Process for the preparation of enantiomerically homogeneous aminopyrrolidinyl naphthyridine and quinolone carboxylic acids

Abstract: A process for the preparation of enantiomerically homogeneous aminopyrrolidinyl naphthyridine carboxylic acids and quinolone carboxylic acids, and for the preparation of intermediates that are useful in the production of these carboxylic acids.

Description: Technical Field This invention relates to a new process for the preparation of enantiomerically homogeneous aminopyrrolidinyl naphthyridine carboxylic acids and quinolone carboxylic acids, particularly to (S)-7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid, to the preparation of intermediates that are useful in the preparation of these carboxylic acids, as well as to a novel azide reduction process for the reductive acetylation or an azido substituent. Background Art Two molecules that possess identical chemical formulas with the same atoms bonded one to another but that differ in the manner that those atoms are arranged in space are referred to as stereoisomers. Stereoisomers that are mirror images of each other such that they are not superimposable one upon the other, because they have opposite configurations, are referred to as enantiomers. A mixture of equal parts of the two mirror image forms, or enantiomeric forms, is referred to as a racemic mixture. Physiological activity has been shown to be closely related to the configuration of a molecule. For example, it is known that one enantiomeric form of adrenalin is over ten times more active in raising blood pressure than is the other form. Additionally, enzymes which catalyze chemical reactions in the body are frequently programmed to accept one enantiomeric form but not the other. 7-(Aminopyrrolidin-1-yl)naphthyridine carboxylic acids (Chu, U.S. Patent No. 4,616,019, issued October 7, 1986) and 7-(aminopyrrolidin-1-yl)quinolone carboxylic acids (Chu, U.S. Patent No. 4,730,000, issued March 8, 1988) are known to be antibacterial agents. A racemic mixture of 7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1, 4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid has been shown to exhibit antibacterial properties. J. Med. Chem., 29, 2363 (1986). A racemic mixture of 7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid is prepared by Reaction Scheme I as illustrated below: In Reaction Scheme I, the oxime (2) is reduced with Raney nickel and hydrogen which results in a racemic mixture having equal parts of the two enantiomeric forms of the molecule (3). This racemic intermediate will subsequently result in the production of a racemic mixture of (A). However, only one enantiomeric form of (A) may possess biological activity. Further, one enantiomeric form of this molecule may be capable of producing an undesirable side effect while the other enantiomeric form may be the form that exhibits antibacterial properties. It is therefore desirable to provide a process for the preparation of a specific enantiomeric form of 7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid. As will be discussed in greater detail below, one alternative is to provide an azide rather than the oxime (2), reductively acetylate the azide and thereafter remove the benzyl group to obtain (4). The reduction of an azide to an amine is a process that is widely used in organic synthesis because of the high stereoselectivity associated with the preparation of the precursor azide. Accordingly, several methods and reagents are known to reduce an azide to an amine. For example, catalytic hydrogenation [Mungall, J. Org. Chem., 40, 1659 (1975); and Corey, Synthesis, 590 (1975)], or lithium aluminum hydride [Hedayatullah, Tetrahedron Lett., 2455 (1975); Brimacombe, Carbohydr. Res., 3, 318 (1967); Bose, J. Org. Chem., 27, 2925 (1962); and Boyer, J. Am. Chem., 73, 5865 (1951)]. Other processes include H₂S/pyridine/H₂O [Adachi, Synthesis, 45 (1977)]; transfer hydrogenation [Gartiser, Tetrahedron Lett., 24, 1609 (1984)]; Ph₃P/NH₄OH [Vaulter, Tetrahedron Lett., 24. 