Antimycotic Spirostanol Saponins from Solanum hispidum Leaves and Their Structure−Activity Relationships

A new spirostanol saponin, together with three known saponins, were isolated from the leaves of Solanum hispidum. The structure of the new saponin was elucidated as 6alpha-O-beta-D-quinovopyranosyl-(25S)-5alpha-spirostan-3beta-ol (1) on the basis of spectroscopic analysis (1H NMR, 13C NMR, 1H-1H COSY, HMQC, HMBC, and HRFABMS). All of the isolated compounds showed antimycotic activity. The most active compound was 6alpha-O-[beta-D-xylopyranosyl-(1-->3)-beta-D-quinovopyranosyl]-(25S)-5alpha-spirostan-3beta-ol (2) (MIC = 25 microg/mL against both Trichophyton mentagrophytes and T. rubrum). The structure-activity relationships of the isolated compounds and those isolated from S. chrysotrichum are discussed.