- Synthesis of l -Pyranosides by Hydroboration of Hex-5-enopyranosides Revisited
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Extensive study of the diastereoselective synthesis of l-pyranosides utilizing hydroboration of substituted exo-glucals (5-enopyranosides) obtained from d-sugars is presented. On the basis of this study we present the empirical rules describing the reacti
- ?opatkiewicz, Grzegorz,Mlynarski, Jacek
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p. 7545 - 7556
(2016/09/09)
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- Probing the influence of a 4,6-O-acetal on the reactivity of galactopyranosyl donors: Verification of the disarming influence of the trans-gauche conformation of C5-C6 bonds
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The effect of a 4,6-O-alkylidene acetal on the rate of acid-catalyzed hydrolysis of methyl galactopyranosides and of spontaneous hydrolysis of 2,4-dinitrophenyl galactopyranosides has been studied through the synthesis and hydrolysis of analogs in which O6 is replaced by a methoxymethylene unit in which the methoxy group adopts either an equatorial or an axial position according to the configuration. Consistent with earlier studies under both acid-catalyzed and spontaneous hydrolysis conditions, the alkylidene acetal, or its 7-carba analog, retards hydrolysis with respect to comparable systems lacking the cyclic protecting group. The configuration at C6 in the 7-carba analogs does not influence the rate of acid-catalyzed hydrolysis but has a minor influence on the rate of spontaneous hydrolysis of the 2,4-dinitrophenyl galactosides, confirming earlier studies on the role played by the hydroxymethyl group conformation on glycoside reactivity. The benzylidene acetal is found to stabilize the α-anomer of galactopyranose derivatives relative to monocyclic analogs. Reasons for the α-selectivity of 4,6-O-benzylidene- protected galactopyranosyl donors bearing neighboring group-active protecting groups at O2 are discussed.
- Moume-Pymbock, Myriame,Furukawa, Takayuki,Mondal, Sujit,Crich, David
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supporting information
p. 14249 - 14255
(2013/10/21)
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- Hydroxy group acidities of partially protected glycopyranosides
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A comprehensive acidity study of carbohydrate hydroxy groups has been carried out. Relative acidities (Ke) were determined spectrophotometrically for partially methylated methyl α-D- glycopyranosides. Apparently, the acidity is strongly affected by intramolecular hydrogen bonding as well as stereochemistry and solvation. By comparison with pKe and pKa values of aliphatic alcohols and polyols the first estimation of the pKa values for partially protected glycopyranosides was obtained. These findings contribute to the understanding of the relative reactivities of carbohydrate hydroxy groups.
- Matwiejuk, Martin,Thiem, Joachim
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p. 2180 - 2187
(2012/06/30)
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- Formation of septanoses from hexopyranosides via 5,6-exo-glycals
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Methyl d-hexo-5-ulosides are obtained in high yield by dihydroxylation of 5,6-exo-glucal compounds. The bicyclic structure (1,6-anhydropyrano-5-ulose) of the products is adopted in solution and in solid state in a 4C 1 conformation.
- Jackowski, Olivier,Chretien, Francoise,Didierjean, Claude,Chapleur, Yves
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scheme or table
p. 93 - 103
(2012/08/08)
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- Synthesis of blockwise alkylated (1→4) linked trisaccharides as surfactants: Influence of configuration of anomeric position on their surface activities
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New carbohydrate-based surfactants consisting of hydrophilic cellobiosyl and hydrophobic glucosyl residues, methyl β-D-glucopyranosyl-(1→4)- α-D-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-α-D- glucopyranoside 1 (GβGαMα, G: glucopyranosyl residue, α and β: α-(1→4)- and β-(1→4) glycosidic bonds, M: methyl group), 2 (GβGβMα), 3 (GβGαMβ), 4 (G βGβMβ), 5 (G βGαEα, E: ethyl group), 6 (GβGβEα), 7 (G βGαEβ), 8 (G βGβEβ) and eight α-and β-glycoside mixtures (a mixture of 1 and 2: 1/2 = 62/38 (9), 32/68 (10); a mixture of 3 and 4: 3/4 = 69/31 (11), 32/68 (12); a mixture of 5 and 6: 5/6 = 62/38 (13), 33/67 (14); a mixture of 7 and 8: 7/8 = 59/41 (15), 29/71 (16)) were synthesized via combined methods consisting of acid-catalyzed alcoholysis of cellulose ethers and glycosylation of phenyl thio-cellobioside derivatives. Their surface activities in aqueous solution depended on their chemical structures: α- or β-(1→4) linkage between hydrophilic cellobiosyl and hydrophobic glucosyl blocks, methyl or ethyl groups of hydrophobic glucosyl block, and α- or β-linked ether group at the C-1 of hydrophobic glucosyl block. The mixing effect of α- and β-glycosides on surface activities was also investigated. As a result, ethyl β-D-glucopyranosyl-(1→4)-α-Dglucopyranosyl-(1→4)-2,3, 6-tri-O-ethyl-β-D-glucopyranoside 7 (GβG αEβ) had the highest surface activity, and its critical micellar concentration (CMC) and γCMC (surface tension at CMC) values of compound 7 were 0.5 mM(ca. 0.03 wt %) and 34.5 mN/m, respectively. The surface tensions of α- and β-glycoside mixtures except for compounds 9 and 10 were almost equal to those of pure compounds. The syntheses of the mixtures of α- and β-glycosides without purification process are easier than those of pure compounds. Thus, the mixtures should be more practical compounds for industrial use as a surfactant.
