Chair conformations saccharide

The conformational behaviour in solution of a dermatan-derived tetra-saccharide has been explored by means of NMR spectroscopy, especially by NOE-based conformational analysis. RDCs were also measured for the tetrasaccharide in a phage solution and interpreted in combination with restrained MD simulations. The RDC-derived data substantially confirmed the validity of the conformer distribution resulting from the NOE-derived simulations, but allowed an improved definition of the conformational behaviour of the oligosaccharides in solution, which show a moderate flexibility at the central glycosidic linkage. Differences in the shapes of the different species with the IdoA in skew and in chair conformations and in the distribution of the sulphate groups were also highlighted.28... 

Scheme 3 Graphical representation of the formation of the two main lysozyme-chito-saccharide complexes considered in the analysis of the data. The unproductive complex involves binding of the reducing end of the substrate (a) to site C of the enzyme and the adjacent pyranose rings bind to sites B and A and then protrude into the solvent. The productive complex involves binding of the non-reducing end of the substrate b) to site A of lysozyme and the adjacent pyranose rings bind to sites B and C and then protrude into the D—F region of the molecule. The chair conformation of the saccharide is...

In 1937 Isbell published an important paper on the conformational analysis of aldopyranoses, in which several of the forms were depicted (see Fig. 2). They comprise a 4C, chair (I), afl03 boat (II), two half-chairs (III and IV), and a coplanar pyranose (V). He correctly favored the chair form (I) and predicted that, in the case of saccharides, the chair would tend to assume a somewhat flatter conformation than that of carbocycles such as cyclohexane because of the smaller bond angles of oxygen as compared to those of carbon (105° instead of 109.5°). We now know that such coplanarity is strongly avoided because of the strain that would be produced and because of the repulsive forces between the substituents. 

Cyclic forms of saccharides are planar structures. The thermodynamically most favourable and therefore most common conformations of pyranoses are chair (C) conformations. Boat (B), skew (S) and half-chair (H) conformations are rarely found. 

Pyranose Six-membered ring form of a saccharide formed by reaction of the appropriate hydroxyl group with the carbonyl carbon. Generally the most stable structure in solution. The conformer resembles cyclohexane and is generally a chair form with axial and equatorial substituents. 

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