinium A (234)	CCRF-CEM CEM/ADR5000	1.50 μM (IC50) >100.00 μM (IC50)	Doxorubicin 0.02 μM, 30.07 μM (IC50)	107
6,4′-O,O-Didemethylancistrocladinium A (235)	CCRF-CEM CEM/ADR5000	>100.00 μM (IC50) >100.00 μM (IC50)	Doxorubicin 0.02 μM, 30.07 μM (IC50)	107
Dioncophylline F (239)	L6 cells INA-6 PMBCs	14.52 μM (IC50) 21.00 μM (EC50) 16.00 μM (EC50)	Podophyllotoxin 0.02 μM (IC50) Melphalan 2.00 μM (EC50); 3.00 μM (EC50)	108
Dioncophylline C2 (240)	L6 cells	43.31 μM (IC50)	Podophyllotoxin 0.02 μM (IC50)	108
Dioncophylline D2 (241)	L6 cells INA-6	62.84 μM (IC50) 32.00 μM (EC50)	Podophyllotoxin 0.02 μM (IC50) Melphalan 2.00 μM (EC50)	108
5′-O-Methyldioncophylline D (242)	L6 cells INA-6 PMBCs	4.02 μM (IC50) 2.60 μM (EC50) 19.00 μM (EC50)	Podophyllotoxin 0.02 μM (IC50) Melphalan 2.00 μM (EC50); 3.00 μM (EC50)	108
Dioncophylline A (243)	INA-6	0.22 μM (EC50)	Melphalan 2.00 μM (EC50)	108
4′-O-Demethyldioncophylline A (244)	INA-6 INA-6 PMBCs	2.70 μM (EC50) P 16.00 μM (EC50) M 50.00 μM (EC50)M	Melphalan 2.00 μM (EC50) 3.00 μM (EC50)	108
Ancistrobrevine C (246)	L6 cells	34.85 μM (IC50)	Podophyllotoxin 0.02 μM (IC50)	108
Ancistrocladisine A (247)	L6 cells INA-6	30.01 μM (IC50) 4.80 μM (EC50)	Podophyllotoxin 0.02 μM (IC50) Melphalan 2.00 μM (EC50)	108
Ancistroyafungine A (249)	PANC-1	22.70 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistroyafungine B (250)	PANC-1	7.60 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistroyafungine C (251)	PANC-1	15.00 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistroyafungine D (252)	PANC-1	9.70 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistroguineine A (253)	PANC-1	15.80 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistrobertsonine A (254)	PANC-1	11.80 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Ancistrobrevine B (255)	PANC-1	20.20 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
6,5′-O,O-Didemethylancistroealaine A (256)	PANC-1	9.80 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
6-O-Demethylancistroealaine A (257)	PANC-1	14.00 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
7-Epi-ancistrobrevine D (258)	PANC-1	29.90 μM (PC50)	Arctigenin 0.80 μM (PC50)	109
Michellamine A2 (260)	Hela PANC-1	32.10 μM (IC50) 19.30 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Michellamine A6 (268)	Hela PANC-1	14.80 μM (IC50) 54.20 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Michellamine A7 (269)	Hela PANC-1	20.60 μM (IC50) 24.30 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Michellamine B4 (270)	Hela PANC-1	46.30 μM (IC50) 50.30 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Michellamine B5 (271)	Hela PANC-1	29.80 μM (IC50) 60.20 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Ancistrobonsoline A1 (272)	Hela PANC-1	14.30 μM (IC50) 7.50 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Ancistrobonsoline A2 (273)	Hela PANC-1	21.50 μM (IC50) 12.10 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Ancistroealaine C (274)	Hela PANC-1	30.50 μM (IC50) >100.00 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Korupensamine A (275)	Hela PANC-1	48.30 μM (IC50) >100.00 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Korupensamine B (276)	Hela PANC-1	37.80 μM (IC50) 94.90 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Michellamine E (277)	Hela PANC-1	8.80 μM (IC50) 18.90 μM (IC50)	5-Fluorouracil 13.90 μM; Arctigenin 0.80 μM (IC50)	111
Mbandakamine A (281)	CCRF-CEM CEM/ADR5000	7.40 μM (IC50) 23.88 μM (IC50)	Doxorubicin 0.02 μM, 30.07 μM (IC50)	113
Mbandakamine C (282)	CCRF-CEM CEM/ADR5000	1.50 μM (IC50) 27.71 μM (IC50)	Doxorubicin 0.02 μM, 30.07 μM (IC50)	113
Mbandakamine D (283)	CCRF-CEM, CEM/ADR5000	2.96 μM (IC50) 19.03 μM (IC50)	Doxorubicin 0.02 μM, 30.07 μM (IC50)	113
Ancistroealaine F (288)	CCRF-CEM CEM/ADR5000	11.69 μM (IC50) 19.94 μM (IC50)	Doxorubicin 0.02 μM, 30.07 μM (IC50)	113
Chelidonine (291)	MOLT-4, Jurkat, HL-60, Raji, U-937, HEL 92.1.7., PBMCs, MRC-5, WI-38	4.60, 2.20, 4.40, 3.20, 5.00, 3.40, >10.00, 1.8., >10.00 μM (IC50)	--	125
Homochelidonine (292)	MOLT-4, Jurkat, HL-60, Raji, U-937, HEL 92.1.7., PBMCs, MRC-5, WI-38	4.80, 5.60, 8.30, 6.80, >10.00, >10.00, >10.00, >10.00, >10.00 μM (IC50)		125
Lycorine (312)	HL-60, Jurkat, MOLT-4, A549, H1299, COLO- 201, HT-29, SW-480, AGS, PANC-1, A2780, HeLa, BT-549, MCF-7, MDA-MD-231, SAOS-2, SK-BR-3	0.80-1.40 μM (IC50)	--	136
Haemanthamine (317)	HL-60, Jurkat, MOLT-4, A549, H1299, COLO-201, HT-29, SW-480, AGS, PANC-1, A2780, HeLa, BT-549, MCF-7, MDA-MD-231, SAOS-2, SK-BR-3	0.30-9.80 μM (IC50)	--	136
Haemanthidine (318)	HL-60, Jurkat, MOLT-4, A549, H1299, COLO- 201, HT-29, SW-480, AGS, PANC-1, A2780, HeLa, BT-549, MCF-7, MDA-MD-231, SAOS-2, SK-BR-3	1.60-9.70 μM (IC50)	--	136
Manzamine A (329)	A549 K562	8.30 μM (IC50) 11.00 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
Kepulauamine A (330)	A549 K562	4.60 μM (IC50) 7.20 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
Manzamine B N-oxide (331)	A549 K562	12.00 μM (IC50) 9.80 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
3,4-Dihydromanzamine B N-oxide (332)	A549 K562	5.80 μM (IC50) 5.20 μM (IC50)	Doxorubicin 0.92μM (IC50) and 1.1μM (IC50)	146
11-Hydroxymanzamine J (333)	A549 K562	6.20 μM (IC50) 8.20 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
31-Hydroxymanzamine A (334)	A549 K562	5.80 μM (IC50) 7.20 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
32,33-Dihydro-31-hydroxymanzamine A (335)	A549 K562	8.20 μM (IC50) 8.40 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
6-Deoxymanzamine X (336)	A549 K562	6.70 μM (IC50) 9.10 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
Manzamine B (337)	A549 K562	6.50 μM (IC50) 9.60 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
neo-Kauluamine (338)	A549 K562	13.00 μM (IC50) 12.00 μM (IC50)	Doxorubicin 0.92 μM (IC50) and 1.10 μM (IC50)	146
8-Hydroxytubulosine (342)	A549 MDA-MB-231 MCF-7 KB KB-VIN	0.21 μM (IC50) 0.06 μM (IC50) 0.12 μM (IC50) 0.09 μM (IC50) 8.90 μM (IC50)	Doxorubicin 0.48 μM, 0.78 μM (IC50), 0.72 μM (IC50), 0.82 μM (IC50), >1.00 μM (IC50)	97
9-Demethyltubulosine (343)	A549 MDA-MB-231 MCF-7 KB KB-VIN	0.36 μM (IC50) 0.19 μM (IC50) 0.25 μM (IC50) 0.29 μM (IC50) >10.00 μM (IC50)	Doxorubicin 0.48 μM, 0.78 μM (IC50), 0.72 μM (IC50), 0.82 μM (IC50), >1.00 μM (IC50)	97
(+)-Sebiferine (344)	A549 A375 BxPC-3	>200.00 μM (IC50) >200.00 μM (IC50) 93.39 μM (IC50)	Cisplatin 17.52 μM, 35.90 μM, 26.86 μM (IC50)	38
(−)-Milonine (345)	A549 A375 BxPC-3	>200.00 μM (IC50) >200.00 μM (IC50) >200.00 μM (IC50)	Cisplatin 17.52 μM, 35.90 μM, 26.86 μM (IC50)	38
(+)-Tengerensine (382)	MDA-MB-468	7.40 μM (IC50)	Paclitaxel 0.01 μM (IC50)	152
Coptichine (385)	NCI-N87 Caco-2	8.92 μM (IC50) >100.00 μM (IC50)	Vinorelbine 12.19 μM (IC50), 21.64 μM (IC50)	61
Noroxyhydrastinine (389)	B16 melanoma cells	Melanin content 76.1% at 10.00 μM	Melanin content 92.7% for arbutin at 10.00 μM	33
Delavatine A (401)	MCF7 HCT116 SKOV3 SMMC-7721 HeLa	22.32 μM (IC50) 19.90 μM (IC50) 15.43 μM (IC50) 17.27 μM (IC50) 23.83 μM (IC50)	Celastrol 2.04 μM (IC50), 3.20 μM (IC50), 3.93 μM (IC50), 1.31μM (IC50), 1.73 μM (IC50)	156
Neotatarine (402)	PC12	At 2.00, 4.00, 8.00 μM inhibit Aβ25-35 induced cell death	--	158

INA-6 Multiple Myeloma Cells and Peripheral Mononuclear Blood Cells (PMBCs); Human breast cancer cell lines: MDA-MB-468, HL-60 (acute promyelocytic leukemia), Jurkat (acute T cell leukemia), MOLT-4 (acute lymphoblastic leukemia), A549 (lung carcinoma), H1299 (non-small cell lung cancer), COLO-201 (colorectal adenocarcinoma), HT-29 (colorectal adenocarcinoma, p53 mutant), SW-480 (colorectal adenocarcinoma), AGS (gastric adenocarcinoma), PANC-1 (pancreas epithelioid carcinoma), A2780 (ovarian carcinoma), HeLa (cervix adenocarcinoma), BT-549 (breast ductal carcinoma, triple negative), MCF-7 (breast adenocarcinoma), MDA-MD-231 (breast adenocarcinoma, triple negative), SAOS-2 (osteosarcoma) and SK-BR-3 (breast adenocarcinoma, p53-deficient), Huh-7 cells (human hepatic carcinoma cell line), Parental pcDNA3.1-HEK293, MDR19-HEK293 (HEK293 cells transfected with human ABCB1), GSC-3^# (glioma stem cells); CCRF-CEM (human leukemia cells), CEM/ADR5000 (human multi-drug-resistant tumor cells).

