Aldoheptoses

How many aldoheptoses are there How many are d sugars, and how many are l sriga rs ... 

A trace component present in a preparation of guanosine 5 -(a-D-mannopyranosyl pyrophosphate) from yeast has been identified as a D-glycero-D-manno-he ptosyl ester of guanosine 5 -pyrophosphate.86 This compound seems to be the only known example of a nucleoside diphosphate aldoheptose. ... 

The equilibrium compositions of aqueous solutions of some aldoheptoses are listed in Table III. Because the additional carbon atom in the side chain does not introduce additional steric interactions, the composition of solutions of heptoses is similar to that of the homomorphous hexoses, with only one exception, namely, n-glycero-n-ido-heptose, 92 a-D-Idopyranose in solution is a mixture of the 4Ci and 1C4 conformant) S. J. Angyal and R. J. Beveridge, Carbohydr. Res., 65 (1978) 229-234. 

Emil Fischer s initial studies [1] focused on dithioacetal formation from a variety of simple aldopentoses, aldohexoses, and aldoheptoses. The products were obtained by simply treating the sugar with an excess of ethanethiol in concentrated hydrochloric acid at low temperature ( 0°C). Many of these dithioacetals have low water solubility, crystallize spontaneously from the reaction mixtures, and can be isolated by simple filtration and washing with odd water. Fischer s key paper [1] also outlined most of the major reaction modes of the diethyl dithioacetal derivatives, later developed in detail, and thus paved the way for subsequent studies into this important class of sugar derivative. 

N. K. Khare, R. K. Sood, and G. O. Aspinall, Diastereoselectivity in the synthesis of D-g/ycero-D-aldoheptoses by 2-(trimethylsilyl)thiazole homologation from hexodialdo-1,5-pyranose derivatives, Can. J. Chem. 72 237 (1994). 

Later, some of the aldoheptoses (and octuloses and nonuloses) were actually found in Nature. 

The basic skeleton of these anhydrides, l,6-dioxabicyclo[3.2.1]octane, is identical to that of 1,6-anhydrohexopyranoses (see Section II.4). For the 32 diastereoisomeric aldoheptoses, three different types of anhydrides may be formed in acid solution 1,6-anhydropyranoses, 1,6-anhydrofuranoses,... 

Only two 1,7-anhydrohexopyranoses have been described thus far l,7-anhydro-D-g/ycero-/J-D-gw/0-heptopyranose (58a)247,250 and the corresponding D-ido isomer (58b).247 They appear in the reaction mixture with 1,6-anhydro derivatives after acid treatment of solutions of the parent aldoheptoses. 

For each D-aldohexose there will be, as one more stereogenic center is added, two aldoheptoses. Altogether, there are 16 D-aldoheptoses. 

GC was performed on a polyester stationary phase (10% of neopentyl glycol sebacate or Carbowax 20M) at 170°C. The method was applied to a mixture of aldopentoses, aldo-hexoses and aldoheptoses in biological material. 

An aldoheptose has 5 chirality centers. Thus, there are 25 = 32 aldoheptoses - 16 D aldoheptoses and 16 L aldoheptoses. 

This work was followed by the detection of an aldoheptose in Escherichia coli products and the subsequent isolation of jj-glycero-i>-manno-heptoee by Weidel, again in connection with phage-receptor studies. The sugar was obtained from the lipocarbohydrate fraction of Escherichia coli B cell-membranes and was isolated, after acid hydrolysis, on a cellulose-powder column. In this case, sufficient of the product was obtained to show that the diethyl dithioacetal and its hexaacetate had equal but opposite optical rotations, as compared with those of the same derivatives prepared from authentic D-glyc o-n-manno-heptose. 

Species Nature of product Aldoheptose Amount present, % Refer- ences... 

In another study, the type 3 specific polysaccharide was obtained by extraction of organisms at pH 4 for 45 minutes at 100° in this case, the analytical figures differed a little from those of the previous preparations. Amino sugar amounted to 16% at least the greater part of this was d-glucosamine and at least the greater part of this was AT-acetylated. L-Rhamnose and D-glucose were separated, identified, and estimated as 30 % and 25%, respectively. Hexose 6-phosphate and aldoheptose phosphate were also present in small proportions. 

A type-specific polysaccharide of Pasteurella septica Type V has been obtained, both from virulent and avirulent forms, by phenol extraction. When freed from nucleic acid, the material gave a single gel-diffusion line with Type V antiserum, and did not cross-react with Types I, II, III, and IV. The Type V material contained hexosamine and aldoheptose similar products from Types I and IV strains contained these sugars also, together with galactose. 

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