Design, Synthesis, and Biological Activity of Novel Ferulic Amide Ac5c Derivatives

Abstract

A total of 34 novel ferulic amide Ac5c derivatives were designed and synthesized and their antipest activities were investigated. The results showed that some compounds exhibited excellent in vitro antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), such as compounds 4q and 5n demonstrated excellent in vitro activity against Xoo, with EC₅₀ values of 4.0, and 1.9 μg/mL, respectively. Compounds 4c, 4h, 4m, 4p, 4q, and 5a had significant in vitro activities against Xoc, with EC₅₀ values of 12.5, 13.9, 9.8 15.0, 9.2, and 19.8 μg/mL, respectively. Moreover, the antibacterial activity in vivo against rice bacterial leaf blight was also evaluated. Scanning electron microscopy (SEM) showed that compound 5n significantly reduced the cell membrane of Xoo, and resulted in cell surface wilting, deformation, breakage, and increased porous attributes. In addition, some of the target compounds also showed moderate biological activity against fungi and acted as potential insecticides.

Plant pathogen invasion accounts for at least 15% of the economic and yield losses in agricultural production per annum.¹ Rice is one of the staple foods for most people in the world and is the main crop cultivated worldwide.² Crop production for rice suffers from damage caused by Xanthomonas oryzae pv oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc) pathogens, which account for reduced rice yield, by up to 50%, and are therefore two of the most destructive pathogens causing rice diseases in the world.³ Moreover, X. axonopodis pv. citri (Xac) causes devastating disease in fruit trees. By invading citruses, it can cause serious citrus canker, thereby reducing the quality of the fresh fruit produced and sometimes causing disastrous results,⁴ including having a serious impact on the international citrus industry.⁵ Currently, chemical pesticides are the main countermeasures used against crop diseases. Some traditional pesticides including thiabendazole, mesomycin, thiazolyl zinc, and others display particular effects on the aforementioned pathogens.^4,6,7 However, as resistance or cross-resistance to these pathogens to the existing agrochemicals continuously increased, prevention and controlling efficiencies became worse.⁸ Consequently, discovering novel active molecules with novel mechanisms and high efficiencies against plant pathogens but that are also low risk for ecological environments are urgently needed.

Due to environmental friendliness, structural novelty, and properties for potential targets or mechanisms, natural products (NPs) play increasingly significant roles in exploring novel pesticides and have attracted more attention recently.⁹ Nowadays, more than 50% of pesticides used all over the world are originated from NPs, for example, phosphinothricin, phosalacine, glyphosate, the conventional neonicotinoids, strobilurins, pyrethroids, ethylicin, fenpiclonil, and fludioxonil, which are all mimicked from NPs.^9,10 Nowadays, NPs and their derivatives are still the main source of active ingredients and inspiration for a wide range of pharmaceutical and agrochemicals.¹¹ As an important natural product, the skeleton of ferulic acid is widely used in the development of new pesticides and is also used as an important lead compound for NP-based drug design. A variety of molecules with excellent biological activities, including antiviral,¹² pharmaceutical,¹³ antioxidant,¹⁴ antibacterial,^15,16 and insecticidal activities,¹⁷ have been discovered in recent years. Some of them have shown promising activities related to plant disease control.¹²

1-Aminocyclopentane carboxylic Acid (Ac5c), also known as cycloleucine, is a nonmetabolizable amino acid and acts as a competitive inhibitor of ATP and plays an important role in drug discovery.¹⁸⁻²⁰ The compounds or unnatural amino acid analogues containing Ac5c have shown excellent bioactivities including anti-immune,¹⁹ anti-inflammatory,²⁰ antagonist,²¹ antimicrobial,²² anticonvulsant,²³ and antibacterial activities.²⁴ In addition, Ac5c-containing peptides may be used as cell-penetrating peptides and helical chiral catalysts.²⁵ The Ac5c fragment possesses several advantages for drug discovery: (1) it shows site selectivity, diastereoselectivity, and (applicable) enantioselectivity;²⁶ (2) it can reduce the conformational flexibility of target sites and enhance the structural specificity of building blocks;²⁷ and (3) Ac5c can enhance hydrophobicity and has a high binding affinity.²⁸ Hence, interest in Ac5c derivatives is attracting increasing amount of attention.

