Purity >98%. FTY720 is a novel immune modulator that prolongs allograft transplant survival in numerous models by inhibiting lymphocyte emigration from lymphoid organs. FTY720 is phosphorylated by sphingosine kinases in vivo, and then acts as a potent agonist at four of the five sphingosine-1-phosphate (S1P) receptors. FTY720 (S)-phosphate is the single stereoisomer formed by phosphorylation of FTY720 in vivo, as determined in rats and humans. It exhibits Ki values of 2.1, 5.9, 23, and 2.2 nM for S1P1, respectively, whereas the R enantiomer binds with 5 to 130-fold lower affinity. FTY720 (S)-phosphate causes internalization of S1P1 on lymphocytes, abrogating S1P-dependent egress of lymphocytes from lymphoid organs. It also enhances endothelial barrier function, stimulates the activity of the sphingosine transporter Abcb1 and the leukotriene C4 transporter Abcc16 and inhibits cytosolic phospholipase A2 activity.