Spectroscopic identification of intermediates and final products of the chiral pool synthesis of sutezolid

Sutezolid is a new oxazolidinone derivative currently in clinical trials to determine its safety and efficacy towards highly drug-resistant tuberculosis. The aim of the study was the spectroscopic identification of selected key intermediate products of the chiral pool synthesis of sutezolid: (S1) (4-(2-fluoro-4-nitrophenyl)thiomorpholine), (S2) 4-[2-fluoro-4-(benzyloxycarbonyl)aminophenyl] thiomorpholine, (S4) (R)-[[3-[3-fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl]-p-toluenesulfonate, (S5) (R)-[[3-(3-fluoro-4-(4-thiomorpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl]azide, as well as (S6) sutezolid, the final synthesis product. Spectroscopic identification was carried out based on infrared spectra analysis (FT-IR) and Raman scattering. This part of the analysis was supported by quantum chemical calculations based on the density functional theory (DFT) utilizing the B3LYP hybrid functional and the 6-31G(d,p) basis set to obtain reference standards for intermediates and sutezolid. Additionally, the sutezolid configuration was confirmed by analysing the electronic circular dichroism (ECD) spectra of (S)- and (R)- isomers, combined with the time-dependent DFT calculations to simulate ECD spectra depending on the solvent and type of conformers.