Subtortins A-C, Pyran-3-one-Containing Malabaricanes Isolated from Cortinarius subtortus

Cortinarius (webcaps) is the most diversified genus of mushrooms, yet mycochemical studies so far seem to have mostly investigated toxic or colorful species. The aim of our project was to leverage HPLC-DAD-HRMS/MS data from our local fungal extract library to target and isolate compounds found specifically in Cortinarius extracts. The selection and fractionation of an ethyl acetate extract obtained from sporophores of Cortinarius subtortus led to the isolation and structure elucidation of three new uncommon triterpenes named subtortins A-C (1-3). These compounds belong to the malabaricane triterpenoid subclass, arising from an incomplete cyclization of squalene, and feature an unprecedented terminal pyran-3-one moiety. To date, only very few malabaricanes of fungal origin have been reported, all from Cortinarius, suggesting a potential chemotaxonomic significance. Structure elucidation and absolute configuration assignment of subtortins A-C (1-3) were established by a combination of experimental spectroscopies (NMR and ECD) and computational approaches based on GIAO NMR and TDDFT-ECD. Antimicrobial assays against the pathogenic models Staphylococcus aureus, Escherichia coli, and Candida albicans showed no activity, while the possible biosynthesis and ecological role of these metabolites are discussed.