Arabinose catalytic oxidation

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. 

In perchloric acid, hexoses and pentoses are oxidized by Ce(IV) via formation of two complex intermediates. The first is partly oxidized following Michaelis-Menten kinetics and partly dissociated to the second, which is oxidized more slowly than the former.180 The first step in the oxidation of aldoses by Tl(III) in the same medium involves the C-l-C-2 cleavage of the aldehydo form of the sugar. Thus, D-glucose gives D-arabinose and formic acid. With an excess of oxidant the final product is carbon dioxide.181 In the presence of a catalytic amount of sulfuric acid in acetic acid, Tl(III) oxidizes maltose and lactose to the corresponding disaccharide aldonic acids. The reaction showed activation enthalpies and enthropies characteristic of second-order reactions.182... 

Titanium-containing zeolites, such as Ti-BEA, Ti-FAU, and TS-1 have been tested as catalysts for the Ruff oxidative degradation of calcium D-gluconate 72 to D-arabinose 55 using diluted hydrogen peroxide as the oxidant. Only large-pore zeolites Ti-BEA and Ti-FAU were found to be active. It was shown, in particular, that a very rapid leaching of titanium occurred and that the titanium species present in the solution were responsible for the catalytic activity observed [67,68]. 

A simple enzymic synthesis of barium glucose 6-phosphate from starch has appeared. Ths use of 2-methylthio-4 -l,3,2-benzodioxaphosphorin-2-oxide (MTBO) (see M. Eto et al.. Tetrahedron Letters, 1971, 4263) continues to receive attention. A study of twenty amines as catalysts has shown that primary n-alkyl and alicyclic amines are the most effective, followed by secondary and tertiary amines. Increasing the branching reduced the catalytic efficacy while cyclic imines gave low yields. MTBO has been used to synthesize adenosine 2, 3 -cyclic phosphate in 50% yield from 5 -0-acetyladenosine (Scheme 5). o-Arabinose 5-phosphate and o-xylose 5-phosphate have been... 

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