Bi-bicyclic and bi-tricyclic compounds from Dendrobium thyrsiflorum

Coumarin-benzofuran, dimeric phenanthrene and phenanthrene-phenanthraquinone derivatives, along with seven known ones, were isolated from Dendrobium thyrsiflorum (Orchidaceae). Four of the compounds showed significant cytotoxic activities against Hela, K-562 and MCF-7 cell lines.