Background: The escalating crisis of antimicrobial resistance (AMR) necessitates the continuous discovery of novel therapeutic agents. Quinoline scaffolds represent a privileged structural motif in medicinal chemistry, exhibiting a broad spectrum of pharmacological activities, particularly as antimicrobial agents. However, the rapid emergence of multi-drug resistant (MDR) pathogens has rendered many existing quinoline-based drugs ineffective.

Objective: This study aims to design, synthesize, and evaluate a novel series of quinoline-derived Schiff base hybrids (4a–j) to overcome MDR mechanisms, specifically targeting Gram-negative ESKAPE pathogens.

Method: The target compounds were synthesized via a condensation reaction between 4-chloroquinoline-3-carbaldehyde and various substituted anilines. The structures were elucidated using FT-IR, ¹H NMR, and ¹³C NMR spectroscopy. In vitro antimicrobial activity was assessed using the broth microdilution method against a panel of six bacterial strains. Molecular docking studies were performed to evaluate the binding affinity of the compounds against DNA gyrase (PDB ID: 4B7Q).

Key Results: Compound 4c, featuring a 4-nitrophenyl substituent, exhibited the most potent antimicrobial activity, with a minimum inhibitory concentration (MIC) of 3.12 µg/mL against Acinetobacter baumannii. Molecular docking revealed that 4c forms critical hydrogen bonds with Asp73 and water-mediated interactions with the active site of DNA gyrase.