Tannin antioxidants from Osbeckia chinensis

Six hydrolysable tannins, casuarinin (1), casuariin (2), punicacortein A (3), degalloyl-punicacortein A (4), 2,3-[(S)-4,4′,5,5′,6,6′-hexahydroxydiphenoyl]-d-glucopyranoside (5), and 4,6-[(S)-4,4′,5,5′,6,6′-hexahydroxydiphenoyl]-d-glucopyranoside (6), and related compounds, gallic acid, methyl gallate and ellagic acid, were isolated from the methanol extract of Osbeckia chinensis. In order to confirm the structure-activity relationship, the antioxidant activities of these compounds were examined both in the food model and in vitro systems. The antioxidative efficiency, using the thiocyanate and TBA methods, increased in the order of gallic acid <α-tocopherol