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. 2024 Jun 5;9(24):25902–25913. doi: 10.1021/acsomega.4c00391

New Essential Oils from Ecuadorian Gynoxys cuicochensis Cuatrec. and Gynoxys sancti-antonii Cuatrec. Chemical Compositions and Enantioselective Analyses

Yessenia E Maldonado †, Evelin A Betancourt ‡, Erika S León ‡, Omar Malagón †, Nixon Cumbicus §, Gianluca Gilardoni †,*
PMCID: PMC11191102  PMID: 38911796

Abstract

graphic file with name ao4c00391_0005.jpg

The present study belonged to an unfunded project, dealing on the systematic description of unprecedented essential oils (EOs), distilled from 12 species of genus Gynoxys Cuatrec. In this very case, the aim was the first chemical and enantiomeric analyses of two volatile fractions, obtained from the leaves of Gynoxys cuicochensis Cuatrec. and Gynoxys sancti-antonii Cuatrec. These EOs were analyzed by GC–MS (qualitatively) and GC–FID (quantitatively), detecting 89 and 60 components from G. cuicochensis and G. sancti-antonii, respectively. Major components for G. cuicochensis EO, on a nonpolar and polar stationary phase, were α-pinene (29.4–29.6%), p-vinylguaiacol (3.3–3.6%), and germacrene D (20.8–19.9%). In G. sancti-antonii EO, the main compounds were α-pinene (3.0–2.9%), β-pinene (12.9–12.1%), γ-curcumene (19.7–18.3%), germacrene D (9.0% on the polar phase), ar-curcumene (5.3% on the polar phase), δ-cadinene (4.1–4.6%), α-muurolol (3.3–2.4%), α-cadinol (3.0% on both columns), and an undetermined compound, of molecular weight 220. In addition to chemical composition, the enantioselective analysis of the main chiral compounds was carried out on two different chiral selectors. In G. cuicochensis EO, (1R,5R)-(+)-α-pinene, (S)-(+)-β-phellandrene, (R)-(−)-piperitone, and (S)-(−)-germacrene D were enantiomerically pure, whereas β-pinene, sabinene, α-phellandrene, limonene, linalool, and terpinen-4-ol were observed as scalemic mixtures. On the other hand, in G. sancti-antonii EO, the pure enantiomers were (1S,5S)-(−)-α-pinene, (1R,5R)-(+)-sabinene, (R)-(−)-β-phellandrene, (S)-(−)-limonene, (1S,2R,6R,7R,8R)-(+)-α-copaene, (R)-(−)-terpinen-4-ol, and (S)-(−)-germacrene D, whereas β-pinene, linalool, and α-terpineol were present as scalemic mixtures. The principal component analysis demonstrated that G. cuicochensis volatile fraction was quite similar to many of the other EOs of the same genus, whereas G. sancti-antonii produced the most dissimilar EO. Furthermore, the enantioselective analyses showed the usual variable enantiomeric distribution, with a greater presence of enantiomerically pure compounds in G. sancti-antonii EO.

1. Introduction

Ecuador is a South American country, crossed by the equatorial line, and characterized by four different climatic regions, whose conditions are almost constantly maintained all year long. Therefore, a great biodiversity evolved in this region, producing an incredible number of so far unprecedented botanical species from a chemical point of view.1,2 This situation led the United Nations to declare Ecuador as one of the 17 “megadiverse” countries in the world.3 For these reasons, our group has been investigating natural products for about 20 years, with the purpose of enhancing and preserving the Ecuadorian flora through the knowledge of its phytochemistry and, possibly, the discovery of pharmacologically interesting metabolites.4,5 During the past few years, we mainly focused on the description of new essential oils (EOs), with emphasis on their chemical and enantiomeric compositions, olfactometric profiles, and biological activities.6−9 Being centered on phytochemistry and chemotaxonomy, high distillation yields, or agricultural availability are not usually leading criteria of plant selection for our research. In this perspective, the present study belonged to un unfunded project, dealing on the systematic description of new EOs from 12 plants of the genus Gynoxys Cuatrec. (Asteraceae) in the province of Loja, Ecuador. So far, the EOs obtained from Gynoxys miniphylla Cuatrec., Gynoxys rugulosa Muschl., Gynoxys buxifolia (Kunth) Cass., and Gynoxys laurifolia (Kunth) Cass. have already been studied and published.10−13 The composition of Gynoxys szyszylowiczii Hieron. volatile fraction is ready to be published, whereas Gynoxys calyculisolvens Hieron., Gynoxys pulchella (Kunth) Cass., Gynoxys reinaldii Cuatrec., Gynoxys hallii Hieron., and Gynoxys azuayensis Cuatrec. are currently under investigation. Finally, Gynoxys cuicochensis Cuatrec. and Gynoxys sancti-antonii Cuatrec. are the object of this report. According to botanical literature, the genus Gynoxys is an Andean endemism, comprising about 120 species diffused from Argentina and Bolivia to Venezuela.14 The diffusion center is Ecuador, where most of these species are endemic or native.15 In this country, G. cuicochensis is an endemic shrub or tree, growing between 2000 and 3500 m above the sea level, in the provinces of Azuay, Cañar, Loja, and Pichincha.16 On the other hand, G. sancti-antonii is a native treelet, growing between 2500 and 3500 m above the sea level in the provinces of Azuay, Cañar, Chimborazo, Loja, and Pichincha.16 No synonyms were reported for G. cuicochensis, whereas G. sancti-antonii var. latifolia Cuatrec. is a synonym of G. sancti-antonii.16 On the one hand, from the chemical point of view, G. cuicochensis is a completely unprecedented species. On the other hand, G. sancti-antonii has been previously studied about its nonvolatile metabolites.17,18 The aim of the present research is the chemical and enantiomeric description of two EOs obtained from G. cuicochensis and G. sancti-antonii leaves that, to the best of the authors’ knowledge, are reported here for the first time. The experimental design is represented in Figure 1.

