Polysaccharides stereochemistry

This symposium presented an unusual opportunity in that we discussed the methods used to determine polymer structures from fiber diffraction data, rather than concentrating on the actual structures derived and their possible implications. At Case Western Reserve University we have been involved in determination of the structures of cellulose and chitin. This paper describes our analyses (1-6) of the structures of cellulose I and II and a- and 6-chitin, emphasizing the manner in which structural decisions were taken in each case. Efforts to determine these structures have a history of over 60 years, and it has only been with the advent of least squares techniques for the refinement of polymer structures (7) [notably the LALS method (8)], and the development of our present knowledge of polysaccharide stereochemistry, that solutions have become possible. In what follows we will look first at our methods for measuring intensities and thereafter will review the work on each of the four structures. 

In both their industrial and biological functions, the 3-dimensional characteristics of carbohydrates are important. Many of these stereochemical features are described for carbohydrates in the classic text by Stoddart (2). The inqportance of stereochemistry is underscored by the unique chemical and physical properties of the individual sugars, many of which are configurational isomers. Stereochemistry also plays a role in detentlining the properties of polysaccharides. Molecular shape is as significant for the properties of an industrially modified starch as it is for the recognition of one particular blood type and the rejection of others. 

Interactions can also be studied at the surface of a coated capillary wall. One binding partner is first immobilized on the capillary wall. As a result of the affinity of the second binding partner, the analyte will be delayed, compared with migration times observed in an untreated capillary. Based on this approach, modified capillaries have been prepared and used successfully to study polysaccharide-protein interactions as well as affinity separations. Coating of the capillary wall with heparin and heparan sulfate has been used to determine the affinity of these polysaccharides for synthetic heparin-binding peptides different only in the stereochemistry of a single... 

The structures of oligosaccharides and polysaccharides are usually determined by a combination of methods specific enzymatic hydrolysis to determine stereochemistry and produce smaller fragments for further analysis methylation analysis to locate glycosidic bonds and stepwise degradation to determine sequence and configuration of anomeric carbons. 

It is a remarkable fact that the main energy-storage polysaccharides and the main structural polysaccharides found in nature both have a primary structure of (l,4)-linked polyglucose. Why should two such closely related compounds be used in totally different roles A closer look at the stereochemistry of the a and /3 glycosidic linkage for polyglucose indicates why this is so. 

Yashima E, Okamoto Y, Chiral recognition mechanism of polysaccharides chiral stationary phase in The Impact of Stereochemistry on Drugs Development and Use (Aboul-Enein, HY, Wainer IW, Eds.), John Wiley Sons, New York, p. 345 (1997). 

This chapter begins with a discussion of the structure and stereochemistry of monosaccharides. Then the formation of cyclic structures front monosaccharides is discussed. This is followed by the presentation of a small number of reactions of these compounds. The classic series of experiments that was used to establish the structure of glucose is presented next. Finally, the structures of disaccharides, polysaccharides, and a few other types of carbohydrate-containing compounds are introduced. 

Ken s geographical transition to the New World was accompanied by a concomitant transition in his research emphasis. Although he maintained an interest in polysaccharide chemistry, the publication record from Queen s University attests to the universality of his interests in carbohydrate chemistry. J. K. made major contributions to synthetic carbohydrate chemistry, stereochemistry, biosynthetic mechanisms, and metabolism of carbohydrates, and the application of such separational techniques as paper and gas-liquid chromatography in the carbohydrate field. The results of his lifetime of research were documented in over 300 scientific publications. Clearly, it would be impractical to review this number of papers individually, and consequently, only a representative sample will be treated. A list of Professor Jones s publications is appended to this article. 

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