When the Salmonella trisaccharide epitope, methyl 3-O-(3,6-dideoxy-α-- xylo-hexopyranosyl)-2-O-(α--galactopyranosyl)-α--mannopyranoside 12 is bound by a monoclonal antibody Sel 55.4, the 3,6-dideoxy-α--hexose is completely buried, while the galactopyranosyl mannopyranosyl units lay across the protein surface. Crystallography of an antibody complexed with 12 also shows that the galactose residue is the most exposed saccharide. A simplified strategy to synthesize 12 and analogues modified at the galactose residue is described. Monosaccharide building blocks containing benzyl ether and ester protecting groups were used for efficient assembly of trisaccharides that can be deprotected by a single hydrogenolysis step, or occasionally preceded by a transesterification stage. Glycosylation of methyl 2-O-benzoyl-4,6-di-O-benzyl-α--mannopyranoside 4 by 2,4-di-O-benzyl-3,6-dideoxy--xylo-hexopyranosyl chloride 8 affords after transesterification the disaccharide acceptor 10. This disaccharide serves as a universal acceptor for glycosylation by glycosyl donors that lead, following facile deprotection, to the α- and β--galacto, α- and β--gluco, and 2-amino-2-deoxy-α-- galactotrisaccharides 12, 14, 17, 18 and 21. Only a small change in binding energy Δ(ΔG) occurs when the α--galactopyranosyl residue of 12 is replaced by either an α--glucopyranosyl 17 or a 2-amino-2-deoxy α--galactopyranosyl unit 21. Whereas binding of the β--glucopyranose congener 18 was tolerated by the antibody, the β--galactopyranose analogue 14, showed a 250 fold loss of affinity. These relative activities of the trisaccharide congeners are correlated with a solved crystal structure for the antibody complex with 12.