| Budget Amount *help |
¥5,100,000 (Direct Cost: ¥5,100,000)
Fiscal Year 1987: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1986: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1985: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
Much attention has recently been focused on rare naturally occurring sugars, with the elucidation of the biological functions of carbohydrates contained in glycoprotains, glycolipids, nucleic acids, and antibiotics. It is thus desirable to develop a methods whereby metal complexes promote transformations of sugars and stereoselective uptake of sugars. During a significant part of study to elucidate sugar-transition-metal interactions, an unprecedented binuclear nickel- (II) complex containing two types of N-glycosides formed from N,N'-dimethyl- ethylenediamine and D-mannose(DMna) was synthesized, and its structure was determined by X-ray crystallography. The metal center is a binuclear nickel complex with a bridbing mannose sugar residue. The bridging sugar ring takes the unusual furanose form. When D-glucose was used as a starting sugar instead of D- mannose, a nickel(II) complex was surprisingly obtained although its yield was very low. Prompted by this knowledge, we chose N,N,N'-trimethylethylenediamine (tmen) as the diamine component, which has one reaction point (secondary amino group) in the molecule. We have found that aldoses are rapidly epimerized at C- 2 in the presence of [Ni(H_2O)_2(tmen)_2]Cl_2 and, of the two C-2 epimers, nickel(II) ions form complexes with only the mannose-type epimers stereoselectively. The EXAFS study suggested that the Key to the stereoselective complexation of mannose type epimers lies in the bridging part of the furanoside residue which seems to have a strong affinity for-nickel(II) ions. The 13 C.NMR. study-of the Ni^<2+>- diamine-[1-^3C]-D-glucose system reveals that a novel stereospecific rearrangement of the carbon skleton, the exchange of C-1 and C-2 atoms by inversion of the C-1-C-2 aldose fragment, is involved in this reaction. The EXAFS study indicated that the reactive complex is mono nuvclear. From these observations obtained we proposed a plausible mechanism for the epimerization in the Ni2+- diamine-aldose system.
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