Gulose solution

Some 40 years ago Isbell (16) observed complex formation between calcium ions and a sugar which possesses the ax-eq-ax sequence—i.e., a-D-gulopyranose. He observed that an equilibrated solution of D-gulose, CaCl2, underwent further mutarotation on dilution with water and he correctly interpreted the phenomenon by postulating that a-D-gulo-pyranose (10), but not -D-gulopyranose, forms a complex with calcium... 

By treatment of D-gulose (XVII) or D-idose (XVIII) with warm aqueous barium hydroxide solution Van Ekenstein and Blanksma were able to isolate D-sorbose (II) with a melting point of 165° and [< ]d + 42.9° in water. The aldoses were prepared from D-gulonic and D-idonic lactones obtained by the cyanohydrin synthesis from D-xylose. 

The glycosides chosen for inclusion in Table VI are those which exist largely in one conformation. Interpretation of the rates of hydrolysis of those glycosides whose solutions contain appreciable concentrations of both chair conformations is more difficult. The methyl pyranosides of a-and 8-D-gulose and n-glycero-a- and -/S-D-gafo-heptose are in this class and their composite rate-constants have been computed to be 58.1, 19.0,... 

Preparation. D-Gulose may be obtained as a pure syrup by the Kiliani synthesis from D-xylose.111 Crystalline a-D-gulose.CaCl2.H2O was obtained upon evaporating in vacuo an aqueous solution of D-gulose containing about two molecular equivalents of calcium chloride.112... 

For the same conformational reasons, the P anomers of d aldoses dominate in aqueous solution when the Cf atom has the D configuration (ribose, xylose, allose, glucose, gulose, galactose). The a anomers, however, predominate when the atom has the l configuration (arabinose, lyxose, altrose, mannose, idose, talose). 

Application of vicinal C- H J values to derivatives of 3 4-0-benzylidene-galactose, 2,3-0-benzylidene-mannose, and 2,3-0-benzyl-idene-gulose, each as separate R and S epimers at the benzylidene carbon, has provided data on the conformations adopted. Where data were also available from jC-ray diffraction, the conformations were found to be the same in solution as in the solid state. 

A method of more general application depends on the reduction of iodo derivatives in which the iodine has replaced the hydroxyl of a primary alcoholic group. These are easily obtained by treatment of the tosyl derivatives with sodium iodide in acetone solution (sealed tube) or in refluxing acetonyl-acetone 228) or acetic anhydride 229). The reduction is often carried out by catalytic methods. The 5-deoxy-n-xylose is synthesized from D-xylose by this method, and by application of the cyanohydrin synthesis 6-deoxy-n-gulose is prepared 230). 

The solution was found in the S "epimer" of D-mannose, namely L-gulose 110 (Scheme 20), which can be readily obtained om commercially available L-gultmo-y-lactone 107. 

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