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(3H)-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 1H NMR, 13C 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 EC50 values of 69.0, 53.3 and 58.9 μg/mL, respectively, as compared with commercialized agrobactericide bismerthiazol (EC50 = 91.4 μg/mL). Additionally, compound 8m displayed an EC50 value of 71.5 μg/mL toward Xanthomonas axonopodis pv. citri, comparable to control bismerthiazol (EC50 = 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.