α-Haloacetophenone and analogues as potential antibacterial agents and nematicides

Bioorganic & Medicinal Chemistry Letters xxx (xxxx) xxxx

Contents lists available at ScienceDirect

Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl

α-Haloacetophenone and analogues as potential antibacterial agents and nematicides Chongfen Yia, Jixiang Chena, Chengqian Wei, Sikai Wu, Shaobo Wang, Deyu Hu, Baoan Song

⁎

State Key Laboratory Breeding Base of Green Pesticide and Agricultural Bioengineering, Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of Education, Research and Development Center for Fine Chemicals, Guizhou University, Huaxi District, Guiyang 550025, China

ARTICLE INFO

ABSTRACT

Keywords: Haloacetophenone Antibacterial activity Nematocidal activity

A series of α-haloacetophenones and analogues were synthesized. The bioassays show that some target compounds have good antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac) and Meloidogyne incognita (M. incognita). Especially, the compound 24 has good in vitro and in vivo antibacterial activities against Xoo, the EC50 value, curative and protection activities are 0.09 mg/L, 48.9%, and 52.3%, respectively, which are better than the thiodiazole copper and bismerthiazol. Meanwhile, the compound 24 has good in vitro antibacterial activity against Xac, and has an EC50 value of 1.6 mg/L. Moreover, the compound 19 exhibits good nematicidal activity M. incognita, with the LC50 value of 1.0 mg/L, which is better than the positive control avermectin. In addition, the compound 24 can inhibit the formation of extracellular polysaccharide and biofilm of Xoo, and change the permeability of cell membrane. α-haloacetophenone and analogues have the advantages of simple structure, high efficiency, broad spectrum of biological activity, and can be used as antibacterial agents and nematicides or lead compounds in the future.

Rice bacterial leaf blight is a common rice bacterial disease caused by Xanthomonas oryzae pv. oryzae (Xoo) that affects every stage of growth of the plant and can result in up to 80% loss.1,2 Simultaneously, citrus canker is a severe bacterial citrus disease caused by Xanthomonas axonopodis pv. citri (Xac), which significantly reduces citrus production.3–5 At present, traditional chemical antibacterial agents are mainly used to control bacterial blight and citrus canker, and their long-term use can lead to an increase in bacterial resistance and serious pollution to the environment, such as bismerthiazol and thiadiazole copper.6–8 Therefore, discovering and developing a new type of antibacterial agent with high efficiency, low toxicity and environmental friendliness and unique mechanism of action has become an urgent problem to be solved. Separation of biologically active natural products from plants or microorganisms and the modification of their structures is one of the important ways to obtain pesticides.9–13 In recent years, studies on the isolation of natural products from plants and testing of their biological activity have widely been reported.14–16 However, acetophenone is a natural product widely found in plants, and has attracted much attention due to its simple structure that is easy to be modified and possesses

excellent antifungal,17 acaricidal,18,19 and plant growth regulating activities.20 But so far, there have been no reports about the direct use of the natural product acetophenones for the control of agricultural bacterial diseases. In other words, we report here for the first time the antibacterial activities of a series of α-haloacetophenone and analogues against Xoo and Xac. In this work, 30 α-haloacetophenones and analogues were synthesized (Fig. 1), and their antibacterial activities in vitro and in vivo were evaluated, and their structure-activity relationships were clarified. Meanwhile, most of the compounds show good antibacterial activity against Xoo and Xac, with the compound 24 having the highest in vitro antibacterial activity which was significantly superior to the commercial thiodiazole copper and bismerthiazol. Furthermore, in order to expand their application, we also tested their nematicidal activity against M. incognita. Some compounds show good nematicidal activity, with the compound 19 being superior to the positive control avermectin. We also explored initially the relationship between biological activities and structure. Finally, the effects of the compound 24 on extracellular polysaccharide production, biofilm synthesis and cell membrane permeability of Xoo were evaluated, and scanning electron microscopy was used to observe the changes in cell