NR: not reached.

--: No determination

Three Amaryllidaceae alkaloids, lycorine (321), haemanthamine (326) and haemanthidine (327), showed the best cytotoxicity against 17 human cell types with individual IC₅₀ values in the range of 0.30-9.80 μM compared with other compounds listed in Table 2. Higher antiproliferative effects also were reported. Unfortunately, the cytotoxic activities of positive agents were not investigated in this reference¹³⁶. The alkaloids caused cells to accumulate preferentially at G1 and G2 stages of the cell cycle with increased p16 expression and Chk1 Ser345 phosphorylation. Concerning a pro-apoptotic effect in the Jurkat leukemia cell line, compound 327 was more active than 326¹³⁰. These results also provided a new clue for developing these alkaloids as potential antitumor agents.

8-Hydroxytubulosine (351) from Alangium longiflorum also exhibited remarkable antiproliferative activity. It presented better activities against A549, MDA-MB-231, MCF-7 and KB cell lines than the positive drug doxorubicin and the known alkaloid 9-demethyltubulosine (352). The IC₅₀ values of 351 were 0.21, 0.06, 0.12 and 0.09 μM, respectively⁹⁷.

The aporphine alkaloid (−)-norboldine (86) exhibited potent cytotoxicity towards pancreatic cancer cell line BxPC-3 with an IC₅₀ value of 27.06 μM, but no toxicity towards the normal pancreatic cell line⁶⁰. Two oxoaporphines, 145 and 146, showed cytotoxicity against glioma stem cells (GSC-3^#) with IC₅₀ values of 32.52 and 32.81 μM, respectively, while the IC₅₀ of the antitumor drug taxol was 15.92 μM⁴⁶. However, the antitumor activity in vivo and the mechanism underlying the cytotoxicity of the compounds are still unclear and should be studied further.

3.1.2. Mechanism of action

During the past five years, numerous studies have investigated and reported antitumor mechanism of known and new isolated isoquinoline alkaloids. In this section, we will briefly introduce the antitumor mechanisms of some prominent molecules.

Berberine (161) shows antitumor effects against various tumor cells. Noteworthy, it presents the strongest cytotoxicity against AZ521 cell with the IC₅₀ value of 2.60 μM, while the IC₅₀ of the antitumor drug cisplatin was 9.50 μM. Berberine inhibited cancer cell proliferation via several mechanisms of action, such as the positive regulation of reactive oxygen species and the apoptotic pathway as well as suppressed cancer metastasis by stopping transferase activity^160-163. The potential targets also include mitochondrial function, DNA topoisomerase and arylamin N-acetyltransferase activity, NF-κB signal pathway, the EGF and the VEGF receptors, etc. In human hepatoma cells, the alkaloid’s antiproliferative effect on might be mediated via the CAR metabolic and the arachidonic acid pathways, cPLA₂, COX-2 gene expression and mitochondria-mediated apoptosis also were suppressed in vitro and in vivo^164-166, and the IC₅₀ values against human hepatoma Bel-7404, H22 and HepG2 HCC cells were 9.21, 43.20 and 82.80 μM, respectively. However, the cytotoxicity of berberine against the normal hepatic embryonic cells was weak, the IC₅₀ value was 122.4 μM for the HL-7702 at 72 h. The further report showed that it blocked the caspase 3-iPLA₂-AA-COX-2-PGE₂ pathway of ovarian cancer cells and reversed the repopulation, which was triggered by the chemotherapy drug VP16¹⁶⁷. In breast tumors, berberine significantly down-regulated the expression of NF-κB and proliferating cell nuclear antigen (PCNA) In vivo¹⁶⁸. However, the targets of berberine against the different breast cancer are different, it activated caspase-9/cytochrome c-mediated apoptosis to inhibit the growth of two triple negative breast cancer cell (TNBC) lines (IC₅₀ 43.28 μM for BT549 and 47.51 μM for MDA-MB-231 cells) in vitro ¹⁶⁹ and inhibited the proliferation and migration of breast cancer ZR-75-30 cells (IC₅₀ 5.30 μM) by targeting Ephrin-B2¹⁷⁰.

Reports indicated that berberine mediates epigenetic reprogramming via HDAC inhibition and regulates Bcl-2/Bax family proteins in the human lung cancer A549 cell line¹⁷¹. Furthermore, it inhibited the growth of intestinal polyps in animals and patients with the familial adenomatous polyposis and cell growth in colon cancer by down-regulating β-catenin signaling via binding RXRα¹⁷². In human glioblastoma cells, berberine induced senescence by down-regulating the EGFR-MEK-ERK signaling pathway¹⁷³, and modulated the expression of epigenetic regulators in acute myelocytic leukemia cell lines HL-60/ADR and KG1-α¹⁷⁴. The PI3K-Akt and mitogen-activated protein kinase (MAPK) signaling pathways in the treatment of thyroid carcinoma also were affected^175,176. As an berberine isoquinoline alkaloid, coptisine (165) also affected PI3K/Akt and mitochondrial-associated apoptotic pathways¹⁷⁷, it exhibited remarkably cytotoxic activities against HCT-116 cells by activating the caspase protease family, inducing G1-phase cell cycle arrest and increasing apoptosis¹⁷⁸.

The protoberberine alkaloid palmatine (166) induced cell apoptosis in MCF-7 breast cancer cells, after the treatment (1 μM, 10.8 J/cm²) the early apoptotic and late apoptotic rates increased significantly up to 21.16% and 9.86% in photodynamic therapy¹⁷⁹. Meanwhile, protoberberine stylopine (195) both functioned as an AKR1C3 inhibitor and significantly inhibited the AKR1C3-mediated reduction of the anthracycline drug daunorubicin within cells, the IC₅₀ was 0.9 μM in DHO assay¹⁸⁰. Liensinine (62) induced apoptosis and mitochondrial dysfunction, and significantly inhibited the proliferation and colony-forming ability of colorectal cancer cells accompanied by activation of the JNK signaling pathway in a dose-dependent manner¹⁸¹. However, the structurally related neferine (61) sensitized A549 cells to low doses of doxorubicin and inhibited human lung cancer cell growth through MAPK activation and cell cycle arrest^182,183.

Through the mitochondria apoptosis pathway, 3,8-diolisoquinoline (1) and 1-methoxy-4,5-diolisoquinoline (2) induced apoptosis in U87 cells with the IC₅₀ values of 3.46 and 2.14 μM, the Bcl-2/Bax protein ratio also was down-regulated²². 6,7-Dimethoxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid (7) had a significant anti-proliferative effect on human hepatoma (Huh-7) cells in vitro (EC₅₀ 13.97 μM) by inhibiting the action of caspase-8¹⁸⁴, and blocked IL-6/JAK2/STAT3 oncogenic signaling in dimethylhydrazine-induced colorectal carcinoma¹⁸⁵. Good in vivo anti-neoplastic properties were also found¹⁸⁴.

Certain naphthylisoquinoline alkaloids are noteworthy due to their anti-pancreatic cancer activity. In one study¹⁰⁹, ancistroyafungines A–D (259–262), 6-O-methylhamatine (235), 4′-O-demethylancistrocladine (236), ancistroguineine A (263), ancistrobertsonine A (264), ancistrobrevine B (265), ancistrotectoriline A (214), 6,5′-O,O-didemethylancistroealaine A (266), 6-O-demethylancistroealaine A (267), 7-epi-ancistrobrevine D (268), and ancistrocladiniums A (243) and B (269) showed moderate to strong anti-austerity activities against PANC-1 pancreatic cancer cells in a concentration-dependent manner. Their preferential cytotoxicity (PC)₅₀ values ranged from 7.60 to 67.80 μM. Among of these compounds, compound 259 (PC₅₀, 22.7 μM) was found to be almost three times less active than its 5′-O-demethyl analog compounds 260 and 262 (PC₅₀, 7.60 μM and 9.70 μM, respectively), which has two methoxy functions at C-5′ and C-4′. Structure-activity relationship (SAR) analysis indicated that O-methylation in the naphthalene portion and the substitution pattern of the isoquinoline portion play a crucial role for the cytotoxic activities of the alkaloids, especially an OMe/OH pattern seems favorable for the activity. In a second study,¹¹¹ ancistrobonsolines A₁ (281) and A₂ (282) also displayed significant PC against PANC-1 cells under nutrient-deprived conditions. Above reports suggest that the naphthylisoquinoline alkaloids are promising lead structures for the advancement of antitumor agents.

The benzophenanthridine alkaloids chelidonine (300) and homochelidonine (301) potently induced cell death in several blood cancer cell lines, such as MOLT-4, Jurkat, HL-60, Raji, PBMCs, MRC-5 and WI-38, their IC₅₀ values ranged from 1.80 to >10 μM. For MOLT-4 and Jurkat cells, treatment with chelidonine induced cell cycle arrest at the G2/M cell cycle (IC₅₀ 4.60 and 2.20 μM, respectively); treated with homochelidonine underwent biphasic dose-dependent G1 and G2/M cell cycle arrest in MOLT-4 cells (IC₅₀ 4.80 μM), and an increase in G2/M cell population in Jurkat cells (IC₅₀ 5.60 μM). Both alkaloids inhibited tubulin polymerization in A549 cells¹²⁵.

In addition, lycorine (321) presented the good therapeutic effect in a patient-derived glioblastoma xenograft by directly interacting with and inhibiting the activation of EGFR cancer cells¹⁸⁶. The potent cytotoxicity against other various cancer cells, including HL-60, Jurkat, MOLT-4, A549, also were found with IC₅₀ values from 0.80 to 1.40 μM. Noroxyhydrastinine (22) exhibited potent melanogenesis-inhibitory activities by inhibiting the expression of protein levels of tyrosinase, TRP-1, and TRP-2 partly in a-MSH-stimulated B16 melanoma cells, the melanin content was 76.10% at 10.00 μM^33,159.

