Ternary deep eutectic solvents catalyzed D-glucosamine self-condensation to deoxyfructosazine: NMR study

Ternary deep eutectic solvents (TDESs) comprising choline chloride (ChCl), glycerol and L-arginine were synthesized as catalysts and solvents for the conversion of D-glucosamine (GlcNH(2)) into deoxyfructosazine (DOF). The interactions between these three components in the prepared TDESs were studied by H-1-, Cl-35-NMR spectra and H-1 diffusion-ordered spectroscopy (DOSY) measurements. The chemical shift changes of active hydrogen in the H-1-NMR spectra of TDES system and widening of signals in the Cl-35-NMR spectra confirmed the hydrogen bonding interaction between the components, which was further supported by the decrease of diffusion coefficients (D) of the TDES components according to H-1 DOSY measurements. The influences of reaction temperature and L-arginine content in the TDESs on the yield of DOF were also studied. The experimental results have shown that when the molar ratio of ChCl, glycerol, and L-arginine was 1:2:0.1, DOF was the major product with a yield of 22.6% at 90 degrees C for 120 min. The chemical shift titration indicated that the carboxyl group of L-arginine in the TDES is the catalytical active site, so the mechanism of the catalytic reaction between GlcNH(2) and the TDES was proposed. Moreover, a reaction intermediate, dihydrofructosazine, was identified in the self-condensation reaction of GlcNH(2) by an in situ H-1 NMR technique. (C) 2020, Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.

Automated summary

Ternary deep eutectic solvents composed of choline chloride, glycerol, and L-arginine were synthesized for the conversion of D-glucosamine into deoxyfructosazine. The interactions between the components were studied through spectroscopic analysis, and the influences of reaction temperature and L-arginine content on the yield of the product were investigated. The active site for catalysis was identified, and a reaction intermediate was detected in the self-condensation reaction using in situ H-1 NMR technique.