Preparation of theasinensin A and theasinensin B and exploration of their inhibitory mechanism on α-glucosidase

Theasinensin A (TSA) and theasinensin B (TSB), dimers of tea catechins produced during the processing of oolong tea and black tea, had superior inhibitory effects on alpha-glucosidase. However, the potential inhibitory mechanisms on alpha-glucosidase are still unclear. In the present study, TSA and TSB were chemically synthesized and purified, and their inhibitory effects on alpha-glucosidase and potential mechanisms were investigated. The results showed that TSA and TSB could inhibit the activity of alpha-glucosidase in a reversible and noncompetitive manner with IC(50)values of 6.342 and 24.464 mu g mL(-1), respectively, which were much lower than that of acarbose. The fluorescence and circular dichroism spectra revealed that TSA and TSB could alter the microenvironment and the secondary structure of alpha-glucosidase, thereby decreasing the alpha-glucosidase activity. Molecular docking results indicated that both TSA and TSB had a strong binding affinity to alpha-glucosidase by hydrophobic interactions and hydrogen bonds. Moreover, the stronger inhibition of TSA on alpha-glucosidase might be related to the closer binding site to the active site pocket of alpha-glucosidase.