The present research work aims on the synthesis of new lomefloxacin derivatives improving antibacterial activity. Structure–activity relationship (SAR) studies have demonstrated that the 1,4-dihydro-4-oxo-3-pyridinecarboxylic acid moiety plays a vital role in maintaining antibacterial activity. However, the increasing prevalence of multidrug-resistant (MDR) infections has greatly decreased the effectiveness of many existing fluoroquinolones, highlighting the immediate need to develop novel analogues with enhanced potency, selectivity and activity against resistant strains. The structural modifications at the N-1, C-7 and C-8 positions of the quinolone nucleus are known to influence drug–target interactions, enhance lipophilicity and facilitate better cellular penetration, thereby contributing to improved biological activity. Lomefloxacin was used as a prototype molecule in the synthesis of novel derivatives. The modification mainly involves an acylation reaction with chloroacetyl chloride, which resulted in the synthesis of N-(chloroacetyl)lomefloxacin. This reaction takes place at the C-4 position of the piperazine ring, with chloroacetyl chloride. The chloroacetyl chloride acts as a linker. The resultant intermediate compound (II) N-(chloroacetyl) lomefloxacin was subsequently reacted with a series of aromatic amines to yield aromatic amide derivatives (IIIa–f). In this phase, the chloroacetyl group's chlorine atom was replaced by an amine group via the creation of an amide bond. Standard analytical methods were used to analyse the synthesised compounds, such as melting point measurement, elemental analysis, FT-IR, ¹H NMR and mass spectrometry. All spectral data were recorded further, quantitative structure-activity relationship (QSAR) parameters such as Log P and drug-likeness were used to examine the physicochemical and pharmacokinetic properties of the synthesised derivatives. Antibacterial activity was evaluated against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) strains at four concentrations (0.25, 0.5, 0.75 and 1.0 mg/mL), using lomefloxacin as the reference drug Compounds IIIa and IIIb in the series showed considerable antibacterial activity against both Staphylococcus aureus and Escherichia coli indicating that they could be attractive antibacterial agents for future research.
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