Mechanistic study on the conversion of D-fructose into deoxyfructosazine: Insights from NMR and DFT study

In situ C-13 and H-1 NMR and selective 1D TOCSY spectra have been used for analyzing reactive intermediates in fructose conversion, where fructose with diammonium hydrogen phosphate [(NH4)(2)HPO4] is consumed via a glucosamine (GlcNH(2)) intermediate. Our data indicate that the nitrogen in (NH4)(2)HPO4 maps onto the intermediate GlcNH(2) and subsequent to the corresponding product deoxyfructosazine (DOF). Pathways leading to isomerization of fructose have furthermore been identified through DFT calculations. The inclusion of solvent effects results in substantial reduction of the fructose ring-opening free energy barrier (19.4 kcal/mol). Interestingly, lower free energy barrier (21.0 kcal/mol) indicating that the formation of intermediate GlcNH(2) is both thermodynamically and kinetically accessible in agreement with the experimental results. Yield of DOF reaches 46% under the optimized conditions. (C) 2019 Elsevier Ltd. All rights reserved.