Showing papers on "Pyranose published in 2010"
TL;DR: The newly developed parameters allow for the modeling of linear, branched, and cyclic pyranose/furanose polysaccharides both alone and in heterogeneous systems including proteins, nucleic acids, and/or lipids when combined with existing additive CHARMM biomolecular force fields.
Abstract: Presented is an extension of the CHARMM additive carbohydrate all-atom force field to enable modeling of polysaccharides containing furanose sugars. The new force field parameters encompass 1 ↔ 2, 1 → 3, 1 → 4, and 1 → 6 pyranose-furanose linkages and 2 → 1 and 2 → 6 furanose-furanose linkages, building on existing hexopyranose and furanose monosaccharide parameters. The model compounds were chosen to be monomers or glycosidic-linked dimers of tetrahydropyran (THP) and tetrahydrofuran (THF) as to contain the key atoms in full carbohydrates. Target data for optimization included two-dimensional quantum mechanical (QM) potential energy scans of the Φ/Ψ glycosidic dihedral angles, with geometry optimization at the MP2/6-31G(d) level followed by MP2/cc-pVTZ single-point energies. All possible chiralities of the model compounds at the linkage carbons were considered, and for each geometry, the THF ring was constrained to the favorable south or north conformations. Target data also included QM vibrational frequencies and pair interaction energies and distances with water molecules. Force field validation included comparison of computed crystal properties, aqueous solution densities, and NMR J-coupling constants to experimental reference values. Simulations of infinite crystals showed good agreement with experimental values for intramolecular geometries as well as for crystal unit cell parameters. Additionally, aqueous solution densities and available NMR data were reproduced to a high degree of accuracy, thus validating the hierarchically optimized parameters in both crystalline and aqueous condensed phases. The newly developed parameters allow for the modeling of linear, branched, and cyclic pyranose/furanose polysaccharides both alone and in heterogeneous systems including proteins, nucleic acids, and/or lipids when combined with existing additive CHARMM biomolecular force fields.
161 citations
TL;DR: This new hypothesis suggests that the stereoselectivity is dictated by two interrelated conformational properties of the reactive complex, namely, the conformational preferences of the oxacarbenium pyranose ring, modulating the steric crowding and exposure of the anomeric carbon toward the α or β face.
Abstract: The mechanism of solvent effects on the stereoselectivity of glycosylation reactions is investigated using quantum-mechanical (QM) calculations and molecular dynamics (MD) simulations, considering a methyl-protected glucopyranoside triflate as a glycosyl donor equivalent and the solvents acetonitrile, ether, dioxane, or toluene, as well as gas-phase conditions (vacuum). The QM calculations on oxacarbenium-solvent complexes do not provide support to the usual solvent-coordination hypothesis, suggesting that an experimentally observed β-selectivity (α-selectivity) is caused by the preferential coordination of a solvent molecule to the reactive cation on the α-side (β-side) of the anomeric carbon. Instead, explicit-solvent MD simulations of the oxacarbenium-counterion (triflate ion) complex (along with corresponding QM calculations) are compatible with an alternative mechanism, termed here the conformer and counterion distribution hypothesis. This new hypothesis suggests that the stereoselectivity is dictated by two interrelated conformational properties of the reactive complex, namely, (1) the conformational preferences of the oxacarbenium pyranose ring, modulating the steric crowding and exposure of the anomeric carbon toward the α or β face, and (2) the preferential coordination of the counterion to the oxacarbenium cation on one side of the anomeric carbon, hindering a nucleophilic attack from this side. For example, in acetonitrile, the calculations suggest a dominant B2,5 ring conformation of the cation with preferential coordination of the counterion on the α side, both factors leading to the experimentally observed β selectivity. Conversely, in dioxane, they suggest a dominant (4)H3 ring conformation with preferential counterion coordination on the β side, both factors leading to the experimentally observed α selectivity.
119 citations
TL;DR: Results from this study indicate that manganese dioxides in soils and sediments could contribute to the decomposition of lincosamide antibiotics released into the environment.
