Screening and structural characterization of potential α-glucosidase inhibitors from Radix Astragali flavonoids extract by ultrafiltration LC-DAD-ESI-MSn

Inhibition of intestinal alpha-glucosidase activity is one important mechanism for the management of diabetes mellitus (DM). Identifying plants with alpha-glucosidase inhibitory activities and screening active compounds (alpha-glucosidase inhibitors) in them has become a popular field of research in the treatment of DM. In the present study, we used an in vitro assay of ultraviolet spectrophotometry to evaluate the a-glucosidase inhibitory activity of Radix Astragali flavonoids extract (RAFE). Then, ultrafiltration liquid chromatography with photodiode array detection coupled to electrospray ionization tandem mass spectrometry (ultrafiltration LC-DAD-ESI-MSn) was used to screen the active compounds in RAFE. As a result, the concentration (final) of RAFE required for 50% enzyme inhibition (IC50) was calculated as 2.888 mg mL(-1). Through ultrafiltration LC-DAD-ESI-MSn analysis, seven compounds were identified as potential active compounds. They were calycosin-7-O-beta-D-glucoside, biochanin A, calycosin-7-O-beta-D-glucoside-6 ''-O-malonate, ononin, calycosin, formononetin-7-O-beta-D-glucoside-6 ''-O-malonate and formononetin. Then, two of the potential active compounds, biochanin A and formononetin, were evaluated for alpha-glucosidase inhibitory activity. Their IC50 values were calculated as 0.020 mM and 0.027 mM respectively, while that of the reference drug acarbose was calculated as 0.382 mM.