共查询到20条相似文献,搜索用时 8 毫秒
1.
Abstract A theoretical conformational study of dextran, a (l?6)-linked α-D-glucan polysaccharide, has been made to allow an explicit comparison with earlier results on pustulan, the corresponding (1 ?6)-linked β-D-glucan. The nonbonded, torsional and hydrogen bond contributions to potential energy were calculated as a function of rotational angles φ, ψ, and ω The (φ, ψ, ω)-space of the disaccharide and of helices contain many local energy minima with very small energy differences. A comparison of (1?6)-α-D-glucans with (1?6)-β-D-glucans indicates significant differences in conformational behavior. Specifically, our results shed light on the fact that dextran does not gel, whereas pustulan does. The difference in tendency to gel may be related to the fact that dextran has no particularly favored conformations with structural regularity whereas pustulan does. 相似文献
2.
Evelyn Jabri David R. Quigley Marjorie Alders Maria Hrmova Cathy S. Taft Patricia Phelps Dr. Claude P. Selitrennikoff 《Current microbiology》1989,19(3):153-161
(1–3)--d-Glucan synthase activity ofNeurospora crassa was localized to the plasma membrane by autoradiography of colloidal gold-labeled plasma membranes. The active site of glucan synthase for substrate hydrolysis was determined to be cytoplasmic facing. However, glucan synthase activity present in intact protoplasts was partially sensitive to Novozym 234 and to glutaraldehyde treatments, suggestive that enzyme activity is transmembrane. Enzyme activity also directed the formation of microfibrils in vitro. Taken together, these and previous results support the following scheme for glucan synthesis: 1. The sequential addition of glucose residues from UDP-glucose to glucan chains occurs on the cytoplasmically facing portion of glucan synthase. 2. As each glucan chain is synthesized, it is extruded to the extracytoplasmic side of the plasma membrane. 3. As each chain is extruded, it forms interchain hydrogen bonds with adjacent chains, resulting in glucan microfibril assembly. 相似文献
3.
《Carbohydrate research》1987,162(1):79-84
The crystalline tris(hydroxymethyl)aminomethane (“Tris”) salt of 2-deoxy-2-[(R)-3-hydroxytetradecanamido]-3-O-[(R)-3-hydroxytetradecanoyl]-α-d-glucopyranose 1-phosphate (lipid X) has been synthesised from 2-amino-2-deoxy-d-glucose hydrochloride in five steps in ∼ 50% overall yield. The key step was 1-O-(dibenzyl) phosphorylation of 4,6-O-benzylidene-2-[(R)-3-benzyloxytetradecanamido]-2-deoxy-d-glucopyranose, catalysed by butyl-lithium. The product was then 3-(R)-3-benzyloxytetradecanoylated, and the benzyl and benzylidene groups were removed by catalytic hydrogenation. 相似文献
4.
Rodrigo Rico-Gómez Ezequiel P. de Inestrosa-Villatoro Juan Manuel López-Romero Francisco Nájera Rafael López-Corpas 《Nucleosides, nucleotides & nucleic acids》2013,32(7-8):1411-1421
Abstract The synthesis of two 7-glycosyl-6-thiotheophylline nucleosides where the sugar moieties are β-D-glucose (1b) and α-D-arabinose (2b) is reported. The syn-anti equilibrium of the peracetyl derivatives was studied by the line-shape and the 1H-NMR nOe methods, and molecular mechanics analysis. 相似文献
5.
