Showing papers on "Pyranose published in 2001"

Purification and Characterization of Pyranose Oxidase from the White Rot Fungus Trametes multicolor

Abstract: We purified an intracellular pyranose oxidase from mycelial extracts of the white rot fungus Trametes multicolor by using ammonium sulfate fractionation, hydrophobic interaction, ion-exchange chromatography, and gel filtration. The native enzyme has a molecular mass of 270 kDa as determined by equilibrium ultracentrifugation and is composed of four identical 68-kDa subunits as determined by matrix-assisted laser desorption ionization mass spectrometry. Each subunit contains one covalently bound flavin adenine dinucleotide as its prosthetic group. The enzyme oxidizes several aldopyranoses specifically at position C-2, and its preferred electron donor substrates are d-glucose,d-xylose, and l-sorbose. During this oxidation reaction electrons are transferred to oxygen, yielding hydrogen peroxide. In addition, the enzyme catalyzes the two-electron reduction of 1,4-benzoquinone, several substituted benzoquinones, and 2,6-dichloroindophenol, as well as the one-electron reduction of the ABTS [2,2′-azinobis(3-ethylbenzthiazolinesulfonic acid)] cation radical. As judged by the catalytic efficiencies ( k cat / K m ), some of these quinone electron acceptors are much better substrates for pyranose oxidase than oxygen. The optimum pH of the pyranose oxidase-catalyzed reaction depends strongly on the electron acceptor employed and varies from 4 to 8. It has been proposed that the main metabolic function of pyranose oxidase is as a constituent of the ligninolytic system of white rot fungi that provides peroxidases with H 2 O 2 . An additional function could be reduction of quinones, key intermediates that are formed during mineralization of lignin.

Fingerprinting polysaccharides with single-molecule atomic force microscopy.

Abstract: We report the use of an atomic force microscopy (AFM)-based force spectroscopy technique to identify, at the single-molecule level, the components of mixtures of polysaccharides. Previously, we showed that the elasticity of certain types of polysaccharides is governed by force-induced conformational transitions of the pyranose ring. These transitions produce atomic fingerprints in the force–extension spectrum that are characteristic of the ground-energy conformation of the pyranose ring and the type of glycosidic linkages. Using this approach we find that commercially available agarose and λ-carrageenan contain molecules that, when stretched in an atomic force microscope, produce a force spectrum characteristic of α-(1→4) d-glucans. We have identified these molecules as amylopectin or floridean starch, a storage polysaccharide in algae. Our methodology can identify individual polysaccharide molecules in solution, which is not possible by any other spectroscopic technique, and therefore is an important addition to the arsenal of analytical techniques used in carbohydrate research.

Highly α- and β-Selective Radical C-Glycosylation Reactions Using a Controlling Anomeric Effect Based on the Conformational Restriction Strategy. A Study on the Conformation−Anomeric Effect− Stereoselectivity Relationship in Anomeric Radical Reactions

Abstract: We hypothesized that, because the stereoselectivity of anomeric radical reactions was significantly influenced by the anomeric effect, which can be controlled by restricting the conformation of the radical intermediate, the proper conformational restriction of the pyranose ring of the substrates would therefore make highly α- and β-stereoselective anomeric radical reactions possible. Thus, the conformationally restricted 1-phenylseleno-d-xylose derivatives 9 and 10, restricted in a 4C1-conformation, and 11 and 12, restricted in a 1C4-conformation, were designed and synthesized by introducing the proper protecting groups on the hydroxyl groups on the pyranose ring as model substrates for the anomeric radical reactions. The radical deuterations with Bu3SnD and the C-glycosylation with Bu3SnCH2CHCH2 or CH2CHCN, using the 4C1-restricted substrates 9 and 10, afforded the corresponding α-products (α/β = 97:3−85:15) highly stereoselectively, whereas the 1C4-restricted substrates 11 and 12 selectively gave the β-...

Epimerases: structure, function and mechanism.

