Alditols sodium salts

The reduction of aldoses/ketoses occurs readily with sodium borohydride and during the reaction the pH increases to about 9 (O Scheme 19) [155]. For the reduction of aldonolactones in water the first step of the reduction has to be carried out at a pH around 5 in order to avoid ring-opening of the lactone to the corresponding sodium salt which will not react with sodium borohydride. The pH control can be achieved by performing the reduction in the presence of an acidic ion-exchange resin, e. g., Amberlite IR-120 [156]. In this way, it is possible to stop the reduction at the aldose step. Alternatively, more sodium borohydride can be added and thereby increasing the pH to 9 by which the alditol is obtained (O Scheme 19). The reduction of aldonolactones to alditols can also be performed in anhydrous methanol or ethanol where hydrolysis of the lactone is not a side reaction [156]. 

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. 

Alditol-l-yl substituted pyrroles or pyrazoles (e.g. 88 and 89) were obtained by addition to per-<7-acetylated 1,2-dideoxy-l-nitro-D- a/acm- and D-manno-l-hep-tenitols of the sodium salt of tosylmethyl isocyanide or the zwitterionic diaryl nitrile imines (e.g. PhC=N -N Ph), respectively. A general one-pot synthesis of alditol-l-yl substituted imidazoles (e.g. 90) involved reaction of aldoses with... 

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