Design, Synthesis, Activity, and Mechanism of Novel Spirocyclic Butenolide Derivatives Containing Thiazolylhydrazone as Potential Fungicides

Novel spirocyclic butenolide derivatives containing a thiazolylhydrazone motif were designed and synthesized, and their structures were characterized by 1H, 13C, and 19F NMR and HR-ESI-MS. Their in vitro and in vivo antifungal activities were evaluated. Compounds 5ab and 5bc displayed the best antifungal activities against Sclerotinia sclerotiorum, and the EC50 were 2.19 and 2.38 μg/mL, respectively. Their protective efficacies were 100% after treatment with 5ab, 5bc, and boscalid, and the curative efficacies were 70.5%, 62.8%, and 79.5% at 100 μg/mL, respectively. Scanning and transmission electron microscopic observations indicated that 5ab influenced the ultrastructure and function of S. sclerotiorum. The propidium iodide staining and relative conductivity assays demonstrated that 5ab destroyed the cytoderm integrity and affected the membrane permeability of S. sclerotiorum in a concentration-dependent manner. Transcriptome analysis indicated that the pathways related to the plasma membrane, the integral component of the membrane, and carbohydrate metabolism were significantly enriched. These results could provide solid evidence for the discovery of novel antifungal agents.