Pyranose

About: Pyranose is a research topic. Over the lifetime, 1619 publications have been published within this topic receiving 35348 citations. The topic is also known as: pyranoses & hexopyranose.

Conformational flexibility of the group B meningococcal polysaccharide in solution.

Abstract: To elucidate the role of secondary structure in the immune response against alpha(2-->8)-linked polysialic acid, the capsular polysaccharide of Group B meningococci, we have investigated its solution dynamics by using specific models of molecular motion and hydrodynamic modeling to interpret experimental NMR data. (13)C-[(1)H] NMR relaxation times and steady-state NOE enhancements were measured for two aqueous solutions of alpha(2-->8)-linked sialic acid polysaccharides. Each contained a unique distribution of polysaccharide chain lengths, with average lengths estimated at 40 or 400 residues. Models for rigid molecule tumbling, including two based on helical conformations proposed for the polysaccharide,(31) could not explain the NMR measurements. In general for these helices, the correlation times for their overall tumbling that best account for the NMR data correspond to polysaccharide chains between 9 and 18 residues in length, far short of the average lengths estimated for either solution. The effects of internal motions incorporated into these helices was modeled with an effective correlation time representing helix tumbling as well as internal motion. This modeling demonstrated that even with extreme amounts of internal motion, "flexible helices" of 25 residues or more still could not produce the NMR measurements. All data are consistent with internal and segmental motions dominating the nuclear magnetic relaxation of the polysaccharide and not molecular tumbling. Statistical distributions of correlation times have been found specifically for the pyranose rings, linkage groups, and methoxy groups that can account for the measured relaxation times and NOE enhancements. The distributions suggest that considerable flexibility attends the polysaccharide in solution, and the ranges of motional frequencies for the linkage groups and pyranose rings are comparable. We conclude that the Group B meningococcal polysaccharide is a random coil chain in solution, and therefore, does not have antigenic epitopes dependent upon a rigid, ordered conformation.

X-ray examination of sucrose.

Abstract: ALTHOUGH the chemical structure of most sugars has been established beyond doubt, a given chemical structure may comprise several geometrical possibilities. In particular, the exact conformations of. the pyranose and furanose rings, which are of general occurrence in sugars and sugar derivatives, have long been the subject of speculation. An X-ray investigation of a series of sugars and their methyl derivatives was made by Cox, Goodwin and Wagstaff1, who came to the conclusion that the five carbon atoms of the pyranose ring lie in a plane but the oxygen atom is raised out of this plane. That this conclusion is not of universal application was shown by Cox and Jeffrey2, who determined the positions of all the atoms (other than hydrogen) in the crystal lattice of glucosamine hydrobromide, and were thus able to prove that in this case the pyranose ring is of the Sachse trans-form. Cox and Goodwin3 have suggested that the four carbon atoms and one oxygen which comprise the furanose ring are coplanar, but direct evidence has hitherto been entirely lacking. The sugars thus merit further attention by the methods of X-ray crystallography.