Title of Invention	"PROCESS FOR THE SYNTHESIS OF [2S, 3AS, 7AS]-1-[(S)-ALANYL-] OCTAHYDRO-1H- INDOLE-2-CARBOXYLIC ACID"
Abstract	Process for the synthesis of compounds of formula (I) : CH wherein R\ represents a hydrogen atom or an alkyl or benzyl group and R2 represents a protecting group for the amine function. Application in the synthesis of perindopril and pharmaceutically acceptable salts thereof.

Full Text

The present invention relates to a process for the synthesis of compounds of formula (I) (Figure Removed) wherein RI represents a hydrogen atom or a linear or branched (C1-C6alkyl or benzyl group and R2 represents a protecting group for the amine function, and to their application in the synthesis of perindopril of formula (II) : (Figure Removed) and pharmaceutically acceptable salts thereof. Perindopril and pharmaceutically acceptable salts thereof, more especially its tert- butylamine salt, have valuable pharmacological properties. Their principal property is that of inhibiting angiotensin I converting enzyme (or kininase II), which prevents, on the one hand, conversion of the decapeptide angiotensin I to the octapeptide angiotensin II (a vasoconstrictor) and, on the other hand, degradation of bradykinin (a vasodilator) to an inactive peptide. Those two actions contribute to the beneficial effects of perindopril in cardiovascular diseases, more especially in arterial hypertension and heart failure. Perindopril, its preparation and its use in therapeutics have been described in the European Patent specification EP 0 049 658. In view of the pharmaceutical value of this compound, it has been important to obtain it by an effective industrial synthesis process that results in perindopril in a good yield and with excellent purity, starting from reasonably priced and readily accessible starting materials. The Patent Application EP 1 256 590 has already described a process for the preparation of compounds of formula (I). However, that process has the disadvantage of using as starting material a (2S)-dihydroindole-2-carboxylic acid ester which is not commercially available and the preparation of which requires several synthesis steps (including a resolution step) starting from indole-2-carboxylic acid. The Applicant has now developed a new process for the synthesis of compounds of formula (I) which has the advantage of using, as sole sources of chirality, alanine (a natural and, therefore, inexpensive starting material) and a compound readily accessible from senne. More specifically, the present invention relates to a process for the synthesis of the compound of formula (I) : (Figure Removed) wherein R\ represents a hydrogen atom or a linear or branched (Ci-Ce)alkyl or benzyl group and R2 represents a protecting group for the amine function, characterised in that l-(l-cyclohexen-l-yl)-pyrrolidine of formula (III) wherein R\ represents a hydrogen atom or a linear or branched (Ci-Ce)alkyl or benzyl group and R2 represents a protecting group for the amine function, characterised in that l-(l-cyclohexen-l-yl)-pyrrolidine of formula (III) (Figure Removed) is reacted with the serine compound of formula (IV): wherein RI is as defined for formula (I) and RS represents a protecting group for the amine function, to yield the compound of formula (V): wherein RI and Rj are as defined hereinbefore, the amine function of which is deprotected before cyclisation is carried out, followed by dehydration, to yield the compound of formula (VI): (FigureRemoved) wherein RI is as defined hereinbefore, which is reacted with the alanine compound of formula (VII) CH3 R2HN (S) CO2H wherein R2 is as defined for formula (I), in an organic solvent such as, for example, tetrahydrofuran or ethyl acetate, in the presence of an amount of dicyclohexylcarbodiimide of from 1 to 1.2 