Design, synthesis, crystal structure and in vitro antimicrobial activity of novel 1,2,4-triazolo[1,5-a]pyrimidine-containing quinazolinone derivatives

A series of novel 1,2,4-triazolo[1,5- a ]pyrimidine-containing quinazolin-4(3 H )-one derivatives ( 8a – 8o ) were designed, synthesized and assessed for their in vitro antibacterial and antifungal activities in agriculture. All the title compounds were completely characterized via 1 H NMR, 13 C NMR, HRMS and IR spectroscopic data. In particular, the molecular structure of compound 8f was further corroborated through a single-crystal X-ray diffraction measurement. The turbidimetric method revealed that some of the compounds displayed noticeable bactericidal potencies against the tested plant pathogenic bacteria. For example, compounds 8m , 8n and 8o possessed higher antibacterial efficacies in vitro against Xanthomonas oryzae pv . oryzae with EC 50 values of 69.0, 53.3 and 58.9 μg/mL, respectively, as compared with commercialized agrobactericide bismerthiazol (EC 50 = 91.4 μg/mL). Additionally, compound 8m displayed an EC 50 value of 71.5 μg/mL toward Xanthomonas axonopodis pv . citri , comparable to control bismerthiazol (EC 50 = 60.5 μg/mL). A preliminary structure–activity relationship (SAR) analysis was also conducted, based on the antibacterial results. Finally, some compounds were also found to have a certain antifungal efficacy in vitro at the concentration of 50 μg/mL. Graphic abstract