Isomeric distribution of monosaccharides in deep eutectic solvents: NMR study

As counter parts of ILs, DESs have received general interest because of their comparable physicochemical properties to Is and facile preparation from readily available chemicals. In this work, the isomeric distributions of fructose, glucose, xylose and GIcNAc in CCU, CCG and CCO, i.e. basic, neutral and acidic DES, have been determined by C-13 NMR. Higher furanose fraction of fructose was observed in CCO compared to CCG and CCU. The glucose was chosen as model compound to reveal the effect of DES on the mutarotation behavior with DMSO d(6) as co-solvents. The experimental results showed that a high ratio of CCU to glucose speed up the mutarotation rate of glucose in DMSO d(6), but have little influence on the anomeric distribution. Furthermore, the mutarotation of glucose in DESs is mainly driven by the HBD, whereas HBA provides little influence. However, HBD and HBA display a synergistic effect on the glucose mutarotation process. Hydrogen bonding between hydrogen of amino in urea and oxygen of hydroxyl in glucose is the driving force for the interconversion of anomers. (C) 2018 Elsevier B.V. All rights reserved.