Oxidation of D-arabinose

A more-direct method of preparation is oxidation of aldoses, and optimal yields are afforded by the action of cupric acetate in methanol or ethanol.417 This method is suitable for large-scale preparation of intermediates however, a pure product is obtained only by chromatographic separation from the unreacted sugar byproducts. The synthesis of D-eryt/wo-pentos-2-ulose and its D-threo isomer by oxidation of D-arabinose and D-xylose, respectively, with cupric acetate followed by anion-exchange chromatography has been reported.418 The only product obtained by oxidation of D-glucose with sodium 2-anthraquinonesulfonate in alkaline... 

D-(—)-eiythrose (use Fischer projections), (b) The two epimeric aldopentoses that one obtains are d-(—)-arabinose and D-(—)-ribose. Nitric acid oxidation of d-(—)-ribose yields an optically inactive aldaric acid, whereas similar oxidation of D-(—)-arabinose yields an optically active product. On the basis of this information alone, which Fischer projection represents d-(—)-arabinose and which represents D-(—)-ribose ... 

FIGURE 22.45 Oxidation of D-arabinose leads to an optically active diacid, which shows that the OH at C(2) in D-arabinose is on the left. 

The second step in the Fischer proof determines the configuration of C(2) in D-ara-binose. Fischer observed that the oxidation of D-arabinose with nitric acid gives an optically active diacid. The possibilities are shown in Figure 22.45. There are only three diacids that can be produced from a D-aldopentose, and two of them are meso. In the third, which is the optically active diacid, the OH at C(2) is on the left. Thus, the C(2) in D-arabinose must have OH on the left. Because 0(2) in D-arabinose becomes 0(3) in the D-glucose and D-mannose of Figure 22.44, we know that 0(3) in both hexoses has the OH on the left. 

The use of periodic acid oxidation in structure determination can be illustrated by a case in which a previously unknown methyl glycoside was obtained by the reaction of D-arabinose with methanol and hydrogen chloride. The size of the ring was identified as five-membered because only one mole of periodic acid was consumed per mole of glycoside and no formic acid was produced. Were the ring six-membered, two moles of periodic acid would be required per mole of glycoside and one mole of formic acid would be produced. 

Using a fluidized bed electrode, this process was studied by Jircny 1985 [118]. Jircny [119] worked with a laboratory scale cell and subsequently a pilot plant. The pilot plant was designed to produce one ton of D-arabinose per year. The electrochemical reactor was 0.3 x 0.6 x 0.6 m and contained five 225 A cells in series. A major advantage of the electrooxidation over the usual chemical route (oxidation with sodium perchlorate) was the ease of separation of D-arabinose from the reactor outflow. In chemical routes, the separation is made difficult by the presence of large amounts of sodium chloride. 

The tetrose, D-erythrose, so obtained can be oxidized with nitric acid to meso-tartaric acid. Show how this information can be organized to establish the configurations of D-arabinose, D-ribose, ribitol, and D-erythrose. 

XCIII —> XCIV (which involves an inversion of configuration at C2). Treatment of XCIV with ammonia leads to the formation of D-arabinose (XCV) plus bis(ethylsulfonyl)methane. Oxidation of the V-acetyl analog of XCI results in de-V-acetylation, with the formation of XCII, stabilized as the crystalline peroxypropionate salt XCIIb. Treatment of XCIIb with ammonia gives a mixture of XCIV, D-arabinose (XCV), and bis(ethylsulfo-... 

The di-(cyclohexylidene)-D-mannitol contained a terminal a-glycol group because (a) oxidative scission with lead tetraacetate consumed one mole of the oxidant and gave one mole of formaldehyde, together with an acid-labile derivative of D-arabinose, and (b) its dimethyl ether yielded the known crystalline 5,6-dimethyl-D-mannitol (1,2- is identical) when heated with aqueous acid.1 0 Since graded acidic hydrolysis of the diketal furnished 3,4-cyclohexylidene-D-mannitol,3 it must have possessed the 1,2 3,4-structure and the parent triketal must have been 1,2 3,4 5,6-tri-(cyclohexylidene)-D-mannitol. 

