Synthesis and antibacterial activity evaluation of N (7) position-modified balofloxacins

A series of small-molecule fluoroquinolones were synthesized, characterized by HRMS and NMR spectroscopy, and screened for their antibacterial activity against MRSA, P. aeruginosa, and E. coli as model G(+)/G(-) pathogens. Compounds 2-e, 3-e, and 4-e were more potent than the reference drug balofloxacin against MRSA and P. aeruginosa (MIC values of 0.0195 and 0.039 mu g/ml for 2-e, 0.039 and 0.078 mu g/ml for each of 3-e and 4-e, respectively). Analysis of the time-dependent antibacterial effect of compound 2-e toward MRSA showed that in the early logarithmic growth phase, bactericidal effects occurred, while in the late logarithmic growth phase, bacterial inhibition occurred because of concentration effects and possibly the development of drug resistance. Compound 2-e exhibited low toxicity toward normal mammalian cell lines 3T3 and L-02 and tumor cell lines A549, H520, BEL-7402, and MCF-7. The compound was not hemolytic. Atomic force microscopy (AFM) revealed that compound 2-e could effectively destroy the membrane and wall of MRSA cells, resulting in the outflow of the cellular contents. Docking studies indicated the good binding profile of these compounds toward DNA gyrase and topoisomerase IV. ADMET's prediction showed that most of the synthesized compounds followed Lipinski's rule of five and possessed good drug-like properties. Our data suggested that compound 2-e exhibited potent anti-MRSA activity and is worthy of further investigation.

Automated summary

A series of small-molecule fluoroquinolones were synthesized and screened for their antibacterial activity. Compound 2-e showed potent anti-MRSA activity, low toxicity towards normal cells, and the ability to disrupt MRSA cell membrane and wall. It also possessed good drug-like properties. These findings suggest that compound 2-e is highly promising for further investigation.