Cytotoxic xanthone derivatives from the twigs of Garcinia oligantha.

Ten undescribed xanthone derivatives, garoliganthins A-I and oliganthaxanthone C, along with eight known compounds, were isolated from the twigs of Garcinia oligantha Merr. Their structures and absolute configurations were determined by extensive spectroscopic methods, single-crystal X-ray diffraction analysis, electronic circular dichroism analysis, and chiral HPLC/HPLC-CD analysis combined with density functional theory calculations. Garoliganthin A is an unprecedented tetrahydro-xanthone derivative possessing a bicycle [3.2.2] nonane skeleton, and garoliganthins B-E are the first examples of a new class of rearranged xanthone derivatives with six-membered lactone core scaffold. The cytotoxic effects of the isolates on four human cancer cell lines (HeLa, PC-3, A549, and K562) were measured using an MTT assay. Seven compounds showed good inhibitory activities against four cancer cell lines with IC₅₀ values ranging from 2.1 to 16.8 μM.