- Glycoside cleavage by a new mechanism in unsaturated glucuronyl hydrolases
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Unsaturated glucuronyl hydrolases (UGLs) from GH family 88 of the CAZy classification system cleave a terminal unsaturated sugar from the oligosaccharide products released by extracellular bacterial polysaccharide lyases. This pathway, which is involved in extracellular bacterial infection, has no equivalent in mammals. A novel mechanism for UGL has previously been proposed in which the enzyme catalyzes hydration of a vinyl ether group in the substrate, with subsequent rearrangements resulting in glycosidic bond cleavage. However, clear evidence for this mechanism has been lacking. In this study, analysis of the products of UGL-catalyzed reactions in water, deuterium oxide, and dilute methanol in water, in conjunction with the demonstration that UGL rapidly cleaves thioglycosides and glycosides of inverted anomeric configuration (substrates that are resistant to hydrolysis by classical glycosidases), provides strong support for this new mechanism. A hydration-initiated process is further supported by the observed UGL-catalyzed hydration of a C-glycoside substrate analogue. Finally, the observation of a small β-secondary kinetic isotope effect suggests a transition state with oxocarbenium ion character, in which the hydrogen at carbon 4 adopts an axial geometry. Taken together, these observations validate the novel vinyl ether hydration mechanism and are inconsistent with either inverting or retaining direct hydrolase mechanisms at carbon 1.
- Jongkees, Seino A. K.,Withers, Stephen G.
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supporting information; experimental part
p. 19334 - 19337
(2012/01/31)
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- Synthesis of apiose-containing oligosaccharide fragments of the plant cell wall: Fragments of rhamnogalacturonan-II side chains A and B, and apiogalacturonan
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Fragments of pectic polysaccharides rhamnogalacturonan-II (RG-II) and apiogalacturonan were synthesised using p-tolylthio apiofuranoside derivatives as key building blocks. Apiofuranose thioglycosides can be conveniently prepared by cyclization of the cor
- Nepogodiev, Sergey A.,Fais, Margherita,Hughes, David L.,Field, Robert A.
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experimental part
p. 6670 - 6684
(2011/11/14)
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- Electroorganic synthesis 66: Selective anodic oxidation of carbohydrates mediated by TEMPO
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The carbohydrates 4-15 are anodically oxidized with 2,2,6,6- tetramethylpiperidin-1-oxyl (TEMPO) as mediator. Selective and complete reaction at the primary hydroxyl groups affords the corresponding carboxylic acids 16-32 in moderate to excellent yield. Methyl α-D-glucopyranoside is converted in 98% yield to the uronic acid 16. Cyclic voltammetry shows that the oxydation is base-catalyzed and the oxidation of the hydroxy group with TEMPO+ (2) is rate determining.
- Schnatbaum, Karsten,Sch?fer, Hans J.
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p. 864 - 872
(2007/10/03)
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- SELECTIVE DEGRADATION OF THE GLYCOSYLURONIC ACID RESIDUES OF COMPLEX CARBOHYDRATES BY LITHIUM DISSOLVED IN ETHYLENEDIAMINE
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Lithium metal dissolved in ethylenediamine had been demonstrated to cleave a 3-linked glycosyluronic acid-containing polysaccharide .The present study with model compounds has established that, by lithium treatment, carbohydrates are cleaved at the sites of the glycosyluronic acid residues, regerdless of the point at which other glycosyl residues are attached to the glycosyluronic acid residue.Treatment of carbohydrates with lithium metal dissolved in ethylenediamine also results in cleavage of methyl glycosides, reduction of aldoses, and cleavage of methyl ethers and pyruvic acetals of glycosyl residues.Model compounds were used to demonstrate that oligosaccharides containing only neutral glycosyl residues are largely stable to the reaction conditions (except for the reduction of the glycose residue of each oligosaccharide).Thus, a general procedure for the selective cleavage of underivatized carbohydrates at the glycosyluronic acid residues is described.
- Lau, James M.,McNeil, Michael,Darvill, Alan G.,Albersheim, Peter
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p. 219 - 244
(2007/10/02)
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- METHANOLYSIS STUDIES OF CARBOHYDRATES, USING H.P.L.C.
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An h.p.l.c. system that separates carbohydrates as their methyl glycosides has been used to study the products obtained on treatment of various carbohydrates with methanolic hydrogen chloride.Results are presented for the monosaccharide composition of several polysaccharides, lactone and ester formation during the treatment of D-glucuronic acid, and relative rates of glycosidation vs. esterification during the treatment of D-galacturonic acid.
- Cheetham, Norman W. H.,Sirimanne, Padmini
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- SYNTHESIS OF METHYL DERIVATIVES OF URONIC ACIDS. I. SYNTHESIS OF METHYL (METHYL Α-D-GALACTOPYRANOSID)URONATE AND ITS 2-, 3-, AND 4-O-METHYL ETHERS
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Alternative unidirectional methods for synthesizing methyl (methyl α-D-galactopyranosid)uronate and its mono-O-methyl ethers by the oxidation (with CrO3-H2SO4-acetone) of the corresponding methyl O-benzyl-O-methyl-α-D-galactopyranosides having unsubstituted 6-OH groups to the corresponding methyl O-benzyl-O-methyl-α-D-galactouronic acids followed by esterification with CH2N2 and the catalytic hydrogenolysis of the benzyl groups are proposed.
- Grishkovets, V. I.,Zemlyakov, A. E.,Chirva, V. Ya.
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p. 255 - 259
(2007/10/02)
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- PROTON AND CARBON-13 NUCLEAR MAGNETIC RESONANCE STUDIES ON METHYL (METHYL D-GALACTOSID)URONATES AND THEIR PER-O-ACETYL DERIVATIVES
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The 1H- and 13C-n.m.r. spectra of the anomeric methyl (methyl D-galactosid)uronates, as well as the 1H-n.m.r. spectra of their acetyl derivatives, were analyzed.The spectra of the unacetylated D-galactopyranosiduronates showed good correlation with those of the corresponding anomeric D-galactopyranuronic acids and their methyl esters, and with those of the anomeric methyl D-galactopyranosides.From the values of the chemical shifts and coupling constants, it was concluded that the anomeric methyl (methyl D-galactopyranosid)uronates and their corrasponding peracetates are in the 4C1(D) conformation.The chemical shifts in the 13C-n.m.r. spectra show good correlation with those of the methyl D-galactosides.The signals of the furanose derivatives appear at fields lower than those of the corresponding pyranose compounds.
- Matsuhiro, Bety,Zanlungo, Alberto B.,Dutton, Guy G. S.
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