Two diastereomeric saponins with cytotoxic activity from Albizia julibrissin

Two diastereomeric saponins, julibrosides J(1) (1) and J(9) (2), both of which show cytotoxic activity, were obtained from the stem bark of Albizia julibrissin Durazz. On the basis of chemical and spectral evidence [L.B. Ma et al., Carbohydr. Res., 281 (1996) 35-46], the structure of I was revised as 3-O-[beta-D-xylopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl-(1 --> 6)-beta-D-glucopyranosyl]21-O-{(6S)-2-trans-2-hydroxymethyl-6-methyl-6-O-[4-O-(6R)-2-trans-2,6-dimethyl-6- O-(beta-D-quinovopyranosyl)-2,7-octadienoyl)-beta-Dquinovopyranosyl]-2,7-octadienoyl}acacic acid-28-O-beta-D-glucopyranosyl-(1 --> 3)-[alpha-L-arabinofuranosyl-(1 --> 4)]-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl ester. The diastereoisomer 2 of 1 was identified as 3-O-[beta-D-xylopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl-(1 --> 6)-beta-D-glucopyranosyl]-21- O-{(6S)-2- trans-2-hydroxymethyl-6-methyl-6-O-[4-O-((6S)-2-trans-2,6-dimethyl-6-O-(beta-D-quinovopyranosyl)-2,7-octadienoyl)-beta-D-quinovopyranosyl)-2,7-octadienoyl} acacic acid-28-O-beta-D-glucopyranosyl-(1 --> 3)-[alpha-L-arabinofuranosyl-(1 --> 4)]-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl ester. Saponin 2 is a new saponin named julibroside J(9). Both julibrosides J(1) and J(9) show good inhibitory action against the KB cancer cell line in vitro. (C) 2000 Elsevier Science Ltd. All rights reserved.