Triterpenes as uncompetitive inhibitors of alpha-glucosidase from flowers of Punica granatum L.

摘要

The alpha-glucosidase and maltase inhibitory effects of Punica granatum L. flowers (PGF) were investigated. The methanol extract (PGFMe), n-hexane extract (PGFH), chloroform extract (PGFC) and the remaining water fraction (PGFW) were assayed for their alpha-glucosidase and maltase inhibitory effects. PGFW showed potent alpha-glucosidase inhibition with IC50 of 0.8 mu g/mL followed by PGFMe (IC50 of 4.0 mu g/mL) then PGFC (IC50 of 5.21 mu g/mL) in comparison to acarbose (0.9 mu M). Due to its selectivity towards alpha-glucosidase, PGFC was subjected to bioactivity-guided isolation of its main active constituents. Five known compounds (1-5) were identified as beta-sitosterol (1), oleanolic acid (2), ursolic acid (3), p-coumaric acid (4) and apigenin (5). Ursolic and oleanolic acids showed potent alpha-glucosidase inhibition (IC50 of 39.0 and 35.0 mu M, respectively), while they did not show significant maltase inhibition. Kinetic study using the double Lineweaver-Burk plot revealed that ursolic acid uncompetitively inhibited alpha-glucosidase in comparison with acarbose as a competitive inhibitor.