Inhibition of Protein Tyrosine Phosphatase 1B (PTP1B) and α-glucosidase by Xanthones from Cratoxylum Cochinchinense, and Their Kinetic Characterization

Cratoxylum cochinchinense displayed significant inhibition against protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase, both of which are key target enzymes to attenuate diabetes and obesity. The compounds responsible for both enzymes inhibition were identified as twelve xanthones (1-12) among which compounds 1 and 2 were found to be new ones. All of them simultaneously inhibited PTP1B with ICs of (2.4-52.5 µM), and α-glucosidase with IC values of (1.7-72.7 µM), respectively. Cratoxanthone A (3) and γ-mangostin (7) were estimated to be most active inhibitors against both PTP1B (IC = 2.4 µM for 3, 2.8 µM for 7) and α-glucosidase (IC = 4.8 µM for 3, 1.7 µM for 7). In kinetic studies, all isolated xanthones emerged to be mixed inhibitors of α-glucosidase, whereas they behaved as competitive inhibitors of PTP1B. In time dependent experiments, compound 3 showed isomerization inhibitory behavior with following kinetic parameters: K = 2.4 µM; k = 0.05001 µM S and k = 0.02076 µM S.