763 (1983)]; H₂/Lindlar catalyst [Corey, Synthesis, 590 (1975); Cr(II)/H + [Kirk, J. Chem. Soc. Chem. Commun., 64 (1970); and Kondo, Tetrahedron, 29, 1801 (1973)]; as well as Na₂S/Et₃N/MeOH [Belinka, J. Org. Chem., 44, 4712 (1979)]. Most recently, there have been reports of procedures using stannous chloride/MeOH [Maiti, Tetrahedron Lett., 27, 1423 (1986)] and NaBH₄/THF/MeOH [Soai, Synthesis, 48 (1986)]. Although many reagents have been proposed, none have proven completely satisfactory because they either lack chemoselectivity or require vigorous reaction conditions to achieve the desired reduction of the azide. Of interest to the present invention is EP-A-0 266 576, which is considered prior art under Article 54(3) EPC. EP-A-0 266 576 discloses the preparation of (R)- and (S)-3-amino-pyrrolidine through the reaction of (R)- and (S)-3-(4-methylsulfonyloxy)-1-phenylmethyl pyrrolidine, respectively, with sodium azide followed by reduction of the azide group to an imino group. Also relevant to the present invention is Rosen, Synthesis, 40-44 (1988) which discloses asymetric synthesis of 2-substituted (4S)-4-aminopyrrolidines involving an S N 2 displacement of the methanesulfonate of an alcohol with azide ion followed by reduction of the azide ion with lithium aluminum hydride and acetylation to form the acetamide. Disclosure of the Invention It has now been discovered that (S)-7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid can be prepared according to Reaction Scheme II, illustrated below: wherein R₁ is an N-1 protecting group such as benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, or alkyl- or arylsulfonyl; R₂ is an activating group such as methanesulfonyl, p-toluenesulfonyl, or trifluoromethanesulfonyl, which transform the hydroxyl group into a leaving group; R₃ is an azido group; and R₄ is an acetyl group which is a nitrogen protecting group that is stable under the conditions required to remove the nitrogen protecting group R₁. Preferably, R₁ is benzyl and R₂ is methanesulfonyl. Reductive acetylation of the azide (10) is achieved with thiolacetic acid to form the corresponding acetamide (11) in a single step. The term "C₁ to C₆ alkyl" as used herein refers to straight or branched chain alkyl radicals containing from 1 to 6 carbon atoms. The term "C₁ to C₆ alkanoyl" as used herein refers to R₅CO- wherein R₅ is C₁ to C₆ alkyl. The term "aroyl" as used herein refers to R₆CO- wherein R₆ is phenyl or substituted phenyl wherein the phenyl ring is substituted with one, two or three substituents independently selected from halogen, loweralkyl, nitro and alkoxy. The term "halogen" as used herein refers to fluoro, bromo, chloro or iodo. The term "C₁ to C₆ alkylsulfonyl" as used herein refers to R₇SO₂- wherein R₇ is C₁ to C₆ alkyl. The term "arylsulfonyl" as used herein refers to R₈SO₂- wherein R₈ is phenyl or p-tolyl. The term "alkoxy" as used herein refers to R₉O- wherein R₉ is a loweralkyl radical. The term "leaving group" as used herein refers to chloro, bromo, iodo, or sulfonate esters such as mesylate, triflate and tosylate. The term "N-1 protecting group" or "nitrogen protecting group" as used herein refers to those groups intended to protect an amino group against undesirable reactions during synthetic procedures and includes but is not limited to benzyl, acetyl, pivaloyl, tert-butoxycarbonyl, carbobenzyloxy or benzoyl. As used herein, the term "pharmaceutically acceptable salts" means the nontoxic acid addition or alkaline earth metal salts of the compound of formula (A). These salts can be prepared in situ during the final isolation and purification of the compound of formula (A), or by separately reacting the base or acid functions with a suitable organic or inorganic acid or base, respectively. Representative