Design, Synthesis, and Biological Activity Evaluation of Eco-Friendly Rosin-Diamide-Based Fungicides as Potential Succinate Dehydrogenase Inhibitors for Sustainable Crop Protection.

To develop novel succinate dehydrogenase (SDH) inhibitors for sustainable crop protection, a series of dehydroabietyl-diamide-based fungicides (a total of 21) were designed. In vitro fungicidal activity measurement showed that compound 3u exhibited excellent fungicidal activity against Valsa mali (half-maximal effective concentration, EC ₅₀ = 0.195 μg/mL), surpassing that of the positive control carbendazim (EC ₅₀ = 1.35 μg/mL). The in vivo fungicidal activity assessment suggested that 3u exhibited a protective effect on apple branches (69.7-48.1%) and apples (94.6-56.6%). Furthermore, biosafety evaluation indicated that 3u was significantly environmentally friendly toward zebrafish. Subsequently, morphology, physiology, and molecular docking were investigated to elucidate the mode of action of 3u against V. mali . Results demonstrated a strong binding between 3u and SDH, resulting in decreased SDH activity (half-maximal inhibitory concentration, IC ₅₀ = 11.7 μg/mL). Moreover, 3u disrupted the mycelial cell membrane and accelerated electrolyte leakage, ultimately resulting in the death of V. mali . These findings suggest that 3u could serve as a potent SDH inhibitor for sustainable crop protection.