2-Keto-3-deoxyaldonic acid

In a third general approach, 2-keto-3-deoxyaldonic acids are prepared from 2-enonolactones. These precursors are readily prepared in good yield by /1-elimination reactions on the protected lactones.37 Starting from... 

G. Limberg and J. Thiem, -Elimination of protected aldono-1,4-lactones as a general approach to the synthesis of 2-keto-3-deoxyaldonic acids containing four to six carbon atoms, Carbohydr. Res., 275 (1995) 107-115. 

Sialic acids were reported to occur in all species of vertebrates and in certain invertebrates as well (Warren, 1963a), NANA is present in some strains of E, coli and other bacteria as a homopolymer, of which colominic acid is one example (Barry and Goebel, 1957 Barry et al., 1962 Watson et al., 1958 Liu et aL, 1971). However, it is lacking in other bacteria (Barry, 1959 Barry et aL, 1%3 Jann, 1969). Earlier claims for the presence of sialic acid in plant extracts have been disputed (Cabezas and Feo, 1969) since the positive test with thiobarbituric acid could not be duplicated by other colorimetric assays. Gielen (1%8) demonstrated that the color-producing substances in certain plant hydrolysates were 2-keto-3-deoxyaldonic acids rather than sialic acid. To date there has been no convincing evidence for the presence of sialic acid in plants. 

As with other colorimetric methods, the thiobarbituric assay is subject to interference by a number of foreign substances in biological materials. In addition to the problem with 2-keto-3-deoxyaldonic acids... 

In vivo, pyruvate lyases serve a catabolic function in the degradation of sialic acids and 2-keto-3-deoxyoctosonate (KDO), and in that of 2-keto-3-deoxyaldonic acid intermediates from hexose or pentose catabolism. Since these freely reversible aldol additions often have unfavorable equilibrium constants [43], S5mthetic reactions are usually driven by an excess of pyruvate to achieve a satisfactory conversion. 

The action of HBr on the diazo compound is similar to that of acetic acid, and a 1-bromo keto acetate is formed. Silver oxide causes a rearrangement to a 2-deoxyaldonic acid 35),... 

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