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Electrospray ionization tandem mass spectrometric study on the effect of N‐terminal β ‐ and γ ‐carbo amino acids on fragmentation of GABA‐hybrid peptides
Author(s) -
Ramesh V.,
Ramesh M.,
Srinivas R.,
Sharma G. V. M.,
Jayaprakash P.
Publication year - 2008
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.3743
Subject(s) - chemistry , fragmentation (computing) , electrospray ionization , tandem mass spectrometry , tandem , amino acid , chromatography , electrospray , mass spectrometry , combinatorial chemistry , biochemistry , computer science , operating system , materials science , composite material
The fragmentations of protonated and deprotonated ions of a new class of N‐blocked hybrid Boc‐carbopeptides containing repeats of γ ‐Caa/ γ Abu‐ and β ‐Caa/ γ Abu‐ (CaaC‐linked carbo γ 4 ‐/ β 3 ‐ amino acids derived from D‐xylose, γ Abu = γ ‐aminobutyric acid) have been studied using electrospray ionization (ESI) ion‐trap tandem mass spectrometry (MS/MS). MS/MS of a pair of these protonated diastereomers produces distinct fragmentation of the Boc group. The formation of [M + H–56] + corresponding to loss of isobutylene is more pronounced for Boc‐NH‐(R)‐ γ ‐Caa‐ γ Abu‐OH (2) whereas it is of low abundance for Boc‐NH‐(S)‐ γ ‐Caa‐ γ AbuOH (1). Similarly, MS 2 of [MH] − of 2 produces an abundant [MHC(CH 3 ) 3 OHCO 2 ] − ion, which is absent for its diastereomeric isomer 1. From this, it can be suggested that MS/MS of N‐blocked Boc‐protected carbopeptides may be helpful in distinguishing the stereochemistry of the N‐terminus Caa. MS 3 of [M + H–Boc + H] + ions of peptides with a γ ‐amino acid ( γ ‐Caa/ γ Abu) at the N‐terminus produces only abundant y n +ions. On the other hand, characteristic fragmentations involving the peptide backbone (b n +and y n + ) and the side chain are seen when β ‐Caa is at the N‐terminus of the peptides. MS 3 of the [MHC(CH 3 ) 3 OH] − ion of peptides containing γ ‐Caa/ γ Abu at the N‐terminus gave y n −and [MHC(CH 3 ) 3 OHCO 2 ] − ions, whereas the presence of β ‐Caa at the N‐terminus yielded predominantly [MHC(CH 3 ) 3 OHHNCO] − . Thus, on the basis of our previous study and that presented here we propose that the fragmentation of these hybrid carbopeptides is highly influenced by the type of carbo amino acid present at the N‐terminus. Copyright © 2008 John Wiley & Sons, Ltd.