Mercapto-pyridines and mercapto-pyrimidines as urease inhibitors

Several mechanisms of urease hydrolysis of urea have been proposed. Major advances in this area were made when it was recognized that nickel played an important role in the hydrolysis of urea. Two recent literature reports indicate that dipyridyls can be used to complex with nickel. In both of these reports, the dipyridyl was used as a ligand for stabilizing an intermediate nickel(II) complex. In addition, it is known that heterocyclic mercapto compounds inhibit urease through the formation of disulfide bonds. Because of the stability of these complexes, compounds with similar structures were examined as potential urease inhibitors. From our initial tests it was not clear which functional group of these multifunctional compounds was responsible for the inhibition or whether it was necessary to retain the disulfide linkage for other potential inhibitors in this class. Therefore, a series of mercapto-pyridines, a series of mercapto-pyrimidines, and pyridine-N-oxide itself were tested for their urease inhibitory characteristics. It appears that the key functional group responsible for the inhibition is the mercapto group itself, with the N-oxide function adding little to the urease inhibitory power in the monomeric compounds. It is suspected that the presence of the N-oxide moiety in the dimeric compounds results in increases in solubility and a weakening of the strength of the disulfide bond, thus producing a more active inhibitor.