Sugar acids aldonic

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. 

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... 

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... 

Comparable to the situation for the sialic acid and KDO lyases (vide supra), sets of stereochemically complementary pyruvate lyases are known, e,g. in Pseudomonas strains, which act on related 2-keto-3-deoxy-aldonic acids [112]. The enzymes cleaving six-carbon sugar acid phosphates—the KdgA and 2-keto-3-deoxy-6-phospho-D-galactonate (20) aldolases (KDPGal aldolase EC 4.1.2.21) [139] — are typified as class I enzymes, whereas those acting on non-phosphorylated five-carbon substrates — 2-keto-3-deoxy-L-arabonate (21) (KDAra aldolase EC 4.1.2,18) [140, 141] and 2-keto-3-deoxy-D-xylonate (22)... 

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. 

Sugar acids Oligomeric aldonic acids Strongly basic anion exchanger (CH3COO ) Havlicek and Samuelson [241]... 

Table 1 lists some examples for the electrophoretic separation of carbohydrates on the supports described above. Table 2 lists the electrophoretic mobilities of some common mono-, di-, oligosaccharides, sugar alcohols, and aldonic acids. Table 3 summarizes the electrophoretic mobilities of sugar acids, sugar phosphates, and amino sugars. In Table 4, the chromatographic conditions used in Tables 2 and 3 can be deduced by the use of the corresponding reference letters (A-G). 

It should be noted that the aldonic acids need not be deionized prior to TLC since the same mobility is observed when either the acid or the calcium salt is applied. In each sugar acid investigated with solvent XXI, the y-lactones had a higher hi / than the corresponding 5-lactone and both moved faster than free acid. This relative mobility of the two lactones may be dependent on the solvent, however, since in neutral solvents the inverse order (5 > y) is observed [47]. 

Simple esters of the sugar acids, as ethyl D-mannonate 102) and diethyl galactarate 103), have long been known (Chapter VI). n-Galacturonic acid occurs in pectins largely esterified with methanol 104), Many of the methyl esters of the 0-acetyl aldonic acids have been obtained by the action of diazomethane upon the fully acetylated aldonic acids. Penta-0-acetyl-D-gluconates of some of the alditols (XVIII) and of cellulose have been described 106), The methyl acid ester of di-0-acetyl-L-(dea ro)-... 

Ketoses may be separated from contaminating aldoses by oxidation of the latter with bromine and removal of the aldonic acids with an ion-ex-change resin (2), Ion-exchange resins are also useful in the recovery of sugar acids and of some nitrogen-containing derivatives of sugars. 

Xylonic acid, cf. Figure 5.3, is a sugar acid that can be obtained by the complete oxidation of xylose. It has been attempted to utilize xylose by converting it to an aldonic acid (19). Xylose was converted to xylonic acid by using commercial glucose oxidase enzyme, palladium catalysis, and microbial bioconversion. 

Aldonic and deoxyaldonic acids (polyhydroxy acids) ( sugar acids )... 

Although the Tollens reaction is a useful test for reducing sugars, it doesn t give good yields of aldonic acid products because the alkaline conditions cause decomposition of the carbohydrate. For preparative purposes, a buffered solution of aqueous Br2 is a better oxidant. The reaction is specific for aldoses ketoses are not oxidized by aqueous Br2. 

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. 

Fig. 4. Sugar derivatives serving as acceptors for glycosylation by dextransucrase alditols, aldosuloses, aldonic acids, a fructose dianhydride, and a glycal.71...

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