Synthesis of new metacetamol azo derivatives and assessment of their antibacterial and pharmacological potential

Abstract

Background: Metacetamol, a regioisomer of paracetamol known for its significantly lower toxicity, remains largely underexplored in medicinal chemistry despite its potential as a safer therapeutic scaffold. While paracetamol can cause hepatotoxicity through the accumulation of toxic metabolites, metacetamol presents an advantageous starting point for derivatisation and developing new pharmacological agents.

Objective: This study aims to synthesise new metacetamol azo derivatives 1–18 and perform structural elucidation with FTIR and NMR spectroscopies. The research further evaluates their antibacterial efficacy through both in vitro assays and in silico modelling.

Methods: The compounds were produced via a diazocoupling reaction between substituted anilines and metacetamol. Antibacterial potential against Staphylococcus aureus and Escherichia coli was pre-screened using the Kirby-Bauer disc diffusion, followed by the turbidimetric kinetic method for Minimum Inhibitory Concentrations (MIC) determination. Molecular docking was performed against the FtsA enzyme to investigate the mechanism of action, while SwissADME predicted druglikeliness and pharmacokinetic properties.

Result: Metacetamol azo 1–18 were successfully synthesised with yields ranging from 32% to 95%. Most derivatives exhibited notable antibacterial inhibition compared to the parent metacetamol, which showed no activity. Specifically, compound 2 (m-F) demonstrated the highest activity against E. coli (MIC = 147.47 ppm), comparable to the reference drug, ampicillin (MIC = 118.14 ppm). All derivatives were found to comply with Lipinski’s Rule of Five, suggesting high oral bioavailability and favourable GI absorption.

Discussion: The enhanced potency of compound 2 (m-F) is attributed to the high electronegativity, specific meta-positional effect and small atomic size of the fluorine atom. These factors minimise steric hindrance while strengthening the C-F bond against metabolic transformation. Molecular docking reveals that 2 (m-F) establishes stable hydrogen bonds with key residues of LYS17 and LYS254 in the FtsA enzyme, potentially inhibiting bacterial cell division. Furthermore, the azo linker improves molecular conjugation and binding affinity, while the secondary phenyl ring facilitates critical interactions with bacterial proteins through π-π stacking and hydrophobic forces.

Conclusion: Collectively, the strategic incorporation of an azo linker into metacetamol scaffold significantly elevates antibacterial activity while preserving desirable pharmacokinetic characteristics. These findings provide a promising starting point for optimising metacetamol-based agents as potential therapeutic candidates.