Showing papers on "Pyranose published in 1974"

A study of 13CH coupling constants in hexopyranoses

Abstract: Proton decoupled and undecoupled 13C n.m.r. spectra have been measured on a number of hexopyranoses. The direct coupling constants between the anomeric carbon atoms and protons {1J[13C–H(1)]} were found to be ca. 160 in the β-anomers and ca. 170 Hz in the α-anomers; the difference of ca. 10 Hz between pairs of anomers was found in almost all cases. Chemical shifts and 1J(13CH) values of the other carbon atoms in the pyranose rings were also measured.

The Crystal Structure of Levoglucosan Triacetate

Abstract: The crystal structure of the acetylated levoglucosan (1,6-anhydro-2,3,4-triacetylglucose) was determined by X-ray crystallography. The crystal data are: P212121, a = 10.916, b = 8.318, c = 15.612 A. It was found that the pyranose ring of the molecule has the 1C(D) chair conformation with the acetate groups occupying the axial positions. The orientation of the acetate groups with respect to the pyranose ring was discussed in conjunction with other acetylated carbohydrate structures.

Reaction Mechanism of d‐Galactose Dehydrogenases from Pseudomonas saccharophila and Pseudomonas fluorescens

Abstract: 1 β-d-Galactopyranose has been shown by specificity studies and by gas-liquid chromatographic investigations to be the substrate of the d-galactose dehydrogenases from Pseudomonas saccharophila and from Pseudomonas fluorescens 2 α-d-Galactopyranose and the two ring-isomeric d-galactofuranoses are oxidized, at high enzyme concentrations, only after their rate-limiting isomerization into the β-d-pyranose The open-chained aldehyde form of d-galactose has been likewise excluded as substrate 3 d-Galactono-1,5-lactone has been shown by gas-liquid chromatography to be the immediate product of the enzymatic dehydrogenation of d-galactose and identified by combined gas-liquid chromatography—mass spectrometry of the isolated trimethylsilylated derivative 4 The primarily formed d-galactono-1,5-lactone rearranges non-enzymatically to the corresponding d-galactono-1,4-lactone by an intramolecular rearrangement without the participation of the open-chained d-galactonate This rearrangement is strongly dependent on the pH-value, having a first-order rate constant k= 10 min−1 at pH 68 under the conditions used 5 The apparent equilibrium constants Were determined at pH 68 under the conditions used, enabling the estimation of the apparent equilibrium constant for the reaction catalyzed by the enzyme 6 Results analogous to those with d-galactose were obtained from investigations with the homeomorphic l-arabinose The pyranose ring with the hydroxyl group at carbon-1 in the equatorial position is likewise the only substrate, and the immediate product, the 1,5-lactone, also rearranges subsequently to the corresponding 1,4-lactone, having a first-order rate constant k= 022 min−1 at pH 68 under the conditions used The l-arabinono-1,5-lactone has also been identified by gas-liquid chromatography — mass spectrometry of the trimethylsilylated derivative

Konformationsanalyse, VIII. Tri‐axiale Konformation des 1‐(Tri‐O‐acetyl‐α‐D‐xylopyranosyl)‐imidazols im Kristall

Abstract: 1-(Tri-O-acetyl-α-D-xylopyranosyl)imidazol (1) liegt im Kristall auch ohne wesentlichen Beitrag eines inversen anomeren Effektes in der 1C4-Konformation 1b mit drei axialen Acetyl- und aquatorialer Imidazolgruppe vor. Sterische Grunde sollten hierfur bestimmend sein. In Losung liegt der Anteil an 1C4-Konformation 1b zwischen 35 und 85%. Die dreidimensionale Rontgenstrukturanalyse von 1 (Raumgruppe rhombisch P 21212) zeigt, das infolge 1,3-syn-diaxialer Wechselwirkung der 2-OAc-und-4OAc-Gruppe das C4 des Pyranosesessels von 1b abgeflacht ist. Der Imidazolring steht senkrecht zum Pyranosering und senkrecht auf der abgedrehten 2-OAc-Gruppe. Die Methylgruppe der 2-OAc-Gruppe weist eine, die der 3-OAc- und 4-OAc-Gruppe zwei statistisch verteilte Wasserstofflagen auf. Conformation Analysis, VIII. Tria-axial Conformation of 1-(Tri-O-acetyl-α-D-xylopyranosyl)imidazol in Crystal In the crystalline state 1-(tri-O-acetyl-α-D-xylopyranosyl)imidazole (1) adopts the 1C4 conformation 1b with three axial acetoxy groups and one equatorial imidazol group without considerable contribution of an inverse anomeric effect. This is a consequence of predominating steric effects. In solution the amount of 1C4 conformation 1b varies from 35–85%. The three dimensional X-ray structure analysis of 1 (space group rhombic P 21212) shows that owing to a 1,3-syn-diaxial interaction of the 2-OAc and the 4-OAc groups the pyranose chair of 1b is flattened at C4. The plane of the imidazol ring is perpendicular to the pyranose chair and also perpendicular to the turned 2-OAc group. The methyl group of the 2-OAc group exhibits one, those of the 3-OAc and 4-OAc groups exhibit two statistically distributed hydrogen positions.

