Development of Fully and Partially Protected Fucosyl Donors for Oligosaccharide Synthesis

The use of fully and partially tert-butyldimethylsilyl (TBDMS) protected fucose thioglycosides as glycosyl donors for oligosaccharide synthesis is described. Both the trisilyl- and disilyl-protected thioglycoside donors were prepared, and their reactivity under a range of activation conditions was investigated. Both silyl-protected donors were found to give good yields of the desired α products and the silyl protecting groups could be removed in the presence of unsaturated bonds. The disilyl-protected donor was found to behave as an efficient, partially protected glycosyl donor. The synthetic scope and limitations of these new donors is presented. Both donors were applied to the synthesis of a Lewis X trisaccharide displaying a propargyl group at the anomeric position. It was determined that the additional steric bulk of the TBDMS group inferred unusual reactivity on these fucosyl donors.