Isolation and identification of phase I metabolites of phillyrin in rats.

Phillyrin was one of the main chemical constituents of the fruit of Forsythia suspensa (Thunb.) Vahl. It showed various bioactivities including antioxidant and anti-inflammatory activities. However, the metabolism of phillyrin remained unknown. This report described the isolation and identification of phase I metabolites of phillyrin in rats. Nine metabolites including six new ones were isolated by various column chromatographies and high-performance liquid chromatography. Their structures were elucidated by extensive spectroscopic analysis. The antiviral activities of phillyrin and the metabolites were evaluated against influenza A (H3N2) virus. Among them, one metabolite M8 showed moderate activity with the IC50 value of 26.39 μM, and three metabolites (M2, M3, M9) showed weak antiviral activities at the concentration of 100 μM. Based on the structures of the metabolites, possible metabolic pathways of phillyrin in rats were also proposed.