Abstract: Carbohydrates are ideally suited for molecular recognition. By varying the stereochemistry of the hydroxyl substituents, the simple six-carbon, six-oxygen pyranose ring can exist as 10 different molecules. With the further addition of simple chemical changes, the potential for generating distinct molecular recognition surfaces far exceeds that of amino acids. This ability to control and change the stereochemistry of the hydroxyl substituents is very important in biology. Epimerases can be found in animals, plants and microorganisms where they participate in important metabolic pathways such as the Leloir pathway, which involves the conversion of galactose to glucose-1-phosphate. Bacterial epimerases are involved in the production of complex carbohydrate polymers that are used in their cell walls and envelopes and are recognised as potential therapeutic targets for the treatment of bacterial infection. Several distinct strategies have evolved to invert or epimerise the hydroxyl substituents on carbohydrates. In this review we group epimerisation by mechanism and discuss in detail the molecular basis for each group. These groups include enzymes which epimerise by a transient keto intermediate, those that rely on a permanent keto group, those that eliminate then add a nucleotide, those that break then reform carbon-carbon bonds and those that linearize and cyclize the pyranose ring. This approach highlights the quite different biochemical processes that underlie what is seemingly a simple reaction. What this review shows is that each position on the carbohydrate can be epimerised and that epimerisation is found in all organisms.

Screening of basidiomycete fungi for the quinone-dependent sugar C-2/C-3 oxidoreductase, pyranose dehydrogenase, and properties of the enzyme from Macrolepiota rhacodes

Abstract: Mycelial cultures of 76 strains of lignocellulose-degrading basidiomycete fungi were screened for the activity of pyranose dehydrogenase, a novel sugar oxidoreductase recently detected in Agaricus bisporus. Of these fungi, 37 strains belonging to seven phylogenetically related genera of mostly litter-decomposing Agaricales were positive for the dehydrogenase, based on activity assays towards D-glucose with 1,4-benzoquinone or ferricenium ion as electron acceptors, and on TLC/HPLC analyses of the reaction products. Lack of activity with O2 as the oxidant, specificity for C-3 of D-glucose, and active extracellular secretion of the enzyme were used as criteria to differentiate pyranose dehydrogenase from pyranose 2-oxidase (EC 1.1.3.10), known to be produced by numerous wood-rotting fungi. Extracellular pyranose dehydrogenase from Macrolepiota rhacodes was heavily glycosylated. The enzyme was characterized as a 78-kDa flavoprotein under denaturing conditions and a 76-kDa native protein using gel filtration. This enzyme had a maximum extracellular activity of 4.1 U ml–1 in 39-day liquid cultures. It exhibited broad selectivity for sugar substrates and oxidized D-glucose (K m=1.82) exclusively at C-3 to 3-dehydro-D-glucose (D-ribo-hexos-3-ulose), in contrast to pyranose dehydrogenases from Agaricus species, which acted at both C-3 and C-2 of D-glucose. The N-terminal sequence, AVVYRHPDEL, showed significant similarity with that reported for A. bisporus.

Variable Strategy toward Carbasugars and Relatives. 2.1 Diversity-Based Synthesis of β-d-Xylo, β-d-Ribo, β-l-Arabino, and β-l-Lyxo 4a-Carbafuranoses and (4a-Carbafuranosyl)thiols

Abstract: The silyloxy diene-based construction of carbasugars, previously exploited for the synthesis of four carbocyclic furanose and pyranose analogues, has been investigated further. By introducing a novel silylative cycloaldolization protocol and by adjusting a couple of minor transformations, the efficiency of this synthetic sequence was greatly improved. Through a series of lactone/thiolactone aldehyde cyclization precursors, four carbafuranoses (4a-carba-β-d-xylofuranose, 4a-carba-β-d-ribofuranose, 4a-carba-β-l-arabinofuranose, and 4a-carba-β-l-lyxofuranose) and four (carbafuranosyl)thiols [(4a-carba-β-d-xylofuranosyl)thiol, (4a-carba-β-d-ribofuranosyl)thiol, (4a-carba-β-l-arabinofuranosyl)thiol, and (4a-carba-β-l-lyxofuranosyl)thiol] were assembled. From this study, it was shown that these constructions tolerate a variety of precursors, and in many instances, they are suitable for scaling-up.