Abstract: Lincosamides are among the most frequently detected antibacterial agents in effluents from wastewater treatment plants and surface runoff at agricultural production systems. Little is known about their transformations in the environment. This study revealed that manganese oxide caused rapid and extensive decomposition of clindamycin and lincomycin in aqueous solution. The reactions occurred mainly at the pyranose ring of lincosamides, initially by formation of complexes with Mn and cleavage of the ether linkage, leading to the formation of a variety of degradation products via subsequent hydrolytic and oxidative reactions. The results of LC-MS/MS and FTIR analysis confirm cleavage of the C−O−C bond in the pyranose ring, formation of multiple carbonyl groups, and transformation of the methylthio moiety to sulfur oxide. The overall transformation was controlled by interactions of cationic species of lincosamides with MnO2 surfaces. The presence of electrolytes (i.e., NaCl, CaCl2, and MnCl2) and dissolved or...
84 citations
TL;DR: It is shown that the complete free energy of puckering is required to evaluate the accuracy of semiempirical methods used to study reactions involving carbohydrates, and it is found that reducing the free energy space to lower dimensions results in near meaningless minimum energy pathways.
Abstract: The puckered conformations of furanose and pyranose carbohydrate rings are central to analyzing the action of enzymes on carbohydrates. Enzyme reaction mechanisms are generally inaccessible to experiments and so have become the focus of QM(semiempirical)/MM simulations. We show that the complete free energy of puckering is required to evaluate the accuracy of semiempirical methods used to study reactions involving carbohydrates. Interestingly, we find that reducing the free energy space to lower dimensions results in near meaningless minimum energy pathways. We analyze the furanose and pyranose free energy pucker surfaces and volumes using AM1, PM3, PM3CARB-1, and SCC-DFTB. A comparison with DFT optimized structures and a HF free energy surface reveals that SCC-DFTB provides the best semiempirical description of five- and six-membered carbohydrate ring deformation.
79 citations
TL;DR: Five different flexible osmium based redox polymers were investigated for their ability to efficiently "wire" the oxidoreductase pyranose dehydrogenase (PDH, EC 1.1.99) from Agaricus meleagris on graphite electrodes for possible applications in biofuel cells.
64 citations
TL;DR: The data suggest that a competent reductive half-reaction requires a side chain at position 169 that is able to form an H-bond within the ES complex, and that the precise position and geometry of the Thr169 side chain are required for intermediate stabilization.
61 citations
TL;DR: It was shown that CuCl/CuCl2/tris(2-dimethylaminoethyl)amine (Me6TREN) catalytic system with an optimized ratio of Cu(I)/Cu(II) produced glycopolymer with high molecular weight and relatively narrow molecular weight distribution, which showed a proportional relationship with the molecular weight of free polymer generated in the solution.
61 citations
TL;DR: A convenient, two-step procedure has been developed for converting sugar derivatives into C-glycosides containing a masked aldehyde functional group that takes advantage of an anodic coupling reaction between an electron-rich olefin and an alcohol.
45 citations
TL;DR: Pyranose dehydrogenase as mentioned in this paper is a fungal flavin-dependent sugar oxidoreductase which is structurally and catalytically related to fungal pyranoses oxidase and cellobiose de-hydrogenase and probably fulfills similar biological functions in lignocellulose breakdown.
Abstract: Pyranose dehydrogenase is a fungal flavin-dependent sugar oxidoreductase which is structurally and catalytically related to fungal pyranose oxidase and cellobiose dehydrogenase and probably fulfills similar biological functions in lignocellulose breakdown. It is a monomeric secretory glycoprotein and is limited to a rather small group of litter-decomposing basidiomycetes. Compared with pyranose oxidase, it displays broader substrate specificity and a variable regioselectivity and is unable to utilize oxygen as electron acceptor using substituted benzoquinones and (organo) metallic ions instead. Depending on the structure of the sugar in pyranose form (mono/di/oligosaccharide or glycoside) and the enzyme source, selective monooxidations at C-1, C-2, C-3, or dioxidations at C-2,3 or C-3,4 of the molecule to the corresponding aldonolactones (C-1), or (di)dehydrosugars (aldos(di)uloses) can be performed. These features make pyranose dehydrogenase a promising and versatile biocatalyst for production of highly reactive, sometimes unique, di- and tri-carbonyl sugar derivatives that may serve as interesting chiral intermediates for the synthesis of rare sugars, novel drugs, and fine chemicals.