Figure 1.

Figure 1

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Experimental design of the present investigation.

2. Results and Discussion

2.1. Chemical Analysis

The dry leaves of G. cuicochensis produced an EO with an analytical yield of 0.08 ± 0.003% by weight. A total of eighty-nine compounds were identified and quantified on at least one of two stationary phases of different polarity. The gas chromatographic (GC) profiles of both essential oils on the nonpolar and polar stationary phases are represented in Figures 2 and 3, whereas the complete qualitative and quantitative analyses are detailed in Table 1. Major components (≥3.0% on at least one column), on the nonpolar and polar stationary phase, respectively, were as follows: α-pinene (29.4–29.6%, peak 1), p-vinylguaiacol (3.3–3.6%, peak 42), and germacrene D (20.8–19.9%, peak 69). Unlike most of the other Gynoxys EOs, the volatile fraction of G. cuicochensis was not dominated by sesquiterpenes, being monoterpene and sesquiterpene fractions almost equal. In fact, monoterpenes and oxygenated monoterpenoids accounted together for 41.6–40.9%, whereas sesquiterpenes and oxygenated sesquiterpenoids corresponded to 41.2–38.7% as a sum. About G. sancti-antonii EO, the distillation yield was 0.08 ± 0.014 by weight. In this volatile fraction, 60 components were identified and quantified on at least one column. Main compounds were as follows: α-pinene (3.0–2.9%, peak 1), β-pinene (12.9–12.1%, peak 3), γ-curcumene (19.7–18.3%, peak 68), germacrene D (9.0% on the polar phase, peak 69), ar-curcumene (5.3% on the polar phase, peak 70), δ-cadinene (4.1–4.6%, peak 79), α-muurolol (3.3–2.4%, peak 92), α-cadinol (3.0% on both columns, peak 93), and an undetermined compound of molecular weight 220 (3.1–4.2%, peak 95). The volatile fraction of G. sancti-antonii was dominated by sesquiterpenes and oxygenated sesquiterpenoids, whose joint fractions corresponded to 64.3–59.3% on the nonpolar and polar stationary phase, respectively. On the other hand, the sum of monoterpenes and oxygenated monoterpenoids corresponded to 18.5–17.3% of the whole oil mass. Interestingly, the characteristic heavy aliphatic fraction, that we could observe in other species of this genus, were not so important in G. cuicochensis and G. sancti-antonii. In fact, despite these compounds were clearly present, their quantitative contribution did not exceed 10% of the entire oil composition in both plants.

Figure 2.

Figure 2

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GC–MS profile of G. cuicochensis (black) and G. sancti-antonii (red) EOs on a 5%-phenyl-methylpolysiloxane stationary phase. The peak numbers refer to major compounds (≥3.0% on at least one column) in Table 1.

Figure 3.

Figure 3

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GC–MS profile of G. cuicochensis (black) and G. sancti-antonii (red) EOs on a polyethylene glycol stationary phase. The peak numbers refer to major compounds (≥3.0% on at least one column) in Table 1.