In the published literature, we found that ferulic amides can be used as potential antimicrobial agents in agriculture. Compared with commercially available compounds, some ferulic amides displayed excellent antibacterial activities.^29,30 In our published work,³¹ we found that some ferulic amide Ac6c derivatives showed excellent antipest activity. Encouraged by this, we envisage changing cyclohexane to cyclopentane to expand our research and develop new lead compounds, which have high levels of biological activity. In this work, we merged the core of ferulic acid and Ac5c via an amide linker through a condensation reaction and etherified in diversity at hydroxyl on ferulic acid to give rise to novel ferulic amide derivatives containing the active substructure of Ac5c (Figure 1).

Figure 1.

Design strategy for the target molecules.

Chemistry

Using different substituted halogen compounds as starting materials, the synthesis of target compounds 4a–4q went through three steps,³²⁻³⁴ including substitution, hydrolysis, and acylation (Figure 1). Then, the target compounds 5a–5q were prepared³³ via hydrolysis of compounds 4a–4q (Scheme S1).

In Vitro Antibacterial Activity

The in vitro antibacterial activities of 4a–4q and 5a–5q against Xoo, Xoc, and Xac were determined using turbidimetric methods,^6,35 and the preliminary screening results are shown in Table 1. As observed in Table 1, all of the target compounds showed moderate and good anti-Xoo, Xac, and Xoc activities. At 100 and 50 μg/mL, the in vitro antibacterial activities of compounds 4k, 4q, 5c, 5f, 5m, and 5n against Xoo showed excellent antibacterial activity, and their inhibition rate can reach 90%, far better than those of bismerthiazol (67.8 and 47.3%, respectively) and thiodiazole copper (65.8 and 34.6%, respectively).

Table 1. In Vitro Antibacterial Activity of the Target Compounds against Xoo, Xac, and Xoc^a.

