Aldose aldonic acids from

Bromine (hypobromite) and hypoiodite oxidations are particularly useful for the preparation of aldonic acids from aldoses and of aldaric acids from glycuronic acids. Primary alcohol groups also undergo oxidation by these reagents, although this conversion is of less value glycosides can thus be converted into glycosiduronic acids, and alditols into aldoses and aldonic acids. 

Anodic oxidation of glucose gives mainly the glucono-(5-lactone (XCI) or gluconic acid (XCII) [Eq. (55)] [133-135]. Formation of aldonic acids from aldoses is the most commonly observed process in other cases [126]. Additional work has been done in the area of indirect anodic oxidation of partially protected carbohydrates at a nickel hydroxide anode [136]. 

Bromine and hypoiodite oxidations are particularly suitable for the preparation of aldonic acids from aldoses. Similarly, uronic acids are converted to saccharic acids. Of less value is the oxidation of primary alcoholic to aldehydic groups. In this manner, glycosides can be converted to uronides and polyols to aldoses and aldonic acids. 

We have devised a very simple procedure for the preparative synthesis of various aldonic acids from the corresponding aldoses. This green chemistry process takes advantage of the availability of cheap, robust industrial enzymes. 

Oxidation of the primary alcohol group on C6 has been noted in a few cases. A small yield of saccharic acid (XIV) has been obtained in the formation of an aldonic acid from an aldose. In several cases glycosides have been oxidized to glycuronides (XV). More drastic action on the glycoside has led to a splitting of the carbon chain at C2—C3 and C3—C4, with elimination of C3, similar to the action of periodic acid diglycolio acid derivatives (XVI) are formed. The oxidation of the primary alcohol group on C6 of ketoses has occasionally led to the formation of 5-keto acids (XIII). 

Everett and coworkers have done extensive work on this overoxidation of aldoses with bromine at 25° for long periods of time (forty to fifty days). Under these conditions, appreciable amounts of the keto acids are obtained. Hart and Everett obtained 5-keto aldonic acids from D-glucose, D-mannose, D-galactose, D-xylose and D-gulonic lactone. The barium salts were isolated and converted to the brucine salts. The structure of the oxidation product from D-xylose was not determined. The stability of these keto acids to further bromine oxidation had been noted earlier by Kiliani. ... 

In the second place, oxidation by Fehling s or Tollens reagent cannot be used for the preparation of aldonic acids (monocarboxylic acids) from aldoses. Both Fehling s and Tollens reagents are alkaline reagents, and the treatment of sugars with alkali can cause extensive isomerization and even decomposition of the chain. Alkali exerts this effect, in part at least, by establishing an equilibrium between the monosaccharide and an enediol structure. 

Aldonic acid (Section 25.6) The monocarboxylic acid resulting from mild oxidation of the -CHO group of an aldose. 

Monocarboxylic acids formally derived from aldoses by replacement of the aldehydic group by a carboxy group are termed aldonic acids (see 2-Carb-20). 

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... 

The first step in the degradation is the preparation, starting from an aldose, of the acylated nitrile of an aldonic acid. The nitrile and the acyl groups may be removed by various methods to yield a new aldose,... 

Among the classic methods for the extension of the aldose chain by one carbon atom from the reducing end [9J, the Kiliani-Fischer cyanohydrin synthesis [10] is a milestone in carbohydrate chemistry. However after 110 years from discovery and numerous applications [11], including the preparation of carbon and hydrogen isotopically labeled compounds for mechanistic and structural studies [12], there are still several drawbacks that make the method impractical. These are the low and variable degree of selectivity and the harsh reaction conditions that are required to reveal the aldose from either the aldonic acid or directly from the cyanohydrin. Synthetic applications that have appeared in recent times confirmed these limitations. For instance, a quite low selectivity was registered [13] in the addition of the cyanide ion to the D-ga/acfo-hexodialdo-l,5-pyranose derivative 1... 

H. Kiliani, as Fischer always emphatically acknowledged, discovered and developed the method of building up the aldose series by the cyanohydrin reaction to give nitriles from the nitrile, the next higher aldonic acid could then be prepared. In 1890, A. Wohl, working in Fischer s Berlin laboratory, elaborated the dehydration of an aldose oxime to the nitrile, from which the next lower aldose could be prepared by loss of hydrocyanic acid. Fischer exploited the possibilities of sugar extension and degradation afforded by the use of these two important methods. 

Aldonic acids are derived from aldoses by oxidation of the terminal aldehyde to a carboxylic acid. 

Three kinds of sugar acids can be formally obtained from the corresponding aldoses. They are aldonic acids, produced by oxidation at C-l of the aldose uronic acids, formed by oxidation of the primary alcohol group of the aldose and aldaric acids, formed by oxidation of both the aldehyde and the primary alcohol group. 

Aldaric acids may be prepared from aldoses or aldonic acids by oxidation in aqueous solution with oxygen over platinum-charcoal255 or platinum-on-alumina.256 The effect of such promoters as bismuth or gold has also been studied.257 Hydrogen peroxide in the presence of iron salts has been used for the oxidation of uronic acids to aldaric acids.258... 

Jeanes and Isbell39 found that, under mild conditions, aldoses are oxidized to aldonic acids, but that nonreducing carbohydrates and ketoses are oxidized only slowly. The rate of oxidation decreases in the order pentoses > hexoses > disaccharides however, in contrast to other oxidants, chlorous acid oxidizes a-hexoses more rapidly than the ft anomers. The yields of aldonic acids are, however, less than those from bromine oxidations.40 The equation for the oxidation in acidic solution was expressed as ... 

Ferric ion catalyzes the formation of the hydroperoxyl radical, according to Eq. (35) such a radical appears to constitute the oxidant in the Ruff method of degrading aldonic acids to the next lower aldoses. A number of examples of the use of this reagent in the laboratory are given in a review article by Moody.108 The hydroperoxyl radical, which is not so effective an oxidant as the hydroxyl radical, does not attack aliphatic alcohols accordingly, a substantial yield (about 50%) of the aldose is obtained from the higher aldonic acid. In the presence of an excess of hydrogen peroxide, however, the accumulation of ferrous ions in solution catalyzes the production of hydroxyl radicals and lowers the yield of aldose [see Eq. (36)]. 

Dahlia tubers, inulin from, II, 254 Dambonitol, III, 46 Damson gum, I, 343 IV, 246, 247 structure of, IV, 253 blood group activity of, IV, 50, 52 Deamination, mechanism of, II, 62 Degradation, of acylated nitriles of al-donic acids, IV, 119-151 of aldonic acids, III, 149 of aldose sugars, I, 254 enzymatic, of starch and glycogen, III, 251-310... 

Starting from a salt of an aldonic acid, the Ruff oxidative degradation reaction1 leads to an aldose with loss of one carbon atom. Known since 1898, the original process used aqueous hydrogen peroxide as oxidant, in the presence of catalytic amounts of ferric salts. 

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