Sphingosine-1-phosphate (S1P) is a bioactive lipid that exhibits a broad spectrum of biological activities including cell proliferation, survival, migration, cytoskeletal organization, and morphogenesis. It exerts its activity by binding to five distinct G protein-coupled receptors, S1P1/EDG-1, S1P2/EDG-5, S1P3/EDG-3, S1P4/EDG-6, and S1P5/EDG-8. W140 is an inactive enantiomer of W146, a selective S1P1 antagonist (Ki = 77 nM), that binds to the S1P1 receptor with a Ki of 4.6 μM (2a = W146; 2b = W140 in supplemental material). It exhibits no biological activity in vivo and can therefore serve as an effective control compound for experiments involving W146.