Yuan Y Elbegdorj O Chen J Akubathini SK Beletskaya IO Selley DE Zhang Y 《Bioorganic & medicinal chemistry letters》2011,21(18):5625-5629
Mu opioid receptor antagonists have been applied to target a variety of diseases clinically. The current study is designed to explore the structure selectivity relationship (SSR) of 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)carboxamido]morphinan (NAP), a lead compound identified as a selective mu opioid receptor antagonist based on the previous study. Among a series of NAP derivatives synthesized, compounds 6 (NMP) and 9 (NGP) maintained comparable binding affinity, selectivity and efficacy to the lead compound. Particularly, the mu opioid receptor selectivity over kappa opioid receptor of NGP was considerably enhanced compared to that of NAP. Overall, the preliminary SSR supported our original hypothesis that an alternate 'address' domain may exist in the mu opioid receptor, which favors the ligands carrying a hydrogen bond acceptor and an aromatic system to selectively recognize the mu opioid receptor. 相似文献
6.
A domain of epiglucan was synthesized by beta-glucosidases. Two beta-glucosidases, an extracellular beta-glucosidase derived from Sclerotinia sclerotiorum grown on xylose, and a commercial lyophilized preparation of beta-glucosidase from Aspergillus niger, were used to synthesize gluco-oligosaccharides from cellobiose and, specially, beta-(1-6) branched beta-(1-3) gluco-oligosaccharides, corresponding to the structure of epiglucan. Gentiobiose, cellotriose, cellotetraose, beta-Glc-(1-3)-beta-Glc-(1-4)-Glc, beta-Glc-(1-6)-beta-Glc-(1-4)-Glc and beta-Glc-(1-6)-beta-Glc-(1-3)-Glc were synthesized from cellobiose by both enzymes. The latter compound was preferentially synthesized by the beta-glycosidase from Sclerotinia sclerotiorum. Under the best conditions, only 7 g l(-1) of beta-Glc-(1-6)-beta-Glc-(1-3)-Glc was synthesized by the beta-glycosidase from Aspergillus niger compared to 20 g l(-1) synthesized with beta-glycosidase from Sclerotinia sclerotiorum. 相似文献
7.
Michael P. Groziak Ronghui Lin William C. Stevens Linda L. Wotring Leroy B. Townsend J. Balzarini 《Nucleosides, nucleotides & nucleic acids》2013,32(5):1041-1057
Abstract ROESY and NOESY NMR spectroscopic analyses of the ribofuranosyl (1a), 2′-deoxyribofuranosyl (1b), and arabinofuranosyl (1c) derivatives of 6-formyluracil in (CD3)2SO and D2O solutions have established that each exclusive 7,05′-cyclic hemiacetal diastereomer of 1a,b and the major 7,O2′-cyclic hemiacetal diastereomer of 1c possess the 7R configuration. In addition, (7R)-1c has been shown to be thermodynamically more stable than (7S)-1c, contrary to our previous indication. A new, higher yielding synthetic route to 1a has been developed, 1b has been obtained for the first time in crystalline form, the route to 1c has been modified to better accommodate large scale preparations, and a new, fourth member of this class, 6-formylthymidine (1d), has been synthesized and its solution structures in (CD3)2SO, D2O, and CD3OD have been determined. Antitumor and antiviral evaluations of 1a-c have revealed no significant levels of activity. 相似文献
8.
Kocharova NA Ovchinnikova OG Bialczak-Kokot M Shashkov AS Knirel YA Rozalski A 《Biochemistry. Biokhimii?a》2011,76(6):707-712
An acidic O-polysaccharide was isolated by mild acid degradation of the lipopolysaccharide of Providencia alcalifaciens O25 followed by gel-permeation and anion-exchange chromatography. The O-polysaccharide was studied by sugar and methylation
analyses along with 1H and 13C NMR spectroscopy, including two-dimensional correlation 1H,13C HMBC, and 1H,1H ROESY experiments both in D2O and, to detect correlations for NH protons, in a 9: 1 H2O/D2O mixture. An amino acid was isolated from the polysaccharide by acid hydrolysis and identified as N
ɛ-[(R)-1-carboxyethyl]-L-lysine (“alaninolysine”, 2S,8R-alaLys) by determination of the specific optical rotation and 13C NMR spectroscopy, using the authentic synthetic diastereomers 2S,8R-alaLys and 2S,8S-alaLys for comparison. The structure of the branched tetrasaccharide repeating unit of the O-polysaccharide was established. 相似文献
9.
