200 mg (0.63 mmol) of ethyl 8-cyano-1-cyclopropyl-6,7-difluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylate are stirred under argon at 40-45° C. for 2 hours with 97 mg (0.75 mmol) of (1S,6S)-2-oxa-5,8-diazabicyclo[4.3.0]nonane and 0.17 ml of triethylamine in 3 ml of acetonitrile. All volatile components are removed in vacuo, the residue is treated with water, insoluble material is filtered off and the filtrate is extracted with dichloromethane. The organic phase is dried over sodium sulphate and then concentrated in vacuo. The resulting residue is dissolved in 6 ml of tetrahydrofuran and 2 ml of water and treated with 30 mg (0.72 mmol) of lithium hydroxide monohydrate. After stirring at room temperature for 16 hours, the mixture is acidified with dil. hydrochloric acid and the resulting precipitate is filtered off with suction and dried.
