Synthesis, Molecular Docking And Biological Evaluation Of Metronidazole Derivatives As Potent Helicobacter Pylori Urease Inhibitors

Urease (urea amidohydrolase; E.C.3.5.1.5) is an enzyme that catalyzes hydrolysis of urea to ammonia and carbamate, which is the final step of nitrogen metabolism in living organisms. It is widely distributed in a variety of bacteria such as Helicobacter pylori and Proteus mirabilis. Helicobacter pylori is a Gram-negative microaerophilic bacterium that infects up to 50% of the world's human population. Urease that comes from Helicobacter pylori is now accepted as a major cause of peptic ulcers. Many urease inhibitors have been investigated in the past decades, like phosphorodiamidates, hydroxamic acid derivatives and imidazoles, but part of them are prevented from using in vivo because of their toxicity or instability and part of them had side effects. Thus, seeking novel urease inhibitors with good bioavailability and low toxicity is significative.Bacterial ureases, including H. pylori urease, are large heteropolymeric metalloproteins with nickel (Ⅱ) ions present in their active sites. A significant amino acid sequence similarity has been observed between all ureases of a bacterial origin. A superposition of the structures of uninhibited and inhibited H. pylori urease reveals a flap motion of the segment composed of residues a313-α346 forming a helix-turn-helix motif which opens the active site when the inhibitor is bound and closes it when not bound. In the X-ray structures available for the H. pylori urease, the two nickels were coordinated by Hisl36, His138, Kcx219, His248, His274, Asp362, and water molecules.Metronidazole (1-[2-hydroxyethyl]-2-methyl-5-nitroimidazole), has been widely used as an antimicrobial medicine. The metronidazole derivative compounds exhibited broad variety of biological activities including urease inhibitors. Also, some salicylic acid derivatives were reported as urease inhibitors. Herein several substituted salicylic acids were selected to join together with metronidazole and 14 new nitroimidazoles (3a-f and 4a-h) of two series were synthesized to test their H. pylori urease inhibitory activities. Most of the nitroimidazoles showed good inhibitory activities, especially nitroimidazole 4b (IC50= 26μM) and 4g (IC50=12μM) exhibited potent in vitro inhibitory activities, which were comparable to acetohydroxamic acid (AHA), a reversible urease inhibitor.A docking analysis using the AutoDock 4.0 program could explain the inhibitory activities of compound 4g against H. pylori urease. In the binding model, compound 4g formed two hydrogen bonds with the His221 and Met366. The result of molecular docking study could explain the inhibitory activities of compound 4g against H. pylori urease.