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-beta-d-sophoroside (1), quercetin 3-O-beta-d-sophoroside (2), isoquercitrin (3), hyperin (4), catechin 7-O-beta-d-glucopyranoside (5), and quercetin 3-O-beta-Dglucopyranosyl( 1 -> 6)-O-beta-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 (IC50: 3.9 mu M), 96.8 +/- 1.7 (IC50: 2.9 mu M), and 97.4 +/- 0.1% (IC50: 3.5 mu M) inhibition, respectively, at a concentration of 40 mu M.