acid addition salts include the hydrochloride, hydrobromide, sulfate, bisulfate, acetate, oxalate, valerate, oleate, palmitate, stearate, laurate, borate, benzoate, lactate, phosphate, tosylate, citrate, maleate, fumarate, succinate, tartrate, napsylate, glucoheptonate, lactobionate, lauryl sulfate salts and the like. Representative alkali metal or alkaline earth metal salts include the sodium, calcium, potassium and magnesium salts. In accordance with the foregoing Reaction Scheme II, an N-1 protected (R)-3-hydroxypyrrolidine intermediate (R)-(8) is utilized to prepare the enantiomerically homogeneous (S)-7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid (A). For example, the enantiomerically homogeneous alcohol (R)-(8), where the N-1 protecting group R₁ is benzyl, is reacted with a sulfonating reagent such as an alkyl- or arylsulfonyl chloride or an alkyl- or arylsulfonic acid anhydride to obtain a sulfonate ester (9). The reaction takes place in an organic solvent such as dimethylformamide (DMF), dichloromethane, tetrahydrofuran (THF), or pyridine in the presence of a base such as triethylamine or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The temperature range is approximately -30 to 60 degrees Celsius (C). Preferably, (R)-(8), is reacted with methanesulfonyl chloride in dichloromethane and in the presence of the base triethylamine to obtain the sulfonate ester (9), where R₂ is methanesulfonyl. This reaction proceeds acceptably at room temperature but is preferably run at approximately 25 degrees C. The sulfonate ester group is displaced with an azide reagent to obtain (10). Azide reagents can include, among others, sodium azide, lithium azide, or tetra-n-butylammonium azide in an organic solvent, such as acetonitrile, DMF, or THF. The reaction can take place within a temperature range of from approximately room temperature to 125 degrees C. Preferably, the sulfonate ester (9) is reacted with tetra-n-butylammonium azide in acetonitrile to provide the azide (10). The azide (10) is then directly converted to an acetamide (11). It has now been discovered that azides will react with thiolacetic acid to provide chemoselective reduction of the azide with an accompanying acetylation to give the corresponding acetamide. The reductive acetylation of azides with thiolacetic acid has been found to have general utility for the reduction of functionally diverse azides. Further, the reaction occurs in the presence of a wide variety of functional groups, such as t-butoxycarbonyl and benzyl protecting groups, methyl esters, olefins, carboxylic esters, and methanesulfonate ester. The reaction is rapid and generally occurs under mild conditions. For example, the reaction takes place at room temperature, with or without a solvent, to reach completion within a matter of minutes. Further, the reaction is extremely convenient to carry out and is accomplished by simply stirring the azide with thiolacetic acid. Thereafter, the reaction mixture can be concentrated with a rotary evaporator and, if desired, further purified by flash column chromatography. The R₁ group of (1) is cleaved to obtain (12). The acylated compound (12) is subsequently reacted to form (A) in a process similar to that found in the reaction illustrated in Reaction Scheme I. In other words, the compound (12), in this case (S)-3-acetamidopyrrolidine, is reacted with 7-chloro-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid or its ethyl ester (5) to obtain (13) after which the ester and amide groups are hydrolyzed to obtain (S)-7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid (A). Additionally, the reductive acetylation of azides with thiolacetic acid is advantageous with molecules that possess functional groups that were previously thought to be incompatible with a free amine. As seen in Reaction Scheme III below, treatment of the azido mesylate (14) with