Influence of the solvent in low temperature glycosylations with O-(2,3,5,6-tetra-O-benzyl-â-D-galactofuranosyl) trichloroacetimidate for 1,2-cis á-D-galactofuranosylation

GABRIEL GOLA; MARIANO J. TILVE; CAROLA GALLO-RODRIGUEZ

CARBOHYDRATE RESEARCH

ELSEVIER SCI LTD

Año: 2011

0008-6215

Glycosylation studies for the construction of 1,2-cis ?¿-linkages with O-(2,3,5,6-tetra-O-benzyl-?À-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 ?¿-D-configuration. In contrast, acetonitrile strongly favored the ?À-D-configuration, whereas no selectivities were observed with Et2O. The use of thiophene as an additive did not enhance the ?¿-D-selectivity as in the pyranose counterpart. Although selectivities strongly depended on the acceptor, trichloroacetimidate 1 constitutes a valuable donor for the synthesis of ?¿-D-Galf-(1?¨2)-L-Rha and ?¿-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.