Formation of Arginine Modifications in a Model System of Nα-tert-Butoxycarbonyl (Boc)-Arginine with Methylglyoxal

The present study deals with the mechanistic reaction pathway of the a-dicarbonyl compound methylglyoxal with the guanidino group of arginine. Eight products were formed from the reaction of methylglyoxal with N-alpha-tert-butoxycarbonyl (Boc)-arginine under physiological conditions (pH 7.4 and 37 C). Isolation and purification of substances were achieved using cation-exchange chromatography and preparative high-performance liquid chromatography (HPLC). Structures were verified by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry. 2-Amino-5-(2-amino-4-hydro-4-methyl-5-imidazolinone-1-yl)pentanoic acid (3) was determined as the key intermediate precursor within the total reaction scheme. Kinetic studies identified N-alpha-(5-methy1-4-oxo-5-hydroimidazolinone-2-y1)-L-omithine and N-alpha-carboxyethylarginine as thermodynamically more stable products from compound 3. Further mechanistic investigations revealed an acidic hydrogen at C-8 of compound 3 to trigger aldol condensations. This reactivity of compound 3 allowed for the addition of another molecule of methylglyoxal to form products, such as N-alpha-(4-carboxy-4,6-dimethyl-5,6-dihydroxy-1,4,5,6-tetrahydropyrimidine-2-yl)-L-omithine and argpyrimidine.