44 citations
TL;DR: The free energy of ring puckering of the glucopyranose ring at the -1 position in vacuum, in water, and bound to the protein is calculated and it is found that the protein induces (4E and (4)H(3) conformations that are much more stable than the usually preferred ( 4)C(1) conformer.
Abstract: Understanding carbohydrate ring pucker is critical to rational design in materials and pharmaceuticals. Recently we have generalized our adaptive reaction coordinate force biasing method to perform calculations on multidimensional reaction coordinates. We termed this the Free Energies from Adaptive Reaction Coordinate Forces (FEARCF) method. Using FEARCF in SCC-DFTB QM/MM non-Boltzmann simulations, we are able to calculate multidimensional ring pucker free energies of conformation. Here we apply this to the six-membered glucopyranose ring located in an eight-membered β 1−4 linked octaose oligosaccharide (cellooctaose). The cellooctaose was built following the conformation of the saccharides bound to cellobiohydrolase I (CBHI) of Trichoderma reesei as reported in the 7CEL crystal structure obtained from the PDB. We calculate the free energy of ring puckering of the glucopyranose ring at the −1 position in vacuum, in water, and bound to the protein. We find that the protein induces 4E and 4H3 conformations ...
38 citations
TL;DR: The results indicate that the covalent linkage is mainly important for a reductiveHalf-reaction in which the FAD cofactor is reduced by d-glucose, while it is not important for an oxidative half-re reaction in which oxygen reacts with the reduced FAD to generate H(2)O(2).
Abstract: Pyranose 2-oxidase (P2O) from Trametes multicolor contains a flavin adenine dinucleotide (FAD) cofactor covalently linked to the N3 atom of His167. The enzyme catalyzes the oxidation of aldopyranoses by molecular oxygen to generate 2-keto-aldoses and H2O2 as products. In this study, the transient kinetics and primary and solvent kinetic isotope effects of the mutant in which His167 has been replaced with Ala (H167A) were investigated, to elucidate the functional role of the 8a-N3-histidyl FAD linkage and to gain insights into the reaction mechanism of P2O. The results indicate that the covalent linkage is mainly important for a reductive half-reaction in which the FAD cofactor is reduced by d-glucose, while it is not important for an oxidative half-reaction in which oxygen reacts with the reduced FAD to generate H2O2. d-Glucose binds to H167A via multiple binding modes before the formation of the active Michaelis complex, and the rate constant of flavin reduction decreases ∼22-fold compared to that of the...
TL;DR: The results demonstrate an elaborate structural fine-tuning of the active site to complete its own formation that couples efficient holoenzyme synthesis to conformational substates of the substrate-recognition loop and concerted movements of side chains near the flavinylation ligand.
TL;DR: In this paper, fungal beta-N-acetylhexosaminidases are shown to be able to hydrolyze and transfer 4-deoxy-Nacetyl hexosaminides with high yields.
Abstract: beta-N-Acetylhexosaminidases feature so-called wobbling specificity, which means that they cleave substrates both in gluco- and galacto- configurations, with the activity ratio depending on the enzyme source. Here we present the new finding that fungal beta-N-acetylhexosaminidases are able to hydrolyze and transfer 4-deoxy-N-acetylhexosaminides with high yields. This clearly demonstrates that the 4-hydroxy moiety at the substrate pyranose ring is not essential for substrate binding to the enzyme active site, which was also confirmed by molecular docking of the tested compounds into the model of the active site of beta-N-acetylhexosaminidase from Aspergillus oryzae. A set of four 4-deoxy-N-acetylhexosaminides was synthesized and screened against a panel of beta-N-acetylhexosaminidases (extracellular and intracellular) from various sources (fungal, human, animal, plant and bacterial) for hydrolysis. The results of this screening are reported here, as well as the structures of three novel 4'-deoxy-disaccharides prepared by transglycosylation reaction with high yields (52% total disaccharide fraction) using beta-N-acetylhexosaminidase from Talaromyces flavus.