Abbreviations: EC50, Semi-inhibitory concentration; LC50, Semilethal concentration; Xoo, Xanthomonas oryzae pv. oryzae; Xac, Xanthomonas axonopodis pv. citri; M. incognita, Meloidogyne incognita; EPS, Extracellular polysaccharide ⁎ Corresponding author. E-mail address: [email protected] (B. Song). a Chongfen Yi and Jixiang Chen contributed equally to this work. https://doi.org/10.1016/j.bmcl.2019.126814 Received 2 July 2019; Received in revised form 2 November 2019; Accepted 8 November 2019 0960-894X/ © 2019 Published by Elsevier Ltd.

Please cite this article as: Chongfen Yi, et al., Bioorganic & Medicinal Chemistry Letters, https://doi.org/10.1016/j.bmcl.2019.126814

Bioorganic & Medicinal Chemistry Letters xxx (xxxx) xxxx

C. Yi, et al.

Fig. 1. Synthesis of the α-haloacetophenones and analogues 1–30.

Table 1 The EC50 value and the in vitro antibacterial activity of the compounds 1–30 against Xoo and Xac at different concentrations. Compounds

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 thiodiazole copper Bismerthiazol

Xoo

Xac

50 mg/L

5 mg/L

EC50 mg/L

50 mg/L

5 mg/L

EC50 mg/L

100 100 100 100 100 100 100 100 81.05 ± 1.15 100 100 100 100 100 100 100 100 100 100 100 100 79.7 ± 1.17 100 100 100 100 100 100 82.31 ± 0.61 77.04 ± 1.14 17.92 ± 3.42 20.04 ± 4.42

100 100 98.69 100 100 98.84 100 100 28.04 100 100 98.19 100 97.59 100 100 100 100 100 100 100 45.08 100 100 100 88.09 100 100 34.57 25.58 / /

0.34 ± 0.03 0.40 ± 0.05 0.54 ± 0.03 0.33 ± 0.03 0.27 ± 0.04 0.63 ± 0.02 0.41 ± 0.05 0.47 ± 0.03 / 0.11 ± 0.06 0.45 ± 0.09 1.14 ± 0.29 0.38 ± 0.11 3.23 ± 2.95 0.45 ± 0.04 0.50 ± 0.03 0.20 ± 0.02 0.35 ± 0.06 0.20 ± 0.04 0.17 ± 0.01 0.33 ± 0.01 6.85 ± 1.00 0.68 ± 0.09 0.09 ± 0.02 0.22 ± 0.04 2.99 ± 0.69 0.19 ± 0.01 0.26 ± 0.02 / / 124.61 ± 3.61 90.96 ± 4.02

100 100 100 100 100 83.27 93.87 100 78.32 100 100 95.27 83.44 100 80.20 100 100 100 100 100 100 89.31 100 100 100 100 100 100 92.29 78.10 40.16 32.94

100 100 77.66 100 100 41.04 48.93 100 29.70 100 100 57.34 49.26 100 40.74 100 100 100 100 100 100 43.85 100 100 80.95 100 100 100 59.88 30.71 / /

0.57 ± 0.27 0.23 ± 0.02 2.02 ± 0.70 0.39 ± 0.03 0.47 ± 0.05 7.87 ± 0.83 5.99 ± 0.74 0.38 ± 0.03 / 0.61 ± 0.06 0.71 ± 0.06 3.55 ± 0.31 5.84 ± 0.94 0.78 ± 0.43 8.19 ± 1.84 0.63 ± 0.03 0.76 ± 0.03 0.45 ± 0.06 0.84 ± 0.06 0.39 ± 0.03 0.67 ± 0.05 6.01 ± 0.55 0.34 ± 0.05 0.16 ± 0.0.2 1.08 ± 0.21 0.76 ± 0.03 0.46 ± 0.04 0.61 ± 0.01 2.77 ± 0.30 / 82.77 ± 4.59 66.31 ± 9.05