10.
The conformational space of methyl 6-O-[(R)- and (S)- 1-carboxyethyl]-α-D-galactopyranoside has been investigated. A grid
search employing energy minimization at each grid point over the three major degrees of freedom, namely φ, ψ and ω, identified
low energy regions. The R-isomer shows five low energy conformers within ca. 1 kcal mol−1 of the global energy minimum. The
S-isomer has two conformers within a few tenths of a kcal mol−1 of the global energy minimum. Langevin dynamics simulations
have been have been performed at 300 K for 30 ns of each isomer. The φ dihedral angle has as its major conformer (g−1) for
the R-isomer whereas it is the (g+) conformer for the S-isomer. For the ψ dihedral angle the (t) conformer has the highest
population for both isomers. The dihedral angle ω has the (g+) conformer most highly populated, both for the R- and S-isomer.
The above five and two conformational states for the R- and S-isomers, respectively, make up 90% in each case of the populated
states during the Langevin dynamics (LD) simulations. Rate constants for the ω dihedral angle have been calculated based on
a number correlation function. Three bond homo- and heteronuclear, i.e. proton and carbon-13, coupling constants have been
calculated from the dynamics trajectories for comparison to experimental values. The heteronuclear coupling constant H2′,C6
has been measured for the S-isomer and found to be 3.3 Hz. The J value calculated from the LD simulations, namely 2.6 Hz,
is in fair agreement with experiment. A comparison to the X-ray structure of the R-isomer shows that the conformation of the
crystalline compound occupies the low energy region most highly populated as a single R-conformer (30%) during the LD simulations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
12.
β-Glucan hydrolases from Aspergillus niger. Isolation of a β-(1→4)-glucan hydrolase and some properties of the β-(1→3)-glucan-hydrolase components
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1. The components of an enzyme preparation from Aspergillus niger, which hydrolysed substrates containing beta-(1-->3)- and beta-(1-->4)-glucosidic linkages, were separated by calcium phosphate and Dowex 1 column chromatography. 2. The hydrolytic activity of each fraction from both types of column towards laminaribiose, laminarin, carboxymethylpachyman, pachydextrins, salicin, cellobiose, cellopentaose and swollen cellulose was tested. 3. The activity towards the beta-(1-->3)-glucosidic substrates was found in three well-separated groups of fractions. The differences in action pattern of these groups is discussed. 4. Preparative-scale chromatography that enabled the separation of a beta-(1-->4)-glucan-glucanohydrolase component substantially free of activity towards beta-(1-->3)-glucosidic substrates is described. Residual beta-(1-->3)-glucan-hydrolase activity was removed by adsorption on to insoluble laminarin at pH3.5. 相似文献
13.
Ossi Renkonen Ritva Niemelä Anne Leppänen Hannu Maaheimo Antti Seppo Leena Penttilä Anja Vilkman 《Glycoconjugate journal》1991,8(4):368-375
Radiolabelled GlcNAc beta 1-3(GlcNAc beta 1-6)Gal (1), GlcNAc beta 1-3)GlcNAc beta 1-6)Gal beta 1-OCH3 (4), GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4Glc (7), and GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc (10) were cleaved partially with jack bean beta-N-acetylhexosaminidase (EC 3.2.1.30), and the digests were analysed chromatographically. All four oligosaccharides were hydrolysed faster at the (1-6) branch, than at the (1-3) branch, but a high branch specificity was observed only with the glycan 4. The saccharides 1 and 7 resembled each other in the kinetics of the enzyme-catalysed release of their two non-reducing N-acetylglucosamine units, but the glycan 10 was rather different. The partial digestions made it possible to obtain radiolabelled GlcNAc beta 1-6Gal, GlcNAc beta 1-6Gal beta 1-OCH3, GlcNAc beta 1-6Gal beta 1-4Glc, and, in particular, GlcNAc beta 1-6Gal beta 1-4GlcNAc. 相似文献
14.
