Cytotoxic xenicane diterpenes from the brown alga Padina pavonia (L.) Gaill.

Column chromatography of the hexane fraction of a methanol extract of Padina pavonia (L.) Gaill. collected from the Red Sea at Hurghada, Egypt yielded 18,19-epoxyxenic-19-methoxy-18-hydroxy-4-acetoxy-6,9,13-triene (1) and 18,19-epoxyxenic-18,19-dimethoxy-4-hydroxy-6,9,13-triene (2). The isolated compounds have various antitumor activities against lung carcinoma (H460) and liver carcinoma (HepG2) human cell lines (in vitro).