Synthesis of C-glycopyranosides by photochemically induced addition of methanol to pyran-3-ulose

Abstract: Photochemically induced addition of methanol to pyran-3-uloses affords a ready method of extending the pyranose ring at C-1.

Conformations of Sugars: Proton Dihedral Angles from Gauche Coupling Constants

Abstract: Proton coupling constants have been used in calculating dihedral angles of vicinal gauche protons in variety of pyranose derivatives of glucose, mannose, arabinose, xylose, altrose, and galactose. The calculations involve the use of a formula which was derived from a correlation of the coupling constants of ethane derivatives with the electronegativities of substituents and their orientation relative to the coupled protons.The results indicate that the formula has general applicability and gives more reasonable values than a Karplus equation in which the constants have been adjusted to fit some compounds of the series. The calculated dihedral angles indicate that an equatorial substituent generally causes little distortion of dihedral angles, whereas an axial substituent generally causes the equatorial proton on the same carbon to have a smaller than normal dihedral angle with the adjacent axial proton and a larger than normal dihedral angle with the adjacent equatorial proton.

Monosaccharide mit stickstoffhaltigem Ring, XXXIV. Darstellung und Reaktionen der freien 2,4‐Diamino‐2,4‐didesoxy‐D‐galactose

Abstract: Durch saure Hydrolyse des Azidozuckers 4, der durch nucleophile Substitution uber das offenkettige Tosylat 2 zuganglich ist, wird 2-Amino-4-azido-2,4-didesoxy-D-galactopyranose·HCl (9) erhalten. Hydrierung von 9 in stark saurer Losung fuhrt zur 2,4-Diamino-2,4-didesoxy-D-galactopyranose·2 HCl (10), in schwach saurer Losung dagegen zu dem Pyrrolidinderivat 12. Aus dem Dihydrochlorid 10 freigesetzte 2,4-Diamino-2,4-didesoxy- D-galactose liegt in einem Gleichgewicht von Pyranose-, Pyrrolidin- und Pyrrolin-Form 15 ⇋ 16 ⇋ 17 vor, in dem die Pyrrolidin-Form 16 sehr stark uberwiegt. Bis-pyrrolidin-Zucker werden nicht gebildet. Monosaccharides Containing Nitrogen in the Ring, XXXIV. Synthesis and Reactions of Free 2,4-Diamino-2,4-dideoxy-D-galactose 2-Amino-4-azido-2,4-dideoxy-D-galactopyranose·HCl (9) is obtained by acid hydrolysis of the azido sugar 4, prepared by nucleophilic substitution of the acyclic tosylate 2. Hydrogenation of 9 in concentrated acid solution yields 2,4-diamino-2,4-dideoxy-D-galactopyranose·2 HCl (10), in diluted acid solution the pyrrolidine derivative 12. Free 2,4-diamino-2,4-dideoxy-D-galactose, obtained from the dihydrochloride 10, exists as an equilibrium mixture of pyranose-, pyrrolidine- and pyrroline-forms 15 ⇋ 16 ⇋ 17, with the pyrrolidine-form predominating. Bis-pyrrolidine-sugars are not formed.

Structure cristalline et moléculaire d'un dérivé méthyl-hexopyranoside à C(4) hybridé sp2

Abstract: The derivative C13H19NO5 crystallizes in space group P212121 with a = 9.371, b = 11.815, c = 13.207 A and Z = 4. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0.058. The pyranose ring exists in the 3S1 conformation (or in the equivalent, but here structurally less consistent, 0S4 conformation). The dioxolane ring has an envelope conformation. Strong intramolecular interactions between the bulky substituents suggest that the ensuing strain energy is assumed, for a significant part, by the twisted-boat conformation of the pyranose ring.

Synthesis of c-glycopyranosides by photochemically induced addition of methanol to pyran-3-ulose

Abstract: Photochemically induced addition of methanol to pyran-3-uloses affords a ready method of extending the pyranose ring at C-1.