Modulators of sphingosine phosphate receptor-1 (S1P1) have recently been focused as a suppressant of autoimmunity. We have discovered a 4-ethylthiophene-based S1P1 agonist 1-({4-Ethyl-5-[5-(4-phenoxyphenyl)-1, 2, 4-oxadiazol-3-yl]-2-thienyl} methyl) azetidine-3- carboxylic acid (CS-2100, 8) showing potent S1P1 agonist activity against S1P3 and an excellent in vivo potency. We report herein the synthesis of CS-2100 (8) and ...