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Identification of imine or enamine drug metabolites using online hydrogen/deuterium exchange and exact mass measurements
Author(s) -
Li Austin C.,
Yu Erya,
Ring Steven C.,
Chovan James P.
Publication year - 2012
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6178
Subject(s) - chemistry , imine , enamine , hydrogen–deuterium exchange , deuterium , mass spectrometry , tandem mass spectrometry , metabolite , stereochemistry , chromatography , organic chemistry , biochemistry , physics , quantum mechanics , catalysis
RATIONALE Drug metabolites that have imine or enamine partial structures cause extra mass‐to‐charge ( m/z ) increases in online hydrogen/deuterium exchange (HDX) in addition to hydroxyl or amine protons. Online HDX and exact mass measurement were used herein to characterize this extra increase property, and to further confirm proposed metabolite structures. METHODS Metabolites of two proprietary compounds as well as two commercially available compounds were analyzed using aqueous and HDX liquid chromatography coupled with an LTQ‐Orbitrap. The exact mass measurements of both the precursor ions and product ions were acquired through data‐dependent acquisition and compared with theoretical values of proposed fragment ions. RESULTS Analysis of exact mass measurements of metabolite product ions under both normal aqueous and HDX conditions led to the identification of the isoxazole ring opening of compound C‐1, and a double‐bond formation on the methylpyrrolidine ring of compound C‐2 during biotransformation. In both cases, imine or enamine structures formed in the metabolites caused extra m/z increases upon HDX that contributed confirmatory information to the structure identification. The compound 3,3‐diphenyl‐2‐ethyl‐1‐pyrroline also demonstrated that the methylene protons adjacent to the imine were exchanged during online HDX. CONCLUSIONS The exchangeability of methylene protons adjacent to imine or enamine moieties proved to be useful to narrow down or even pinpoint the metabolism sites of parent drugs when high‐resolution exact mass measurement and online HDX were used. Copyright © 2012 John Wiley & Sons, Ltd.