Significance in the Degradation of Carbohydrates

3-Deoxyglycosuloses (45) have been regarded as being products of a side reaction of the Lobry de Bruyn-Alberda van Ekenstein transformation. The transformation is subject to general, acid-base catalysis and, although it proceeds most rapidly in alkaline solution, it also takes place under neutral and acidic conditions. The Lobry de Bruyn-Alberda van Ekenstein transformation consists of the interconversion of two epimeric aldoses through the intermediate enediol (43) or its anion, and, where R = H, the 2-ketose also enters into the equilibrium. 

Enolization of a 2- or 3-ketose to a 2,3-enediol, for example (46), rields the l-deoxy-hexo-2,3-diulose (47) or the 4-deoxy-hexo-2,3-diulose (48). - Although but few of these reactions are known, they seem to proceed by a 

The 3-deoxyglycosuloses formed in the degradation of carbohydrates readily react further under various conditions to a variety of products. The mechanisms of the reactions catalyzed by alkali, acid, sulfite, or amines will be dealt with separately. 

2-0-Methylaldoses are epimerized by alkali but do not yield metasac-charinic acids. A study of these reactions led to the isolation of 2-methyl ethers of the enol form of 3-deoxyhexosuloses (52) (see Section IV, la p. 188). The formation of 3-deoxyhexosuloses is blocked by the stabilization of the enols as methyl ethers (44).  

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).  

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