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.

Molecular dynamics-derived conformation and intramolecular interaction analysis of the N-acetyl-9-O-acetylneuraminic acid-containing ganglioside GD1a and NMR-based analysis of its binding to a human polyclonal immunoglobulin G fraction with selectivity for O-acetylated sialic acids.

Abstract: The influence of 9-O-acetylation of GD1a, yielding GD1a (eNeu5,9Ac2) with a 9-O-acetylated sialic acid moiety linked to the outer galactose residue, on the spatial extension and mobility of the carbohydrate chain and on recognition by a natural human antibody is analysed. To study a potential impact of the O-acetyl group on the overall conformation of the carbohydrate chain, molecular dynamics (MD) simulations of oligosaccharide chain fragments of increasing length starting from the non-reducing end have been carried out for the first time in this study. They revealed a considerable loss in chain flexibility after addition of the internal N-acetylneuraminic acid onto the chain. Besides MD calculations with different dielectric constants, the conformational behaviour of the complete oligosaccharide chain of the 9-O-acetylated GD1a ganglioside was simulated in the solvents water and dimethyl sulfoxide. These solvents were also used in NMR measurements. The results of this study indicate that 9-O-acetylation at the terminal sialic acid does not influence the overall conformation of the ganglioside. An extended interaction analysis of energetically minimized conformations of GD1a (eNeu5,9Ac2) and GD1a, obtained during molecular dynamics simulations, allowed assessment of the influence of the different parts of the saccharide chains on spatial flexibility. Noteworthy energetic interactions, most interestingly between the 9-O-acetyl group and the pyranose ring of N-acetylgalactosamine, were ascertained by the calculations. However, the strength of this interaction does not force the ganglioside into a conformation, where the 9-O-acetyl group is no longer accessible. Binding of GD1a (eNeu5,9Ac2) to proteins, which are specific for 9-O-acetylated sialic acids, should thus at least partially be mediated by the presence of this group. To experimentally prove this assumption, a NMR study of 9-O-acetylated GD1a in the presence of an affinity-purified polyclonal IgG fraction from human serum with preferential binding to 9-O-acetylated sialic acid was performed. The almost complete disappearance of the intensity of the 9-O-acetyl methyl signal of the GD1a (eNeu5,9Ac2) clearly indicates that the assumed interaction of the 9-O-acetyl group with the human protein takes place.

[Concerning a new glycoside preparation method. Synthesis of epidopodophyllotoxin-beta-D-glucopyranoside].

Abstract: A new method for the synthesis of glycosides is described. Epipodophyllotoxin (4) reacts with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranose in the presence of BF3-etherate at low temperature to yield tetra-O-acetyl-epipodophyllotoxin-β-D-glucopyranoside (6). This compound, which is sensitive to acid and base, can be converted into the free glucoside 8 by zinc acetate catalysed methanolysis. Glycosidation of podophyllotoxin (1) occurs under the same conditions but is associated with an inversion at C-1 of the aglycone moiety, leading also to the acetylated epi-glucoside 6. It is assumed that the glycosidation proceeds through a common carbonium ion intermediate (12), generated from 1 and 4 respectively by the action of BF3. The intermediate 12 is substituted by the pyranose component from the less hindered side, giving exclusively 1-epi derivatives (e.g.6). The glycosidation reaction is also highly stereoselective with respect to the glycosidic linkage. The stereochemistry of this bond is determined by the configuration at C-1 of the pyranose compound employed for the glycosidation. Further experimental evidence for the proposed mechanism consists in the glycosidation of diphenylmethanol (14) to the corresponding β-D-glucoside 15. Scope and limitation of the new glycosidiation method are briefly discussed.

Characteristics of Interactions in the Pectin–Chitosan System

Abstract: Interpolymeric complexes have been obtained from citric pectin and chitosan, the latter synthesized from crab chitin. The composition and structure of complexes obtained from different ratios of the components were studied by IR spectroscopy, rheological investigation of gel structure, and mathematical modelling of system properties. Rheological investigation of the processes involved in the formation of interpolymeric complexes with gel structures from citric pectin and chitosan was conducted in moderately concentrated solutions containing different ratios of the components. It was shown that the toughness of the gel structures was determined by the ratio of the amounts of the heterogeneous polymers. The toughest product (τ=121.4 Pa) was obtained by use of equimolar quantities of pectin and chitosan. With deviation of the composition of the mixture from equimolar the toughness of the gel decreased. It is proposed that the polyelectrolyte pectin–chitosan complex with a network structure is formed at the expense of electrostatic interaction between positively charged amino groups at C-2 of the chitosan pyranose ring and negatively charged carboxyl groups at the C-5 of the pectin pyranose ring.

A new synthetic method for the preparation of amino sugars through an allyl cyanate-to-isocyanate rearrangement

Abstract: A new approach for the synthesis of amino sugars using an allyl cyanate-to-isocyanate rearrangement has been developed. The key feature in this method involves introduction of the nitrogen substituent into the pyranose framework by [3,3] sigmatropic rearrangement of an allyl cyanate. Subsequent functionalization of the allylamine moiety by either hydroxylation or cyclofunctionalization completes the synthesis of two amino sugars, D-perosamine and D-vicenisamine.