Studies on peroxidized lipids. II. Fluorescent products relevant to aging pigments derived from malondialdehyde and methylamine.

Abstract

Malondialdehyde (MDA) is a secondary product of in vitro and in vivo lipid peroxidation. Reactions of MDA, prepared by acid hydrolysis of malonaldehyde bis (dimethylacetal), with methylamine were performed at 37°under various pH conditions (pH 1-8). Two major fluorescent compounds, 1, 4-dimethyl-1, 4-dihydropyridine-3, 5-dialdehyde (1) and 1-methyl-4-(dimethoxyethyl)-1, 4-dihydropyridine-3, 5-dialdehyde (2), and two nonfluorescent UV-absorbing by-products, β-methylaminoacrolein (3) and 2, 6-dimethyl-2, 6-diazabicyclo [3.3.1] 3, 7-nonadiene-4, 8-dialdehyde (4), were isolated. The structures of these products were elucidated by analysis of their 13C and 1H NMR spectra, mass spectra and UV absorption spectra. Compounds 1 and 2 were produced in the best yields at pH 6-8, 3 was produced at every pH, and 4 was produced at pH 2-5. The 1, 4-dihydropyridine-3, 5-dialdehyde fluorophore in 1 and 2 may have been formed via a Hantzsch-type reaction of MDA and methylamine. The fluorescence spectrum of 1 with a maximum at 460 nm was the same as that of a conjugated Schiff base of MDA and amino acid or those of aging or lipofuscin pigments accumulated in the cells.