Epimerization of epigallocatechin gallate to gallocatechin gallate and its anti-diabetic activity

Compared with epigallocatechin gallate (EGCG), its epimer gallocatechin gallate (GCG) is more stable and more bioactive, even when least contained in green tea. In this study, EGCG can be selectively epimerized into GCG catalyzed by a phosphate buffer (pH 5.8) at 60 A degrees C for 2 h with the highest yield of 65.6 %. A plausible mechanism for this conversion was also presented. To evaluate the anti-diabetic activity of GCG, we had investigated an oral glucose tolerance test and determined the plasma levels of glucose, insulin, triglyceride, and free fatty acid in a streptozotocin-induced diabetic rat model system. The results suggested that both GCG and EGCG might have anti-diabetic effects by increasing sensitivity of insulin, and GCG is more active than EGCG.