Enzyme reaction-guided identification of active components from the flowers of Sophora japonica var. violacea
The flower of S. japonica is a favorite food and used as traditional medicine. In the present study, a facile and effective method based on the changes in the composition before and after the enzyme reaction was established to screen the active compounds from complex natural products. The separation of an active compound from the ethanolic extracts of Sophora japonica var. violacea, which exhibited the α-amylase inhibitory activity is presented as an example. The analysis of HPLC showed that one component was reduced by 25% after the enzyme reaction. The potential active compound was isolated via LH-20 gel permeation chromatography and identified as kaempferol 3-O-α-L-rhamnopyranosyl-(1 → 6)-β-D-galactopyranosyl-7-O-α-L-rhamnopyranoside by 1H and 13C NMR. The in vitro test indicated that the compound had the α-amylase inhibitory activity, and the IC50 was 88.56 ± 0.60 μg mL−1. The molecular docking study of this compound showed that the compound enfolded in the active sites of α-amylase completely and interacted with the amino acid residues through hydrogen bonds, van der Waals force and hydrophobic interactions.