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 <i>in vitro</i> fungicidal bioassay found that compound <b>5o</b> showed broad-spectrum activity with EC₅₀ values falling between 0.50 and 20.85 μg/mL against <i>Phytophthora capsici</i> and <i>Fusarium verticillioides</i>, respectively, which was more potent than <b>7c</b> and natural lead xanthatin. Compound <b>5o</b> also showed 44% <i>in vivo</i> efficacy against <i>Pseudoperonospora cubensis</i>, even at a concentration of 0.5 μg/mL. Fluorescence quenching and microscale thermophoresis determination suggested that compound <b>5o</b> 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 <b>5o</b> was discovered as a good fungicidal candidate targeting OSBP deserving further studies.