The present invention encompasses compounds of Formula I: as well as the pharmaceutically acceptable salts thereof. The compounds are S1P.sub.1/Edg1 receptor agonists and thus have immunosuppressive, anti-inflammatory and hemostatic activities by modulating leukocyte trafficking, sequestering lymphocytes in secondary lymphoid tissues, and enhancing vascular integrity. The invention is also directed to pharmaceutical compositions containing such compounds and methods of treatment or prevention.