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The syntheses of the metabolites of grepafloxacin, 7-(2-aminoethylamino)-1-cyclopropyl-6-fluoro-5-methyl-4-oxo-1,4-dihydro quinoline-3-carboxylic acid (III), 7-(2-aminopropylamino)-1-cyclopropyl-6-fluoro-5-methyl-4-oxo-1,4-dihydr oquinoline-3-carboxylic acid (V), 7-amino-1-cyclopropyl-6-fluoro-5-methyl-4-oxo-1,4-dihydroquinoline-3-ca rboxylic acid (VIII), 7-(carboxymethylamino)-1-cyclopropyl-6-fluoro-5-methyl-4-oxo-1,4-dihydr oquinoline-3-carboxylic acid (XI), 1-cyclopropyl-6-fluoro-5-(hydroxymethyl)-7-(3-methylpiperazin-1-yl)-4-o xo-1,4-dihydroquinoline-3-carboxylic acid (XVIII) and 7-amino-1-cyclopropyl-6-fluoro-5-(hydroxymethyl)-4-oxo-1,4-dihydroquino line-3-carboxylic acid (XX) have been reported: 1) Compound (III): By condensation of 7-bromo-1-cyclopropyl-6-fluoro-5-methyl-4-oxo-1,4-dihydroquinoline-3-ca rboxylic acid diacetoxyborane ester (I) with 2-(tert-butoxycarbonylamino)ethylamine (II) by heating at 110 C followed by a treatment with HCl in ethanol/water. 2) Compound (V): By condensation of quinolone (I) with 2-(tert-butoxycarbonylamino)ethylamine (IV) by heating at 110 C, followed by hydrolysis with HCl as before. 3) Compound (VIII): The condensation of quinolone (I) with 4-methoxybenzylamine (VII) by heating at 110 C gives 1-cyclopropyl-6-fluoro-7-(4-methoxybenzylamino)-5-methyl-4-oxo-1,4-dihy droquinoline-3-carboxylic acid (VII), which is then debenzylated by treatment with a mixture of trifluoroacetic acid and concentrated sulfuric acid. 4) Compound (XI): The condensation of quinolone (I) with glycine ethyl ester (IX) by heating at 110 C gives 1-cyclopropyl-7-(ethoxycarbonylmethylamino)-6-fluoro-5-methyl-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (X), which is then saponified with NaOH in refluxing ethanol.