New Diosgenin Glycosides from Costus afer

Two new steroidal saponins, aferosides B (1) and C (2), together with the known saponins, dioscin (3) and paryphyllin C (4), were isolated from the roots of Costus afer. The known flavonoid glycoside, kaempferol 3-O-α-l-rhamnopyranoside (5), was obtained from the aerial parts. The structures of the new compounds were elucidated principally by 2D NMR spectral methods. A structural revision of the sugar sequence was made for the previously reported saponin aferoside A (6) on the basis of detailed spectroscopic analysis. Saponins 1−4 and 6 did not show any ability to potentiate in vitro cisplatin cytotoxicity in a human colon cancer cell line.