Oxidations 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. 

A D-aldohexose A is formed from an aldopentose B by the Kiliani-Fischer synthesis. Reduction of A with NaBH4 forms an optically inactive alditol. Oxidation of B forms an optically active aldaric acid. What are the structures of A and B ... 

A considerable medicinal chemistry effort has gone into devising inhibitors of aldose reductase their inhibition shows a dominant or even exclusive anticompetitive component when measured as inhibitors of aldose reduction, since they form tight complexes of the form E.NAD.I the inhibition is competitive when alditol oxidation is measured. 

Smith degradation of PI. A sample of FI (50 mg) was dissolved in 0.5 M NaOH (5 mL) and acetic acid added to pH 7, followed by NaI04 to a final concentration of 50 mM. At the conclusion of the oxidation (7 days) the product was reduced with NaBH4 and dialyzed. An aliquot was removed and the remainder immediately treated with NaI04 and then reduced with NaBH4. Samples of material subjected to one and two cycles of oxidation-reduction were hydrolyzed and reduced, and the products analyzed by GLC as alditol acetates. 

Oxidation of PI with chromium trioxide. Fraction PI was twice acetylated as described above. The peracetylated polysaccharide (75 mg), together with 20 mg of mannitol hexacetate as internal standard was dissolved in 1.5 mL of HCCI3, and treated with 1.89 mL of glacial acetic acid and 189 mg of chromium trioxide, at 50°C. Aliquots were removed at zero, 30, 60 and 120 min, water then added, and the material recovered by extraction with chloroform, hydrolyzed and analysed by GLC of derived alditol acetates. 

Another spectrophotometric method measuring both simple and combined sugars was described in papers by Johnson and Sieburth [158] and Burney and Sieburth [159]. The basic method comprised reduction of sugars to alditols with sodium borohydride, and oxidation of the alditols to form free formaldehyde. The formaldehyde was then determined spectrophotometrically with 3-methyl-2-benzothiazolinone hydrazone hydrochloride. 

The redox and complexation chemistry of alditol/Cr(VI) systems64 and the my<9-inositol/Cr(VI) system65 has been reported. In the first case, when an excess of the alditol over Cr(VI) is used, the secondary OH groups are inert to oxidation, and alditols are selectively oxidized at the primary OH group to yield the aldonic acid as the only oxidation product. The corresponding reaction involves a Cr(VI) —> Cr(V) —> Cr(III) reduction pathway, and the relative rate of each step depends on [H+] at... 

The fact that each monosaccharide may give more than one peak owing to the formation of anomeric derivatives has led to a search for means to eliminate this complication. The anomeric center may be removed either by conversion into the oxime5 or the nitrile,394,3943 by oxidation followed by formation of the lactone (see Section IX, p. 71), or by reduction to the alditol. The last method is simpler than oxidation, and the separation of alditols and of aldononitriles will be discussed here additional examples are given in Table V (see p. 119). The early work on the separation of alditols has been discussed by Bishop.4 The necessity of decomposing borate complexes... 

A procedure has been reported473 for the direct determination, on a column of Polypak, of polyhydric compounds without conversion into derivatives. Separation of pentitols was not complete, but the method was found excellent for determining the amount of one alditol, as in the oxidation of L-arabinitol by Acetobacter suboxydans. This rapid method of monitoring the utilization of L-arabinitol permitted the reaction to be stopped as soon as all of the substrate had been consumed, before side reactions interfered. 

The key sequence in the determination of the structures of 2,5-anhydro-D-mannose (2) and -D-talose (4) was their reduction to the corresponding 2,5-anhydroalditols (5 and 6) and identification of the asymmetric dialdehyde (7) resulting from oxidation of the anhydro-alditols with periodate.37,43... 

As regards the l,l-bis(acylamido)-l-deoxyalditols, the first structural study was that of Fletcher and coworkers,69 who conducted oxidations with lead tetraacetate. These authors postulated an empirical relationship between the position of the oxidation curve in a graph and the number of hydroxyl groups present. They compared the curves afforded by a series of l,l-bis(acetamido)-l-deoxyalditols with those of alditols having the same number of free hydroxyl groups, and observed a close correspondence. At present, periodate oxidation is widely applied to these mono- or di-saccharide derivatives. Under controlled conditions, the methylation technique can also be applied.42... 

This oxidation has been used to determine the anomeric nature of sugar residues in oligosaccharides.153 The oligosaccharide is reduced to the alditol, this is acetylated, and the ester is treated with chromium trioxide in acetic acid in the presence of an internal standard. From the sugar analysis of the product, the residues that have survived (and, consequendy, are a-D-linked) may be identified. The... 

Hydrazones 10 derived from aldose monosaccharides (9) and 2-hydrazinopyrimidine (8) gave, upon oxidative cyclization with bromine in methanol, the corresponding 3-(alditol-l-yl)-l,2,4-triazolo[4,3-a]pyrim-idines 11 [97JHC(34)1115] (Scheme 7). 

A number of 3-(alditol-l-yl)-5-methyl-7-oxo-l,2,4-triazolo[4,3-a]pyrim-idines l,2,4-triazolo[4,3-a]pyrimidines acyclo C-nucleosides (30) were synthesized (95PHA784) by oxidative cyclization of the corresponding aldehydo-sugar pyrimidin-2-ylhydrazones 27 with bromine in water. The alternative structure 29 was eliminated based on finding that acetylation of 30 afforded the same acetylated acyclo C-nucleosides 31 as those obtained by oxidative cyclization of the (A3-acetyl-poly-0-acetyl)hydrazones 28. Compounds 31 were also obtained by one-pot oxidative cyclization and acetylation of 27. In contrast to the oxidation and concurrent bromination of 19 to 25, it was possible to avoid nuclear bromination of 27 and 28 by performing the reaction in the absence of light (Scheme 13). 

L-fucitol by it conforms with this extended interpretation of the Hann, Tilden and Hudson rule. Further studies of the action, or lack of action, of Acetobacter suboxydans on other w-deoxy-alditols are being reported169 and so far they indicate the general applicability of the rule under the extended interpretation that a terminal methyl group is to be regarded as qualitatively equivalent to a hydrogen atom, insofar as the specificity of the oxidation by Acetobacter suboxydans is concerned. 

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