Structure and Potential Cross‐linking Reactivity of a New Pentose-Specific Maillard Product

The Maillard reaction of model compounds for peptide-bound lysine (4-aminobutyric acid, 6-aminocaproic acid, N^α-acetyl-l-lysine) with reducing sugars (d-ribose, d-xylose, d-arabinose, d-glucose, d-fructose, d-glyceraldehyde) was investigated under both stringent and mild conditions. With pentoses the corresponding co-(dimethylmaleimido)carboxylic acids 1‐3 were identified as substantial, hitherto unknown components by GC/MS and NMR. Their structure was confirmed by synthesis. A pathway to compounds 1‐3 was derived from the results of 4-aminobutyric acid/[1-¹³C]-d-arabinose isotopic labeling experiments. The new N-(dimethylmaleoyl)-ω-aminocarboxylic acid derivatives are shown to react under very mild conditions (pH 7, 32 °C) with thiols (methyl 3-mercaptopropionate, N^α-acetyl-l-cysteine methyl ester) to form the addition products 4-6. This reaction demonstrates that compounds of type 1-3 can be considered as potential protein crosslinkers in Maillard reactions.