Heterocycle-Substituted α-Methylene-γ-Butyrolactone Derivatives: Design, Synthesis, and Bioactivity against Phytopathogenic Fungi and Bacteria

A series of 37 heterocycle-substituted α-methylene-γ-butyrolactone (MBL) derivatives were designed and synthesized. Bioassays showed that these derivatives possessed prominent fungicidal and bactericidal activities against Phytophthora capsici and Pseudomonas syringae pv actinidiae (Psa). Compound A6 exhibited the strongest antioomycete activity against P. capsici with an EC50 of 1.24 mg/L, presenting excellent in vivo protective (83.2%) and curative (81.2%) efficacies, while compound B12 exerted potent antibacterial activity against Psa (EC50 = 12.07 mg/L) with 72.3% protective efficacy against kiwifruit bacterial canker. Mechanistically, compound A6 functions mainly by binding to respiratory chain complex III. Notably, compound A6 caused no obvious adverse effects on chili pepper seed germination and plant growth at the tested concentrations of 100-400 mg/L. This study offers a basis for developing novel heterocycle-substituted MBL-derived agricultural antimicrobial agents.