A new phenanthrenequinone from Dendrobium draconis.

A number of Dendrobium species (Orchidaceae) have been used as health foods. In Thailand, the tea prepared from the stems of Dendrobium draconis Rchb.f. (Orchidaceae) has been used as a blood tonic. Our phytochemical investigation of this plant led to the isolation of a new compound namely 5-methoxy-7-hydroxy-9,10-dihydro-1,4-phenanthrenequinone, along with four known stilbenoids including hircinol, gigantol, batatasin III, and 7-methoxy-9,10-dihydrophenanthrene-2,4,5-triol. The structures of these compounds were determined through extensive spectroscopic studies, including (1)H and (13)C NMR, DEPT, COSY, NOESY, HMQC, HMBC, ESI-MS, and HR-ESI-MS experiments. In the DPPH-free radical assay, these stilbene derivatives showed appreciable antioxidant activity.