Two diastereomeric saponins with cytotoxic activity from Albizia julibrissin

Two diastereomeric saponins, julibrosides J(1) (1) and J(9) (2), both of wh ich show cytotoxic activity, were obtained from the stem bark of Albizia ju librissin Durazz. On the basis of chemical and spectral evidence [L.B. Ma e t al., Carbohydr. Res., 281 (1996) 35-46], the structure of I was revised a s 3-O-[beta-D-xylopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl-(1 --> 6)-be ta-D-glucopyranosyl]21-O-{(6S)-2-trans-2-hydroxymethyl-6-methyl-6-O-[4-O-(6 R)-2-trans-2,6-dimethyl-6- O-(beta-D-quinovopyranosyl)-2,7-octadienoyl)-bet a-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 identifi ed 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-octadieno yl)-beta-D-quinovopyranosyl)-2,7-octadienoyl} acacic acid-28-O-beta-D-gluco pyranosyl-(1 --> 3)-[alpha-L-arabinofuranosyl-(1 --> 4)]-alpha-L-rhamnopyra nosyl-(1 --> 2)-beta-D-glucopyranosyl ester. Saponin 2 is a new saponin nam ed julibroside J(9). Both julibrosides J(1) and J(9) show good inhibitory a ction against the KB cancer cell line in vitro. (C) 2000 Elsevier Science L td. All rights reserved.