Showing papers on "Pyranose published in 2012"

Metalloenzyme-like catalyzed isomerizations of sugars by Lewis acid zeolites

Abstract: Isomerization of sugars is used in a variety of industrially relevant processes and in glycolysis. Here, we show that hydrophobic zeolite beta with framework tin or titanium Lewis acid centers isomerizes sugars, e.g., glucose, via reaction pathways that are analogous to those of metalloenzymes. Specifically, experimental and theoretical investigations reveal that glucose partitions into the zeolite in the pyranose form, ring opens to the acyclic form in the presence of the Lewis acid center, isomerizes into the acyclic form of fructose, and finally ring closes to yield the furanose product. The zeolite catalysts provide processing advantages over metalloenzymes such as an ability to work at higher temperatures and in acidic conditions that allow for the isomerization reaction to be coupled with other important conversions.

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

Dependence of pyranose ring puckering on anomeric configuration: methyl idopyranosides.

Abstract: In the aldohexopyranose idose, the unique presence of three axial ring hydroxyl groups causes considerable conformational flexibility, rendering it challenging to study experimentally and an excellent model for rationalizing the relationship between puckering and anomeric configuration. Puckering in methyl α- and β-l-idopyranosides was predicted from kinetically rigorous 10 μs simulations using GLYCAM11 and three explicit water models (TIP3P, TIP4P, and TIP4P-EW). In each case, computed pyranose ring three-bond (vicinal) 1H–1H spin couplings (3JH,H) trended with NMR measurements. These values, calculated puckering exchange rates and free energies, were independent of the water model. The α- and β-anomers were 1C4 chairs for 85 and >99% of their respective trajectories and underwent 1C4→4C1 exchange at rates of 20 μs–1 and 1 μs–1. Computed α-anomer 1C4↔4C1 puckering rates depended on the exocyclic C6 substituent, comparing hydroxymethyl with carboxyl from previous work. The slower kinetics and restricted p...

Synthesis, crystal structure, electronic spectroscopy, electrochemistry and biological studies of carbohydrate containing ferrocene amides

Abstract: A series of four new ferrocene–carbohydrate amides was prepared from pentose and hexose sugar derivatives. These include (5-amino-5-deoxy-1,2-O-isopropylidene-α-d-xylofuranose)-1-ferrocene carboxamide (2a), (5-amino-3-O-benzyl-5-deoxy-1,2-O-isopropylidene-α-d-xylofuranose)-1-ferrocene carboxamide (2b), (methyl-6-amino-6-deoxy-2,3-O-isopropylidene-β-d-ribofuranoside)-1-ferrocene carboxamide (2c) derived from furanose sugars and (6-amino-6-deoxy-1,2:3,4-di-O-isopropylidene-α-d-galactopyranose)-1-ferrocene carboxamide (2d) derived from pyranose sugar. The compounds were characterized by spectroscopic means and the structure of amide derived from α-d-xylofuranose (2a) was determined by X-ray crystallography. The electronic and optical properties of the compounds were studied by means of cyclic voltammetry and absorption spectroscopy. The UV and electrochemical studies of these compounds, performed in aqueous solutions under physiological conditions (at pH 7.4), confirmed their stability. These results indicated that the compounds were suitable for conducting biological studies. The CD spectral analysis displays the effect of sugar substituents on the compounds. The cytotoxicity and antimicrobial activity of these conjugates were investigated on different cancer cell lines and microbes respectively. The degree of inhibition varied over a broad spectrum of Gram- positive and Gram-negative bacteria. In addition, the compounds also exhibited antioxidant properties. Copyright © 2012 John Wiley & Sons, Ltd.

Reversible and efficient inhibition of UDP-galactopyranose mutase by electrophilic, constrained and unsaturated UDP-galactitol analogues.

Abstract: A series of UDP-galactitols were designed as analogues of high-energy intermediates of the UDP-galactopyranose mutase (UGM) catalyzed furanose/pyranose interconversion, an essential step of Mycobacterium tuberculosis cell wall biosynthesis. The final compounds structurally share the UDP and the galactitol substructures that were connected by four distinct electrophilic connections (epoxide, lactone and Michael acceptors). All molecules were synthesized from a common perbenzylated acyclic galactose precursor that was derivatized by alkenylation, alkynylation and cyclopropanation. The inhibition study against UGM could clearly show that slight changes in the relative orientation of the UDP and the galactitol moieties resulted in dramatic variations of binding properties. Compared to known inhibitors, the epoxide derivative displayed a very tight, reversible, inhibition profile. Moreover, a time-dependent inactivation study showed that none of these electrophilic structures could react with UGM, or its FAD cofactor, the catalytic nucleophile of this still intriguing reaction.

