Four new daphnane-type diterpenes, genkwadanes A-D (1-4), together with 19 known ones, were isolated from ethanol extract of the flower buds of Daphne genkwa. Their structures were determined on the basis of extensive spectroscopic data. Among them, daphnane-type diterpene with a 1,10-double bond (1) was isolated from this plant for the first time. The cytotoxicity of all compounds 1-23 against the 10 selected human cancer cell lines was assayed. A number of compounds exhibited significant activities against the 10 cancer cell lines (IC50<9.56 μM). and most interestingly, all the compounds revealed preferred cytotoxicities on the HT-1080 cell line and displayed much stronger inhibitory activities (IC50<29.94 μM) compared with positive control 5-fluorouracil (IC50=35.62 μM), particularly, compounds 9-11, 13, 16 and 19 exhibited the strongest cytotoxicity activities against the HT-1080 cell line (IC50<0.1 μM).
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