Bi-, tri-, and polycyclic acylphloroglucinols from Hypericum empetrifolium

The ¹H NMR-guided fractionation of a petroleum ether extract of Hypericum empetrifolium led to the isolation of four new bicyclic (1-4), four known bicyclic (5-8), three new tricyclic (9-11), and three new polycyclic acylphloroglucinols (12/13 and 14) possessing a monoterpenoid citran moiety. Compounds 12/13 were isolated as a mixture of two inseparable structural isomers. The compounds showed in vitro antiproliferative activity against human microvascular endothelial cells (HMEC-1) with IC₅₀ values in the range 9.2 ± 2.0 to 29.6 ± 3.5 μM.