hydrogen and metal catalyst such as palladium in the presence of methanol, results in the reduction of the azide and subsequent intramolecular cyclization to yield the bicyclic amine (15). This cyclization occurs spontaneously and no amino mesylate is obtained. However, treatment of (14) with thiolacetic acid results in the acetamido mesylate (16). It is believed that the acetylation occurs so rapidly that the amine is trapped before intramolecular displacement can occur. The differences in in vivo antibacterial activity of racemic (R,S) compound (A) versus the (S) enantiomeric form of compound (A) are shown in Table I. The foregoing may be better understood from the following examples, which are presented for the purposes of illustration and are not intended to limit the scope of the inventive concepts. As used in the following examples, the references to compounds, such as (1), (2), (3), etc. and to substituents, such as R, R₁, R₂, etc., refer to the corresponding compounds and substituents in the foregoing reaction schemes. EXAMPLE 1 (3S)-3-Acetamidopyrrolidine (12) (a) Under a nitrogen atmosphere, 3.8 ml (6.1 g, 60.8 mmol) of methanesulfonyl chloride was slowly added to a solution of 4.3 g (24.3 mmol) of an N-1 protected (R)-(8) (J. Org. Chem. 51 4298 (1986)), where R₁ is benzyl, 8 ml of dichloromethane, and 8.5 ml (6.1 g, 60.8 mmol) of triethylamine. The solution was stirred at room temperature for approximately 16 hours after which the reaction mixture was diluted with dichloromethane and washed with saturated aqueous sodium bicarbonate and brine. The dichloromethane solution was dried (sodium sulfate) and concentrated with a rotary evaporator. The crude product was then purified by flash column chromatography utilizing 4:1 ethyl acetate/hexanes as eluant to obtain 3.3 g of the sulfonate ester (9), where R₁ is benzyl and R₂ is SO₂CH₃, as a yellow oil. ¹H NMR (CDCL₃): 2.10 (m, 1H), 2.30 (m, 1H), 2.50 (m, 1H), 2.75-2.90 (comples m, 3H), 3.00 (s, 3H), 3.62 (d, 1H, J=12.6 Hz), 3.68 (d, 1H, J=13.5 Hz), 5.20 (m, 1H), 7.30 (m, 5H). (b) Under a nitrogen atmosphere, 7.5 g (26.4 mmol) of tetra-N-butylammonium azide was added to a solution of 3.2 g (12.5 mmol) of the sulfonate ester (9) and 4 ml of acetonitrile. The solution was heated at approximately 65 degrees C for 3 hours. The reaction mixture was then diluted with ether, washed with saturated aqueous sodium bicarbonate, dried, and concentrated with a rotary evaporator. The crude material was purified by flash column chromatography as above to obtain 2.29 g of (10), where R₁ is benzyl and R₃ is azido, as a colorless oil. ¹H NMR (CDCl₃): 1.90 (m, 1H), 2.20 (m, 1H), 2.46 (m, 1H), 2.70 (complex m, 3H), 3.60 (d, 1H, J=12 Hz), 3.68 (d, 1H, J=13.5 Hz), 3.95 (m, 1H), 7.35 (m, 5H). (c) Under a nitrogen atmosphere, a solution of 216 mg (1.07 mmol) of the azide (10), and 0.85 ml (0.9 g, 11 mmol) of thiolacetic acid was stirred at room temperature for approximately 5 hours and concentrated with a rotary evaporator. The crude material was subjected to flash column chromatography, increasing the polarity of the eluant from chloroform to 1:9 methanol/chloroform, to obtain (11), where R₄ is acetyl and R₁ is benzyl, as an oil. ¹H NMR (CDCl₃): 1.60 (m, 1H), 1.94 (s, 3H), 2.25 (m, 2H), 2.53 (dd, 1H, J=6, 10.5 Hz), 2.61 (dd, 1H, J=3, 10.5 Hz), 2.85 (m, 1H), 3.59 (s, 2H), 4.45 (m, 1H), 5.95 (bd, NH, J=6 Hz), 7.30 (m, 5H). The oil was dissolved in methanol and 50 mg of 20% Pd/C was added to the solution. The mixture was then placed under 4 atm of hydrogen for 24 hours. An additional 0.46 g 20% Pd/c was added to the system during this time. The catalyst was filtered out and the solvent was removed with a rotary evaporator to yield 130 mg of (12), where R₄ is acetyl, as a yellow oil. ¹H NMR (CDCl₃): 1.67 (m, 1H), 1.97 (s, 3H), 2.16 (m, 1H), 2.85 (dd, 1H, J=3, 11 Hz), 2.96 (m, 1H), 3.11 (m, 2H), 3.48 (s, 1H), 4.41 (m, 1H), 