TL;DR: The present study lends support to the hypothesis that 1,4‐benzoquinone is a physiologically relevant alternative electron acceptor in the oxidative half‐reaction of pyranose 2‐oxidase.
Abstract: Pyranose 2-oxidase from Trametes multicolor is a 270 kDa homotetrameric enzyme that participates in lignocellulose degradation by wood-rotting fungi and oxidizes a variety of aldopyranoses present in lignocellulose to 2-ketoaldoses. The active site in pyranose 2-oxidase is gated by a highly conserved, conformationally degenerate loop (residues 450-461), with a conformer ensemble that can accommodate efficient binding of both electron-donor substrate (sugar) and electron-acceptor substrate (oxygen or quinone compounds) relevant to the sequential reductive and oxidative half-reactions, respectively. To investigate the importance of individual residues in this loop, a systematic mutagenesis approach was used, including alanine-scanning, site-saturation and deletion mutagenesis, and selected variants were characterized by biochemical and crystal-structure analyses. We show that the gating segment ((454)FSY(456)) of this loop is particularly important for substrate specificity, discrimination of sugar substrates, turnover half-life and resistance to thermal unfolding, and that three conserved residues (Asp(452), Phe(454) and Tyr(456)) are essentially intolerant to substitution. We furthermore propose that the gating segment is of specific importance for the oxidative half-reaction of pyranose 2-oxidase when oxygen is the electron acceptor. Although the position and orientation of the slow substrate 2-deoxy-2-fluoro-glucose when bound in the active site of pyranose 2-oxidase variants is identical to that observed earlier, the substrate-recognition loop in F454N and Y456W displays a high degree of conformational disorder. The present study also lends support to the hypothesis that 1,4-benzoquinone is a physiologically relevant alternative electron acceptor in the oxidative half-reaction.
TL;DR: Improved approach to the calibration procedure yielded a calibration curve with an excellent linearity and quantitative evaluation of chromatograms of D-galactose suggested that not only anomers but even pyranose and furanose forms of the anomers could be resolved.
Abstract: Calibration based on the "single-point calibration method", a simple exponential transformation of the response function of an evaporative light scattering detector was improved and applied to analysis of selected saccharides under hydrophilic interaction chromatography mode (a polar phase LiChrospher100 DIOL, mobile phase acetonitrile/water). The improved approach to the calibration procedure yielded a calibration curve with an excellent linearity (quality coefficient <5%). This quantitative evaluation of chromatograms of D-galactose suggested that not only anomers but even pyranose and furanose forms of the anomers could be resolved--the resulting calculations of abundance of the anomeric form strongly correlated with data from the literature obtained mostly by NMR studies (analogous results were also obtained for D-arabinose, D-glucose, and D-mannose). Because of the rapid separation (retention time less than 10 min), the observed correlation enabled to monitor anomeric conversion (mutarotation) of monosaccharides.
TL;DR: The NAD(+)-dependent redox mechanism of glycosidic bond hydrolysis as catalyzed by GlvA is investigated through the combined application of density functional theory and a self-consistent reaction field to a large active-site model obtained from the crystallographic structure of the enzyme.
Abstract: Glycosidic bonds are remarkably resistant to cleavage by chemical hydrolysis. Glycoside hydrolases catalyze their selective hydrolysis in oligosaccharides, polysaccharides, and glycoconjugates by following nonredox catalytic pathways or a net redox-neutral catalytic pathway using NAD+ and divalent metal ions as cofactors. GlvA (6-phospho-α-glucosidase) is a glycosidase belonging to family GH4 and follows a regioselective redox-neutral mechanism of glycosidic-bond hydrolysis that favors α- over β-glycosides. Its proposed catalytic mechanism can be divided into two half-reactions: the first one activates the glucopyranose ring by successively forming intermediates that are oxidized at the 3-, 2-, and 1-positions of the ring, which ultimately facilitate the heterolytic deglycosylation. The second half-reaction is essentially the reverse of the first half-reaction, beginning with the pyranose ring hydroxylation at the anomeric carbon, and it is followed by 3-reduction and regeneration of the active forms of t...
