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Desorption chemical ionization tandem mass spectrometry of polyprenyl and dolichyl phosphates
Authors:Beata A. Wolucka  Raoul Rozenberg  Edmond de Hoffmann  Tadeusz Chojnacki
Affiliation:1. Department of Chemistry, University of Louvain, Place Louis Pasteur 1/1B, B-1348, Louvain-la-Neuve, Belgium
2. Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
Abstract:
Negative-ion desorption chemical ionization (DCI) tandem mass spectrometry was applied to the analysis of nanomole quantities of semisynthetic polyisoprenyl phosphates, the chain length of which ranged from 7 to 20 isoprene units. The DCI spectrum of all the compounds tested show the presence of independently generated ions [M-HPO3-H]?, [M-H3PO2-H]? and [M-H3PO4-H]? resulting from the loss of a part of or the entire phosphate group of a polyisoprenyl-P. In tandem mass spectrometry, the [M-H3PO4-H]? fragment produces series of ions 68 mass units apart, indicative of the polyisoprenoid nature of a compound. Studies with deuterated and α-saturated polyisoprenyl phosphates demonstrated that fragmentations of the [M-H3PO4-H]? ion proceed from both ends (α and ω) of a polyisoprenoid chain and may occur at either allylic (A) or vinylic (V) sites. Fragments of masses equal to [n×68 ? 1] and [n×68 ? 13] (where n is the number of isoprene units and 3≤n is less than the total number of isoprene residues within a polyisoprenoid chain) comprise the αA and ωV series, respectively, and represent the most abundant ions in tandem mass spectra of the [M-H3PO4-H]? fragment of polyprenyl phosphates, α-Saturated dolichyl phosphates can be distinguished easily from corresponding polyprenyl phosphates not only on the basis of a 2-u shift of the [M-H3PO4-H]? ion and the α series of fragments, but also because of the presence of an additional (A+14) series of ions 14 u heavier than fragments resulting from the allylic cleavages of an α-saturated polyisoprenoid chain. Possible mechanisms of the collision-induced dissociation reactions of polyprenyl phosphates are discussed.
Keywords:
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