Two diastereomeric saponins with cytotoxic activity from Albizia julibrissin

Abstract 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 1 was revised as 3 -O- [β- d -xylopyranosyl-(1→2)-α- l -arabinopyranosyl-(1→6)-β- d -glucopyranosyl]-21 -O- {(6 S )-2- trans -2-hydroxymethyl-6-methyl-6 -O- [4 -O- ((6 R )-2- trans -2,6-dimethyl-6 -O- (β- d -quinovopyranosyl)-2,7-octadienoyl)-β- d -quinovopyranosyl]-2,7-octadienoyl}acacic acid-28 -O -β- d -glucopyranosyl-(1→3)-[α- l -arabinofuranosyl-(1→4)]-α- l -rhamnopyranosyl-(1→2)-β- d -glucopyranosyl ester. The diastereoisomer 2 of 1 was identified as 3 -O- [β- d -xylopyranosyl-(1→2)-α- l -arabinopyranosyl-(1→6)-β- d -glucopyranosyl]-21 -O- {(6 S )-2- trans -2-hydroxymethyl-6-methyl-6 -O- [4 -O- ((6 S )-2- trans -2,6-dimethyl-6 -O- (β- d -quinovopyranosyl)-2,7-octadienoyl)-β- d -quinovopyranosyl]-2,7-octadienoyl}acacic acid-28 -O- β- d -glucopyranosyl-(1→3)-[α- l -arabinofuranosyl-(1→4)]-α- l -rhamnopyranosyl-(1→2)-β- 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.