Novel Immunomodulator FTY720 Is Phosphorylated in Rats and Humans To Form a Single Stereoisomer. Identification, Chemical Proof, and Biological Characterization of the Biologically Active Species and Its Enantiomer

In vivo phosphorylation of FTY720 (1) in rats and humans resulted exclusively in the biologically
active (S)-configured enantiomer, which was proven by an ex vivo o-phthaldialdehyde
derivatization protocol especially elaborated for phosphates of 1. Starting from the prochiral
amino alcohol 1, racemic and enantiomerically pure phosphates of 1 were synthesized. Pure
enantiomers were obtained after purification of a partially protected key intermediate on an
enantioselective support. The absolute stereochemistry was determined by X-ray diffraction.