Journal
ANALYTICAL BIOCHEMISTRY
Volume 354, Issue 1, Pages 111-126Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ab.2006.04.010
Keywords
epoxide migration; hydroperoxylinoleic acid; ion trap mass spectrometry; keto-enol tautomerism; keto fatty acids
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Hydroperoxides of polyunsaturated fatty acids can be transformed to epoxyalcohols and keto fatty acids by metal enzymes, hematin, and various catalysts. In the current study, we used hematin to transform 9-hydroperoxy-10E,12Z-octadecadienoic acid and 13-hydroperoxy-9Z, 11E-octadecadienoic acid to epoxyalcohols (with trans epoxide configuration) and to keto fatty acids. The products were separated by normal phase high-performance liquid chromatography (NP-HPLC) and analyzed using postcolumn addition of isopropanol/ water and online negative ion electrospray ionization mass spectrometry (MS). The tandem MS (MS/MS) spectra were studied using analogs prepared from [9,10,12,13-H-2(4)]linoleic acid (18:2n-6) and from alpha-linolenic acid (18:3n-3). We also studied the MS/MS spectra of epoxyalcohols formed from 11-hydroperoxy- and 8-hydroperoxy-9Z, 12Z-octadecadienoic acids. Results were confirmed by MS/MS analysis of a series of authentic standards. MS/MS ions of 9-keto-10E,12Z-octadecadienoic acid and 13-keto-9Z,11E-octadecadiciloic acid could be explained by keto-enol tautomerism. MS/MS spectra of regioisomeric allylic epoxyalcohols differed in relative intensities of characteristic ions. The MS/MS spectra of the epoxyalcohols with 1-hydroxy-2,3-epoxy-4Z-pentene or 3-hydroxy-1,2-epoxy-4Z-pentene elements were virtually identical and showed two characteristic ions that differed by 30 in m/z values (CH(OH)). The results suggested that epoxide migration (Payne rearrangement) occurred during collision-induced dissociation. We conclude that regioisomeric allylic epoxyalcohols can be identified by their MS/MS spectra, whereas regioisomeric epoxyalcohols can be identified by MS/MS in combination with their retention times on NP-HPLC. (c) 2006 Elsevier Inc. All rights reserved.
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