Metasaccharinic acid, formation from

Only the racemic form of this acid is obtained from the sugar-alkali reaction. As in the formation of lactic acid, a non-asymmetric enediol is an intermediate in its production (see Section III), and hence the racemate is the sole representative of the four-carbon metasaccharinic acid class. 

As would be expected from the above considerations, substitution at C6 of a hexose has, at most, only a minor effect on the course of saccha-rinic acid formation. Thus, 6-0-(a-D-galactosyl)-D-glucose (melibiose) plus lime-water gives lactic acid and a mixture of the corresponding metasac-charinic, isosaccharinic, and saccharinic acids.The qualitative experiments with melibiose and with 6-0-methyl-D-glucose, based mainly on paper chromatography, suggest that the metasaccharinic acids may be the principal products from hexoses substituted at C6. 

In contrast to the above formation of metasaccharinic acid, fragment recombination appears to be a predominant feature in the formation of the branched-chain a -D-glucosaccharinic acid from D-mannose-l-C plus lime-water. In this case, the radioactivity originally present in Cl of the hexose was found to have become distributed almost entirely between the methyl carbon atom and the tertiary carbon atom of the saccharinic acid, with the latter atom more heavily labeled than the former. In contrast to these observations, the Isbell mechanism, in the absence of compli-... 

J. Kenner and G. N. Richards, J. Chem. Soc., 3019 (1957), have recently reported the same kind of catalytic effects in the formation of metasaccharinic acids from 3-0-methyl-D-glucose. 

The formation of metasaccharinic acids from reducing sugars involves 1,2-enolization (43), elimination of the functional group at C-3 to give (44), which tautomerizes to the glycosulose (45), and a benzilic acid rearrangement of (49) to (50). ... 

Figure 4.31 Formation of metasaccharinic acids and furan-3-ones from 3-deoxy-D-erythro-hexos-2-ulose.

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