Ascorbic acid analogs

L-Rhamnosone was prepared by the action of hydrochloric acid on L-rhamnose phenylosazone9 and was identified by reconversion to the osazone. This method was later employed186 as a stage in the synthesis of the ascorbic acid analog, L-rhamnoascorbic acid. The benzaldehyde decomposition of the osazone gave a low yield of osone93 and o-nitrobenzaldehyde was not a satisfactory aldehydic substitute. 

Of unpredictable potentialities are the halogen addition compounds. Although their production and use is complicated by the existence of several isomers, they have been intermediates in the production of crystalline osone derivatives and of kojic acid. The osone derivatives, in turn, have been converted to ascorbic acid analogs through 2-ketoacids not actually isolated. 

The second route to an ascorbic acid analog consisted in oxidation by bromine to a 2-ketoacid with the same number of carbon atoms, enoliza-tion, and lactonization. The product was not crystallized, but the optical rotation of the sirup, [ ]d —20° (in water), was in fair agreement with that for the expected D-arabo-ascorbic acid. The sirup was strongly reducing and gave the absorption peak at 2450 A. characteristic of the ascorbic-acid structure. 

Chelation, in osazone formation, III, 43 Chemical constitution, physiological activity and, of ascorbic acid analogs,... 

Okamura, M. Distribution of ascorbic acid analogs and associated glycorides in mushrooms. J. Nutr. Sci. Vita-minol. 1994, 40, 81-94. 

The work described here on the Cu(II)- and Fe(III)-catalyzed autoxidation of ascorbic acid has been extended to catalytic systems involving vanadyl (12) and uranyl (13) ions. On the basis of the results described above it would seem that there are potentially many other metal ions that are capable of undergoing redox reactions with the ascorbate ion, and that may function as catalysts in the autoxidation of ascorbic acid. Analogous mechanisms may also apply to systems involving metal-ion catalysis of ascorbate oxidation in which the primary oxidant is a reagent other than molecular oxygen. 

Copper-Free Ascorbic Add Oxidase. A totally different specific ascorbic acid oxidase has been prepared from fungal spores. This enzyme is not sensitive to copper inhibitors but is inhibited by sulfhydryl reagents. It does not attack ascorbic acid analogs. Like the copper-containing enzyme, fungal ascorbic acid oxidase gives rates proportional to oxygen tension. 

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