Design, synthesis, antimicrobial and antioxidant evaluation, cytotoxicity assessment, and molecular dynamics-based computational studies of novel PABA analogues as dual DHPS/DHFR inhibitors

Abstract

The rapid emergence of antimicrobial resistance (AMR) has become a global threat, limiting the clinical effectiveness of the drugs against microbial infections. As Methicillin-resistant Staphylococcus aureus (MRSA) and Extensively drug-resistant (XDR) Escherichia coli continue to evolve rapidly, it is critical to develop novel therapeutic agents and structurally unique antibacterial medicines. The selective bacterial folate biosynthesis pathway, which includes dihydropteroate synthase (DHPS) and dihydrofolate reductase (DHFR), represents an attractive therapeutic target; however, the alarming rise of microbial sulfonamides necessitates the development of novel inhibitors. Sulphonamide antibiotics are analogues of p-aminobenzoic acid (PABA), which serves as a substrate for folate biosynthesis. Taking this into account, we developed novel PABA-imidazole analogues to combat antimicrobial resistance. In this study we designed and synthesized seven novel PABA analogues and characterized them by various spectroscopy techniques. These synthesized PABA analogues show comparatively better efficiency against both the Gram-positive (S. aureus and S. pyogenes) and Gram-negative (E. coli and P. aeruginosa) strains. Furthermore, they also show potential activity against MRSA and XDR E. coli. The DHPS/DHFR enzyme assay demonstrated that the SB2 compound suppresses the sulfamethoxazole (SUL) in DHPS inhibition, and the SB5 compound shows comparatively increased DHFR inhibitory activity compared to the trimethoprim (TMP). These results have been validated by molecular dynamics simulations and free energy analyses. In addition, the lead compounds also showed strong antioxidant activity, low cytotoxicity, and good DNA nicking behaviour, which supports their therapeutic potential.