Bioassay-directed fractionation using multidrug-resistant (MDR) Staphylococcus aureus resulted in the isolation of four new polyprenylated benzophloroglucinol derivatives, sampsoniones N-Q (1-4), and four known compounds, 7-epiclusianone (5) and sampsoniones B, L, and R, from the roots of Hypericum sampsonii. The structures of these compounds were established by analysis of spectroscopic data, and the structures of 4 and 5 were determined by single-crystal X-ray diffraction crystallography. In the bioassay, 7-epiclusianone (5) showed promising activity with a minimum inhibitory concentration (MIC) of 7.3 microM against the NorA overexpressing MDR S. aureus strain SA-1199B; the positive control antibiotic norfloxacin showed activity at MIC 100 microM.

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Bioassay-directed fractionation employing a multidrugresistant (MDR) strain of Staphylococcus aureus resulted in the isolation of an antibacterial prenyl substituted xanthone derivative (1) named hyperixanthone A from the root of Hypericum sampsonii Hance (Hyperiaceae). Compound 1 showed promising inhibitory activity against the norfloxacin-resistant S. aureus strain SA-1199B at a minimum inhibitory concentration (MIC) of 2 µg/mL (4.3 µM), wheres the positive standard antibacterial drug norfloxacin showed an MIC of 32 µg/mL (100 µM). This strain overexpresses the NorA multidrug efflux transporter, the major characterized drug pump in Staphylococcus aureus. The activity of this compound against an effluxing strain of S. aureus is reported here for the first time. Compound 1, together with 1,7-dihydroxyxanthone (2) and 2-hydroxyxanthone (3), were obtained by silica gel column chromatography, and their structures were determined by means of extensive NMR and MS spectra.

Two new prenylated benzophenone peroxide derivatives, peroxysampsones A and B (1 and 2, resp.), together with a known compound, plukenetione C (3), were isolated from the roots of the Chinese medicinal plant Hypericum sampsonii, and their structures were elucidated by detailed spectral analysis. These compounds are the unusual peroxides of polyprenylated benzophenone derivatives, containing the unique caged moiety of 4,5-dioxatetracyclo[9.3.1.1(9,13).0(1,7)]hexadecane-12,14,15-trione. In the biological test, peroxysampsone A (1) showed comparable activity with norfloxacin against a NorA over-expressing multidrug-resistant (MDR) strain of Staphylococcus aureus SA-1199B.