Multidrug-resistant (MDR) cancers present a critical clinical problem. Bringmann et al. have investigated the effects of naphthylisoquinolines. Mbandakamines C, D and F (291, 2923, 297) showed strong cytotoxic effects against human leukemia (CCRF-CEM) and MDR tumor cells (CEM/ADR5000) with IC₅₀ values from 1.50 to 19.94 μM¹¹³. This result indicated that the axial chirality is necessary to the bioactivity. Ancistectorine D (212) and ancistrobenomine B (220) also demonstrated comparable cytotoxic effects against both cell lines (IC₅₀ 4.5 and 3.5 μM for 212; 25.83 and 21.38 μM for 220; 0.017 and 30.07 μM for positive control doxorubicin)^105,106. The overexpression of ATP-binding cassette (ABC) transporters is a common mechanism leading to MDR cancer cells. Tetrandrine (57) and tangchinoline (58) from Stephania tetrandra reversed multidrug resistance by increasing the intracellular concentration of anticancer drugs and inhibiting P-glycoprotein activity in the MDR human cancer cells Caco-2 and CEM/ADR5000, the IC₅₀ values were 19.38 and 24.98 μM respectively for compound 57⁴⁹. Hernandezine (51) selectively inhibited the transport function of the ABC drug transporter ABCB1 and enhanced drug-induced apoptosis in cancer cells at nanomolar concentrations (IC₅₀ 3.85-27.25 nM). It could be further developed as a novel reversal agent for combination therapy in patients with MDR cancer due to its nontoxicity⁴⁵.

Scoulerine (204) exhibited promising suppression of cancer cell growth and reduced the mitochondrial dehydrogenases activity of the evaluated leukemic cells with IC₅₀ values ranging from 2.70 to 6.50 μM. Further study showed that it also interfered with microtubule elements of the cytoskeleton, checkpoint kinase signaling and p53 proteins⁹⁶.

3.2. Effect on diabetes and its complications

Diabetes mellitus (DM) is mainly characterized by abnormal hyperglycemia, polydipsia, polyuria, polyphagia, and emaciation^187,188, and persistent hyperglycemia can lead to several chronic diabetic complications, including neuropathy, nephropathy, cardiopathy, and retinopathy¹⁸⁹. Currently, the global prevalence of DM is 8.5% among adults and is rising most rapidly in middle- and low-income countries¹⁹⁰. Natural products have been increasingly applied to treat DM^191,192. Over the past five years, the beneficial effects of berberines and protoberberine alkaloids on DM, atherosclerosis and hyperlipidemia have been proved in different animal models^193,194.

Berberine (161) affects multiple pathways, including p38 MAPK-GLUT4, JNK, and PI3K-Akt, related to the metabolism of glucose and lipids^89,195. For anti-diabetic activity, berberine regulated the glyco- and lipo-metabolism and stimulated of adenosine 5′-monophosphate-activated protein kinase (AMPK)¹⁹⁶ in Zucker diabetic fatty (ZDF) rats, and also inhibited miR-106b/SIRT1 pathway by reversing miR-106b over-expression and up-regulating sirtuin 1 (SIRT1) both in islets of diabetic mice and pancreatic NIT-1 cells induced by high glucose^88,197. By activating the AMPK pathway, the pioglitazone-induced bone loss in diabetic rats also were protected¹⁹⁸. The toxic towards to mice or rats in vivo test is weak. Meanwhile, it may improve insulin resistance by increasing the expression of adiponectin receptors and the ratio of high-molecular weight to total adiponectin in rats fed a high fat diet (HFD)¹⁹⁹, and improved glucose uptake and insulin-stimulated glucose consumption in palmitate-induced insulin-resistant H9c2 cardiomyocytes^200-202.

DM is closely related to the development of cardiovascular diseases²⁰³. Vascular dysfunction is a distinctive phenotype in DM, and diabetic vascular complication is associated with impaired endothelial function, augmented vasoconstriction, and increased oxidative stress²⁰⁴. Berberine can exert a cardio-protective effect by attenuating myocardial apoptosis via Notch1/Hes1-PTEN/Akt signaling as well as inhibiting excessive autophagy in cardiomyocytes through the regulation of AMPK and mTOR signaling^205,206. In addition, berberine relieved cerebral arterial contractility in a STZ-induced diabetic rat model by regulating intracellular Ca²⁺ management in smooth muscle cells and, thus, has an extra-protective effect on diabetic vascular dysfunction²⁰⁷.

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in patients with diabetes and is highly prevalent in end-stage renal disease²⁰⁸. Many studies have reported that berberine exhibits renoprotective effects in DN rats via regulating the various pathways, such as the PGE₂-EP1-Gαq-Ca²⁺ signaling pathway²⁰⁹, TLR4/NF-κB²¹⁰ and S1P2/MAPK signaling pathway²¹¹. Tang et al.²¹² suggested that berberine (50-100 mg/kg) improved histopathological changes in the diabetic kidney, while it significantly reversed the diabetic-induced increases in the levels of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) as well as the decreases in the levels of β-arrestins 1 and 2. In NIT-1 pancreatic β cells, it inhibited PA-induced lipid accumulation by decreasing lipogenesis and increasing lipid oxidation²¹³. In an experimental diabetic kidney model and high glucose-cultured glomerular mesangial cells (GMCs), berberine suppressed the expression of FN, ICAM-1, and TGF-β1 possibly by negatively regulating NF-κB and RhoA/ROCK^214,215. Furthermore, it inhibited the Sphk1/S1P signaling pathway and MAPK activation, lowered AP-1 activity, and ultimately deceased fibronectin overproduction^216-218. In 2016, Zhou et al.²¹⁹ reported that berberine can positively affect DN by improving micro pathology and increasing neuritin expression via the MAPK pathway. In diabetic rats, the alkaloid exhibited renoprotective effects by changing the levels and regulation of the AGEs-RAGE-PKC-b-TGF-b1 signaling pathway²²⁰.

Obesity has become a worldwide public health problem. It is an established risk factor for metabolic diseases including type 2 diabetes^221,222 and closely related to the metabolism of triacylglycerol (TG) in adipocytes. Adipose triglyceride lipase (ATGL) and hormone-sensitive lipase are rate-limiting enzymes that control the hydrolysis of TG. Berberine affects the metabolism of TG²²³ by increasing the expression of ATGL and therefore stimulating basal lipolysis in mature adipocytes through the coupled mechanisms linked to the AMPK pathway²²⁴. In addition, coptisine (165), a related alkaloid, inhibited obesity-related inflammation in Syrian golden hamsters through the LPS/TLR4-mediated signaling pathway²²⁵. The aporphine isoquinoline alkaloid stephalagine (94) could be used as a potential anti-obesity agent due to its significant pancreatic lipase inhibitory activity (IC₅₀ 8.35 μg/ml).⁷⁰

In 2016, berberine (161), coptisine (165), palmatine (166), epiberberine (163), and jatrorrhizine (162) were evaluated for antihyperglycemic, antidyslipidemic and antidiabetic hyperlipidemic effects in HepG2 cells and diabetic KK-Ay mice²²⁶. All five alkaloids effectively modulated hyperglycemia and hyperlipidemia. Berberine and coptisine promoted glucose consumption in vitro as well as suppressed fasting blood glucose level and improved glucose tolerance in vivo. In the mice, the levels of serum total cholesterol and triglycerides were decreased by palmatine and jatrorrhizine. Moreover, diminished hepatomegaly was found in jatrorrhizine-treated mice²²⁶. SAR analysis showed that the methylene-dioxy groups at C2, C3, C9, and C10 positions are the key functional groups for the antihyperglycemic and antihyperlipidemic effects. Briefly, the oxidized form of methylene-dioxy group at the C-2 and C-3 positions and/or at C-9 and C-10 positions of compound 163 would inhibit the activities of rat lens aldose reductase and human recombinant aldose reductase activities, and the methylene-dioxy group is very important to the binding activity of coptisine to β-cell membranes. Berberine and coptisine had better antihyperglycemic effects than compounds 162, 163, 166 that may be associated with the methylene-dioxy group at the C-2 and C-3 positions, because the C-2 and C-3 positions of the latter three compounds were substituted by methoxy group or phenolic hydroxyl group.

In a subsequent study, a combination of the five alkaloids showed synergistic cholesterol-lowering in HepG2 cells and hypercholesterolemic hamsters, which was greater than that of the single alkaloids²²⁷. Activation of AMPK activation and alteration of neutral lipid metabolism may explain the hypoglycemic effect of berberine in differentiated cardiomyocytes²²⁸. Berberine and its metabolites exert lipid-lowering effects in human hepatoma cells metabolites likely by low density lipoprotein receptor up-regulation²²⁹. A meta-analysis of randomized clinical trials indicated that berberine can improve lipid profiles in dyslipidemia with acceptable safety²³⁰.

He et al.²³¹ suggested that the related alkaloid coptisine might be used as an anti-hypercholesterolemia agent as it inhibited cholesterol synthesis by suppressing 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) expression and increasing the use and excretion of cholesterol through up-regulation of low-density lipoprotein receptor (LDLR) and CYP7A1 expression.

Atherosclerotic coronary artery disease is a leading cause of death and disability in diabetic patients, and diabetic patients with atherosclerosis usually show moderate hyperhomocysteinemia (HHCY). Berberine increased atherosclerotic plaque stability in Apoe^−/− mice with HHCY by activating the peroxisome proliferator-activated receptor-γ (PPARG) and suppressing oxidative stress in endothelial cells²³². It also protected rat retinal Müller cells from high-glucose-induced apoptosis by enhancing autophagy and activating the AMPK/mTOR signaling pathway²³³. Acting on the TGFβ1-PI3K/Akt pathway, berberine reduced injury to podocytes caused by exosomes derived from high glucose-induced mesangial cells²³⁴. Berberine showed good effects on bone parameters in the treatment of HFD-fed/streptozocin-induced diabetic rats and, thus, could have therapeutic potential in diabetic osteoporosis²³⁵.

