Hexonic acids

Let us now return to the pioneering work of Fischer and Tiemann.4 Chitonic acid is produced from D-glucosamine by deamination and oxidation, in that order. If the order is reversed, however, i. e., if D-glucos-amine is first oxidized to D-glucosaminic acid (2-amino-D-gIuconic acid) and the latter substance subsequently deaminated, chitonic acid is not the product. Instead an isomeric 2,5-anhydro hexonic acid (chitaric acid) is obtained. These facts may be summarized thus ... 

An application to n-xylose (LXII) of the Fischer synthesis of 2-amino hexonic acids from pentoses would lead theoretically to a mixture of 2-amino-D-gulonic acid (LXIII) and 2-amino-D-idonic acid (LXIV). 

Furthermore, deamination and oxidation of the mixture of amino hexonic acids should yield 2,5-anhydro-D-gulosaccharic acid (LXV) and... 

The preparation of sirupy 1-methyl-D-glucosone and crystalline 1-phenyl-D-glucosone (XXII), via the corresponding 2,3 4,5-di-0-isopropylidene derivatives, by Ohle and his colleagues61 64 (by treatment of 2,3 4,5-di-O-isopropylidene-2-oxo-D-arabmo-hexonic acid (XXI) with the requisite... 

The conversion of L-xylosone into L-ascorbic acid has been reversed by treating the latter with pert-naphthindan-2,3,4-trione hydrate184 2,3-dioxo-L-zj/fo-hexonic acid is formed and is decarboxylated to L-xylosone. It was suggested that the destruction of ascorbic acid in vivo by this mechanism might explain the relatively high requirements for the vitamin in many species. 

Levene, P.A., The specific rotations of hexonic and 2-amino-hexonic acids and of their sodium salts. 7. Biol. Chem., 1924, 59, 123. 

Gelidium pacificum Okam. Chrondus ocellatus Holmes D-galactose D-galactose, methyl pentose, 2-keto-hexonic acid (7), sulfate, D- and irerythrose 111... 

In all known instances, the deamination of 2-amino-2-deoxyaldo-hexonic acids by nitrous acid takes place with formation of a 2,5-anhydro ring and with retention of the configuration at C-2, as illustrated in the sequence 21—>22—>23. 

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