Topic
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.
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TL;DR: Using IRMPD spectroscopy (InfraRed Multiple Photon Dissociation), a straightforward diagnostic of the ring-size of N-acetyl galactosamine ions is proposed and opens the way to facile identification of theRing-size in oligosaccharides.
Abstract: Hexoses are mainly found in nature in the pyranose form (6-membered ring). Yet, furanose forms (5-membered ring) are observed in some rare polysaccharides. Using IRMPD spectroscopy (InfraRed Multiple Photon Dissociation), we propose a straightforward diagnostic of the ring-size of N-acetyl galactosamine ions. The furanose form of N-acetyl galactosamine was synthesized and its protonated ion was isolated in an ion trap to measure its gas phase vibrational spectrum by IRMPD. Comparison with the IRMPD spectrum of its pyranose counterpart reveals that they have distinctive optical fingerprints. This new MS-based diagnostic opens the way to facile identification of the ring-size in oligosaccharides. Our experimental data also provide new insights to support the theoretical description of the conformational behavior of the furanose ring, which is notoriously more flexible than the pyranose form but remains difficult to assess.
10 citations
TL;DR: The calculated glycosidic torsion angles of the lowest free energy conformation of GA1 in the hydrated state are in accord with the structures of relevant oligosaccharides deduced from nmr experiments and hard sphere exoanomeric calculations, suggesting that the medium- and long-range interactions are also of consequence.
Abstract: In order to investigate the significance of preferred conformations of the saccharide for the steric orientation and recognition of glycosphingolipids at the membrane surface, the conformational free energy calculations were carried out on the asialo-GM1 [GA1; beta-D-Gal (1-->3) beta-D-GalNac(1-->4) beta-D-Gal(1-->4) beta-D-Glc-O-ceramide) using a new program CONCARB (CONformational study program for CARBohydrate) in the unhydrated and hydrated states. The overall backbone conformational of GA1 appears to be extended with a little bent at the glycosidic II-III linkage, in which two pyranose rings of Gal(IV)-GalNAc-(III) moiety orient approximately perpendicular to those of Gal(II)-Glc(I) moiety. This is consistent with the structures deduced from high-sensitivity differential scanning calorimetry experiments and the nmr study on GA1. The calculated glycosidic torsion angles of the lowest free energy conformation of GA1 in the hydrated state are in accord with the structures of relevant oligosaccharides deduced from nmr experiments and hard sphere exoanomeric calculations. A comparison of the values of glycosidic torsion angles phi and psi of GA1 and its constituent oligosaccharides indicates that the overall backbone conformation of each oligosaccharide is retained when the oligosaccharide chain becomes longer. This implies that the short-range interactions between the nearest-neighbored saccharides are of significant importance in stabilizing the overall backbone conformation of GA1 in both the unhydrated and hydrated states. The different orientation and hydrogen bonds of hydroxymethyl and hydroxyl groups from one oligosaccharide to another suggest that the medium- and long-range interactions are also of consequence. Hydration seems to affect significantly the confirmation of these groups, but not to perturb remarkably the overall backbone conformation of GA1.
10 citations
TL;DR: A series of di- and trisaccharides containing 6-O-linked galactofuranose were synthesized as an anomeric mixture of methyl glycosides using silica-supported perchloric acid as discussed by the authors.
Abstract: A series of di- and trisaccharides containing 6-O-linked galactofuranose were synthesized as an anomeric mixture of methyl glycosides using silica-supported perchloric acid.
10 citations
TL;DR: Application of these new ligands in asymmetric cyclopropanation revealed strong steric and configurational effects of position 3 on asymmetric induction, and further dramatic effects of the pyranose conformation were also observed.
Abstract: In previous studies we found that the asymmetric induction of bis(oxazolines) based on D-glucosamine strongly depended on the steric demand of the 3-O-substituents. To further probe the impact of the 3-position of the pyranose scaffold, we prepared 3-epimerised and 3-defunctionalised versions of these ligands as well as a 3-O-formyl derivative. Application of these new ligands in asymmetric cyclopropanation revealed strong steric and configurational effects of position 3 on asymmetric induction, further dramatic effects of the pyranose conformation were also observed.
10 citations
TL;DR: Substrate destabilisation of the particular type commonly envisaged for lysozyme catalysis therefore plays no part in catalysis by this particular glycosidase, and the C-5 hydroxymethyl group plays a role only in binding.
Abstract: Removal of the C-5 hydroxymethyl group of the galactopyranosyl substrates of E. coliβ-galactosidase has only a slight effect—usually a decrease—on the rate of the conformation-change step with aryl glycosides, on the rate of cleavage of the C–N bond of the glycosylpyridinium ion, or on the rate of hydrolysis of the glycosyl-enzyme. Values of Km are all substantially increased. Substrate destabilisation of the particular type commonly envisaged for lysozyme catalysis therefore plays no part in catalysis by this particular glycosidase, and the C-5 hydroxymethyl group plays a role only in binding.
10 citations