A mixture of 1.65 g 1-(4-fluorophenyl)-1,4-di-hydro4-oxo-7-(4-pyridinyl)-3-quinolinecarboxylic acid, 2.2 g of 1,1'-carbonyldiimidazole and 15 ml dimethylformamide (DMF) was heated at 150° C. for 1.5 hrs. The reaction mixture was poured into 50 ml concentrated ammonium hydroxide. The product was extracted with methylene dichloride and recovered therefrom to give 2.2 g 1-(4-fluorophenyl-1,4-dihydro-4-oxo-7-(4-pyridinyl)-3-quinolinecarboxamide which was converted to its monomethanesulfonate salt hemihydrate, m.p. 301°-303° C. (decompn.). The free base, prepared from the salt with potassium carbonate solution, had m.p. 315°-317° C. when recrystallized from DMF.