		Xoo		Xoc		Xac
		inhibition rate (%)		inhibition rate (%)		inhibition rate (%)
compd.	R	100 μg/mL	50 μg/mL	100 μg/mL	50 μg/mL	100 μg/mL	50 μg/mL
4a	2-CH3-Ph	39.6 ± 1.1	36.8 ± 1.2	38.5 ± 3.5	37.0 ± 1.1	47.8 ± 1.4	14.0 ± 5.0
4b	3-CH3-Ph	92.8 ± 1.6	76.9 ± 4.7	62.5 ± 3.3	48.3 ± 1.2	45.2 ± 0.7	18.0 ± 3.4
4c	4-F-5-CF3-Ph	51.4 ± 4.4	49.4 ± 3.7	63.6 ± 3.1	57.8 ± 0.8	33.2 ± 2.8	28.6 ± 3.8
4d	4-Cl-Ph	96.2 ± 1.2	62.4 ± 1.3	62.4 ± 1.0	55.8 ± 3.6	70.0 ± 4.0	49.5 ± 3.6
4e	CH2CH2CH2Cl	80.2 ± 0.6	78.9 ± 4.4	70.8 ± 3.2	57.5 ± 2.6	38.8 ± 4.0	19.0 ± 3.3
4f	2-F-3-Cl-Ph	29.3 ± 1.8	27.6 ± 3.5	47.7 ± 3.7	41.9 ± 1.8	24.9 ± 2.9	22.4 ± 2.3
4g	2-F-5-CF3-Ph	21.2 ± 1.8	9.4 ± 4.8	46.5 ± 0.1	25.9 ± 2.3	47.7 ± 2.6	32.2 ± 2.4
4h	2,6-2F-Ph	73.2 ± 1.9	59.7 ± 0.7	64.7 ± 4.5	56.6 ± 5.0	45.0 ± 1.4	22.3 ± 0.6
4i	2-Cl-4-F-Ph	61.5 ± 2.7	31.7 ± 2.5	51.7 ± 2.7	46.3 ± 0.6	18.0 ± 0.9	21.9 ± 0.2
4j	4-OCF3-Ph	53.1 ± 1.5	36.8 ± 2.7	54.7 ± 3.7	41.8 ± 4.2	48.0 ± 4.2	20.8 ± 2.0
4k	3-F-Ph	98.2 ± 4.2	95.8 ± 3.2	47.5 ± 1.9	43.6 ± 1.4	36.9 ± 3.9	32.2 ± 1.5
4l	3,5-2F-Ph	77.8 ± 1.6	61.5 ± 2.7	53.6 ± 4.4	51.8 ± 2.3	41.9 ± 2.1	9.5 ± 0.3
4m	2-Cl-5-F-Ph	89.8 ± 3.7	79.5 ± 0.5	77.8 ± 4.0	68.6 ± 3.5	8.0 ± 2.8	7.5 ± 2.1
4n	Ph	83.7 ± 0.7	69.9 ± 2.6	45.6 ± 2.4	43.5 ± 1.9	6.6 ± 2.1	6.3 ± 3.1
4o	4-CF3-Ph	31.9 ± 4.5	36.9 ± 4.0	76.5 ± 1.3	53.1 ± 2.7	37.8 ± 0.8	33.1 ± 0.8
4p	2,5-2F-Ph	95.4 ± 2.2	74.8 ± 4.4	88.5 ± 2.8	78.0 ± 4.6	52.0 ± 0.5	25.5 ± 0.5
4q	4-F-Ph	96.8 ± 0.9	95.4 ± 4.1	63.0 ± 4.1	61.3 ± 3.6	64.2 ± 0.2	27.5 ± 2.9
5a	2-CH3-Ph	27.4 ± 0.2	9.0 ± 1.2	61.0 ± 0.6	57.4 ± 0.7	65.4 ± 1.4	44.2 ± 1.3
5b	3-CH3-Ph	55.0 ± 4.0	48.8 ± 3.5	30.7 ± 3.9	25.8 ± 2.7	39.2 ± 4.0	28.9 ± 2.9
5c	4-F-5-CF3-Ph	93.4 ± 2.8	90.9 ± 2.2	46.7 ± 4.2	43.3 ± 1.6	57.8 ± 3.8	51.8 ± 4.9
5d	CH2CH2CH2Cl	65.9 ± 3.5	35.9 ± 0.2	39.9 ± 0.5	36.6 ± 1.4	49.7 ± 0.2	14.2 ± 1.4
5e	2-F-3-Cl-Ph	88.3 ± 4.9	58.0 ± 4.6	39.2 ± 2.8	32.3 ± 0.2	35.1 ± 1.0	24.1 ± 2.6
5f	2-Cl-4-F-Ph	98.3 ± 0.2	97.7 ± 0.3	61.7 ± 3.0	52.6 ± 3.6	49.2 ± 3.9	23.3 ± 2.9
5g	4-OCF3-Ph	79.3 ± 2.5	68.9 ± 2.1	54.6 ± 0.9	45.3 ± 4.3	36.8 ± 1.9	26.2 ± 2.3
5h	3-F-Ph	90.9 ± 4.6	67.0 ± 0.2	48.5 ± 2.6	43.6 ± 2.1	12.0 ± 4.0	2.9 ± 2.3
5i	2-Cl-Ph	65.3 ± 3.3	51.1 ± 0.3	62.1 ± 3.3	59.1 ± 4.3	48.0 ± 4.6	24.4 ± 4.2
5j	3,4-2F-Ph	65.8 ± 2.7	60.3 ± 2.5	39.6 ± 0.4	38.9 ± 4.1	18.3 ± 1.3	22.9 ± 0.6
5k	3,5-2F-Ph	48.2 ± 2.9	30.7 ± 2.5	55.2 ± 3.2	52.9 ± 3.0	24.4 ± 1.1	28.1 ± 4.5
5l	2-Cl-5-F-Ph	49.9 ± 0.2	21.7 ± 2.9	67.3 ± 4.9	61.7 ± 0.4	40.7 ± 2.3	37.1 ± 3.9
5m	Ph	92.8 ± 2.0	90.4 ± 3.7	49.3 ± 2.8	38.7 ± 2.7	56.3 ± 2.2	40.8 ± 3.8
5n	4-CF3-Ph	96.4 ± 1.4	92.5 ± 2.3	54.8 ± 2.6	48.6 ± 1.7	45.6 ± 4.2	45.1 ± 0.1
5o	2,5-2F-Ph	61.6 ± 1.0	32.9 ± 1.5	48.7 ± 3.5	42.7 ± 3.8	6.0 ± 2.4	6.5 ± 1.6
5p	3-Br-Ph	86.2 ± 1.1	64.8 ± 0.4	58.3 ± 4.3	54.6 ± 1.3	51.9 ± 1.2	41.6 ± 3.7
5q	4-F-Ph	40.1 ± 2.8	32.7 ± 3.2	67.4 ± 4.1	43.5 ± 0.7	39.6 ± 1.1	36.8 ± 1.2
BMTb		67.8 ± 2.6	47.3 ± 2.7	63.9 ± 0.7	39.8 ± 2.8	62.8 ± 1.7	44.8 ± 5.0
TDCb		65.8 ± 0.5	34.6 ± 1.9	60.8 ± 3.4	32.0 ± 2.2	51.0 ± 1.2	22.0 ± 2.4

