Flavonoids with α-glucosidase inhibitory activities and their contents in the leaves of Morus atropurpurea

Background: This study aims to isolate the alpha-glucosidase inhibitory compounds from mulberry leaves (Morus atropurpurea Roxb., Moraceae) and to develop an analytical method for quantification of the compounds. Methods: Four flavonoids, rutin (1), isoquercetin (2), kaempferol-3-O-rutinoside (3) and astragalin (4), were isolated by column chromatography from mulberry leaf water extracts (MWE). The alpha-glucosidase inhibitory activities of MWE and the four isolated compounds were evaluated by a microplate-based in vitro assay. The content of the isolated flavonoids in M. atropurpurea leaves purchased from different local herbal stores or collected in different locations was determined by high performance liquid chromatography. Results: The four flavonoids (1-4) showed a-glucosidase inhibitory activities, with rutin (1) and astragalin (4) showing high a-glucosidase inhibitory activities (IC50 values of 13.19 +/- 1.10 and 15.82 +/- 1.11 mu M, respectively). The total contents of the four flavonoids were different among eight samples examined, ranging from 4.34 mg/g to 0.53 mg/g. Conclusions: The four flavonoids in M. atropurpurea leaves could inhibit a-glucosidase activity.