TL;DR: A new aqueous-based, one-pot strategy that involves first converting the sugar to a C-glycoside ketone, followed by conversion to ketohydrazones or oximes is described, which demonstrates the versatility of the approach to diverse glycans, including bead immobilization and lectin analysis of acarbose.
Abstract: Glycosylation often mediates important biological processes through the interaction of carbohydrates with complementary proteins. Most chemical tools for the functional analysis of glycans are highly dependent upon various linkage chemistries that involve the reducing terminus of carbohydrates. However, because of ring opening, the structural integrity of the reducing sugar ring (pyranose or furanose) is lost during these techniques, resulting in derivatized carboydrates that markedly differ from the parent molecule. This paper describes a new aqueous-based, one-pot strategy that involves first converting the sugar to a C-glycoside ketone, followed by conversion to ketohydrazones or oximes. Hence, the C-glycoside ketones are tagged with fluorescence, colored, cationic or biotin-labeled groups or immobilized onto hydrazine-functionalized beads. No activating or protecting groups are required, and the chemistry is mild enough for a wide range of carbohydrates. We demonstrate the versatility of the approach to diverse glycans, including bead immobilization and lectin analysis of acarbose, an antidiabetic drug, to dabsyl-tagged enzyme substrates to screen cellulases, and for the analysis of plant cell wall hemicellulosics.
TL;DR: The heterologous production of the industrially relevant fungal enzyme pyranose 2-oxidase in the prokaryotic host E. coli was investigated using 3 different expression systems, i.e. the well-studied T7 RNA polymerase based pET21d+, the L-arabinose inducible pBAD and the pCOLD system.
Abstract: The heterologous production of the industrially relevant fungal enzyme pyranose 2-oxidase in the prokaryotic host E. coli was investigated using 3 different expression systems, i.e. the well-studied T7 RNA polymerase based pET21d+, the L-arabinose inducible pBAD and the pCOLD system. Preliminary experiments were done in shaking flasks at 25°C and optimized induction conditions to compare the productivity levels of the different expression systems. The pET21d+ and the pCOLD system gave 29 U/L·h and 14 U/L·h of active pyranose 2-oxidase, respectively, whereas the pBAD system only produced 6 U/L·h. Process conditions for batch fermentations were optimized for the pET21d+ and the pCOLD systems in order to reduce the formation of inactive inclusion bodies. The highest productivity rate with the pET21d+ expression system in batch fermentations was determined at 25°C with 32 U/L·h. The pCOLD system showed the highest productivity rate (19 U/L·h) at 25°C and induction from the start of the cultivation. Using the pCOLD system in a fed batch fermentation at 25°C with a specific growth rate of μ = 0.15 h-1resulted in the highest productivity rate of active pyranose oxidase with 206 U/L·h.
TL;DR: The heterologous expression of one of the pyranose dehydrogenase genes, encoding the major PDH protein in Agaricus meleagris, is reported here, for the first time, in the filamentous fungi Aspergillus nidulans, and AsperGillus niger.
Abstract: Pyranose dehydrogenase (PDH) is a flavin-dependant sugar oxidoreductase found in the family Agaricaceae, basidiomycetes that degrade lignocellulose-rich forest litter, and is catalytically related to the fungal enzymes pyranose 2-oxidase and cellobiose dehydrogenase. It has broad substrate specificity and displays similar activities with most sugar constituents of lignocellulose including disaccharides and oligosaccharides, a number of (substituted) quinones, and metal ions are suitable electron acceptors rather than molecular oxygen. In contrast to pyranose 2-oxidase and cellobiose dehydrogenase, which oxidize regioselectively at C-2 and C-1, respectively, PDH is capable of oxidation on C-1 to C-4 as well as double oxidations, depending on the nature of the substrate. This makes it a very interesting enzyme for biocatalytic applications, as many of the reaction products are otherwise unaccessible by chemical or enzymatic means. PDH was characterized in detail in a limited number of fungi, and the first encoding genes were isolated only recently. We report here, for the first time, the heterologous expression of one of these genes, encoding the major PDH protein in Agaricus meleagris, in the filamentous fungi Aspergillus nidulans, and Aspergillus niger.
