Characterization and detection of lysine–arginine cross-links derived from dehydroascorbic acid

Synthesis are reported for the lysine–arginine cross-links 9 , 11 , and 16 . Covalently cross-linked proteins are among the major modifications caused by the advanced Maillard reaction. So far, the chemical nature of these aggregates is largely unknown. l-Dehydroascorbic acid (DHA, 5 ), the oxidation product of l-ascorbic acid (vitamin C), is known as a potent glycation agent. Identification is reported for the lysine–arginine cross-links N 6-[2-[(4-amino-4-carboxybutyl)amino]-5-(2-hydroxyethyl)-3,5-dihydro-4 H-imidazol-4-ylidene]- l-lysine ( 9 ), N 6-[2-[(4-amino-4-carboxybutyl)amino]-5-(1,2-dihydroxyethyl)-3,5-dihydro-4 H-imidazol-4-ylidene]- l-lysine ( 11 ), and N 6-[2-[(4-amino-4-carboxybutyl)amino]-5-[(1 S,2 S)-1,2,3-trihydroxypropyl]-3,5-dihydro-4 H-imidazol-4-ylidene]- l-lysine ( 13 ). The formation pathways could be established starting from dehydroascorbic acid ( 5 ), the degradation products 1,3,4-trihydroxybutan-2-one ( 7 , l-erythrulose), 3,4-dihydroxy-2-oxobutanal ( 10 , l-threosone), and l- threo-pentos-2-ulose ( 12 , l-xylosone) were proven as precursors of the lysine–arginine cross-links 9 , 11 , and 13 . Products 9 and 11 were synthesized starting from DHA 5 , compound N 6-[2-[(4-amino-4-carboxybutyl)amino]-5-[(1 S,2 R)-1,2,3-trihydroxypropyl]-3,5-dihydro-4 H-imidazol-4-ylidene]- l-lysine ( 16 ) via the precursor d- erythro-pentos-2-ulose ( 15 ). The present study revealed that the modification of lysine and arginine side chains by DHA 5 is a complex process and could involve a number of reactive carbonyl species.