± 0.31 ± 0.17 ± 4.18 ± 0.26 ± 1.20

± 0.46

± 2.35 ± 0.40 ± 0.46

surface and morphology of cell membranes of Xoo. The in vitro antibacterial activity of the compounds 1–30 against Xoo and Xac was initially evaluated at the concentrations of 50 and 5 mg/L, as shown in Table 1. The compounds 1–5, 8, 10, 11, 14, 16–21, and 23–28 show good in vitro antibacterial activities against Xoo and Xac, with an inhibition rate of 100% at a concentration of 50 mg/L. Interestingly, some compounds, such as 1, 2, 4, 5, 8, 10, and 11, still

± 0.80 ± 0.95 ± 0.70 ± 1.38 ± 0.82 ± 0.67

± 1.19

± ± ± ±

0.65 0.67 3.62 4.75

± 0.73 ± 1.91 ± 0.42 ± 1.46 ± 1.12 ± 0.50 ± 1.46

± 0.89 ± 0.53

± 1.09 ± 2.94

show antibacterial activities with the inhibition rates of 100% against Xoo and Xac when the test concentration is reduced to 5 mg/L. In order to more accurately assess the antibacterial activities of the compounds, the EC50 values of the compounds were tested. The EC50 values of the test compounds against Xoo and Xac range from 0.09 to 6.85 mg/L, and 0.16 to 8.19 mg/L, respectively. Among these target compounds, the most prominent compound with in vitro antibacterial activity is 24 with

2

Bioorganic & Medicinal Chemistry Letters xxx (xxxx) xxxx

C. Yi, et al.

the compound 21 (R1 = 4-F, X = Br, EC50 = 0.67 mg/L) > 6 (R1 = 4F, X = Cl, EC50 = 7.78 mg/L), the activity of the compound 4 (R1 = 2,4-diF, X = Br, EC50 = 0.39 mg/L) > 13 (R1 = 2,4-diF, X = Cl, EC50 = 5.84 mg/L), and the activity of the compound 2 (R1 = 4-OCH3, X = Br, EC50 = 0.23 mg/L) > 15 (R1 = 4-OCH3, X = Cl, EC50 = 8.19 mg/L). When X = Br and the 4-position of the benzene ring is substituted with F, Cl, and I atoms, respectively, the antibacterial activity of the compounds gradually decreases against Xoo, which is the compound 21 (R1 = 4-F, EC50 = 0.33 mg/L) > 1 (R1 = 4-Cl, EC50 = 0.34 mg/L) > 26 (R1 = 4-I, EC50 = 2.99 mg/L). When X = Br and the 4 position of the benzene ring is substituted with OH, OCH3, and OCH2CH3, respectively, the antibacterial activity of the compounds gradually increases against Xoo, with an order of the compound 23 (R1 = 4-OH, EC50 = 0.68 mg/L) < 2 (R1 = 4-OCH3, EC50 = 0.40 mg/ L) < 10 (R1 = 4-OCH2CH3, EC50 = 0.11 mg/L). The in vivo antibacterial activity of the compound 24 was evaluated at the concentration of 50 mg/L under greenhouse conditions against rice bacterial leaf blight. The curative activity (Table 2 and Fig. 2) of the compound 24 against rice bacterial leaf blight is 48.9%, which is better than the bismerthiazol (34.9%), and thiodiazole copper (29.9%). At the same time, the protective activity (Table 3 and Fig. 2) of the compound 24 against rice bacterial leaf blight is 52.1%, which is better than the bismerthiazol (39.8%), and thiodiazole copper (35.7%). The nematicidal activity of the compounds 1–30 was evaluated against M. incognita, and the results are shown in Table 4. The compounds 1, 2, 4, 6, 12, 16, 17, 19, 20, 21, 23, and 26 show good in vitro nematicidal activities against M. incognita, with the mortality of 100% at the concentrations of 50 mg/L. To further evaluate the nematicidal activity of the compounds against M. incognita at a low concentration, we reduced the test concentration to 5 mg/L. Test results show that the nematicidal activity of some compounds decreases rapidly. However, the nematicidal activity of the compounds 19 and 20 are superior to that of the positive control avermectin (77.4%) with mortality of 87.0% and 83.6%, respectively. In order to further assess the nematicidal

