Cytotoxic cardenolides from the stems of Periploca forrestii.

Six new cardenolides, periforosides D-E (1-2), periforgenin C (3) and periforosides F-H (4-6), as well as 10 previously identified cardenolides (7-16) were isolated from the ethanol extract of the stems of Periploca forrestii. The structures of the new compounds were determined using extensive spectroscopic analyses including HRESI-MS, 1D and 2D NMR data. Evaluation of the cytotoxic activity of all the isolated compounds in five different human cancer cell lines indicated that compounds 2-6, 8, 9 and 12-16 have potent activity.