Table 1. Qualitative (GC–MS) and Quantitative (GC–FID) Chemical Composition of G. cuicochensis and G. sancti-antonii EO on 5%-Phenyl-methylpolysiloxane and Polyethylene Glycol Stationary Phasesc.

no. compounds 5%-phenyl-methylpolysiloxane
 polyethylene glycol
    LRIa LRIb G. cuicochensis
 G. sancti-antonii
 reference LRIa LRIb G. cuicochensis
 G. sancti-antonii
 reference
        % σ % σ       % σ % σ  
1 α-pinene 933 932 29.4 4.84 3.0 0.51 (19) 1016 1016 29.6 4.26 2.9 0.24 (20)
2 sabinene 974 969 1.9 0.43 0.4 0.07 (19) 1103 1100 1.9 0.27 0.4 0.04 (21)
3 β-pinene 979 974 2.1 0.32 12.9 1.86 (19) 1115 1116 2.0 0.29 12.1 1.21 (22)
4 myrcene 992 988 0.7 0.08 0.2 0.02 (19) 1161 1161 0.7 0.08 0.2 0.16 (23)
5 pentyl furan 995 984 0.2 0.07     (19) 1231 1230 0.2 0.06     (24)
6 n-decane 1000 1000     trace     1000 1000     0.2 0.02  
7 α-phellandrene 1009 1002 0.9 0.10     (19) 1155 1153 0.7 0.08     (25)
8 (2E,4E)-heptadienal 1014 1007 0.1 0.02     (19) 1460 1461 0.2 0.02     (26)
9 α-terpinene 1020 1014 0.4 0.03     (19) 1171 1173 0.1 0.02     (27)
10 p-cymene 1029 1020 0.5 0.08 trace   (19) 1263 1264 0.6 0.07 0.1 0.01 (28)
11 limonene 1032 1024 1.5 0.18 0.6 0.08 (19) 1190 1190 1.5 0.16 0.3 0.21 (29)
12 β-phellandrene 1034 1025 0.2 0.04 0.4 0.06 (19) 1199 1198 trace   0.4 0.04 (30)
13 (E)-β-ocimene 1051 1044 0.5 0.05     (19) 1250 1251 0.6 0.05     (31)
14 benzene acetaldehyde 1061 1036 0.1 0.01     (19) 1677 1669 trace       (32)
15 γ-terpinene 1062 1054 0.1 0.02     (19) 1238 1238 0.1 0.02     (33)
16 (2E)-octen-1-al 1074 1049 0.2 0.02     (19) 1422 1425 0.1 0.01     (34)
17 trans-linalool oxide (furanoid) 1082 1084 0.1 0.01     (19) 1466 1466 trace       (35)
18 terpinolene 1088 1086 0.1 0.01     (19) 1274 1274 0.1 0.01   - (36)
19 linalool 1110 1113 0.3 0.03 0.5 0.04 (37) 1553 1556 0.1 0.01 0.3 0.04 (38)
20 nonanal 1116 1100 1.4 0.11     (19) 1390 1390 1.1 0.07     (39)
21 (2E)-hexenyl propanoate 1116 1111     trace   (40) 1390 1392     0.3 0.04 (40)
22 α-campholenal 1138 1122 trace       (19) 1478 1485 0.1 0.01     (41)
23 (3Z)-hexenyl isobutanoate 1155 1142 0.1 0.01     (19) 1384 1385 0.3 0.03     (42)
24 (2E)-nonen-1-al 1175 1157 0.1 0.01     (19) 1527 1524 0.2 0.01     (35)
25 safranal 1178 1197 trace       (19) 1631 1622 0.2 0.01     (43)
26 p-mentha-1,5-dien-8-ol 1186 1166 0.2 0.02     (19) 1723 1723 0.1 0.01     (44)
27 terpinen-4-ol 1191 1184 0.5 0.04 0.2 0.03 (45) 1594 1594 0.7 0.04 0.2 0.03 (46)
28 n-dodecane 1200 1200 0.1 0.01       1200 1200 0.3 0.04      
29 p-cymen-8-ol 1202 1179 trace       (19) 1845 1845 0.1 0.01     (31)
30 myrtenol 1209 1194 0.1 0.01     (19) 1784 1786 trace       (47)
31 α-terpineol 1209 1207 -   0.3 0.06 (39) 1692 1692     0.2 0.04 (23)
32 decanal 1217 1214 0.2 0.01 trace   (48) 1494 1492 0.2 0.03 0.1 0.01 (49)
33 β-cyclocitral 1232 1217 0.1 0.01     (19) 1605 1606 0.1 0.01     (50)
34 trans-carveol 1235 1215 0.1 0.01     (19) 1830 1830 trace       (35)
35 geraniol 1265 1249 trace       (19) 1849 1849 0.2 0.01     (51)
36 piperitone 1272 1249 0.1 0.01     (19) 1710 1710 trace       (52)
37 2-(E)-decenal 1276 1260 0.1 0.01     (19) 1635 1630 0.2 0.01     (39)