6.26 (bs, 1H). An alternate preparation of (3S)-3-acetamidopyrrolidine (12) involves repeating steps (a)-(c) descirbed above, but replacing benzyl as the N-1 protecting group R₁ with a tert-butoxycarbonyl N-1 protecting group. The tert-butoxycarbonyl protecting group is removed under acidic conditions to obtain (12), where R₄ is acetyl. EXAMPLE 2 (S)-7-(3-Aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic Acid (A) Hydrochloride (a) Under a nitrogen atmosphere, 430 mg (1.13 mmol) of (5) was added to a solution of 120 mg (0.94 mmol) of the product (12) from Example 1, 0.3 ml of pyridine, and 0.17 ml (120 mg, 1.2 mmol) of triethylamine. J. Med. Chem., 29, 2363 (1986). The solution was heated at approximately 65 degrees C for 21 hours to allow the reaction to come to completion before concentrating with a rotary evaporator. The crude material was purified by subjecting the product to flash column chromatography, gradually increasing the polarity of the eluant from chloroform to 5% methanol/chloroform, to obtain 343 mg of (13) as an orange solid (mp 240-243 degrees C). (b) Under a nitrogen atmosphere, 9.5 ml of a 1M aqueous sodium hydroxide solution was added to a suspension of 223 mg (2.48 mmol) of the product (13) from step (a) and 3 ml of THF. The reaction mixture was heated at approximately 65 degrees C for 2 hours before being concentrated with a rotary evaporator. (c) The residue from step (b) was suspended in 6 M aqueous hydrochloric acid and heated to reflux (110 degrees C). The mixture was then cooled and concentrated. Thereafter, H₂O was added to the concentrated mixture resulting in an off-white solid (A) hydrochloride which was collected and dried in a vacuum oven yielding 101 mg of product. 1 H NMR (dmso-d₆) 2-3.9 (complex), 7.38 (m,1H), 7.57 (m,1H), 7.83 (m,1H), 8.23 (d,1H,J=14), 8.83 (s,1H). EXAMPLE 3 (2S,4S)-4-Acetamido-1-t-butoxycarbonyl-2-methylpyrrolidine Under a nitrogen atmosphere, 0.27 ml (280 mg, 3.7 mmol) of thiolacetic acid was added to 210 mg (0.93 mmol) of (2S,4S)-4-azido-1-t-butoxycarbonyl-2-methylpyrrolidine. The reaction mixture was stirred at room temperature for approximately four hours and concentrated with a rotary evaporator. The resulting oil was subjected to flash column chromatography using 1:1 ethyl acetate/hexane followed by ethyl acetate as eluant to obtain 190 mg of (2S,4S)-4-acetamido-1-t-butoxycarbonyl-2-methylpyrrolidine (84% yield) as a yellow oil which solidified on standing. Recrystallization of a small sample from hexanes provided a white solid, mp 108-110 degrees C. The material thus obtained was found to be identical to the material obtained by a two-step procedure that provides for the hydrogenation of (2S,4S)-4-azido-1-t-butoxycarbonyl-2-methylpyrrolidine with hydrogen and Pd/C followed by a separate acetylation step utilizing acetic anhydride. EXAMPLE 4 Benzylacetamide Under a nitrogen atmosphere, 1.2 ml (1.3 g, 17.2 mmol) of thiolacetic acid was added to 570 mg (4.3 mmol) of benzyl azide. The reaction mixture was stirred at room temperature for approximately one hour and the thioacetic acid was removed with a rotary evaporator. The resulting oil was subjected to flash column chromatography using 1:1 ether/pentane followed by ether as eluant to obtain 580 mg of benzylacetamide (91% yield) as a white crystalline solid, mp 58-60 degrees C. The physical and spectral properties of the material obtained in this manner were identical with those of the product obtained upon treatment of benzylamine with thiolacetic acid. EXAMPLE 5 In the fashion described in the foregoing Examples and corresponding to the transformation of (10) wherein R₃ is azide into (11) wherein R₄ is acetyl, the azide compounds listed in Table II were reacted with four to ten mole equivalents of thiolacetic acid. The resulting acetamide was concentrated with a rotary evaporator before being purified by flash column chromatography.

