An antioxidant lignan and other constituents from the root bark of Hibiscus syriacus

A new lignan named as hibiscuside, (+)-pinoresinol 4-O-[beta-glucopyranosyl (1-->2)-alpha-rhamnoside] (1), and a known lignan, syringaresinol (2) were isolated from the root bark of Hibiscus syriacus together with two feruloy ltyramines (3,4) and three known isoflavonoids (5,6,7). The structures of t hese compounds have been established on the basis of their NMR, mass, UV sp ectra. Among these phenolic compounds, 6-O-acetyldaidzein (5), 6"-O-acetylg enistin (6), and 3'-hydroxydaidzein (7) with IC50 values of 8.2, 10.6, and 4.1 mu M, respectively, significantly inhibited lipid peroxidation in rat l iver microsomes. Hibiscuside (1), E- and Z-N-feruloyl tyramines (3,4) exhib ited moderate antioxidant activity.