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

Abstract

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 (&amp;gt;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.