Design, Synthesis, and Antifungal Evaluation of Novel Cuminic Acid Derivatives as Potential Laccase Inhibitors.

In search of novel natural product-based fungicides, 49 cuminic acid derivatives were designed, synthesized, and screened for their in vitro antifungal effects toward seven phytopathogenic fungi and oomycetes. Consequently, several derivatives exhibited strong antifungal activities toward Fusarium graminearum, Botryosphaeria dothidea, and Valsa mali. Among them, compound 2b exhibited the most potent antifungal activity toward B. dothidea (EC₅₀ = 0.96 mg/L), more powerful than chlorothalonil. The in vivo assay against B. dothidea found that the protective and curative effects of 2b were comparable to chlorothalonil. Meanwhile, SEM and TEM observations indicated that 2b could ruin the integrity of mycelial morphology and organelles of B. dothidea. Preliminary mechanism research showed that 2b increased the cell membrane permeability and intracellular ROS level, as well as conspicuously decreased the mycelial dry weight and cell wall chitin contents of B. dothidea. The phytotoxicity test revealed that 2b showed good safety on seeds of mung bean and radish. The in vitro laccase inhibitory activity assay and molecular docking study demonstrated that 2b could be a promising laccase inhibitor. This type of cuminic acid hydrazide derivative would provide valuable inspiration for developing novel fungicides against B. dothidea.