FTY720 (2-amino-2-[2-(4-octylphcnyl)ethyl]-l,3-propanediol hydrochloride), a novel synthetic immunosuppressant led by modification of ISP-I (myriocin, thermozymocidin) displayed potent immunosuppressive activity both b~ ~tro and/~ vivo. As reported in the preceding communication 1, simplification of the structure of ISP-I including removal of the side chain functionalities as well as elimination of chiral centers led to 2-alkyl-2-amino-l,3-propanediols such as la-c (Figure 1). Some of them displayed more potent immunosuppressive activity than ciclosporin, which is currently used clinically. In addition to that, the toxicity of ISP-I was reduced to a considerable extent although it was still insufficient. Here, we displaced a part of the alkyl chain of la-e with sterically equivalent 1,4-phenylene group in expectation of modifying their physicochemical, pharmacological, toxicological, or pharmacokinetical property. In this communication, we describe the design, synthesis, and structure-activity relationships of thus modified compounds.