Fluorescent pyrrole products from carbonyl-amine reactions

Abstract

The reaction of (E)-4,5-epoxy-(E)-2-heptenal with butylamine and glycine methyl ester produced brown macromolecular pigments, which showed fluorescent characteristics similar to lipofuscins. This polymerization reaction implies in the first step the formation of 1-alkyl-2-(1'-hydroxyalkyl)pyrroles (IV, VI). Compounds IV and VI have been isolated and characterized from the above reactions, and their structures confirmed with the synthesis of 2-(1'-hydroxyethyl)-1-methylpyrrole (V). Compounds IV-VI resulted very unstable and even diluted solutions of them polymerized with time. The first step was the production of a dipyrrymethane VIII, which evolved more stable dipyrrylmethenes IX and X by intramolecular dehydration. These dimers continued polymerizing to produce 16H-tripyrrin derivatives XI and XII, and, in the next step, hexahydroglobins XIII and XIV. All these compounds have been characterized by 1H NMR and/or gas chromatography coupled with mass spectrometry or mass spectrometry. Additional polymerization produced higher molecular weight polymers that were the responsible for the brown color and the fluorescence. The above results suggest that the fluorescence produced by reaction between some oxidized lipids and amino acids may be related to polymerization more than to the formation of single structures.