Talaty Erach R, Cooper Travis J, Piland Debra L, Bateman David J, Syed Adeel, Stevenson William, Van Stipdonk Michael J
Department of Chemistry, Wichita State University, Wichita, KS 67260-0051, USA.
Rapid Commun Mass Spectrom. 2006;20(20):3007-17. doi: 10.1002/rcm.2694.
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.
采用广泛的同位素标记（2H、13C和15N）、碰撞诱导解离（CID）和多级串联质谱法，研究了一系列模型金属阳离子化三肽甲酯中H2O的消除情况。目前的结果证实了我们早期的推测，即锂化肽中水分子的丢失是由N端一侧对酰胺羰基碳原子的亲核攻击引发的，形成一个五元环作为中间体，随后进行1,2-水消除。我们表明，在[AcGGGOMe+Li]+以及[GGGOMe+Li]+的碎片化过程中，亲核原子是N端酰胺基团的氧原子。然而，由于游离氨基的不存在和存在，两种情况下随后的碎片化明显不同。特别是，观察到GGGOMe的α位质子发生了广泛的重排，推测这是碱性氨基干预的结果。
