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.

Synthesis, Crystal Structure, Electronic Spectroscopy, Electrochemistry and Biological Studies of Ferrocene–Carbohydrate Conjugates

Abstract: A series of six new ferrocene–carbohydrate conjugates was prepared from pentose and hexose sugar derivatives. These include the ferrocenecarbaldehyde acetal 2, four ferrocenyltriazoles 4a–d derived from furanose sugar and the ferrocenyltriazole 4e derived from a pyranose sugar. The compounds were characterised by spectroscopic means and the structures of the new conjugates 2 and 4a were determined by means of X-ray crystallography. A UV/Vis study of these compounds performed in aqueous solutions under physiological conditions confirmed their stability. The CD spectral analysis shows the effect of the nature of substituents of the carbohydrate moieties. The electrochemical studies conducted in a buffer solution display one-electron reversible oxidation processes for these compounds. These results indicate that the compounds are suitable for conducting bio

The 1.6 Å crystal structure of pyranose dehydrogenase from Agaricus meleagris rationalizes substrate specificity and reveals a flavin intermediate.

Abstract: Pyranose dehydrogenases (PDHs) are extracellular flavin-dependent oxidoreductases secreted by litter-decomposing fungi with a role in natural recycling of plant matter. All major monosaccharides in lignocellulose are oxidized by PDH at comparable yields and efficiencies. Oxidation takes place as single-oxidation or sequential double-oxidation reactions of the carbohydrates, resulting in sugar derivatives oxidized primarily at C2, C3 or C2/3 with the concomitant reduction of the flavin. A suitable electron acceptor then reoxidizes the reduced flavin. Whereas oxygen is a poor electron acceptor for PDH, several alternative acceptors, e.g., quinone compounds, naturally present during lignocellulose degradation, can be used. We have determined the 1.6-A crystal structure of PDH from Agaricus meleagris. Interestingly, the flavin ring in PDH is modified by a covalent mono- or di-atomic species at the C(4a) position. Under normal conditions, PDH is not oxidized by oxygen; however, the related enzyme pyranose 2-oxidase (P2O) activates oxygen by a mechanism that proceeds via a covalent flavin C(4a)-hydroperoxide intermediate. Although the flavin C(4a) adduct is common in monooxygenases, it is unusual for flavoprotein oxidases, and it has been proposed that formation of the intermediate would be unfavorable in these oxidases. Thus, the flavin adduct in PDH not only shows that the adduct can be favorably accommodated in the active site, but also provides important details regarding the structural, spatial and physicochemical requirements for formation of this flavin intermediate in related oxidases. Extensive in silico modeling of carbohydrates in the PDH active site allowed us to rationalize the previously reported patterns of substrate specificity and regioselectivity. To evaluate the regioselectivity of D-glucose oxidation, reduction experiments were performed using fluorinated glucose. PDH was rapidly reduced by 3-fluorinated glucose, which has the C2 position accessible for oxidation, whereas 2-fluorinated glucose performed poorly (C3 accessible), indicating that the glucose C2 position is the primary site of attack.

Conformational aspects of oligosaccharides

Abstract: The three dimensional structure of oligosaccharides determines their interaction with receptors and hence is important for their biological activity. Conformational analysis of oligosaccharides makes the three dimensional structure available. The analysis of the conformation of oligosaccharides is usually determined by a combination of computational methods and experimental techniques. NMR spectroscopy is the most important experimental tool. The calculational techniques cover a wide range with most emphasis put into force field calculations. Conformational flexibility plays an important role in many though not in all oligosaccharide structures. Glycosidic linkages to a side chain of a pyranose ring are more flexible than are linkages to the pyranose ring. The major attempts are described to determine the three dimensional structure of oligosaccharides with the exception of homooligomers. This review covers conformational analyses of blood group antigens of N-linked and of O-linked oligosaccharide chains, of glycolipids, of oligosaccharides related to O-specific polysaccharides of bacteria, and of oligosaccharides related to proteoglycans.

The Cetus Process Revisited: A Novel Enzymatic Alternative for the Production of Aldose-Free D-Fructose

Abstract: In the Cetus process crystalline D-fructose is produced from D-glucose via the intermediate 2-keto-D-glucose. Whereas the first step in the traditional process is catalyzed by the immobilized enzyme pyranose 2-oxidase, the ensuing reduction is performed by catalytic hydrogenation. In an entirely enzymatic variation of this process, soluble pyranose 2-oxidase from Trametes multicolor was employed. This biocatalyst could be efficiently stabilized under operational conditions by the addition of bovine serum albumin (BSA) together with catalase which decomposes hydrogen peroxide formed as a by-product. D-Glucose could be converted into 2-keto-D-glucose in yields above 98%. When the biocatalyst together with both stabilizing agents was separated from the product solution by ultrafiltration, it could be reutilized for several subsequent batch operation cycles. 2-Keto-D-glucose thus obtained was quantitatively reduced to D-fructose by NAD(P)-dependent aldose reductase from Candida tenuis. Two different enzymatic...