- Synthesis of positional thiol analogs of β-D-galactopyranose
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Approaches toward the synthesis of thio-β-D-galactose derivatives are described. These compounds were prepared from the parent carbohydrates: D-galactose, methyl β-D-galactoside and methyl β-D-glucoside, respectively. It was found that not only the strategies of protecting group introduction and selective deprotection, but also the choices of solvent and nucleophilic reagent concentration were crucial to allow the efficient introduction of sulfur at different positions of the galactose ring. The effects from the solvent, the nucleophilic reagent concentration, and the protecting group patterns have been investigated. The results clearly show that ester protecting groups play highly important roles for the synthesis of thio-containing carbohydrates, requiring nonpolar solvents to suppress the neighboring group participation. For the Lattrell-Dax (nitrite-mediated) inversion reaction, employed in the synthetic route to the 2-thio-β-D- galactoside, intramolecular nucleophilic attack, as well as stronger stereospecific ester activation, are necessary to overcome hindrance from 4,6-O-benzylidene protection. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Pei, Zhichao,Dong, Hai,Caraballo, Remi,Ramstroem, Olof
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p. 4927 - 4934
(2008/03/14)
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- Reagent-dependent regioselective control in multiple carbohydrate esterifications
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(Chemical Equation Presented) Regioselective control in organotin-mediated multiple acylation of carbohydrates is presented. The acylation reagent could be efficiently used to direct the product formation. Reagent-dependent thermodynamic and kinetic contr
- Dong, Hai,Pei, Zhichao,Bystroem, Styrbjoern,Ramstroem, Olof
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p. 1499 - 1502
(2007/10/03)
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- Stereospecific ester activation in nitrite-mediated carbohydrate epimerization
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The Lattrell-Dax method of nitrite-mediated substitution of carbohydrate triflates is an efficient method to generate structures of inverse configuration. In the present study, epimerization of gluco- and galactopyranoside derivatives to the corresponding
- Dong, Hai,Pei, Zhichao,Ramstroem, Olof
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p. 3306 - 3309
(2007/10/03)
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- A mild and efficient approach for the regioselective silyl-mediated protection-deprotection of C-4 hydroxyl group on carbohydrates
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A regioselective route is reported, which makes the free 4-OH group of hexopyranoses and derivatives easily and rapidly available. This protocol shows high efficiency on intermediates, such as 1a, which contain a TIPS protective group at C-6 and necessarily a benzoyl group at C-4. Treatment of 1a with TBAF cleaves the TIPS protecting group and gives rise to an intramolecular migration of the benzoyl group at C-4 to the less crowded C-6 position.
- Graziani, Andrea,Passacantilli, Pietro,Piancatelli, Giovanni,Tani, Simona
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p. 3857 - 3860
(2007/10/03)
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- NOVEL D-GLUCANS OBTAINED BY DIMETHYL SULFOXIDE EXTRACTION OF THE LICHENS Letharia vulpina, Actinogyra muehlenbergii, AND AN Usnea SP.
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Extraction of certain lichens with cold dimethyl sulfoxide provided a β-D-glucan virtually free of contaminating α-D-glucan and galactomannan.Applied to Letharia vulpina, the method gave β-D-glucan, and extraction of the residue with hot water followed by cooling gave α-D-glucan.From Usnea sp. a β-D-glucan was isolated, but little α-D-glucan was present.Extraction of Actinogyra muehlenbergii provided a (16)-linked β-D-glucopyranan containing one acetyl group of every 8-9 glucosyl units, being present almost exclusively as monosubstituent at O-2, O-3, and O-4.
- Iacomini, Marcello,Gorin, Philip A. J.,Baron, Madalena,Tulloch, Alexander P.,Mazurek, Mytosk
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p. 117 - 126
(2007/10/02)
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- Dioxolanylium Ions Derived from Carbohydrates. IX. Rearrangement between Dioxolanylium and Dioxanylium Ions
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The formation of 4,6-acetoxonium and benzoxonium ion derivatives of methyl gluco-, manno-, galacto- and idopyranosides from the 6-azido-6-deoxy compounds on treatment with nitrosonium ion is described and the formation and rearrangement of the 3,5-benzoxonium ion derived from methyl α-d-xylofuranoside discussed.
- Jacobsen, Steffen
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p. 157 - 164
(2007/10/02)
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