Thiohydantoins and hydantoins derived from amino acids as potent urease inhibitors: Inhibitory activity and ligand-target interactions

We report the investigation of hydantoins and thiohydantoins derived from L and d-amino acids as inhibitors against the Canavalia ensiformis urease (CEU). The biochemical in vitro assay against CEU revealed a promising inhibitory potential for most thiohydantoins with six of them showing %I higher than the reference inhibitor thiourea (56.5%). In addition, thiohydantoin derived from l-valine, 1b, as well as the hydantoin 2d, derived from l-methionine, were identified as the most potent inhibitors with %I = 90.5 and 85.9 respectively. Enzyme kinetic studies demonstrated a mixed and uncompetitive inhibition profile for these compounds with K_i values of 0.42 mM for 1b and 0.99 mM for 2d. These kinetic parameters, obtained from traditional colorimetric assay, were strictly related to the K_D values measured spectroscopically by the Saturation Transfer Difference (STD) technique for the urease complex. STD was also used to evince the moieties of the ligands responsible for the binding with the enzyme. Molecular docking studies showed that the thiohydantoin and hydantoin rings can act as a pharmacophoric group due to their binding affinity by hydrogen bonding interactions with critical amino acid residues in the enzyme active and/or allosteric site. These findings agreed with the experimental alpha values, demonstrating that 1b has affinity by free enzyme, and 2d derivative, an uncompetitive inhibitor, has great binding affinity at the allosteric site. The results for the thiohydantoin 1a, derived from d-valine, demonstrated a drastic stereochemical influence on inhibition, kinetics, and binding parameters in comparison to its enantiomer 1b.