^aAverage of three replicates.

^bCommercial bactericides bismerthiazol (BMT) and thiodiazole copper (TDC) were used as positive control agents.

The EC₅₀ values of the compounds were determined via preliminary bioassay tests, as shown in Tables 2 and 3. Table 2 demonstrates that compounds 4a, 4d, 4e, 4h, 4k, 4l, 4m, 4n, 4p, 4q, 5c, 5e, 5f, 5g, 5h, 5i, 5j, 5m, 5n, and 5p exhibited excellent antibacterial effects against Xoo with EC₅₀ values of 23.8, 36.2, 29.1, 39.8, 14.1, 28.0, 10.7, 28.4, 37.3, 4.0, 18.3, 47.5, 57.2, 12.8, 28.0, 82.8, 25.8, 25.1, 1.9, and 43.6 μg/mL, respectively, far more than those of both bismerthiazol (EC₅₀ = 84.3 μg/mL) and thiodiazole copper (EC₅₀ = 137.8 μg/mL). Furthermore, Table 3 indicates that compounds 4b, 4c, 4d, 4e, 4h, 4l, 4m, 4o, 4p, 4q, 5a, 5i, 5k, 5l, and 5p showed better biological activity against Xoc with EC₅₀ values of 94.4, 12.5, 69.8, 50.3, 13.9, 53.3, 9.8, 61.4, 15.4, 9.2, 19.8, 37.5, 18.2, 22.6, and 58.4 μg/mL, respectively, making them superior to both bismerthiazol (EC₅₀ = 80.1 μg/mL) and thiodiazole copper (EC₅₀ = 122.4 μg/mL). It is worth noting that compounds 5n and 4q showed the best bacterial activity against Xoo (EC₅₀ = 1.9 μg/mL) and Xoc (EC₅₀ = 9.2 μg/mL), respectively.

