通过正离子和负离子电喷雾串联质谱法（ESI-MS/MS）对Boc-α,β-和β,α-肽以及一对非对映体β,α-二肽进行区分。

Differentiation of Boc- alpha,beta- and beta,alpha-peptides and a pair of diastereomeric beta,alpha-dipeptides by positive and negative ion electrospray tandem mass spectrometry (ESI-MS/MS).

作者信息

Reddy P Nagi, Srikanth R, Swamy N S, Srinivas R, Sharma G V M, Nagendar Pendem, Krishna Palakodety Radha

机构信息

National Center for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad 500007, India.

出版信息

J Mass Spectrom. 2005 Nov;40(11):1429-38. doi: 10.1002/jms.931.

DOI:10.1002/jms.931

PMID:16220504

Abstract

Positive and negative ion electrospray ionization (ESI) tandem mass spectral study of a new series of hybrid peptides, viz, BocN-alpha,beta-peptides and BocN-beta,alpha-peptides, synthesized from C-linked carbo-beta3-amino acids [Caa (S)] and L-Ala has been carried out. The alpha,beta-peptides have been differentiated from beta,alpha-peptides by the collision-induced dissociation (CID) of [M + H]+ and [M - H]- ions in positive and negative ion ESI-MS respectively. The fragment ion [M + H - C(CH3)3 + H]+ formed from [M + H]+ ions by the loss of 2-methyl-prop-2-ene in alpha,beta-peptides with L-Ala at the N-terminus is insignificant or totally absent for beta,alpha-peptides which have the Caa (S) at N-terminus. The fragment ion [M - H-C(CH3)3OH - HNCO]- formed from [M - H]- of beta,alpha-peptide acids is totally absent for alpha,beta-peptide acids. This has been attributed to the absence of the beta-methylene group in alpha,beta-peptides, and the participation of the beta-methylene group in the loss of HNCO in beta,alpha-peptide acids is confirmed by the deuteration experiments. The CID of [M + H-Boc + H]+ ions of these peptides also produce characteristic fragmentation. In the CID spectra of alpha,beta-peptides, the b(n)+ ions and the resulting y(n)+ ions occur at a mass difference of 243 and 71 Da corresponding to the successive losses of Caa and L-Ala, whereas a mass difference of 71 and 243 Da is observed for beta,alpha-peptides. In contrast to the CID of protonated peptides, the CID of [M - H]- ions of the alpha,beta- and beta,alpha-peptide acids do not give b(n)- ions and show abundant z(n) (-) ions. Further, a pair of diastereomeric dipeptide esters and acids have been distinguished by the CID of [M + H]+ ions. The loss of 2-methyl-prop-2-ene is more pronounced for Boc-NH-Caa(R)-D-Ala-OCH3 (21) and Boc-NH-Caa(R)-D-Ala-OH (23) with Caa (R) at the N-terminus, whereas it is totally absent for Boc-NH-Caa (S)-D-Ala-OCH3 (22) and Boc-NH-Caa(S)-D-Ala-OH (24) peptides, which have Caa (S) at the N-terminus. Thus, on the basis of our previous and present studies, we propose that the CID of [M + H]+ ions provides a simple and useful method for distinguishing the configuration of Caa (S or R) at the N-terminus of BocN-carbo beta,alpha- and beta,beta-dipeptides.

摘要

对一系列新的杂合肽，即由碳连接的碳-β3-氨基酸[Caa (S)]和L-丙氨酸合成的BocN-α,β-肽和BocN-β,α-肽，进行了正离子和负离子电喷雾电离(ESI)串联质谱研究。α,β-肽和β,α-肽分别通过正离子和负离子ESI-MS中[M + H]+和[M - H]-离子的碰撞诱导解离(CID)来区分。对于N端为L-丙氨酸的α,β-肽，由[M + H]+离子通过失去2-甲基-丙烯形成的碎片离子[M + H - C(CH3)3 + H]+，对于N端为Caa (S)的β,α-肽则不显著或完全不存在。α,β-肽酸的[M - H]-形成的碎片离子[M - H-C(CH3)3OH - HNCO]-，对于α,β-肽酸则完全不存在。这归因于α,β-肽中不存在β-亚甲基，氘代实验证实了β-亚甲基在β,α-肽酸中HNCO的损失中起作用。这些肽的[M + H-Boc + H]+离子的CID也产生特征性碎片。在α,β-肽的CID谱中，b(n)+离子和由此产生的y(n)+离子的质量差为243和71 Da，分别对应于Caa和L-丙氨酸的连续损失，而对于β,α-肽则观察到质量差为71和243 Da。与质子化肽的CID不同，α,β-和β,α-肽酸的[M - H]-离子的CID不产生b(n)-离子，而是显示出丰富的z(n) (-)离子。此外，一对非对映异构二肽酯和酸已通过[M + H]+离子的CID进行了区分。对于N端为Caa (R)的Boc-NH-Caa(R)-D-Ala-OCH3 (21)和Boc-NH-Caa(R)-D-Ala-OH (23)，2-甲基-丙烯的损失更为明显，而对于N端为Caa (S)的Boc-NH-Caa (S)-D-Ala-OCH3 (22)和Boc-NH-Caa(S)-D-Ala-OH (24)肽则完全不存在。因此，基于我们之前和现在的研究，我们提出[M + H]+离子的CID为区分BocN-碳β,α-和β,β-二肽N端Caa (S或R)的构型提供了一种简单而有用的方法。