Structural confirmation of sulconazole sulfoxide as the primary degradation product of sulconazole nitrate

Sulconazole has been reported to degrade into sulconazole sulfoxide via sulfur oxidation; however, structural characterization data was lacking and the potential formation of an N-oxide or sulfone could not be excluded. To clarify the degradation pathways and incorporate the impurity profile of sulconazole into the United States Pharmacopeia–National Formulary (USP–NF) monographs, a multifaceted approach was utilized to confirm the identity of the degradant. The approach combines stress testing of sulco-nazole nitrate, chemical synthesis of the degradant via a hydrogen peroxide-mediated oxidation reaction, semi-preparative HPLC purification, and structural elucidation by LC―MS/MS and NMR spectroscopy. Structural determination was primarily based on the comparison of spectroscopic data of sulconazole and the oxidative degradant. The mass spectrometric data have revealed a McLafferty-type rearrange-ment as the characteristic fragmentation pathway for alkyl sulfoxides with aβ-hydrogen atom, and was used to distinguish the sulfoxide from N-oxide or sulfone derivatives. Moreover, the generated sulco-nazole sulfoxide was utilized as reference material for compendial procedure development and valida-tion, which provides support for USP monograph modernization.