Two New Bibenzyls from Dendrobium hercoglossum

Two new bibenzyl compounds 3-hydroxy-4, 5, 3′-trimethoxybibenzyl ( 1) and (R)-4-hydroxy-3, 5, 3′, α-tetramethoxybibenzyl (2), along with twelve known compounds (3-14), were isolated from the stems of Dendrobium hercoglossum Reichb.f.The structures of the new compounds were elucidated on the basis of detailed spectroscopic analysis.The cytotoxic effects of the isolated compounds on two human tumors cell lines (MDA-MB-231 and Hela) were evaluated by the MTT assay.