Xanthone derivatives from the leaves of Garcinia oligantha.

Nine new and unique xanthone derivatives, including one novel hybrid monoterpene-tetrahydroxanthone (1), three dihydro-xanthone derivatives (2-4), and five skeleton-rearranged xanthone derivatives (5-9), were obtained from a 95% EtOH extract of Garcinia oligantha leaves by a LC-MS-guided fractionation procedure. The structures of the new compounds were elucidated by analysis of their 1D and 2D NMR and MS data. The relative configurations of 2 and 8 were determined via X-ray crystallographic data analysis, while the absolute configurations of 1-2, 5-9 were assigned based on a comparison of calculated and experimental ECD and/or OR data. In SRB, PI-exclusion and Hoechst staining assays, 6 showed strong cytotoxic activities which could dose-dependently induce Taxol-insensitive quiescent LNCaP cell death. Additionally, a preliminary mechanism investigation using immunoblotting and Caspase-3 activity assay, indicated that 6 induced quiescent LNCaP cell death potentially through caspase-dependent mitochondrial apoptosis pathway.