Use of methyl oxime derivatives to enhance structural information in thermospray high-performance liquid chromatography-mass spectrometry: Analysis of linoleic acid lipoxygenase metabolites in maize embryos

Abstract

Lipoxygenase derived metabolites of linoleic acid generated by incubation with protein extracts from maize embryos treated with abscisic acid have been analysed by thermospray high-performance liquid chromatography-mass spectrometry (HPLC-TSP-MS). TSP-MS data for various isomeric α-and γ-ketols, ketodiols and trihydroxyacids are reported. The molecular weight and the minimum number of oxygenated functions in the structures can be readily characterized from the TSP spectra obtained in the positive and negative ion modes of acquisition. TSP analysis of the methoximated compounds allows the characterization of ketone or aldehyde groups. Additionally, the methoximated derivatives show abundant ions derived from concomitant losses of methanol and the breakdown of the CC bond α to the methoxime. These ions are the base peaks in the TSP spectra of compounds bearing an α-ketol moiety in their structures. The TSP data and fragment assigments are in agreement with the structures previously elucidated by gas chromatography (GC)-MS techniques. Furthermore, the characteristic fragmentation pattern of the methoxime derivatives allows the characterization of a pair of positional isomer α-ketols not detected previously by GC-MS. Some of these metabolites have not been described before in maize