3.3. Antibacterial and antifungal activities

Isoquinoline alkaloids exhibit good antibacterial and antifungal activities. A high content of berberine (161) is found in the well-known Chinese drug (Huangliansu) taken to treat intestinal infections caused by Escherichia coli, Bacillus dysteriae, and other microorganisms. The authors have recently described the significant antifungal activity of sanguinarine (299) and its possible use as a bio-fungicide for crop protection²³⁶. From 2014 to 2018, many publications have reported the antibacterial and antifungal activities of isoquinoline alkaloids; findings are briefly discussed below or listed in Table 3.^{23,71,77,237,94,146}.

Table 3.

The antibacterial and antifungal activities of isoquinoline alkaloids

Compound	Bacteria	Biological results	Positive drug	Ref.
Carnegine (4)			Gentamicine	24
	Staphylococcus aureus Bacillus cereus Enterococcus faecalis Escherichia coli Pseudomonas aeruginosa Klebsiella pneumoniae Proteus vulgaris	1129.69 μM (MIC) 2259.38 μM (MIC) 1129.69 μM (MIC) 564.84 μM (MIC) 2259.38 μM (MIC) 1129.69 μM (MIC) 1129.69 μM (MIC)	1438.11 μM (MIC) 719.06 μM (MIC) 11504.91 μM (MIC) 1438.11 μM (MIC) 1438.11 μM (MIC) 1438.11 μM (MIC) 1438.11 μM (MIC)
N-Methylisosalsoline (5)			Gentamicine	24
	Staphylococcus aureus Bacillus cereus Enterococcus faecalis Escherichia coli Pseudomonas aeruginosa Klebsiella pneumoniae Proteus vulgaris	19298.50 μM (MIC) 9649.24 μM (MIC) 9649.24 μM (MIC) 19298.50 μM (MIC) 2412.31 μM (MIC) 19298.50 μM (MIC) 19298.50 μM (MIC)	1438.11 μM (MIC) 719.06 μM (MIC) 11504.91 μM (MIC) 1438.11 μM (MIC) 1438.11 μM (MIC) 1438.11 μM (MIC) 1438.11 μM (MIC)
N-Formyl-asimilobine-2-O-β-D-glucoside (87)	Staphylococcus aureus MRSA strains	Diameters of inhibition zones 8.0 and 8.0 mm	Kanamycin sulfate was 40 and 34 mm	71
Isomoschatoline (120)	Staphylococcus aureus Staphylococcus epidermidis Escherichia coli Candida albicans Candida dubliniensis	Non-irradiated (CFU/mL) 1.55×107; 9.10 ×107; 1.10×107; 1.03×107; 9.10×107 Irradiated (CFU/mL) 1.38×104; 4.05×104; 1.12×105; 8.53×103; 6.68×103	Methylene blue (0.01 mg/mL) Non-irradiated 2.61×105; 6.53×104; 0; 4.78×107; >1×108 Irradiated (CFU/mL) 0; 0; 0; 0; 0	237
Berberine (151)	Clostridium perfringens Candida albicans	52.20 μM (MIC) 75.53 μM (MIC)	Ampicillin 300 nM (MIC)	77 238
Palmatine (156)	Clostridium perfringens	44.70 μM (MIC)	Ampicillin 300 nM (MIC)	77
(−)-1-O-β-D-Glucoside-8-oxotetrahydropalmatine (190)	Staphylococcus aureus	Diameters of inhibition zones 15 mm	Kanamycin sulfate was 34 mm	71
N-Methylcanadine (191)	ATCC 25923, Clinical isolates Staphylococcus aureus strains 1-4	307.80 μM (MIC) 76.90 μM (MIC) 153.90 μM (MIC) 153.90 μM (MIC) 307.80 μM (MIC)	Chloramphenicol >49.51 μM (MIC); >198.10 μM (MIC); >24.76 μM (MIC); >24.76 μM (MIC); 198.1μM (MIC)	94
Michellamine B (263)	Bacillus subtilis	21.14 μM (MIC)	--	110
Dihydrocheleryhtrine (303)	Clinical isolates Staphylococcus aureus strains 1-4	76.9 - 307.8 μM (MIC)	--	94
Manzamine A (329)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	>0.18 μM (MIC) 0.09 μM (MIC) 0.09 μM (MIC) 0.01 μM (MIC) >0.18 μM (MIC) >0.18 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
Kepulauamine A (330)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	0.014 μM (MIC) 0.055 μM (MIC) 0.028 μM (MIC) 0.028 μM (MIC) 0.014 μM (MIC) 0.110 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
Manzamine B N-oxide (331)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	>0.176 μM (MIC) 0.176 μM (MIC) 0.176 μM (MIC) 0.088 μM (MIC) >0.176 μM (MIC) >0.176 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
3,4-Dihydromanzamine B N-oxide (332)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	0.023 μM (MIC) 0.011 μM (MIC) 0.005 μM (MIC) 0.005 μM (MIC) 0.044 μM (MIC) >0.176 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM( MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
11-Hydroxymanzamine J (333)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	0.003 μM (MIC) 0.007 μM (MIC) 0.007 μM (MIC) 0.014 μM (MIC) 0.003 μM (MIC) 0.027 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
31-Hydroxymanzamine A (334)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	0.044 μM (MIC) 0.011 μM (MIC) 0.011 μM (MIC) 0.003 μM (MIC) 0.023 μM (MIC) >0.176 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
32,33-Dihydro-31-hydroxymanzamine A (335)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	0.088 μM (MIC) 0.044 μM (MIC) 0.023 μM (MIC) 0.003 μM (MIC) 0.176 μM (MIC) >0.176 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
6-Deoxymanzamine X (336)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	0.177 μM (MIC) 0.177 μM (MIC) 0.089 μM (MIC) 0.005 μM (MIC) >0.177 μM (MIC) >0.177 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
Manzamine B (337)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	>0.182 μM (MIC) 0.182 μM (MIC) 0.182 μM (MIC) 0.091 μM (MIC) >0.182 μM (MIC) >0.182 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)
neo-Kauluamine (338)			Ampicillin	146
	Staphylococcus aureus Bacillus subtilis Kocuria rhizophila Salmonella enterica Proteus hauseri Escherichia coli	>0.086 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) >0.086 μM (MIC) >0.086 μM (MIC)	0.001 μM (MIC), 0.002 μM (MIC) 0.001 μM (MIC) 0.001 μM (MIC) 0.005 μM (MIC) 0.018 μM (MIC)

Berberine (161) exhibited antibacterial activity against Candida albicans with an MIC value of 75.53 μM. It affected the synthesis of membrane ergosterol and induced increased membrane permeability causing loss of intracellular material to the outer space (DNA/protein leakage) as well as membrane depolarization and lipid peroxidation of membrane constituents²³⁸. Berberine also effectively protected mice infected with Salmonella typhimurium²³⁹. Further studies reported that this alkaloid could treat H. pylori-induced chronic gastritis by attenuating the BAFF-triggered Th17 response⁸⁷. Berberine as well as palmatine (166), coptisine (165), epiberberine (163), and jatrorrhizine (162) acted as concentration-dependent inactivators of urease with IC₅₀ values from 3.0 to 5087 μM for HPU (Helicobacter pylori urease) and 2.3 to >10,000 μM for JBU (jack bean urease). Epiberberine was the most potent inhibitor against both ureases with IC₅₀ values of 3.0 μM for HPU and 2.3 μM for JBU and was more effective than the standard urease inhibitor acetohydroxamic acid (83 μM for HPU and 22 μM for JBU). The further studies showed that two methoxyl groups in the A ring as the polar systems and the dimethylene group in the D ring as the hydrophobic ring system of epiberberine are the functional structural groups for the potent urease inhibition. This alkaloid could be used in the treatment of diseases associated with ureolytic bacteria and could be further developed into a promising therapeutic approach for the treatment of urease-related diseases²⁴⁰. Meanwhile, berberine (161) and palmatine (166) suppressed Clostridium perfringens growth with MIC values of 44.7 and 52.2 μM, respectively⁷⁷.

In 2017, some manzamine alkaloids from Acanthostrongylophora sp. sponge were found to show antibacterial activity¹⁴⁶. neo-Kauluamine (347) showed the best activity (MIC ~0.001 μM) against Bacillus subtilis, Kocuria rhizophila and Salmonella enterica, and 11-hydroxymanzamine J (342) had the best activity (MIC 0.053 μM) of all isolated compounds against Staphylococcus aureus and Proteus hauseri. MIC values of the positive drug ampicillin were around 0.001 μM. 3,4-Dihydromanzamine B N-oxide (341) and 31-hydroxymanzamine A (343) demonstrated marked activities against some tested microorganisms. neo-Kauluamine and the hydrogen chloride salt of manzamine J N-oxide displayed mild inhibition against isocitrate lyase from Candida albicans, and the latter manzamine alkaloid was the only compound with activity against bacterial sortase A¹⁴⁶.

The simple isoquinoline alkaloid carnegine (3) showed antibacterial activity with MIC ranging from 564-2259 μM against various strains. The time-kill curves indicated potent and rapid bactericidal activity²³. Michellamine B (276), a dimeric naphthylisoquinoline alkaloid, inhibited E. coli MraY (IC₅₀ 456 μM) and B. subtilis MraY (IC₅₀ 386 μM) and showed antimicrobial activity against B. subtilis²⁴¹.

Photodynamic therapy was discovered at the beginning of the last century and mostly used as a cancer therapy; however, it has emerged as a promising treatment alternative against infectious diseases. The oxoaporphine alkaloid isomoschatoline (129) had an absorption profile with bands at 600-700 nm, was positive for singlet oxygen production and exhibited photodynamic antimicrobial activity against both gram-positive and gram-negative bacteria and some Candida ssp. yeast strains at sub-inhibitory concentrations²³⁷.

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that is resistant to many antibiotics and can cause various problems ranging from skin infections to pneumonia to bloodstream infections²⁴². Much effort has been put into the fight against this bacterium. Berberine (161) was active in vitro against clinical isolates of MRSA and lowered the MICs of ampicillin and oxacillin²⁴³. It also was synergistic with ceftazidime and cefepime against MRSA⁴¹. Bacteria do not develop resistance to berberine since its MIC within the same bacterial cultures (E. coli, S. aureus, B. subtilis, Proteus vulgaris, S. typhimurium and Pseudomonas aeruginosa) did not increase over 200 generations²⁴⁴.

