A new steroidal saponin from Dioscorea cayenensis

The new 26-O-beta-D-glueopyranosyl-3beta,26-dihydroxy-20,22-seco-25(R)-furost-5-en-20,22-dione-3-O-alpha-L-rhamnopyranosyl-(1 --> 4)-alpha-L-rhamnopyranosyl-(1 --> 4)-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (1), along with the known methyl protodioscin (2), asperoside (3) and prosapogenin A of dioscin (4) were isolated from the rhizomes of Dioscorea cayenensis LAM.-HOLL (Dioscoreaceae). Their structures were established mainly on the basis of 600 MHz 2D-NMR spectral data. 4 exhibited antifungal activity against the human pathogenic yeasts Candida albicans, C. glabrata and C tropicalis (MICs of 20.8, 6.25, 25 mug/ml, respectively), whereas saponins 1-3 were inactive.