2-Methylpiperazine → 5-Amino-1-cyclopropyl-6-fluoro-7-(3-methyl-1-piperazinyl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid

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Reaction Steps

A mixture of 1.0 g of 5-amino-1-cyclopropyl-6,7-difluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid, 1.18 g of 2-methylpiperazine and 10 ml of pyridine was heated under reflux for 3 hours. The reaction mixture was concentrated under reduced pressure, and the solution was neutralized with a 10% aqueous solution of acetic acid and cooled with ice. The crystals were collected by filtration, dissolved in a 10% aqueous solution of acetic acid, treated with activated charcoal, adjusted to pH 8-9 with 29% aqueous ammonia, and cooled with ice. The crystals were collected by filtration and washed successively with water and ethanol to give 0.80 g of 5-amino-1-cyclopropyl-6-fluoro-7-(3-methyl-1-piperazinyl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid. m.p. 181°-183° C.

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