AU748779B2 - The preparation of 3-pyroline-2-carboxylic acid amine derivatives - Google Patents

Description

-I

I-/uu/U 1 1 2815/91 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged:

S

S.

Invention Title: THE PREPARATION OF 3-PYROLINE-2-CARBOXYLIC ACID AMINE

DERIVATIVES

The following statement is a full description of this invention, including the best method of performing it known to us THE PREPARATION OF 3-PYRROLINE-2-CARBOXYLIC ACID AMINE DERIVATIVES The present invention relates to a novel process for preparing pyrroline-2-carboxylic acid amine derivatives.

Replacement of proline by 3,4-dehydroproline in biologically active peptides or peptide mimetics rarely causes a loss of activity Felix et al. Int. J. Pept. Prot. Res. 12, (1977) 299; C.R. Botos et al. J. Med. Chem. 22, (1979) 926; G.H. Fisher, W. Ryan, FEBS Lett. 107, (1979) 273); on the contrary, in some cases the effect is increased while there is a simultaneous reduction in toxicity Fisher, W. Ryan FEBS Lett. 107, (1979) 273; S. Natarajan et al., in Peptide, Structure and Biological Function, E. Gross, J. Meienhofer, Eds., Pierce Chemical Company, 1979, p. 463).

Synthesis of N-protected 3,4-dehydroprolines on the industrial 20 scale by processes disclosed in the literature is very elaborate as shown, for example, by the thermal cis elimination of the S-methylxanthate from hydroxyproline by the Tchugaeff method. The disadvantages of this process are that large amounts of methyl iodide are used, and methyl mercaptan and carbon oxysulfide are produced Dormay et al., Angew. Chem. (1980) 761; *Houben-Weil, Methoden der Organischen Chemie, Vol. 5/lb, 126 (1972)).

The reduction of pyrrole-2-carboxylic acid with phosphonium 30 iodide in fuming hydroiodic acid is also problematic because of the use of a large excess of gaseous hydrogen iodide, and of a marked reduction in yield and onset of polymerization in large reactions Scott et al., Synth. Commun. 10(7), (1980) 529).

On the other hand, elimination of the Boc-protected 4-phenylseleninylproline methyl ester takes place under distinctly milder conditions Dormay, Synthesis 2, (1982) 753. The elimination takes place at room temperature and results in the A 3 -olefin with high selectivity. Thermal cis eliminations afford considerable amounts of the isomeric A4 olefin. However, elimination of the selenium oxide is also disadvantageous because of the production of toxic selenium-containing residues which require costly disposal precisely in the case of reactions on the pilot-plant scale, and addition of the previously eliminated selenigenic acid to the double bond is advantageous especially in the case of pharmaceutical active ingredients in 2 which even tiny amounts of selenium-containing compounds result in toxic properties.

Small amounts of 3-pyrroline have been obtained from N-substituted 3-methylsulfonyloxypyrrolidine Uno et al., J. Heterocycl. Chem. 24, (1987) 1025). Elimination of sulfonates, eg. methylsulfonate, to prepare 3 -pyrroline-2-carboxylic acid derivatives has not'previously been described.

Said processes disclosed in the literature for preparing 3-pyrroline-2-carboxylic acid derivatives are unsuitable for industrial syntheses.

S In parent application AU-36949/97 a new process for preparing 3-pyrroline-2-carboxylic acid derivatives of the formula I

O

N R2

I

where RI is H, C 1 -Cs-alkyl, benzyl, benzyl substituted on the phenyl, allyloxycarbonyl, Ci-C 6 -alkyloxycarbonyl, benzyloxycarbonyl where the benzyl residue can be substituted by OCH 3 radicals, or Cl-C 4 -alkylcarbonyl or 30

R

1 is a residue of an amino acid which is linked via the C terminus and may be alkylated or acylated on the nitrogen, and

R

2 is OH, C 1

-C

4 -alkyloxy, benzyloxy or NR 3

R

4 where R 3 and R 4 are, independently of one another, H, Ci-C 4 -alkyl, benzyl, phenyl or pyridyl, it being possible for the aromatic systems in R 3 and R 4 to be substituted by up to three identical or different substituents selected from the group consisting of methyl, methoxy, hydroxyl, cyano or Ac halogen, which comprises eliminating the sulfonic acid residue with the aid of a base from a sulfonate of the formula II SO2- R 0 R1 where R 1 and R 2 have the meanings described above, and R 5 is

C

1

-C

6 -alkyl, benzyl, trifluoromethyl, naphthyl or phenyl which may be unsubstituted or substituted by radicals from the group consisting of methyl, nitro or halogen.

