Present address: Department of Chemistry and Biochemistry, Northern Arizona University, PO Box 5698, S. Beaver Street, Bldg 20, Room 125, Flagstaff, AZ 86011–5698, USA.
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Research Article
A study of fragmentation of protonated amides of some acylated amino acids by tandem mass spectrometry: observation of an unusual nitrilium ion
Article first published online: 12 APR 2011
DOI: 10.1002/rcm.4965
Copyright © 2011 John Wiley & Sons, Ltd.
Additional Information
How to Cite
Talaty, E. R., Young, S. M., Dain, R. P. and Van Stipdonk, M. J. (2011), A study of fragmentation of protonated amides of some acylated amino acids by tandem mass spectrometry: observation of an unusual nitrilium ion. Rapid Commun. Mass Spectrom., 25: 1119–1129. doi: 10.1002/rcm.4965
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Present address: Department of Chemistry and Biochemistry, Northern Arizona University, PO Box 5698, S. Beaver Street, Bldg 20, Room 125, Flagstaff, AZ 86011–5698, USA.
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Present address: Department of Chemistry, University of Utah, 315 S. 1400 E. Rm. 2020, Salt Lake City, Utah 84112–0850.
Publication History
- Issue published online: 12 APR 2011
- Article first published online: 12 APR 2011
- Manuscript Accepted: 24 JAN 2011
- Manuscript Revised: 21 JAN 2011
- Manuscript Received: 30 NOV 2010
- Abstract
- Article
- References
- Cited By
A tandem mass spectrometric study of a series of secondary amides of acetylglycine and hippuric acid utilizing electrospray ionization (ESI) was conducted. Among the fragment ions observed was an unusual one, which we have determined to be a nitrilium ion having the structure 
or 
by loss of the full mass of glycine as a neutral fragment. A mechanism that we propose involves an initial protonation of the oxygen atom at the N-terminus, followed by cyclization to a five-membered imidazolium ring, and its subsequent collapse to the nitrilium ion. This mechanism is supported by extensive isotopic labels and considerable variation of substituents. A similar study of the amides of acyl β-alanine and acyl γ-aminobutyric acid revealed that the former furnishes the same nitrilium ion, but not the latter. Thus, a six-membered intermediate is also possible and capable of losing the full mass of β-alanine as a neutral fragment. When the size of the ring is forced to be seven-membered, this pathway is blocked. When this study was expanded to include a variety of N-acylproline amides, the nitrilium ion was observed in 100% abundance only when the acyl group was acetyl. Thus a proline effect (involvement of a strained bicyclic [3.3.0] structure) is being observed. Copyright © 2011 John Wiley & Sons, Ltd.