Formation of [b3 − 1 + cat]+ ions from metal-cationized tetrapeptides containing β-alanine, γ-aminobutyric acid or ε-aminocaproic acid residues
✍ Scribed by Sandra M. Osburn; Sila O. Ochola; Erach R. Talaty; Michael J. Van Stipdonk
- Book ID
- 102377112
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 296 KB
- Volume
- 43
- Category
- Article
- ISSN
- 1076-5174
- DOI
- 10.1002/jms.1418
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✦ Synopsis
Abstract
The presence and position of a single β‐alanine (βA), γ‐aminobutyric acid (γABu) or ε‐aminocaproic acid (Cap) residue has been shown to have a significant influence on the formation of b~n~^+^ and y~n~^+^ product ions from a series of model, protonated peptides. In this study, we examined the effect of the same residues on the formation of analogous [b~3~ − 1 + cat]^+^ products from metal(Li^+^, Na^+^ and Ag^+^)‐cationized peptides. The larger amino acids suppress formation of b~3~^+^ from protonated peptides with general sequence AAXG (where X = β‐alanine, γ‐aminobutyric acid or ε‐aminocaproic acid), presumably because of the prohibitive effect of larger cyclic intermediates in the ‘oxazolone’ pathway. However, abundant [b~3~ − 1 + cat]^+^ products are generated from metal‐cationized versions of AAXG. Using a group of deuterium‐labeled and exchanged peptides, we found that formation of [b~3~ − 1 + cat]^+^ involves transfer of either amide or α‐carbon position H atoms, and the tendency to transfer the atom from the α‐carbon position increases with the size of the amino acid in position X. To account for the transfer of the H atom, a mechanism involving formation of a ketene product as [b~3~ − 1 + cat]^+^ is proposed. Copyright © 2008 John Wiley & Sons, Ltd.