Deep Eutectic Solvents: Green Solvents and Catalysts for the Preparation of Pyrazine Derivatives by Self-Condensation of d‑Glucosamine

Deep eutectic solvents (DESs) exhibit similar physicochemical properties to the ionic liquids. They are inexpensive, renewable, nontoxic, and environmentally benign solvents and have gradually attracted attention in several fields, for example, biorefinery. Here choline chloride-based DESs have been used as solvents and catalysts for the preparation of deoxyfructosazine (DOF) through a self-condensation reaction of d-glucosamine (GlcNH₂). The catalytic performances of a “green cocatalyst”, amino acids, and the reaction mechanism were also studied. The results displayed that choline chloride/urea was capable to convert GlcNH₂ efficiently, with a 13.5% yield of DOF at low temperature and with a short reaction time (100 °C, 150 min). Among the screened amino acids, arginine showed the highest activity and gave the highest yield of DOF (30.1%) under the optimized reaction conditions. Nuclear magnetic resonance (NMR) studies revealed a strong hydrogen bond interaction between GlcNH₂ and arginine. Moreover, a detectable intermediate, namely dihydrofructosazine, in the condensation of GlcNH₂ to DOF/fructosazine (FZ) was captured by in situ NMR technique.