Bio-assay guided isolation and identification of α-glucosidase inhibitors from the leaves of Aquilaria sinensis

Eight alpha-glucosidase inhibitors including four new compounds were isolated from the 70% aqueous ethanolic extract of leaves of Aquilaria sinensis (Lour.) Gilg by activity-directed fractionation and purification processes. The ethanolic extract was first separated into petroleum ether, ethyl acetate, n-butanol and water soluble fractions and screened for inhibitory activity against alpha-glucosidase. Further activity-directed investigation lead to the isolation of four new compounds with moderate inhibitory activity, viz, aquilarisinin (1), aquilarisin (2), hypolaetin 5-O-beta-D-glucuronopyranoside (3) and aquilarixanthone (4) from the n-butanol fraction, and four known compounds showing potent activity including mangiferin (5), iriflophenone 2-O-alpha-L-rhamnopyranoside (6), iriflophenone 3-C-beta-D-glucoside (7) and iriflophenone 3,5-C-beta-D-diglucopyranoside (8) from the most potent ethyl acetate fraction. The structures of these compounds were determined by extensive spectroscopic analyses, including IR. UV, ESIMS, HRESIMS, 1D and 2D NMR. (C) 2011 Published by Elsevier Ltd.