Hexosuloses

The multiplicity of peaks obtained on trimethylsilylation of 3-de-oxy-D-en/fforo-hexosulose has already been mentioned (see p. 24) however, the isomeric 3-deoxyhexitols formed on reduction with borohydride were readily separated as their trimethylsilyl ethers.234 El-Dash and Hodge234 gave a large amount of tabular and graphical data on relative retention-times and showed that, when these values... 

The first dehydration products formed by general, acid-base catalysis are represented by the enolic forms (7, 9, and 10) of the deoxydicarbonyl sugars 7a, 9a, and 10a. The enolic compounds are formed from enediols by the removal of a molecule of water through -elimination of a hydroxyl group. For example, from the 1,2-enediol (6) derived from D-glucose or D-fructose, the enolic form (7)of3-deoxy-D-eryf/iro-hexosulose (7a) is produced, whereas from the 2,3-enediol... 

Deoxyaldosuloses are capable of existing in numerous ring modifications. For 3-deoxy-D-erythro-hexosulose, El-Dash and Hodge43 found that, of the 16 possible ring-forms (excluding enolic structures), evidence could be obtained for 11, although only 6 were stable in anhydrous pyridine. These varied ring-structures, and the many acyclic forms possible, introduce alternative pathways for dehydration to the same or different products and, where the structures are nonreactive, these forms would affect the kinetic pattern of the mechanism thus, they would influence the reaction rate and product distribution. 

D-glucose or D-fructose into 5-(hydroxymethyl)-2-furaldehyde in solution in acidified deuterium oxide.17 The 2-furaldehyde was isolated as 5-(hydroxymethyl)-2-furoic acid, and thus this experiment did not permit an evaluation of reversible equilibration of 1,2-enediols with the parent sugars. However, the 2-furoic acid was devoid of measurable carbon-bound deuterium, which indicated the absence of 3-deoxyglycosulose intermediates. It is also noteworthy that 3-deoxy-D-en/fhro-hexosulose is converted, in acidified deuterium oxide, into 5-(hydroxymethyl)-2-furaldehyde with no solvent exchange84 this result lends further support to the conclusion that 45 does not participate in the reaction as an intermediate. 

The imidazoles formed in the reaction of aqueous ammonia with other a-hydroxycarbonyl compounds, for example, the triose DL-glyceraldehyde, and such a-dicarbonyl compounds as 3-deoxy-D-glycero-pentosulose (59), and the 3,6-dideoxy-L-erythro-, D-arabino-, and 3-deoxy-D-erytforo-hexosuloses (60, 61, and 62), respectively, are summarized in Table VIII for reactions in which formaldehyde was added, and in Table IX for reactions in which it was not added. 

The stereospecificity of the reduction of these hexosulose nucleosides, trans to the aglycon, parallels previous observations62-64 with several hexopyranosulose derivatives. Attempted, similar reduction of the unprotected 2 -ketonucleoside 36a gave 7-(6-deoxy-/ -L-talopyranosyl)-theophylline (87) in 60% yield. This lesser stereospecificity may be ex-... 

In alkaline solutions D-glucose forms 3-deoxy-D-en/f/iro-hexosulose and 4-deoxy-D-gft/cero-2,3-hexodiulose which yield saccharinic acids. Machell and Richards (57) have shown that 3-deoxy-D-en/fhro-hexosulose (14) is oxidized by 30% hydrogen peroxide to formic acid and 2-deoxy-D-erythro-pentonic acid (15). Recently Rowell and Green (58) found that 14 in the presence of oxygen also forms 15 in addition to the saccharinic acids. They inferred that the reactions with oxygen and hydrogen peroxide are very similar, but they did not present reaction mechanisms. 

Scheme X. Reaction of 3-deoxy-D-erythro-hexosulose with oxygen...

Experiment with 3-deoxy-D-erythro-hexosulose (1). The experiment with unlabelled glucose at initial pH 3.0 was repeated after replacing the glucose by an equimolar amount of 1, prepared via its bis(benzoylhydrazone) (8). The yields of l - J in the two experiments are compared in Figure 8. This further supports the proposed routes to 4 and 6 but also shows that 1 is not an important intermediate in the formation of 5 or 7 Thus, the route to 5 proposed by Shaw and Berry (Figure 2) must also be discarded. 

Figure 8. Yields of compounds 4-7 on refluxing an aqueous solution of 0.17 M D-glucose or 3-deoxy-D-erythro-hexosulose (1) and 3.4 M glycine (pH 3.0).

Group 1 includes methyl-branched sugars and sugars having a two-carbon branch. These sugars arise by transfer of a Cj or C2 unit from appropriate donors to nucleotide-bound hexosuloses. 

Group 2 consists of sugars having a hydroxymethyl or formyl branch. These sugars are formed by intramolecular rearrangement of nucleotide-bound hexosuloses, with ring contraction and expulsion of one carbon atom. 

Springer and coworkers874 reported an extensive list of saccharides that were weakly inhibiting or noninhibiting. These included the 2-acetamido-2-deoxy derivatives of D-galactose, D-glucose, D-ribose, D-talose, and D-arabinose, 3,6-dideoxy-L- and -D-xy/o-hexose, L-lyxo-hexosulose, L-arabinose, D-fructose, and 2-deoxy-D-erythro-pentose. 

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