Showing papers on "Pyranose published in 2008"

Additive empirical force field for hexopyranose monosaccharides.

Abstract: We present an all-atom additive empirical force field for the hexopyranose monosaccharide form of glucose and its diastereomers allose, altrose, galactose, gulose, idose, mannose, and talose. The model is developed to be consistent with the CHARMM all-atom biomolecular force fields, and the same parameters are used for all diastereomers, including both the alpha- and beta-anomers of each monosaccharide. The force field is developed in a hierarchical manner and reproduces the gas-phase and condensed-phase properties of small-molecule model compounds corresponding to fragments of pyranose monosaccharides. The resultant parameters are transferred to the full pyranose monosaccharides, and additional parameter development is done to achieve a complete hexopyranose monosaccharide force field. Parametrization target data include vibrational frequencies, crystal geometries, solute-water interaction energies, molecular volumes, heats of vaporization, and conformational energies, including those for over 1800 monosaccharide conformations at the MP2/cc-pVTZ//MP2/6-31G(d) level of theory. Although not targeted during parametrization, free energies of aqueous solvation for the model compounds compare favorably with experimental values. Also well-reproduced are monosaccharide crystal unit cell dimensions and ring pucker, densities of concentrated aqueous glucose systems, and the thermodynamic and dynamic properties of the exocyclic torsion in dilute aqueous systems. The new parameter set expands the CHARMM additive force field to allow for simulation of heterogeneous systems that include hexopyranose monosaccharides in addition to proteins, nucleic acids, and lipids.

Detection of a C4a-hydroperoxyflavin intermediate in the reaction of a flavoprotein oxidase.

Abstract: This work describes for the first time the identification of a reaction intermediate, C4a-hydroperoxyflavin, during the oxidative half-reaction of a flavoprotein oxidase, pyranose 2-oxidase (P2O) from Trametes multicolor, by using rapid kinetics. The reduced P2O reacted with oxygen with a forward rate constant of 5.8 × 104 M−1 s−1 and a reverse rate constant of 2 s−1, resulting in the formation of a C4a-hydroperoxyflavin intermediate which decayed with a rate constant of 18 s−1. The absorption spectrum of the intermediate resembled the spectra of flavin-dependent monooxygenases. A hydrophobic cavity formed at the re side of the flavin ring in the closed state structure of P2O may help in stabilizing the intermediate.

Stereocontrolled Photocyclization of 1,2-Diketones: Application of a 1,3-Acetyl Group Transfer Methodology to Carbohydrates

Abstract: Photolysis of 1-glycosyl-2,3-butanodione derivatives using visible light is a mild and selective procedure for the synthesis of chiral 1-hydroxy-1-methyl-5-oxaspiro[3.5]nonan-2-one carbohydrate derivatives. The results strongly suggest that stereocontrol of the cyclization is dependent on conformational and stereoelectronic factors. Further oxidative opening of the 1-hydroxy-1-methyl-2-cyclobutanone moiety affords new C-ketoside derivatives either in C- and O-glycoside series. This tandem two-step process could be considered to be a stereocontrolled 1,3-transference of an acetyl group, and it can be applied either to pyranose and furanose models.

Biomimetic seleninates and selenonates.

Abstract: The synthesis of a variety of pyranose-, nucleoside-, (amino acid)-, and polyhydric-based seleninic and selenonic acids by DMDO oxidation of the corresponding selenoesters is reported, as well as some unusual coupling reactions of the seleninate and selenonate functionality with biological nucleophilic groups (sulfhydryl, indole, phenol, imidazole, carboxamide) that are found in proteins and enzyme active sites.

