Caspicaosides E–K, triterpenoid saponins and cytotoxic acylated saponins from fruits of Gleditsia caspica Desf.

Abstract

Seven bisdesmosidic triterpenoid saponins named caspicaosides E–K, were isolated from the methanolic fruit extract of Gleditsia caspica Desf. Their structures were determined by 1D and 2D NMR spectroscopy as well as high resolution mass spectrometry and acid hydrolysis. The saponins comprised echinocystic acid or oleanolic acid as the aglycone and saccharide moieties at C-3 and C-28. Like most Gleditsia saponins, the oligosaccharide moiety at C-3 was identified as β-d-xylopyranosyl-(1→2)-α-l-arabinopyranosyl-(1→6)-β-d-glucopyranosyl. The common oligosaccharide moiety linked to C-28 was determined as β-d-xylopyranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-α-l-rhamnopyranosyl-(1→2)-β-d-glucopyranosyl with the presence of additional β-d-galactopyranose unit and/or another α-l-rhamnopyranose moiety. The C-28 saccharide moiety was acylated with a monoterpenic acid unit or a monoterpenic acid linked to a monoterpene-arabinoside unit at the ester-β-d-glucopyranose C-6. Esterification of C-2 and C-3 hydroxyl groups of the terminal α-l-rhamnopyranose unit with a monoterpenic acid and epoxy-monoterpenic acid units, respectively, or with two identical monoterpenic acid units, was also shown. The acylated saponins caspicaosides G–K were assayed for their in vitro cytotoxicities against the three cell lines HCT116, HepG2 and MCF7. The tested saponins showed moderate to strong activities.