Synthesis and Absolute Configuration of the Enantiomers of 7-Fluoro-1-methyl-3-(methylsulfinyl)-4(1H)-quinolinone (Flosequinan)

The enantiomers of 7-fluoro-1-methyl-3-(methylsulfinyl)-4(1H)-quinolinone [(±)-1, flosequinan], a new drug for the treatment of heart failure, were synthesized from the optically active (R)-α-methylbenzylamine derivatives of quinoline. The key intermediates, (R)-α-methylbenzylamine derivatives, were prepared by diastereomeric separation. The configuration of (+)-1 was assigned on the basis of an X-ray crystallographic analysis of the synthetic precursor (4a). The absolute configuration was found to be (R)-(+)-1 and (S)-(-)-1.