Ring-Opening of Aziridine-2-Carboxamides with Carbohydrate C1-O-Nucleophiles. Stereoselective Preparation of α- and β-O-Glycosyl Serine Conjugates

Abstract: The stereoselective formation of the α-GalNAc-Ser linkage via the ring opening of aziridine-2-carboxamides with pyranose C1-O-nucleophiles is described. The process is tolerant to the native C2-NHAc group, can be modulated to provide either the α- or β-glycoside through judicious choice of solvent and metal counterion, and is amenable to other classes of O-glycosyl-Ser constructs such as the β-GlcNAc-Ser and α-Man-Ser linkages. This coupling reaction also led to the development of the o-allylbenzyl (ABn) moiety as a new C-terminus carboxyl protective group, which allows for the use of novel methods for N- and C-terminus extension of amino acids following carbohydrate conjugation.

Site-specific synthesis and characterization of oligonucleotides containing an N6-(2-deoxy-D-erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5-N-methylformamidopyrimidine lesion, the ring-opened product from N7-methylation of deoxyguanosine.

Abstract: A phosphoramidite reagent of N6-(2-deoxy-d-erythro-pentofuranosyl)-2,6-diamino-1,4-dihydro-4-oxo-5-N-methylformamidopyrimidine (MeFapy-dGuo) lesions was synthesized in four steps from 2′-deoxyguanosine. Fapy nucleosides can rearrange to the pyranose form when the 5′-hydroxyl group is unprotected. The phosphoramidite was incorporated into oligonucleotides using solid-phase synthesis by adjusting the deprotection time for removal of the 5′-dimethoxytrityl group of the MeFapy-dGuo nucleotide, thereby minimizing its rearrangement to the ribopyranose. The furanose and pyranose forms were differentiated by a series of two-dimensional NMR experiments.

Intramolecular 1,8-hydrogen-atom transfer reactions in (1-->4)-O-disaccharide systems: conformational and stereochemical requirements.

Abstract: The stereochemical and conformational factors controlling the intramolecular hydrogen-atom transfer (HAT) reaction between the two pyranose units in a (1-->4)-O-disaccharide when promoted by a primary 6-O-yl radical are studied. Models with alpha-D-Glcp-(1-->4)-beta-D-Glcp, alpha-L-Rhamp-(1-->4)-alpha-D-Galp or alpha-D-Manp-(1-->4)-beta-L-Gulp skeletons led exclusively to the abstraction of the hydrogen from H--C-5' and the formation, through a nine-membered transition state, of a 1,3,5-trioxocane ring system in a stable boat-chair conformation. Notwithstanding, derivatives of alpha-L-Rhamp-(1-->4)-alpha-D-Glcp or alpha-D-Manp-(1-->4)-alpha-D-Galp exclusively abstract the hydrogen from H--C-1' through a seven-membered transition state and, therefore, lead to an interglycosidic spiro ortho ester.

Experimental Measurement of Carbohydrate–Aromatic Stacking in Water by Using a Dangling‐Ended DNA Model System

Abstract: Protein-carbohydrate recognition is of fundamental importance for a large number of biological processes; carbohydrate-aromatic stacking is a widespread, but poorly understood, structural motif in this recognition. We describe, for the first time, the measurement of carbohydrate-aromatic interactions from their contribution to the stability of a dangling-ended DNA model system. We observe clear differences in the energetics of the interactions of several monosaccharides with a benzene moiety depending on the number of hydroxy groups, the stereochemistry, and the presence of a methyl group in the pyranose ring. A fucose-benzene pair is the most stabilizing of the studied series (-0.4 Kcal mol -1 ) and this interaction can be placed in the same range as other more studied interactions with aromatic residues of proteins, such as Phe-Phe, Phe-Met, or Phe-His. The noncovalent forces involved seem to be dispersion forces and nonconventional hydrogen bonds, whereas hydrophobic effects do not seem to drive the interaction.

Sequential Norrish type II photoelimination and intramolecular aldol cyclization of 1,2-diketones in carbohydrate systems: stereoselective synthesis of cyclopentitols

Abstract: Opened and closed: Visible-light photostimulation of 2,3-diuloses I triggers an unprecedented sequential rearrangement: A Norrish type II photoelimination to give an isolable acyclic photoenol intermediate II is followed by an intramolecular enolexo aldolization. The contraction of the pyranose ring in this process leads to a new type of cyclopentitol derivative III. R=acyl, alkyl, silyl group.

