Oxidation arabinoses

Now that we know the structures of o-erythrose and o-threose, we continue as follows. Chain extension of o-erythrose (Exercise 24-23) gives a mixture of two pentoses o-ribose and D-arabinose. Their configurations at C3 and C4 must be the same as those of C2 and C3 in o-erythrose they differ at C2, the new stereocenter created in the lengthening procedure. Nitric acid oxidation of o-ribose gives an optically inactive (meso) add thus D-ribose has structure 3. o-Arabinose oxidizes to an optically active acid it must have structure 4. 

Oxidation of (—) arabinose with warm nitnc acid gave an optically active aldanc acid... 

Note Aldoses other than glucose can also be used e.g. arabinose [1], xylose [2, 3, 7] or ribose [4]. The background color is least on cellulose layers when cellulose acetate, aluminium oxide 150, silica gel, RP, NH2 or polyamide layers are employed the background is a more or less intense ochre. The detection limit of carboxylic acids on cellulose layers is ca. 0.5 pg substance per chromatogram zone. 

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. 

Deoxy-3-fluoro-D-glucose (see Section 11,2), a weak substrate for yeast hexokinase, is phosphorylated enzymically - to give the 6-phosphate 588, which is transformed into 2-deoxy-2-fluoro-D-arabinose 5-phos-phate (589) by lead tetraacetate oxidation. 

Gums are hydrophilic materials that easily undergo chemical hydrolysis with depolymerization, oxidation and microbiological attack. Leaching is a well-known phenomenon, and the inversion between arabinose and xylose content has been reported [164,165],... 

A strategy has been described for the synthesis of 2-ethyIthio-6-(3-hydroxy-1,2-0-isopropylidenepropyl)pteridin-4(3//)-one 90 which can be used as a useful intermediate for the conversion of neopterin to biopterin. Diaminopyrimidinone 86 reacts with D-arabinose phenylhydrazone 87, the obtained diastereomeric mixture 88 is converted into its isopropylidene derivative 89 which under oxidation conditions yields 90 <00H(53)1551>. 

L-Arabinose was formed on periodate oxidation, borohydride reduction, and mild, acid hydrolysis of the pentasaccharide, demonstrating that it contains a D-galactofuranosyl residue. The amino sugar residue was resistant to periodate oxidation but was oxidized after N-deacetylation, showing that this residue is substituted at 0-4, not at 0-3. The structure of the pentasaccharide 21 was thereby established. It showed [a]D —36°, indicating that all sugar residues are /3-D-linked. 

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. 

On oxidation of the phenylosotriazole derivative of the disaccharide with sodium periodate, three moles of periodate are consumed with the formation of one mole each of formic acid and formaldehyde per mole of the phenylosotriazole derivative. If the D-glucose in the u-glucopyrano-syl-L-arabinose phenylosotriazole were attached to carbon atom 4 of the L-arabinose derivative, oxidation of this compound with sodium periodate would require two moles of periodate and would liberate one mole of... 

Other workers140 have also examined the products derived by hydrolysis of periodate-oxidized xylan. Both wheat straw and com cob xylan, after oxidation and hydrolysis, yield small amounts of L-arabinose and D-xylose. These sugars are obtained even after the xylans have been subjected to extended periods of oxidation. It is concluded that the D-xylose constituted branch points in the xylan. Likewise, the L-arabi-nose molecules must not have been terminal units in a xylan chain but must have been either interior units in the xylan molecule or have constituted an araban-like polysaccharide which is in combination or admixture with the xylan polysaccharide. 

Photolysis of three 2,4-dinitroanilino-substituted carbohydrates, compounds that differ considerably from each other in photochemical reactivity, has been reported.150,151 l-Deoxy-l-(2,4-dinitroanilino)-D-glucitol (73) is photochemically unreactive in contrast, sodium 2-deoxy-2-(2,4-dinitroanilino)-D-gluconate (74) produces D-arabinose in 52% yield upon irradiation.150 The behavior of compounds 73 and 74 indicates that oxidative loss of the 2,4-dinitroanilino group during photolysis is only possible when it is accompanied by simultaneous decarboxylation. The evidence gathered from the considerable study of this reaction for noncarbohydrate systems suggested that this process is quite complex. Although useful, mechanistic proposals have... 

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