Synthesis of new 4-aminobenzoic acid (PABA) hydrazide-hydrazone/sulfonate hybrids and antimicrobial evaluation with ascorbic acid/salicylic acid/N-acetyl cysteine combinations

Abstract

One of the most serious threats to human health is the increasing prevalence of drug-resistant pathogens. The development of new antibiotics capable of combating drug resistance is critical. In various bacteria and plant species, 4-aminobenzoic acid (PABA) is produced and used as a substrate for folate generation. In this study, a new series of PABA analogs were synthesized and evaluated for their antimicrobial activity. Thirteen novel compounds were prepared by linking PABA hydrazide to sulfonate esters via a hydrazone bridge (4a–m). The structures of these compounds were characterized by ¹H and ¹³C NMR and FT-IR spectroscopy as well as by LC-MS. Following structural characterization, all compounds were tested for their antimicrobial activity against Staphylococcus aureus (ATCC 29213), Enterococcus faecium (ATCC 19434), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), and Candida albicans (ATCC 10231) strains. Four compounds were found to have moderate antimicrobial activity against the P. aeruginosa strain. These compounds, including 4e, 4f, 4g, and 4m, containing a hydrazide-hydrazone sulfonate functionality, showed the best MIC value of 64 μg/mL. In addition, synergistic effects of ascorbic acid, salicylic acid, and N-acetyl cysteine (NAC) with synthesized compounds were also investigated. It was observed that the combination of compounds 4f and 4g with NAC showed antipseudomonal activity with MIC values of 32 μg/mL and 16 μg/mL, respectively, against the P. aeuriginosa strain. The antimicrobial activity of 4f and 4g was enhanced by two folds in combination with NAC. Our findings in this study can be crucial for the development of new potent antimicrobial agents.