Asymmetric epoxidation by chiral ketones derived from carbocyclic analogues of fructose.

Abstract: A number of carbocyclic analogues of the fructose-derived ketone 1 have been prepared and investigated for asymmetric epoxidation. The studies show that the oxygen atom of the pyranose ring of 1 has an impact on the catalyst's activity and selectivity. Conformational, electronic, and steric effects are discussed.

Studies on the synthesis of landomycin A: synthesis and glycosidation reactions of L-rhodinosyl acetate derivatives.

Abstract: An efficient, eight-step synthesis of L-rhodinosyl acetate derivative 3 is described. The synthesis originates from methyl (S)-lactate and involves a highly stereoselective, chelate-controlled addition of allyltributylstannane to the lactaldehyde derivative 7. The beta-anomeric configuration of 3 was established with high selectivity by acetylation of the pyranose precursor with Ac(2)O and Et(3)N in CH(2)Cl(2). Preliminary studies of glycosidation reactions of 3 and L-rhodinosyl acetate 10 containing a 3-O-TES ether revealed that these compounds are highly reactive glycosidating agents and that trialkylsilyl triflates are effective glycosylation promoters. The best conditions for reactions with 15 as the acceptor involved use of diethyl ether as the reaction solvent and 0.2 equiv of TES-OTf at -78 degrees C. However, the TES ether protecting group of 10 proved to be too labile under these reaction conditions, and mixtures of 16a, 17, and 18a are obtained in reactions of 10 and 15. Disaccharide 17 arises via in situ cleavage of the TES ether of disaccharide 16a, while trisaccharide 18a results from a glycosidation of in situ generated 17 (or of 16a itself) with a second equivalent of 10. These problems were largely suppressed by using 3 with a 3-O-TBS ether protecting group as the glycosyl donor and 0.2 equiv of TES-OTf as the reaction promoter. Attempts to selectively glycosylate the C(3)-OH of diol acceptors 20 or 28 gave a 70:30 mixture of 21 and 22 in the reaction of 20 and a 43:27:30 mixture of regioisomeric trisaccharides 29 and 30 and tetrasaccharide 31 from the glycosidation reaction of 28. However, excellent results were obtained in the glycosidation of differentially protected disaccharide 34 using 1.5 equiv of 3 and 0.05 equiv of TBS-OTf in CH(2)Cl(2) at -78 degrees C. The latter step is an important transformation in the recently reported synthesis of the landomycin A hexasaccharide unit.

Reductive fragmentation of carbohydrate anomeric alkoxy radicals. Synthesis of alditols with potential utility as chiral synthons.

Abstract: A series of anomeric nitrate esters and N-phthalimido glycosides of carbohydrates in furanose and pyranose forms have been synthesized in order to generate the corresponding alkoxy radicals and study the C1−C2 fragmentation reaction under reductive conditions. This reaction constitutes a two-step method for the transformation of carbohydrates into the corresponding alditols with one less carbon. Using this methodology, interesting four- and five-carbon building blocks for natural products synthesis possessing d-erythritol, d-threitol, d-xylitol, and d-arabinitol stereochemistry have been prepared. The synthesis of 1,2-O-isopropylidene-β-l-threose (40) and 1-acetamido-2,4,5-tri-O-acetyl-d-arabinitol (50) have also been achieved from 1,2:5,6-di-O-isopropylidene-β-d-glucofuranose and 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-d-glucopyranose, respectively.

Gas-phase reactivity of glycosides and methyl glycosides with Cu + , Ag + and Pb 2+ ions by fast-atom bombardment and tandem mass spectrometry

Abstract: The analytical potential of the complexation of three isomeric monosaccharides (D-glucose, D-galactose, D-fructose)and two methyl glycosides (O-methyl-α-D-glucose and O-methyl-β-D-glucose)by three metal ions, Ag+, Cu+ and Pb2+, has been investigated by fast-atom bombardment (FAB)ionization and tandem mass spectrometry. Our results have shown that the unimolecular reactivity of Ag+ complexes allows the characterization of the C(4)stereochemistry of the pyranose ring, whereas a distinction between D-glucose and D-fructose is not achieved. On the other hand, each of the three [Cu + monosaccharide]+ complexes exhibits specific dissociation patterns. We have also observed that Pb2+ ions induce the richest reactivity and are of particular interest for the identification of the three isomers. Finally, this study has demonstrated that the stereochemistry of the anomeric center of O-methyl-D-glucose is easily determined by reaction with Ag+ or Pb2+ ions. Several mechanisms are proposed to account for the main frag...

