Preparation of theasinensins A and B and exploration of their inhibitory mechanism on -glucosidase
Theasinensin A (TSA) and theasinensin B (TSB), dimers of tea catechins produced during the processing of Oolong tea and black tea, showed superior inhibitory effect on -glucosidase. However, the potential inhibitory mechanisms on -glucosidase are still unclear. In the present study, TSA and TSB were chemically synthesized and purified, their inhibitory effects on -glucosidase and potential mechanisms were investigated. The results showed that TSA and TSB could inhibit the activity of -glucosidase in a reversible and noncompetitive manner with IC50 values of 6.342 and 24.464 g/mL, 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 -glucosidase, thereby decreased the -glucosidase activity. The molecular docking indicated that both TSA and TSB had strong binding affinity to -glucosidase by hydrophobic interaction and hydrogen bonds. Moreover, the stronger inhibition of -glucosidase by TSA might be related to the closer binding site to the active site pocket of -glucosidase.