Preferred as RI are Cl-C 4 -alkylcarbonyl, benzyl, benzyl 20 substituted on the phenyl, Ci-C 6 -alkyloxycarbonyl and benzyloxycarbonyl. If the benzyloxycarbonyl radical is substituted by OCH3, it preferably has one methoxy group in the p position. The Cl-C 6 -alkyloxycarbonyl radical is particularly preferred.

25 Preferred R 2 radicals are OH and Ci-C 4 -alkoxy.

Preferred R 5 radicals are C 1 i 6 -alkyl and benzyl, in particular

C

1 _4-alkyl.

Compounds I have one asymmetric carbon atom, and compounds II have two asymmetric carbon atoms, in the 5-membered ring.

Compounds of the formula II can be employed as racemates, mixtures of diastereomers, and as diastereomerically pure and 3enantiomerically pure compounds. Compounds I may therefore be obtained, depending on the stereochemical structure of the compounds II employed as precursors, and the reaction conditions, as racemates or in optically active form.

Compounds of the formula II can be prepared by methods disclosed in the literature (for example D.J. Abraham, M. Mokotoff, L. Sheh, J. E. Simmons, J. Med. Chem. 26(4), (1983) 549).

Elimination of the sulfonic acid residue, ie. of the -O-S0 2

-R

group, from optically active compounds of the formula II takes place with racemization if R 2 is C1-C 4 -alkoxy or benzyloxy. This results in racemic esters of 3,4-dehydroproline, which provide 4 access, by subsequent enzymatic racemate resolution, both to Dand to L-3,4-dehydroproline derivatives (process A): Process A: (R5=CH 3 R2 OCH 3 o--CH- R 22 RHI O C H A particularly preferred embodiment of the process consists in using compounds of the formula II where R 2 is OH and the absolute configuration of the carboxylic acid residue is fixed, ie.

corresponds either to the R or to the S configuration, to permit the corresponding carboxylic acids of the formula I to be *obtained without racemization. (Process B): e Process

B:

(R5=CH3, R2 OH) O g 0 1. base N COH 2. H COH RI Ri Aprotic solvents are suitable for elimination reactions A and B, in particular DMF, dioxane, THF, DME, DMSO, CH 3 CN, it being possible for the solvent to contain small amounts of water or alcohol.

Depending on the process, 1.0-1.5 equivalents of base (process A) or 2.0-3.0 equivalents of base (process B) are employed, suitable bases being hydrides, amides and alcoholates of lithium, sodium, potassium, rubidium, cesium, calcium or magnesium, but preferably those of sodium and potassium. Sodium alcoholates are preferably employed as bases, suitable alcoholate residues therein being of primary, secondary and tertiary alcohols. It is also possible to employ diols, triols, ether alcohols of the tri-, di- or monoethylene glycol monoether type or amino alcohols. Those which may be preferably mentioned are: triethylene glycol monomethyl ether, diethylene glycol monomethyl ether or ethylene glycol monomethyl ether, dimethylaminoethanol or 2-[2-(dimethylamino)ethoxy]-ethanol.

Elimination of the sulfonate group takes place even at a temperature of -200C. The reaction can in general be carried out at from -20 0 C to +1000C. It is preferably carried out at from -100C to 600C. Elimination of the sulfonate group from the corresponding esters by process A takes place with racemization even at -20 0 C on the a carbon atom of the 3,4-dehydroproline ester produced thereby.

