Steroidal saponins from Dioscorea preussii.

Three new steroidal saponins, named diospreussinosides A-C (1-3), along with two known ones (4, 5) were isolated from rhizomes of Dioscorea preussii. Their structures were elucidated mainly by 1D and 2D NMR spectroscopic analysis and mass spectrometry as (25S)-17α,25-dihydroxyspirost-5-en-3β-yl-O-α-L-rhamnopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→4)-β-D-glucopyranoside (1), (25S)-17α,25-dihydroxyspirost-5-en-3β-yl-O-α-L-rhamnopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→4)-[α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyranoside (2), and (24S,25R)-17α,24,25-trihydroxyspirost-5-en-3β-yl-O-α-L-rhamnopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→4)-[α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyranoside (3). The spirostane-type skeleton of compound 3 possessing an unusual dihydroxylation pattern on the F-ring is reported for the first time. Cytotoxicity of compounds 2-5 was evaluated against two human colon carcinoma cell lines (HT-29 and HCT 116).