Design, Synthesis, and Bioactivity of Novel Coumarin-3-carboxylic Acid Derivatives Containing a Thioether Quinoline...

A series of coumarin-3-carboxylic acid derivatives containing a thioether quinoline moiety were designed and synthesized. The structures of these compounds were determined using ¹H NMR, ¹³C NMR, and HRMS. The antibacterial activity of the compounds was evaluated against Xanthomonas oryzae pv oryzae (Xoo), Ralstonia solanacearum (Rs), and Acidovorax citrulli (Aac). The results showed that most of the compounds exhibited significant antibacterial activity against these pathogens. Particularly, compound A9 demonstrated potent activity against Xoo and Aac, with EC₅₀ values of 11.05 and 8.05 μg/mL respectively. In addition, A9 indicated strong protective and curative effects against Aac in vivo, with efficacy rates of 61.50 and 54.86%, respectively, surpassing those of the positive control thiodiazole copper. The scanning electron microscopy observations revealed that treatment of Aac cells with A9 at a concentration of 2EC₅₀ resulted in a curved and sunken cell morphology, along with destroyed cell membrane integrity. Additionally, the motility and exopolysaccharide production of Aac were inhibited, and biofilm formation was prevented. Consequently, these newly developed derivatives of coumarin-3-carboxylic acid, incorporating the thioether quinoline moiety, hold promise as potential templates for the development of innovative antibacterial agents.