Bi-bicyclic and bi-tricyclic compounds from Dendrobium thyrsiflorum

Abstract

One bi-bicyclic and two bi-tricyclic derivatives of coumarin–benzofuran, phenanthrene–phenanthrene and phenanthrene–phenanthraquinone, along with seven known compounds, were isolated from stems of <i>Dendrobium thyrsiflorum</i> Rchb.f. (Orchidaceae). On the basis of chemical, NMR (¹H, ¹³C, HMQC, HMBC and NOESY) and mass spectrometry data, their structures were elucidated as denthyrsin [3-(5′,6′-dimethoxybenzofuran-2′-yl)-6,7-dimethoxy-2H-chromen-2-one; <b>1</b>], denthyrsinol (4,5′-dimethoxy-[1,1′]biphenanthrenyl-2,5,4′,7′-tetraol; <b>2</b>), and denthyrsinone (7,4′,7′-trihydroxy-2,2′,8′-trimethoxy-[5,1′]biphenanthrenyl-1,4-dione; <b>3</b>). Compounds <b>1</b>–<b>3</b> and denthyrsinin (1,5,7-trimethoxyphenanthrene-2,6-diol; <b>4</b>) showed significant cytotoxic activities against Hela (13.5, 9.3, 9.9 and 2.7 μM, respectively), K-562 (0.45, 1.6, 6.0 and 2.3 μM, respectively) and MCF-7 (18.1, not tested, 3.5 and 4.8 μM, respectively) cell lines.