Synthesis, in Silico Molecular Docking Analysis, Pharmacokinetic Properties and Evaluation of Antibacterial and Antioxidant Activities of Fluoroquinolines

Background: Quinolines have demonstrated various biological activities such as antimalarial, antibacterial and anticancer. Hence, compounds with such scaffold have been used as lead in drug development. This project is, therefore, aimed to synthesis and evaluates some biological activities of quinoline analogs.

Methods: 2-Chloro-7-fluoroquinoline-3-carbaldehydes were synthesized by the application of Vilsmeier-Haack reaction. The chlorine in the fluoroquinoline-3-carbaldehyde was replaced with various nucleophiles. The aldehyde functional group was also converted to carboxylic acid and imine groups using oxidizing agent and various amines, respectively. The structures of the compounds synthesized were characterized by spectroscopic methods. Disc diffusion and DPPH assays were used to evaluate the antibacterial and antioxidant activities, respectively. The in silico molecular docking analysis of the synthesized compounds were done using AutoDock Vina against E. coli DNA Gyrase B and human topoisomerase IIα. The drug likeness properties were assessed using SwissADME and PreADMET.

Results: Nine novel quinoline derivatives were synthesized in good yields. The in vitro antibacterial activity of the synthesized compounds was beyond 9.3 mm inhibition zone (IZ). Compounds 4, 5, 6, 7, 8, 10, 15, and 16 exhibited activity against E. coli, P. aeruginosa, S. aureus and S. pyogenes with IZ ranging from 7.3 ± 0.67 to 15.3 ± 0.33 mm at 200 μg/mL. Compound 9 displayed IZ against three of the bacterial strains except S. aureus. The IC for the radical scavenging activity of the synthesized compounds were from 5.31 to 16.71 μg/mL. The binding affinities of the synthesized compounds were from - 6.1 to - 7.2 kcal/mol against E. coli DNA gyrase B and - 6.8 to - 7.4 kcal/mol against human topoisomerase IIα. All of the synthesized compounds obeyed Lipinski's rule of five without violation.

Conclusion: Compounds 4, 5, 6, 7, 8, 10, 15, and 16 displayed activity against Gram positive and Gram negative bacterial strains indicating that these compounds might be used as broad spectrum bactericidal activity. Compound 8 (13.6 ± 0.22 mm) showed better IZ against P. aeruginosa compared with ciprofloxacin (10.0 ± 0.45 mm) demonstrating the potential of this compound as antibacterial agent against this strain. Compounds 5, 6, 7, 8, 9 and 10 showed comparable binding affinities in their in silico molecular docking analysis against E. coli DNA gyrase B. All of the synthesized compounds also obeyed Lipinski's rule of five without violation which suggests these compounds as antibacterial agents for further study. Compounds 7 and 8 were proved to be a very potent radical scavenger with IC values of 5.31 and 5.41 μg/mL, respectively. Compound 5, 6, 8, 10 and 16 had comparable binding affinity against human topoisomerase IIα suggesting these compounds as a possible candidate for anticancer drugs.