Synthetic studies toward the anthrax tetrasaccharide: alternative synthesis of this antigen

The synthesis of the anthrax tetrasaccharide, amenable for conjugation, has been envisaged by both [2+2] and [1+3] approaches from D-fucose and L-rhamnose. The successful route reported herein relies on a [1+3] strategy in which the 1,2-trans-glycosidic linkages have been secured using a participating group at the 2-position of the donors using conventional thio as well as trichloroacetimidate glycosylation chemistry. The exchange of the ester to benzyl protective groups on the rhamnosyl moiety was key to achieve the final assembly and functionalization of the tetrasaccharide.