Heptoses

Most free pentoses, hexoses, and heptoses occur primarily in less strained pyranose rings, but the furanose ring is also quite important. The furanose ring is formed in the same way as the pyranose ring and also occurs in a and P forms. This is demonstrated with L-arabinose, which is commonly found in polysaccharides in the form of a-L-arabinofuranosyl units (see Fig. 2). 

The parent with the greatest number of carbon atoms in the chain, e.g. a heptose rather than a hexose. 

D-glycero-D-galacto-Heptose has been found in different bacterial poly-... 

Two 6-deoxyheptoses, namely 6-deoxy-D-wa o-heptose and 6-deoxy-D-a//ra-heptose, are components of bacterial polysaccharides. The former occurs as o-pyranosyl residues in the LPS from some strains of Yersinia pseudotuberculosis,and the latter as terminal a-furanosyl groups (II) in... 

Monosaccharides are those carbohydrates that cannot be hydrolyzed into simpler carbohydrates They may be classified as trioses, tetroses, pentoses, hex-oses, or heptoses, depending upon the number of carbon atoms and as aldoses or ketoses depending upon whether they have an aldehyde or ketone group. Examples are listed in Table 13-1. 

II. Reaction of Aldoses with Dicarbonyl Compounds 1. Hexoses and Heptoses... 

In the same way, condensation experiments have been performed with v-glycero-D-gulo-heptose and ethyl acetoacetate, and a crystalline product has been isolated this also gave the aldehyde V16 when oxidized with periodate. Hence, in this case also, the reaction is analogous to that with the hexoses, although the yield is lower. 

A large proportion of the condensation products of sugars with dicarbonyl compounds have been obtained in the crystalline state however, some have not yet been crystallized. All are more soluble in hot than in cold water. Those resulting from the condensations with heptoses, hexoses, and pentoses are almost insoluble in benzene. Generally speaking, all are soluble in ethyl acetate. 

In alkaline solution, glycolaldehyde gives rise to tetroses.160- 169 Tetroses combine with dihydroxyacetone in alkaline solution to give heptoses, as indicated by the results of paper chromatography.16 43... 

Scheme 5.72 Preparation of modified 1,6-anhydromannosides and their use in the synthesis of heptose-containing oligosaccharide.

Fig. 40 Baylis-Hillman reaction as a key step in the synthesis of heptoses.

The synthesis shown in Fig. 40 provided access to heptoses,55 but according to our definition, this is not a higher sugar synthesis. However, the approach to such derivative was based on the Baylis-Hillman reaction of acyclic sugar-derived aldehydes, a reaction not commonly applied in sugar chemistry and worth to mention in this review. 

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