Targeted design of a novel fungicide against the cytochrome bc1 complex: Mechanistic insights and potent antifungal activity

Conventional non-covalent bc₁ complex inhibitors are widely used in plant Fungal disease control, but their efficacy is increasingly compromised by resistance, underscoring the need for new agents. To address this, a series of cytochrome bc₁ inhibitors featuring covalent warheads were designed and synthesized. In vitro Antifungal results demonstrated that compound G₂ exhibited significantly lower EC₅₀ values compared to kresoxim-methyl against A. solani (0.05 μg/mL), G. zeae (6.80 μg/mL), C. gloeosporioides (17.37 μg/mL), and F. oxysporum f. sp. melonis (21.33 μg/mL). In vivo assays against A. solani demonstrated the highly effective curative efficacy of tomato early blight by compound G₂. Further mechanistic investigation revealed that G₂ inhibits the cytochrome bc₁ complex, thereby impairing ATP synthesis and suppressing ATPase activity, while also inducing a burst of Reactive Oxygen Species. These effects collectively compromise plasma membrane integrity and ultimately suppress Fungal growth. Molecular docking studies suggested a potential covalent binding mode between G₂ and Cys39 of cytochrome b. Through an innovative exploration of the covalent drug strategy in agrochemical design, this work provides valuable insights for the development of novel cytochrome bc₁ complex inhibitors.