Low-energy fast atom bombardment tandem mass spectrometry of monohydroxy substituted unsaturated fatty acids

Abstract

The low-energy collision-induced dissociation (CID) of the carboxylate anions generated by fast atom bombardment ionization of monohydroxy unsaturated fatty acids derived from oleic, linoleic, linolenic and arachidonic acids were studied in a tandem quadrupole mass spectrometer. The collisional activation spectra revealed structurally informative ions as to the position of the hydroxyl substituent in relationship to the sites of unsaturation. Five mechanisms are proposed for the fragmentation of hydroxyl substituted unsaturated fatty acids and are dependent upon the presence of alpha- or beta-unsaturation sites. These mechanisms include charge-remote allylic fragmentation, charge-remote vinylic fragmentation, charge-driven allylic fragmentation, charge-driven vinylic fragmentation, and homolytic fragmentation by an oxy-Cope rearrangement process. The assignment of specific fragmentation pathways was supported in many instances with deuterium-labeled analogs. Although no single fragmentation mechanism appears to predominate, a rational approach to the interpretation of these CID spectra is proposed. The CID spectra of unknown compounds could be used to establish the hydroxyl substituent position in relationship to certain sites of unsaturation but would not be indicative of all double bond locations. The oxy-Cope rearrangement is specific for a structural unit, namely the 3-hydroxy-1,5-diene moiety.

Barley Lipid Transfer Protein, LTP1, Contains a New Type of Lipid-like Post-translational Modification*

“…7C. This spectrum is dominated by successive losses of water and carbon dioxide as reported to be characteristic for low energy collision-induced dissociation of monohydroxylated unsaturated fatty acid anions (33). In addition, numerous low abundance fragment ions derived from the cleavage of the hydrocarbon backbone are observed, many of which are not visible in Fig.…”

Mass spectrometric analysis of leukotriene A4 and other chemically reactive metabolites of arachidonic acid

“…These ions were produced at much lower abundance than the previous described ions. The ion at m/z 203 has been observed in the collisional activation of other eicosanoids with a single oxygen substitution at carbon atom 5 such as 5-HETE [16] and 5-oxo-ETE [17]. The appearance of m/z 189 has been previously observed in the mass spectra of other leukotrienes which contain a conjugated triene motif [18].…”

On the cellular metabolism of the click chemistry probe 19-alkyne arachidonic acid

“…In cells incubated with AA-alk, a peak corresponding to AA-alk was observed on chromatograms, as well as second peak eluting dehydration/decarboxylation products with m/z of 297 and 253, respectively, were present, as were the expected fragmentation ions of a 12-hydroxylated product with m/z of 179 and 208 (supplemental Figure S3B) (18,42). Importantly, the expected fragmentation ion of 11-HETE-alk with an m/z of 167 (18,42) was absent. Platelets stimulated in the presence of exogenous AA-alk also produced 12-HETE and HHTrE generated from endogenous AA.…”