Synthesis of 2-(4-trifluoroacetamidophenyl)ethyl O-(L-glycero-alpha-D-manno-heptopyranosyl)-(1----7)-O-(L-glycero-alpha- D-manno- heptopyranosyl)-(1----3)-L-glycero-alpha-D-manno-heptopyranoside, corresponding to the heptose region of the Salmonella Ra core structure.

The title trisaccharide was synthesized from methyl 2,3,4-tri-O-benzyl-L-glycero-alpha-D-manno-heptopyranoside by acetolysis, followed by conversion into ethyl thioglycosides and also glycosyl bromides, which were both used in glycosylation reactions. In glycosylations using thioglycosides as glycosyl donors, N-iodosuccinimide-silver triflate and dimethyl(methylthio)sulfonium triflate were used as promoters, and in glycosylations with glycosyl bromides silver triflate was used. The protecting groups introduced into intermediates during the synthesis of the title trisaccharide were designed to allow later glycosylation at O-3' to give larger oligosaccharide fragments of the Salmonella LPS core region, and also to allow the introduction of phosphate groups at O-4 and O-4', a structural element that is suggested to be present in the Ra core.