Enzymatic redox isomerization of 1,6-disaccharides by pyranose oxidase and NADH-dependent aldose reductase

Abstract: Pyranose 2-oxidase, a homotetrameric FAD-flavoprotein from the basidiomycete Trametes multicolor, catalyzes regioselectively the oxidation of the 1→6 disaccharides allolactose [β- d -Galp-(1→6)- d -Glc], gentiobiose [β- d -Glcp-(1→6)- d -Glc], melibiose [α- d -Galp-(1→6)- d -Glc], and isomaltose [α- d -Glcp-(1→6)- d -Glc] at position C-2 of their reducing moiety. The resulting glycosyl d -arabino-hexos-2-uloses can be reduced specifically at C-1 by NAD(P)H-dependent aldose reductase from the yeast Candida tenuis. By this novel, two-step redox isomerization process the four disaccharide substrates could be converted to the corresponding keto-disaccharides allolactulose [β- d -Galp-(1→6)- d -Fru], gentiobiulose [β- d -Glcp-(1→6)- d -Fru], melibiulose [α- d -Galp-(1→6)- d -Fru], and isomaltulose (palatinose, [α- d -Glcp-(1→6)- d -Fru]) in high yields. These products could find application in food technology as alternative sweeteners.

Quantum chemical studies of carbohydrate reactivity: Acid catalyzed ring opening reactions

Abstract: The appropriate quantum mech. method for the investigation of enzymic reactions, which involve oxocarbenium ions as reactive intermediates, is examd. 2-Methoxy-tetrahydro-2H-pyran was chosen as a model acetal for pyranose sugars, and its reactivity upon protonation of the glycosidic and the ring oxygen atom has been investigated using various d. functional and post Hartree-Fock methods. Proton affinities calcd. at the DFT levels of theory predict glycosidic protonation to be favorable by 2.5 kcal/mol. For ring-protonated 2-methoxy-tetrahydro-2H-pyran, among the d. functionals, a strong dependence of the mol. structure on the d. functional employed is found. Structures obtained with the BLYP and B3LYP functionals are at variance with those from the ab initio methods, MP2 and CCSD, as shown by differences in bond lengths of more than 0.4 .ANG. for equiv. structures. By means of a valence bond anal. of the electron densities obtained at the DFT levels of theory, it is shown that this method dependence in this closed-shell species is caused by spurious self-interaction. This failure appears to be due to the subtle interplay between electron donating and accepting groups present. The BHLYP functional is found to perform best among the functionals under investigation, for describing the hypersurfaces for protonated pyranose sugars. [on SciFinder (R)]

Reaction of sugar allyltins with aldehydes. A remarkable difference in reactivity between furanose and pyranose organometallic derivatives

Abstract: The reaction of organometallic derivatives of monosaccharides with aldehydes catalyzed with BF3·OEt2 was studied. A significant difference in reactivity between the pyranosidic and furanosidic allyltins was noted. The former reacted readily with aldehydes affording precursors of higher carbon sugars with very high stereoselectivity, while the latter underwent rearrangement with elimination of the stannyl moiety prior to reaction with the aldehyde.

