Pyrido [1,2-] Pyrimidinone Mesoionic Compounds Containing Vanillin Moiety: Design, Synthesis, Antibacterial Activity, and Mechanism.

() is a plant pathogen responsible for rice bacterial blight disease that remains challenging for prevention and cure. To discover innovative and extremely potent antibacterial agents, vanillin moiety was introduced to develop a series of novel mesoionic derivatives. Compound demonstrated excellent in vitro antibacterial activity against , with a 50% effective concentration value (EC) of 27.5 μg/mL, which was superior to that of the positive control agent thiodiazole copper (97.1 μg/mL) and comparable to that of compound "" (17.4 μg/mL). The greenhouse pot experiment also revealed that compound had 38.5% curative and 36.8% protective efficacy against rice bacterial leaf blight in vivo at 100 μg/mL, which was higher than those of thiodiazole copper (31.2 and 32.6%, respectively) and compound "" (29.6 and 33.2%, respectively). Compound enhanced the activities of related defense enzymes, increased chlorophyll content, and promoted the resistance of rice to bacterial infection by modulating the photosynthetic pathway. This study provides a basis for the subsequent structural modification and mechanism research of mesoionic derivatives.