合成路线1

A new synthesis of DU-6859 has been described: This compound is obtained by condensation of 8-chloro-6,7-difluoro-1-[2(S)-fluoro-1(R)-cyclopropyl]-4-oxo-1,4-dihydr oquinoline-3-carboxylic acid (I) with 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (II) by means of triethylamine in refluxing acetonitrile, followed by deprotection with 35% aqueous HCl. The starting compounds (I) and (II) are obtained as follows: 1) The reaction of (+/-)-cis-2-fluorocyclopropane-1-carboxylic acid (III) with 1(R)-phenylethylamine (IV) by means of N,N'-carbonyldiimidazole (CDI) gives the corresponding amide (V) as a mixture of diastereomers, which is submitted to preparative HPLC yielding 2(S)-fluorocyclopropane-1(R)-carboxylic acid 1(R)-phenylethylamide (VI). Hydrolysis of (VI) with hot 35% HCl affords the corresponding free acid (VII), which by reaction with diphenyl phosphorazidate in tert-butanol is converted to 1(R)-(tert-butoxycarbonylamino)-2(S)-fluorocyclopropane (VIII). The deprotection of (VIII) with trifluoroacetic acid gives the corresponding free amine as trifluoroacetate (IX), which is condensed with 2-(3-chloro-2,4,5-trifluorobenzoyl)-3-ethoxyacrylic acid ethyl ester (X) by means of triethylamine in dichloromethane to yield the chiral 3-aminoacrylate (XI). The cyclization of (XI) by means of NaH in dioxane affords 8-chloro-6,7-difluoro-1-[2(S)-fluoro-1(R)-cyclopropyl]-4-oxo-1,4-dihydroquinoline-3-carboxylic acid ethyl ester (XII), which is finally saponified to the desired acid (I) with hot 35% HCl.