Bromoacetylation of methyl 2,4-di-O-benzoyl-3-deoxy-3-fluoro-β-D-galactopyranoside, followed by the cleavage of the methoxy group from the resulting 6-O-bromoacetyl derivative 2 with 1,1-dichloromethyl methyl ether gave 2,4-di-0-benzoyl-6-0-bromoacetyl-3-deoxy-3-fluoro-α-D-galactopyranosyl chloride (3). Reaction of 3 with methyl 2,3,4-tri-O-benzoyl-β-D-galactopyranoside promoted by silver trifluoromethanesulfonate afforded methyl0-(2,4-di-O-benzoyl-6-O-bromoacetyl-3-deoxy-3-fluoro-β-D-galacto-pyranosyl)-(1→6)-2,3,4-tri-O-benzoyl-β-D-galactopyranoside (5).O-Debromoacetylation of5with thiourea gave the disaccharide nucleophile6which was condensed with 2,3,4,6-tetra-O-benzoyl-α-D-galactopyranosyl bromide to afford the expected β-(trans)-linked trisaccharide derivative7. Debenzoylation of7gave the methyl β-glycoside 8 of the (1→6)-linked D-galactotriose having the HO-3 of the internal residue replaced by a fluorine atom. Compound 8 was used to further delineate the subsites in the combining area of the monoclonal anti-(1→6)-β-D-galactan-specific immunoglobulin IgA J539.