Table 2 The curative activity of the compound 24 against rice bacterial leaf blight at 50 mg/L. Treatments

Disease index (%)c

Curative activity (%)d

24 thiodiazole copper Bismerthiazol Negative control

42.5 58.3 54.2 83.3

48.9 ± 3.0a 29.9 ± 4.6a 34.9 ± 6.2b –

c

Disease index, which is a comprehensive indicator of the overall incidence and severity. d Curative activity, which refers to the use of a chemical agent to kill or prevent invasion of the pathogen before it invades the host plant, so that the plant can be protected from damage. Statistical analysis was performed by analysis of variance (ANOVA) in SPSS 17.0 software with equal variances assumed (p > 0.05). The different lowercase letters indicate curative activity with difference treatment groups at p < 0.05.

the EC50 of 0.09 and 0.16 mg/L against Xoo and Xac, respectively, which is superior to commercial antibacterial thiodiazole copper (124.61 and 82.77 mg/L) and bismerthiazol (90.96 and 66.31 mg/L). The antibacterial activities of the compounds 1–30 against Xoo and Xac are shown in Table 1. When the α position of the compound is replaced with a Br atom, the antibacterial activity against Xoo is superior to the compound in which the α position is replaced with a Cl atom, such as the antibacterial activity of the compound 21 (R1 = 4-F, X = Br, EC50 = 0.33 mg/L) > 6 (R1 = 4-F, X = Cl, EC50 = 0.63 mg/L), the activity of the compound 4 (R1 = 2,4-diF, X = Br, EC50 = 0.33 mg/ L) > 13 (R1 = 2,4-diF, X = Cl, EC50 = 0.38 mg/L), and the activity of the compound 2 (R1 = 4-OCH3, X = Br, EC50 = 0.40 mg/L) > 15 (R1 = 4-OCH3, X = Cl, EC50 = 0.45 mg/L). When R1 is the same substituent, the antibacterial activity of the compound with X = Br is superior to that of X = Cl against Xac, such as the antibacterial activity of

Fig. 2. In vivo activities assay of the compound 24 against rice bacterial leaf blight. (A) The disease symptoms and lesion lengths of rice after treatment with the compound 24 at the concentration of 50 mg/L, which are reduced relative to treatment with negative control, bismerthiazol and thiodiazole copper in the curative activity assay. (B) After pretreatment with the compound 24 at the concentration of 50 mg/L, the disease symptoms and lesion lengths on rice were reduced relative to pretreatment with negative control, bismerthiazol and thiodiazole copper in the protective activity assay.