Surprisingly, the process in the particularly preferred variant of process B can be carried out with precursors of the formula II where R 2 is OH, and the carboxylic acid residue has either the R *or S configuration, almost without racemization. The bases 20 2preferably employed in this variant are hydrides, primary alcoholates, primary ether alcoholates or primary amino alcoholates. 2-Methoxyethanolate, 2-(2-methoxyethoxy)ethanolate or 2-(2-(dimethylamino)ethoxy]ethanolate are particularly preferably employed. From 2.0 to 2.5 equivalents of base are preferably employed per equivalent of precursor. The preferred temperature range for the reaction in process B is from -10°C to 0

C.

30 The base used for the elimination can be introduced in solid form into the reaction mixture, but it can also be prepared in situ before the reaction. If, for example, the base used for the elimination is sodium 2-methoxyethanolate, this base can advantageously be prepared in situ by dropwise addition of the appropriate alcohol to a solution or suspension of a sodium salt of a stronger base such as sodium hydride, sodium tert-butoxide or sodium bis(trimethylsilyl)amide. The reaction can be carried out semibatchwise either by running the base solution into a dissolved precursor of the formula II or, preferably, running a solution of precursor II into the solution or suspension of base.

The reaction mixture can be worked up by distillation, extraction, crystallization, chromatography or a combination thereof.

6 The required enantiomer can be isolated from racemic 3,4-dehydroproline with either or (-)-tartaric acid (see J.W. Scott et al., Synthetic Communications 10 (1980) 529 and U.S. 4,111,951), or the racemate resolution can be carried out with optically active l-(4-nitrophenyl)ethylamine after preparation of the Boc-protected amino acid 4,066,658, Kahl, T. Wieland, Liebigs Ann. Chem. (1981) 1445).

N-protected 3,4-dehydroprolines prepared without racemization by preferred process B can advantageously be purified by crystallization as ammonium salts with achiral amines. It is possible in particular to obtain L-boc-3,4-dehydroproline in pure form as diethylammonium salt.

1The invention therefore relates to compounds of the formula IV S--COOH x amine N (IV),

R

6 where R 6 is an amino protective group and amine is a mono-, di- or trialkylamine where the alkyl radicals contain 1-4 carbon atoms and can be replaced by Cs 5 7 -cycloalkyl radicals, and their optically active D and L forms. R 6 is preferably the boc protective group and "amine" is preferably diethylamine or dicyclohexylamine.

30 Esters obtained by process A can be very effectively partially cleaved using enzymes such as lipases, esterases and proteases, resulting in one antipode of the free acid, while the other antipode remains in the form of the ester.

A large number of enzymes can be employed as hydrolases in the said process. Proteases, esterases and, in particular, lipases are preferably used. Microbial lipases are particularly suitable lipases and can be isolated, for example, from yeasts or bacteria. Further particularly suitable hydrolases are the enzymes commercially obtainable from Novo Nordisk (Enzyme Toolbox), in particular the lipases SP 523, SP 524; SP 525, SP 526 and ®Novozym 435.

It is furthermore possible to employ the lipases "Chirazyme L1 to L8", which are commercially available (Boehringer Mannheim), advantageously in the process according to the invention.

7 Esterases (such as pig liver esterase) can also be employed.

The enzymes can be employed in native or in immobilized form.

The ester cleavage is carried out in a buffer at pH 6-8 and preferably at room temperature.

The novel process makes it possible to prepare compounds I in a very simple manner. It is particularly important for preparing dehydroproline derivatives which it has hitherto been possible to prepare only with difficulty and, in some cases, with poor yield.

Optically active N-protected 3-pyrroline-2-carboxylic acid derivatives are obtained particularly favorably by the novel process as free acid or in the form of an ester from which the free acid can be liberated, preferably enzymatically.

If optically active acid is prepared from the ester 20.enzymatically, as a rule one antipode of the ester remains unchanged. The latter can be, for example, racemized with bases and subjected to the enzymatic cleavage again.

The advantage of the present invention is that it makes it possible for the first time to prepare 3,4-dehydroproline derivatives in sterically pure form simply and under mild and, at the same time, environmentally acceptable reaction conditions even on the industrial scale. It is surprising that elimination of the sulfonic acid residue can be carried out even at low 30 temperatures.