The Study of the Reaction of Pectin-Ag(0) Nanocomposites Formation

Abstract: Pectin polysaccharides (PSs) were isolated from a bark of Larix sibirica Ledeb. Structure of PS fragments determined by chemical transformations, chromatography, and spectroscopic analyses was found to be a linear galacturonane comprising 1,4-linked α-D-Gal pA residues and a rhamnogalacturonan I (RG-I). The fifth part of galacturonane residues was methyl esterified at at C-2 and/or C-3 and C-6 atoms. Some of RG-I side chains were identified as arabinogalactan subunits with highly branched structure consisting of linear backbone with 3,6)- β-D-Gal p-(1 residues, substituted at C-6 by neutral side chains. This side chains contained 2,5)- α-L-Ara f-(1 and 3,5)- α-L-Ara f-(1 residues and terminal arabinose in the pyranose and furanose form. It was found that “pectin-Ag(0)” nanobiocomposites were formed via the interaction between PS aqueous solutions and silver nitrate, with PS playing both reducing and stabilizing functions. It was shown that the content of Ag(0) particles in “pectin-Ag(0)” depended on the reaction conditions and can range from 0.1 to 72 %, the size of Ag(0) particles being 3–27 nm. Using 13C NMR technique, it was revealed that PS underwent destructive changes and they they were more considerable, more than the lot of Ag(I) that was inputed into the reactionary medium.

Conformational heterogeneity in pyranose 2-oxidase from Trametes multicolor revealed by ultrafast fluorescence dynamics

Abstract: Ultrafast fluorescence dynamics of flavin adenine dinucleotide (FAD) in wild type pyranose 2-oxidase (P2O) has been investigated in solution by means of fluorescence up-conversion method. Fluorescence decays were well described by two-exponential model function. Fluorescence lifetimes were τ1 ∼ 110 fs and τ2 ∼ 360 ps, respectively. The (τ2/τ1) ratio (∼3200) was extraordinary high compared to other flavoproteins without subunit structure. The heterogeneous distribution of emission lifetimes were elucidated in terms of two different conformers of P2O; conformer 1 with τ1 and conformer 2 with τ2. Emission peaks of conformer 1 and conformer 2 were determined to be at ∼540 nm and 510 nm, respectively, using transient spectral reconstruction procedure. Using dynamics analysis by Kakitani and Mataga (KM) theory, both quenching processes were ascribed to photoinduced electron transfer (ET) reactions mainly from Trp168 to the excited isoalloxazine (Iso*) in different protein tetramers having different static dielectric constants (ɛ1 ∼ 3.25 for conformer 1 and ɛ2 ∼ 5.93 for conformer 2). The quaternary structure seems to be responsible for the observed conformational heterogeneity.

Assigning kinetic 3D-signatures to glycocodes

Abstract: Reconciling glycocodes and their associated bioactivities, via 3D-structure, will rationalise burgeoning high-throughput functional glycomics data and underpin a new era of opportunity in chemical biology. A major impasse to achieving this goal is a detailed understanding of pyranose sugar ring 3D-conformation (or pucker) and the affiliated microsecond-timescale exchange kinetics. Here, we perform hardware-accelerated kinetically-rigorous equilibrium simulations of fundamental monosaccharides to produce the hypothesis that pyranoses have microsecond-timescale kinetic puckering signatures in water, classified as unstable (rare in the glycome), metastable (infrequently observed) and stable (prevalent). The predicted μs-metastability of β-D-glucose explained hitherto irreconcilable experimental measurements. Twisted puckers seen in carbohydrate enzymes were present in the aqueous 3D-ensemble (suggesting preorganization) and pyranose-water interactions accounted for the relative stability of β-D-galactose. Characteristic 3D-shapes for biologically- and commercially-important carbohydrates and new rules linking chemical modifications with pyranose μs-puckering kinetics are proposed. The observations advance structural-glycomics towards dynamic 3D-templates suitable for structure-based design.

