Tautomers carbohydrates

Interconversion of Carbohydrates in Base Section 25.4 Interconversion of Carbonyl and Enol Tautomers in Acid Section 20.1 Figure 20.1... 

The decarbonylation reaction is not confined to aldehydes, but also embraces those compounds that have aldehyde tautomers. Thus, both carbohydrates and allylic alcohols can be decarbonylated. When glucose is allowed to react with frani -[RhCl(CO)(PPh3)2] in A -methylpyrrolidin-2-one, decarbonylation occurs and arabinitol is formed with retention of configuration. The decarbonylation of fructose to arabinitol is complicated by the simultaneous dehydration to furfinyl alcohol, which is the major product. Analogous reactions occur with lower carbohydrates in the limit, glycolaldehyde is decarbonylated to methanol. Aldose derivatives can also be converted to their C i analogues, but the yields are only about half of those obtained with the parent aldoses. Disaccharides usually give better yields. 

M. B. Thygesen, J. Sauer, and K. J. Jensen, Chemoseleetive capture of glycans for analysis on gold nanoparticles Carbohydrate oxime tautomers provide functional recognition by proteins, Chem. Eur. J., 15 (2009) 1649-1660. 

The keto tautomer has been isolated in crystalline form for a number of D-fruc-tose-A -alkylanilines and the structure was unequivocally confirmed by IR and solid-state NMR spectroscopic data, " as well as by X-ray diffraction studies. " The ability of D-fructose-A -alkylanilines to crystallize spontaneously in the acyclic keto form is unprecedented among six-carbon reducing carbohydrates, and is matehed only by ribulos- and xylulos-amines, " which themselves are the Amadori rearrangement products. This phenomenon may be explained on the basis of an interplay of the hydrophobic effect and crystal-packing forces, given that many D-fruetose-A -alkylanilines still crystallize in the p-pyranose form, and for the majority of those which crystalhze in the keto form, the acyclic tautomer constitotes a minor eonstituent in equilibrated solutions. 

V. V. Mossine, C. L. Barnes, M. S. Feadier, and T. P. Mawhiimey, Acyclic tautomers in crystalline carbohydrates The keto forms of 1-deoxy-l-carboxy-methylamino-D-2-pentuloses (pentulose-glycines), J. Am. Chem. Soc., 124 (2002) 15178-15179. 

V. V. Mossine, C. L. Barnes, G. V. Glinsky, and M. S. Feather, Interaction between two Cl-X-CT branched ketoses Observation of an unprecedented crystalline spiro-hicycXic hemiketal tautomer of A,A-di(l-deoxy-D-fructos-l-yl)-glycine ( difractose glycine ) having open chain carbohydrate, Carbohydr. Lett, 1 (1995) 355-362. 

The simplest aldose. Configurational standard for carbohydrates. In aq. soln., undergoes equilibration with dimers and with l,3-Dihydroxy-2-propanone, D-710 via the enediol tautomer. 

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