Paulose Justin, Achuthan Revi P, Linsha Maria P L, Mathai George, Prasanth B, Kumar Talluri M V N, Srinivas Ragampeta
Department of Chemistry, Sacred Heart College, Thevara, Kochi, India.
Bharathiyar University, Coimbatore, Tamilnadu, India.
Rapid Commun Mass Spectrom. 2015 Sep 15;29(17):1577-1584. doi: 10.1002/rcm.7256.
The collisional-induced dissociations (CID) of the [M+H] ions of molecules having benzyl groups attached to N-atoms have been proposed to involve migration of the benzyl group through the intermediacy of ion/neutral complexes (INCs). We report the investigation of the mechanism of dissociation of protonated N-benzyl- and N-(1-phenylethyl)tyrosine amides by electrospray ionization (ESI) tandem mass spectrometry (MS/MS) and density functional theory (DFT) calculations.
The amides were synthesized from the corresponding amino acids and amines. The ESI-MS/MS spectra were recorded using an Agilent QTOF 6540 mass spectrometer. The DFT calculations were performed by using Gaussian 09 software. The structures of the [M+H] ions, intermediates, products and transition states (TS) were optimized at the B3LYP/6-31G(d,p) level of theory.
CID of the [M+H] ions of N-benzyltyrosine amide yields two product ions due to rearrangements: (i) the [M+H-74] ion (m/z 197) due to benzyl migration to the hydroxyphenyl ring and (ii) the [M+H-45] ion (m/z 226) due to benzyl migration to the NH group. DFT calculations suggest that the rearrangements occur through an INC in which the benzyl cation is the cation partner. The [M+H] ion of N-(1-phenylethyl)tyrosine amide rearranges to an INC of the 1-phenylethyl cation. Subsequent elimination of styrene occurs by transfer of a proton from the 1-phenylethyl cation to the neutral partner.
The [M+H] ions of both N-benzyl (1) and N-(1-phenylethyl) (2) tyrosine amide rearrange into INCs. The dissociation of [M+H] ion of 1 yields the benzyl cation and [M+H-74] and [M+H-45] due to benzyl migration to the hydroxyphenyl ring and NH group, respectively. However, the formation of the [M+H-74] ion is not observed when the aromatic ring is deactivated. The [M+H] ion of 2 either dissociates to form the 1-phenylethyl cation or [M+H-styrene] . Copyright © 2015 John Wiley & Sons, Ltd.
已提出连接在氮原子上带有苄基的分子的[M + H]离子的碰撞诱导解离（CID）涉及苄基通过离子/中性复合物（INC）中间体的迁移。我们通过电喷雾电离（ESI）串联质谱（MS/MS）和密度泛函理论（DFT）计算报告了质子化的N-苄基和N-（1-苯乙基）酪氨酸酰胺的解离机制研究。
酰胺由相应的氨基酸和胺合成。使用安捷伦QTOF 6540质谱仪记录ESI-MS/MS光谱。DFT计算使用高斯09软件进行。[M + H]离子、中间体、产物和过渡态（TS）的结构在B3LYP/6-31G(d,p)理论水平上进行了优化。
N-苄基酪氨酸酰胺的[M + H]离子的CID由于重排产生两个产物离子：（i）由于苄基迁移到羟基苯环而产生的[M + H - 74]离子（m/z 197），以及（ii）由于苄基迁移到NH基团而产生的[M + H - 45]离子（m/z 226）。DFT计算表明重排通过一个INC发生，其中苄基阳离子是阳离子伙伴。N-（1-苯乙基）酪氨酸酰胺的[M + H]离子重排为1-苯乙基阳离子的INC。随后通过将质子从1-苯乙基阳离子转移到中性伙伴上发生苯乙烯的消除。
N-苄基（1）和N-（1-苯乙基）（2）酪氨酸酰胺的[M + H]离子均重排为INCs。1的[M + H]离子的解离分别由于苄基迁移到羟基苯环和NH基团而产生苄基阳离子以及[M + H - 74]和[M + H - 45]。然而，当芳环失活时未观察到[M + H - 74]离子的形成。2的[M + H]离子要么解离形成1-苯乙基阳离子，要么形成[M + H - 苯乙烯]。版权所有© 2015 John Wiley & Sons, Ltd.