Controlled feeding of hydrogen peroxide as oxygen source improves production of 5-ketofructose From L-sorbose using engineered pyranose 2-oxidase from Peniophora gigantea

Abstract: 5-Keto-D-fructose is a useful starting material for the synthesis of pyrrolidine iminosugars. It can be prepared by regioselective oxidation of L-sorbose using pyranose 2-oxidase (P2Ox) and O2 as a cosubstrate. As the solubility of O2 in aqueous solution is low and the affinity of P2Ox for O2 is poor, we developed a new and efficient process for the production of 5-keto-D-fructose based on engineered P2Ox from Peniophora gigantea and in situ generation of O2 from H2O2 with catalase. This kind of oxygen supply required efficient mixing of the bioreactor which was achieved by controlled feeding of H2O2 close to the impeller tip where energy dissipation rate is highest. Thus bubbling, known to affect enzyme stability, was largely avoided, and the process could be run up to 145% oxygen super-saturation which speeds-up P2Ox activity. Under these conditions quantitative oxidation of 180 g L−1 L-sorbose to 5-keto-D-fructose could be achieved within 4 h, resulting in a threefold higher overall productivity of the process compared to a process using gaseous oxygen supply. In addition, in situ generation of O2 from H2O2 lowered the oxygen demand of the process by a factor of 100 compared to gaseous oxygen supply. Biotechnol. Bioeng. 2012; 109: 2941–2945. © 2012 Wiley Periodicals, Inc.

Modelling enzymatic oxidation of d-glucose with pyranose 2-oxidase in the presence of catalase

Abstract: To evaluate the activity of a commercial pyranose 2-oxidase (P2Ox) used to catalyze the oxidation of β- d -glucose in the presence of catalase, systematically batch experiments have been carried out at 30 °C and an optimal pH = 65 A complex kinetic model was proposed including the main reaction (of Ping-Pong–Bi-Bi type) but also P2Ox inactivation by the hydrogen peroxide produced, and in situ H2O2 decomposition by catalase (of a generalized Yano-Koya kinetics) While the presence of catalase drastically slows down the P2Ox inactivation, a considerable decrease of the main reaction rate is observed The estimated free enzyme rate constants match with the values reported in the literature, while turnover numbers are correlated with the catalase concentration The model is recommended for further process developments and reactor optimization, its parameters being easily adaptable for every type of P2Ox

Intramolecular 1,8-hydrogen atom transfer reactions in disaccharide systems containing furanose units.

Abstract: A previously developed 1,8-hydrogen atom transfer (HAT) reaction promoted by 6-O-yl alkoxyl radicals between the two pyranose units in Hexp-(1→4)-Hexp disaccharides has been extended to other systems containing at least a furanose ring in their structures. In Penf-(1→3)-Penf (A) and Hexp-(1→3)-Penf (B) disaccharides, the 1,8-HAT reaction and concomitant cyclization to a 1,3,5-trioxocane ring are in competition with radical β-scission of the C4–C5 bond and formation of dehomologated products. The influence of the stereoelectronic β-oxygen effect on the β-scission and consequently on the 1,8-HAT reaction has been studied using the four possible isomeric d-furanoses. d-xylo- and d-lyxo-derivatives afforded preferentially 1,8-HAT products, whereas d-arabino- and d-ribo-derivatives gave exclusively direct β-scission of the alkoxyl radical. When the 6-O-yl radical is on a pyranose ring, as occurs in Penf-(1→4)-Hexp (C), it has been shown to provide the cyclized products exclusively.

Crystal structure of a new benzoic acid inhibitor of influenza neuraminidase bound with a new tilt induced by overpacking subsite C6