The substances prepared by the novel process are of great interest. They are, for example, valuable intermediates for preparing low molecular weight peptide derivatives which are thrombin inhibitors (cf. WO 94/29336) and in which a proline residue is replaced by a dehydroproline residue. It has furthermore been found that 3,4-dehydroproline can be used to inhibit collagen synthesis (US 4,066,658).

It is particularly advantageous for further processing that the crude product obtained by the process according to the invention can be reacted without further purification to prepare the next intermediates for the peptide derivatives which in turn can be purified very easily. These intermediates have the formula 8 CO-NH -CHz X

II

R

where R 1 has the stated meaning, and X is

R

6 N N 0 C N, CN or

J

(R

6 H, CH 3

OCH

3 OH or halogen).

::.They can be prepared from compounds I by activating the latter in the presence of a base such as triethylanine or 20 'diisopropylethylamine and a condensing agent such as PPA, pivaloyl chloride or dicyclohexylcarbodiimide/hiydroxysuccinimide, and subsequently linking with H 2

N-CH

2 -X to give compounds of the formula III. The reaction is expediently carried out in a solvent such as dichloromethane, THF, dioxane, tert-butyl methyl ether, DME or acetonitrile at from -20 to +300.

Examples ***The following abbreviations are used in the examples: Bns Benzylsulfonyl Boc tert-Butyloxycarbony.

DIPEA Diisopropylethylamine 3DME =Dimethoxyethane DMF Dimethylformamide KOtBu Potassium tert-butoxide Ms =Methylsulfonyl 4PPA Propylphosphonic (sic) anhydride Pro Proline Pyr 3,4-Dehydroproline RT Room temperature 4THF Tetrahydrofuran A. Preparation of the starting materials a) (4R)-N-Boc-(4-MsO)-Pro-OH: 186 g (575 mmol) of the methyl ester Boc-(L)-(4-MsO)-Pro-OCH 3 were hydrolyzed in 500 ml of dioxane and 1150 ml of 1N NaOH at 0°C for 2.5 h. After extraction with ether, the aqueous phase was adjusted to pH3 with 2N hydro-chloric acid, and the product was extracted with ethyl acetate. Drying over Na 2

SO

4 and stripping off the solvent completely resulted in 164 g (92 of a yellowish oil which was 94 pure. The product slowly solidified; [(I]d 22 -50.5 (C 1.01; MeOH); after crystallisation from diisopropyl ether 1 H-NMR (CDC3, 5 in ppm) ca. 9 8 (COOH), 5.35 5.20 (m, 1H, O-CH), 4/60 4.40 (1H, N-CH), 3.95 3.65 (2H, N-CH 2 3.08 3H, S0 2

CH

3 2.85 2.25 (2H, CH 2 1.50 and 1.40 (s, 9H, Boc); (2 rotamers) B. Preparation of the final products Example 1 Preparation of Boc-(L)-Pyr-OH: a) 50.0 g (161.1 mmol) of Boc-(L)-(4-MsO)-Pro-OH dissolved in 650 ml of DME (to which 25 mmol of water were added) were added dropwise in 45 min to 14.5 g of 55-65 NaH (about 364 mmol) in 400 ml of DME at room temperature, the temperature rising without additional cooling to about 30QC. The mixture was stirred at RT for a further 15 h and then at 5 0 9C for 1 h, subsequently poured into ice-water and washed three times with ether/ethyl acetate 2:1. The aqueous phase was acidified to pH 2 with 2N hydrochloric acid, and the product was extracted with ethyl acetate. Drying over Na 2

SO

4 and stripping off the solvent completely resulted in 36 g of crude substance as yellowish oil which contained 70% of product. The product/precursor ratio was found to be 97:3 (HPLC water/acetonitrile 8:2 0.1 TFA; Merck Purospher RP-19e; detection at 210.4 nm) and the enantiomer ratio THIS PAGE IS INTENTIONALLY BLANK was 90:10. The proportions of enantiomers were detected on a chiral HPLC column as Boc-3,4-dehydroprolyl (sic] 3-picolylamide after coupling the acidic group with a 3-picolylamine derivative. Previous investigations have shown that the coupling itself takes place virtually without racemization.

