Conformations carbohydrates

Haworth formulas are satisfactory for representing configurational relationships in pyranose forms but are uninformative as to carbohydrate conformations X ray crystal lographic studies of a large number of carbohydrates reveal that the six membered pyra nose ring of D glucose adopts a chair conformation... 

The fact that the absolute magnitudes of these two sets of coupling constants are different is also expected on the basis of the Pople, Bothner-By treatment (48). It would clearly be of some considerable interest if a general study were to be made of the stereospecificity of this geminal dependence since this may lead to another method for determining carbohydrate conformations. 

Carbohydrate conformation plays a key role for molecular recognition processes, and their determination contributes to the understanding of many biological processes. The latest NMR methodological developments for conformation determination are discussed here, and representative examples are given. 

Molecular dynamics (MD) simulations are a class of molecular mechanics calculation which directly model the motions of molecular systems, often providing considerable information which cannot be obtained by any other technique, theoretical or experimental. MD simulations have only recently been applied to problems of carbohydrate conformation and motions, but it is likely that this technique will be widely used for modeling carbohydrates in the future. This paper introduces the basic techniques of MD simulations and illustrates the types of information which can be gained from such simulations by discussing the results of several simulations of sugars. The importance of solvation in carbohydrate systems will also be discussed, and procedures for including solvation in molecular dynamics simulations will be introduced and again illustrated from carbohydrate studies. 

The conformers in Figure 2 are named descriptively and given a rotational label using terminology appropriate for acyclic carbohydrate conformers [(5, (pp 182-203)]. 

Carbohydrate-conformations at the surface of a membrane were studied from a static as well as from a dynamic point of view. Molecular mechanics... 

Current methods take root in the early 1960s, when the conformational analysis of macromolecules became of general interest [29-30]. Anderson et al. [31] used model building and X-ray diffraction studies to determine the double helical structures of polysaccharides using crystalline structure data as an initial set of coordinates followed by computational sampling of new structures by rotation around selected covalent bonds. The details of these so-called hard-sphere calculations are described in Rees and Skerrett [32] and Rees and Smith [33]. This approach was also applied to carbohydrate conformations in the analysis of bacteria and polysaccharidic structures and linkages [34-35]. 

Machado, A. S., Dubreuil, D., Cleophax, J., Gero, S. D., Thomas, N. F. Expedient syntheses of inososes from carbohydrates conformational and stereoelectronic aspects of the Ferrier reaction. Carbohydr. Res. 1992, 233, C5-C8. 

K. N. Kirschner and R. J. Woods, Solvent interactions determine carbohydrate conformation, Proc. Natl. Acad. Sci., 98 (2001) 10541-10545. 

Significant advances have been made in incorporating RDCs into the conformational studies of carbohydrates since the appearance of the first reports at the end of the last decade. It quickly became obvious that the interpretation of RDCs in carbohydrates is not straightforward and model dependent. Inherent flexibility of carbohydrates poses the greatest challenge for the interpretation of RDCs in terms of carbohydrate conformation. 

ANALYSIS OF CARBOHYDRATE CONFORMATION AND CONFIGURATION BY NMR - THE KEY ROLE OF THE KARPLUS EQUATION... 

Many carbohydrate conformations follow simply from the same considerations that govern alicyclic conformations, that bulky substituents prefer equatorial... 

Although the determination of both the configuration and the conformation of carbohydrates involves the same general considerations, the quantitative nature of the latter requires a rather more fundamental approach. Accordingly, the following discussion is divided into two main sections the first refers to the development and applications of nuclear magnetic resonance to stereochemical problems, and deals mainly with substituent resonances the second discusses in some detail the Karplus relationship and the determination of carbohydrate conformations. 

Tel. 212-280-2577, fax 212-678-9039, e-mail sl model%cuchem.bitnet A user-friendly molecular modeling package for molecular mechanics and conformational searching of organic molecules, proteins, nucleic acids, and carbohydrates. Conformational analysis. AMBER-, MM2-, and MM3-like and OPLS force fields implicit solvation model. Reads Cambridge and Brookhaven PDB files. VAX, Convex, Alliant, Cray, and workstations. 

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