A study of fragmentation of protonated amides of some acylated amino acids by tandem mass spectrometry: observation of an unusual nitrilium ion
作者:Erach R. Talaty、Sarah M. Young、Ryan P. Dain、Michael J. Van Stipdonk
DOI:10.1002/rcm.4965
日期:2011.5.15
ionization (ESI) was conducted. Among the fragment ions observed was an unusual one, which we have determined to be a nitrilium ion having the structure or by loss of the full mass of glycine as a neutral fragment. A mechanism that we propose involves an initial protonation of the oxygen atom at the N‐terminus, followed by cyclization to a five‐membered imidazolium ring, and its subsequent collapse to
利用电喷雾电离(ESI)进行了一系列串联的乙酰甘氨酸和马尿酸仲酰胺的质谱研究。中观察到的碎片离子是一个不寻常的,这是我们确定为具有以下结构的nitrilium离子 或损失了作为中性片段的甘氨酸的全部质量。我们提出的一种机制涉及在N端使氧原子初始质子化,然后环化为五元咪唑环,然后其折叠为腈离子。广泛的同位素标记和大量取代基支持这种机制。对酰基β-丙氨酸和酰基γ-氨基丁酸的酰胺的类似研究表明,前者提供相同的腈离子,而后者则没有。因此,六元中间体也是可能的,并且能够失去作为中性片段的完整β-丙氨酸的质量。当环的大小强制为七元时,该路径将被阻塞。当这项研究扩展到包括各种N-酰基脯氨酸酰胺,仅当酰基为乙酰基时才观察到100%的腈离子。因此,观察到脯氨酸效应(涉及双环[3.3.0]结构的应变)。版权所有©2011 John Wiley&Sons,Ltd.