Triterpenoid saponins from corms of Crocus sativus: Localization, extraction and characterization

A mixture of highly glycosilated triterpenoid saponins (CS5) isolated from the corm of Crocus sativus or saffron showed cytotoxic activity against HeLa tumoral cells. The main reverse phase HPLC fraction of this mixture (CS5-1) contains two new oleanane-type saponins, denominated Azafrine 1 (1) and Azafrine 2 (2). The bidesmosidic saponins were respectively characterized as (1) 3-O-β-d-glucopyranosiduronic acid echinocystic acid 28-O-β-D-galactopyranosyl-(1 → 2)-α-l-arabinopyranosyl-(1 → 2)-[β-d-xylopyranosyl-(1 → 4)]-α-d-rhamnopyranosyl-(1 → 2)-[4-O-di-α-L-rhamnopyranosyl-3,16-dihydroxy-10-oxo-hexadecanoyl]-α-D-fucopyranoside and (2) 3-O-β-D-galactopyranosiduronic acid echinocystic acid 28-O-β-D-galactopyranosyl-(1 → 2)-α-L-arabinopyranosyl-(1 → 2)-[β-D-xylopyranosyl-(1 → 4)]-α-L-rhamnopyranosyl-(1 → 2)-[4-O-di-α-L-rhamnopyranosyl-3,16-dihydroxy-10-oxo-hexadecanoyl]-β-D-fucopyranoside. The surfactant properties of saponins, probably involved in the cytotoxic activity of CS5 and their exclusive localization in the external part or the corm, indicate their possible role as phytoprotectans. The similarity of their structural compositions to that of other triterpenoid saponins which are of special use in the pharmaceutical industry suggest a new application for C. sativus crops through the exploitation of corm for saponin extraction.

Two new oleanane-type saponins from Crocus sativus have been characterized. It is the first time that galacturonic acid is described in saponins, as well as echinocystic acid glycosides are detected in a monocotyledonous plant.Figure optionsDownload as PowerPoint slideHighlights
► Azafrine 1 and 2 are echinocystic acid glycosides described for the first time in a monocotyledonous plant such as Crocus sativus, exclusively located in the external part of the corm.
► Both are highly glycosilated bidesmosidic saponins which contain a fatty acyl group in the pentasaccharide located at C28 of the echinocystic acid.
► The unique difference between azafrine 1 and 2 is the presence, at C3 of the aglycone, of β-d-glucuronic acid or β-d-galacturonic acid, respectively.
► The whole structure is necessary in order to achieve the activity against HeLa Cells, in fact, such activity disappears when the structure is cleaved.