through five specific G-protein coupled receptors numbered S1P1 through S1P5. Agonists of the S1P1 receptor block the egress of T-lymphocytes from thymus and lymphoid organs and hold promise for the oral treatment of autoimmune disorders. Here, we report on the discovery and detailed structure−activity relationships of a novel class of S1P1 receptoragonists based on the 2-imino-thiazolidin-4-one scaffold