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

• Published in: Carbohydrate research 2011-09, Vol.346 (12), p.1495-1502
• Main Authors: Gola, Gabriel, Tilve, Mariano J., Gallo-Rodriguez, Carola
• Format: Article
• Language: English
• Subjects: 1,2-Cis; Acetamides; acetonitrile; Antigens, Bacterial - chemistry; Antigens, Fungal - chemistry; Bacteria - chemistry; Chloroacetates; Chromatography, Thin Layer; Cold Temperature; Diastereoselectivity; Fungi - chemistry; Furans - chemistry; Galactofuranose; Glycoconjugates - chemical synthesis; Glycosylation; Magnetic Resonance Spectroscopy; methylene chloride; microorganisms; oligosaccharides; Oligosaccharides - chemical synthesis; Solvents; Solvents effects; Stereoisomerism; temperature; thiophene; Trichloroacetic Acid - chemistry; Trichloroacetimidate
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/j.carres.2011.04.005

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 CH2Cl2, Et2O, and acetonitrile as solvents. A non-participating solvent such as CH2Cl2 at −78°C, favored the α-d-configuration. In contrast, acetonitrile strongly favored the β-d-configuration, whereas no selectivities were observed with Et2O. 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.