38 nonanoic acid 1297 1267 0.1 0.01     (19)              
39 n-tridecane 1300 1300 0.1 0.01       1300 1300 0.1 0.01      
40 cis-pinocarvyl acetate 1305 1311 0.1 0.01     (19) 1639   0.1 0.01     §
41 undecanal 1318 1319 0.1 0.01 0.2 0.04 (53) 1580 1580 0.5 0.08 trace   (54)
42 p-vinylguaiacol 1327 1324 3.3 0.19 1.8 0.42 (55) 2189 2193 3.6 0.11 2.4 0.47 (56)
43 (2E,4E)-decadienal 1335 1315 0.3 0.01     (19) 1799 1795 0.3 0.05     (57)
44 α-copaene 1376 1374     2.8 0.61 (19) 1474 1477     2.6 0.23 (58)
45 α-ylangene 1377 1373 0.1 0.01     (19) 1474 1472 0.6 0.05     (25)
46 2-epi-α-funebrene 1388 1380     0.4 0.10 (19) 1724       1.0 0.12 §
47 β-cubebene 1389 1387     0.3 0.07 (19) 1523 1521     0.2 0.02 (59)
48 (Z)-β-damascenone 1390 1361     0.3 0.06 (19) 1806 1791     0.1 0.02 (60)
49 geranyl acetate 1390 1379 1.4 0.14     (19) 1756 1756 1.4 0.14     (61)
50 n-tetradecane 1400 1400 0.2 0.01       1400 1400 0.3 0.01      
51 α-gurjunene 1407 1409 0.2 0.02     (19) 1510 1511 0.3 0.01     (62)
52 undetermined (MW: 192) 1408       2.7 0.44   1882       2.4 0.21  
53 (E)-β-damascenone 1418 1416 0.4 0.03     (19)              
54 (E)-β-caryophyllene 1421 1421 2.1 0.20 1.8 0.40 (19) 1575 1575 2.4 0.24 1.6 0.18 (63)
55 β-copaene 1432 1430 0.1 0.01     (19) 1570 1567 0.1 0.01     (64)
56 β-gurjunene 1432 1431     0.3 0.06 (19) 1671 1655     0.5 0.07 (41)
57 cis-α-bergamotene 1434 1433     trace   (65) 1528 1530     0.7 0.06 (66)
58 (Z)-β-farnesene 1443 1440     0.2 0.04 (19) 1633 1632     0.2 0.03 (67)
59 myltayl-4(12)-ene 1447 1445 0.1 0.01     (19)              
60 trans-muurola-3,5-diene 1448 1451     trace   (19) 1611       0.1 0.02 §
61 (E)-β-farnesene 1456 1454     0.6 0.13 (19) 1665 1660     0.5 0.07 (68)
62 α-humulene 1458 1452 2.6 0.21 0.5 0.10 (19) 1647 1649 2.6 0.23 0.2 0.03 (69)
63 cis-cadina-1,(6),4-diene 1465 1461     0.2 0.05 (19) 1689       0.2 0.02 §
64 cis-muurola-4(14),5-diene 1466 1465 0.1 0.01     (19) 1523   trace       §
65 (E)-β-farnesene 1472 1454 0.3 0.05     (19) 1665 1664 0.1 0.01     (25)
66 dauca-5,8-diene 1475 1471     0.3 0.05 (19) 1642 1654     0.2 0.04 (70)
67 γ-muurolene 1480 1478 0.1 0.01     (19) 1671 1676 0.2 0.01     (71)
68 γ-curcumene 1482 1481 0.4 0.09 19.7 4.63 (19) 1682 1689 0.3 0.10 18.3 2.11 (72)
69 germacrene D 1486 1495 20.8 2.48 14.9 3.32 (19) 1689 1683 19.9 2.50 9.0 0.84 (73)
70 ar-curcumene 1487 1479         (19) 1763 1763     5.3 0.69 (74)
71 (E)-β-ionone 1492 1487 1.2 0.15     (19) 1922 1923 1.4 0.18     (22)
72 trans-muurola-4(14),5-diene 1497 1493 0.4 0.03     (19) 1695   trace       §
73 α-zingiberene 1500 1493 2.3 0.25     (19) 1714 1713 2.2 0.22     (75)
74 bicyclogermacrene 1500 1500     0.8 0.18   1712 1706     1.2 0.14 (76)
75 α-muurolene 1503 1500 0.1 0.01 3.8 1.01 (19) 1708 1700 0.1 0.01 1.9 0.22 (77)
76 3-methyl-phenyl ethyl butanoate 1504 1495         (78) 1960 1964     0.4 0.05 (74)
77 β-curcumene 1513 1514     1.1 0.26 (19) 1731 1733     1.0 0.12 (79)
78 γ-cadinene 1518 1513 0.3 0.03     (19) 1739 1738 trace       (79)
79 δ-cadinene 1523 1522 1.5 0.15 4.1 0.88 (19) 1742 1744 2.2 0.19 4.6 0.54 (44)
80 (E)-nerolidol 1570 1561 0.2 0.03     (19) 2042 2045 0.1 0.02     (80)
