Coumarins with α-glucosidase and α-amylase inhibitory activities from the flower of Edgeworthia gardneri

The flower of Edgeworthia gardneri is consumed in beverages in Tibet and has potential health benefits for diabetes. As a part of our continuous studies on dietary supplements for diabetes, two monomers, five dimers and one trimer of coumarins were isolated from the flowers of E. gardneri. One dimer was a new compound (1) and its structure was determined by spectroscopic methods, including multiple NMR techniques and mass spectrometry. The inhibitory activities of all coumarins against a-amylase and a-glucosidase were evaluated. Compound 4 displayed potent inhibitory effect on both a-amylase and a-glucosidase, with an IC50 of 90 and 86 mu g/mL, respectively. The IC50 of compound 3 against a-glucosidase was 18.7 mu g/mL, and its inhibition mode was noncompetitive. Based on the fluorescence analysis, the binding constant and the number of binding sites of compound 3 were calculated as 2.05 x 10(5) and 124, respectively. Furthermore, the interaction between compound 3 and alpha-glucosidase was a spontaneous process that was driven mainly by hydrophobic force. This study could facilitate the utilization of E gardneri as functional food ingredient. (C) 2015 Elsevier B.V. All rights reserved.