Pseudomonas aeruginosa employs pili to mediate adherence to epithelial cell surface receptors. Previously, it has been shown that the pilus adhesin of P. aeruginosa PAK binds to the ganglioside asialo-GM1. In particular, it was found that the carbohydrate sequence beta-D-GalNAc(1-->4)beta-D-Gal is the minimal carbohydrate receptor sequence of asialo-GM1. To study the binding specificity of P. aeruginosa, O-modified and N-modified sugar analogs, where each hydroxyl group was substituted either by O-methyl or O-propyl and the acetamido group was changed to a propionamido group, were synthesized. The sugar analogs were evaluated as inhibitors in a competitive solid phase binding assay. The results demonstrate that the pili of P. aeruginosa PAK accepts a variety of sugar analogs possessing the sequence beta-D-GalNAc(1-->4)beta-D-Gal. Most sugar analogs bind with a similar order of magnitude (50% inhibitory concentration (IC50) = 60-130 microM) except for the 2-O-propyl derivative 7 (IC50 = 8 +/- 4 microM) compared with an IC50 of 79 +/- 18 microM for the native compound. The significant increase in binding affinity of 2-O-propyl derivative 7 suggests that improved inhibitors of adhesion may be prepared by introducing a hydrophobic side chain at the 2-position of galactose.