Amadori rearrangement reversed

When 15 mM /Va-formyl-/Ve-fructosyl-lysine (fFL) in 0.2 M phosphate buffer, pH 7.4, was incubated in air for 15 d at 37 °C, not only was CML formed, but a substantial amount of lysine was recovered, which N. Ahmed el al.50 and M.U. Ahmed el al.51 interpreted as due to reversal of the Amadori rearrangement. The reduction of the reaction mixture with NaBH4 and subsequent identification of both glucitol and mannitol supports the interpretation. 

Carson 66) induced a reverse Amadori rearrangement with the conversion of V-alkylfructosylamines to aldose derivatives. By the reaction of primary alkylamines with fructose under anhydrous conditions, crystalline monoamino condensation products were obtained. V-Ethylfructosyl-amine was the only fructosylamine isolated. Usually the products were 2-amino-2-deoxyaldoses, probably of glucose configuration. Presumably. 

Radical reaction mechanisms during the early Maillard reaction were first detected by Namiki et al. (7, 2). He identified iV.A -dialkylpyrazine-cation radicals that originated from the primary Schiff base formed by reaction between glucose and amino acids. The glycolaldehyde alkylimine formed by a reverse aldol reaction of the Schiff base leads to a dialkylpyrazinium radical cation after self-condensation. The formation of dialkylpyrazinium radical cations, which could be detected by EPR spectrometry, represents an alternative pathway of the Maillard reaction it starts at the very beginning of die reaction, well before the formation of Amadori rearrangement products and depends on the pH value it starts around pH 7 and increases up to pH 11. 

Ketoses also react with both aliphatic and aromatic amines, and the derived ketosylamines (XXXIII) can also rearrange in a reverse of the Amadori rearrangement with the formation of a 2-amino-2-deoxy-aldose (XXXIV). 

The nonenzymatic condensation of glucose with protein amino groups results in a Schiflf base which may rearrange to form the Amadori product (Fig. 1). Both of these early products of glycation form reversibly (Roth, 1983 Baynes and Monnier, 1988). 

FIGURE 1. Protein glycation. The open chain form of glucose can react with protein reversibly, forming a Schiff base. This may then rearrange to form the Amadori product, which in turn can form advanced glycation end products (AGE). The formation of AGE, attached or unattached to protein, occurs in a transition metal-dependent oxidative process. This process has also been termed glycoxidation. 

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