Scalemic caged xanthones isolated from the stem bark extract of Garcinia propinqua

Seven new caged xanthones, doitunggarcinones E−K (1−7), all as scalemic mixtures and 10 known compounds (8−17), were isolated from the stem bark extract of Garcinia propinqua. The structures were elucidated on the basis of spectroscopic methods. The separation of the enantiomers of 1−6 was achieved by semipreparative chiral HPLC. The absolute configuration of compound (+)-1 was determined by single-crystal X-ray crystallographic analysis using Cu Kα radiation. The absolute configurations of the other related compounds were determined from comparisons of their ECD spectra with that of compound (+)-1. Compounds (−)-6 and 7 showed cytotoxicity against a colon cancer cell line with IC50 values of 14.23 and 23.95 μM, respectively.