A study of the elimination of water from lithium-cationized tripeptide methyl esters by means of tandem mass spectrometry and isotope labeling.
Extensive isotope labeling (2H, 13C and 15N), collision-induced dissociation (CID) and multiple-stage tandem mass spectrometry were used to investigate the elimination of H2O from a series of model, metal-cationized tripeptide methyl esters. The present results corroborate our earlier suggestion that loss of water from lithiated peptides is initiated by a nucleophilic attack from the N-terminal side upon an amide carbonyl carbon atom to form a five-membered ring as an intermediate followed by 1,2-elimination of water. We show that the nucleophilic atom is the oxygen atom of the N-terminal amide group in the fragmentation of [AcGGGOMe+Li]+ as well as [GGGOMe+Li]+. However, the subsequent fragmentation is markedly different in the two cases as a result of the absence and presence of a free amino group. In particular, extensive scrambling of protons in the alpha-positions of GGGOMe is observed, presumably as a consequence of intervention of the basic amino group.
Talaty
Erach R
ER
Department of Chemistry, Wichita State University, Wichita, KS 67260-0051, USA. erach.talaty@wichita.edu
Cooper
Travis J
TJ
Piland
Debra L
DL
Bateman
David J
DJ
Syed
Adeel
A
Stevenson
William
W
Van Stipdonk
Michael J
MJ
D002412:Cations; D003198:Computer Simulation; D004952:Esters / Q000737:chemistry; D007553:Isotope Labeling / Q000379:methods; D008094:Lithium / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D014867:Water / Q000737:chemistry*
D002412:Cations; D004952:Esters; D010455:Peptides; D014867:Water; D008094:Lithium