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Electrospray ionization tandem mass spectrometry of protonated and alkali‐cationized Boc‐N‐protected hybrid peptides containing repeats of D‐Ala‐APyC and APyC‐D‐Ala: Formation of [b n–1 + OCH 3 + Na] + and [b n–1 + OH + Na] + ions
Author(s) -
Raju G.,
Purna Chander C.,
Srinivas Reddy K.,
Srinivas R.,
Sharma G. V. M.
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.6381
Subject(s) - chemistry , tandem mass spectrometry , electrospray ionization , protonation , mass spectrometry , fragmentation (computing) , peptide , electrospray , protein mass spectrometry , ion , stereochemistry , chromatography , organic chemistry , biochemistry , computer science , operating system
RATIONALE Differentiation and structural characterization of positional isomers of non‐natural amino acid hybrid peptides by using electrospray ionization tandem mass spectrometry (ESI‐MS n ) is desirable because of their fundamental importance from the view point of peptide mass spectrometry and also of their increasing importance in the area of research towards biomedical and material applications; hence, the present study is undertaken. METHODS Electrospray ionization ion‐trap tandem mass spectrometry (ESI‐MS n ) was used to characterize and differentiate three pairs of positional isomers of Boc‐N‐protected hybrid peptides containing repeats of D‐Ala‐APyC and APyC‐D‐Ala (D‐Ala = D‐alanine and APyC = trans ‐3‐aminopyran‐2‐carboxylic acid). RESULTS ESI‐MS n spectra of protonated and alkali‐cationized positional isomeric peptides display characteristic fragmentation involving the peptide backbone, the Boc group, and the side chain. It is observed that abundant rearrangement ions [b n–1 + OCH 3 + Na] + or [b n–1 + OH + Na] + are formed when D‐Ala is present at C‐terminus and the presence of APyC at the C‐terminus inhibits the formation of rearrangement ions. In addition, abundant b n–1 + ions are formed, presumably with stable oxazolone structures, when the C‐terminus of b n–1 + ions possessed D‐Ala. CONCLUSIONS The present study demonstrates that ESI tandem mass spectrometry is very useful for differentiating positional isomers of hybrid peptides containing D‐Ala and APyC amino acids. While the protonated peptides give rise to characteristic sequencing ions, the cationized peptides produce additional rearrangement ions ([b n–1 + OCH 3 + Na] + and [b n–1 + OH + Na] + ) which helps distinguish between the presence of D‐Ala and APyC amino acids at the C‐terminus. Copyright © 2012 John Wiley & Sons, Ltd.