81 germacrene D-4-ol 1586 1583 0.5 0.11 0.8 0.37 (81) 2034 2035 0.7 0.09 0.5 0.07 (82)
82 spathulenol 1589 1577 0.9 0.09     (19) 2106 2106 0.9 0.08     (83)
83 caryophyllene oxide 1588 1588 0.9 0.10 0.6 0.15 (19) 1967 1968 0.5 0.05 0.5 0.08 (35)
84 n-hexadecane 1600 1600 0.1 0.03 0.2 0.04   1600 1600 0.1 0.01 0.2 0.03  
85 salvial-4(14)-en-1-one 1604 1594 0.2 0.06     (19) 1979 1995 0.1 0.01     (36)
86 ledol 1616 1616 0.7 0.07 0.1 0.02 (84) 2005 2014 0.1 0.01 0.1 0.03 (85)
87 humulene epoxide II 1623 1608 0.7 0.05     (19) 2009 2011 0.2 0.02     (44)
88 1-epi-cubenol 1639 1638     0.1 0.01 (26) 2044 2035     0.4 0.02 (86)
89 cis-cadin-4-en-7-ol 1639 1635 0.2 0.04     (87) 2044   0.3 0.03     §
90 epi-α-cadinol 1655 1652 0.8 0.09 1.0 0.48 (19) 2157 2154 0.7 0.07 0.1 0.01 (88)
91 epi-α-muurolol 1658 1640 0.8 0.10     (19) 2173 2176 0.9 0.11     (25)
92 α-muurolol 1660 1652 0.4 0.06 3.3 0.46 (89) 2187 2187 trace   2.4 0.44 (28)
93 α-cadinol 1670 1670 2.4 0.34 3.0 0.41 (90) 2211 2212 2.5 0.31 3.0 0.29 (76)
94 ar-turmerone 1679 1668 0.4 0.04     (19) 2226   0.1 0.01     §
95 undetermined (FW:220) 1682       3.1 0.47   2248       4.2 0.52  
96 n-heptadecane 1700 1700 0.2 0.03       1700 1700 0.2 0.01      
97 amorpha-4,9-dien-2-ol 1706 1700 0.3 0.04 0.1 0.01 (19) 2275   0.3 0.03 0.4 0.29 §
98 pentadecanal 1727 1724 0.9 0.08     (19) 2022 2024 1.3 0.09     (91)
99 (2Z,6E)-farnesol 1730 1722     trace   (19) 2280 2291     0.2 0.21 (92)
100 n-octadecane 1800 1800 0.1 0.02       1800 1800 0.9 0.13      
101 hexadecanal 1833 1828 0.1 0.01     (19) 2129 2132 0.2 0.02     (91)
102 (2E,6E)-farnesyl acetate 1843 1845 trace   0.1 0.07 (19) 2233 2234 0.1 0.01 0.4 0.17 (93)
103 6,10,14-trimethyl-2-pentadecanone 1856 1846 0.1 0.01     (19) 2122 2125 0.1 0.02     (80)
104 heptadecanal 1932 1932 0.2 0.04 0.2 0.02 (88) 2238 2247 0.5 0.05 0.5 0.03 (88)
105 1-eicosene 1995 1993     0.7 0.07 (19) 2047 2047     1.0 0.08 (94)
106 n-heneicosane 2100 2100 0.1 0.02 0.1 0.02   2100 2100 0.1 0.02 0.8 0.39  
107 1-octadecanol acetate 2194 2205     0.2 0.02 (95) 2529 2521     0.1 0.03 (96)
108 n-docosane 2200 2200 trace   trace     2200 2200 0.1 0.01 0.3 0.14  
109 1- tricosene 2295 2292     2.1 0.26 (19) 2356       2.0 0.13 §
110 n-tricosane 2300 2300 0.7 0.12 0.5 0.09   2300 2300 0.1 0.02 0.4 0.27  
111 1-tetracosene 2400 2402     1.5 0.33 (97) 2452       2.0 0.17 §
112 n-tetracosane 2400 2400 trace   0.3 0.06   2400 2400 0.3 0.06 0.2 0.10  
113 docosanal 2440 2434 0.1 0.03     (19) 2682   0.3 0.05     §
114 n-pentacosane 2500 2500 0.2 0.05 0.2 0.03   2500 2500 0.1 0.02 0.1 0.05  
115 1-pentacosene 2506 2496     0.1 0.01 (98) 2478 2488     0.1 0.03 (58)
116 n-hexacosane 2600 2600 0.3 0.07       2600 2600 0.3 0.06      
  monoterpene hydrocarbons     38.4   17.5         37.9   16.5    
  oxygenated monoterpenes     3.2   1.0         3.0   0.8    
  sesquiterpene hydrocarbons     31.7   52.1         31.0   49.6    
  oxygenated sesquiterpenes     9.5   12.2         7.7   12.4    
  others     11.7   10.8         14.2   13.7    
  total     94.5   93.6         93.8   93.0    
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a

