α-Glucosidase Inhibitory and Antioxidant Activities of Ethanolic Extracts of Different Parts of Lysiphyllum strychnifolium and Their Constituents

ABSTRACT The crude ethanolic extracts of different parts (root, stem, leaves and flower) of Lysiphyllum strychnifolium were tested for α-glucosidase inhibitory and antioxidant activities. Since all extracts showed good inhibitory activity, active constituents were isolated. Thirteen known compounds, including three dihydroflavanones, three dihydrochalcones, two stilbenes, flavan-3-ol, flavonol, cyclitol, phenolic ethyl ester and phenolic acid were isolated, and their α-glucosidase inhibitory effect and antioxidant activity were evaluated. Phloretin 4’-O-(6”-O-galloyl)-β-D-glucoside from the leaves extract showed potent α-glucosidase inhibitory activity (IC50 = 0.0162 ± 0.0014 mM) and potent antioxidant activity (IC50 = 19.26 ± 0.95 μM), each more potent than the positive controls. The compounds were investigated for their structure–activity relationship (SAR) in both activities. The number and position of hydroxy groups seemed to play a crucial role in increasing α-glucosidase inhibitory and antioxidant activities.