New steroidal glycosides from the fruits of Tribulus terrestris

Three new steroidal saponins (1-3) were isolated from the fruits of Tribulu s terrestris. Their structures were assigned by spectroscopic methods (IR, HRESIMS, 1D- and 2D-NMR) as 26-O-beta -D-glucopyranosyl-(25S)-5 beta -furos t-20(22)-en-3 beta ,26-diol-3-O-alpha -L-rhamnopyranosyl-(1->2)-[alpha -L-r hamnopyranosyl-(1->4)]-beta -D-glucopyranoside (1), 26-O-beta -D-glucopyran osyl-(25S)-5 beta -furost-20(22)-en-3 beta ,26-diol-3-O-alpha -L-rhamnopyra nosyl-(1->2)- [beta -D-glucopyranosyl-(1->4)]-beta -D-galactopyranoside (2) , and 25(S)-5 beta -spirostan-3 beta-alpha -3-O-alpha -L-rhamnopyranosyl-(1 ->2 -[beta -D-glucopyranosyl-(1->4)]-beta -D-galactopyranoside (3). Compoun d 3 showed cytotoxicity against a human malignant melanoma cell line (SK-ME L).