Two new steroidal saponins from the biotransformation product of the rhizomes of Dioscorea nipponica.

Two new steroidal saponins, dioscins E (1) and F (2), along with nine known steroidal saponins, were isolated from the biotransformation product of the rhizomes of Dioscorea nipponica using Aspergillus oryzae. The structures of new compounds were established as 25(R)-spirost-5-en-21β-methyl-3β-ol-3-O-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranoside (1) and (25R)-spirost-5-en-3β-ol-7-one 3-O-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranoside (2) by detailed spectroscopic analyses including 1D and 2D NMR spectral data ((1)H-(1)H COSY, HSQC, and HMBC) and MS spectrometry.