Isolation and Antioxidant Activity of Flavonoid Glycosides from Leaves of Caragana korshinskii Kom.

The eluted fraction of Caragana korshinskii Kom. leaves, which was eluted with 30% ethanol on a macroporous resin, was used to separate the compounds by high-speed counter-current chromatography (HSCCC) and preparative high-performance liquid chromatography (prep-HPLC). A solvent system of ethyl acetate∶n-butanol∶water (volume ratio=3∶7∶10) was utilized for the initial HSCCC separation. Subsequently, the fractions obtained from HSCCC underwent further purification through prep-HPLC. Structural identification of the isolated compounds was conducted using ¹H-NMR and ¹³C-NMR. A total of 11 flavonoid glycosides were separated, identified as follows: (1) quercetin-3-O-α-L-rhamnosyl (1→6)-β-D-galactopyranoside-7-O-α-L-rhamnoside, (2) rutin-7-O-α-L-rhamnoside, (3) isorhamnetin-3-O-α-L-rhamnosyl (1→6)-β-D-galactopyranoside-7-O-α-L-rhamnoside, (4) isorhamnetin-3-O-α-L-rhamnosyl (1→6)-β-D-glucoside-7-O-α-L-rhamnoside, (5) kaempferol-3-O-α-L-rhamnosyl (1→6)-β-D-galactoside-7-O-α-L-rhamnoside, (6) quercetin-3-O-β-D-galactoside-7-O-α-L-rhamnoside, (7) quercetin-3-O-β-D-glucoside-7-O-α-L-rhamnoside, (8) isorhamnetin-3-O-β-D-galactoside-7-O-α-L-rhamnoside, (9) isorhamnetin-3-O-β-D-glucoside-7-O-α-L-rhamnoside, (10) kaempferol-3-O-β-D-galactoside-7-O-α-L-rhamnoside, and (11) kaempferol-3-O-β-D-glucoside-7-O-α-L-rhamnoside. The antioxidant activities were evaluated using DPPH (2, 2-diphenyl-1-picrylhydrazyl), hydroxyl radicals (·OH), superoxide anion (O₂^−·), and ABTS (2, 2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) assays. Additionally, molecular docking studies were performed to assess the interactions of the compounds with 9 oxidative stress enzymes. In vitro antioxidant assays revealed that compounds 1, 2, 6, and 7 exhibited significant antioxidant activities. Structure-activity relationship analysis indicated that the dihydroxyl groups at positions 3' and 4' were the primary active moieties. Molecular docking studies demonstrated that compounds 1, 2, 6, and 7 possessed high binding affinities with the 9 oxidative stress enzymes, primarily through hydrogen bonding facilitated by the dihydroxyl groups at positions 3' and 4', consistented with the findings from the antioxidant assays and structure-activity relationship analysis. This study provided a theoretical foundation and technical support for the comprehensive development and utilization of Caragana korshinskii Kom. leaf resources.