Structure Elucidation of the Diagnostic Product Ion at <Emphasis Type="Italic">m/z</Emphasis> 97 Derived from Androst-4-en-3-One-Based Steroids by ESI-CID and IRMPD Spectroscopy |
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Authors: | Mario Thevis Simon Beuck Sebastian Höppner Andreas Thomas Joseph Held Mathias Schäfer Jos Oomens Wilhelm Schänzer |
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Institution: | 1.Institute of Biochemistry–Center for Preventive Doping Research,German Sport University Cologne,Cologne,Germany;2.Department of Chemistry,University of Cologne,Cologne,Germany;3.FOM-Institute for Plasma Physics Rijnhuizen,Nieuwegein,The Netherlands;4.University of Amsterdam,Amsterdam,The Netherlands |
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Abstract: | Structure elucidation of steroids by mass spectrometry has been of great importance to various analytical arenas and numerous
studies were conducted to provide evidence for the composition and origin of (tandem) mass spectrometry-derived product ions
used to characterize and identify steroidal substances. The common product ion at m/z 97 generated from androst-4-ene-3-one analogs has been subject of various studies, including stable isotope-labeling and
(high resolution/high accuracy) tandem mass spectrometry, but its gas-phase structure has never been confirmed. Using high
resolution/high accuracy mass spectrometry and low resolution tandem mass spectrometry, density functional theory (DFT) calculation,
and infrared multiple photon dissociation (IRMPD) spectroscopy employing a free electron laser, the structure of m/z 97 derived from testosterone was assigned to protonated 3-methyl-2-cyclopenten-1-one. This ion was identified in a set of
six cyclic C6H9O+ isomers as computed at the B3LYP/6-311++G(2d,2p) level of theory (protonated 3-methyl-2-cyclopenten-1-one, 2-methyl-2-cyclopenten-1-one
and 2-cyclohexen-1-one). Product ions of m/z 97 obtained from MS2 and MS3 experiments of protonated 3-methyl-2-cyclopenten-1-one, 2-methyl-2-cyclopenten-1-one, 2-cyclohexen-1-one, and testosterone
corroborated the suggested gas-phase ion structure, which was eventually substantiated by IRMPD spectroscopy yielding a spectrum
that convincingly matched the predicted counterpart. Finally, the dissociation pathway of the protonated molecule of testosterone
to m/z 97 was revisited and an alternative pathway was suggested that considers the exclusion of C-10 along with the inclusion of
C-5, which was experimentally demonstrated with stable isotope labeling. |
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