Table 2. Antibacterial Activities of Target Compounds 4x and 5x against Plant Pathogens Xoo in Vitro^a.

compd.	toxic regression equation	r	EC50 (μg/mL)	compd.	toxic regression equation	r	EC50 (μg/mL)
4a	y = 1.29x + 3.22	0.91	23.8 ± 6.9	5a
4b				5b
4c				5c	y = 0.47x + 4.41	0.92	18.3 ± 5.4
4d	y = 1.58x + 2.54	0.92	36.2 ± 1.3	5d
4e	y = 0.20x + 3.25	0.95	29.1 ± 3.3	5e	y = 1.49x + 2.50	0.91	47.5 ± 8.9
4f				5f	y = 0.46x + 4.20	0.91	57.2 ± 9.9
4g				5g	y = 0.41x + 4.55	0.92	12.8 ± 2.1
4h	y = 0.47x + 4.25	0.91	39.8 ± 0.3	5h	y = 1.34x + 3.01	0.94	28.0 ± 0.2
4i				5i	y = 0.85x + 3.37	0.97	82.8 ± 2.9
4j				5j	y = 0.54x + 4.24	0.96	25.8 ± 6.3
4k	y = 0.45x + 4.49	0.91	14.1 ± 0.4	5k
4l	y = 0.75x + 3.92	0.91	28.0 ± 9.0	5l
4m	y = 1.25x + 3.71	0.94	10.7 ± 5.8	5m	y = 1.69x + 2.64	0.94	25.1 ± 0.5
4n	y = 1.01x + 3.53	0.91	28.4 ± 1.6	5n	y = 0.35x + 4.90	0.9	1.9 ± 1.5
4o				5o
4p	y = 2.00x + 1.86	0.93	37.3 ± 6.9	5p	y = 1.21x + 3.01	0.9	43.6 ± 7.1
4q	y = 0.28x +4.83	0.93	4.0 ± 2.7	5q
BMTb	y = 0.83x + 3.39	0.91	84.3 ± 9.1	TDCb	y = 1.30x + 2.21	0.94	137.8 ± 4.3

^aAverage of three replicates.

^bCommercial bactericides bismerthiazol (BMT) and thiodiazole copper (TDC) were used as positive control agents.

Table 3. EC₅₀ Values of Target Compounds 4x and 5x against Xoc^a.

compd.	toxic regression equation	r	EC50	compd.	toxic regression equation	r	EC50
			(μg/mL)				(μg/mL)
4a				5a	y = 0.25x + 4.67	0.94	19.8 ± 7.7
4b	y = 0.81x + 3.39	0.99	94.4 ± 6.2	5b
4c	y = 0.22x + 4.76	0.98	12.5 ± 10.0	5c
4d	y = 0.84x + 3.58	0.91	69.8 ± 1.6	5d
4e	y = 0.59x + 4.00	0.93	50.3 ± 3.8	5e
4f				5f	y = 0.91x + 3.16	0.91	>100
4g				5g	y = 0.59x + 3.75	0.93	>100
4h	y = 0.21x + 4.76	0.91	13.9 ± 5.9	5h
4i	y = 0.65x + 3.59	0.98	>100	5i	y = 0.41x + 4.35	0.93	37.5 ± 3.1
4j	y = 0.47x + 3.97	0.91	>100	5j
4k				5k	y = 0.42x + 4.20	0.92	78.2 ± 3.6
4l	y = 0.18x + 4.68	0.99	53.3 ± 9.5	5l	y = 0.48x + 4.35	0.96	22.6 ± 7.8
4m	y = 0.42x + 4.59	0.95	9.8 ± 0.7	5m	y = 0.59x + 3.55	0.94	>200
4n				5n	y = 0.39x + 4.20	0.97	>100
4o	y = 0.32x + 4.50	0.94	61.4 ± 4.6	5o	y = 0.53x + 3.82	0.91	>100
4p	y = 0.85x + 4.00	0.94	15.0 ± 2.9	5p	y = 0.30x + 4.47	0.92	58.4 ± 9.4
4q	y = 0.14x + 4.87	0.99	9.2 ± 6.4	5q
BMTb	y = 0.47x + 4.10	0.98	80.1 ± 4.3	TDCb	y = 0.79x + 3.35	0.9	122.4 ± 5.4

^aAverage of three replicates.

^bCommercial bactericides bismerthiazol (BMT) and thiodiazole copper (TDC) were used as positive control agents.