Abstract: Influenza neuraminidase (NA) is an important target for antiviral inhibitors since its active site is highly conserved such that inhibitors can be cross-reactive against multiple types and subtypes of influenza. Here, we discuss the crystal structure of neuraminidase subtype N9 complexed with a new benzoic acid based inhibitor (2) that was designed to add contacts by overpacking one side of the active site pocket. Inhibitor 2 uses benzoic acid to mimic the pyranose ring, a bis-(hydroxymethyl)-substituted 2-pyrrolidinone ring in place of the N-acetyl group of the sialic acid, and a branched aliphatic structure to fill the sialic acid C6 subsite. Inhibitor 2 {4-[2,2-bis(hydroxymethyl)-5-oxo-pyrrolidin-1-yl]-3-[(dipropylamino)methyl)]benzoic acid} was soaked into crystals of neuraminidase of A/tern/Australia/G70c/75 (N9), and the structure refined with 1.55 A X-ray data. The benzene ring of the inhibitor tilted 8.9° compared to the previous compound (1), and the number of contacts, including hydrogen bonds, increased. However, the IC50 for compound 2 remained in the low micromolar range, likely because one propyl group was disordered. In this high-resolution structure of NA isolated from virus grown in chicken eggs, we found electron density for additional sugar units on the N-linked glycans compared to previous neuraminidase structures. In particular, seven mannoses and two N-acetylglucosamines are visible in the glycan attached to Asn200. This long, branched high-mannose glycan makes significant contacts with the neighboring subunit. We designed inhibitor 2 with an extended substituent at C4-corresponding to C6 of sialic acid-to increase the contact surface in the C6-subsite and to force the benzene ring to tilt to maximize these interactions while retaining the interactions of the carboxylate and the pyrolidinone substituents. The crystal structure at 1.55 A showed that we partially succeeded in that the ring in 2 is tilted relative to 1 and the number of contacts increased, but one hydrophobic branch makes no contacts, perhaps explaining why the IC50 did not decrease. Future design efforts will include branches of unequal length so that both branches may be accommodated in the C6-subsite without conformational disorder. The high-mannose glycan attached to Asn200 makes several inter-subunit contacts and appears to stabilize the tetramer.

P/S ligands derived from carbohydrates in Rh-catalyzed hydrosilylation of ketones.

Abstract: Reported is the synthesis of a number of diastereomerically pure cationic Rh(I)-complexes I starting from phosphinite thioglycosides. These complexes were used in the asymmetric hydrosilylation of prochiral ketones. The reactivity and enantioselectivity of the reaction was shown to be dependent on the pyranose ring, the substituent at the sulfur atom, the hydroxylic protective groups and most significantly on the alkene co-ligand.

Computational studies of protonated β-D-galactose and its hydrated complex: structures, interactions, proton transfer dynamics, and spectroscopy.

Abstract: We present an exploration of proton transfer dynamics in a monosaccharide, based upon ab initio molecular dynamic (AIMD) simulations, conducted "on-the-fly", in β-d-galactose-H(+) (βGal-H(+)) and its singly hydrated complex, βGal-H(+)-H2O. Prior structural calculations identify O6 as the preferred protonation site for O-methyl α-d-galactopyranoside, but the β-anomeric configuration favors the inversion of the pyranose ring from the (4)C1 chair configuration, to (1)C4, and the formation of proton bridges to the (axial) O1 and O3 sites. In the hydrated complex, however, the proton bonds to the water molecule inserted between the O6 and Ow sites, and the ring retains its original (4)C1 conformation, supported by a circular network of co-operatively linked hydrogen bonds. Two distinct proton transfer processes, operating over a time scale of 10 ps, have been identified in βGal-H(+) at 500 K. One of them leads to chemical reaction and the formation of an oxacarbenium ion (accompanied by the loss of an H2O molecule). In the hydrated complex, βGal-H(+)-H2O, this reaction is suppressed, and the proton transfer, which involves multiple jumps between the sugar and the H2O, creates an H3O(+) ion, relevant, perhaps, to the reactivity of protonated sugars both in the gas and condensed phases. Anticipating future spectroscopic investigations, the vibrational spectra of βGal-H(+) and βGal-H(+)-H2O have also been computed through AIMD simulations conducted at average temperatures of 300 and 40 K and also through vibrational self-consistent field (VSCF) calculations at 0 K.

l-Arabinose Conformers Adsorption on Ruthenium Surfaces: A DFT Study

Abstract: Adsorption of five l-arabinose tautomers, one acyclic and four cyclic (α, β, pyranose, and furanose) species, on a ruthenium surface was studied as a precursor process of the, nowadays more and more, industrially important sugar catalytic hydrogenation on metal surfaces in water medium. The study was mostly referred to a 37 atom metal catalyst fragment even though border effects on the adsorption processes were also checked employing a 61 atom metal fragment. To figure out conformational effects on the title process, the tautomer flexibility was, at first, investigated by the genetic algorithm based code Balloon considering the conformational spaces of the different aquo tautomers. On the whole, 30 l-arabinose conformers, representing the complete conformational set (of a realistic water solution), were isolated by the genetic algorithm based code Balloon. These were further refined at density functional theory (DFT) level and then were analyzed when interacting with a ruthenium surface, always at DFT lev...

