Synthesis and antimicrobial activities of novel quinazolin-4(3 H )-one derivatives containing a 1,2,4-triazolo[3,4- b ][1,3,4]thiadiazole moiety

A series of novel quinazolin-4(3 H )-one derivatives ( 6a – 6y ) containing a 1,2,4-triazolo[3,4- b ][1,3,4]thiadiazole moiety were designed and synthesized, and their structures were fully characterized by 1 H NMR, 13 C NMR, HRMS and IR spectra. Among them, the structure of compound 6u was unambiguously confirmed via single crystal X-ray diffraction analysis. The obtained bioassay results showed that compounds 6h , 6k , 6l and 6y had the EC 50 (half-maximal effective concentration) values of 34.8, 28.2, 41.5 and 42.5 μg/mL against the phytopathogenic bacterium Xanthomonas oryzae pv. oryzae ( Xoo ), respectively, which were significantly better than commercial bactericide Bismerthiazol (EC 50 = 95.8 μg/mL). Additionally, compounds 6a and 6b exhibited the strong inhibition activity against the pathogen Xanthomonas axonopodis pv. citri ( Xac ).