Glyoxal reaction with arginine

Imidazolone adducts formed by reaction of 3-deoxyglucosone or methylglyoxal with arginine and the imidazolium cross-links formed by the reaction of glyoxal and methylglyoxal with lysine residues in protein are also considered as biomarkers of protein oxidative damage (08). 

A detailed study of the reaction of methyl glyoxal 72 with iV-acetyl arginine and iV-acetyl cysteine has been performed and, importantly, it has been demonstrated that with reagent 72, PEGylation at lysine residues does not occur [256]. 

The reaction of dicarbonyl compounds, such as glyoxal or phenylglyoxal, with a guanidinyl group, such as that of an arginine residue, proceeds to yield a more stable linkage due to the formation of a cyclic derivative (Reaction 46). 

Much attention has recently been paid to arginine as a melanoidin precursor. In a model system, lV -acetylarginine was first allowed to react with glyoxal in aqueous solution at pH 7, followed by furfural. Repeated chromatography of the aqueous residue after ethyl acetate extraction led to a 1% yield of the deep red 29.180 Such a compound provides an example of a potentially coloured crosslink in proteins derived by the Maillard reaction (see Chapter 8). 

T. Hofmann, 4-Alkylidene-2-imino-5-[4-alkylidene-5-oxo-l,3-imidazol-2-inyl]aza-methylidine-l,3-imidazolidine —A novel colored substructure in melanoidins formed by Maillard reactions of bound arginine with glyoxal and furan-2-carboxaldehyde, J. Agric. Food Chem., 1998, 46, 3896-3901. 

U. Schwarzenbolz, T. Henle, and H. Klostermeyer, Studies on the reaction of glyoxal with protein-bound arginine, in F, 1998, 443. 

A more convenient method for the site-selective PEGylation of arginine has only recently been disclosed [255,256]. The process relies on the thermodynamic selectivity obtained upon reaction of the protein with methyl glyoxal analog 72. In aqueous solution, dimethyl acetal derivative 72 is in equilibrium with the unprotected forms, which are the actual PEGylating reagents (Equation 3.41). 

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