- Nakagawa, Atsushi,Kamitakahara, Hiroshi
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p. 1671 - 1683
(2011/11/12)
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- Defining oxyanion reactivities in base-promoted glycosylations
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Saccharide oxyanions obtained by base treatment could be employed in glycosylation to give oligosaccharides with high stereo- and regioselectivities.
- Matwiejuk, Martin,Thiem, Joachim
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p. 8379 - 8381
(2011/09/14)
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- (2,6-Dichloro-4-alkoxyphenyl)-(2,4-dichlorophenyl)methyl trichloroacetimidates: Protection of alcohols and carboxylic acids in solution or on polymer support
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(2,6-Dichloro-4-methoxyphenyl)-(2,4-dichlorophenyl)-methyl trichloroacetimidate can be efficiently activated by TMSOTf (10-100 mol%) to react with alcohols and carboxylic acids. Under these conditions a wide variety of alcohols can be transformed into the corresponding ethers in excellent yields with a slight excess of the trichloroacetimidate. The resulting ethers are not susceptible to typical deprotection conditions for benzyl and 4-methoxybenzyl ether groups, however, they can be conveniently deprotected by treatment with 30-50% trifluoroacetic acid in dichloromethane. Polymer-bound (2,6-dichloro-4-alkoxyphenyl)-(2,4-dichlorophenyl)methyl trichloroacetimidate is useful for immobilization of alcohols and carboxylic acids.
- Kurosu, Michio,Li, Kai
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experimental part
p. 3633 - 3641
(2010/03/05)
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- The disarming effect of the 4,6-acetal group on glycoside reactivity: Torsional or electronic?
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An evaluation of whether the well-known deactivating effect of a 4,6-acetal protection group on glycosyl transfer is caused by torsional or an electronic effect from fixation of the 6-OH in the tg conformation was made. Two conformationally locked probe m
- Jensen, Henrik Helligso,Nordstrom, Lars Ulrik,Bols, Mikael
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p. 9205 - 9213
(2007/10/03)
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- Regioselective reductive ring opening of cyclic 1,2- and 1,3-benzylidene acetals
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A combination of polymethylhydrosiloxane (PMHS) and AlCl3 was found to be a superior hydride source for reductive ring opening of cyclic benzylidene acetals of both 1,2- and 1,3-diols.
- Chandrasekhar,Ravindra Reddy,Raji Reddy
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p. 1273 - 1274
(2007/10/03)
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- Hydrogenolysis of the 4,6-o-ketals of glucopyranosides. Configuration-dependent high regio- and stereo-selectivity of the diastereoisomeric acetophenone derivatives
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Hydrogenolysis (reductive cleavage) of the (R) isomers of the acetophenone 4,6-O-derivatives of glucopyranosides with LiAlH4/AlCl3 gives the 4-O-(1′-phenylethyl) ethers with (R) configuration; the corresponding (5) isomers produce the respective (R) 6-O-(1′-phenylethyl) ethers are produced. The hydrogenolysis of other 4,6-O-ketals affords O 4 ether derivatives; the two diastereoisomeric 4,6-O-s-butylidene derivatives (cyclic ketals) give O 4-ethers with the opposite absolute configuration. The stereoselectivity of these reactions is explained by the development of a four-centre transition state. The absolute configuration of the ethers has been determined by means of circular dichroism measurements.