A similar reaction but with 3 equivalents of NaH and stirring at RT for 4 h resulted in 65 of product (product:precursor 94:6; 96:4).

1 H-NMR (CDCI3, 6 in ppm) 10.5-9.5 (COOH), 6.10-5.90 (1H, 5.88-5.70 (1H, 5.12-4.95 (1H, N-CH), 4.30-4.15 (2H, N-CH2), 1.55-1.35 (9H, Boc); (2 rotamers) By classical racemate resolution methods, Boc-3,4-dehydroproline and (+)-dehydroabietylamine were crystallized as corresponding ammonium salt from acetone and, without further recrystallization and after elimination of the amine, Boc-(L)-3,4-dehydroproline was isolated with a purity of 85 and an enantiomer ratio 96 4.

b) 46.2 g of sodium tert-pentoxide (398.5 mmol) were introduced into 150 ml of THF. Then, at 10 0 C, 32.9 g of 2-methoxyethanol (429.5 mmol) were added. A solution of 50 g of Boc-(L)-(4-MsO)-Pro-OH (159.4 mmol) in 100 ml of THF was then added dropwise in such a way that the 30 internal temperature did not exceed 8-10 0 C. The mixture was stirred at 10 0 C for a further 20 h after the end of the addition. Addition of 300 ml of ice-water at 5-10°C was followed by one extraction with 50 ml of methyl tert-butyl ether and then acidification to pH 2 with hydrochloric acid. The crude product was extracted with methylene chloride and, after the solvent had been evaporated off, isolated as yellow oil.

The weight was 40.9 g, of which 18 g was Boc-(L)-3,4dehydroproline, determined by HPLC analysis calibrated with external standard (initial gradient water (0.1

H

3 PO4)/acetonitrile 70:30; column: Prodigy (ODS3) 100A; detection at 210 nm). The enantiomer ratio of 99:1 was likewise determined by HPLC analysis (hexane/isopropanol 8.75:1.25, 0.1 HCOOH; column: Chiracel OD; detection at 230 nm).

12 g of Boc-(L)-(4-MsO)-Pro-OH (224 mmol) were reacted under similar conditions. After extraction with methylene chloride, the crude product was transferred into 220 ml of methyl tert-butyl ether by distillative solvent exchange, and then the Boc-(L)-3,4-dehydroproline present therein was precipitated as diethylammonium salt by adding 16.5 g of diethylamine (224 mmol).

23.8 g of this salt were obtained. The enantiomer was undetectable by the HPLC analytical methods indicated above in the product precipitated in this way.

1 H-NMR (DMSO, 6 in ppm): 5.86-5.67 (2H, 4.6-4.5 4.1-3.9 (N-CH2), 2.88-2.7 (4H q, NCH2CH 3 1.45-1.25 (9H, Boc 2 rotamers), 1.2-1.05 (6H, NCH 2

CH

3 (a)D 22 (sic] -240.1 0 1.08, MeOH) Melting point: 130-133°C c) 10.52 g of sodium bis(trimethylsilyl)amide (57.4 mmol) were introduced into 25 ml of THF and, after dropwise S 20 addition of 8.25 g of 2-(2-(dimethylamino)ethoxy)ethanol (62 mmol) in 15 ml of THF over the course of 15 min with cooling, stirred at RT for 30 min. Then, at 7.1 g of Boc-(L)-(4-MsO)-Pro-OH (23.0 mmol) dissolved in 15 ml of THF were added dropwise over the course of 20 min, and the mixture was stirred at -5°C for 1 h, at 0°C for 2 h and at RT overnight. It was then poured onto 125 g of ice-water and extracted four times with methyl tert-butyl ether, and the aqueous phase was acidified to pH 2.2 with ml of 10 strength citric acid and stirred at RT 30 overnight. After the reaction solution had been extracted with methyl tert-butyl ether three times, the collected organic phases were washed successively with water, saturated brine and water, dried over magnesium sulfate and concentrated under reduced pressure. 4.1 g of Boc-(L)-3,4-dehydroproline were obtained as crude product which was then dissolved in 20 ml of methyl tert-butyl ether, and a solution of 1.35 g of diethylamine (18.52 mmol) in 10 ml of methyl tert-butyl ether was added dropwise. Petroleum ether was added to complete precipitation of the salt. The product was filtered off with suction and dried to afford 4.0 g of Boc-(L)-3,4dehydroproline. A second batch of 0.3 g of crystals was also obtained from the mother liquor, which means that the total yield of required product was 66 13 Use Example 1 Preparation of H-(L)-Pyr (6-carboxamido)-3-picolylamide dihydrochloride: 5.3 ml (30.3 mmol) of DIPEA were added dropwise to 1.5 g of crude Boc-Pyr- OH from Example 1 in 30 ml of dichioromethane at -109C and, after 5 min, 1.58 g (7.0 mmol) or (6-carboxamido)-3picolylamide dihydrochloride were added and, after a er a further 5 min, 5.7 ml (7.9 mmol) of PPA (50 strength solution in ethyl acetate) in 5 ml of dichloromethane were added. The reaction mixture was allowed to warm from -100C to 0OC over 1 h and was then diluted with dichloromethane and washed successively with saturated NaHCO 3 solution, 5 strength citric acid and saturated brine. Drying of the organic phase over Na 2