3

Bioorganic & Medicinal Chemistry Letters xxx (xxxx) xxxx

C. Yi, et al.

LC50 = 3.6 mg/L) > 6 (R1 = 4-F, X = Cl, LC50 = 3.9 mg/L), the activity of the compound 4 (R1 = 2,4-diF, X = Br, LC50 = 4.2 mg/ L) > 13 (R1 = 2,4-diF, X = Cl, LC50 = 8.1 mg/L), and the activity of the compound 2 (R1 = 4-OCH3, X = Br, LC50 = 7.8 mg/ L) > 15(R1 = 4-OCH3, X = Cl, LC50 = 9.1 mg/L). When X = Br and the 4-position of the benzene ring is substituted with H, F, Cl, and I atoms, respectively, the nematicidal activity against M. incognita of the compound 20 (R1 = 4-H, LC50 = 1.9 mg/L) > 26 (R1 = 4-I, LC50 = 2.3 mg/L) > 21 (R1 = 4-F, LC50 = 3.6 mg/L) > 1 (R1 = 4-Cl, LC50 = 6.6 mg/L). Meanwhile, when X = Br and the 2-position of the phenyl ring is substituted with 2-OCH3 and F, respectively, the nematicidal activity against M. incognita of the compound 19 (R1 = 2-OCH3, X = Br, LC50 = 1.0 mg/L) > 16 (R1 = 2-F, X = Br, LC50 = 6.3 mg/L). The extracellular polysaccharides production of Xoo treated with the compound 24 was evaluated. Extracellular polysaccharides are not only an important virulence factor related to the pathogenicity of Xoo, but also are considered as the fundamental component that determines the physiochemical properties of the biofilm. The effect of the compound 24 on the exopolysaccharide production of Xoo is shown in Fig. 3A. When Xoo was treated with the compound 24 at the concentration of 0.9, 0.45 and 0.09 mg/L, its extracellular polysaccharide productions are reduced by 100%, 100% and 19.01%, respectively, relative to the negative control treatment. These results indicate that the compound 24 can significantly inhibit the production of extracellular polysaccharides, which may destroy the integrity of biofilm and reduce the pathogenicity of Xoo. The effects of the compound 24 on biofilm formation and membrane permeability of Xoo were evaluated. As shown in Fig. 3B, when the Xoo is treated with the compound 24 at the concentration of 0.9, 0.45 and 0.09 mg/L, the biofilm formation is reduced by 69.84%, 57.75%, and 45.15%, respectively, compared to the negative control treatment. At the same time, the relative permeability of the membrane of Xoo (Fig. 3C) increases with the concentration and time after the compound 24 treatment, and is higher than the negative control treatment. Especially, the relative permeability of the cell membrane of Xoo increases rapidly in the treatment time of 30, 60, 90, and 120 min, and the relative permeability of the cell membrane of Xoo increases slowly in the treatment time of 150, 180, 210, 240, 270 and 300 min. The cell morphology of the Xoo was observed by scanning electron microscope. As shown in Fig. 3D, the cells of the negative control treatment are full in shape and have no wrinkles on the surface. While after the compound 24 treatment, the cell surface is wrinkled, the shape is distorted, and even wizened appears. It may be that the extracellular polysaccharide and biofilm formation of Xoo are inhibited, reducing the pathogenicity of Xoo to the host, which contributes to the good in vitro antibacterial activity of the compound 24. In conclusion, thirty α-haloacetophenones and analogues were synthesized, and bioassays show that all target compounds have good biological activity against Xoo, Xac and M. incognita. In particular, the EC50 value of the compound 24 for Xoo is 0.09 mg/L. The biofilm structure of Xoo treated with the compound 24 can be destroyed by inhibiting extracellular polysaccharide and biofilm formation of Xoo, resulting in the death of the microorganisms. Considering that α-haloacetophenone and analogues have the advantages of simple structure, high efficiency and broad spectrum of biological activity, they are considered as the highly effective antibacterial agents and nematicides in the future.

Table 3 The protection activity of the compound 24 against rice bacterial leaf blight at 50 mg/L. Treatments

Disease index (%)c

Protection activity (%)d

24 thiodiazole copper Bismerthiazol Negative control

39.2 52.5 49.2 81.7

52.1 ± 1.7a 35.7 ± 8.1ab 39.8 ± 4.7b –

c

Disease index, which is a comprehensive indicator of the overall incidence and severity. d Protection activity, which refers to the use of a chemical agent against the plant or pathogen after the disease or pathogen invades the host plant. It acts in plants to change the pathogenic process of the pathogens, thereby achieving the purpose of reducing or eliminating the disease. Statistical analysis was performed by analysis of variance (ANOVA) in SPSS 17.0 software with equal variances assumed (p > 0.05). The different lowercase letters indicate protection activity with difference treatment groups at p < 0.05. Table 4 The in vitro nematocidal activities of the compounds 1–30 against M. incognita. Compounds