Dihydrocheleryhtrine (312) and N-methylcanadine (200) from Zanthoxylum tingoassuiba presented anti-MRSA activity against the four tested clinical isolates S. aureus strains 1-4 (MIC ranging from 76.9 to 307.8 μM) and were more active than chloramphenicol against strain 4 and ATCC25923⁹⁴. N-Formyl-asimilobine-2-O-β-D-glucoside (95) was equipotent against S. aureus and MRSA strains; the inhibition zone against both strains was 8.0 mm in diameter. The inhibitory diameters with the positive control kanamycin sulfate were 40 and 34 mm, respectively⁷¹. Bavarsadi et al.²⁴⁵ reported that the administration of incremental levels of sanguinarine (299) decreased microbial counts in the ileum and improved other intestinal health indices in laying hens.

3.4. Antiviral activity

Antiviral activity is one of the important bioactivities for berberine (161). In vitro, it regulated signaling pathways related to inflammation, such as NF-κB²⁴⁶ and AMPK/mTOR²⁴⁷ signaling pathways. In addition, berberine attenuated autophagy in adipocytes by targeting BECN1²⁴⁸ and inhibited the replication of respiratory syncytial virus (RSV), herpes simplex virus (HSV), human papillomavirus (HPV), and human cytomegalovirus (HCMV)^249-251. Berberine suppressed viral infection-induced up-regulation in the TLR7 signaling pathway, such as TLR7, MyD88, and NF-κB (p65), at both the Mrna and protein levels, as well as significantly inhibited the viral-induced increases in Th1/Th2 and Th17/Treg ratios and inflammatory cytokine production²⁵². In addition, berberine inhibited EV71 replication by down-regulating autophagy and the MEK/ERK signaling pathway, while the 50% toxicity concentration (TC₅₀) was 73.10 μmol/L in Vero cells and the TC₅₀ of the positive agent pirodavir was 27.49 μmol/L²⁵³.

Corydine (90) and norisoboldine (91), aporphine alkaloids from Croton echinocarpus leaves, displayed significant in vitro anti-HIV potential. The latter compound more potently inhibited HIV-1 reverse transcriptase enzyme activity⁶⁹. Several michellamine-type dimeric naphthylisoquinoline alkaloids inhibited replication of HIV reference strain IIIB/LAI in A3.01 T lymphoblast cell cultures: michellamine A₂ (270) (IC₅₀, 29.6 μM), A₃ (271) (IC₅₀, 15.2 μM), A₄ (272) (IC₅₀, 35.9 μM), and B (276) (IC₅₀, 20.4 μM). However, michellamines A (275) and B₃ (274) were not active¹¹⁰.

Emetine (348) inhibits protein synthesis in mammalian, yeast and plant cells by inhibiting the aminoacyl-sRNA transfer reaction at the 40S ribosomal subunit^254-256. It also inhibits DNA synthesis in mammalian cells²⁵⁷. Emetine inhibited replication of DNA viruses [buffalopoxvirus (BPXV) and bovine herpesvirus 1 (BHV-1)] as well as RNA viruses [peste des petits ruminants virus (PPRV) and Newcastle disease virus (NDV)]. After treatment, the syntheses of viral RNA (PPRV and NDV) and DNA (BPXV and BHV-1) as well as viral entry (NDV and BHV-1) were reduced and inhibited. Emetine significantly inhibited replication of NDV. Moreover, this alkaloid significantly inhibited BPXV-induced pock lesions on chorioallantoic membrane (CAM) along with associated mortality of embryonated chicken eggs. It significantly delayed NDV-induced mortality in chicken embryos associated with reduced viral titers. Hence, emetine could have significant therapeutic value against certain viruses by inhibiting viral RNA and DNA replication without producing an antiviral drug-resistant phenotype¹⁴⁸.

Japanese encephalitis virus (JEV) is a major cause of severe encephalopathy. Huang et al.²⁵⁸ suggested that the protoberberine isoquinoline alkaloid (−)-tetrahydropalmatine (192) could be a strong drug candidate for the treatment of JEV infection, because it exhibited a neuroprotective effect in a JEV strain GP-78 infected mouse model.

3.5. Anti-inflammatory and immunosuppressive activities

The major isoquinoline alkaloid berberine (161) exerts significant anti-inflammatory activity^259,260 and could be used to treat inflammation and other related diseases via different mechanisms of action, for example, ischemic stroke through downregulation of pro-inflammatory cytokines and upregulation of anti-inflammatory cytokines²⁶¹ or acute pancreatitis via JNK deactivation²⁶². Meanwhile, berberine suppressed Th17 responses and improved chronic relapsing colitis induced with dextran sulfate sodium (DSS) in C57BL/6 mice²⁶³. The alkaloid also improved the survival of septic and LPS-intoxicated mice and decreased inflammation and tissue injuries in the lung, spleen and gut as well as improved disrupted energy utilization, oxidative status, amino acid metabolism and nucleic acid metabolism^264,265. In macrophages, berberine has no cellular toxicity on RAW264.7 cells at the concentration up to 5 μM, however, it inhibited M1 polarization via the AKT1/SOCS1/NF-κB signaling pathway²⁶⁶ and exerted anti-inflammatory effects by inhibiting NF-κB signaling via Sirt1-dependent mechanisms at the same concentration²⁶⁷.

Furthermore, by inhibiting TH17 cell response, berberine could exert an anti-arthritic effect and improve various autoimmune diseases, such as rheumatoid arthritis²⁶⁸. It suppressed NLRP3 (nucleotide-binding oligomerization domain-like receptor [NLR] pyrin domain-containing-3) inflammasome activation in monosodium urate (MSU) crystal-stimulated RAW 264.7 macrophages and pro-inflammatory cytokines through the upregulation of Nrf2 (nuclear factor erythroid-2-related factor 2) transcription factor and alleviated MSU crystal-induced inflammation in rats²⁶⁹. One mechanism of action against rheumatoid arthritis was inhibition of IL-21/IL-21R-mediated inflammatory proliferation via attenuation of the PI3K/Akt signaling pathway and amelioration of IL-21 mediated osteoclastogenesis²⁷⁰.

Norisoboldine (91) exerts anti-arthritic activity via anti-inflammatory and immune-regulatory effects. Mechanism of action studies showed that this alkaloid prevented both the infiltration of inflammatory cells and destruction of bone and cartilage in joints in adjuvant-induced arthritic rats, as a substrate of P-glycoprotein (P-gp)^271-273. The anti-arthritic mechanism involved inhibition of inflammatory synovial hyperplasia by promoting the release of cytochrome C and regulating the expression of Bax and Bcl-2 proteins via a mitochondrial-dependent pathway²⁷⁴, as well as prevention of synovial angiogenesis by moderating the Notch1 pathway-related endothelial tip cell phenotype^275,276. Tong et al.²⁷⁷ suggested that norisoboldine induced the generation of intestinal Treg cells by the activation of AhR (aryl hydrocarbon receptor) as well as promoted Treg differentiation and then reduced the development of colitis by regulating AhR/glycolysis axis and subsequent NAD⁺/SIRT1/SUV39H1/H3K9me3 signaling pathway²⁷⁸. Furthermore, norisoboldine reduced IL-1β production in LPS-stimulated RAW264.7 cells and decreased the serum level of IL-1β in collagen-induced arthritis^273,279. Finally, the compound inhibited activation of the NLRP3 inflammasome by regulating the AhR/Nrf2/ROS signaling pathway and thereby improved the TNBS (2,4,6-trinitrobenzene sulfonic acid)-induced colitis in mice²⁷¹.

Nuclear transcription factor-κB (NF-κB) plays an important role in inflammation, sepsis and immunity²⁸⁰. Hence, great attention has been focused on compounds that produce inhibitory effects on the NF-κB pathway. Demethyleneberberine (164) reduced inflammatory responses by inhibiting the NF-κB pathway and regulating the balance of Th cells²⁸¹. Chelidonine (300) also significant inhibited NF-κB activity and related pathways at the concentrations of 5-20 μM, such as the TLR4/NF-κB signaling pathway, in HCT116 cells and RAW264.7 macrophages²⁸², and it did not display cytotoxic effect with concentrations up to 20 μM. These results indicated that NF-κB pathway is very important to the anti-inflammatory activity of isoquinoline alkaloids. In addition, this alkaloid inhibited mitogen-activated protein kinase pathway activation by blocking c-Jun N-terminal kinase and p38 phosphorylation²⁸³. Salutaridine (366), dauricumine (369), dauriporphine (128) and cheilanthifoline (197) significantly inhibited receptor activator of NF-κB ligand-induced differentiation of mouse bone marrow-derived macrophages into multinucleated osteoclasts⁷³. Zhang et al.¹⁵⁶ reported that delavatine A (406) significantly decreased LPS-induced activation of NF-κB by suppressing the p65 subunits and the phosphorylation of IκBα¹⁵⁷. Palmatine (166) promoted the proliferation of goat endometrial epithelial cells at the concentrations of 10–100 μg/mL, and reduced LPS-induced inflammatory responses through inhibition of the TRIF-dependent NF-κB pathway²⁸⁴.

Boldine (85) and reticuline (23) from Litsea cubeba exerted anti-inflammatory activity and potential synergistic effects in vivo partly by inhibiting the expression of pro-inflammatory cytokines, such as TNF-α and IL-6, perhaps resulting from interaction with JAK2/STAT3 and NF-κB pathways⁶⁷. Tetrandrine (57) inhibited IκBα and NF-κB p65 phosphorylation in LPS-induced RAW 264.7 and chondrogenic ATDC5 cells²⁸⁵. Coptisine (165) inhibited IL-1β-induced inflammatory responses by suppressing the NF-κB and MAPK pathways signaling pathway, as well as suppressing the expression of iNOS, COX-2, matrix metalloproteinase-3 (MMP-3) and MMP-13, and NF-κB activation in IL-1β-induced human OA chondrocytes^286,287.

Other anti-inflammatory mechanisms of action of isoquinoline alkaloids were also investigated. Palmatine (166), which has been used to treat abdominal pain, enteritis, gastritis, chronic endometritis, and pelvic inflammation, exerted protective effects on acute and chronic inflammation in experimental animal models^288-290. Zhou et al.²⁹¹ reported that this compound exerted chondroprotective effects in IL-1β-induced rabbit chondrocytes and an experimental OA model by inhibiting the Wnt/β-catenin and Hedgehog signaling pathways. As a potent IDO-1 inhibitor, palmatine improved dextran sulfate sodium-induced colitis by mitigating colonic injury, preventing gut microbiota dysbiosis, and regulating tryptophan catabolism²⁹².

