Synthesis of β-D-glucopyranuronosylamine in aqueous solution: kinetic study and synthetic potential

A systematic study of the synthesis of β-D-glucopyranuronosylamine in water is reported. When sodium D-glucuronate was reacted with ammonia and/or volatile ammonium salts in water a mixture of β-D-glucopyranuronosylamine and ammonium N-β-D-glucopyranuronosyl carbamate was obtained at a rate that strongly depended on the experimental conditions. In general higher ammonia and/or ammonium salt concentrations led to a faster conversion of the starting sugar into intermediate species and of the latter into the final products. Yet, some interesting trends and exceptions were observed. The use of saturated ammonium carbamate led to the fastest rates and the highest final yields of β-D-glucopyranuronosylamine/carbamate. With the exception of 1 M ammonia and 0.6 M ammonium salt, after 24 h of reaction all tested protocols led to higher yields of β-glycosylamine/carbamate than concentrated commercial ammonia alone. The mole fraction of α-D-glucopyranuronosylamine/carbamate at equilibrium was found to be 7-8% in water at 30°C. Concerning bis(β-D-glucopyranuronosyl)amine, less than 3% of it is formed in all cases, with a minimum value of 0.5% in the case of saturated ammonium carbamate. Surprisingly, the reaction was consistently faster in the case of sodium D-glucuronate than in the case of D-glucose (4-8 times faster). Finally, the synthetic usefulness of our approach was demonstrated by the synthesis of three N-acyl-β-D-glucopyranuronosylamines and one N-alkylcarbamoyl-β-D-glucopyranuronosylamine directly in aqueous-organic solution without resorting to protective group chemistry.