Abstract

The structure and tautomerism of N-(1-naphthyl)-3-amino-5-oxo-4-phenyl-1H-pyrazole-1-carboxamide with antibacterial activity have been investigated with experimental approaches (X-ray studies, IR, ¹H and ¹³C NMR spectra, including NOESY and N-HSQC spectra) and quantum chemical calculations. It is found that the tautomer with the keto group in position 5 is energetically privileged in the crystalline state while in DMSO and water solution the equilibrium is shifted towards the form with the hydroxyl group at this position. These findings are related to antibacterial activity of the studied compound and are crucial for future molecular docking and structure-activity relationship studies.

Keywords: Antibacterial compounds, pyrazolones, quantum chemical calculations, tautomerism, X-ray structure determination.