A new acylated flavonol triglycoside and evaluation of the antioxidant activity of Astragalus armatus subsp. numidicus (Murb.) Emb. & Maire.

Abstract

A new acylated flavonol triglycoside, quercetin-3-O-(5'-p-hydroxybenzoyl)-β-D-apiofuranosyl-(1→2)[α-L-rhamnopyranosyl-(1→6)]-β-D-galactopyranoside (1), was isolated from the aerial parts of Astragalus armatus subsp. numidicus (Murb.) Emb. & Maire as well as ten known compounds, one phenolic compound, one flavonol-aglycone and eight flavonol-glycosides distributed into two monoglycosides, three diglycosides and three triosides. Their structures were mainly determined by 1D- and 2D-NMR experiments (¹H,¹³C, COSY, HSQC, HMBC). The chloroform, ethyl acetate, n-butanol and hydroethanol extracts were tested for their antioxidant activity using five methods (DPPH, ABTS, Reducing power, CUPRAC and Phenanthroline). The ethyl acetate extract was the most active in CUPRAC (A_0.5: 50.28 ± 2.16 µg/mL), ABTS (IC₅₀: 49.73 ± 1.55 µg/mL) and Reducing power (A_0.5: 58.13 ± 4.35 µg/mL) assays, whereas the hydroethanol and n-BuOH exhibited the highest activity in the Phenanthroline assay (A_0.5: 9.93 ± 0.16) and (A_0.5: 10.27 ± 0.44 µg/mL), respectively.