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, IT, LI, NL, SE A process for the preparation of a single enantiomeric form of a compound having the formula; wherein R₄ is an acetyl group, the process comprising: (a) transforming the hydroxyl group of a N-1 protected enantiomericaliy pure 3-hydroxypyrrolidine into a leaving group; (b) introducing a nitrogen containing substituent by displacing the leaving group with an azide; (c) converting in a single step the azide to an acetylamine by reaction with thiolacetic acid; and (d) cleaving the N-1 protecting group. The process as defined in claim 1 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, C₁ to C₆ alkylsulfonyl and arylsulfonyl; and the leaving group is chloro, bromo, iodo or a sulfonate ester; The process as defined in Claim 1 for the preparation of enantiomerically pure (S)-3-acetamidopyrrolidine, the process comprising: (a) reacting an enantiomerically pure N-1 protected (R)-3-hydroxypyrrolidine with methanesulfonyl chloride to convert the hydroxyl group of the N-1 protected (R)-3-hydroxypyrrolidine to a sulfonate ester; (b) reacting the sulfonate ester with tetra-n-butylammonium azide to obtain the corresponding azide; (c) reductively acetylating the azide with thiolacetic acid to form the corresponding acetamide in a single step; and (d) cleaving the N-1 protecting group to obtain enantiomerically pure (S)-3-acetamidopyrrolidine. The process as defined in Claim 3 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butyloxycarbonyl, C₁ to C₆ alkanoyl, aroyl, C₁ to C₆ alkylsulfonyl and arylsulfonyl. A process for the preparation of the (S) enantiomeric form of 7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid, the process comprising: (a) reacting the (S) enantiomeric form of a compound of the formula prepared by the process of Claim 1 wherein R₄ is acetyl with 7-chloro-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid or its ethyl ester; and (b) hydrolyzing the ester and cleaving the acetyl group to obtain (S)-7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid. The process as defined in Claim 5 wherein the compound of formula I is prepared by the process comprising: (a) reacting the hydroxyl group of a N-1 protected (R)-3-hydroxypyrrolidine with a sulfonating reagent to form a sulfonate ester; (b) reacting the sulfonate ester group with an azide reagent to form the corresponding azido substituent; and (c) reductively acetylating the azide with thiolacetic acid and cleaving the N-1 protecting group to form (S)-3-acetamidopyrrolidine. The process as defined in claim 6 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, alkylsulfonyl and arylsulfonyl; and the azide reagent is selected from the group consisting of sodium azide, lithium azide, and tetra-n-butylammonium azide. A process for the chemoselective reduction of an azide substituent with an accompanying acetylation to obtain the corresponding acetamide, the process comprising reacting thiolacetic acid with a molecule containing the azide substituent. An enantiomerically pure compound of the formula: wherein R₁ is hydrogen, benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, C₁ to C₆ alkylsulfonyl or arylsulfonyl; and R₄ is an acetyl group. The (S) enantiomeric form of the compound of the formula: or a pharmaceutically acceptable salt thereof. Claims for the following Contracting State : ES A process for the preparation of a single enantiomeric form of a compound having the formula; wherein R₄ is an acetyl group, the process comprising: (a) transforming the hydroxyl group of a N-1 protected enantiomerically pure 3-hydroxypyrrolidine into a leaving group; (b) introducing a nitrogen containing substituent by displacing the leaving group with an azide; (c) converting in a single step the azide to an acetylamine by reaction with thiolacetic acid; and (d) cleaving the N-1 protecting group. The process as defined in claim 1 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, C₁ to C₆ alkylsulfonyl and arylsulfonyl; and the leaving group is chloro, bromo, iodo or a sulfonate ester; The process as defined in Claim 1 for the preparation of enantiomerically pure (S)-3-acetamidopyrrolidine, the process comprising: (a) reacting an enantiomerically pure N-1 protected (R)-3-hydroxypyrrolidine with methanesulfonyl chloride to convert the hydroxyl group of the N-1 protected (R)-3-hydroxypyrrolidine to a sulfonate ester; (b) reacting the sulfonate ester with tetra-n-butylammonium azide to obtain the corresponding azide; (c) reductively acetylating the azide with thiolacetic acid to form the corresponding acetamide in a single step; and (d) cleaving the N-1 protecting group to obtain enantiomerically pure (S)-3-acetamidopyrrolidine. The process as defined in Claim 3 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butyloxycarbonyl, C₁ to C₆ alkanoyl, aroyl, C₁ to C₆ alkylsulfonyl and arylsulfonyl. A process for the preparation of the (S) enantiomeric form of 