Structure–Activity Relationship Analysis

Data in Tables 1–3 indicate that the substitutes in the framework of ferulic acid may affect antibacterial activity. At the same time, the antibacterial efficiency of the same substituent to compound 4x and compound 5x was also different. Three main conclusions can be summarized. First, compounds 4x and 5x with the same substituent had different antibacterial effects against Xoo and Xoc; it is speculated that the reason behind this is that the parent structure of compound 5x has −COOH, which makes it more hydrophilic^36,37 and therefore improves the antibacterial activity of compound 5x. The corresponding compounds’ in vitro bioactivities against Xoo and Xoc were as follows: 5m (R=Ph) > 4n (R=Ph), 5n (R=4-CF₃-Ph) > 4o (R=4-CF₃-Ph), and 5a (R=2-CH₃-Ph) > 4a (R=2-CH₃-Ph). Second, different substitutions at the halogen group position could influence antibacterial activity. Among compounds 4a–4q and 5a–5q’s in vitrobioactivities against Xoo and Xoc, the compounds with single halogen on substituted phenyl had the best antibacterial activity. This included compounds 4q (R=4-F-Ph)> 4m (R=2-Cl-5-F-Ph), 5n (R=4-CF₃-Ph) > 5g (R=4-OCF₃-Ph), and 4q (R=4-F-Ph) > 4m (R=2-Cl-5-F-Ph); in contrast, the compounds’ in vitro bioactivities against Xoc follows the order of 5i (R=2-Cl-Ph) > 5l (R=2-Cl-5-F-Ph). Third, the results showed that the sequence of in vitro antibiological activities of the corresponding compounds containing electron-donating groups against Xoo and Xoc was as follows 4b (R=3-CH₃-Ph) > 4n (R=Ph) > 4e (R=CH₂CH₂CH₂Cl) > 4a (R=2-CH₃-Ph), 5m (R=Ph) > 5d (R=CH₂CH₂CH₂Cl) > 5b (R=3-CH₃-Ph) > 5a (R=2-CH₃-Ph), and 4e (R=CH₂CH₂CH₂Cl)> 4b (R=3-CH₃-Ph) > 4n (R=Ph) > 4a (R=2-CH₃-Ph), 5a (R=2-CH₃-Ph) > 5m (R=Ph) > 5d (R=CH₂CH₂CH₂Cl) > 5b (R=3-CH₃-Ph). In general, the antibacterial activities of the corresponding compounds containing fluorine atoms on the R substituents were excellent. This activity may be because of improved lipophilicity, metabolic stability, and bioavailability of these compounds after the introduction of fluorine substituents, which makes it a potential factor of interest.^38,39

In Vivo Antibacterial Activity

The in vivo antibacterial activity of compound 5n was carried out at a concentration of 200 μg/mL against rice bacterial leaf blight, as shown in Table 4 and Figure 2. According to Table 4 and Figure 2, compound 5n had good in vivo protective activity (41.5%), when compared to those of bismerthiazol (35.3%) and thiodiazole copper (31.9%). Concomitantly, Table 4 and Figure 2 show that compound 5n showed outstanding in vivo curative activity (44.4%), which was even better than bismerthiazol (33.2%) and thiodiazole copper (28.5%).

Table 4. Protection and Curative Activities of Compound 5n against Rice Bacterial Leaf Blight under Greenhouse Conditions at 200 μg/mL in Vivo.

	protection activity (14 days after spraying)			curative activity (14 days after spraying)
treatment	morbidity (%)	disease index (%)	control efficiency (%)a	morbidity (%)	disease index (%)a	control efficiency (%)a
5n	100	51.2	41.5	100	46.7	44.4
BMT	100	56.9	35.3	100	56.0	33.2
TDC	100	60.0	31.9	100	60.0	28.5
CKb	100	88.1		100	83.9

^aStatistical analysis was conducted by ANOVA, method under the condition of equal variances assumed (P > 0.05) and equal variances not assumed (P < 0.05).

^bBlank control.

Figure 2.

Curative and protection activities of compound 5n against rice bacterial leaf blight under greenhouse conditions at 200 μg/mL, with BMT and TDC as the positive control agents.

