Cytotoxic cardenolide glycosides of Roupellina (Strophanthus) boivinii from the Madagascar rainforest.

Bioassay-guided fractionation of an ethanol extract of Roupellina (Strophanthus) boivinii from the rainforest of Madagascar afforded the six new cardenolide glycosides boivinides 1-6, as well as the four known cardenolide glycosides digitoxigenin 3-O-[beta-D-glucopyrananosyl-(1-->4)-alpha-L-acofriopyranoside], corotoxigenin 3-O-beta-D-boivinoside, 17alpha-corotoxigenin 3-O-beta-D-sarmentoside, and uzarigenin 3-O-alpha-L-rhamnoside. The structures of these compounds were elucidated by various 1D and 2D NMR techniques. All new compounds showed significant antiproliferative activity against the A2780 human ovarian cancer cell line, with boivinide A being the most active at IC50 = 0.17 microM.