Mutations of Thr169 affect substrate specificity of pyranose 2-oxidase from Trametes multicolor

Abstract: Site-directed mutagenesis was used to enhance the catalytic activity of pyranose 2-oxidase (P2Ox) from Trametes multicolor with different substrates. To this end, threonine at position 169 was repl ...

Lactide polymerization co‐initiated by carbohydrate esters and pyranoses

Abstract: The polymerization of [S]-lactide was accomplished using an initiating system comprising an alkyl zinc complex and a series of well defined carbohydrate co-initiators derived from D-glucose, D-xylose, and 2-deoxy-D-ribose. The monosaccharide co-initiators were aldonate esters and pyranoses, they were all prepared in high yield and had only a single alcohol co-initiating group; the remaining carbohydrate hydroxyl functionalities were protected as acetyl, benzyl ether and isopropylidene acetal groups. The polymerizations were all well controlled, illustrated by the linear increase in poly(S-lactide) M n with percentage conversion of lactide, the increase in poly(S-lactide) M n with [lactide] 0 -[lactide] t /[co-initiator] and the narrow polydispersity indices of the polylactides. Thus, the novel initiating systems were used to produce poly(S-lactides) end functionalized with a variety of different aldonate ester and pyranose groups and with degrees of polymerization from 10 to 250. The polyesters were fully characterized, including by NMR spectroscopy, size exclusion chromatography (SEC), matrix-assisted laser deposorption/ionization (MALDI) mass spectrometry and by static water contact angle measurements.

Optical film, polarizing plate and liquid crystal display apparatus

Abstract: Disclosed is an optical film having a hard coat layer on a cellulose ester film, which contains an ester compound composed of a furanose structure or a pyranose structures and a sum of a number of the furanose structures or the pyranose structure is 1 to 12, provided that a part of hydroxy groups of the furanose structure or the pyranose structure has been esterified and a part of hydroxy groups of the furanose structure or the pyranose structure remains.

Optical film and polarizing plate

Abstract: PROBLEM TO BE SOLVED: To provide an optical film which excels in the inhibition of haze when the optical film is stretched at a high draw ratio on widening the film and slit aptitude and a polarizing plate which inhibits dimensional change, warpage, and the occurrence of color shading and excels in face contrast. SOLUTION: The optical film comprises at least a cellulose ester and a (meth)acrylic copolymer or a sugar ester compound obtained by esterifying all OH groups or part of OH groups of a compound having at least one furanose structure or pyranose structure, 1-12 furanose structures or pyranose structures being connected with one another and has an average acetyl substitution degree in the above entire cellulose ester of ≥1.9, an elongation at breakage on stretching in a 23°C, 55%RH environment of not less than 10% in both the TD direction and the MD direction, and a tear strength of not less than 40 mN in both the TD direction and the MD direction. COPYRIGHT: (C)2010,JPO&INPIT

Optical film and polarizing plate using same

Abstract: PROBLEM TO BE SOLVED: To provide an optical film improved in curling and blocking properties in a broad and lengthy roll, and high in stability to haze and retardation in drawing, and a polarizing plate with excellent front contrast using the same. SOLUTION: The optical film contains at least a cellulose ester, and an acrylic copolymer or a sugar ester compound including at least one furanose structure or pyranose structure, all or a part of OH groups of the compound to which 1-12 furanose structures or pyranose structures are bonded being esterified. The elastic modulus of the optical film is 3.4 GPA (measured in a 23°C, 55 RH% environment) in both a carrying direction (MD direction) and a direction orthogonal to the carrying direction (TD direction) with TD elastic modulus/MD elastic modulus=1.05-2.0. COPYRIGHT: (C)2009,JPO&INPIT