Scanning Electron Microscopy (SEM)

The SEM results of compound 5n are shown in Figure 3. It can be concluded that with increasing compound concentrations, the bacterial external morphological changes also increased significantly. For example, when the compound concentration was 25 μg/mL, the morphology of the bacterial cell membrane was atrophic and unhealthy (Figure 3B). However, when the concentration of the compound increased to 50 μg/mL, the appearance of the bacteria was gradually more broken and porous (Figure 3C). In contrast, the external morphology of the bacteria in the untreated control group was intact (Figure 3A). This phenomenon revealed that compound 5n has strong interactions with plant pathogens and can attack pathogens.

Figure 3.

SEM images for Xoo after being incubated with different concentrations of compound 5n: (A) 0 μg/mL, (B) 25.0 μg/mL, and (C) 50.0 μg/mL.

Antifungal Activity

The antifungal activity of the target compounds against six strains in vitro was evaluated using a mycelium growth rate method. The biological data (Table S1) revealed that some compounds had moderate antifungal activity, for example, the title compounds 4o (92.1%) and 5o (85.8%) exhibited obvious anti-S. s. and R. s. effects at 50 μg/mL, which were similar to that of the commercial fungicide carbendazim (97.0 and 100.0%, respectively). These data show that the substituent position of compounds has a significant impact on bioassay activity.

Insecticidal Activity

The insecticidal activity against Plutella xylostella was determined by a leaf dipping method,⁴⁰ and the bioassay results are shown in Table S2. The results show that the target compounds 4a–4q and 5a–5q had weak insecticidal activity against P. xylostella at 500 μg/mL. In addition to showing good antibacterial activity, the target compound also exhibited moderate insecticidal activity, for example, compounds 4o, 5e, 5f, 5g, and 5n (90.3, 83.0, 90.0, 80.3, and 90.0%) at 500 μg/mL, which is equivalent to the control chlorpyrifos (100.0%). Among them, the biological activities of the substituents they contain are 5g (R=4-CF₃-Ph) > 5f (R=2-Cl-4-F-Ph) or 5n (R=4-CF₃-Ph) > 5e (R=2-F-3-Cl-Ph) > 5g (R=4-OCF₃-Ph).

In conclusion, a series of novel ferulic amide Ac5c derivatives were designed and synthesized and their antibacterial, antifungal, and insecticidal activities were investigated. Bioassays showed that the target compounds exhibited excellent bioactivity. In particular, compounds 4m, 4q, 5m, and 5n showed excellent antibacterial activities toward Xoo and with EC₅₀ values of 10.7, 4.0, 3.9, and 1.9 μg/mL, respectively. Moreover, compounds 4c, 4h, 4m, 4q, and 5a had significantly lower EC₅₀ values (12.5, 13.9, 9.8, 9.2, and 19.8 μg/mL) against Xoc than bismerthiazol (80.1 μg/mL) and thiodiazole copper (122.4 μg/mL). Some of the compounds showed good antifungal and moderated insecticidal activities. Considering that the corresponding compounds are easy to synthesize, have a simple structure, and the target compounds exhibited high levels of antibacterial activity, compounds containing novel ferulic amide Ac5c derivatives could be considered as promising molecules in the development of more efficient agrochemicals in the future.

Glossary

Abrreviations

Xoo

Xanthomonas oryzae pv. oryzae

Xoc

Xanthomonas oryzae pv. oryzicola

SEM

scanning electron microscopy

Xac

Xanthomonas axonopodis pv. citri

NPs

natural products

Ac5c

1-aminocyclopentane carboxylic acid

TDC

thiodiazole copper

BMT

bismerthiazol

NMR

nuclear magnetic resonance

HRMS

high-resolution mass spectrum

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c04644.

• Materials and experimental procedures and supplementary biochemical and compound characterization data, including ¹H NMR, ¹³C NMR, and ¹⁹F NMR spectra of synthesized compounds (PDF)

The authors declare no competing financial interest.