Lavandulyl Flavanones from the Stems of Hypericum calycinum L. by Thida Win* a ) 1 ), Thant Thant Htwe b ), Htay Htay Shwe c ), and Jçrg Heilmann* d ) 1 ) a )Department of Chemistry, Kyaukse University, Myanmar (phone: þ 95 66 40247; fax: þ 95 66 40248 e-mail: thida09@gmail.com) b )Department of Chemistry, Yadanabon University, Myanmar c ) Department of Chemistry, Panlong University, Myanmar d ) Department of Pharmaceutical Biology, Universität Regensburg, DE-93053 Regensburg (phone: þ 499419434759; fax: þ 49 941 943 4990; e-mail: joerg.heilmann@chemie.uni-regensburg.de) One novel lavandulyl flavanone ( ¼ 2,3-dihydro-2-phenyl-4H-1-benzopyran-4-one) with an unusual 5,2’,4’,6’-tetrahydroxy substitution, calycinigin A (1), was isolated from the stems of Hypericum calycinum L. (Hypericaceae) . The structure was elucidated on the basis of 1D- and 2D-NMR analysis, as well as mass spectrometry (LR-EI- and HR-EI-MS) and circular dichroism. Three known lavandulyl flavanones with 5,7,2’,4’,6’-pentahydroxy substitution, i.e. , 2 – 4, were also isolated. Chemosystematically, this is the first report on the occurrence of prenylated flavanones in the family Hypericaceae. Reduction of cell viability by all compounds was evaluated in a MTT ( ¼ 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl- 2H-tetrazolium bromide) assay using HeLa cells. Compound 1 showed moderate activity with an IC 50 value of 9.7  1.8 mm, whereas compounds 2 – 4 were less active exhibiting IC 50 values of 11.6  0.9, 19.3  1.5, and 40.7  2.4 mm, respectively. The antioxidant activity was evaluated by an ORAC (Oxygen Radical Absorbance Capacity) assay, and calycinigin A (1) was again the most active compound with a Trolox equivalent of 2.3  0.2. None of the compounds was able to reduce the TNF-a induced ICAM-1 expression in vitro using human microvascular endothelial cells (HMEC-1). Introduction. – In Myanmar, the health care system based on herbal and medicinal plants has a long history as a national heritage, and the study of indigenous medicinal plants and their use in therapy plays a very important role [1] . Hypericum calycinum L., as one example, is called Pyin-nyar-lin-kar and mainly used in treatment of malaria in Myanmar traditional medicin. This Hypericum species is widespread from south-east Europe to Asia and was object of several phytochemical investigations dealing with a broad diversity of secondary metabolites comprising flavonoids [2] [3], xanthones [4], volatile constituents [5], anthranoids [6], and phloroglucinol derivatives. The phloroglucinols have been reported to exhibit cell-growth-inhibitory and in vitro antimalarial activity [7] [8]. As it can be seen from the different composition of the essential oils of Asian [5] and European [9] provenances, the distribution in ecologically very different habitats contributes to the chemical diversity of H. calycinum. Previous investigations on the flavonoid spectrum of H. calycinum mainly dealt with the isolation of several flavonols of the quercetin type [2] [6]. Our phytochemical CHEMISTRY & BIODIVERSITY – Vol. 9 (2012) 1198  2012 Verlag Helvetica Chimica Acta AG, Zürich 1 ) To whom correspondence should be addressed: T. W., isolation and structure elucidation; J. H., pharmacological data, instrumentation, and manuscript.