Calculated linear retention index (LRI).

b

Reference LRI; % = percent by weight of EO; σ = standard deviation; § = identification by mass spectrometer (MS) only; and trace = <0.01%.

c

Major components in at least one EO are reported in bold.

The comparison through principal component analysis (PCA) among the main constituents of the EOs from the species G. miniphylla, G. rugulosa, G. buxifolia, G. laurifolia, G. cuicochensis, and G. sancti-antonii (see Figure 4), permitted to determine the relative closeness of the Gynoxys spp. so far studied for their volatile fraction compositions. In this statistical analysis, only major components were considered. On the one hand, G. miniphylla, G. cuicochensis, G. buxifolia, and G. laurifolia appeared to belong for similarity to the same group, whereas G. szyszylowiczii and G. rugulosa generated a different cluster. On the other hand, G. sancti-antonii was quite far from all the other plants of this family. These results were peculiarly counterintuitive since all these taxa, except G. buxifolia, apparently presented a quite similar chemical profile. In this sense, α-pinene and germacrene D were major components in practically all volatile fractions, whereas β-pinene, p-vinylguaiacol, (E)-β-caryophyllene, α-humulene, δ-cadinene, and α-cadinol were constantly present in all EOs, despite not always as major constituents.10−13 Finally, p-vinylguaiacol did not appear in G. buxifolia EO just because it was quantitatively dissolved in the hydrolate.12 Occasionally, a specific metabolite was a major component of a particular EO. This was for instance the case of δ-3-carene and trans-myrtanol acetate for G. miniphylla, and γ-curcumene for G. sancti-antonii. Furthermore, a series of heavy aliphatic compounds (mainly long-chained aldehydes, alkenes, and alkanes) was a characteristic pattern in the final part of many GC profiles.10,11,13 Finally, a special consideration must be given to G. buxifolia EO, whose chemical composition was completely different from all the other species, the major compounds being the very rare furanoeremophilane and bakkenolide A.12

Figure 4.

Figure 4

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PCA plot of major components identified in the EOs of G. miniphylla, G. rugulosa, G. buxifolia, G. laurifolia, G. cuicochensis, and G. sancti-antonii.

2.2. Enantioselective Analysis

The enantioselective analyses permitted to identify four enantiomerically pure compounds in G. cuicochensis EO and seven in G. sancti-antonii volatile fraction. They were (1R,5R)-(+)-α-pinene, (S)-(+)-β-phellandrene, (R)-(−)-piperitone, and (S)-(−)-germacrene D for the first plant, whereas (1S,5S)-(−)-α-pinene, (1R,5R)-(+)-sabinene, (R)-(−)-β-phellandrene, (S)-(−)-limonene, (1S,2R,6R,7R,8R)-(+)-α-copaene, (R)-(−)-terpinen-4-ol, and (S)-(−)-germacrene D were the ones of the second plant. All the other analyzed chiral compounds were present as scalemic mixtures in both EOs. Unlike the chemical compositions, the enantiomeric distributions of all the known Gynoxys EOs did not apparently present a common pattern.10−13 The detailed results of the enantioselective analyses on G. sancti-antonii and G. cuicochensis EOs are shown in Table 2, where two chiral selectors (2,3-diacetyl-6-tert-butyldimethylsilyl-β-cyclodextrin and 2,3-diethyl-6-tert-butyldimethylsilyl-β-cyclodextrin) were used in order to ensure the best enantiomeric separations. As usual, the variable enantiomeric distribution of the same chiral metabolites, within a botanical genus or even the same species, is the result of different biological functions and properties, that two optical isomers can exert in a living organism.99,100

Table 2. Enantioselective Analysis of Some Chiral Terpenes from G. cuicochensis and G. sancti-antonii EOsc.

