Sugars aldoses

SchifT s reagent A solution of rosaniline in water decolorized with sulphurous acid. Aliphatic aldehydes and aldose sugars give a magenta colour with this reagent with aromatic aldehydes and aliphatic ketones the colour develops more slowly aromatic ketones do not react. 

Kiliani-Fischer synthesis (Section 25.6) A method for lengthening the chain of an aldose sugar. 

Figure 2 Formation of l-amino-2-keto sugars from aldose sugar...

Cataracts are not a feature of this disease because fructose is not an aldose sugar and therefore not a substrate for aldose reductase in the lens. 

Glucose 6-phosphate is then isomerized to fructose 6-phosphate. This conversion of an aldose sugar to a ketose sugar is easy to rationalize in terms of keto-enol tautomerism (see Box 10.1). 

However, the applicability of this strategy is limited by the substrate specificity of the isomerases so that only a fraction of the ketoses that can be obtained from the aldose-catalyzed reaction can be enzymatically isomerized to the corresponding aldose. Moreover, the isomerization reaction is reversible and, as a ketone is generally more stable than an isomeric aldehyde, the equilibrium produces substantial aldose isomer only if the aldose sugar can exist in a very stable aldopyra-nose form [38b]. 

Aldose sugars make up a large part of the carbohydrate family, but the ones that are really worth knowing are part of the D-family. The simplest of these D-sugars is the triose glyceraldehyde. From there you have 2 tetroses, 4 pentoses, and 8 hexoses. Each of these aldose sugars has an enantiomer. 

In the case of the oximes of the aldose sugars, the situation is more complicated because of the possibility of both open-chain and cyclic structures. That aldose oximes can react in the open-chain form follows from the formation of the nitriles and from the isolation of acylated open-chain aldose oximes as secondary products in preparation of nitriles. For example, Wolfrom and Thompson, by the action of sodium acetate-acetic anhydride on n-glucose oxime, not only obtained pentaacetyl-D-glucononitrile, in 40% yield, but also isolated a small amount of hexaacetyl-oWeAydo-D-glucose oxime (V) identical with that prepared by mild acetylation of pentaacetyl-aWe%do-D-glucose oxime (IV) whose structure was assured by its formation from pentaacetyl-aldehydo-D-glucoae (III). 

Hinton, C. L. and Macara, T. 1927. The determination of aldose sugars by means of chloramine-T, with special reference to the analysis of milk products. Analyst 52, 668-688. 

III. Early Attempts to Condense Nitromethane with Aldose Sugars. 297... 

In 1921 Pictet and Barbier28 recorded an attempt to produce higher-carbon sugar alcohols from aldose sugars by means of the reaction sequence ... 

It must be concluded that these experiments did not demonstrate unequivocally that a nitromethane-aldose sugar condensation had been achieved. 

The condensation of ethyl glyoxylate with aldose sugars in the presence of sodium cyanide was reported by Helferich and Peters in... 

The above method of producing a carbohydrate C-nitroalcohol is now of only minor interest since subsequent experiments have shown that substituted aldoses with a free reducing group as well as the unsubsti-tuted aldose sugars will undergo the aldehyde-nitroparaffin condensation reaction.29... 

Hydrolysis of the benzylidene acetals with dilute sulfuric acid produced the unsubstituted sugar nitroalcohols. The configurations of the latter were proved by converting them via the Nef reaction (see page 307) to the corresponding known aldose sugars. 

The minimum time required for completion of the condensation, which may be expected to vary from one aldose sugar to another, has not been determined. As judged visually, the precipitation of the sodium ocf-nitroalcohols is essentially complete in less than one hour in the most favorable instances. However, a total reaction time of from six to eighteen hours has been employed. 

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