Towards cyclic, conformationally constrained, fluorine-containing β-amino acid derivatives from d-glucose

Abstract: Novel, potentially bioactive, fluorinated branched-chain monosaccharides were obtained by reaction of diethylaminosulphur trifluoride (DAST) with a series of methyl 3-C-cyano-3-ethoxycarbonyl-β- d -glucopyranoside derivatives, including the 4,6-O-benzylidene derivative and their 3-C-(N-protected aminomethyl) reduction products, as well as the phenyl 3-C-cyano-3-ethoxycarbonyl-1-thio-α- d -(and β- d -)glucopyranosides. The absolute configuration at C(3) was unambiguously assigned for all compounds on the basis of X-ray crystallographic analysis of methyl 4,6-O-benzylidene-3-C-cyano-3-deoxy-3-ethoxycarbonyl-β- d -glucopyranoside, corroborating the previous tentative assignment by other authors for the 4,6-unprotected compound. The course of the fluorination depended on the reaction temperature and the substitution pattern of the substrate. Thus, for methyl 3-C-cyano-3-ethoxycarbonyl-β- d -glucopyranoside, fluorination occurred exclusively at C(6), but for the phenylthio analogue, a 2-deoxy-2-phenylthio-α- d -manno-configured glycosyl fluoride and its 6-fluoro derivative were obtained, resulting from the expected rearrangement reaction, whilst starting from the phenylthio α anomer, only the unrearranged 6-fluoro compound was formed. Rearrangement was also observed in the fluorination of methyl 4,6-O-benzylidene-3-C-(N-protected aminomethyl)-β- d -glucopyranoside, which led to the 2-O-methyl-α- d -mannopyranosyl fluoride derivative as the sole product. This methodology may constitute a simple route to enantiopure conformationally constrained cyclic fluorinated β-amino acids having the α carbon atom shared with a pyranose ring, although only moderate yields were achieved, particularly in the fluorination step.

The Shape of Things to Come

Abstract: This chapter begins with the work of Hassel, whose work supported the belief that the pyranose ring was non-planar. He used electron diffraction studies in the gas phase which revealed the cyclohexane ring to have a non-planar shape (conformation), that of a chair. It then mentions the Barton's research of the two different types of bonds present in cyclohexane (equatorial and axial). He used this information to explain the conformation and reactivity in molecules such as steroids. In the chair conformation for cyclohexane, each carbon was almost exactly tetrahedral in shape with no “angle strain.” Hassel predicted that the conformation of the pyranose ring would also be non-planar and again a chair. The boat conformation is mentioned, and establishing the preferred conformation is discussed. Other high energy conformations, such as, the boat and the skew are described. A summary of the limiting conformations for the pyranose ring, including the chair, boat, half-chair, and skew are described. The anomeric effect by Lemieux, the exoanomeric effect, conformation of the exocyclic alkoxy group, and oligosaccharides are discussed.

CRYSTAL STRUCTURE ANALYSIS OF A 1,2,3,4-TETRA-OACETYL-5-DEOXY-5- PHENYLPH0SPHINYL-D-ribo-PYRANOSE DERIVATIVE

Abstract: X-Ray crystallographic analysis was performed on a single crystal of 1,2,3,4-tetra-0-acetyl-5deoxy-5-phenylphosphinyl-D-r/öo-pyranose derivative. The compounds have the (f?P) configuration at the phosphorus atom with the 'C, conformation for the pyranose ring. We previously reported [1] the transformation of methyl 2,3-O-isopropylideneβ -D-r/bo-pentodialdo1,4-furanoside 1 via several step functional group interconversions from methyl 2,3-0-isopropylidene-5methoxy(phenyl)phosphinyl-/3-D-a//oand a-L-fa/o-pentofuranosides (2) to 5-deoxy-5-phenylphosphinyl-Dr/'bopyranoses (6) as well as usual ring-transposition procedure to give 1,2,3,4-tetra-0-acetyl-5-deoxy-5phenylphosphinyl-D-r/'too-pyranoside derivatives [2]. We are interested in further investigation on the physico-chemical as well as biological properties of various phospha sugar analogues. In the preparative methodology (Scheme 1), four kinds of stereoisomeric phospha sugar derivatives might be preparated, and the stereoisomers were separated and isolated each other. To progress the study on the phospha sugar chemistry, here, we describe the X-ray crystallographic analysis of one of these 5-deoxy-5phenylphosphinyl-D-ribo-pyranose derivatives to confirm the structural and conformational assignments previously made by NMR spectroscopy [1]. Determination of the absolute configuration at the phosphorus atom and conformational analysis of the pyranose ring were carried out for the previously prepared phospha sugars 7a-d, and the precise