- Conformationally restricted 3,5-O-(di-tert-butylsilylene)-d- galactofuranosyl thioglycoside donor for 1,2-cis α-d-galactofuranosylation
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A conformationally restricted 2-O-benzyl-3,5-O-di-tert-butylsilylene- β-d-thiogalactofuranoside donor was prepared from benzyl α-d-galactofuranoside and its donor capability was studied for stereoselective 1,2-cis α-d-galactofuranosylation. An unusual chemical behavior in benzylation and hydrogenolysis reactions was observed after the introduction of the 3,5-O-di-tert-butylsilylene protecting group into the galactofuranosyl moiety. The influence of the solvent, temperature, and activating system was evaluated. The NIS/AgOTf system, widely used in 1,2-cis β-arabinofuranosylation, was not satisfactory enough for 1,2-cis galactofuranosylation. However, moderate to high α-selectivity was obtained with all the acceptors employed when using p-NO2PhSCl/AgOTf as a promoting system, in CH2Cl2 at -78 °C. The order of the addition of the reactants (premixing or preactivation) did not affect substantially the stereochemical course of the glycosylation reaction. The α-d-Galf-(1→6)-d-Man linkage was achieved with complete diastereoselectivity by preactivation of the conformationally constrained thioglycoside donor.
- Tilve, Mariano J.,Gallo-Rodriguez, Carola
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- Glycosylation studies on conformationally restricted 3,5-O-(di-tert- butylsilylene)-d-galactofuranosyl trichloroacetimidate donors for 1,2-cis α-d-galactofuranosylation
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Conformationally restricted 3,5-O-di-tert-butylsilylene-d-galactofuranosyl trichloroacetimidate donors were synthesized from allyl α-d- galactofuranoside for the construction of 1,2-cis α-d-galactofuranosyl linkages. Glycosylation reactions were performed
- Tilve, Mariano J.,Gallo-Rodriguez, Carola
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experimental part
p. 2838 - 2848
(2012/01/03)
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