Phloroglucinol derivatives from Hypericum empetrifolium with antiproliferative activity on endothelial cells

Five acylphloroglucinols substituted with monoterpenoids (empetrifelixin A-D and empetrikajaforin), three known monocyclic acylphloroglucinols and one monocyclic acylphloroglucinol were isolated from a petrol ether extract of Hypericum empetrifolium after fractionation by flash chromatography on silica gel, RP-18 and subsequent purification by preparative HPLC (RP-18). Their structures were elucidated by 1D, 2D NMR techniques and HREIMS. To determine a possible anti-angiogenic activity, inhibition of cell proliferation was measured using a human microvascular endothelial cell line (HMEC-1). Subconfluent grown HMEC-1 cells were treated with all compounds isolated in sufficient amounts and stained with crystal violet. Highest activity was observed for empetrifelixin A and empetrifelixin D showing a concentration dependent inhibition of cell proliferation with IC(50) values of 6.5 ± 0.1 and 7.3 ± 0.4 μM, respectively. Empetrifelixin A also showed activity in a cell migration assay with HMEC-1 cells in low micromolar concentrations.