Aldonate esters

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)- 

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Kochetkov and Dmitriev have reported66,79 an investigation on the hydroxylation of certain a,)3-unsaturated aldonic esters. The hydrox-ylation was performed by treatment of these compounds with chloric or iodic acid (or their salts) and a catalytic amount of osmium tetra-oxide in a suitable solvent. The resulting diastereoisomers were then separated as their cadmium salts. 

As part of a general program (1—4) on synthetic transformations of sugars having potential value for access to enantiomerically pure, polysubstituted carbocycles, we have made a systematic study of the reactions of various dienes with sugar-derived alkenes serving as dienophiles. Here we present the results of reactions between cyclopentadiene and a complete stereoisomeric set of seven-carbon trans-2,3-unsaturated aldonic esters derived from the D-aldopentoses. 

In addition to lactone formation, it is probable that extramolecular esterification may take place with the formation of aldonic esters of aldonic acids (e.g., gluconic acid gluconate) and chain polymerization also may occur. In such systems, the concentration of water present would be expected to exert a profound influence on the composition of the equilibrium solution. Lactic acid forms external esters (lactides), but this type of condensation through carboxyls and a-hydroxyls has not been observed for hexonic and pentonic acids. 

By catalytic hydrogenation, aldonic esters and lactones are reduced to glycitols (37). The reduction of lactones to sugars by sodium amalgam was introduced by Fischer and has been extensively employed for the purpose (see Chapter II). Esters, but not the free acids, are reducible. In order to obtain maximal yields, the acidity must be maintained in the range 3 to 3.5. The temperature should be kept below 15 , and a minimum of 2.5 equivalents of sodium are required (theory, 2) (38), Other methods are also available (see Chapter II). 

The reverse of the above oxidation reactions can be accomplished. Aldonic esters and lactones (but not the free acid) can be catal dically hydrogenated to glycitols. Sodium amalgam has been widely used for the reduction of lactones to sugars. In order to obtain good yields the reaction should be carried out at pH 3-3.5 with slight excess of sodium at temperatures below 15°. In this connection sodium borohydride has found wide application in recent years. ... 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

Esters derived from the acid function are also named using the ending -onate . The name of the alkyl (aryl, etc.) group is given before the aldonate name. Alternative periphrase names like aldonic acid alkyl (aryl, etc.) ester may be suitable for an index. 

Esters, lactones, lactams, acyl halides etc. are named by modifying the ending -ic acid as described for aldonic acids (2-Carb-20.2). 

Aldono-1,5-lactones and free aldonic acids react with alcohols in the presence of hydrogen chloride to give the corresponding alkyl aldonates (84). The reaction is slower with 1,4-lactones. Because esterification takes place very slowly in the absence of an acidic catalyst, aldonic acids and their lactones may be recrystallized from boiling alcohols without appreciable esterification (85). However, in some instances, alkyl esters are formed under these conditions. For example, essentially pure ethyl L-mannonate was isolated (6.4% yield) from the mother liquors of crystallization L-man-nono-1,4-lactone, obtained by Kiliani synthesis from L-arabinose (86). Similarly, repeated recrystallization from ethanol of crude 2,3,4,6-tetra-O-acetyl-D-glucono- 1,5-lactone afforded the corresponding ethyl gluconate derivative (87). 

In the carbohydrate series, the acids encountered are aldonic, aldaric, uronic, or saccharinic acids. Often, these acids are readily transformed into their lactones or methyl esters, and it is as derivatives of these that they are commonly studied. Table VIII (see p. 136) records examples in which derivatives of such acids and lactones have been subjected to gas-liquid chromatography. 

Aldonic Acids, Their Derivatives and Nitric Esters. Aldonic Acids are hydroxy-... 

Aldonic acids, their derivs and nitric esters 1 A122 A123... 

Aldonic Acids, Their Derivatives and Nitric Esters. Aldonic Acids are hydroxy-aciu of aldoses, which arc carbohydrates contg aldehyde gtoups (pentose, hexose, etc). The acids can be obtained by mild... 

A number of such compds were prepd and then converted to the corresponding nitric esters by Wolfram et al of Ohio State Univ while working under a US Ordnance Corps contract(Ref 5 6). They found that all the pentanitrates prepd by them could be detonated by gentle heat or by a hammer blow on steel. Thermal stability tests have shown that the aldonamide pentanitrates are more stable than aldonic acid pentanitrates or their methyl esters and that the esters were less stable than the corresponding acids. All of their purified nitrates underwent rapid decompn at their mp s, accompanied by violent bubbling and evolution of nitrogen oxides. No residue was visible after decompn... 

Under dehydrating conditions, it is probable that, in addition to lactonization, intermolecular esterification also occurs, yielding esters of aldonic acids and polymers. 

Aldonic acids form crystalline esters, amides, hydrazides, and benzimidazoles. Many of these derivatives, as well as the lactones, have been valuable... 

Esters are prepared by reaction of aldonic acids or lactones with an alcohol in the presence of hydrogen chloride 80 the reaction is slower with 1,4-lactones. Amides are readily formed from lactones by reaction with liquid ammonia followed by evaporation of the solvent.81 D-Gluconamide has also been prepared by treatment of D-glucono-1,5-lactone with concentrated ammonium hydroxide and subsequent precipitation with ethanol.82 A-Substituted aldonamides may be obtained by reaction of the aldono-lactones with ethanolamine, diethanolamine, and related species.83... 

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