Condensation of 7-chloro-1-(p-fluorophenyl)-6-fluoro-1,4-dihydro-4-oxoquinoline-3 carboxylic acid (I) with N-carboethoxypiperazine (II) in hot 1-methyl-2-pyrrolidinone yields 7-(4-carboethoxypiperazinyl)-1-(p-fluorophenyl)-6-fluoro-1,4-dihydro-4 oxoquinoline-3-carboxylic acid (III). Hydrolysis of (III) with aqueous sodium hydroxide in ethanol followed by treatment with dilute hydrochloric acid gives A-56620.
Condensation of 2,4-dichoro-5-fluoroacetophenone (I) with diethyicarbonate (II) in the presence of sodium hydride gives ethyl 2,4-dichloro-5-fluorobenzoylacetate (III). The condensation of (III) with triethylorthoformate in reftuxing acetic anhydride yields ethyl 2-(2,4-dichloro-5-fluornbenzoyl)-3-ethoxyacrylate (IV), which is treated with p-fluoroaniline in methylene chloride to yield ethyl 2-(2,4-dichloro-5-fluorobenzoyl)-3-(p-fluoroanilino)acrylate (V). Cyclization of (V) with sodium hydride in tetrahydrofuran followed by hydrolysis yields 7-chloro-1-(p-fluorophenyl)-8 fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid (VI). Condensation of (VI) with N-methylpiperazine in 1-methyl-2-pyrrolidinone followed by treatment with hydrochloric acid yields A-56619.