Compared with mice administered TNBS, mice treated with capnoidine (378) showed significantly improved clinical symptoms as well as reduced colon pathology and histological inflammation in the colon. Moreover, inflammatory cytokines profiles within the colon were altered and levels of p-IκB-α (Ser32) and p-NF-κB p65 (Ser536) were reduced¹⁵¹.

Alkaloids from Portulaca oleracea inhibited NO production in lipopolysaccharide-induced murine macrophage RAW 264.7 cells (EC₅₀ 18.0–498 μM). Among them, oleracein E (403) and (S)-(−)-salsolinol (15) were more potent (EC₅₀ 35.4 and 58.7 μM, respectively) than the positive control 3,4-dihydroxybenzohydroxamic acid. Additionally, some alkaloids showed β2-adrenergic receptor (β2-AR) agonist activity in the CHO-K1/GA15 cell line, which stably expresses β2-AR as detected by a calcium assay. The EC₅₀ value of (R)-(+)-1-benzyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline was 87.9 nM³¹.

Corynoline (314) from Corydalis bungeana inhibited inflammatory mediators in LPS-stimulated RAW264.7 cells and attenuated LPS-induced acute lung injury in mice by activating Nrf2^129,293,294. The unique alkaloid dactyllactone A (126) inhibited the expression of IL-1β and PGE2 in a dose-dependent manner in LPS-induced RAW264.7 cells⁷⁸. Decarine (313) significantly inhibited IL-6 and IL-8 production in TNF-α + IL-1β-induced Caco-2 cells at a concentration of 20 μM¹²⁸.

6aR-2′-Carboxylthaliadine (116), 3-methoxy-2′-methoxycarbonyl-oxohernandalincin (141), predicentrine (119), oxopurpureine (143) and laudanosine (43) from Thalictrum cirrhosum. significantly inhibited T lymphocytes with IC₅₀ values of 43.90, 40.80, 43.70, 39.70 and 42.30 μM, respectively⁴³.

3.6. Antioxidant activity

Berberine hydrochloride (161) has beneficial effects against cellular oxidative stress^295,296. It reduced H₂O₂-induced growth inhibition and DNA damage as well as apoptosis in C2C12 cells by suppressing the accumulation of intracellular reactive oxygen species via activation of the Nrf2/HO-1 pathway²⁹⁷. Additionally, the alkaloid improved the antioxidant status of intestinal tissue in mice²⁹⁸. The related alkaloid coptisine (165) exerted an antioxidant activity against AAPH-induced toxicity by activating Akt and JNK/Nrf2/NQO1 pathways²⁹⁹.

The bisbenzylisoquinoline alkaloid (−)-O-O-dimethylgrisabine (36) exhibited potent antioxidant activity (44.3%) in the reducing power assay and IC₅₀ values of 18.38 and 64.30 μg/mL in DPPH and metal chelating assays, respectively. Thus, it is a good reductant with the ability to chelate metals and prevent pro-oxidant activity³⁸. By preventing NF-κB translocation, neferine (61) from the same compound classification protected muscle cells from oxidative stress. It also prevented apoptosis by decreasing the mitochondrial membrane potential and reactive oxygen species (ROS) production in cells subjected to hypoxia as well as inhibited the expression of the downstream regulator COX-2^59,300.

Two aporphine isoquinoline alkaloids, (−)-boldine (85) and (−)-norboldine (86), exhibited good to low potency in three antioxidant activity assays, DPPH (IC₅₀ 136.96, 255.21 μM), reducing power (34.37, 52.10%), and metal chelating (IC₅₀ 785.64, 501.55 μM)⁵⁹. Two other aporphines, isocorydine (92) and norisocorydine (93), also showed antioxidant effects in these assays⁵⁹.

The protoberberine phellodendrine (198) showed good antioxidant effects in vivo. It improved the decreased survival rate and abnormally elevated heart rate of zebrafish embryos. In vitro, the compound decreased the increased ROS production, lipid-peroxidation and cell death rate caused by AAPH-induced oxidative stress, most likely by down-regulation of AKT phosphorylation and NF-κB3 expression⁹³.

Oleracein E (403) has a rare tetrahydroisoquinoline/pyrrolidone tricyclic skeleton and a catechol moiety³⁰¹. It improved cognitive function, reversed abnormal brain antioxidant biomarkers (GSH, T-AOC, MDA and SOD) to normal levels, and inhibited hippocampal neuronal apoptosis in d-galactose/NaNO₂-induced senescent mice and in some apoptotic indices induced by AlCl₃^302,303.

3.7. Antiparasitic and insecticidal activities

Parasitic diseases present a threat worldwide, particularly among developing countries, and cause considerable morbidity and mortality globally. Examples include trypanosomiasis, leishmaniasis and schistosomiasis^304-310. Compared with synthetic molecules, natural products are believed to have significant advantages as lead compounds against these diseases, and some isoquinoline alkaloids have demonstrated antiparasitic activity.

The naphthylisoquinoline alkaloid ancistectorine D (212) showed the highest potency against the protozoan parasites Trypanosoma cruzi and Leishmania donovani with IC₅₀ values of 4.40 μM and 1.20 μM, respectively, while ancistrobonsolines A₁ and A₂ (281, 282) showed weak-to-moderate antiprotozoal activities¹¹¹. The bisbenzylisoquinoline 6,5′,6′,7′,12-pentamethoxy-2,2′-dimethyloxyacathan (50) effectively killed both wild type L. donovani (EC₅₀ 6.8 μM) and sodium antimony gluconate (SAG)-resistant promastigotes (EC₅₀ 8.2 μM). Also, at a concentration of 50 μM, it almost completely inhibited the protozoan DNA topoisomerase IB activity⁴⁴. Alternamine A (397) showed moderate antiprotozoal effects against T. cruzi trypomastigotes and L. amazonensis amastigotes with IC₅₀ values of 0.23 and 0.16 μM, respectively. The IC₅₀ values of the positive drugs (crystal violet against T. cruzi and amphotericin B against L. amazonensis) were 0.18 and <0.01 μM¹⁵³.

Ealapasamines A–C (287–289) exhibited excellent in vitro antimalarial activity against chloroquine-sensitive (NF54) and chloroquine-resistant (K1) strains of the malaria parasite P. falciparum; the IC₅₀ values were 418, 210 and 34 nM (NF54) and 452, 138 and 6.3 nM (K1). Thus, ealapasamine C was the most active naphthylisoquinoline against the resistant strain K1. Its cytotoxicity was comparatively low (6.0 μM), giving a high selectivity index of nearly 1000¹⁰⁶. Dioncophyllines F, C₂ and D₂ (249–251) showed high and specific activity against P. falciparum¹⁰⁸, while mbandakamines C (291) and D (292) exhibited promising activity against the same parasite³².

Two morphinandienones, (+)-sebiferine (353) and (−)-milonine (354), from Dehaasia longipedicellata showed potent to moderate activity against a chloroquine-resistant strain of P. falciparum K1 with IC₅₀ values ranging from 0.03 to 30.40 μM. (−)-Milonine exhibited potent activity with an IC₅₀ value of 0.10 μM, comparable to that of the positive standard, chloroquine (0.09 μM). Meanwhile, they showed no toxicity towards the normal pancreatic cell line (hTERT-HPNE)⁶⁰.

Bisbenzylisoquinolines also exhibit significant antiparasitic activity. In 2014, Omole et al.⁴⁸ found that two new bisbenzylisoquinoline (−)-pseudocurine (55) and (−)-pseudoisocurine (56) exhibited strong to moderate anti-plasmodial activity against both strains of P. falciparum D6 (CQ-susceptible) (IC₅₀ 0.49 μM, 1.26 μM), and W2 (CQ resistant) (IC₅₀ 0.522 μM, 2.798 μM). (−)-O-O-Dimethylgrisabine (59), isolated from Dehaasia longipedicellata, exhibited significant activity against a chloroquine-resistant strain of P. falciparum K1 with an IC₅₀ value of less than 0.031 μM and no toxicity towards the normal pancreatic cell line (hTERT-HPNE)³⁸. (+)-Laurotetanine (87) and (+)-norstephasubine (69) exhibited strong antiplasmodial activity against P. falciparum strain K1 with IC₅₀ values of 0.19 and 0.12 μM, respectively⁶⁸.

Two aporphines, (−)-boldine (85) and (−)-norboldine (86), showed moderate activity against a chloroquine-resistant strain of P. falciparum K1 with IC₅₀ values of 2.60 and 9.28 μM, respectively, while that of chloroquine was 0.09 μM. Isocorydine (92), norisocorydine (93) and boldine (85) bound free heme and neutralized the electrons produced during the P. falciparum-mediated hemoglobin destruction and prevented oxidative damage in the host⁶⁰. Stephanine (149), a dehydroaporphine, displayed antiplasmodial activity against P. falciparum strains 3D7 and W2 with IC₅₀ values of 0.69 μM and 1.32 μM, but its cytotoxicity against 184B5 cells led to low selectivity indexes (9.10 and 4.70). The positive drug chloroquine had IC₅₀ values of 2628.3 and 134.2 against the two respective parasite strains.

Berberine chloride (161), coptisine chloride (165), palmatine chloride (166) and dehydrocorydaline nitrate showed strong anti-malarial effects (IC₅₀ < 50 nM) against the P. falciparum 3D7 strain. Their cytotoxicity to host cells was low (cell viability > 90%)³¹¹. Berberine also displayed in vivo anticoccidial activity³¹².

Among four isoquinoline alkaloids, sanguinarine (299) presented the strongest insecticidal activity against 3rd instar Lymantria dispar with a LD₅₀ value of 4.96 μg/larva. The rank order of insecticidal capacity was sanguinarine > chelidonine (300) > berberine hydrochloride (161) > coptisine (165), and the methylenedioxyphenyl(l,3-benzodioxole) group might play a key role in the larvicidal activity on L. dispar. Except for coptisine, the alkaloids also significantly reduced the food intake of the larvae and suppressed activity of digestive enzymes. Hence, the alkaloids induced antifeeding and larval lethality on L. dispar larvae¹²⁴. Heitziquinone (308) from Zanthoxylum heitzii presented the weak or inactive toxicity against brine shrimp (Artemia salina) ¹²⁷.

