A Novel Chromone-Sulfonyl Hydrazone Scaffold Targeting Fungal Tubulin: Design, Synthesis, and Antifungal Mechanism Against <i>Sclerotinia sclerotiorum</i>

The growing prevalence of fungicide resistance in pathogenic fungi, particularly broad-host-range pathogens like <i>Sclerotinia sclerotiorum</i> (<i>S. sclerotiorum</i>), poses a severe threat to global crop yields and food security. Consequently, there is an urgent need to develop novel antifungal agents capable of circumventing this resistance. Herein, a series of novel chromone-sulfonyl hydrazone derivatives were designed and synthesized as potential fungal tubulin inhibitors. In vitro bioassays demonstrated that compound <b>G2</b> exhibited exceptional antifungal activity against <i>S. sclerotiorum</i>, with an EC₅₀ value of 0.62 μg/mL, significantly surpassing the efficacy of conventional fungicides. In vivo experiments demonstrated that compound <b>G2</b> effectively inhibited <i>S. sclerotiorum</i> infection on rapeseed leaves at a concentration of 100 μg/mL. Further mechanistic investigations, integrating molecular docking, molecular dynamics simulations, immunofluorescence staining, and scanning electron microscopy, elucidated that <b>G2</b> effectively disrupts tubulin polymerization. This disruption is achieved through the formation of hydrogen bonds with critical residues within the tubulin protein, subsequently leading to severe damage to mycelial morphology and compromise of cell membrane integrity. Importantly, <b>G2</b> demonstrated high fungicide selectivity and remarkably low cytotoxicity against mammalian cells, indicating a favorable safety profile. This targeted design strategy presents an innovative and promising approach to combat fungicide resistance. The identified compound <b>G2</b> serves as a lead candidate, providing a robust framework for the development of next-generation crop protection agents with enhanced efficacy and safety.