N-[2(4-(-Octylphenyl))butanoic Acid] Fingolimod-d4 is the isotopic analog of N-[2(4-(-Octylphenyl))butanoic Acid] Fingolimod. N-[2(4-(-Octylphenyl))butanoic Acid] Fingolimod, is an impurity of Fingolimod (F805000, HCl salt). Fingolimod is a novel immune modulator that prolongs allograft transplant survival in numerous models by inhibiting lymphocyte emigration from lymphoid organs.