Calaxanthones A-C, three new xanthones from the roots of Calophyllum calaba and the cytotoxicity.

Three new xanthones, named calaxanthones A-C (1-3), along with 17 known xanthones (4-20) were isolated from the roots of Calophyllum calaba. Their structures were determined by spectroscopic analysis. All isolated compounds were evaluated for their cytotoxicity against five cancer cell lines (KB, HeLa S-3, HT-29, MCF-7 and HepG-2). Compound 3 showed potent cytotoxicity against all the five cancer cell lines with IC50 values in the range of 0.82-5.04 μM. Furthermore, compound 6 showed potent cytotoxicity against KB, HeLa S-3 and HepG2 cells with IC50 values of 7.06, 5.27 and 9.64 μM, respectively. Additionally, compound 7 showed potent cytotoxicity against KB cell with an IC50 value of 4.62 μM.