Two novel phloroglucinols from Hypericum empetrifolium with antiproliferative activity on endothelial cells

Acylphloroglucinols are often accumulated in the familiy Clusiaceae. They seem to contribute to the antidepressant efficacy of St. John's wort and have antibacterial activities. More recently, a potent anti-angiogenic activity has been described [1]. Aim of the present study was to identify compounds from the endemic greek Hypericum species H. empetrifolium (Clusiaceae) with antiproliferative activity on endothelial cells to identify possible new anti-angiogenic substances. As a first result, two novel acylphloroglucinol derivatives were isolated from a petrol ether extract of H. empetrifolium after fractionation by LC on silica gel, RP-18 and purification by preparative HPLC (RP-18), namely 1-O-(p-1-menthen-8-yl)-4-geranyl-2-(2-methylpropionyl)-phloroglucinol (1) and 1-O-(p-1-menthen-8-yl)-4-geranyl-2-(2-methylbutyryl)-phloroglucinol (2). Their structures were elucidated by 1D-, 2D-NMR techniques and ESI-MS. To determine a possible anti-angiogenic activity, the inhibition of endothelial cell proliferation was measured. Subconfluent grown HMEC-1 cells (human microvascular endothelial cell line) were treated with (1) and (2) for 3 days before cells were stained with crystal violet. Both substances showed a concentration dependent activity by inhibiting the cell proliferation between 1 and 20µM.

Fig.1: 1-O-(p-1-menthen-8-yl)-4-geranyl-2-(2-methylpropionyl)-phloroglucinol

Fig.2: 1-O-(p-1-menthen-8-yl)-4-geranyl-2-(2-methylbutyryl)-phloroglucinol

Acknowledgements: Thanks are due to Prof. Theophanis Constantinidis, University of Athens, Faculty of Biology, for botanical classification as well as to Dr. E. Ades and Mr. F. J. Candal of CDC (USA) and Dr. T. Lawley of Emory University (USA) for providing the HMEC-1 cells

References: 1. Martinez-Poveda, B. et al. (2010) PLoS One 5(3): e9558.