Synthesis of New Pyrazolo Pyrimidine Disazo Dyes, Theoretical and Experimental Comparison of their Characteristic Properties and <i>in silico</i> Prediction of their Possible Antibacterial Activity

This study outlines the synthesis and both experimental and theoretical characterization of novel 5-(4-arylazo-3-methyl-1H-pyrazol-5-ylazo)-4-hydroxy-6-methyl-1H-pyrimidin-2-one dyes (3a–3e). Aniline and 4-substituted aniline derivatives, along with 3-aminocrotonitrile, were used as starting materials. The intermediates underwent cyclization with hydrazine monohydrate to produce mono-azo dyes (2a–2e), which were then diazotized. The resulting salts were reacted with ethyl acetoacetate to obtain intermediates. These intermediates were subsequently reacted with urea in the presence of heat to obtain the desired dyes (3a–3e). The synthesized dyes were characterized via FT-IR and 1 H-NMR spectroscopy for their structural confirmation. The effects of various solvents (six in number), substituents and acid-base characteristics were examined via UV–Vis spectroscopy. Furthermore, DFT calculations were performed to investigate the electronic structure and reactivity of the compounds, and the results were compared with experimental findings. Computational analyses included localized orbital locator (LOL), electron localization function (ELF), and density of states (DOS) analyses to explore the electronic structure of the compounds. Intermolecular interactions, specifically hydrogen bonding and van der Waals interactions, were identified and examined via non-covalent interaction (NCI) analysis as well as reduced density gradient analysis. As per HOMO–LUMO energy gap of compounds, it is found that dye 3cwas found to have a softer electronic character and higher reactivity. In addition to DFT, a purely computational molecular docking analysis was performed using Thymidylate Kinase receptor (PDB, 4qgg) to provide an in silicoprediction of the possible antibacterial relevance of the compounds. The binding affinity of dye 3c was calculated as −8.2 kcal/mol. However, all biological interpretations in this study are purely computational and lack experimental validation. The reliability of the docking results and the stability of the complexes were further supported through 100 ns molecular dynamics (MD) simulations. The results of this study indicate that compound 3c may be a promising candidate for future research; however, its antibacterial activity remains a theoretical prediction requiring experimental confirmation.