FORMATION OF 4-AMINOBUTYRIC ACID-SPECIFIC MAILLARD PRODUCTS FROM [1-C-13]-D-GLUCOSE, [1-C-13]-D-ARABINOSE, AND [1-C-13]-D-FRUCTOSE

The Maillard reaction of 1-C-13-labeled D-glucose, D-arabinose, and D-fructose with 4-aminobutyric acid was investigated. The extent and position of the isotopic labeling (from MS data) were used to evaluate origin, reactive intermediates, and formation pathways of pyrroles, 2-pyrrolidones, and some related products. The results are representative for peptide-bound lysine and systems with blocked Strecker amines. The observed distribution of the label supports 3-deoxyaldoketoses as intermediates of 2-formylpyrroles 1/3 and disqualifies 4-deoxy- and 1-deoxydiketose routes to 2-acetylpyrroles 2/4, respectively. 1,3-Dideoxy-1-amino-2,4-diketose C is postulated as a new key intermediate in the formation route to pyrroles 2/4 from glucose. Starting with 1-C-13]-D-fructose, a distinct tendency to a C-3/C-3-cleavage is observed. If the carbon skeleton remains intact, the reactions initiated by 2,3-enolization of the primarily formed fructosylamine are favored against those initiated by 1,2-enolization.