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-MSⁿ)

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.

In vivo metabolic investigation of moxifloxacin using liquid chromatography/electrospray ionization tandem mass spectrometry in combination with online hydrogen/deuterium exchange experiments

“…MS n experiments were performed using a quadrupole ion trap mass spectrometer (Thermo Finnigan, San Jose, CA, USA), equipped with an ESI source. The data acquisition was under the control of Xcalibur software (Thermo Finnigan) …”

Identification and structural characterization of in vivo metabolites of ketorolac using liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS)

“…MS n experiments were performed using quadrupole ion trap mass spectrometer (Thermo Finnigan, San Jose, CA, USA), equipped with an ESI source. The data acquisition was under the control of Xcalibur software …”

“…The metabolite K12 at m/z 816.1823 ([M + H] + ; C 33 H 38 NO 23 ) was detected at 2.6 min. Its deuterated molecule ion at m/z 829.2811 (C 33 H 25 NO 23…”

Characterization of N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives using electrospray ionization multi‐stage mass spectrometry

“…Tandem mass spectrometry (MS/MS) in electrospray ionization (ESI) is an established technique for the structure elucidation of peptides [35][36][37][38][39][40][41][42][43][44][45][46] and peptidomimetics, [47][48][49][50][51][52][53][54][55][56][57] but the characterization of peptides containing a gem-diaminoalkyl moiety has received little attention. [58][59][60][61] This has prompted us to undertake a detailed mass spectrometric study on a series of N-alkoxycarbonyl-N′-formyl-gemdiaminoalkyl derivatives using the ESI technique both in the positive and negative ion mode.…”