Development of Sugar Transformation System Using New Complex Catalysis

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Effective synthetic procedures for naturally rare carbohydrates and their derivatives are highly desirable in the field of industry. Form this point of view we have carried out the following investigations. We examined the C-2 epimerization of aldoses in methanol, by combinations of diamines, monoamines or aminoalcohols with some transition metal, alkaline earth metal and rare earth metal ions which have affinity for carbohydrates. Among the metal ions used, Ni^<2+>, Co^<2+> and Ca^<2+> proved to be effective. The Ca^<2+> -N-substituted monoamine system in particular has many advantage for practical use. The reaction mechanisms of these sugar transformation reactions have been clarified by nuclear magnetic resonance, electronic absorption, circular dichroism and EXAFS spectroscopies. We observed that stereselective uptake of mannose type of the epimeric aldoses by nickel (II) complexes of N-subsituted diamines. In order to elucidate the factor that caused the stereoselective uptake we carried out the EXAFS study. This EXAFS study suggested that the key to the stereoselctive complexation of mannose-type aldoses having some donor groups lies in the briding part of the mannofuranoside residue which seems to have a strong affinity for nickel (II) ions. New nickel (II) N-glycoside complexes were formed from tris (2-aminoethyl) amine with aldoses. The amine ligands act as effective anchors for the accumulation of three sugar molecules. The newly discovered sugar trans formation reaction using Ca^<2+>-diethylamine (DEA) system was applied to the synthesis of D-mannitol, which is useful as a dietary sweeteners, from naturally abundant D-glucose. Isomerization and C-2 epimerization of the starting D-glucose by Ca^<2+>-DEA system and subsequent hydrogenation by rany nickel catalyst gave D-mannitol and D-glucitol in moderato yield. This simple system of Ca^<2+>- monoamine system might have much potential from a industrial point of view.