A novel acylated flavonol tetraglycoside and rare oleanane saponins with a unique acetal-linked dicarboxylic acid substituent from the xero-halophyte Bassia indica

Abstract

In recent years, the scientific interest and particularly the economic significance of halophytic plants has been highly demanding due to the medicinal and nutraceutical potential of its bioactive compounds. A xero-halophyte Bassia indica is deemed to be a very cheap source of natural entities without chemical or biological investigation. In this context, a new acylated flavonol tetraglycoside, kaempferol-3-O-β-d-glucopyranosyl-(1→6)-O-[β-D-galactopyranosyl-(1→3)-2-O-trans-feruloyl-α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyranoside (14), together with rare occurring flavonol triglycoside, isorhamnetin-3-O-β-d-glucopyranosyl-(1→6)-O-[α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyranoside (15), were isolated from the aqueous methanol extract of the aerial parts of B. indica. The study also reported an optimal separation and characterization of a new seco-glycosidic oleanane saponin with 2′R,3′S stereocenters, identified as (2′R,3′S)-3-O-[2′-hydroxy-3′-(2"-O-glycolyl)-oxo-propionic acid-β-D-glucuronopyranosyl]-28-O-β-D-glucopyranosyl-olean-12-en-3β-ol-28-oic acid (17), in addition to its derivative, 3-O-[2′-(2"-O-glycolyl)-glyoxylyl-β-D-glucuronopyranosyl]-28-O-β-d-glucopyranosyl-olean-12-en-3β-ol-28-oic acid (16). The structures of all isolated compounds were elucidated based on 1D, 2D NMR, and HR-MS analysis, as well as comparing with similar derivatives published in the literature. Furthermore, thirteen known compounds were isolated and identified as β-sitosterol (1), vanillic acid (2), o-hydroxybenzoic acid (3), р-hydroxybenzoic acid (4), 6,7-dihydroxycoumarin (5), methyl caffeate (6), caffeic acid (7), quercetin (8), uracil (9), thymidine (10), tachioside (11), isorhamnetin-3-O-β-D-glucopyranoside (12), kaempferol-3-O-rutinoside (13). The anticholinesterase activity of all isolated compounds was evaluated.