Tryptophan Amadori rearrangement product (ARP) was synthesized, and its decomposition was studied at two different temperatures and concentrations over a period of 6 h. RP-HPLC analysis of the reaction mixtures indicated the presence of hydroxymethylfurfural (HMF), maltol, tryptophan, indole, norharman and harman. Kinetic analysis showed that the activation energy (Ea) for the decomposition of ARP and for the formation of maltol from ARP depended on the water content of the reaction mixture; on the other hand, the Ea (4.1 kcal/mol) for the formation of HMF from the ARP was independent of the water content. A comparative study of the formation of HMF and maltol from ARP and from glucose alone showed that the Amadori rearrangement provides a low-energy pathway for the formation of these two compounds. The kinetic data were used to propose plausible mechanisms for the decomposition of the ARP.

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The various tautomeric forms of the tryptophan Amadori rearrangement product, including the openchain keto form, were separated at room temperature, for the first time by HPLC, on a C-18 Ultrasphere, 5 pm, 2.0 x 150 mm reversed-phase column using 5% H3P04 (0.01 M) in CH3CN (pH 2.8) as mobile phase. The flow rate was 0.6 mL/min, and the UV detector was set a t 280 nm. At these conditions, the concentration of @-pyranose was 45.2%, a-furanose, 27.4%, @-furanose 12.5%, a-pyranose 10.lCu, and keto form 4.77". The effect of pH on the relative concentrations of each tautomer was also determined.

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