Two Unusual Phenolic Substances and One New Xanthone from Hypericum sampsonii

Sampsone A (1), a novel prenylated aromatic lactone, and sampsone B (2), an unusual dihydrodibenzodioxinone, together with sampsone C (3), a new xanthone, were isolated from the aerial parts of Hypericum sampsonii. Their structures were determined by spectroscopic methods which were mainly 1D- and 2D-NMR techniques, and the structure of sampsone B (2) was also confirmed by Xray crystallographic analysis. All of these compounds were evaluated for in vitro antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). Only sampsone A showed moderate antibacterial activities at a minimum inhibitory concentration (MIC) of 32 mg/ml.