enantiomers LRI G. cuicochensis
 G. sancti-antonii
    distribution (%) ee (%) distribution (%) ee (%)
(1R,5R)-(+)-α-pinene 924a 100.0 100.0    
(1S,5S)-(−)-α-pinene 926a     100.0 100.0
(1R,5R)-(+)-β-pinene 949a 44.7 10.6 19.3 61.3
(1S,5S)-(−)-β-pinene 959a 55.3   80.7  
(1R,5R)-(+)-sabinene 1008b 68.2 36.4 100.0 100.0
(1S,5S)-(−)-sabinene 1014b 31.8      
(R)-(−)-α-phellandrene 1019a 4.7 90.7    
(S)-(+)α-phellandrene 1022a 95.3      
(R)-(−)-β-phellandrene 1051a     100.0 100.0
(S)-(−)-limonene 1058a 97.5 95.0 100.0 100.0
(R)-(+)-limonene 1074a 2.5      
(S)-(+)-β-phellandrene 1075b 100.0 100.0    
(R)-(−)-linalool 1179a 56.3 12.5 47.8 4.5
(S)-(+)-linalool 1189a 43.7   52.2  
(R)-(−)-piperitone 1294a 100.0 100.0    
(S)-(+)-α-terpineol 1300a     84.7 69.5
(R)-(−)-α-terpineol 1313a     15.3  
(1S,2R,6R,7R,8R)-(+)-α-copaene 1322a     100.0 100.0
(R)-(−)-terpinen-4-ol 1339b 40.7 18.6 100.0 100.0
(S)-(+)-terpinen-4-ol 1376b 59.3      
(S)-(−)-germacrene D 1465a 100.0 100.0 100.0 100.0
Open in a new tab
a

2,3-diacetyl-6-tert-butyldimethylsilyl-β-cyclodextrin.

b

2,3-diethyl-6-tert-butyldimethylsilyl-β-cyclodextrin column.

c

Linear retention indice = calculated LRI; ee = enantiomeric excess.

3. Conclusions

The dry leaves of G. cuicochensis and G. sancti-antonii produced, by steam-distillation, two EOs with the same yield of about 0.08% by weight. The yield was therefore a little higher than the one of most of the other Gynoxys EOs (about 0.02%), but lower than the one of G. buxifolia (about 0.1%). The PCA demonstrated that G. cuicochensis volatile fraction was quite similar to most of the other EOs of the same genus, whereas G. sancti-antonii produced the most dissimilar EO. Furthermore, the heavy aliphatic fraction that characterizes many Gynoxys EOs was much less important in these two species. Finally, the enantioselective analyses showed the usual variable enantiomeric distribution, with a greater presence of enantiomerically pure compounds in G. sancti-antonii EO. A more exhaustive statistical analysis of the chemical compositions and enantiomeric distributions will be conducted once the investigation on the genus is complete. Furthermore, after preparative distillation, this EO is suitable to be evaluated for possible biological activities.

4. Methods

4.1. Plant Material

The leaves of both wild plants were collected on March 6, 2021, from different shrubs of each species located within the radius of about 200 m around two reference points. For G. cuicochensis, the point coordinates were 03°39′57″S and 79°15′15″W, at the altitude of 2950 m above the sea level. For G. sancti-antonii, the collection point was located at 03°34′24″S and 79°11′10″W, whose altitude was 2973 m above the sea level. Both sites corresponded to the Province of Loja, Ecuador. The botanical identification was carried out by one of the authors (N.C.), and it was based on the original specimens conserved at the Missouri Botanical Garden Herbarium (St. Louis, MO, USA), with codes 05035975 (G. cuicochensis) and 2810342 (G. sancti-antonii). A reference botanical voucher for each collected species was also deposited at the herbarium of the Universidad Técnica Particular de Loja (UTPL), with codes 14273 and 14677 for G. cuicochensis and G. sancti-antonii, respectively. The plant materials were submitted to gentle drying the same day of collection, at 35 °C for 48 h, before being stored in a fresh dark place until use. Both investigation and collection were conducted under permission of the Ministry of Environment, Water and Ecological Transition of Ecuador, with MAATE registry number MAE-DNB-CM-2016-0048.

4.2. Distillation and Sample Preparation

The dry leaves of both plants were analytically steam-distilled in a modified Dean–Stark apparatus, as previously described in literature.11 Each species was distilled in four repetitions, for 4 h each. Each distillation was based on 80.6 g of dry plant material for G. cuicochensis, and 81.0 g for G. sancti-antonii. Each time, the volatile fraction was condensed over 2 mL of cyclohexane, containing n-nonane as internal standard (0.7 mg/mL). The obtained EO solutions in cyclohexane were stored at −15 °C and they were directly injectable in GC. Both cyclohexane and n-nonane were analytical grade and they were purchased from Sigma-Aldrich (St. Louis, MO, USA).

