Showing papers on "Pyranose published in 1983"

Deoxy‐nitrosugars. 6th communication. Stereoelectronic control in the reductive denitration of tertiary nitro ethers. A synthesis of ‘C‐glycosides’

Abstract: The separate, radical denitration with Bu3SnH of the pyranose derivatives 3, 4, 9, and 10 gave in good yields exclusively the ‘C-glycosides’ 5 and 11, respectively (Scheme 1). Similar reduction of the cyclohexyl derivatives 15, 16, 19 and 20 gave 4:1 mixtures of 17, 18, 21 and 22, respectively, always with predominant formation of an axial C,H-bond. In the furanose series a divergent behaviour was observed for the D-mannose-derived nitro ethers 25 and 27 and the D-ribose-derived nitro ethers 30 and 31, respectively, in that the former two gave isomerically homogeneous reduction products (26 and 28, respectively; Scheme 3) and the latter a 1:1 mixture of the diastereoisomers 32 and 33(Scheme 4). The stereochemical results were explained on the basis of the stereoelectronic effect of the ring O-atom, the preferred conformation of the intermediate, pyramidal alkoxyalkyl radicals and steric effects in the trioxabicyclo [3.3.0]octane ring system.

The hydrogen‐bonding patterns in the pyranose and pyranoside crystal structures

Abstract: The hydrogen-bonding patterns in the crystal structures of the simple cyclic carbohydrates attempt to comply with three rules: (1) Maximize the hydrogen-bond energy by including all the hydroxyls and as many of the ring and glycosidic oxygens as possible. (2) Maximize the energy through the cooperative effect by forming infinite or long finite chains of hydrogen bonds. (3) Take into account the anomeric effect by including the anomeric hydroxyls as strong donors and poor acceptors of hydrogen bonds. These three rules are mutually incompatible. Compromises give rise to patterns of hydrogen bonding which can be divided into four distinct classes with related sub-groups. These patterns are distributed almost equally between the crystal structures of the 58 pyranoses, furanoses, pyranosides and furanosides included in this survey.

Sugar-Nucleotide Precursors of Arabinopyranosyl, Arabinofuranosyl, and Xylopyranosyl Residues in Spinach Polysaccharides

Abstract: Cultured spinach ( Spinacia oleracea L. cv Monstrous Viroflay) cells incorporated exogenous l-[ 3 H]arabinose sequentially into β-l-arabinopyranose-1-phosphate, uridine diphospho-β-l-arabinopyranose, uridine diphospho-α-d-xylopyranose and (in some experiments) α-d-xylopyranose-1-phosphate. The amount of 3 H in each of these compounds reached a plateau after a few minutes, and could be rapidly chased with nonradioactive l-arabinose, demonstrating rapid turnover. After a few minutes9 lag, incorporation of 3 H into the arabinofuranosyl, arabinopyranosyl, and xylopyranosyl residues of polysaccharides was linear with respect to time. The kinetics of labeling were compatible with UDP-β-l-arabinopyranose and UDP-α-d-xylopyranose being the immediate precursors of arabians (both the pyranose and the furanose residues) and xylans, respectively. No other radioactive nucleotides were formed; in particular, UDP-arabinofuranose was absent. There was no evidence for conversion of arabinopyranose to arabinofuranose within the polysaccharides, suggesting that this conversion occurs during polymer synthesis. The glycolipids detected showed too slow a turnover to be intermediates of pentosan synthesis.

Energy of Binding of Aspergillus Oryzae Beta-Glucosidase With the Substrate, and the Mechanism of Its Enzymic Action

Abstract: Several beta-D-glucopyranosides (p-nitrophenyl, phenyl, and ethyl), 1-thio-beta-D-glucopyranosides, and phenyl 2-deoxy, 3-deoxy, 4-deoxy, and 6-deoxy beta-D-glucopyranosides were synthesized and used to study the mechanism of the enzymatic action of Taka-beta-glucosidase [EC 3.2.1.21 Aspergillus oryzae]. Kinetic constants of the enzyme for these glycosides were determined from S/V-S or 1/V-1/S plots, and the hydrolysis rates of these compounds with the enzyme, acid (3 N HCl) and alkali (3 N NaOH) were compared. Inhibition of the enzyme by 1,5-anhydroglucitol, glucal, dihydroglucal, and 1,6-anhydroglucopyranose was also examined. Glucal and 1,5-anhydroglucitol showed strong competitive inhibition. Free energy of binding of each hydroxyl group of glucosidic glucose with the enzyme was estimated from Kms of phenyl beta-glucoside and its deoxy analogues, and also Ki values of some inhibitors. The free energies of binding of 2-OH, 3-OH, 4-OH, and 6-OH were calculated to be 1.1, 2.4, 0.7, and 1.8 kcal/mol, respectively. The free energy of binding of phenoxide at C-1 (0.3 kcal/mol) was calculated from the Km of Ph-beta-Glc and Ki of 1,5-anhydroglucitol. The energy of binding of 5-CH2OH (2.3 kcal/mol) was obtained from the Km of Ph-beta-Glc and that of Ph-beta-Xyl. The sum (6.8 kcal/mol) of each partial binding free energy was close to the value of binding free energy of Ph-beta-Glc (7.0 kcal/mol) calculated by the equation; -delta Gbind = -RT ln Km-T delta Smix, showing that the methods of estimation of each binding energy used in the present study seemed reasonable. Glucal, having a pyranose form distorted slightly, showed strong competitive inhibition and the Ki of this inhibitor was smaller than the Km of Ph-beta-Glc, suggesting that the sugar ring bound to the active site was distored to a half chair form which is labile to acid hydrolysis.

