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Differentiation of three pairs of positional isomers of hybrid peptides with repeats of phenylalanine‐ β 3 ‐h‐valine/ β 3 ‐h‐valine‐phenylalanine by electrospray ionization tandem mass spectrometry
Author(s) -
Ramesh V.,
Reddy P. Nagi,
Srinivas R.,
Srinivasulu G.,
Kunwar A. C.
Publication year - 2007
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.2975
Subject(s) - chemistry , phenylalanine , dipeptide , electrospray ionization , fragmentation (computing) , tandem mass spectrometry , valine , mass spectrometry , stereochemistry , peptide , amino acid , chromatography , biochemistry , computer science , operating system
Electrospray ionization ion trap mass spectrometry has been used to distinguish three pairs of positional isomers of a new series of N‐blocked hybrid peptides derived from repeats of phenylalanine(D)‐ β 3 ‐h‐valine/ β 3 ‐h‐valine‐phenylalanine(D) (F β V/ β VF) non‐natural amino acids. MS n of protonated isomeric peptides produces characteristic fragmentation involving the peptide backbone, the Boc group and the side chain. F β V‐peptides can be distinguished from β VF‐peptides by the loss of R‐OH from [M+H−Boc+H] + , which is either of relatively low abundance or totally absent for the latter peptides. In contrast, β VF‐peptides show abundant Mannich base characteristic ions by the elimination of ammonia, and imine due to a retro‐Mannich cleavage. This fragmentation is absent for F β V‐peptides. When β ‐valine is at the C‐terminus, abundant b n−1 +ions are produced. This is ascribed to the probable formation of a stable diketopiperazine structure, and this has been supported by the loss of H 2 O and CO in the CID spectra of b n−1 +ions. The hybrid dipeptide acids have also been distinguished in negative ion mass spectrometry. Copyright © 2007 John Wiley & Sons, Ltd.