### Differentiation of Positional Isomers of Hybrid Peptides Containing Repeats of β-Nucleoside Derived Amino Acid (β-Nda-) and L-Amino Acids by Positive and Negative Ion Electrospray Ionization Tandem Mass Spectrometry (ESI-MS$^{ n }$)Differentiation of Positional Isomers of Hybrid Peptides Containing Repeats of β-Nucleoside Derived Amino Acid (β-Nda-) and L-Amino Acids by Positive and Negative Ion Electrospray Ionization Tandem Mass Spectrometry (ESI-MS$^{ n }$)

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 Author Raju, B. ♦ Ramesh, M. ♦ Srinivas, R. ♦ Chandrasekhar, S. ♦ Kiranmai, N. ♦ Sarma, V. U. M. Source SpringerLink Content type Text Publisher Springer-Verlag File Format PDF Copyright Year ©2011 Language English
 Subject Domain (in DDC) Natural sciences & mathematics ♦ Chemistry & allied sciences Subject Keyword Electrospray ionization ♦ Tandem mass spectrometry ♦ Hybrid peptides ♦ Non-natural amino acid ♦ Positional isomers ♦ Proteomics ♦ Bioinformatics ♦ Organic Chemistry ♦ Biotechnology ♦ Analytical Chemistry Abstract A new class of positional isomeric pairs of -Boc protected oligopeptides comprised of alternating nucleoside derived β-amino acid (β-Nda-) and L-amino acid residues (alanine, valine, and phenylalanine) have been differentiated by both positive and negative ion electrospray ionization ion-trap tandem mass spectrometry (ESI-MS$^{ n }$). The protonated dipeptide positional isomers with β-Nda- at the N-terminus lose CH$_{3}$OH, NH$_{3}$, and C$_{2}$H$_{4}$O$_{2}$, whereas these processes are absent for the peptides with L-amino acids at the N-terminus. Instead, the presence of L-amino acids at the N-terminus results in characteristic retro-Mannich reaction involving elimination of imine. A good correlation has been observed between the conformational structure of the peptides and the abundance of y n + and b n + ions in MS$^{ n }$ spectra. In the case of tetrapeptide isomers that are reported to form helical structures in solution phase, no y n + and b n + ions are observed when the corresponding amide -NH- participates in the helical structures. In contrast, significant y n + and b n + ions are formed when the amide -NH- is not involved in the H-bonding. In the case of tetra- and hexapeptides, it is observed that abundant b n + ions are formed, presumably with stable oxazolone structures when the C-terminus of the b n + ions possessed L-amino acid and the β-Nda- at the C-terminus appears to prevent the cyclization process leading to the absence of corresponding b n + ions. ISSN 10440305 Age Range 18 to 22 years ♦ above 22 year Educational Use Research Education Level UG and PG Learning Resource Type Article Publisher Date 2011-02-08 Publisher Institution The American Society for Mass Spectrometry Publisher Place New York e-ISSN 18791123 Journal Journal of The American Society for Mass Spectrometry Volume Number 22 Issue Number 4 Page Count 15 Starting Page 703 Ending Page 717