title: Conformationally restricted 3,5-O-(di-tert-butylsilylene)-D-galactofuranosyl thioglycoside donor for 1,2-cis α-D-galactofuranosylation.
abstract: 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.
authors.affiliation: CIHIDECAR, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina.
authors.forename: Mariano J
authors.initials: MJ
authors.lastname: Tilve
authors.affiliation: CIHIDECAR, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina. Electronic address: cgallo@qo.fcen.uba.ar.
authors.forename: Carola
authors.initials: C
authors.lastname: Gallo-Rodriguez
mesh_terms: D002073:Butanes / Q000737:chemistry; D002236:Carbohydrate Conformation; D060326:Chemistry Techniques, Synthetic; D006031:Glycosylation; D012821:Silanes / Q000737:chemistry; D012997:Solvents; D013237:Stereoisomerism; D013862:Thiogalactosides / Q000138:chemical synthesis / Q000737:chemistry*; D013865:Thioglycosides / Q000737:chemistry*
chemical_list: C000598995:3,5-O-di-tert-butylsilylene-beta-D-thiogalactofuranoside; D002073:Butanes; D012821:Silanes; D012997:Solvents; D013862:Thiogalactosides; D013865:Thioglycosides; C512229:di-tert-butylsilylene
keywords: 1,2-cis; Galactofuranose; Glycosylation; Protecting groups; Solvents effects; Thioglycoside