title: Payne rearrangement during analysis of epoxyalcohols of linoleic and alpha-linolenic acids by normal phase liquid chromatography with tandem mass spectrometry.
abstract: 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 [9,10,12,13-2H4]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-octadecadienoic 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.
authors.affiliation: Department of Pharmaceutical Biosciences, Biomedical Center, Uppsala University, SE-751 24 Uppsala, Sweden. ernst.oliw@farmbio.uu.se
authors.forename: Ernst H
authors.initials: EH
authors.lastname: Oliw
authors.forename: Ulrike
authors.initials: U
authors.lastname: Garscha
authors.forename: Tomas
authors.initials: T
authors.lastname: Nilsson
authors.forename: Mirela
authors.initials: M
authors.lastname: Cristea
mesh_terms: D002384:Catalysis; D002853:Chromatography, Liquid / Q000379:methods*; D006427:Hemin / Q000378:metabolism / Q000494:pharmacology; D019787:Linoleic Acid / Q000032:analysis* / Q000737:chemistry*; D008054:Lipid Peroxides / Q000378:metabolism; D008084:Lipoxygenase / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods*; D010105:Oxygenases / Q000378:metabolism; D013237:Stereoisomerism; D017962:alpha-Linolenic Acid / Q000031:analogs & derivatives / Q000032:analysis* / Q000737:chemistry*
chemical_list: D008054:Lipid Peroxides; D017962:alpha-Linolenic Acid; D006427:Hemin; D019787:Linoleic Acid; D010105:Oxygenases; D008084:Lipoxygenase; C122014:linoleate diol synthase