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Avermectin

R1

4-Cl 4-OCH3 2,4-Cl 2,4-diF 4-CF3 4-F 4-Cl 4-CN 2-OH 4-OCH2CH3 4-NO2 4-Br 2,4-diF 2-NO2 4-OCH3 2-F 3,4-diCl 3-F 2-OCH3 H 4-F 3-OCH3 4-OH 4-CH2CH3 3-NO2 4-I 4-S(O)2CH3 3-Cl 5-Cl 5-Br –

X

Br Br Cl Br Br Cl Cl Br Br Br Br Cl Cl Br Cl Br Br Br Br Br Br Br Br Br Br Br Br Br Br Br –

Mortality/%

LC50 mg/L

50 mg/L

5 mg/L

100 100 42.1 100 65.6 100 87.4 68.6 44.6 93.1 90.8 100 86.2 62.9 96.6 100 100 30.5 100 100 100 78.5 100 98.5 71.4 100 72.8 37.9 51.6 45.3 100

48.4 ± 4.3 43.2 ± 3.7 13.8 ± 0.6 53.5 ± 6.3 28.3 ± 4.1 54.1 ± 2.4 37.7 ± 3.3 25.1 ± 3.6 15.3 ± 0.4 33.4 ± 2.1 25.7 ± 1.8 38.3 ± 1.9 39.3 ± 0.9 18.6 ± 1.4 28.9 ± 3.3 44.4 ± 2.8 41.1 ± 0.8 5.8 ± 0.9 87.0 ± 1.9 83.6 ± 1.1 51.5 ± 6.3 31.9 ± 4.7 52.9 ± 2.4 41.8 ± 4.9 31.2 ± 3.3 74.2 ± 1.9 32.6 ± 2.3 6.7 ± 1.3 27.1 ± 2.1 11.6 ± 2.2 77.4 ± 0.5

± 1.4 ± 3.0 ± ± ± ± ±

1.6 3.1 1.2 2.3 2.8

± 2.6 ± 3.1 ± 1.2 ± 1.9

± 7.3 ± 0.3 ± 2.2 ± ± ± ±

2.2 0.9 2.1 2.1

6.6 ± 0.5 7.8 ± 2.0 / 4.2 ± 1.0 / 3.9 ± 1.5 11.5 ± 0.6 / / 13.1 ± 1.3 13.3 ± 0.5 7.7 ± 5.3 8.1 ± 5.0 / 9.1 ± 0.8 6.3 ± 1.8 5.1 ± 2.2 / 1.0 ± 0.3 1.9 ± 0.6 3.6 ± 0.2 / 4.0 ± 1.6 5.9 ± 1.3 / 2.3 ± 1.3 / / / / 2.0 ± 0.1

activity of the compounds against M. incognita, the LC50 values of some compounds were tested. The LC50 values of the test compounds range from 1.0 to 13.3 mg/L. The nematicidal activity of the compounds 19 and 20 consistently outperform the positive control avermectin (2.0 mg/L) with LC50 values of 1.0 and 1.9 mg/ L, respectively. The LC50 values of some compounds are summarized in the Table 4. When the α position of the compound is replaced with a Br atom, the nematicidal activity against M. incognita is superior to those of the compound in which the α position is replaced with a Cl atom, such as the nematicidal activity of the compound 21 (R1 = 4-F, X = Br,

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

4

Bioorganic & Medicinal Chemistry Letters xxx (xxxx) xxxx

C. Yi, et al.

Fig. 3. Changes in the extracellular polysaccharide production (A), biofilm formation (B), cell membrane permeability (C) and cell morphology (D) of Xoo after treatment with the compound 24 at the concentrations of 0.9, 0.45, and 0.09 mg/L.

