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.