Naturally Occurring Higher-carbon Sugars

To date, aldoheptoses have only been found in Gram-negative bacteria, generally as components of polysaccharides which determine the dominant 

In Rough bacteria, the heptoses appear to be present in the free form in Smooth forms they may be phosphorylated. No evidence is as yet available as to whether an aldoheptose can form a specific, antigenic, determinant group of its parent polysaccharide. The heptose contents of polysaccharides vary widely, from more than 50% with P. pestis, to only 5% for some strains of P. pseudotvberculosis. °  

In Sedum sp., free sedoheptulose accumulates and is depleted much more slowly than are sucrose, n-glucose, and n-fructose. It is believed that this relative inactivity of the sedoheptulokinase accounts for the unique accumulation of sedoheptulose by these plants sedoheptulose is present to an extent of about 1%. 

The barium salt of sedoheptulose 1,7-diphosphate has been isolated by use of the first of these reactions and has been converted, by sedoheptulose 1,7-diphosphatase, into sedoheptulose 7-phosphate, also isolated as its barium salt.  

In the general metabolism of carbohydrates, sedoheptulose functions in the hexose monophosphate shunt (or pentose phosphate pathway), which operates through the following reactions. 

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The discovery of empirical rules of rotation of derivatives of the aldonic acids which indicated the configuration of the y-, and later the a-carbon atoms, made possible an advance in the solution of the problem of establishing the configurations of the synthetic higher-carbon sugars and the naturally-occurring rhamnose and fucose. The lactone rule was the earliest of these generalizations it was inferred from very extensive data. 

In total about 250 different, naturally occurring monosaccharides have been isolated and identified. Interestingly, the monosaccharides produced by nature are almost exclusively in the form of pentoses and hexoses, with the higher carbon sugars (more than nine) rarely occurring in nature. 

The higher-carbon sugars formed the subject matter of the first review to appear in this Series on that occasion, particular attention was devoted to the Fischer cyanohydrin synthesis which, until 1942, had been the only method available for preparing these sugars. Since that time, considerable advances have been made in the field of the higher sugars, notably in the development of new synthetic methods and in determination of the role played by heptoses, especially sedoheptulose, in natural systems. Moreover, the recently reported isolations of the first naturally occurring... 

In specific natural products, double bonds often occur within the ring system, (c) Squalene folded so as to demonstrate its relationship to the pentacyclic ring systems in stractmes d, e, and f (d) The hopane carbon skeleton, (e) Tetrahymanol. (f) Bacteriohopane tetrol, an extended hopanoid that includes five carbons deriving from the C5 sugar ribose. (g) p-Amyrin, a typical pentacyclic isoprenoid produced by higher plants. 

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