Acknowledgments

7. Li P, Shi L, Yang X, et al. Antibacterial activities against rice bacterial leaf blight and tomato bacterial wilt of 2-mercapto-5-substituted-1,3,4-oxadiazole/thiadiazole derivatives. Bioorg Med Chem Lett. 2014;24:1677–1680. 8. Chen JX, Yi CF, Song BA, et al. Novel amide derivatives containing 1,3,4-thiadiazole moiety: design, synthesis, nematocidal and antibacterial activities. Bioorg Med Chem Lett. 2019;29:1203–1210. 9. Chen JT, Su HJ, Huang JW. Isolation and identification of secondary metabolites of Clitocybe nuda responsible for inhibition of zoospore germination of Phytophthora capsici. J Agric Food Chem. 2012;60:7341–7344. 10. Butler MS. The role of natural product chemistry in drug discovery. J Nat Prod. 2004;67:2141–2153. 11. Dixon RA. Natural products and plant disease resistance. Nature. 2001;411:843–847. 12. Gershenzon J, Dudareva N. The function of terpene natural products in the natural world. Nat Chem Biol. 2007;3:408–414. 13. Newman DJ. Impact of natural products on developing new anti-cancer agents. Chem Rev. 2009;109:3012–3043. 14. Caboni P, Saba M, Oplos C, et al. Nematicidal activity of furanocoumarins from parsley against Meloidogyne spp. Pest Manag Sci. 2015;71:1099–1105. 15. Dorman HJD, Deans SG. Antimicrobial agents from plants: antibacterial activity of plant volatile oils. J Appl Microbiol. 2010;88:308–316. 16. Elgayyar M, Draughon FA, Golden DA, et al. Antimicrobial activity of essential oils from plants against selected pathogenic and saprophytic microorganisms. J Food Protect. 2001;64:1019–1024. 17. Ma YT, Fan HF, Gao YQ, et al. Natural products as sources of new fungicides (i): synthesis and antifungal activity of acetophenone derivatives against phytopathogenic fungi. Chem Biol Drug Des. 2013;81:545–552. 18. Oh MS, Yang JY, Lee HS. Acaricidal toxicity of 2′-hydroxy-4′-methylacetophenone isolated from Angelicae koreana roots and structure-activity relationships of its derivatives. J Agric Food Chem. 2012;60:3606–3611. 19. Kim HK, Tak JH, Ahn YJ. Acaricidal activity of Paeonia suffruticosa root bark-derived compounds against Dermatophagoides farinae and Dermatophagoides pteronyssinus (Acari: Pyroglyphidae). J Agric Food Chem. 2004;52:7857–7861. 20. Spedes CLC, Uchoa A, Salazar JR, et al. Plant growth inhibitory activity of p-hydroxyacetophenones and tremetones from chilean endemic Baccharis species and some analogous: a comparative study. J Agric Food Chem. 2002;50:2283–2292.

The authors are grateful to the National Natural Science Foundation of China (No. 21672044) and Subsidy Project for Outstanding Key Laboratory of Guizhou Province in China (20154004) and the Key Agricultural Technologies R&D Program of Guizhou University in China (No. 2016047) and Collaborative Innovation Center for Natural Products and Biological Drugs of Yunnan for supporting the project. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.bmcl.2019.126814. References 1. Huang N, Angeles ER, Domingo J, et al. Pyramiding of bacterial blight resistance genes in rice: marker-assisted selection using RFLP and PCR. Theor Appl Genet. 1997;95:313–320. 2. Li P, Hu DY, Song BA, et al. Design, synthesis, and evaluation of new sulfone derivatives containing a 1,3,4-oxadiazole moiety as active antibacterial agents. J Agric Food Chem. 2018;66:3093–3100. 3. Das AK. Citrus canker a review. J Appl Hortic. 2003;5:52–60. 4. Li P, Tian PY, Song BA, et al. Novel bisthioether derivatives containing a 1,3,4-oxadiazole moiety: design, synthesis, antibacterial and nematocidal activities. Pest Manag Sci. 2018;74:844–852. 5. Acquaye AKA, Alston JM, Lee H, et al. Economic consequences of invasive species policies in the presence of commodity programs: theory and application to citrus canker. Rev Agr Econ. 2010;27:498–504. 6. Lin Y, He Z, Lazarovits G, et al. A nylon membrane bag assay for determination of the effect of chemicals on soilborne plant pathogens in soil. Plant Dis. 2010;94:201–206.

5