4.3. Qualitative (GC–MS) Chemical Analyses

The qualitative analyses were carried out with a Thermo Fisher Scientific GC, model Trace 1310, coupled to an ISQ 7000 MS from the same provider (Waltham, MA, USA). The instrument was equipped with two capillary columns, both 30 m long, 0.25 mm internal diameter, and 0.25 μm film thickness (Agilent Technology, Santa Clara, CA, USA). The stationary phases were nonpolar (DB-5 ms) and polar (HP-INNOWax) based on 5%-phenyl-methylpolysiloxane and polyethylene glycol, respectively. The injector was operated in the split mode (1 μL sample volume injected at 40:1 split ratio), set at the temperature of 230 °C. Helium was the carrier gas used at the constant flow of 1 mL/min (Indura S.A., Guayaquil, Ecuador). The GC oven was programmed, with both columns, according to the following thermal program: 40 °C for 10 min, a first gradient of 3 °C/min until 100 °C, a second gradient of 5 °C/min until 200 °C, and a third gradient of 10 °C/min until 230 °C, which were maintained for 20 min. The GC–MS transfer line and the electron ionization ion source (70 eV) were set at 230 °C. The MS, equipped with a single quadrupole analyzer, was operated in the SCAN mode and programmed for 40–400 m/z mass range. A mixture of n-alkane C9–C26, purchased from Sigma-Aldrich, was also injected in the same conditions as the EOs. The components of the volatile fractions were identified by comparing the linear retention indices (LRIs), calculated according to Van den Dool and Kratz,101 and mass spectra with data from literature (see Table 1).

4.4. Quantitative (GC–FID) Chemical Analyses

The quantitative chemical analyses were conducted on the same GC, columns, ad instrument configuration, as the qualitative ones, except for the use of a flame ionization detector (FID) instead of MS. The FID temperature was set at 230 °C, whereas the injector was operated at the split ratio of 10:1. All the EO constituents were quantified with external calibration, using n-nonane as internal standard and isopropyl caproate as calibration standard. The internal standard was purchased from Sigma-Aldrich, whereas the calibration standard was synthetized in one of the authors’ laboratories and purified to 98.8% (GC–FID purity). A six-point calibration curve was traced for each column, as previously described in literature,102 obtaining a correlation coefficient of 0.997 in both cases. A relative response factor was calculated for each EO component versus isopropyl caproate, according to combustion enthalpy, as described in literature.103,104 The percent results were obtained as a mean value and standard deviation over four repetitions, relating the amount of each compound to the whole mass of the distilled EO, analytically calculated.

4.5. PCA of Some Gynoxys spp. EOs

The PCA was carried out on SIMCA software, purchased from Sartorius (Göttingen, Germany). The analysis was conducted only on major constituents, accounting for at least 1% in at least one EO. The compounds included in the analysis were as follows: α-pinene, β-pinene, δ-3-carene, β-phellandrene, trans-myrtanol acetate, p-vinylguiacol, (E)-β-caryophyllene, α-humulene, γ-curcumene, germacrene D, ar-curcumene, byciclogermacrene, δ-cadinene, α-muurolol, α-cadinol, furanoeremophilane, bakkenolide A, n-heneicosane, 1-docosene, 1-tricosene, n-tricosane, 1-tetracosene, n-pentacosane, 1-hexacosene, and n-heptacosane. The quantitative data submitted to PCA were the mean values of each component on both nonpolar and polar columns. The analysis included data from G. szyszylowiczii that, despite being still unpublished, are currently partially available.

4.6. Enantioselective Analyses

The enantioselective analyses were carried out in the same GC–MS instrument as the qualitative ones. Two enantioselective capillary columns were used: one based on a 2,3-diacetyl-6-tert-butyldimethylsilyl-β-cyclodextrin chiral selector and the other one based on a 2,3-diethyl-6-tert-butyldimethylsilyl-β-cyclodextrin stationary phase. The columns were 25 m long, 250 μm internal diameter and 0.25 μm phase thickness, both purchased from MEGA S.r.l. (Legnano, MI, Italy). The enantiomers were identified according to mass spectra and injection of enantiomerically pure standards, that were purchased from Sigma-Aldrich. The GC oven was programmed according to the following thermal program: 50 °C for 1 min, a thermal gradient of 2 °C/min until 220 °C, finally maintained for 10 min. As usual, the enantiomer identification was limited by standard availability.

Acknowledgments

We are grateful to the Universidad Técnica Particular de Loja (UTPL) for supporting this investigation and open access publication. We are also grateful to Prof. Carlo Bicchi (University of Turin, Italy) and Dr. Stefano Galli (MEGA S.r.l., Legnano, Italy) for their support with enantioselective columns.

The authors declare no competing financial interest.

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