Heptose aqueous solution

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. 

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. 

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. ... 

---