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.