A series of novel 6-sulfonyl-1,2,4-triazolo [3,4-b][1,3,4]thiadiazole derivatives were designed and synthesized. CoMFA models were established to analyze the quantitative structure−activity relationships on the basis of the EC 50 values of the compounds. The models were used to design and synthesize compounds 32 and 33 with higher activities. The EC 50 values of compound 33 against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc) were 0.59 and 1.63 mg/L, respectively, which were higher than those of thiodiazole copper (90.43 and 97.93 mg/L) and bismerthiazol (68.37 and 75.59 mg/ L). Moreover, protective activities of compound 33 against bacterial leaf streak (BLS) and bacterial leaf blight (BLB) were 49.65% and 49.42%, respectively, which were superior to those of thiodiazole copper (44.28% and 41.51%) and bismerthiazol (38.89% and 40.09%). Protective activity of compound 33 against BLS was closely related to the improvement of defense-related enzyme activities, chlorophyll content, and photosynthesis activation. This is consistent with the upregulated expression of defense responses and photosynthesis-related proteins.

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BACKGROUNDThe rice bacterial leaf blight (BLB) is one of the most serious bacterial diseases caused by Xanthomonas oryzae pv. oryzae (Xoo), which can cause yield loss of rice up to 50%. The three‐dimensional quantitative structure–activity relationship (3D‐QSAR) is an important auxiliary method to find potential high‐efficient pesticides active structures.RESULTSA series of novel 1,3,4‐oxadiazole compounds were designed and synthesized based on the 3D‐QSAR model, and their antibacterial activities in vitro against Xoo were evaluated. The results indicated that all the target compounds showed excellent in vitro antibacterial activities. For example, the compounds 6, 12, 13, 20, 21, and 23 exhibited excellent antibacterial activities against Xoo, with half‐maximal effective concentration (EC50) values of 0.24, 0.31, 0.36, 0.29, 0.19, and 0.31 mg/L, respectively, which were superior to the antibacterial agents thiodiazole copper (127.44 mg/L) and bismerthiazol (91.08 mg/L). Meanwhile, compound 21 showed good antibacterial activity in vivo against BLB, with curative and protective activities of 46.7% and 56.4%, respectively, which were superior to thiodiazole copper (28.5% and 32.5%) and bismerthiazol (37.6% and 38.4%). Compound 21 can significantly reduce the extracellular polysaccharides production of Xoo, increase the permeability of the cell membranes, and also can cause cell surface wrinkles, deformation and dryness.CONCLUSIONThe 3D‐QSAR model can be used to find sulfone compounds containing a 1,3,4‐oxadiazole moiety with higher antibacterial activity, and compound 21 can be used as a potential antibacterial agent in the future. © 2020 Society of Chemical Industry

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