Two new steroidal saponins from the rhizomes of Dioscorea panthaica and their cytotoxic activity

Two new steroidal saponins, dioscoresides C (1) and D (2), along with a new natural product, pregnadienolone 3-O-beta -gracillimatriose (3), and two known compounds, pregnadienolone 3-O-beta -chacotrioside (4) and pseudoprotodioscin (5), were isolated from the rhizomes of Dioscorea panthaica Prain et Burkill. On the basis of extensive NMR studies and chemical evidence, dioscoresides C and D were determined to be 26-O-beta -D-glucopyranosyl-3 beta ,26-dihydroxy-23(S)-methoxy-25(R)-furosta-5,20(22)-dien-3-O-alpha -L-rhamnopyranosyl-(1 -->2)-[alpha -L-rhamnopyranosyl-(1 -->r)]-beta -D-glucopyranoside and 26-O-beta -D-glucopyranosyl-3 beta ,26-dihydroxy-20,22-seco-25(R)-furosta-5-en-20,22-dine-3-O-alpha -L-rhamnopyranosyl-(1 -->2)-[alpha -L-rhamnopyranosyl-(1 -->4)]-beta- D-glucopyranoside. These compounds showed mild cytotoxicity against the cancer cell lines, A375, L929, and HeLa, in a dose-dependent manner.