Cis- and trans-protopinium (187, 188) from Fumaria parviflora showed nematicidal activity against the southern root-knot nematode Meloidogyne incognita. In an in vitro study, the application of cis- and trans-protopinium at a concentration of 561.18 μM to nematode eggs and second stage juveniles for 120 h of incubation led to 100% values for the area under cumulative percent hatch inhibition and mortality. In the greenhouse and field settings during spring and autumn, application of the alkaloids at a concentration of 841.77 μM significantly reduced the nematode galling index, the number of females per gram of root, and the reproduction factor, as well as increased plant height, fresh and dry shoot weights, and root length⁹¹.

3.8. Neuroprotective Effects

Alzheimer’s disease (AD), a common neurodegenerative disease, is characterized by low levels of the neurotransmitter acetylcholine in the brain region involved with cognition. Berberine was highly tolerated when taken orally and freely blood-brain-barrier permeable³¹³. Hence, it shows significant promise and activity for treating numerous neurodegenerative conditions, including Alzheimer’s, Huntington’s, and Parkinson’s diseases^314,315. Berberine (161) provided neuroprotection via inhibition of the mTOR signaling pathways and activation of cell survival and antioxidative signaling pathways, such as up-regulated PI3K/AKT/Bcl-2 and Nrf2/HO-1 antioxidative signaling pathways^246,316. Berberine reduced the accumulation of amyloid β (Aβ) and decreased the expression of β-site APP cleaving enzyme-1 by activating AMPK in N2a mouse neuroblastoma cells stably expressing human Swedish mutant APP695 (N2a/APP695sw), N2a cells³¹⁶, and also inhibited Aβ-protein-induced apoptosis in primary cultured hippocampal neurons via the mitochondria-related caspase pathway³¹⁷. Subsequently, Huang et al.³¹⁸ suggested that berberine improves cognitive impairment by promoting autophagic clearance and inhibits production of Aβ in an APP/tau/PS1 mouse model of Alzheimer’s disease. Furthermore, berberine presented a neuroprotective effect against environmental heavy metal-induced neurotoxicity and Alzheimer’s-like disease in rats via its anti-inflammatory/antioxidant mechanisms³¹⁹.

Postoperative cognitive dysfunction (POCD) is a significant cause of morbidity after surgery, especially in elderly patients. In an in vivo study, berberine alleviated POCD by suppressing neuroinflammation in aged mice and, in an in vitro study, it suppressed LPS stimulated production of TNF-α and IL-1β in BV2 cells³²⁰. Meanwhile, the alkaloid markedly improved aging-related reductions in cognitive ability and muscular function and activation of the AMPK/SIRT1/PGC-1α pathway in skeletal muscle³²¹. Also, berberine is a potential alternative therapy for TDP-43-related neuropathology in frontotemporal dementia and amyotrophic lateral sclerosis³²².

Depression is the most common mental disorder in humans. Berberine up-regulated BDNF expression in the hippocampus to lessen corticosterone-induced depressive-like behavior in mice ³²³ and enhanced dopamine expression to alleviate symptoms of anxiety in rats with post-traumatic stress disorder³²⁴. It also exerted antidepressant-like effects in ovariectomized mice and decreased immobility time in a dose-dependent manner. Berberine’s activation of the 5-HT₂ receptor via the BDNF-CREB and eEF₂ pathways activation may be partially related to these antidepressant-like effects. Furthermore, after berberine treatment, greater reduction was seen in c-Fos induced by ovariectomy³²⁵.

Epileptogenesis transforms a normal brain to an epileptic condition, eventually leading to seizures. Status epilepticus is a life-threatening neurologic condition with seizures of longer duration. Studies showed that berberine relieved status epilepticus and spontaneous recurrent seizures in an intrahippocampal kainite model of epilepsy and exerted neuroprotective effect via suppression of oxidative stress, neuroinflammation, and possibly apoptosis. Berberine also reduced cognitive deficits and hyperphosphorylation of tau by inhibiting the activation of the NF-κB signaling pathway³²⁶.

Cholinesterase (acetylcholinesterase, AChE; butyrylcholinesterase, BChE) inhibitors enhance cholinergic function by prolonging the availability of ACh released into the neuronal synaptic cleft. While several isoquinoline alkaloids, (+)-nornantenine (88), (+)-laurotetanine (79), (+)-N-methyllaurotetanine (89), (+)-oridine (153), (+)-N-methylisococlaurine (24) and (+)-reticuline (23), were inactive or exhibited poor inhibitory effects against AChE (IC₅₀ > 200 μM), they exhibited a wide range of BChE inhibitory activity (IC₅₀ 3.95–288.34 μM)³⁷. The protoberberine alkaloids (−)-stylopine (195) and (−)-sinactine (196) displayed weak inhibitory activity against AChE; however, sinactine potently inhibited the activity of prolyl oligopepetidase (POP), a neuronal enzyme involved in cognitive disorders, with IC₅₀ of 53 μM²⁴. Protopine (210) and cryptopine (211) showed weak inhibitory activities against AChE (IC₅₀ 230 and 209 μM) and BuChE (IC₅₀ 477 and 271 μM)²⁴. Among phthalideisoquinoline alkaloids, (−)-mucroniferanine D (382), mucroniferanine F (384) and mucroniferanine G (385), exhibited AChE inhibitory activities with IC₅₀ values of 28.3, 12.2 and 11.3 μM, respectively⁹⁹, while (+)-bicuculline (372) was only weakly active against AChE, BuChE, and POP with higher IC₅₀ values of 626 μM, 329 μM and 190 μM, respectively^24,150. The pyrrolophenanthridine alkaloids seco-isopowellaminone (336), haemanthamine (326) and incartine (337) also exhibited weak anti-human AChE activity¹³⁸. (+)-Parfumidine (79), a spirobenzylisoquinoline alkaloid, exhibited POP inhibitory activity with an IC₅₀ value of 99 μM, compared with 3.27 μM for the positive drug (Z)-pro-prolinal²⁴.

The known benzophenanthridine alkaloid chelerythrine potently and selectively inhibited an isoform of recombinant human monoamine oxidase A (MAO-A) with an IC₅₀ value of 0.55 μM. It acted as a reversible competitive inhibitor (IC₅₀ 0.22 μM) and was more potent than the antidepressant drug toloxatone (IC₅₀ 1.10 μM), which also is a selective, reversible MOA inhibitor. Chelerythrine can be deemed a potential lead compound for the design of novel reversible MAO-A inhibitors³²⁷.

3.9. Hepatoprotective

Berberine (161) caused signification reduction in hepatic steatosis^328,329. Although its bioavailability was less than 1% in some studies^330,331, the alkaloid was typically concentrated in the liver after oral administration³³². Berberine exerts anti-hyperglycemic and anti-dyslipidemic effects and can also ameliorate nonalcoholic fatty liver disease (NAFLD) via regulation of the hepatic SIRT1-UCP2 pathway^332-334. By regulating cholesterol metabolism and inhibiting COX2-prostaglandin synthesis, the compound improved blockade of autophagic flux in the liver³³⁵. Moreover, berberine lessened the deposition of triglycerides in the liver following intraperitoneal injection or oral gavage³³⁶. It also protected against methotrexate-induced liver injury and attenuated oxidative stress and apoptosis, possibly through up-regulating the Nrf2/HO-1 pathway and PPARγ³³⁷. Moreover, berberine reduced staphylococcal enterotoxin B-mediated acute liver injury via regulation of HDAC expression³³⁸.

Wang et al.³³⁹ investigated the effects of tetrahydroberberine (179) and tetrahydropalmatine (192) on the expression of mouse liver cytochrome P450s and their liver toxicity in mice. Tetrahydroberberine induced mRNA expression of Cyp1a2, Cyp3a, and Cyp2e1, while tetrahydropalmatine inhibited Cyp1a2. While oral tetrahydroberberine increased mouse serum aspartate transaminase, total bilirubin, and liver malondialdehyde levels, as well as induced liver edema, tetrahydropalmatine did not cause such effects.

In 2018, study results showed that tiliamosine (54) could be used to treat non-alcoholic steatohepatitis⁵³. Norsanguinarine (316), (−)-6-acetonyldihydrisanguinarine (317) and cavidilinine (318) from Corydalis tomentella exhibited moderate hepatoprotective activities at a concentration of 10 μM²⁸. At a concentration of 10 μM, three stereoisomeric isoquinoline alkaloids (9S,7′S) tomentelline A (374), (9S,7′R) tomentelline A (375), (9R,7′S) tomentelline B (376), together with hendersine B methyl ester (46), bicucullinine (47), hendersine B (48), and (+)-capnoidine (378) presented moderate hepatoprotective activities with relative survival rates of 33.28–52.57%²⁸.

3.10. Anti-platelets and myocardial protective effect

The aporphine alkaloid norpurpureine (101) exhibited activity (IC₅₀ 80 μM) against platelet aggregation stimulated by adenosine 5′-diphosphate (ADP), collagen and thrombin. It gradually inhibited granule secretion and adhesion of activated platelets to immobilized fibrinogen. At the intra-platelet level, norpurpureine prevented agonist-stimulated calcium mobilization and cAMP reduction. Its molecular target could be an effector common effector to Ca²⁺ and cAMP signaling, such as the PLC-PKC-Ca²⁺ pathway and phosphodiesterases⁷⁴.

In addition, the isoquinoline alkalkaloid berberine (161) has been associated with myocardial protective effects^340-342. By differentially modulating the activities of p-STAT1, p-STAT3 and p-STAT4 and, thus, suppressing Th17 and Th1 cell differentiation, the compound protected against myosin-induced myocardial injury in rats³⁴⁰. Subsequent reports showed that berberine protected the heart from ischemia/reperfusion injury induced by NaH₂PO₄ partly though reducing myocardial autophagy and apoptosis via the AMPK/mTOR and AK2/STAT3 signaling pathways in vivo and in vitro^343,344 as well as reducing the striatum apoptosis via activation of the BDNF-TrkB-PI3K/Akt signaling pathway in the middle cerebral artery occlusion-induced cerebral ischemia/reperfusion model³⁴⁵. The related compound coptisine (165) also attenuated pro-inflammatory cytokines, including IL-1β, IL-6, and tumor necrosis factor-α, in heart tissue after myocardial ischemia/reperfusion injury³⁴⁶.

