Ibuprofen is an α-arylpropionic acid used largely in the treatment of rheumatoid arthritis and widely used over-the counter drug for headache and minor pains. This drug has a chiral center and exists as a pair of enantiomers. (S)-Ibuprofen, the eutomer, is responsible for the desired therapeutic effect. The inactive (R)-enantiomer, the distomer, undergoes a unidirectional chiral inversion to give the active (S)-enantiomer, the former acting as a prodrug for the latter. That is, when the ibuprofen is administered as a racemate the distomer is converted in vivo into the eutomer while the latter is unaffected.
