Currently, as immunosuppressive agents, for example, cyclosporine, tacrolimus, and the like are utilized, which suppress the production of cytokines such as IL-2. In recent years, research has been conducted with regard to compounds which suppress the activity of the immune system by inducing a decrease in the number of lymphocytes in the blood. For example, fingolimod shows no action of suppressing the production of cytokines in vitro, but acts as a S1P receptor agonist after being phosphorylated in vivo, inducing a decrease in the number of lymphocytes in the blood. This allows the activity of the immune system to be suppressed (see, e.g., Non-Patent Document 1).
As compounds inducing a decrease in the number of lymphocytes in the blood by means of a mechanism other than as a S1P receptor agonist, 2-acetyl-4-tetrahydroxybutylimidazole (THI) (see, for example, Patent Document 1) is known. THI induces a decrease in the number of lymphocytes in the blood by inhibiting S1P lyase (see, e.g., Non-Patent Document 2, Non-Patent Document 3, etc.).
As such S1P lyase inhibitors, other than THI, an imidazole derivative having a polyol as a substituent (see, e.g., Patent Document 2, Patent Document 3, Non-Patent Document 4, Non-Patent Document 5, etc.), an imidazole derivative with a hetero ring being bonded directly thereto (see, e.g., Patent Document 4, Patent Document 5, Non-Patent Document 4, Non-Patent Document 5, etc.), and the like are known. Further, as compounds inducing a decrease in the number of lymphocytes, a thiazole derivative having a polyol as a substituent (see, e.g., Patent Document 6), and the like are known.