STEREOCHEMICAL APPLICATIONS OF MASS-SPECTROMETRY - PART 5 - FRAGMENTATION OF PROTONATED AND METHYLATED MALEIC AND FUMARIC-ACID AND DERIVATIVES

Authors
Citation
Yp. Tu et Ag. Harrison, STEREOCHEMICAL APPLICATIONS OF MASS-SPECTROMETRY - PART 5 - FRAGMENTATION OF PROTONATED AND METHYLATED MALEIC AND FUMARIC-ACID AND DERIVATIVES, Journal of mass spectrometry, 33(9), 1998, pp. 858-871
Citations number
29
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry Inorganic & Nuclear",Spectroscopy,Biophysics
ISSN journal
1076-5174
Volume
33
Issue
9
Year of publication
1998
Pages
858 - 871
Database
ISI
SICI code
1076-5174(1998)33:9<858:SAOM-P>2.0.ZU;2-X
Abstract
The unimolecular metastable ion and collision-induced dissociation (CI D) fragmentation reactions of protonated and methylated monoamides, mo nomethyl esters and methyl esters of the monoamides of maleic and fuma ric acids were studied. In addition, some studies of the fragmentation of protonated and methylated maleic and fumaric acids were carried ou t. The [MH - H2O](+) ions derived from protonated maleic and fumaric a cids show distinctly different CID mass spectra, that for the [MH - H2 O](+) ion from the maleic acid being the same as that of protonated ma leic anhydride; the results show that the stereochemistry about the do uble bond is retained in the [MH - H2O](+) ions. Fragmentation of spec ifically deuterium-labelled and protonated or deuterated maleic acids show that the added proton becomes scrambled with the carboxylic hydro gens prior to loss of H2O, The fragmentation of similarly labelled fum aric acids show that a 1,3-H+ migration followed by elimination of H2O is not the only pathway to water elimination; the results implicate p roton migration from one carboxyl group to the other as well as some i nvolvement of the C-bonded hydrogens in the water-loss reaction, A maj or fragmentation reaction of protonated maleamic acid forms NH4+; this reaction is of only minor importance for protonated fumamic acid, Oth er primary fragmentation reactions involve elimination of NH3 and H2O from the protonated species. The protonated monomethyl esters fragment initially by loss of H2O or loss of CH3OH; the former is more promine nt for the maleate whereas the latter dominates for the fumarate, Prot onation of methyl maleamate and methyl fumamate results in loss of NH3 or CH3OH as primary fragmentation reactions; these primary fragment i ons undergo less facile further fragmentation for the maleamate than f or the fumamate, The CH3+ adducts of the monoamides fragment by loss o f NH3, H2O and CH3OH; the CID spectra of the adducts are distinctly di fferent from those of the protonated methyl esters of the monoamides, indicating predominant addition of the methyl to the amide oxygen. The CH3+ adduct of monomethyl maleate fragments primarily by loss of meth anol, the two methyl groups having become equivalent prior to fragment ation. A minor fragmentation route involves loss of dimethyl ether, a reaction not observed for protonated dimethyl maleate. Elimination of dimethyl ether is a major fragmentation channel for the CH3+ adduct of monomethyl fumarate, Since this reaction channel is not observed for protonated dimethyl fumarate, the results indicate predominant CH3+ ad dition to the carbomethoxy group of the monoester, (C) 1998 John Wiley & Sons, Ltd.