Glycosylation studies on conformationally restricted 3,5-O-(di-tert-butylsilylene)-d-galactofuranosyl trichloroacetimidate donors for 1,2-cis α-d-galactofuranosylation
作者:Mariano J. Tilve、Carola Gallo-Rodriguez
DOI:10.1016/j.carres.2011.10.004
日期:2011.10
Conformationally restricted 3,5-O-di-tert-butylsilylene-D-galactofuranosyl trichloroacetimidate donors were synthesized from allyl alpha-D-galactofuranoside for the construction of 1,2-cis alpha-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 alpha-selectivities were obtained at -78 degrees C in diethyl ether as solvent. 6-O-Acetyl substitution on constrained donor increased the alpha-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 alpha-selectivity suggesting a participating effect in the reaction intermediate. (C) 2011 Elsevier Ltd. All rights reserved.