The screening of potential α-glucosidase inhibitors from the Polygonum multiflorum extract using ultrafiltration combined with liquid chromatography-tandem mass spectrometry

α-Glucosidase inhibitors have been used for the management of type 2 diabetes (T2DM) for a long time. The natural α-glucosidase inhibitors from Chinese herbal medicine have become an attractive therapeutic approach for treating T2DM due to their low toxicity. In this study, a new kind of in vitro α-glucosidase inhibition assay based on using maltose as the substrate was developed, and this new established method was used to determine the α-glucosidase inhibitory activities of Polygonum multiflorum and four anthraquinone compounds. As a result, Polygonum multiflorum showed 50% α-glucosidase inhibition at the concentration of 0.0032 mg mL−1 and four anthraquinone compounds including emodin, aloe-emodin, physcion and rhein showed strong α-glucosidase inhibitory activities with IC50 values ranging from 4.12 μM to 5.68 μM, respectively. Moreover, the centrifugal ultrafiltration with LC-ESI-MSn was used to screen and identify active α-glucosidase inhibitors from Polygonum multiflorum extract and nine small-molecule active compounds were successfully identified as potential α-glucosidase inhibitors. Five compounds belonged to the anthraquinone group including emodin, physcion, aloe-emodin, rhein and physcion-8-O-glucoside, while the others were catechin, resveratrol, 2,3,5,4′-tetrahydroxystilbene-2-O-glucoside and torachryson-8-O-glucoside.