Sugars to aldonic acids

FIGURE 16.22 Redox reactions in the oxidation of aldose sugars to aldonic acids. 

This method involves the oxidation of aldoses to aldonic acids by potassium hypoiodite in methanol and the condensation of the isolated potassium salt of the aldonic acid in hot acid with o-phenylenediamine (M3). The specific aldobenzimidazole can be identified by the solubility in water, optical rotation in acid, and melting point. This method is not as simple as chromatography. It requires dehydration of the sample and a relatively high concentration of the sugars to be identified. 

Reducing sugars are those sugars that are oxidized by mild oxidizing agents to aldonic acids. 

Number of Stereoisomers op the Aldehydo-Sugars and Aldonic Acids Containing 2 to 7 Carbons and op The Corresponding Alcohols and Dibasic Acids... 

Oxidation to Sugar Acids and Lactones. When the aldehyde group of an aldose is oxidized, the resulting compound is an aldonic acid (salt form = aldonate) (11)4. Some aldonic acids are products of carbohydrate metaboHsm. 

Attack of the OH radical on carbohydrates of low molecular mass gives rise to a variety of products. Indeed, the reaction of radiolytically-generated OH radical with lower hexose sugars produces lower saccharides (for di- and higher saccharide species), uronic and aldonic acids, and 3-, 2- and 1-carbon aldehydic fragments, e.g. 

Oxidation of Aldonic Acids. Preferential oxidation of the secondary alcoholic group adjacent to the carboxyl group in sugar acids or aldonic acids such as L-gulonic acid (XXV) can be carried out with chromic acid12 or with chlorates in the presence of a vanadium catalyst.13... 

In a similar fashion it should be a relatively simple task to relate the well-known D-gala-L-manno-heptose (XX) to a-rhamnohexose (XXII)81 through the known 1-desoxy-D-gala-L-mcmno-heptitol (syn., 7-desoxy-L-manno-L- aZa-heptitol) (XXI).81 In. this particular case, however, there is already ample proof of the configuration of the latter sugar (XXII) because nitric acid has been found to oxidize the corresponding aldonic acid to mucic acid.82... 

Fischer s involvement with the relative configurations of the sugars required the preparation of pure substances and he gradually accumulated experimental data (20-22), which required the formation of epimeric aldonic acids in unequal amounts (see Table I). Thus, he was able to write (23) in 1892 ... 

The bromodeoxyaldonolactones have been used for the preparation of aminodeoxy aldonic acids and aminodeoxy sugars via azido derivatives (45,46). Likewise, a- and /J-aminopolyhydroxy acids have been prepared by treatment of the bromodeoxyaldonolactones with liquid ammonia (47). Thus, 3-amino-3-deoxy-D-threonic acid and 3-amino-3-deoxy-D-arabin-onic acid (40b) were obtained from 2-bromo-2-deoxy-L-threono- or D-xy-lono-1,4-lactone (38). It was shown that 2,3-epoxy carboxamides (namely, 39) are intermediates of the reaction. Heating at 90° for long periods led to the 3-amino-3-deoxyaldonamides, which upon acid hydrolysis yielded the corresponding aldonic acids. 

There are three possible classes of sugar acids which may be produced by the oxidation of monosaccharides (Figure 9.11). The aldonic acids are produced from aldoses when the aldehyde group at carbon 1 is oxidised to a carboxylic acid. If, however, the aldehyde group remains intact and only a primary alcohol group (usually at carbon 6 in the case of hexoses) is oxidised then a uronic acid is formed. Both aldonic and uronic acids occur in nature as intermediates in... 

---