Effect of Anomeric Configuration on Stereocontrolled α-Glycosylation of L-Fucose.

In this letter, we report an approach to the stereoselective α- glycosylation of L-fucose that is exemplified by effect of anomeric configuration. The neighboring group participation is not compatible with α-glycosylation of L-fucose, therefore the remote participation by 4-OBz was employed to control the formation of 1,2-cis-glycosidic bond. Furthermore, we found the anomeric configuration of fucose donor is crucial to stereoselectivity of the glycosylated products. The α/β-mixed products were generated by using β-anomeric donor while the glycosyl donor in α configuration yielded products in high α-selectivity possibly due to the distinct pathway to forming the key intermediates. This phenomenon supplies the basis for the synthesis of complicated natural carbohydrates containing fucose α-glycoside, such as fucoidans, fucosylated N-glycans, and fucosylated chondroitin sulfates, etc. [ABSTRACT FROM AUTHOR]