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.