A mixture of 2.8 g of ethyl 1-(4-fluorophenyl)1,4 -dihydro-4-oxo-7-(4-pyridinyl)-3-quinolinecarboxylate, 20 ml of 10% potassium hydroxide solution and 10 ml ethanol was heated on a steam bath for 3 hrs. The reaction mixture was cooled and acidified with acetic acid. The solid product was collected and washed with acetone to give 2.6 g 1-(4-fluorophenyl)-1,4-dihydro-4-oxo-7-(4-pyridinyl)-3-quinolinecarboxylic acid. A sample of the compound was converted to its monomethanesulfonate salt, m.p. 280-281° C. when recrystallized from acetonitrile.
