Nuclear Magnetic Resonance Spectra of α-D-Glucans in the Presence of 1, 1, 3, 3-Tetramethylurea

抄録

1, 1, 3, 3-Tetramethylurea (Me₄U) promotes the alkylation of α-D-glucans and prevents caramelization and side reactions in acetolysis and acid hydrolysis of α-D-glucans even at high reaction temperatures. This might be caused by strong intermolecular hydrogen bondings between hydroxyls of carbohydrates and the carbonyl group of Me₄U, which prevail over intramolecular hydrogen bondings between the alcoholic hydroxyls. The hydrogen bondings as such induce deformation of the rigid higher structure of polyglucans to promote the alkylation, while they protect hydroxyls from side reactions during the course of modified acetolysis and acid hydrolysis even at high temperature to produce oligosaccharide fragments in good yields.In the present study the interaction betwen Me₄U and hydroxyls of glucans has been demonstrated by means of proton and carbon-13 nuclear magnetic resonance (¹H- and ¹³C-NMR) spectroscopy.The ¹H- and ¹³C-NMR spectra of carbohydrates remain unchanged even after heating for 30 min at 160°C in the presence of d₁₂-Me₄U in d₆-dimethyl sulfoxide, whereas without d₁₂-Me₄U in the medium, heating the solution causes remarkable changes.