Heterologous expression and biochemical characterization of novel pyranose 2-oxidases from the ascomycetes Aspergillus nidulans and Aspergillus oryzae

Abstract: A gene encoding a pyranose 2-oxidase (POx; pyranose/oxygen 2-oxidoreductase; glucose 2-oxidase; EC 1.1.3.10) was identified in the genome of the ascomycete Aspergillus nidulans. Attempts to isolate POx directly from A. nidulans cultures or to homologously overexpress the native POx (under control of the constitutive gpdA promoter) in A. nidulans were unsuccessful. cDNA encoding POx was synthesized from mRNA and expressed in Escherichia coli, and the enzyme was subsequently purified and characterized. A putative pyranose 2-oxidase-encoding gene was also identified in the genome of Aspergillus oryzae. The coding sequence was synthetically produced and was also expressed in E. coli. Both purified enzymes were shown to be flavoproteins consisting of subunits of 65 kDa. The A. nidulans enzyme was biochemically similar to POx reported in literature. From all substrates, the highest catalytic efficiency was found with D-glucose. In addition, the enzyme catalyzes the two-electron reduction of 1,4-benzoquinone, several substituted benzoquinones and 2,6-dichloroindophenol. As judged by the catalytic efficiencies (k cat/k m), some of these quinone electron acceptors are better substrates for pyranose oxidase than oxygen. The enzyme from A. oryzae was physically similar but showed lower kinetic constants compared to the enzyme from A. nidulans. Distinct differences in the stability of the two enzymes may be attributed to a deletion and an insertion in the sequence, respectively.

Cellulose acylate film, its production method, polarizer and liquid crystal display device

Abstract: A cellulose acylate film containing a cellulose acylate and a sugar ester compound having from 1 to 12 pyranose structures or furanose structures in which at least one hydroxyl group is esterified, the film satisfying 40 nm≦Re(550)≦60 nm and 100 nm≦Rth(550)≦140 nm, and having a dimensional change of −0.5 to 0.5% and an internal haze of at most 0.1%.

The use of coupled HSQC spectra to aid in stereochemical assignments of molecules with severe proton spectral overlap.

Abstract: Introduction A simple glycoside with only 13 carbons exhibited extensive overlapping of four of the glycosidic protons, causing extreme difficulty in the determination of the stereochemistry of the pyranose unit. However, acquisition of a high-resolution coupled heteronuclear single-quantum coherence (HSQC) spectrum overcame this problem. This spectrum provides a useful method for determining vicinal proton coupling constants between strongly coupled protons. Objective To show the potential of high-resolution coupled HSQC spectra in overcoming spectral overlap. Methodology The sample was obtained by methanol extraction, followed by fractionation and column chromatography of the dried leaves of Montrichardia arborescens (Araceae). NMR spectra were obtained on 1.5 mg of sample dissolved in 120 μL of CD3OD containing 0.1% trimethylsilyl (TMS) as internal standard. A gradient-selected HSQC spectrum was obtained using standard Varian library pulse sequences in phase sensitive mode. The high-resolution coupled HSQC spectrum focused on the saccharide region with a 1025 Hz 1H spectral window, a 6300 Hz 13 C spectral window, 1024 data points, a 0.3 Hz relaxation delay, 384 time increments (linear predicted to 4096), and 80 scans per time increment. Results The use of a high-resolution coupled HSQC spectrum allowed determination of the coupling patterns of the various pyranose protons with sufficient accuracy. This enabled completion of the assignments and identification of the pyranose unit as glucose. Conclusion The study has shown the effectiveness of the use of a high-resolution coupled HSQC spectrum in the assignment of molecules with severe spectral overlap. Copyright © 2011 John Wiley & Sons, Ltd.

Free energy landscapes of the α-d- and β-d-glucopyranose conformations in both vacuum and aqueous solution

Abstract: The pathway for pyranose ring conformational transitions in both anomers of glucose has been studied using molecular mechanics calculations both in vacuum and in aqueous (SPC/E) solution. The pathw...

Deoxyfluorination of Peracetylated Pyranose Hemiacetal with Fluoroalkanesulfonyl Fluoride

Abstract: The deoxyfluorination of peracetylated pyranose hemiacetals with 5-H-3-oxa-1,1,2,2,4,4,5,5octafluoropentanesulfonyl fluoride (HCF2CF2OCF2CF2SO2F) in the presence of an organic base was investigated resulting in the smooth formation of corresponding glycosyl fluorides in the yield of 44%~94%. The mild reaction conditions and easy work-up procedure are the two advantages for this methodology and it can be used as an alternative method for the preparation of glycosyl fluorides.