Synthesis and Biological Evaluation of Novel Bisbenzimidazoles as Escherichia coli Topoisomerase IA Inhibitors and Potential Antibacterial Agents

Novel bisbenzimidazole inhibitors of bacterial type IA topoisomerase are of interest for the development of new antibacterial agents that are impacted by target-mediated cross resistance with fluoroquinolones. The present study demonstrates the successful synthesis and evaluation of bisbenzimidazole analogues as Escherichia coli topoisomerase IA inhibitors. 5-(4-Propylpiperazin-1-yl)-2-[2′-(4-ethoxyphenyl)-5′-benzimidazolyl]benzimidazole (12b) showed significant relaxation inhibition activity against EcTopo 1A (IC50 = 2 ± 0.005 μM) and a tendency to chelate metal ion. Interestingly, these compounds did not show significant inhibition of E. coli DNA gyrase and hTop 1 even up to 100 μM. Compound 12b has shown lowest MIC against E. coli strains among 24 compounds evaluated. The binding affinity constant and binding free energy of 12b with EcTopo 1A was observed 6.8 × 106 M–1 and −10.84 kcal mol–1 from isothermal titration calorimetry (ITC), respectively. In vivo mouse systemic infection and neutropenic thigh model experimental results confirmed the therapeutic efficacy of 12b, suggesting further development of this class of compounds as antibacterial agents.