Neferine (61), a bisbenzylisoquinoline-type alkaloid, prevented hyperglycemia-induced endothelial cell apoptosis through suppression of ROS/Akt/NF-κB³⁴⁷. Also, it blocked Na_v1.5 channels in myocardia under the open and inactivating states and, thus, was an open channel blocker of Na_v1.5 channels^348,349. Finally, ambinine (315), a benzophenanthridine alkaloid, had protective effects on H9C2 myocardial cells. It demonstrated anticoagulation and thrombolytic effects in vitro by significantly degrading blood clots and delaying plasma recalcification time in a dose-dependent manner (1.21-4.84 mM)²²⁸.

3.11. Anti-ulcer activity

Gastric ulcers are one of the most common gastrointestinal disorders. The anti-ulcer/gastroprotective effect of berberine (161) might involve positive regulation of antioxidant and anti-inflammatory status mediated, at least partially, through the Nrf2 signaling pathway and p38 MAPK translocation³⁵⁰. Palmatine (166) hydrochloride tablets have been used clinically to cure intestinal and gynecological inflammation, bacillary dysentery, respiratory and urinary tract infections, surgical infections and eye conjunctivitis. Wang et al.³⁵¹ also reported that this alkaloid may protect the gastric mucosa by increasing PGE₂ and decreasing PAF as well as against gastric ulcers, perhaps associated with anti-inflammatory status. After orally administrating palmatine for seven consecutive days, ulcer areas were significantly decreased with inhibitory rates of 51% to 62%.

Cavidine (194), a protoberberine isoquinoline alkaloid and potent inhibitor of COX-2, exerted a gastroprotective effect against gastric ulceration, which might be associated with the stimulation of PGE2, reduction of oxidative stress, suppression of NF-κB expression and subsequently reduced COX-2 and pro-inflammatory cytokines^352,92. Pretreatment with this compound had a protective effect on acetic acid-induced ulcerative colitis in mice²⁶⁴.

3.12. Renoprotective effects

Berberine (161) is a good candidate to protect against the deleterious effect of chronic lead intoxication on the kidney³⁵³. Molecular, biochemical, and histopathological analysis indicated that this alkaloid exerted renoprotective effects in an animal model of lead-induced nephrotoxicity by inhibiting lipid peroxidation and enhancing antioxidant defense system mechanisms. Berberine also protected against renal ischemia/reperfusion injury by regulating the Sirt1/p53 pathway³⁵⁴.

3.13. Anti-muscle atrophy activity

Magnoflorine (100), an aporphine isoquinoline alkaloid, efficiently enhanced myoblast differentiation by activating the p38 MAP kinase and Akt pathways and increased the numbers of multinucleated and cylinder-shaped myotubes. It might be a promising lead compound for the development of a drug to combat muscle atrophy⁷³.

3.14. Retinal effects

Berberine (161) exhibited a protective effect against light-induced photoreceptor degeneration associated with diminished oxidative stress in the mouse retina. Thus, it could provide protection against retinal diseases²⁵⁰.

3.15. Analgesic effects

Neuropathic pain is a major public health problem. Berberine (161) administration (i.p.) increased both mechanical and thermal pain thresholds in a dose-dependent manner. Moreover, berberine administration reversed the mRNA and protein expression of TRPV1 in dorsal root ganglion neurons after peripheral nerve injury and significantly inhibited capsaicin-induced pain behaviors. This action on neuropathic pain may be associated with the down-regulation of the heat and capsaicin receptor, TRPV1, in the dorsal root ganglia of rat neurons. Accordingly, berberine could be used to treat neuropathic pain originated in the peripheral nervous system³⁵⁵.

3.16. Others

Osteoarthritis, a common degenerative joint disease, is a major cause of joint dysfunction in the elderly³⁵⁶. Berberine (161) prevented articular degeneration cartilage by activating the Akt/p70S6K/S6 signaling pathway in interleukin-1β-induced rat chondrocytes as well as a rat model³⁵⁷. It also prevented NO-induced rat chondrocyte apoptosis and cartilage degeneration via AMPK and p38 MAPK signaling³⁵⁸. Moreover, the compound promoted sodium nitroprusside-stimulated chondrocyte proliferation by promotion of G1/S phase transition and synthesis of proliferating cell nuclear antigen in cartilage and bone marrow-derived mesenchymal stem cells as well as osteogenic differentiation through activation of the Wnt/β-catenin signaling pathway^359,360.

In addition, berberine may be used to treat adenomyosis by inhibiting growth and inflammatory invasive phenotypes of ectopic stromal cells³⁶¹ and acute respiratory distress syndrome (ARDS) by alleviating endothelial glycocalyx degradation and promoting glycocalyx restoration in LPS-induced ARDS³⁶².

4. CONCLUSION

As an important class of alkaloids, isoquinoline alkaloids have various chemical structures and pharmacological activities. However, the potential of this promising and expanding platform of active natural compounds has only been partially developed by both the academic community and the pharmaceutical industry to date. Over the past century, the discovery of morphine opened a new area for the development of central analgesic agents, and the application of berberine in the clinic has inspired a new wave for the discovery of alternative, green antibacterial drugs. During the past five years, the identification of additional new compounds, significant biological activities or novel mechanism of actions will undoubtedly contribute to the continual development of future new drugs. Continued attention and long-lasting research on the isolation and identification of naturally occurring isoquinoline alkaloids will open the way to targeted pharmacological modelling and synthetic modifications, resulting in new and better drugs based on the original effects of these alkaloids.

Biography

Xiaofei Shang received his B.S. degree in Bioscience from Londong University in 2007, and his M.S degree in Biochemistry from Lanzhou University in 2010, now he is Ph.D candidate in medicinal chemistry from Lanzhou University. He is currently an associate professor of Key Laboratory of Veterinary Pharmaceutical Development of Ministry of Agriculture, Lanzhou Institute of Husbandry and Pharmaceutical Sciences, CAAS. His research interests include the isolation, structural elucidation, and structural modification of bioactive compounds from natural products. He has published about 30 articles, applied for more than 10 patents and received several projects.

Cheng-Jie Yang received his B.S. degree in Pharmacy from Lanzhou University in 2016, and now he is Ph.D. candidate in medicinal chemistry from Lanzhou University. His research interests include the design and synthesis of bioactive compounds and natural products as potential anticancer agents, as well as exploring the potential mechanism.

Susan L. Morris-Natschke received her B.S. in chemistry from the University of Maryland-College Park in 1975 and her Ph.D. in organic chemistry from the University of North Carolina-Chapel Hill (UNC-CH) in 1982. She is currently Research Professor in the Division of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, UNC-CH, where she has been on the faculty since 1983. Her interests include scientific writing/editing, as well as the synthesis and structure-activity relationships of bioactive natural products.

Jun-Cai Li received his B.S. degree in Pharmaceutical engineering from School of Life Science and Engineering of Southwest Jiaotong University in 2016, and he is currently a M.S. student in School of Pharmacy of Lanzhou University. His research interests include the design and synthesis of bioactive compounds and natural products, and development of novel methodologies in medicinal chemistry.

Xiao-Dan Yin received her B.S. degree in pharmacy from Lan Zhou University in 2018 and she is currently a M.S. student in School of Pharmacy of Lanzhou University. Her research interests include the design and synthesis of bioactive compounds and natural products, as well as the discovery of antimicrobial lead compounds.

Ying-Qian Liu received his B.S. in chemistry from Yebei Normal University in 2002, and his Ph.D. degree in bioorganic chemistry from Lanzhou University in 2007. He worked as a postdoctoral scholar in School of Life Sciences of Lanzhou University in 2008-2013, and worked as a visiting scholar at the University of North Carolina at Chapel Hill in 2011-2012. He is currently a professor at School of Pharmacy in Lanzhou University. His research interests include the design and synthesis of bioactive compounds as potential anticancer or pesticide agents, development of novel methodologies in organic chemistry, as well as drug mechanism and pharmacokinetics evaluation. He has published more than 50 research articles, applied for more than 30 patents, and received several projects.

Xiao Guo received her B.S. degree in Bioscience from Northwest Normal University in 2010 and her M.S degree in Plant sciences from Northwest Normal University in 2013, and her Ph.D. degree in Veterinary Science from Chinese Academy of Agricultural Science in 2017. now she is currently an assistant professor of Tibetan Medicine College in Qinghai University. Her research interests include the isolation, structural elucidation, and bioactivity of natural products.

Jing-Wen Peng received her B.S. degree in Pharmacy from Weifang Medical University in 2016, and she is currently a M.S. student in School of Pharmacy of Lanzhou University. Her research interests include the design and synthesis of bioactive compounds and natural products, and research of novel methodologies in medicinal chemistry.

Masuo Goto received his B.S. degree in pharmacology in 1987, M.S. in pharmaceutical science in 1989, and Ph.D. in molecular biology in 1993 from Kanazawa University. He was a research fellow in cell and developmental biology at the National Institutes of Health from 1999 to 2003, followed by a postdoctoral fellow at the School of Medicine, UNC-CH from 2003-2009. Currently, he is Research Assistant Professor, UNC Eshelman School of Pharmacy, UNC-CH. He is interested in elucidating the molecular mechanisms of action of antiproliferative small molecules mainly discovered and developed from natural products. His research goals are to develop novel strategies to prevent and overcome multidrug-resistant cancers.

Ji-Yu Zhang received his B.S. in veterinary science from Beijing Agricultural University in 1991 and his Ph.D. in basic veterinary medicine from Jilin University in 2002. He is currently a Professor at Lanzhou Institute of Husbandry and Pharmaceutical Sciences, CAAS. His research interests include the design and synthesis of bioactive compounds as veterinary medicines, as well as drug resistance and safety evaluation. He has published more than 100 research articles, applied for more than 30 patents, and directed several projects.

Kuo-Hsiung Lee received his B.S. in pharmacy from Kaohsiung Medical University, Taiwan (1961), M.S. in pharmaceutical chemistry from Kyoto University, Japan (1965), and Ph.D. in medicinal chemistry from University of Minnesota, Minneapolis (1968). He joined the faculty of UNC Eshelman School of Pharmacy, University of North Carolina-Chapel Hill, in 1970 and is now Kenan Distinguished Professor of Medicinal Chemistry and Director of the Natural Products Research Laboratories. He has published over 942 research articles, been granted over 121 patents, and received numerous awards, including most recently, the Third Cheung On Tak International Award for Outstanding Achievement in Chinese Medicine from Hong Kong Baptist University in 2016.