Design, synthesis and antibacterial activity of coumarin-3-carboxylic acid derivatives containing acylhydrazone moiety

Plant diseases caused by bacteria lead to enormous yield and economic losses in agricultural production. To develop innovative bactericides for controlling plant disease, a series of coumarin-3-carboxylic acid derivatives containing acylhydrazone thioether/sulfoxide were designed and synthesized by utilizing the principles of bioisosterism and active splicing. The bactericidal activities of these derivatives were subsequently evaluated. The result indicated that E2 exhibited the highest antibacterial activities in vitro against Xanthomonas oryzae pv. oryzae, Ralstonia solanacearum, and Acidovorax citrulli, with EC50 values of 2.97, 1.17, and 1.23 µg/mL, respectively. Moreover, in vivo experiments showed that E2 exhibited robust protective properties against Ralstonia solanacearum, and Acidovorax citrulli, with efficacies of 72.52% and 63.90%, respectively, at a concentration of 100 µg/mL, which was comparable to the positive control kasugamycin at the same concentration. Scanning electron microscopy analysis revealed that E2 induced changes in the cellular morphology of Acidovorax citrulli, such as shrinkage and collapse. Subsequent investigation revealed that E2 had the capacity to compromise the structural stability of the bacterial membrane of Ralstonia solanacearum. This study represents the first report on the antibacterial activities of this series of coumarin-3-carboxylic acid derivatives containing the acylhydrazone thioether/single-sulfoxide moiety, and the results suggest that coumarin-3-carboxylic acid derivatives containing the acylhydrazone single-sulfoxide may hold potential as effective antibacterial agents. And coumarin-3-carboxylic acid derivatives exhibited promise as plant bacterial agent to prevent rice bacterial leaf blight, tomato bacterial wilt, and melon bacterial fruit blotch.