Glycosylation studies on conformationally restricted 3,5-O-(di-tert-butylsilylene)-D-galactofuranosyl trichloroacetimidate donors for 1,2-cis a-D-galactofuranosylation

MARIANO J. TILVE; CAROLA GALLO -RODRIGUEZ

CARBOHYDRATE RESEARCH

ELSEVIER SCI LTD

Año: 2011 vol. 346 p. 2838 - 2848

0008-6215

Conformationally restricted 3,5-O-di-tert-butylsilylene-D-galactofuranosyl trichloroacetimidate donors were synthesized from allyl a-D-galactofuranoside for the construction of 1,2-cis a-D-galactofuranosyl linkages. Glycosylation reactions were performed with several acceptors, including D-galactono-1,4-lactone, D-rhamnopyranosyl, and D-mannopyranosyl derivatives. The influence of the temperature and the reaction solvents was evaluated, as well as the 6-O-substitution pattern of the donor. The higher a-selectivities were obtained at 78 C in diethyl ether as solvent. 6-O-Acetyl substitution on constrained donor increased the a-selectivity compared to the 6-O-benzyl substitution. Almost no selectivities were observed in the non-participating solvent CH2Cl2. In contrast, ethereal solvents enhanced the a-selectivity suggesting a participating effect in the reaction intermediate.