NMR and DFT analysis of the major diastereomeric degradation product of clopidogrel under oxidative stress conditions

•Investigation of degradation products of clopidogrel hydrogen sulfate under ICH prescribed peroxide-mediated oxidative stress testing conditions.•First report regarding the characterization and NMR spectral assignment of the diastereomeric degradation product N-oxide.•The signals of the CH2 groups in the diastereomeric degradation appear influenced by the polarization of the NO bond.•DFT calculations were used to understand the intramolecular magnetic effects.