Bioactive Prenylated Xanthones from the Young Fruits and Flowers of Garcinia cowa

Five new xanthones, garciniacowones A-E (1-5), together with 14 known xanthones, 6-19, were isolated from the young fruits and fresh flowers of Garcinia cowa. The structures of 1-5 were elucidated by analysis of their 1D and 2D NMR spectra and mass spectrometric data. The compounds 1-19 were tested in vitro for their antimicrobial activity and for their ability to inhibit alpha-glucosidase. Compounds 16 and 17 showed the most potent alpha-glucosidase inhibitory activity, with IC50 values of 7.8 +/- 0.5 and 8.7 +/- 0.3 mu M, respectively. Compounds 8, 9, and 19 showed antibacterial activity against Bacillus subtilis TISTR 088 with identical MIC values of 2 mu g/mL, while 8, 10, and 19 exhibited antibacterial activity against Bacillus cereus TISTR 688 with identical MIC values of 4 mu g/mL.