Flavone C-glycosides from Dendrobium gratiosissimum

A phytochemical investigation of Dendrobium gratiosissimum Rchb. f. (Orchidaceae) led to the isolation of four new flavone C-glycosides (1-4) together with four known ones (5-8). The chemical structures of the new flavone C-glycosides (1-4) were elucidated by extensive spectroscopic data analysis including 1D- and 2D NMR, HR-ESI-MS, ESI-MS2 and careful comparison of the sugar unit spectroscopic data with those of reported in the literature. Biological assay revealed that compounds 6 and 7 showed moderate cytotoxicity against the human tumor cell line HepG2 by suppressing cell viability with an inhibition rate of 76.7 % and 79.6 % at 10.0 mu M, respectively.