Structure-reactivity relationship of Amadori rearrangement products compared to related ketoses

Structure-reactivity relationships of Amadori rearrangement products compared to their related ketoses were derived from multiple NMR spectroscopic techniques. Besides structure elucidation of six Amadori rearrangement products derived from D-glucose and D-galactose with L-alanine, L-phenylalanine and L-proline, especially quantitative C-13 selective saturation transfer NMR spectroscopy was applied to deduce information on isomeric systems. It could be shown exemplarily that the Amadori compound N-(1-deoxy-D-fructos-1-yl)-L-proline exhibits much higher isomerisation rates than D-fructose, which can be explained by C-1 substituent mediated intramolecular catalysis. In combination with a reduced carbonyl activity of Amadori compounds compared to their related ketoses which results in an increased acyclic keto isomer concentration, the results on isomerisation dynamics lead to a highly significant increased reactivity of Amadori compounds. This can be clearly seen, comparing approximated carbohydrate milieu stability time constants (ACuSTiC) which is 1 s for N-(1-deoxy-D-fructos-1-yl)-L-proline and 10 s for D-fructose at pD 4.20 +/- 0.05 at 350 K. In addition, first NMR spectroscopic data are provided, which prove that alpha-pyranose of (amino acid substituted) D-fructose adopts both, C-2(5) and C-5(2) conformation. (C) 2016 Elsevier Ltd. All rights reserved.