Alditols synthesis

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

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. 

The reaction of 1-amino-1-deoxyketoses, and their N-alkyl and N-aryl derivatives, with alkyl or aryl isothiocyanates (Huber et al, 1960) was studied in more detail, and new 4-(alditol-l-yl)-l-alkyl(aryl)-3-alkyl(aryl)-l,3-dihydro-2H-imidazole-2-thiones were obtained. These compounds were used as starting materials for the synthesis of OL-histidines, DL-histidine-2-thiol, and other imidazole derivatives of biological interest. 

In the course of their studies of pseudouridine,164 Asbun and S. B. Binkley183 reported the synthesis of 5-/3-D-arabinofuranosyl- and 5-/3-D-xylofuranosyl-uracil (258 and 259) by the acid-catalyzed ring-closure of the corresponding alditol derivatives. The configuration at the anomeric carbon atom was determined on the basis of optical rotatory dispersion studies. 

Homopolycarbonates based on 1 and 2 have been prepared by several groups. The interfacial polycondensation typical for the synthesis of aromatic polycarbonates is not useful with alditols, including 1, because they are water-soluble and less acidic than diphenols. The 1-based homopolycarbonate was prepared by phosgena-tion of the sugar diol, with phosgene or diphosgene in pyridine-containing solvent mixtures at low temperatures. The polycondensation of the isosorbide bischloro-formate in pyridine is an alternative approach. 

Anhydroalditol compounds of a rather unusual type are the C-glycosyl compounds (erroneously called C-glycosides ). As pointed out by Treibs,33 these are not glycosides, but they are anhydro-alditols.3 A variety of approaches has been employed for synthesis of... 

The synthesis of an alditol having a 4-membered (oxetane) ring was first reported by Ustyuzhanin and coworkers,50 who prepared 1,3-anhydro-5,6-di-0-methyl-2,4-0-methylene-D-glucitol by saponification of the 1-p-toluenesulfonate of the corresponding derivative of D-... 

Aminomercuration aminoalditols The synthesis of the natural aza-alditol 1-deoxynojirimycin (4) from methyl a-D-glucopyranoside involves the reductive ring-opening (Zn) and reductive amination (NaBH3CN) of 1 to give 2 in 91% yield. Aminomercuration of 2 results mainly in the bromomercurial 3, which was converted into the aza-sugar 4 by reductive oxygenation and deprotection. 

The catalytic hydrogenation of nitro alcohol to amino alcohol has been applied to the synthesis of an intermediate leading to sugar alcohols. The condensation of ni-tromethane with pentoses in the presence of sodium methoxide, followed by hydrogenation over platinum oxide and deamination with nitric acid, gave the alditols with one more carbon atom.22 The reaction sequence is as follows pentose — 2-epimeric sodio aci-nitro alcohols —> 2-epimeric hexitylamines —> 2-epimeric hexitols + 2-epi-meric 1,4-anhydrohexitols. The 2-epimeric sodio a -nitro alcohols were hydrogenated to 2-epimeric hexitylamines over platinum oxide in acetic acid. An example is shown in eq. 9.8 with D-ribose. 

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