Design, Synthesis, and Antimicrobial Activity Evaluation of Novel Isocryptolepine Derivatives against Phytopathogenic Bacteria.

Plant pathogens harm crops and reduce yields. We urgently need safe and effective antimicrobial agents to treat plant diseases. In this study, a series of isocryptolepine derivatives were efficiently synthesized using 4-oxoquinolinones, employing active functional group modification and bioisosteric substitution strategies. The MIC of compound Mb-1 against Xoo was 3.12 μg/mL, which was better than that of the commercial drug copper quinolate. The MICs of compound Mb-7 against Xac and Rs were 1.56 and 0.39 μg/mL respectively. In the in vivo antibacterial experiment, compound Mb-1 exhibited a superior protection effect (32.7%) and therapeutic effect (31.0%) compared to copper quinolate against rice. Furthermore, compound Mb-1 could inhibit the secretion of extracellular polysaccharides, affect biofilm formation, disrupt cell membrane integrity, increase intracellular reactive oxygen species content, and suppress the normal growth of Xoo and had low phytotoxicity. Thus, compound Mb-1 is expected to be a novel broad-spectrum antibacterial candidate, which is worthy of further investigation.