Fast Identification of Radical Scavengers from Securigera varia by Combining (13)C-NMR-Based Dereplication to Bioactivity-Guided Fractionation

Securigera varia (Fabaceae) is a common herbaceous perennial plant widely growing in Europe and Asia and purposely established for erosion control, roadside planting, and soil rehabilitation. The aim of this study was to determine the radical scavenging activity of a crude methanol extract of S. varia aerial parts by using the free radical DPPH (1,1-diphenyl-2-picrylhydrazyl) and to rapidly identify the compounds involved in this activity. The crude extract was initially separated in five fractions on Diaion HP20 resin and the most active part was fractionated by Centrifugal Partition Extraction (CPE). Known compounds were directly identified by a (13)C-NMR-based dereplication method. Semi-preparative high performance liquid chromatography purification experiments were further performed to identify unknown or minor active compounds. As a result, one new (13) and twelve known flavonoid glycosides together with three nitropropanoylglucopyranoses were isolated, including astragalin (1), kaempferol-3-O-(6-O-acetyl)-β-d-glucopyranoside (2), kaempferol-3,4′-di-O-β-d-glucopyranoside (3), trifolin (4), isoquercitrin (5), hyperoside (6), isovitexin (7), isoorientin (8), isovitexin 4′-O-β-d-glucopyranoside (9), apigenin 7-O-β-d-glucuronopyranoside (10), luteolin 7-O-β-d-glucuronopyranoside (11), apigenin 7-O-α-l-rhamnopyranosyl-(1→2)-β-d-glucuronopyranoside (12), apigenin 7-O-β-d-glucopyranosyl-(1→2)-β-d-glucuronopyranoside (13), 6-O-(3-nitropropanoyl)-β-d-glucopyranoside (14), coronillin (16) and coronarian (15). 120 mg of the most active compound isoorientin against the free radical DPPH was recovered by CPE with an HPLC purity of 99%.