TL;DR: The structure of the Mn2+‐bound enzyme indicated that the catalytic site interconverts between two forms with the displacement of the metal ion to recognize both pyranose and furanose ring substrates, and the metal‐mediated hydride‐shift mechanism of l‐RhI was examined in detail.
Abstract: l-Rhamnose isomerase (l-RhI) catalyzes the reversible isomerization of l-rhamnose to l-rhamnulose. Pseudomonas stutzeril-RhI, with a broad substrate specificity, can catalyze not only the isomerization of l-rhamnose, but also that between d-allose and d-psicose. For the aldose–ketose isomerization by l-RhI, a metal-mediated hydride-shift mechanism has been proposed, but the catalytic mechanism is still not entirely understood. To elucidate the entire reaction mechanism, the X-ray structures of P. stutzeril-RhI in an Mn2+-bound form, and of two inactive mutant forms of P. stutzeril-RhI (S329K and D327N) in a complex with substrate/product, were determined. The structure of the Mn2+-bound enzyme indicated that the catalytic site interconverts between two forms with the displacement of the metal ion to recognize both pyranose and furanose ring substrates. Solving the structures of S329K–substrates allowed us to examine the metal-mediated hydride-shift mechanism of l-RhI in detail. The structural analysis of D327N–substrates and additional modeling revealed Asp327 to be responsible for the ring opening of furanose, and a water molecule coordinating with the metal ion to be involved in the ring opening of pyranose.
Structured digital abstract
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MINT-7384817: l-RhI (uniprotkb:Q75WH8) and l-RhI (uniprotkb:Q75WH8) bind (MI:0407) by X-ray crystallography (MI:0114)
TL;DR: 2-Azido- 4-benzylamino-4-N-,3-O-carbonyl-2,4,6-trideoxy-d-galactopyranosyl trichloroacetimidate (14) was conveniently prepared by regioselective introduction of an N-benzyl carbamate at O-3 of 6-deoxy- d-glucal 6, followed by mesylation atO-4.
TL;DR: Recombinant P2Ox from L. shimeji shows properties that are comparable to those of P2 Ox from white-rot fungal origin, and is in general characterised by lower Km and kcat values both for electron donor (sugar) as well as electron acceptor.
Abstract: The flavin-dependent enzyme pyranose 2-oxidase (P2Ox) has gained increased attention during the last years because of a number of attractive applications for this enzyme. P2Ox is a unique biocatalyst with high potential for biotransformations of carbohydrates and in synthetic carbohydrate chemistry. Recently, it was shown that P2Ox is useful as bioelement in biofuel cells, replacing glucose oxidase (GOx), which traditionally is used in these applications. P2Ox offers several advantages over GOx for this application, e.g., its much broader substrate specificity. Because of this renewed interest in P2Ox, knowledge on novel pyranose oxidases isolated from organisms other than white-rot fungi, which represent the traditional source of this enzyme, is of importance, as these novel enzymes might differ in their biochemical and physical properties. We isolated and over-expressed the p2ox gene encoding P2Ox from the ectomycorrhizal fungus Lyophyllum shimeji. The p2ox cDNA was inserted into the bacterial expression vector pET21a(+) and successfully expressed in E. coli Rosetta 2. We obtained active, flavinylated recombinant P2Ox in yields of approximately 130 mg per L of medium. The enzyme was purified by a two-step procedure based on anion exchange chromatography and preparative native PAGE, yielding an apparently homogenous enzyme preparation with a specific activity of 1.92 U/mg (using glucose and air oxygen as the substrates). Recombinant P2Ox from L. shimeji was characterized in some detail with respect to its physical and catalytic properties, and compared to the well-characterised enzymes from Phanerochaete chrysosporium and Trametes multicolor. L. shimeji P2Ox shows properties that are comparable to those of P2Ox from white-rot fungal origin, and is in general characterised by lower Km and kcat values both for electron donor (sugar) as well as electron acceptor (ferrocenium ion, 1,4-benzoquinone, 2,6-dichloroindophenol). While L. shimeji P2Ox is the least thermostable of these three enzymes (melting temperature Tm of 54.9°C; half-life time of activity τ1/2 of 0.12 at 50°C and pH 6.5), P. chrysosporium P2Ox showed remarkable thermostability with Tm of 75.4°C and τ1/2 of 96 h under identical conditions.
