A PRACTICAL SYNTHESIS OF (S)-(-)-NADIFLOXACIN - NOVEL ACID-CATALYZED RACEMIZATION OF TETRAHYDROQUINALDINE DERIVATIVE

(S)-(-)-Nadifloxacin hyl-1-oxo-1H,5H-benzo[i,j]quinolizine-2-carboxyli c acid, (S)-(-)-OPC-7251], an antibacterial agent, was synthesized fro m -5,6-difluoro-2-methyl-1,2,3,4-tetrahydroquinoline (DFTQ), which was prepared by the optical resolution of racemic DFTQ with 2,3-di-O-benz oyl-L-tartaric acid. Racemization of the undesired enantiomer [(R)-(+) -DFTQ] was studied in the presence of various acids and the best resul t was obtained in the case of methanesulfonic acid, The absolute confi guration of(-)-nadifloxacin was determined as S by X-ray crystallograp hic analysis.