Potential α-glucosidase inhibitors from thermal transformation of (+)-catechin.

Thermal transformation of the (+)-catechin (1) with heating processing afforded a new oxidation product, gambiriin D (2), along with catechin [6'-8]-catechin (3), and (+)-epicatechin (4). The structure of a new catechin dimer with C-C linkage was determined on the basis of spectroscopic data interpretation. The catechin dimers 2 and 3 exhibited significantly improved inhibitory activities against α-glucosidase, with IC50 values of 0.16±0.2 and 0.14±0.2μM, respectively, when compared to parent (+)-catechin. Kinetic analysis showed that the two effective compounds 2 and 3 have noncompetitive modes of action.