Bacterial quorum sensing has received much attention in recent years because of its relevance to pathological events such as biofilm formation. Based on the structures of two lead inhibitors (IC50: 35-55 microM) against autoinducer-2-mediated quorum sensing identified through virtual screening, we synthesized 39 analogues and examined their inhibitory activities. Twelve of these new analogues showed equal or better inhibitory activities than the lead inhibitors. The best compound showed an IC50 value of approximately 6 microM in a whole-cell assay using Vibrio harveyi as the model organism. The structure-activity relationship is discussed herein.