Antifungal Steroid Saponins from Dioscorea cayenensis

From the rhizomes of Dioscorea cayenensis Lam.-Holl (Dioscoreaceae), the new 26-O-β-D-glucopyranosyl-22-methoxy-3β,26-dihydroxy-25(R)-furost-5- en-3-O-α-L-rhamnopyranosyl-(1 →4)-α-L-rhamnopyranosyl-(1 →4)-[α-L-rhamnopyranosyl-(1 →2)]-β-D-glucopyranoside (1) was isolated together with the known dioscin (2) and diosgenin 3-O-α-L-rhamnopyranosyl-(1 →4)-α-L-rhamnopyranosyl-(1 →4)-[α-L-rhamnopyranosyl-(1 →2)]-β-D-glucopyranoside (3). Their structures were established on the basis of spectral data. Compound 2 exhibited antifungal activity against the human pathogenic yeasts Candida albicans, C. glabrata and C. tropicalis (MICs of 12.5, 12.5 and 25 μg/mL, respectively) whereas 3 showed weak activity and 1 was inactive.