Acetic Acid → (RS)-7,9-difluoro-1-methyl-8-(3-methyl-1-piperazinyl)-4-oxo-1,4-dihydro-benzo[b][1,8]naphthyridine-3-carboxylic acid

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Reaction Steps

A suspension of 1.5 g of (RS)-3-ethoxycarbonyl-7,9-difluoro-1-methyl-8-(3-methyl-1-piperazinyl)-4-oxo-1,4-dihydro-benzo[b][1,8]naphthyridine in 20 cm3 of ethanol and 20 cm3 of N aqueous potassium hydroxide solution is heated at a temperature close to 75° C. for 1 hour and a half. 12 g of a 10% aqueous solution of acetic acid is added to the solution obtained, at this latter temperature. The insoluble matter obtained is drained at about 75° C. and washed 3 times with 30 cm3 of water at about 20° C. After recrystallizing once from 100 cm3 of dimethylformamdide, 0.9 g of (RS)-7,9-difluoro-1-methyl-8-(3-methyl-1-piperazinyl)-4-oxo-1,4-dihydro-benzo[b][1,8]naphthyridine-3-carboxylic acid is obtained in the form of a yellow solid melting at 380°-382° C.

Provenance & Evidence