The 2'-amino-2'-deoxy, 6-amino-6-deoxy, and 6-carboxy analogs of the reference inhibitors 2-(trimethylsilyl)ethyl (alpha-D-galactopyranosyl)-(1-->4)-ss-D-galactopyranoside were synthesized and evaluated as inhibitors of the binding of the Escherichia coli-derived pilus protein PapGj96, using an ELISA assay. The inhibitory efficiencies (Krel; relative to the reference inhibitor) were: 157,13, and < 8, respectively. The results support the previously proposed combining site model, where the protein carries a negatively charged amino acid residue near HO-2' and HO-6 of the galabio-side.