SO

4 and stripping off the solvent completely resulted in 1.8 g of crude Boc-(L)-Pyr (6-carboxamido)-3-picolylamide which was stirred in 30 ml of 0.9 molar isopropanolic HCL at 500C for min. The precipitate which was produced during this was removed on a suction filter, dissolved in a little methanol, precipitated with isopropanol and again removed. Drying at 45 0 C under reduced pressure resulted in 2.0 g of H-(L)-Pyr (6-carboxamido)-3- 15 Picolylamide dihydrochloride as white powder (purity 95 99 1.

1 .1H-NMR (DMSO-d 6 6 in ppm) 10.9 and 8.9 (each 1H, -NH 2 9.77 1H, CO-NH), 8.60, 8.10 and 8.00 (each 1H, aromatic 8.25 and 7.75 (each 1H, CO-NH 2 6.03 2H, 5.10 (1H, N-CH- 20 CO) 4.47 2H, CH 2 4.00 (2H, CH 2 Use Example 2 Preparation of H-(L)-Pyr 4-CN-benzylamide hydrochloride: 10.0 g of crude Boc-Pyr-OH were reacted with 6.2 g of p-cyanobenzylamine as in Use Example 1. Workup resulted in 14.7 g of crude Boc-(L)-Pyr 4-CN-benzylamide which was stirred in 230 ml of 1 molar isopropanolic HC1 at 500C for 2 h. After the solution 30 had cooled to RT, the substance began slowly to precipitate. The solid was removed on a suction filter. 3.7 g of H-(L)-Pyr 4-CN-benzylamide hydrochloride were obtained as a white powder (purity 96 99. 1).

1 H-NMR (DMSO-d 6 6 in ppm) 10.9 and 8.9 (each 1H, -NH 2 7.82 and 7.47 (each 2H, aromatic 6.02 2H, 5.10 (1H, N-CH-CO) 4.45 2H, CH2) 4.02 (2H, CH 2

Claims (2)

1. A compound of the formula IV 00 0 5 Oe 0 S@0 S *500 0S S 0 S @0 0

555. S 06 S 0* COOH x amine N R (IV), where R 1 is an amino protective group selected from allyloxycarbonyl, Ci-C6- alkyloxycarbonyl, benzyloxycarbonyl or C1-C 4 -alkylcarbonyl, and amine is a mono-, di- or trialkylamine where the alkyl radicals contain 1-4 carbon atoms and may be replaced by Cs. 7 -cycloalkyl radicals. 2. A compound of the formula IV as claimed in claim 1, where R 1 is the Boc protective group and the amine is diethylamine or dicyclohexylamine. 3. A compound as claimed in claim 1 or 2 in the D form. 4. A compound as claimed in claim 1 or 2 in the L form. A compound according to claim 1 and substantially as herein disclosed with reference to the examples. DATED this 28th day of February 2000 BASF AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA VAX D0C029 AU6190.DOC LCG/CLRRES