In vitro production of long chain pyrrole fatty esters from carbonyl-amine reactions.

The reaction of lipoxygenase pathway products methyl 9,10(Z)-epoxy-13-oxo-11(E)-octadecenoate (13-MZEO) and methyl 12,13(Z)-epoxy-9-oxo-10(E)-octadecenoate (9-MZEO), with butylamine and lysine was studied in order to investigate whether some oxidized fatty acids are able to react with amino groups, analogously to volatile aldehydes, and, therefore, contribute to the overall protein damage produced during oxidative stress. The reaction mixtures were incubated at room temperature or 37 degrees C; the products were fractionated by semipreparative high performance liquid chromatography, and characterized by 1H and 13C nuclear magnetic resonance spectroscopy and mass spectrometry. The products identified were methyl 9-hydroxy-9-(5-pentyl-N-alkylpyrrole-2-)nonanoate and N-alkyl-2-pentylpyrrole for the 13-MZEO, and methyl 8-[5-(1'-hydroxyhexyl)-N-alkyl-pyrrole-2-]octanoate and methyl 8-(N-alkylpyrrole-2-)octanoate for the 9-MZEO. Formation of these pairs of analogs suggested that compounds were produced by one mechanism with the loss of the 5-substituent as a short-chain aldehyde, which was identified for the 13-MZEO. A reaction mechanism that explains the formation of all these compounds is proposed and the biological significance of these findings in relation to low density lipoprotein oxidation is discussed. Although these results do not demonstrate the formation of long-chain pyrrole fatty acids in vivo, they suggest that these pyrroles could be produced as an ultimate step in the lipid peroxidation process.