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Eur. J. Mass Spectrom.
11, 107–118 (2005)
DOI:
10.1255/ejms.733 |
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Characterization of electrospray ionization mass spectrometry for N-diisopropyloxyphosphoryl dipeptide methyl esters |
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Shi-
Zhong Luo, Yan-Mei Li,* Yan-Ling Niu, Yi Chen, Yu-Yang Jiang, Jing Chen and Yu-Fen Zhao
The Key Laboratory for Bio-organic Phosphorus Chemistry
(Tsinghua University), Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, PR China. E-mail: liym@mail.tsinghua.edu.cn |
| ABSTRACT: |
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A systematic study
of the fragmentation pattern of N-diisopropyloxyphosphoryl (DIPP) dipeptide methyl esters in an electrospray ionization (ESI) tandem mass spectrometry (MS/MS) was
presented. A combination of accurate mass measurement and tandem mass spectrometry had been used to characterize the major fragment ions observed in the ESI mass
spectrum. It was found that the alkali metal ions acted as a fixed charge site and expelled the DIPP group after transferring a proton to the amide nitrogen. For all the N-phosphoryl
dipeptide methyl esters, under the activation of a metal ion, the rearrangement product ion at m/z 163 was observed and confirmed to be the sodium adduct of phosphoric
acid mono-isopropyl esters (PAIE), via a specific five-membered penta-coordinated phosphorus intermediate. However, no rearrangement ion was observed when a β-
amino acid was at the N-terminal. This could be used to develop a novel method for differentiating isomeric compounds when either α- or β-amino acid are at the
N-terminus of peptides. From the [M + Na]+ ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters (DIPP – Xaa1 – Xaa2 – OMe), the
peaks corresponding to the [M + Na – Xaa1 – C3H6]+ were observed and explained. The [M + Na]+
ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters with Phe located in the C-terminal, such as DIPP–Val–Phe–OMe,
DIPP–Leu–Phe–OMe, DIPP–Ile–Phe–OMe, DIPP–Ala–Phe–OMe and DIPP–Phe–Phe–OMe,
had characteristic fragmentation. Two unusual gas-phase intramolecular rearrangement mechanisms were first proposed for this fragmentation. These rearrangements were not
observed in dipeptide methyl ester analogs which did not contain the DIPP at the N-terminal, suggesting that this moiety was critical for the rearrangement. |
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Keywords:
N–
diisopropyloxyphosphoryl dipeptide methyl esters, ESI-MS, alkali metal ions, rearrangement, five-member penta-coordinated phosphorus intermediate |
