Two new xanthones from the root of Thai Calophyllum inophyllum and their toxicity against colon and liver cancer cells.

Two new xanthones, 1,3,6,7-tetrahydroxy-5-methoxy-4-(1',1'-dimethyl-2'-propenyl)-8-(3″,3″-dimethyl-2″-propenyl)-xanthone (1) and (2'S)-7-hydroxy caloxanthone B (2), were isolated from the root of Thai Calophyllum inophyllum Linn., together with twelve known xanthones (3-14). The structures of new compounds were elucidated based on spectroscopic data. In addition, compounds 4, 6 and 8 were isolated from the genus Calophyllum for the first time. The isolated compounds were evaluated for their cytotoxic activity against colon HCT-116 and liver Hep-G2 cancer cells. Among tested compounds, xanthones 5 and 14 possessing a prenyl moiety and a pyranyl ring fused at C-2 and C-3 displayed the most potent and selective cytotoxicity against HCT-116 colon cancers with the same IC50 values of 3.04 µM.