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

Abstract In situ 13C and 1H NMR and selective 1D TOCSY spectra have been used for analyzing reactive intermediates in fructose conversion, where fructose with diammonium hydrogen phosphate [(NH4)2HPO4] is consumed via a glucosamine (GlcNH2) intermediate. Our data indicate that the nitrogen in (NH4)2HPO4 maps onto the intermediate GlcNH2 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 GlcNH2 is both thermodynamically and kinetically accessible in agreement with the experimental results. Yield of DOF reaches 46% under the optimized conditions.