New 7-piperazinylquinolones containing (benzo[ d ]imidazol-2-yl)methyl moiety as potent antibacterial agents

series of 7-piperazinylquinolones containing a (benzo[ d ]imidazol-2-yl)methyl moiety were designed and synthesized as new antibacterial agents. The antibacterial activity of title compounds was evaluated against Gram-positive ( Staphylococcus aureus , Staphylococcus epidermidis and Bacillus subtilis ) and Gram-negative ( Escherichia coli , Pseudomonas aeruginosa and Klebsiella pneumonia ) microorganisms. Among the tested compounds, the N1-cyclopropyl derivative 4a showed the highest activity against S. aureus , S. epidermidis , B. subtilis and E. coli ( MIC = 0.097 g/mL), being 2–4 times more potent than reference drug norfloxacin. A structure-activity relationship study demonstrated that the effect of the nitro group on the benzimidazole ring depends on the pattern of substitutions on the piperazinylquinolone.