Liquid chromatography/tandem mass spectrometric analysis of 7,10-dihydroxyoctadecenoic acid, its isotopomers, and other 7,10-dihydroxy fatty acids formed byPseudomonas aeruginosa42A2

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen, which oxidizes oleic acid to 7(S),10(S)-dihydroxy-8(E)-octadecenoic acid (7,10-(OH)(2)-18:1) of biological and industrial interest. Electrospray tandem mass spectrometric (MS/MS) analysis of hydroxylated fatty acids usually generates characteristic fragments containing the carboxylate anion and formed by alpha-cleavage at the oxidized carbon. These fragments indicate the positions of the hydroxyl group. In contrast, liquid chromatography (LC)/MS/MS analysis of 7,10-(OH)(2)-18:1 yielded a series of other ions with structural information. To study the fragmentation mechanism, we prepared (2)H- and (18)O-labeled isotopomers. We also performed MS(3) analysis of the major ions, and for comparison we generated the corresponding 7,10-dihydroxy metabolites of 16:1n-7, 18:2n-6, and 20:1n-11 with a protein extract of P. aeruginosa. The MS/MS spectra of 7,10-(OH)(2)-18:1 and its isotopomers, 7,10-(OH)(2)-16:1, and 7,10-(OH)(2)-20:1, contained a series of prominent fragments that all hold the omega end. The 8,9-double bond was not essential for this fragmentation, as 7,10-(OH)(2)-18:0, and its isotopomers, formed essentially the same fragments in the lower mass range. In contrast, 7,10-dihydroxy-8(E),12(Z)-octadecadienoic acid (7,10-(OH)(2)-18:2) fragmented by alpha-cleavage at the oxidized carbons with formation of carboxylate anions. Our results demonstrate that C(16)-C(20) fatty acids with a 7,10-dihydroxy-8(E) functionality undergo charge-driven fragmentation after charge migration to the omega-end, whereas the main ions of 7,10-(HO)(2)-18:2 retain charge at the carboxyl group.

Charge migration fragmentation in the negative ion mode of cyclopentenone and cyclopentanone intermediates in the biosynthesis of jasmonates

“…7,8 trans-12-OPA was obtained by catalytic hydrogenation (Pt in MeOH) of trans-12-OPEA. [9,10,13,15, [7,8,10,11,13,…”

“…7,8 The biosynthesis of 12-OPDA and 12-OPEA from the allene oxides by AOC is shown in Figure 1 or charge migration fragmentation (CMF). Oxylipins with hydroperoxy, hydroxy, and epoxy groups can form informative anions by CRF via dehydration or elimination of aldehydes, [9][10][11][12][13][14][15] whereas CMF typically yields anions due to loss of water or CO 2 from the carboxyl group ([M-H-H 2 O] − and ([M-H-CO 2 ] − , respectively, and due to displacement reactions or acyl chain cleavages. [16][17][18][19] The…”

Fragmentation reactions using electrospray ionization mass spectrometry: an important tool for the structural elucidation and characterization of synthetic and natural products

“…Therefore, the negative charge remains at the oxygen atom. 128 The elimination of formaldehyde from deprotonated compounds containing methoxyl groups attached to aromatic rings has been reported for many classes of natural products. Herath and co-workers 129 investigated the fragmentation of deprotonated dimethoxybenzoic acid derivatives and proposed that the elimination of carbon dioxide and formaldehyde involves a-elimination (Fig.…”

Stereoselective oxidation of regioisomeric octadecenoic acids by fatty acid dioxygenases

“…The fragmentation of HpOME with 1-hydroperoxy-2-propene elements thus varies with the position. For comparison, 7,10-DiHOME(8 E ) fragments in a different way than 5,8-DiHOME, 7,8-DiHOME, and 8,11-DiHOME ( 47 ). If needed, GC-MS analysis can usually be used to identify regioisomeric HOME and other oxylipins without ambiguity ( 48 ).…”