Design, synthesis, biological evaluation and mechanistic investigation of quinazolinone-hydrazonothioate conjugates against multidrug-resistant bacteria.

Three new series of quinazolinone derivatives (5a-d, 5e-h, 5i-l) were developed through attachment of aryl hydrazone moieties to the quinazolinone core via methanethioate linker. The resulting quinazolinone-hydrazonothioate conjugates 5a-l were evaluated against clinically isolated multidrug-resistant (MDR) pathogens, including Klebsiella pneumoniae, Pseudomonas aeruginosa, Streptococcus pneumoniae, Bacillus cereus, and Campylobacter jejuni. Agar-well diffusion and minimum inhibitory concentration (MIC) assays identified 5a, 5e, and 5 l as the most active derivatives, with 5a and 5e showing the broadest spectrum and lowest MIC values, ranging from 45 to 85 μg/mL, notably against C. jejuni and K. pneumoniae. The antibacterial effect of the selected quinazolinones was associated with oxidative stress leading to higher malondialdehyde and intracellular ROS than untreated controls. Bacterial carbonic anhydrase inhibition assays were also conducted on selected derivatives (5a, 5d, 5e, 5 h, 5i, and 5 l) on both α- and γ-CA isoforms, with 5a achieving the strongest inhibition (69.8% and 77.8%, respectively). Hemolytic and WI-38 normal cell cytotoxicity assays for 5a, 5e, and 5 l were also evaluated, yielding favorable selectivity indices, most notably for 5a, which reached a CC₅₀ of 483.5 μg/mL and selectivity indices up to 6.05. The molecular docking for the selected compounds (5a, 5e, and 5 l) was also tested against DNA gyrase that is essential for bacterial growth and survival, giving a favorable docking scores of -8.78, -9.62, and - 8.35 kcal/mol, respectively.