Fungicidal Activity of Carboxamides Containing Spiropiperidinyl-α-methylene-γ-butyrolactones Targeting Oxysterol Binding Protein

Oxysterol binding protein (OSBP) is a new target for oomycide development. To find more fungicidal active compounds targeting OSBP, a series of carboxamides containing spiropiperidinyl-α-methylene-γ-butyrolactone and heterocyclic carboxylic acids were rationally designed and synthesized by using a computer-aided pesticide design method. The in vitro fungicidal bioassay found that compound 5o showed broad-spectrum activity with EC50 values falling between 0.50 and 20.85 μg/mL against Phytophthora capsici and Fusarium verticillioides, respectively, which was more potent than 7c and natural lead xanthatin. Compound 5o also showed 44% in vivo efficacy against Pseudoperonospora cubensis, even at a concentration of 0.5 μg/mL. Fluorescence quenching and microscale thermophoresis determination suggested that compound 5o bound to Osh4p and showed stronger interactions than oxathiapiprolin. RNA sequencing analysis discovered that the ergosterol (ERG) gene cluster and ribosome biogenesis in eukaryotes were downregulated. Compound 5o was discovered as a good fungicidal candidate targeting OSBP deserving further studies.

氧固醇结合蛋白（Oxysterol binding protein, OSBP）是杀卵菌剂开发的新型靶标。为筛选更多靶向OSBP的杀菌活性化合物，本研究采用计算机辅助农药设计方法，合理设计并合成了一系列含有螺哌啶基-α-亚甲基-γ-丁内酯与杂环羧酸结构的酰胺类化合物。体外杀菌生物活性测定结果显示，化合物5o对辣椒疫霉（Phytophthora capsici）与串珠镰孢霉（Fusarium verticillioides）的半最大效应浓度（EC50）分别为0.50 μg/mL和20.85 μg/mL，展现出广谱杀菌活性，其活性优于化合物7c与天然先导化合物苍耳素（xanthatin）。在0.5 μg/mL的给药浓度下，化合物5o对古巴假霜霉菌（Pseudoperonospora cubensis）仍表现出44%的体内防治效果。荧光猝灭与微量热泳动检测结果表明，化合物5o可与氧固醇结合蛋白同源物4（Osh4p）结合，且二者之间的相互作用强度强于氟噻唑吡乙酮（oxathiapiprolin）。RNA测序分析发现，真核生物中的麦角固醇（Ergosterol, ERG）基因簇以及核糖体生物发生相关通路的基因均呈现下调表达。综上，化合物5o是一款优质的靶向OSBP的杀菌候选化合物，值得开展进一步研究。