A fraction of the sirupy diketal was obtained in crystalline form (m. p. 55-56°). This material consumed one mole of periodate (or lead tetraacetate), with the liberation of 0.86 mole of formaldehyde, which fact eliminated all but the 1,2,3,4- and 3,4,5,6-isomers.144 Hydrolysis of the diisopropylidene-ofde/ij/do-pentose formed during the oxidation yielded D-arabinose and so the diisopropylidene-D-sorbitol must have been one of the three members of the latter group. That it was in fact the 3,4 5,6-compound was demonstrated by its partial hydrolysis to 3,4-isopropyli-dene-D-sorbitol.144 Consequently the triketal from which both had been derived must have been l,2 3,4 5,6-triisopropylidene-D-sorbitol. This being so, the sirupy diketal mentioned above should have contained some of the 1,2 3,4- compound, a hypothesis which found support in the observation that periodate oxidation of the sirup and subsequent hydrolysis of the products afforded a mixture of D-arabinose and L-xylose (identified by filter paper chromatography).144... 

D-ribonate. In critical cases, such as the study of a mixture in which the presence of small quantities of D-arabinose is being considered, oxidation with bromine and a barium benzoate buffer according to Hudson and Isbell27 may be substituted, even though the procedure becomes more complicated if one wishes to fractionate the aldonic acids through their potassium and barium salts. While other examples of epimerization under these alkaline conditions have not been reported, the possibility of such rearrangements must always be kept in mind. 

The condensation of 2,5,6-triamino-4(3//)-pyrimidone with L-arabinose-phenylhydrazone leads to analogous tricyclic adducts which are, however, more sensitive to oxidation and more difficult to handle. The same type of adducts have also been observed during the condensation of 5,6-diamino-2-methyl-4(3//)pyrimidone with the phenylhydrazones of D-arabinose (e.g., (346)) or 5-deoxy-L-arabinose (e.g., (347)) (Scheme 56) <89MI 718-05). The various hydrofuro- and hydropyrano[3,2- ]pteridine derivatives are expectedly valuable intermediates for the synthesis of 6-substituted pteridines which were obtained by air oxidation in alkaline medium or more directly by treatment with p-benzoquinone <90MI 718-08) and iodine/H202, respectively (348) and (349) (Scheme 56). 

The oxidation of D-glucose to D-gluconic acid is also readily carried out by use of a platinum-on-carbon catalyst (a substantially more-active catalyst) in the presence of an equivalent of alkali. With the aid of the same catalysts, n-galactose, D-mannose, D-xylose, and L-arabinose can be converted to the corresponding aldonic acids. By this method, the pentoses are oxidized more rapidly than the hexoses. A reaction time of only 45 minutes is required at 22°, whereas the oxidation of D-glucose is complete only after five hours. 

Of the two chair conformations of an alkyl /S-D-arabinopyranoside (81), the IC form is the more stable. In this conformation, the hydroxyl group on C-4 is axial, and catalytic oxidation (in the presence of Adams catalyst, in neutral solution at 45°) proceeds smoothly to afford " the alkyl /8-D-starting material, because the oxidation product is obtained as an unstable sirup which isomerizes " and decomposes to give acids. A better starting material is benzyl /3-d-arabinopyranoside, which yields a relatively stable, crystalline mono-hydrate of a benzyl pentosidulose (82) this is obtained pure by recrystallization or by column chromatography. The structure of the product was determined by reduction with sodium amalgam to a mixture of D-arabinose and L-xylose. 

D-Arabinose 88 l-Deoxy-l,l-bis(ethylsulfonyl)-D-mannitol (1 g) (prepared by oxidation of D-mannose diethyl dithioacetal with peroxypropionic acid in dioxan) is made into a slurry with water (10 ml), and then concentrated aqueous ammonia solution (1 drop) is added. The sulfone dissolves rapidly and after 30 min the precipitated diethyl methylene disulfone is filtered off. The filtrate is extracted four times with chloroform (10-ml portions), and the aqueous phase is evaporated in a vacuum at 40°. The residue is treated with hot methanol (5 ml) and after being kept for 24 h at 4° affords / -D-arabinose (0.32 g, 86%), [a]D20 —102° (c 3.5 at equilibrium in water). 

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