Synthesis of a hexasaccharide corresponding to part of the heptose-hexose region of the Salmonella Ra core, and a penta- and a tetra-saccharide that compose parts of this structure.

The synthesis of the hexasaccharide 2-(4-trifluoroacetamidophenyl)ethyl O-alpha-D-galactopyranosyl-(1-->3)-[O-alpha-D-galactopyranosyl-(1-->6)]- O-alpha-D-glucopyranosyl-(1-->3)-[O-L-glycero-alpha-D-manno-heptopyranos yl- (1-->7)]-O-L-glycero-alpha-D-manno-heptopyranosyl-(1-->3)-L-glycero-alph a-D- manno-heptopyranoside, corresponding to the heptose and part of the hexose region in the Salmonella Ra core, is described. Syntheses of the pentasaccharide 2-(4-trifluoroacetamidophenyl)ethyl O-alpha-D-galactopyranosyl-(1-->3)-O-alpha-D-glucopyranosyl-(1-->3)-[O-L - glycero-alpha-D-manno-heptopyranosyl-(1-->7)]-O-L-glycero-alpha-D-manno- heptopyranosyl-(1-->3)-L-glycero-alpha-D-manno-heptopyranoside and the tetrasaccharide 2-(4-trifluoroacetamidophenyl)ethyl O-alpha-D-glucopyranosyl-(1-->3)-[O-L-glycero-alpha-D-manno-heptopyranos yl- (1-->7)]-O-L-glycero-alpha-D-manno-heptopyranosyl-(1-->3)-L-glycero-alph a-D- manno-heptopyranoside are also described. Coupling of methyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D- glucopyranoside and methyl 2-O-benzyl-4,6-O-benzylidene-3-O-(2,3,4,6-tetra-O-benzyl-alpha-D- galactopyranosyl)-1-thio-beta-D-glucopyranoside to a triheptoside derivative with a free HO-3', using dimethyl(methylthio)sulfonium triflate and N-iodosuccinimide-silver triflate as promoters, gave the protected tetra- and penta-saccharide, respectively. Removal of the benzylidene group from the pentasaccharide followed by a regio- and stereo-selective coupling using halide-assisted conditions and 2,3,4,6-tetra-O-benzyl-alpha-D- galactopyranosyl bromide as donor gave the protected hexasaccharide. Deprotection then gave the target structures.