METHOD OF QUINOLINE-3-CARBOXYL ACID'S DERIVATIVES PREPARATION

An improved process for the preparation of 7-substituted amino-1-cyclopropyl-6, 8-difluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids of formula and pharmaceutically acceptable acid addition or base salts thereof, wherein A is a substituted amino group, X is hydrogen or fluorine, and R2 is alkyl of one to three carbon atoms or cycloalkyl of three to six carbon atoms, is described. An alkyl ester precursor is converted via an anhydrous preparation to an alkali metal salt which in a separate step or in situ is displaced and hydrolyzed to the desired product.