Aldoses acetate

In summary, it may be stated that the reaction of acyl esters of aldoses and aldobioses (see Section III, p. 92) with ammonia consists of a set of competitive pathways, including intramolecular O —> N migrations of acyl groups, deacylations, and transesterifications, with formation of aldose amides and variable proportions of the free sugar as the principal products. Significant proportions of basic or insoluble polymeric substances were not observed with aldose acetates or benzoates, although occurrence of extensive browning indicates the probable formation of soluble melanoidins. 

A g.l.c. procedure that establishes the DP of oligo- and poly-saccharides has been developed. The oligo(poly)saccharide was reduced prior to hydrolysis and conversion of the reducing sugars liberated into their oxime derivatives the DP was determined from the ratio of acetylated aldononitrile to acetylated alditol. A similar technique, which determined the ratio of aldose acetate to alditol acetate, was used to measure the DP of amylose. ... 

Note Aldoses other than glucose can also be used e.g. arabinose [1], xylose [2, 3, 7] or ribose [4]. The background color is least on cellulose layers when cellulose acetate, aluminium oxide 150, silica gel, RP, NH2 or polyamide layers are employed the background is a more or less intense ochre. The detection limit of carboxylic acids on cellulose layers is ca. 0.5 pg substance per chromatogram zone. 

Development of (Z, )-5-(2-methyl-3-phenyl-2-propenylidene)4-oxo-2-thio-xothiazolidine-3-acetic acid (Epalrestat, Kinedak), an aldose reductase inhibitor 97YGK651. 

Conversion of the aldehyde into a nitrile is accomplished by treatment of an aldose with hydroxvlamine to give an oxime (Section 19.8), followed by dehydration of the oxJme with acetic anhydride. The Wohl degradation does not give particularly high yields of chain-shortened aldoses, but the reaction is general for all aldopentoses and aldohexoses. For example, D-galactose is converted by Wohl degradation into n-lyxose. 

Carbohydrates such as aldoses that undergo oxidation with metal ions are referred to as reducing sugars. Both copper(II) ions and silver ions are capable of oxidizing aldoses. Oxidation by copper(II) ions is the basis for Fehling s test and Benedict s test, whereas oxidation by silver ions is the key to Tollen s test. (Note These tests work for any sugar with a hemiacetal, but they don t work on acetals or ketals.)... 

Wohl prepared the acylated nitriles of the aldonic acids by heating the aldose oximes with a mixture of sodium acetate and acetic anhydride. With careful control of the reaction, this method may be used for preparative work with fairly good results. 

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). 

Acetylated aldose oximes with a ring structure have also been obtained during the preparation of the nitriles, both with sodium acetate-acetic anhydride and with pyridine-acetic anhydride. Thus it appears that under these conditions at least a certain amount of the oxime is present in the ring form. 

Names of cyclised (hemi-acetalised) aldoses and ketoses contain the infixes pyran or furan to indicate the six- or five-membered heterocyclic structure and a stereodescriptor, a or p, to indicate the configuration of the anomeric or hemi-acetal carbon atom. 

The generic term glycosides defines all mixed acetals formed by the acetalisation of the cyclic forms of aldoses and ketoses. Glycosyl groups are monosaccharides that have lost their anomeric -OH group the suffix -yl is used to indicate the change that has occurred at C-1. 

Aldoses and aldosides, cyclic acetals of, 20, 219-302 Alkaline degradation, of polysaccharides, 13, 289-329 Altrose,... 

The following Tables list the aldose oxirane derivatives that have been prepared. The solvents used in determination of the specific rotation are given by A, acetone C, chloroform E, Ethanol E.A., ethyl acetate M, methanol P, pyridine and W, water. 

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