Radical reactions of carbohydrates. Part 4. Electron spin resonance studies of radical-induced oxidation of some aldopentoses, sucrose, and compounds containing furanose rings

Abstract: E.s.r. spectra detected when ·OH reacts with the aldopentoses xylose and ribose are attributed to pyranose ring radicals, formed in essentially unselective attack; in contrast, in the corresponding reactions of the model compound tetrahydrofurfuryl alcohol, as well as some isopropylidene derivatives of glucofuranose, the hydrogen atoms on the carbon atoms adjacent to oxygen in a furanose ring are activated towards abstraction. A similar activation, evidently stereoelectronic in origin, is also proposed to account for the enhanced reactivity of C(5′)–H in the furanose ring of sucrose, a finding which may have particular relevance to the mechanism of radiation damage in DNA.

Mercury iodide as a catalyst in oligosaccharide synthesis.

Abstract: The disaccharide 4-O-alpha-D-mannopyranosyl-alpha-L-rhamnopyranose and the trisaccharide 2-O-alpha-D-galactopyranosyl-4-O-beta-D-mannopyranosyl-alpha-L-rhamno pyranose determinants, which are analogs of the repeating unit of Salmonella sero-group A, B and D, have been synthesized using mercury(II) iodide as a catalyst in the glycosylation reaction. The reducing end of the di- and the trisaccharide was substituted with a linking arm for covalent attachment to a protein carrier. Reaction of 8-ethoxycarbonyloct-1-yl 2,3-di-O-benzoyl-alpha-L-rhamnopyranoside with acetobromomannose in the presence of mercury(II) iodide gave, after deprotection, the disaccharide in 49% yield. The trisaccharide was prepared by a block synthesis in which 6-O-acetyl-4-O-allyl-2-O-(6-O-acetyl-2-O-allyl-3,4-di-O-benzoyl-alpha-D- galactopyranosyl)-3-O-benzyl-alpha-D-mannopyranosyl bromide (21) and 8-methoxycarbonyloct-1-yl 2,3-O-cyclohexylidene-alpha-L-rhamnopyranoside were condensed in the presence of mercury(II) iodide. These conditions gave the trisaccharide (26) in 26% yield. The disaccharide 21 was prepared by mercury(II) iodide catalyzed condensation of the protected galactopyranosyl bromide (15) and 4-O-allyl-1,6-anhydro-3-O-benzyl-beta- D-mannopyranose followed by acetolysis and reaction with titanium tetrabromide.

Aralkyl and aralkenyl glycosides as inhibitors of antigen-specific T-cell proliferation

Abstract: The invention disclosed herein relates to novel 1-deoxyglycosides, preferably 1-deoxy-D-mannopyranosides and 1-deoxy-L-rhamnopyranosides, having in the 1-position of the pyranose ring an aralkylthio/aralkenylthio, aralkyloxy/aralkenyloxy or aralkanoylamino/aralkenoylamino substituent; and to novel processes for preparing these 1-substituted-1-deoxyglycosides starting with the corresponding tetra-O-acetylglycopyranosyl bromide or amine. The 6-hydroxy group of 1-substituted-1 deoxyglycopyranosides can also be replaced by other functional groups. These aralkylthio/aralkenylthio, aralkyloxy/aralkenyloxy and aralkanoylamino/aralkenoylamino 1-deoxyglycosides are potent inhibitors of antigen-specific T-cell proliferation and are also useful as inhibitors of delayed-type hypersensitivity reactions.

The Reaction of D-Arabinopyranosylurea with Malononitrile and Triethyl Orthoformate

Abstract: Three-component coupling of arabinosylurea (or its triacetyl derivative), malononitrile and triethyl ortho-formate affords 1-(α-D-arabinopyranosyl)-ureidomethylene-malononitriles. These compounds in the presence of triethylamine undergo cyclization to give 2-oxo-4-imino-5-cyano-3-(α-D-arabinopyranosyl)-2,3,4,5-tetrahydropyrimidines. The pyranose structure of arabinosylurea was demonstrated by X-ray analysis. The synthesized compounds were studied by 1H, 13C NMR spectroscopy.

13C NMR spectra of parent hexopyranoses

Abstract: 1. The13C NMR spectra were obtained and interpreted for aqueous solutions of three parent hexoses: D-talose, D-gulose, and L-idose. The parameters of the PMR spectra for solutions of these compounds in D2O are given. 2. The13C NMR spectra of the L-idose derivatives in aqueous solutions were interpreted for 6-deoxy- and 6-O-methyl-L-idose. 3. The dependence of the13C chemical shifts and\(^1 J_{1_H 1 - 13_C 1} \) spin-spin coupling constants in eight parent hexopyranoses on the position of the conformational equilibrium of the pyranose rings in solutions is discussed.