Flavonoid glycosides from cowpea seeds (Vigna sinensis K.) inhibit LDL oxidation

Six flavonoid glycosides were isolated from the n-butanol fraction of cowpea seeds (Vigna sinensis K.) through silica gel (SiO₂) and octadecyl silica gel (ODS) column chromatographies. Based on their chemical structures determined via interpretation of spectroscopic data including NMR, MS, and IR, the compounds were identified as kaempferol 3-O-β-D-sophoroside (1), quercetin 3-O-β-D-sophoroside (2), isoquercitrin (3), hyperin (4), catechin 7-O-β-D-glucopyranoside (5), and quercetin 3-O-β-D-glucopyranosyl(1→6)-O-β-D-galactopyranoside (6). This is the first report of the isolation of these flavonoids from this plant. Among these flavonoids, compound 2, 5, and 6 significantly inhibited LDL oxidation exhibiting 96.0±0.1 (IC∧50: 3.9 μM), 96.8±1.7 (IC∧50: 2.9 μM), and 97.4±0.1% (IC∧50: 3.5 μM) inhibition, respectively, at a concentration of 40 μM.