New hepatoprotective saponins, bupleurosides III, VI, IX, and XIII, from Chinese Bupleuri Radix: Structure-requirements for the cytoprotective activity in primary cultured rat hepatocytes

New hepatoprotective saponins, bupleurosides III, VI, IX, and XIII, were isolated from Chinese Bupleuri Radix, the roots of Bupleurum scorzonerifolium Willd., together with nine new and sixteen known saponins. The structures of bupleurosides III, VI, IX, and XIII were elucidated on the basis of chemical and physicochemical evidence. By examination of the structure requirements in saponins for the protective effect on the d-galactosamine-induced cytotoxicity in primary cultured rat hepatocytes, the 11-oxygen function, the 16β-hydroxyl group, and the 3-O-diglycoside moiety were found to be essential to exerting the hepatocytoprotective activity.