Design, Synthesis, And Biological Evaluation Of Novel Quinolone Derivatives (Ciprofloxacin And Moxifloxacin Analogues) As Dual Inhibitors Of DNA Gyrase And Topoisomerase IV In Multidrug-Resistant Bacterial Strains

Abstract

Background: The emergence of multidrug-resistant (MDR) bacterial strains has led to reduced efficacy of fluoroquinolones, necessitating the development of novel quinolone derivatives. Ciprofloxacin and Moxifloxacin, key fluoroquinolone antibiotics, target DNA Gyrase and Topoisomerase IV; however, bacterial resistance mechanisms, including target site mutations and efflux pumps, have diminished their clinical effectiveness. This study aims to design, synthesize, and evaluate novel Ciprofloxacin and Moxifloxacin analogues with enhanced antibacterial activity and reduced resistance potential.
Methods: Cipro-1 (piperazine-modified Ciprofloxacin) and Moxi-2 (aminomethyl-modified Moxifloxacin) were synthesized via nucleophilic substitution at the C-7 position. The derivatives were structurally characterized using ¹H and ¹³C NMR, FT-IR, and ESI-MS. In vitro antibacterial activity was assessed via Minimum Inhibitory Concentration (MIC) assays against MDR Gram-positive (MRSA) and Gram-negative (E. coli, K. pneumoniae) bacterial strains. Enzyme inhibition assays measured the IC₅₀ values for DNA Gyrase and Topoisomerase IV. Time-kill kinetics, resistance development studies, and MTT cytotoxicity assays were performed to determine bactericidal effects, mutation frequency, and safety profiles in mammalian cell lines.
Results
• Moxi-2 exhibited the lowest MIC values (0.25 µg/mL against MRSA, 0.5 µg/mL against MDR E. coli), outperforming Moxifloxacin.
• Cipro-1 showed enhanced bacterial uptake, with a MIC reduction against K. pneumoniae from 3.5 µg/mL (Ciprofloxacin) to 2.0 µg/mL.
• Moxi-2 demonstrated the strongest enzymatic inhibition (IC₅₀ = 0.10 µM for DNA Gyrase, 0.18 µM for Topoisomerase IV).
• Time-kill kinetics showed Moxi-2 completely eradicated bacteria by 12 hours, whereas Ciprofloxacin took ~24 hours.
• Moxi-2 and Cipro-1 exhibited significantly lower resistance development (2×–4× MIC fold change) compared to Ciprofloxacin (8×–12× MIC fold change).
• Cytotoxicity assays confirmed high selectivity for bacterial cells, with Moxi-2 having the highest Selectivity Index (SI = 550.0).
Conclusion: The novel quinolone derivatives Cipro-1 and Moxi-2 demonstrated enhanced antibacterial potency, dual inhibition of DNA Gyrase and Topoisomerase IV, and lower resistance potential than their parent compounds. Moxi-2, in particular, exhibited superior efficacy, rapid bacterial clearance, and a favorable safety profile, making it a promising candidate for further preclinical development and clinical translation in combating MDR infections.