《Carbohydrate research》1985,140(2):277-288
Condensation of 2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-α-d-galactopyranosyl bromide (3) with methyl 2,3,4-tri-O-acetyl-β-d-galactopyranoside (4) gave a fully acetylated (1→6)-β-d-galactobiose fluorinated at the 3′-position which was deacetylated to give the title disaccharide. The corresponding trisaccharide was obtained by reaction of 4 with 2,3,4-tri-O-acetyl-6-O-chloroacetyl-α-d-galactopyranosyl bromide (5), dechloroacetylation of the formed methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β-d-galactopyranosyl)-(1→6)- 2,3,4-tri-O-acetyl-β-d-galactopyranoside to give methyl O-(2,3,4-tri-O-acetyl-β-d-galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β-d-galactopyranoside (14), condensation with 3, and deacetylation. Dechloroacetylation of methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β-d-galactopyranosyl)-(1→6)-O-(2,3,4-tri-O-acetyl- β-d-galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β-d-galactopyranoside, obtained by condensation of disaccharide 14 with bromide 5, was accompanied by extensive acetyl migration giving a mixture of products. These were deacetylated to give, crystalline for the first time, the methyl β-glycoside of (1→6)-β-d-galactotriose in high yield. The structures of the target compounds were confirmed by 500-MHz, 2D, 1H- and conventional 13C- and 19F-n.m.r. spectroscopy. 相似文献
15.
David A. Berry Linda L. Wotring John C. Drach Leroy B. Townsend 《Nucleosides, nucleotides & nucleic acids》2013,32(1-3):405-420
Abstract Chemical modification of the 4-nitrile group in 5-amino-1-(2,3,5-tri-O-benzyl-β-D-ribofuranosyl)pyrazole-4-carbonitrile (1) afforded 5-amino-4-(5-methyl-1,2,4-oxadiazol-3-yl)-1-(2,3,5-tri-O-benzyl-β-D-ribofuran osyl)pyrazole (3). The methylation of 3, via a three step procedure, gave 5-methylamino-4-(5-methyl-1,2,4-oxadiazol-3-yl)-1-(2,3,5-tri-O-benzyl-β-D-ribofuranosyl)pyrazole (3a). The mononuclear heterocyclic rearrangement (m.h.r) of 3 and 3a, provided a convenient route to the novel azapentalene adenosine analogs 3-amino-6-(β-D-ribofuranosyl)pyrazolo[3,4-c]pyrazole (6) and 3-amino-1-methyl-6-(β-D-ribofuranosyl)pyrazolo[3,4-c]pyrazole (6a), respectively. Compound 6 exhibited no cytotoxicity when screened in vitro against either mouse L1210 leukemic cells or human foreskin fibroblasts. Nor was it active against human cytomegalovirus. Compound 6a was designed and prepared to investigate the possibility that the lack of biological activity of 6 might be due to annular tautomerization limiting the ability of 6 to serve as a substrate for the activating enzyme adenosine kinase. This hypothesis was neither supported nor disproved by the results, as compound 6a was also inactive in both the antiproliferative and antiviral test systems. 相似文献
16.