- Hajko, Janos,Szabovik, Gabriella,Kerekgyarto, Janos,Kajtar, Marton,Liptak, Andras
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p. 357 - 363
(2007/10/03)
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- Syntheses of 6-Deoxyhex-5-enopyranosides from 6-Bromo-6-deoxy- or 6-O-p-Tolylsulfonylhexopyranosides by the Use of DBU in DMSO
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Various kinds of nonbranched and methyl-branched 6-deoxyhex-5-enopyranoside derivatives were prepared from 6-bromo-6-deoxy or 6-O-p-tolylsulfonylhexopyranoside in a one-pot procedure by a successive treatment with iodide anion and 1,8-diazabicyclou
- Sato, Ken-ichi,Kubo, Noriyuki,Takada, Ritsuko,Sakuma, Shogo
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p. 1156 - 1165
(2007/10/02)
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- Dialkyl and diaryl boron halides: reductive opening of benzylidene acetals
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Dimethylboron bromide or diphenylboron bromide can be used in combination with borane to achieve the regiocontrolled conversion of benzylidene acetals to their corresponding hydroxy benzyl ethers with moderate to high yields.
- Guindon, Yvan,Girard, Yves,Berthiaume, Sylvie,Gorys, Vida,Lemieux, Rene,Yoakim, Christiane
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p. 897 - 902
(2007/10/02)
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- SYNTHESIS AND MASS SPECTRA OF 4-O-ACETYL-1,5-ANHYDRO-2,3,6-TRI-O-ETHYL-D-GLUCITOL AND THE POSITIONAL ISOMER OF 4-O-ACETYL-1,5-ANHYDRO-DI-O-ETHYL-O-METHYL-D-GLUCITOL AND 4-O-ACETYL-1,5-ANHYDRO-O-ETHYL-DI-O-METHYL-D-GLUCITOL
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Reductive cleavage of fully methylated, partially O-ethylated cellulose or fully ethylated, partially O-methylated cellulose and subsequent acetylation had previously been shown to produce 4-O-acetyl-1,5-anhydro-2,3,6-tri-O-methyl-, -6-Oethyl-2,3-di-O-methyl-, -3-O-ethyl-2,6-di-O-methyl-, -2-O-ethyl-3,6-di-O-methyl-, -2,3,di-O-ethyl-6-O-methyl-, -2,6-di-O-ethyl-3-O-methyl-, -3,6-di-O-ethyl-2-O-methyl-, and -2,3,6-tri-O-ethyl-D-glucitol.Described herein is the independent synthesis of these derivatives, except for the first (which had been reported); and their (1)H-n.m.r. spectra, chemical-ionization (NH3) mass spectra, and electron-impact mass spectra are tabulated.
- Zeller, Samuel G.,D'Ambra, Anello J.,Rice, Michael J.,Gray, Gary R.
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- Preparation of Some Partially Methylated Galactosides from Methyl α-D-Galactopyranoside
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Methyl 2,3,6-tri-O-methyl-α-D-galactopyranoside (3) and methyl 2,6-di-O-methyl-α-D-galactopyranoside (2) have been synthesized starting from isopropylidene derivatives of methyl α-D-galactopyranoside.
- Roy, Abhijit,Batavyal, Lakshmi,Roy, Nirmolendu
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p. 498 - 499
(2007/10/02)
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- SYNTHESIS OF METHYL DERIVATIVES OF URONIC ACIDS. II. SYNTHESIS OF THE 2,3-, 2,4-, AND 2,4-DI- AND 2,3,4-TRI-O-MEETHYL ETHERS OF METHYL (METHYL α-D-GALACTOPYRANOSID)URONATE
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Unidirectional methods are proposed for the synthesis of the 2,3-, 2,4-, and 3,4-di-, and 2,3,4-tri-O-methyl ethers of methyl (methyl α-D-galactopyranosid)uronate by the oxidation (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-galactosid)uronic acids followed by the esterification with CH2N2 and catalytic hydrogenolysis of the benzyl groups.
- Grishkovets, V. I.,Zemlyakov, A. E.,Chirva, V. Ya.
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p. 259 - 261
(2007/10/02)
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