Synthesis and spectroscopic characterization of thioparacetamol: Evidence for solvent-dependent changes in conformational equilibrium

LEZAMA, JOSÉ OSVALDO GUY; ARENA, MARIO EDUARDO; ROBLES, NORMA LIS

JOURNAL OF MOLECULAR STRUCTURE

ELSEVIER SCIENCE BV

Año: 2024 vol. 1295

0022-2860

The search for analogs of compounds with proved pharmacological activity frequently starts by obtaining those that result from simple chemical substitutions, have structural and mechanical characteristics suitable for inclusion in a formulation and close similarity with related lead compounds. With this aim, the isosteric replacement of the carbonyl functional group of paracetamol to obtain solid thioparacetamol was achieved through microwave mediated thionation of parent compound in very good yield (85 %). A thorough characterization of the compound prepared was performed by GC/MS spectrometry, FTIR and NMR (1H, 13C, COSY, HSQC and HMBC) spectroscopies and quantum chemical calculations derived from density functional theory. From the experimental and theoretical spectra, it was evidenced that the structural, vibrational and conformational properties of this compound vary whether the sample is solved in a solvent or not. The anti form (anti of the Cdouble bondS and Nsingle bondH bonds) was the preferred conformational isomer in the solid phase, while a conformational equilibrium of anti and syn forms was found for samples solved in different solvents. As polarity of solvents increased, proportion of the anti isomer increased as well.