mol per mol of compound of formula (V) used and an amount of triethylamine of from 1 to 1.2 mol per mol of compound of formula (V) used and optionally in the presence of 1-hydroxy- benzotriazole, at a temperature of from 20 to 50°C, to yield, after isolation and then recrystallisation, the compound of formula (VIII): (Figure Removed) wherein RI and R2 are as defined hereinbefore, which is hydrogenated in the presence of a catalyst such as, for example, palladium, platinum, rhodium or nickel, under a hydrogen pressure of from 1 to 30 bars, preferably from 1 to 10 bars, to yield, after optional deprotection or reprotection of the acid function, the compound of formula (I). The compound of formula (I) obtained in that manner is then subjected, if desired, to a reaction deprotecting the acid and amine functions, followed by a coupling reaction either with ethyl 2-oxo-pentanoate under conditions of reductive amination or with a compound of formula (IX): CH, X (R) C02Et (IX), wherein X represents a leaving group selected from a halogen atom, — 0— SO2CH3 and — to yield optically pure perindopril, which is converted, if desired, into a pharmaceutically acceptable salt such as the tert-butylamine salt. The compounds of formula (VIII) are new compounds which are useful as synthesis intermediates in the chemical or pharmaceutical industry, especially in the synthesis of the compound of formula (I), and as such they form an integral part of the invention. The Example hereinbelow illustrates the invention but does not limit it in any way. EXAMPLE : (2S, 3aS, 7aS)-l-{(2S)-2[(tert-Butoxycarbonyl)-amino]-propionyl}-octahydro-l//-indole-2-carboxylic acid Step A : Benzyl (2S)-2-[(tert-butoxycarbonyl)-amino]-3-(2-oxocyclohexyl)-propanoate Introduce 200 g of l-(l-cyclohexen-l-yl)-pyrrolidine, 535 g of benzyl (2S)-2-[(tert-butoxycarbonyl)-amino]-3-iodopropanoate and 1.5 litres of acetonitrile into a reactor equipped with a reflux column. Reflux for 1 hour and then return the mixture to ambient temperature. After evaporating off the solvent, add 2 litres of water and then acetic acid. Extract with ethyl acetate and evaporate to dryness. Benzyl (2S)-2-[(tert-butoxycarbonyl)-amino]-3-(2-oxocyclohexyl)-propanoate is obtained in that manner in a yield of 80 %. Step B : Benzyl (2S)-2-amino-3-(2-oxocyclohexyl)-propanoate Introduce 200 g of the compound obtained in the previous Step, 1.5 litres of dichloromethane and 60 g of trifluoroacetic acid into a reactor. After stirring for 1 hour 30 minutes at ambient temperature, add 2 litres of saturated sodium hydrogen carbonate solution. Extract with dichloromethane and evaporate to dryness. Benzyl (2S)-2-amino-3-(2-oxocyclohexyl)-propanoate is obtained in that manner in a yield of 90%. StepC: Benzyl (2S)-2,3,4,5,6,7-hexahydro-m-indole-2-carboxylate In a reactor, reflux 200 g of the compound obtained in the previous Step, 13.8 g of p-toluenesulphonic acid and 1 litre of toluene, the water formed being removed by azeotropic distillation. When no more water is separated off, evaporate off the toluene. Benzyl (2S)-2,3,4,5,6,7-hexahydro-l//-indole-2-carboxylate is obtained in that manner in a crude yield of 97%. StepD: Benzyl (2S)-l-{(2S)-2-[(tert-butoxycarbonyl)-amino]-propionyl}-2,3,4,5,6,7-hexahydro-lH-indole-2-carboxylate With stirring, introduce 200 g of the compound obtained in the previous Step, 65 g of triethylamine and 2 litres of tetrahydrofuran into a reactor followed by, after stirring for 10 minutes at ambient temperature, 123 g of N-[tert-butoxycarbonyl]-(.S)-alanine and 130g of dicylohexylcarbodiimide. The heterogeneous mixture is then stirred at ambient temperature for 6 hours and it is then cooled to 0°C and filtered. The filtrate is then washed and then recrystallised from a mixture of hexane/ethyl acetate 10/1 to yield the