7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid, the process comprising: (a) reacting the (S) enantiomeric form of a compound of the formula prepared by the process of Claim 1 wherein R₄ is acetyl with 7-chloro-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid or its ethyl ester; and (b) hydrolyzing the ester and cleaving the acetyl group to obtain (S)-7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid. The process as defined in Claim 5 wherein the compound of formula I is prepared by the process comprising: (a) reacting the hydroxyl group of a N-1 protected (R)-3-hydroxypyrrolidine with a sulfonating reagent to form a sulfonate ester; (b) reacting the sulfonate ester group with an azide reagent to form the corresponding azido substituent; and (c) reductively acetylating the azide with thiolacetic acid and cleaving the N-1 protecting group to form (S)-3-acetamidopyrrolidine. The process as defined in claim 6 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, alkylsulfonyl and arylsulfonyl; and the azide reagent is selected from the group consisting of sodium azide, lithium azide, and tetra-n-butylammonium azide. A process for the chemoselective reduction of an aside substituent with an accompanying acetylation to obtain the corresponding acetamide, the process comprising reacting thiolacetic acid with a molecule containing the azide substituent. Claims for the following Contracting State : GR A process for the preparation of a single enantiomeric form of a compound having the formula; wherein R₄ is an acetyl group, the process comprising: (a) transforming the hydroxyl group of a N-1 protected enantiomerically pure 3-hydroxypyrrolidine into a leaving group; (b) introducing a nitrogen containing substituent by displacing the leaving group with an azide; (c) converting in a single step the azide to an acetylamine by reaction with thiolacetic acid; and (d) cleaving the N-1 protecting group. The process as defined in claim 1 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, C₁ to C₆ alkylsulfonyl and arylsulfonyl; and the leaving group is chloro, bromo, iodo or a sulfonate ester; The process as defined in Claim 1 for the preparation of enantiomerically pure (S)-3-acetamidopyrrolidine, the process comprising: (a) reacting an enantiomerically pure N-1 protected (R)-3-hydroxypyrrolidine with methanesulfonyl chloride to convert the hydroxyl group of the N-1 protected (R)-3-hydroxypyrrolidine to a sulfonate ester; (b) reacting the sulfonate ester with tetra-n-butylammonium azide to obtain the corresponding azide; (c) reductively acetylating the azide with thiolacetic acid to form the corresponding acetamide in a single step; and (d) cleaving the N-1 protecting group to obtain enantiomerically pure (S)-3-acetamidopyrrolidine. The process as defined in Claim 3 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butyloxycarbonyl, C₁ to C₆ alkanoyl, aroyl C₁ to C₆ alkylsulfonyl and arylsulfonyl. A process for the preparation of the (S) enantiomeric form of 7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid, the process comprising: (a) reacting the (S) enantiomeric form of a compound of the formula prepared by the process of Claim 1 wherein R₄ is acetyl with 7-chloro-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid or its ethyl ester; and (b) hydrolyzing the ester and cleaving the acetyl group to obtain (S)-7-(3-aminopyrrolidin-1-yl)-1-(o,p-difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-1,8-naphthyridine-3-carboxylic acid. The process as defined in Claim 5 wherein the compound of formula I is prepared by the process comprising: (a) reacting the hydroxyl group of a N-1 protected (R)-3-hydroxypyrrolidine with a sulfonating reagent to form a sulfonate ester; (b) reacting the sulfonate ester group with an azide reagent to form the corresponding azido substituent; and (c) reductively acetylating the azide with thiolacetic acid and cleaving the N-1 protecting group to form (S)-3-acetamidopyrrolidine. The process as defined in claim 6 wherein the N-1 protecting group is selected from the group consisting of benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, alkylsulfonyl and arylsulfonyl; and the azide reagent is selected from the group consisting of sodium azide, lithium azide, and tetra-n-butylammonium azide. A process for the chemoselective reduction of an azide substituent with an accompanying acetylation to obtain the corresponding acetamide, the process comprising reacting thiolacetic acid with a molecule containing the azide substituent. An enantiomerically pure compound of the formula: wherein R₁ is hydrogen, benzyl, carbobenzyloxy, tert-butoxycarbonyl, C₁ to C₆ alkanoyl, aroyl, C₁ to C₆ alkylsulfonyl or arylsulfonyl; and R₄ is an acetyl group.

Inventors: CHU DANIEL TIM-WO, ROSEN TERRY JAY, CHU, DANIEL TIM-WO, ROSEN, TERRY JAY
Applicants: ABBOTT LAB, ABBOTT LABORATORIES
Application year: 1989
Main classification: C07D207
IPC codes: A61K31, C07D471, C07D207, A61P31