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