C-2 Epimerization of Aldoses by Calcium Ion in Basic Solutions. A Simple System to Transform d-Glucose and d-Xylose into d-Mannose and d-Lyxose

Abstract

Aldoses were epimerized at C-2 by Ca2+ in aqueous or alcoholic basic solutions through a stereospecific [1-2] rearrangement of the carbon skeletons of the aldose. The skeletal rearrangement was confirmed by 13C NMR analysis of the reaction products. The reaction of [1-13C]- and [2-13C]-d-glucose afforded [2-13C]- and [1-13C]-d-mannose, respectively, as major products. The effects of metal ions, bases, and solvents were examined, and it was found that a high concentration of Ca2+ and a base (>pH 12.3) were especially effective for the present rearrangement. Separation of the reaction products was also effected by using Ca2+ cation-exchange chromatography. Thus, under the optimized conditions, d-mannose and d-lyxose, which are rare in nature and expensive, were easily obtained in high isolated yields from d-glucose and d-xylose, respectively.

Catalytic Isomerization of Biomass‐Derived Aldoses: A Review

“…The calcium-catalyzed epimerization was discovered by Kusin in 1936. [94] Much later,t his process was revisited andi nvestigated by Yanagihara et al [95,101] and Angyal. [102] It has been suggestedt hat, under alkaline conditions, glucosef orms complexes with selected cations, such as Ca 2 + ,L a 3 + ,a nd Nd 3 + .…”

Kinetic analysis for the isomerization of glucose, fructose, and mannose in subcritical aqueous ethanol

“…[5][6][7] In alkaline aqueous solutions, fructose isomerized to glucose with the highest rate and excellent selectivity. However, the isomerization of mannose was the slowest, and both glucose and fructose were produced almost in the same yield.…”

“…5) Moreover, mannose isomerized slower than glucose in many ethanolic and methanolic solutions of metal ions. 6,7) Many studies reported that glucose was isomerized to fructose more easily than mannose under alkaline conditions. 15,19,20) These studies were carried out at low reaction temperatures.…”

“…The promoting effect of ethanol at low temperatures is usually attributed to changes in both the conformation and configuration of saccharides in aqueous ethanol 15) and the change in the apparent chemical equilibrium. 7) We have previously reported that the degree of hydrolysis of sucrose changed by the addition of ethanol under subcritical conditions.…”

“…The product distribution in metal-catalyzed isomerization depends on the type of metal ion, saccharides, cosolvents, and metal ion carrier. [6][7][8] Metal-catalyzed isomerization cannot meet commercial demands because of the low feed concentration of the substrates or the difficulty in synthesizing the catalysts. The current industrial isomerization process to produce fructose involves the utilization of an immobilized glucose isomerase.…”