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.