7-[(4S)-4-Amino-6-azaspiro[2.4]heptan-6-yl]-8-chloro-6-fluoro-1-[(2S)-2-fluorocyclopropyl]-4-oxoquinoline-3-carboxylic acid

(1R-(1a(S*),2a))-7-(7-Amino-5-azaspiro[2.4]hept-5-yl)-8-chloro-6-fluoro-1-(2-fluorocyclopropyl)-1,4-dihydro-4-oxo-3-quinolinecarboxylic Acid

SYNTHESIS……….http://www.drugfuture.com/synth/syndata.aspx?ID=176447

127254-10-8 [RN]

127254-10-8(ACETATE)

Sitafloxacin (INN; also called DU-6859a) is a fluoroquinolone antibiotic^[1] that shows promise in the treatment of Buruli ulcer. The molecule was identified by Daiichi Sankyo Co., which brought ofloxacin and levofloxacin to the market. Sitafloxacin is currently marketed in Japan by Daiichi Sankyo under the tradename Gracevit.

Sitafloxacin is a new-generation, broad-spectrum oral fluoroquinolone antibiotic.It is very active against many Gram-positive, Gram-negative and anaerobic clinical isolates, including strains resistant to other fluoroquinolones, was recently approved in Japan for the treatment of respiratory and urinary tract infections. Sitafloxacin is active against methicillin-resistant staphylococci, Streptococcus pneumoniae and other streptococci with reduced susceptibility to levofloxacin and other quinolones and enterococci

163253-35-8

AU 8933702; EP 0341493; JP 1990231475; JP 1995300416; JP 1999124367; JP 1999124380; US 5587386; US 5767127
The condensation of 3-chloro-2,4,5-trifluorobenzoylacetic acid ethyl ester (I) with (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) and ethyl orthoformate (II) in hot acetic anhydride gives (1R,2S)-2-(3-chloro-2,4,5-trifluorobenzoyl)-3-(2-fluorocyclopropylamino)acrylic acid ethyl ester (IV). The cyclization of (IV) by means of NaH yields the quinolone (V), which is hydrolyzed with HCl to the free acid (VI). The condensation of (VI) with 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) by means of triethylamine in refluxing acetonitrile affords the protected final product (VIII), which is finally deprotected with trifluoroacetic acid and anisole.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) is obtained as follows: 1) The cyclization of butadiene (IX) with dibromofluoromethane by means of BuONa, followed by oxidation with KMnO4, esterification with ethanol – sulfuric acid and reduction with tributyltin hydride gives 2-fluorocyclopropanecarboxylic acid ethyl ester as a cis/trans mixture (X), which is separated by crystallization. The cis-racemic-isomer (XI) is hydrolyzed with NaOH to the corresponding acid (XII), which is condensed with (R)-alpha-methylbenzylamine (XIII) by means of diphenyl chlorophosphate to give the mixture of diastereomers (XIV). This mixture is separated by crystallization, yielding pure (1S,2S)-2-fluoro-N-[alpha(R)-methylbenzyl]cyclopropanecarboxamide (XV), which is hydrolyzed with HCl to the corresponding free acid (XVI). Finally, this compound is converted into (III) by treatment with diphenylphosphoryl azide in refluxing tert-butanol.

b) The intermediate 7(S)-(tert-Butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) can also be obtained as follows: 1) The cyclopropanation of ethyl acetoacetate (XXXI) with 1,2-dibromoethane (XXXII) by means of K2CO3 in DMF gives 1-acetylcyclopropane-1-carboxylic acid ethyl ester (XXXIII), which is brominated with Br2 in ethanol yielding the bromoacetyl derivative (XXXIV). The cyclization of (XXXI) with (R)-alpha-methylbenzylamine (XIII) by means of triethylamine affords 5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane-4,7-dione (XXXV), which by reaction with hydroxylamine is converted into the monooxime (XXXVI). The reduction of (XXXVI) with H2 over RaNi in methanol affords 7-amino-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptan-4-one as a diastereomeric mixture (XXXVII) + (XXXVIII), which is separated by column chromatography. The reduction of the (7S)-isomer (XXXVIII) with LiAlH4 in THF gives 7(S)-amino-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane (XXXIX), which is protected in the usual way to the tert-butoxycarbonyl derivative (XL). Finally, this compound is debenzylated to (VII) by hydrogenation with H2 over Pd/C in ethanol.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) is obtained as follows: 1) The cyclization of butadiene (IX) with dibromofluoromethane by means of BuONa, followed by oxidation with KMnO4, esterification with ethanol – sulfuric acid and reduction with tributyltin hydride gives 2-fluorocyclopropanecarboxylic acid ethyl ester as a cis/trans mixture (X), which is separated by crystallization. The cis-racemic-isomer (XI) is hydrolyzed with NaOH to the corresponding acid (XII), which is condensed with (R)-alpha-methylbenzylamine (XIII) by means of diphenyl chlorophosphate to give the mixture of diastereomers (XIV). This mixture is separated by crystallization, yielding pure (1S,2S)-2-fluoro-N-[alpha(R)-methylbenzyl]cyclopropanecarboxamide (XV), which is hydrolyzed with HCl to the corresponding free acid (XVI). Finally, this compound is converted into (III) by treatment with diphenylphosphoryl azide in refluxing tert-butanol.

b) The intermediate 7(S)-(tert-Butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) can also be obtained as follows: 2) The reaction of 1-acetylcyclopropane-1-carboxylic acid ethyl ester (XXXIII) with (R)-alpha-methylbenzylamine (XIII) by means of NaOH and ethyl chloroformate gives the corresponding amide (XLI), which by reaction with ethylene glycol and p-toluenesulfonic acid is converted into the ethylene ketal (XLII). The bromination of (XLII) with Br2 in dioxane affords the bromomethyl dioxolane (XLIII), which is finally cyclized to 5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane-4,7-dione (XXXV), already obtained as an intermediate in the preceding synthesis.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) can also be obtained as follows: 3) A study of the influence of different substituents in the cis/trans ratio of the cyclopropanation process has been performed. The general method is as follows: the reaction of benzylamine (XXIII) with acetaldehyde and trichloromethyl chloroformate gives the N-benzyl-N-vinylcarbamoyl chloride (XXIV), which by treatment with alcohol yields the N-vinylcarbamate (XXV). The cyclopropanation of (XXV) with fluorodiiodomethane and diethyl zinc as before preferentially affords the cis-N-(2-fluorocyclopropyl)carbamate (XXVI), which is purified by crystallization. The hydrogenolysis of (XXVI) with H2 over Pd/C in acetic acid gives cis-racemic-2-fluorocyclopropylamine (XXVII), which is submitted to optical resolution with L-menthyl chloroformate to afford pure (1R,2S)-isomer (XXII). Finally, this compound is converted into (III) with tert-butoxycarbonyl anhydride as before.

References

• Keating GM (April 2011). “Sitafloxacin: in bacterial infections”. Drugs 71 (6): 731–44. doi:10.2165/11207380-000000000-00000.PMID 21504249.

• (Japanese) Gracevit グレースビット (PDF) Daiichi Sankyo Co. January 2008.