S Spieser K Mazeau M.C Brochier C Gey J.P Utille F.R Taravel 《Glycoconjugate journal》1998,15(5):511-521
The title compound is a cyclic oligosaccharide having six glucopyranose residues linked alternatively by -(14) and -(16) glycosidic linkages. Like cyclodextrin analogues it is expected to exhibit an internal cavity and to form inclusion complexes with other species. In order to investigate its conformational preferences, an extensive conformational search was carried out using a combination of Metropolis Monte-Carlo (MMC) procedure in the glycosidic torsion angle space and molecular mechanics procedures. To this end a specific program (METROCYCLIX) was developed. To reduce the MMC search, conformational maps of parent disaccharides were considered as starting entries. Fully minimized conformations were gathered into families using a clustering technique based on RMS fitting over the glycosidic torsion angle values. A wide range of local energy minima were identified in spite of ring closure conditions that constrained the structure of the oligosaccharide. Low energy conformers were stabilized by intramolecular interactions between distant residues. From the Bolzmann population of the best structures derived from the clustering results, various average properties were calculated and compared with experimental data obtained by high resolution NMR. Interpretation of these experimental values (heteronuclear coupling constants, rotating frame nuclear Overhauser effects, relaxation times) relies on the use of Karplus like equations (coupling constants) and analysis of the full relaxation rate matrix treatment (ROE). The quality of the molecular modelling strategy used is assessed by the agreement obtained between calculated and measured observables. 相似文献
17.
S. H. Gray C. F. Ainsworth C. L. Bell S. S. Danyluk M. Maccoss 《Nucleosides, nucleotides & nucleic acids》2013,32(5):481-491
Abstract The solution conformations of all eight deoxynucleotidyl (3′-5′) arabinonucleosides containing 9-B-D-arabinofuranosyladenine and 1-B-D-arabinonfuranosylcytosine have been analyzed by NMR methods and compared to dinucleoside monophosphates containing the corresponding deoxyriboside units. 相似文献
18.
The aim of the present work was to improve the solubility and dissolution profile of Irbesartan (IRB), a poorly water-soluble
drug by formation of inclusion complex with β-cyclodextrin (βCD). Phase solubility studies revealed increase in solubility
of the drug upon cyclodextrin addition, showing AL—type of graph with slope less than one indicating formation of 1:1 stoichiometry inclusion complex. The stability constant
(K
s) was found to be 104.39 M−1. IRB–βCD binary systems were prepared by cogrinding, kneading using alcohol, kneading using aqueous alcohol, and coevaporation
methods. Characterization of the binary systems were carried out by differential scanning calorimetry, Fourier transform infrared
spectroscopy, scanning electron microscopy, X-ray diffraction, and proton nuclear magnetic resonance. The dissolution profiles
of inclusion complexes were determined and compared with those of IRB alone and physical mixture. Among the various methods,
coevaporation was the best in which the solubility was increased and dissolution rate of the drug was the highest. The study
indicated the usefulness of cyclodextrin technology to overcome the solubility problem of IRB. 相似文献
19.
Abstract 6-(3-methyl-2-butenylamino)-2-methylthio-9-(β-D-ribofuranosyl)purine (1) is a naturally occurring nucleoside with potent cytokinin activity. It has been isolated and identified in the t-RNA of E. coli,1,2 the t-RNA from wheat germ3,4 and from Staphylococcus epidermidis.5 In addition, compound 1 has been found in t-RNA species corresponding to each of six amino acids whose codons start with uridine, i.e., t-RNACys 相似文献
20.
Gargallo R Cedano J Mozo-Villarias A Querol E Oliva B 《Journal of molecular modeling》2006,12(6):835-845
The dependence of some molecular motions in the enzyme 1,3-1,4-β-glucanase from Bacillus licheniformis on temperature changes and the role of the calcium ion in them were explored. For this purpose, two molecular dynamics simulated trajectories along 4 ns at low (300 K) and high (325 K) temperatures were generated by the GROMOS96 package. Several structural and thermodynamic parameters were calculated, including entropy values, solvation energies, and essential dynamics (ED). In addition, thermoinactivation experiments to study the influence of the calcium ion and some residues on the activity were conducted. The results showed the release of the calcium ion, which, in turn, significantly affected the movements of loops 1, 2, and 3, as shown by essential dynamics. These movements differ at low and high temperatures and affect dramatically the activity of the enzyme, as observed by thermoinactivation studies.
The first two authors contributed equally to this work 相似文献