Cellulose ester film

Abstract: PROBLEM TO BE SOLVED: To provide a cellulose ester film excellent in front contrast SOLUTION: In the cellulose ester film having an internal haze of ≤002, the cellulose ester film includes a cellulose ester in which the haze in an ASTM-A solvent is ≤5%, and at least one of an aromatic-terminated polyester-based compound represented by the general formula (I) and an ester compound having 1 to 12 units of at least one of the pyranose structure or the furanose structure, wherein all or a portion of OH groups of each structure is esterified The general formula (I) is as follows: B-(G-A)n-G-B (wherein, B represents aryl-carboxylic acid residue; G represents 2-12C alkylene glycol residue or the like; A represents 4-12C alkylene dicarboxylic acid residue or the like; and n is an integer of ≥1) COPYRIGHT: (C)2010,JPO&INPIT

Stereocontrolled Photocyclization of 1,2-Diketones: Application of a 1,3-Acetyl Group Transfer Methodology to Carbohydrates.

Abstract: Photolysis of 1-glycosyl-2,3-butanodione derivatives using visible light is a mild and selective procedure for the synthesis of chiral 1-hydroxy-1-methyl-5-oxaspiro[3.5]nonan-2-one carbohydrate derivatives. The results strongly suggest that stereocontrol of the cyclization is dependent on conformational and stereoelectronic factors. Further oxidative opening of the 1-hydroxy-1-methyl-2-cyclobutanone moiety affords new C-ketoside derivatives either in C- and O-glycoside series. This tandem two-step process could be considered to be a stereocontrolled 1,3-transference of an acetyl group, and it can be applied either to pyranose and furanose models.

A mild and efficient synthesis of chiral tetrahydroquinolino pyranose derivatives catalyzed by lanthanum(iii) nitrate hexahydrate

Abstract: A mild and highly efficient synthesis of chiral tetrahydroquinolino pyranose derivatives is described. The reaction of a chiral α,β-unsaturated aldehyde containing a hydroxyl group with different aryl amines using lanthanum(III) nitrate hexahydrate as a catalyst afforded corresponding chiral tetrahydroquinolinated pyranosides in excellent yields. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:429–433, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20441

Methyl 3-amino-2,3,6,-trideoxy-L-hexopyranosides in DFT level theory conformational studies.

Abstract: Geometry optimizations at the B3LYP level of density functional theory are reported for the (1)C4 and (4)C1 conformations of four theoretically possible alpha and beta methyl 3-amino-2,3,6-trideoxy-L-hexopyranosides. The Gibbs free energies, relative Gibbs free energies, and geometry parameters are presented for all the optimized structures. Conformational analysis of the pyranose ring is performed for each stereoisomer on the basis of calculated rotamer populations. It is demonstrated that the alpha/beta-L-arabino, alpha/beta-L-lyxo, and alpha-L-ribo stereoisomers adopt the (1)C4 conformation, whereas beta-L-ribo and alpha/beta-L-xylo stereoisomers remain in (1)C4 (4)C1 conformational equilibrium. The preference of the alpha over the beta anomers is due to the endo-anomeric effect. The factors affecting the stability of pyranose ring conformations are discussed, as is the influence of hydrogen bonds on the orientation of the hydroxyl and amino groups. Figures of the most stable conformers are presented.

Configurational and conformational classification of pyranose sugars.

Abstract: Automated cluster analysis is used to examine the conformation and configuration of pyranose sugars. Previous findings on this issue are confirmed, importantly from an analysis that requires no prior knowledge of the significant factors determining the conformational classification. The findings on the conformations adopted in the crystalline solid state are found to be different to existing quantum chemical calculations performed for D-glucose in the gas phase, but consistent with empirically determined conformations in the solution state. The use of this clustering analysis in studying chirality in the determined structures is discussed, as is the ability of this type of method to examine higher dimensions within the metric multi-dimensional scaling formalism.