TL;DR: To improve some of the catalytic properties of P2Ox from Trametes multicolor, saturation mutagenesis of the amino acid His450 located at a pivotal point of the active site loop and subsequent screening of the libraries thus obtained for improved activity with the sugar substrate d-galactose is selected.
Abstract: The homotetrameric flavoprotein pyranose 2-oxidase (P2Ox) has several proposed biotechnological applications, among others as a biocatalyst for carbohydrate transformations toward higher-value products. To improve some of the catalytic properties of P2Ox from Trametes multicolor, we selected a semirational enzyme engineering approach, namely, saturation mutagenesis of the amino acid His450 located at a pivotal point of the active site loop and subsequent screening of the libraries thus obtained for improved activity with the sugar substrate d-galactose. A variant with improved catalytic characteristics identified was H450G, which showed a significant, 3.6-fold decrease in KM together with a 1.4-fold increase in kcat for its substrate d-galactose and an overall improvement in the catalytic efficiency by a factor of 5. By combining H450G with other amino acid replacements, we obtained the P2Ox variants H450G/V546C and H450G/E542K/V546C, which can be of interest for applications in food industry due to their...
TL;DR: The pyrolysis of monosaccharides with less than six carbon atoms and glucose was described in this paper, and the pyrolyses and the programs were obtained in identical conditions as for glucose, at 900°C.
Abstract: Publisher Summary Carbohydrates (saccharides or sugars) are organic compounds containing one or more carbonyl groups in their molecules and two or more alcohol groups on an aliphatic hydrocarbon chain. These compounds can be classified as monosaccharides, oligosaccharides, and polysaccharides. The oligosaccharides and polysaccharides are generated by the elimination of water from two or more monosaccharide molecules, the sugar units being connected by an ether group. Glyceraldehyde and dihydroxyacetone (n=3) can be considered the simplest monosaccharides. The chapter describes pyrolysis of monosaccharides with less than six carbon atoms and glucose. The programs of two other hexoses, mannose, and galactose that are found mainly in pyranose form are given in the chapter. The pyrolysis and the programs were obtained in identical conditions as for glucose, at 900°C. Fructose is a hexose that is found mainly in furanose form. The pyrolysis products of fructose are similar in nature with those of other monosaccharides. Disaccharides are formed by the elimination of a water molecule between two monosaccharides (different or identical) with the formation of an ether bond. Pyrolysis of disaccharides takes place following reactions very similar to those of monosaccharides. The nature of pyrolysis products from a disaccharide depends on the nature of the component monosaccharides and on the type of connection between the two monosaccharide molecules. Pyrolysis of three disaccharides—maltose, lactose, and sucrose—was performed in identical conditions as for glucose and the programs. Pyrolysis of three disaccharides—maltose, lactose, and sucrose—was performed in identical conditions as for glucose. A large variety of compounds are derived from carbohydrates. These compounds are generated by the modification of the initial carbohydrate molecule, either adding or subtracting functionalities. Several of the more common carbohydrate derivatives are given in the chapter.
TL;DR: In this article, the Δ2 effect was investigated for the stability of the pyranose ring conformation when the hydroxyl group at carbon 2 (C2) is in the axial position.
