Design, synthesis, and antimicrobial behavior of novel oxadiazoles containing various N‐containing heterocyclic pendants

Abstract BACKGROUND The gradually elevated outbreak of plant bacterial diseases severely limits agricultural products and small amounts of pesticides can manage them. Our group has previously synthesized and screened the antimicrobial activity of diverse 1,3,4‐oxadiazole thioether/sulfone compounds bridged by a sulfur atom at the 2‐position of 1,3,4‐oxadiazole. However, few studies have evaluated the effect of eliminating the sulfur atom on bioactivity. Herein, a novel type of N ‐containing heterocyclic pendants‐tagged 1,3,4‐oxadiazoles bridged by alkyl chains only was systematically synthesized and evaluated for their antimicrobial activities. RESULTS Bioassay results revealed that antibacterial efficacy increased by 551‐ and 314‐fold against the corresponding phytopathogens Xanthomonas oryzae pv. oryzae and X. axonopodis pv. citri compared to commercial agents bismerthiazol and thiodiazole copper. In vivo trials showed that C 1 exerted remarkable curative activity against rice bacterial blight with a control effectiveness of 52.9% at 200 μg mL −1 . Antibacterial mechanism research found that C 1 could reduce the hypersensitive response behavior and pathogenicity of Xoo through targeting the type III secretion system (T3SS) at a lower drug dose. This outcome was verified by observing the significantly down‐regulated proteins and representative genes from the related quantitative proteomics and qRT‐PCR assays. CONCLUSION This study can inspire the design of innovative molecular frameworks targeting the T3SS of phytopathogens for controlling bacterial infections. © 2020 Society of Chemical Industry