Rational Design and Biological Evaluation of Imidazole-Based Tetrapeptides as Antibacterial Leads Against Staphylococcus aureus.

The increasing prevalence of methicillin and vancomycin-resistant Staphylococcus aureus (MRSA/VRSA) necessitates new antibacterial agents. Penicillin-binding protein 2a (PBP2a) plays a crucial role in bacterial cell wall synthesis. In this work, 125 imidazole-based tetrapeptides were rationally designed and evaluated in silico and experimentally. Molecular docking studies revealed binding energies from -6.6 to -4.0 kcal/mol against MRSA target. The six most promising compounds (A-F) were synthesized and screened against methicillin-susceptible S. aureus (MSSA), MRSA and VRSA. Compound C showed the most promising antibacterial analogue with minimum inhibitory concentration (MIC) of 29.8 ± 4.2 μg/mL among the analogues. Time-kill assays demonstrated bactericidal activity against MSSA and MRSA and bacteriostatic activity against VRSA. All compounds showed < 5% haemolysis, suggesting low toxicity. ADME predictions indicated favourable physicochemical properties and safety profiles. The molecular dynamics simulation (MDS) for compound C shows stable interactions with Ser403, Tyr446, Glu447, Ser462, Lys597, Ser598 and Thr600 key residues in the PBP2a active site. The DFT study confirms the stability of compound C in the PBP2a active site with a binding energy of -42.73 kcal/mol. Overall, compound C is a promising lead for anti-staphylococcal drug development; however, the mechanism of action requires further experimental validation.