Design, Synthesis, and Antimicrobial Evaluation of Novel 6‐Fluoroquinazolinone Derivatives Incorporating Thioether and Ethyl Ester Pharmacophores

A total of structural 6-fluoroquinazolinone derivatives (D₁-D₁₆) bearing units of thioether and ethyl ester were strategically designed, systematically synthesized, and comprehensively evaluated for their potential as agricultural antimicrobial agents. All the title compounds were fully characterized by use of ¹H NMR, ¹³C NMR, IR, HRMS, and HPLC techniques. The bioassay results revealed that some of the compounds possessed noticeable antibacterial activities against the tested phytopathogenic bacteria in vitro. For instance, compounds D₁, D₂, D₃, and D₄ demonstrated good inhibition efficacies, having EC₅₀ values of 3.4, 4.4, 4.1, and 4.7 µg/mL towards Xanthomonas campestris pv. campestris (Xcc), respectively, which were at least 16-fold more active than that of the commercial agrobactericide bismerthiazol (76.8 µg/mL). In addition, antifungal assays revealed that all the compounds possess weak inhibition capabilities against eight phytopathogenic fungi at 50 µg/mL, except compound D₁₆ against the fungus Fusarium oxysporum, achieving an inhibition rate of 61.3%. Overall, the present study collectively established that 6-fluoroquinazolinone derivatives bearing thioether and ethyl ester units are promising candidates for the development of new agricultural bactericides against the pathogenic bacterium Xcc.