Synthesis, spectroscopic characterization and in vitro biological studies on azo colorants containing a 3-amino-6-bromopyridine nucleus

Four new heterocyclic azo dyes (D1–D4) were synthesized from 3-amino-6-bromopyridine via a diazo-coupling approach at 0–4 °C. Structural characterization using FT-IR, 1 H NMR, ESI-MS, and UV-visible spectroscopy confirmed the formation of the target compounds with yields ranging from 68% to 81%. Electronic absorption spectra in various solvents (DMF, DMSO, CHCl 3 , and Methanol) revealed significant bands at 338–495 nm, attributed to n→π* and π→π* transitions. Biological evaluation demonstrated that all synthesized dyes possess appreciable antimicrobial properties. In antibacterial assays, dyes D2 and D3 exhibited the highest potency against Staphylococcus aureus and Pseudomonas aeruginosa. Antifungal testing against Aspergillus niger and Candida albicans established an efficacy sequence of D2 > D3 > D4 > D1. These results were corroborated by in silico molecular docking studies, where compound D2 showed superior binding energy (–5.13 kcal/mol against E.coli and –7.6 kcal/mol against cytochrome P450 14α-sterol demethylase), outperforming standard drugs like Ciprofloxacin and Fluconazole in theoretical binding affinity. These findings suggest that these pyridine-incorporated azo dyes are promising candidates for developing new antibiotic pharmaceuticals.