Bioassay-guided isolation of antioxidant and α-glucosidase inhibitory constituents from stem of Vigna angularis.

Stem of Vigna angularis (Willd.) Ohwi & H. Ohashi (VAS) is a main byproduct with considerable bioactivities. In present study, a bioassay-guided phytochemical investigation was used and led to the isolation of 16 compounds including one new compound (1) and one compound (2) isolated from nature source firstly along with 14 known compounds (3-16). The structures of isolates were identified by NMR and HR-ESI-MS data. The ability of antioxidant and α-glucosidase inhibition of the compounds were measured in vitro. Most of the ingredients shown strong ABTS radical scavenging activity (IC₅₀ = 4.21-14.93 μM) and α-glucosidase inhibitory activity (IC₅₀ = 0.05-34.14 μM). Enzyme kinetic analysis and molecular docking of compounds 1 and 2 were conducted. Compounds 1 and 2 were competitive inhibitor for α-glucosidase, with the inhibition kinetic constant value of 1.03 and 1.06 μM, respectively. The potent α-glucosidase inhibitory ability of compounds 1 and 2 resulted from firm binding with the active site of α-glucosidase.