Isolation and characterization of rosmarinic acid oligomers in Celastrus hindsii Benth leaves and their antioxidative activity.

Antioxidative compounds were isolated from the 50% methanol extract of dried leaves of Celastrus hindsii. Eight phenolic compounds (1-8) were finally obtained by reversed-phase high-performance liquid chromatography, and their structures were elucidated by nuclear magnetic resonance spectrometry and mass spectrometry analyses. They were the five known compounds, rutin (1), kaempferol 3-rutinoside (2), rosmarinic acid (3), lithospermic acid (4), and lithospermic acid B (6), and three novel oligomers of rosmarinic acid, a dimer (5) and two trimers (7 and 8). The major components in the extract were rosmarinic acid (3) and lithospermic acid B (6). These phenolic compounds were shown to have antioxidative activities against the autoxidation of methyl linoleate in bulk phase and the radical-initiated peroxidation of soybean phosphatidylcholine in liposomes. In the liposomal peroxidation, the number of phenolic hydroxyl group in each molecule was correlated with the effectiveness of antioxidative activity.