Structures and histamine release inhibitory effects of prenylated orcinol derivatives from Rhododendron dauricum.

Four new prenylated orcinol derivatives, daurichromenes A-D (1-4), along with three known compounds, confluentin (5), grifolin (6), and orcinol (7), have been isolated from the Chinese medicinal plant Rhododendron dauricum. Their structures were established as 2R-(7'-hydroxy-4',8'-dimethyl-3'E,8'-nonadienyl)-5-hydroxy-2,7-dimethyl-2H-chromene (1), 2R-(3'-hydroxy-8'-methyl-4'-methyliden-7'-nonaenyl)-5-hydroxy-2,7-dimethyl-2H-chromene (2), 2R-(8'-hydroxy-4',8'-dimethyl-3'E,6'Z-nonadienyl)-5-hydroxy-2,7-dimethyl-2H-chromene (3), and 2R-(9'-hydroxy-4',8'-dimethyl-3'E,7'E-nonadienyl)-5-hydroxy-2,7-dimethyl-2H-chromene (4) by analysis of spectral data. The absolute configuration of the asymmetric carbons at the chromene ring in 1-5 was determined as R from their circular dichroism spectra. Compounds 1-6 significantly inhibited compound 48/80-induced histamine release from rat peritoneal mast cells.