Heptose solution

In alkaline solution, glycolaldehyde gives rise to tetroses.160- 169 Tetroses combine with dihydroxyacetone in alkaline solution to give heptoses, as indicated by the results of paper chromatography.16 43... 

The equilibrium compositions of aqueous solutions of some aldoheptoses are listed in Table III. Because the additional carbon atom in the side chain does not introduce additional steric interactions, the composition of solutions of heptoses is similar to that of the homomorphous hexoses, with only one exception, namely, n-glycero-n-ido-heptose, 92 a-D-Idopyranose in solution is a mixture of the 4Ci and 1C4 conformant) S. J. Angyal and R. J. Beveridge, Carbohydr. Res., 65 (1978) 229-234. 

It has been noted92 that, in aqueous solutions of the D-glycero-L-hep-toses, the a- to y -pyranose ratio is somewhat higher than that for the homomorphous hexoses, whereas, for the D-gh/cero-D-heptoses the ratio is the same, or even slightly lower. No explanation is apparent for this observation. 

By means of the cyanohydrin reaction, higher sugars of the heptose. octosc, and nonosc types have been prepared. A monosaccharide such as an aldohexosc may be converted into the next lower monosaccharide, such as an aldopeniosc. by oxidation to the acid, which corresponds to the aldohexose. then treating the calcium salt solution of this acid with a solution or ferrous acetate plus hydrogen peroxide. Carbon dioxide is evolved and aldopentose formed. 

L. C. Stewart and N. K. Richtmyer, Formation of 1,6- and 1,7-anhydro-D-g7ycero-fi-D-gw/o-heptopyranose from D-glycero-fi-D-gulo-heptoses in acid solution, J. Am. Chem. Soc., 77 (1955) 424-427. 

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,... 

In summary, it can be said that, in homogeneous alkaline solution, either methanolic or aqueous, an equilibrium is established between the aldose, nitromethane, and deoxynitroalditols, and that, for successful addition, this equilibrium must be displaced in favor of the alditols, either through precipitation of their sodium salts from methanolic solution, or by direct crystallization from aqueous solution. Because of these requirements, the method is not so widely applicable as the cyanohydrin synthesis, but, for selected sugars, such as n-gZgcero-D-ZaZo-heptose and o-erythro-i -manno-octose, its simplicity and the satisfactory yields obtained make it the method of choice. 

This involves exactly the same kinds of steps but puts the transketolase step before the aldolase step. Clearly it results in a solution just as short as the first one, but is it any simpler Apparently not, because it involves all of the same molecules as the first solution (3, triose 5, pentose 6, hexose 7, heptose) with one additional one, a 9-carbon sugar. So it is a more complicated solution, as it not only requires a new molecule not needed in the first solution, but this new molecule must be of a larger and more complicated kind than any of the others. We are left with the conclusion therefore that the original solution is indeed the simplest. 

Heating dihydroxyacetone in aqueous solution at pH 5 produced a complex mixture containing substituted pyranones, dipyranones, substituted quinones, hydroxylated benzenes and toluenes, and the sugar derivatives (3), (4), and (5). The syntheses from telomerization of vinylene carbonate of racemic o-glycero-L-gulo f D-g/ycero-D-irfo-heptose, and v-threo-D-ido-octose in reasonable yield has been reported. ... 

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