A pair of isomeric saponins with cytotoxicity from Albizzia julibrissin

Two new saponins have been isolated from the stem barks of Albizzia julibrissin Durazz, and their structures identified as 3-O-β-d-xylopyranosyl-(1 → 2)-β-d-fucopyranosyl-(1 → 6)-β-d-2-deoxy-2-acetoamidoglucopyranosyl]-21-O-{(6S)-2- trans -2-hydroxymethyl-6-methyl-6-O-4-O-((6S )-2- trans -2-hydroxymethyl-6-hydroxy-6-methyl-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 (1) and 3-O-β-d-xylopyranosyl-(1 → 2)-β-d-fucopyranosyl-(1 → 6)-β-d-2-deoxy-2-acetoamidoglucopyranosyl]-21-O-{(6S)-2-trans-2-hydroxymethyl-6-methyl-6-O-3-O-((6S)-2-trans-2-hydroxymethyl-6-hydroxy-6-methyl-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 (2), based on chemical and spectral evidences, named as julibroside J₁₉ and julibroside J₁₈, respectively. Both compounds show significant inhibition action against HeLa, Bel-7402 and MDA-MB-435 cancer cell lines in vitro.