TL;DR: A scanning approach using a library of pyranose-based peptidomimetics that is structurally diverse in a systematic manner, designed to cover all possible conformations of tripeptide motifs containing two aromatic groups and one positive charge is described.
Abstract: Success in discovering bioactive peptide mimetics is often limited by the difficulties in correctly transposing known binding elements of the active peptide onto a small and metabolically more stable scaffold while maintaining bioactivity. Here we describe a scanning approach using a library of pyranose-based peptidomimetics that is structurally diverse in a systematic manner, designed to cover all possible conformations of tripeptide motifs containing two aromatic groups and one positive charge. Structural diversity was achieved by efficient selection of various chemoforms, characterized by a choice of pyranose scaffold of defined chirality and substitution pattern. A systematic scanning library of 490 compounds was thus designed, produced, and screened in vitro for activity at the somatostatin (sst(1-5)) and melanin-concentrating hormone (MCH(1)) receptors. Bioactive compounds were found for each target, with specific chemoform preferences identified in each case, which can be used to guide follow-on drug discovery projects without the need for scaffold hopping.
TL;DR: In this paper, the anomeric effect associated with the nitrogen atom in the isocyano group was investigated by using 1 H NMR spectroscopic analysis of an anomersic pair of xylopyranosyl iso-yanides 8 and 7.
TL;DR: In this paper, a simple method using mild conditions for the preparation of secondary and tertiary glycosyl amides (III and V) was described by treatment of sugar-based N-acylbenzotriazoles (I) and (IV) with the corresponding amines (II).
Abstract: A simple method using mild conditions for the preparation of secondary and tertiary glycosyl amides (III) and (V) is described by treatment of sugar-based N-acylbenzotriazoles (I) and (IV) with the corresponding amines (II).
TL;DR: The chelating properties of the common aldohexoses d-glucose, d-mannose, and d-galactose are characteristically modified in 2-substituted derivatives, and furanose-1,3 chelation becomes an important metal-binding mode due to the decreased acidity of the 2-deoxy-glycose's 1-hydroxy function.
Abstract: The chelating properties of the common aldohexoses D-glucose, D-mannose, and D-galactose are characteristically modified in 2-substituted derivatives. The 2-amino-2-deoxy-aldohexoses provide mono- and bis-metallisable anionic ligands after their reaction with metal probes of the PdIIN2 type (N2 = bidentate nitrogen ligand). The 2-amino function reliably participates in metal binding of the, mostly pyranoidic, carbohydrate chelators. Acetylation of the amino function yields the biologically important 2-N-acetylamino-2-deoxy-hexoses (GlcNAc, ManNAc, and GalNAc). On reaction with the palladium probe, the metal-binding properties of the deprotonated acetylamino function depends on the steric requirements introduced by the acetyl residue which is forced into a coplanar arrangement with the chelate ring. In the two 2-deoxy-aldohexoses, 2-deoxy-arabino-D-hexose (the 2-deoxy derivative of both D-glucose and D-mannose, ‘2-deoxy-glucose’) and 2-deoxy-lyxo-D-hexose (‘2-deoxy galactose’), the 2-position cannot contribute to metal binding. As a result, furanose-1,3 chelation becomes an important metal-binding mode. Due to the decreased acidity of the 2-deoxy-glycose's 1-hydroxy function, monometallation also takes place at the pyranose's 3,4-site.
TL;DR: Application of these new ligands in asymmetric cyclopropanation revealed strong steric and configurational effects of position 3 on asymmetric induction, and further dramatic effects of the pyranose conformation were also observed.
Abstract: In previous studies we found that the asymmetric induction of bis(oxazolines) based on D-glucosamine strongly depended on the steric demand of the 3-O-substituents. To further probe the impact of the 3-position of the pyranose scaffold, we prepared 3-epimerised and 3-defunctionalised versions of these ligands as well as a 3-O-formyl derivative. Application of these new ligands in asymmetric cyclopropanation revealed strong steric and configurational effects of position 3 on asymmetric induction, further dramatic effects of the pyranose conformation were also observed.