α-Glucosidase Activity Of Oleanolic Acid And Its Oxidative Metabolites: DFT and docking studies

A natural pentacyclic triterpenoid, oleanolic acid 1 and its biotransformed metabolites 2 and 3 are potential α-glucosidase inhibitors. To elucidate the inhibitory mechanism of compounds 1-3 against α-glucosidase, (i) their electronic and optical properties were calculated using DFT and TD-DFT methods at the B3LYP/6-31G(d) level of theory in gas and IEF-PCM solvent; and (ii) their binding energies to α-glucosidase were determined via a docking study. DFT results showed that the α-glucosidase inhibtion is mainly dependent on the polarity parameters of the studied compounds. Docking results revealed that the activity is increased with binding energies (i.e. the stability of ligand-receptor complex). The NMR spectroscopic data revealed that ¹³C and ¹H chemical shifts of 1 and its hydroxylated metabolites 2 and 3 are well predicted with R²of 99% and 90%, respectively. The UV/vis spectra of substrate 1 and its transformed products 2 and 3 are well reproduced. The detailed assignments of ¹H and ¹³C chemical shifts, and bathochromic shift of λ^MAXabsorption bands have been presented.