The autoinducer (AI) that initiates the quorum sensing (QS) signaling cascade in Pseudomonas aeruginosa is an acyl-homoserine lactone (acyl-HSL). We initiated a study of the requirements for binding of the AI to its protein effector LasR by synthesizing a library of analogs with the HSL moiety replaced with different amines and alcohols. We tested each compound for both agonist and antagonist activity using a QS-controlled reporter gene assay and found several new agonists and antagonists. A representative antagonist was further tested for its ability to inhibit virulence factors. This data progresses our understanding of the LasR-AI interaction toward the rational design of therapeutic inhibitors of QS.