title: Influence of the solvent in low temperature glycosylations with O-(2,3,5,6-tetra-O-benzyl-β-D-galactofuranosyl) trichloroacetimidate for 1,2-cis α-D-galactofuranosylation.
abstract: Glycosylation studies for the construction of 1,2-cis α-linkages with O-(2,3,5,6-tetra-O-benzyl-β-D-galactofuranosyl) trichloroacetimidate (1) and several acceptors, including D-mannosyl and l-rhamnosyl derivatives were performed. The reactions were conducted at low temperatures using CH(2)Cl(2), Et(2)O, and acetonitrile as solvents. A non-participating solvent such as CH(2)Cl(2) at -78°C, favored the α-D-configuration. In contrast, acetonitrile strongly favored the β-D-configuration, whereas no selectivities were observed with Et(2)O. The use of thiophene as an additive did not enhance the α-D-selectivity as in the pyranose counterpart. Although selectivities strongly depended on the acceptor, trichloroacetimidate 1 constitutes a valuable donor for the synthesis of α-D-Galf-(1→2)-l-Rha and α-D-Galf-(1→6)-D-Man. As these motifs are present in pathogenic microorganisms, these procedures described here are useful for the straightforward synthesis of natural oligosaccharides.
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: Gabriel
authors.initials: G
authors.lastname: Gola
authors.forename: Mariano J
authors.initials: MJ
authors.lastname: Tilve
authors.forename: Carola
authors.initials: C
authors.lastname: Gallo-Rodriguez
mesh_terms: D000081:Acetamides; D000942:Antigens, Bacterial / Q000737:chemistry; D000946:Antigens, Fungal / Q000737:chemistry; D001419:Bacteria / Q000737:chemistry; D062845:Chloroacetates; D002855:Chromatography, Thin Layer; D003080:Cold Temperature; D005658:Fungi / Q000737:chemistry; D005663:Furans / Q000737:chemistry*; D006001:Glycoconjugates / Q000138:chemical synthesis*; D006031:Glycosylation; D009682:Magnetic Resonance Spectroscopy; D009844:Oligosaccharides / Q000138:chemical synthesis*; D012997:Solvents; D013237:Stereoisomerism; D014238:Trichloroacetic Acid / Q000737:chemistry
chemical_list: D000081:Acetamides; D000942:Antigens, Bacterial; D000946:Antigens, Fungal; D062845:Chloroacetates; D005663:Furans; D006001:Glycoconjugates; D009844:Oligosaccharides; D012997:Solvents; D014238:Trichloroacetic Acid; C009528:trichloroacetamide