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.