- Tin-mediated regioselective benzylation and allylation of polyols: Applicability of a catalytic approach under solvent-free conditions
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The first catalytic version of the stannylene-mediated benzylation and allylation of polyols is reported. The methodology is based on a simple solvent-free protocol that significantly advances, in terms of both experimental ease and synthetic scope, the a
- Giordano, Maddalena,Iadonisi, Alfonso
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p. 213 - 222
(2014/01/17)
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- Deoxy and deoxyfluoro analogues of acetylated methyl β-D- xylopyranoside - Substrates for acetylxylan esterases
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Four modified substrates for acetylxylan esterases, 2-deoxy, 3-deoxy, 2-deoxy-2-fluoro, and 3-deoxy-3-fluoro derivatives of di-O-acetylated methyl β-D-xylopyranoside were synthesized via 2,3-anhydropentopyranoside precursors. Methyl 2,3-anhydro-4-O-benzyl-β-D-ribopyranoside was transformed into methyl 2,3-anhydro-4-O-benzyl-β-D-lyxopyranoside in three steps. The epoxide ring opening of 2,3-anhydropentopyranosides was accomplished either by hydride reduction or hydrofluorination. Methyl β-D-xylopyranoside 2,3,4-tri-O-, 2,4-di-O-, and 3,4-di-O-acetates, and the prepared diacetate analogues were tested as substrates of acetylxylan esterases from Schizophyllum commune and Trichoderma reesei. Measurement of their rate of deacetylation pointed to unique structural requirements of the enzymes for the substrates. The enzymes differed particularly in the requirement for the trans vicinal hydroxy group in the deacetylation at C-2 and C-3 and in the tolerance to the presence of trans vicinal acetyl groups esterifying the OH group at C-2 and C-3.
- Mastihubova, Maria,Biely, Peter
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p. 2101 - 2110
(2007/10/03)
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- Regioselective Protection Strategies for D-Xylopyranosides
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The acylation of D-xylopyranosides can be effected at any position by selective hydroxyl activation with dibutyltin oxide in refluxing benzene and proper choice of starting anomer.Methyl 4-O-benzyl-β-D-xylopyranoside, available from methyl 2,3-O-isopropyl
- Helm, Richard F.,Ralph, John,Anderson, Laurens
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p. 7015 - 7021
(2007/10/02)
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- Regioselective Monoalkylation of Non-protected Glycopyranosides by the Dibutyltin Oxide Method
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Regioselective monoalkylation of some pento- and hexopyranosides (Me β-L-Ara, Ph α-L-Ara, Me α-D-Xyl, Me β-D-Xyl, Me α-D-Glc, Me β-D-Glc, Me α-D-Gal, Me β-D-Gal, and Me α-D-Man) was examined by using the dibutyltin oxide method without protecting the hydroxyl groups.By this method, alkylation proceeds more or less in the same fashion as reported for acylation (through the formation of cyclic tin intermediates) and selectively activates an equatorial hydroxyl group which has an oxygenated function (OH or OMe) in a cis relationship at an adjacent position, even in the presence of a more reactive primary hydroxyl group.However, in some instances the position of activation is different.Various monoalkyl ethers thus prepared were identified by analyses of their carbon-13 nuclear magnetic resonance spectra.Keywords-regioselective monoalkylation; glycopyranoside; dibutyltin oxide; cis-vicinal glycol; benzylation; allylation; methoxymethylation; methylation;13C-NMR
- Haque, Mohammed Ekramul,Kikuchi, Tohru,Yoshimoto, Kimihiro,Tsuda, Yoshisuke
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p. 2243 - 2255
(2007/10/02)
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