expected product in a yield of 81 % and a chemical purity of 98 %. StepE: (2S, 3aS, 7aS)-l-{(2S)-2[(tert-Butoxycarbonyl)-amino]-propionyl}-octahydro-JH-indole-2-carboxylic acid Introduce 200 g of the compound obtained in the previous Step, dissolved in acetic acid, and then 5 g of Pt/C 10 % into a hydrogenator. Hydrogenate under a pressure of 5 bars at ambient temperature until the theoretical amount of hydrogen has been absorbed. Remove the catalyst by filtration and then cool to a temperature of from 0 to 5°C and collect the resulting solid by filtration. Wash the filter cake and dry it to constant weight. (2S, 3aS, 7aS)-l-{(2S)-2[(tert-Butoxycarbonyl)-amino]-propionyl}-octahydro-l//-indole-2-carboxylic acid is obtained in that manner in a yield of 87 % and an enantiomeric purity of 99%. CLAIMS 1. Process for the synthesis of compounds of formula (I): (Figure Removed) wherein RI represents a hydrogen atom or a linear or branched (C1-C6)alkyl or benzyl group and R2 represents a protecting group for the amine function, characterised in that l-(l-cyclohexen-l-yl)-pyrrolidine of formula (III): is reacted with the serine compound of formula (IV): CO2R, NH-R, (IV), wherein RI is as defined for formula (I) and R^ represents a protecting group for the amine function, to yield the compound of formula (V): wherein RI and RT, are as defined hereinbefore, the amine function of which is deprotected before cyclisation is carried out, followed by dehydration, to yield the compound of formula (VI): wherein RI is as defined hereinbefore, which is reacted with the alanine compound of formula (VII) wherein R2 is as defined for formula (I), in an organic solvent, in the presence of an amount of dicyclohexylcarbodiimide of from 1 to 1.2 mol per mol of compound of formula (V) used and an amount of triethylamine of from 1 to 1.2 mol per mol of compound of formula (V) used and optionally in the presence of 1 - hydroxybenzotriazole, at a temperature of from 20 to 50°C, to yield, after isolation and then recrystallisation, the compound of formula (VIII): wherein RI and R2 are as defined hereinbefore, which is hydrogenated in the presence of a catalyst, under a hydrogen pressure of from 1 to 30 bars, to yield, after optional deprotection or reprotection of the acid function, the compound of formula (I). 2. Synthesis process according to claim 1, characterised in that the hydrogen pressure in the hydrogenation reaction is from 1 to 10 bars. 3. Synthesis process according to claim 1, wherein the catalyst is selected from palladium, platinum, rhodium and nickel. 4. Synthesis process according to claim 1, wherein RI represents a hydrogen atom and Ra represents a tert-butoxycarbonyl group. 5. Process for the synthesis of perindopril or pharmaceutically acceptable salts thereof, wherein the compound of formula (III) is converted into the intermediate compound of formula (I) according to the process of claim 1, and then the intermediate compound of formula (I) is converted into perindopril or pharmaceutically acceptable salts thereof. 6. Compound of formula (VIII): wherein RI represents a hydrogen atom or a linear or branched (C-C6)alkyl or benzyl group and R2 represents a protecting group for the amine function , .

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3205-delnp-2005-abstract.pdf

3205-delnp-2005-claims.pdf

3205-DELNP-2005-Correspondence-Others-(26-12-2008).pdf

3205-delnp-2005-correspondence-others.pdf

3205-delnp-2005-correspondence-po.pdf

3205-delnp-2005-description (complete).pdf

3205-delnp-2005-form-1.pdf

3205-delnp-2005-form-18.pdf

3205-delnp-2005-form-2.pdf

3205-delnp-2005-form-3.pdf

3205-delnp-2005-form-5.pdf

3205-delnp-2005-gpa.pdf

3205-delnp-2005-pct-308.pdf

3205-delnp-2005-pct-332.pdf

3205-delnp-2005-pct-409.pdf

3205-delnp-2005-pct-416.pdf

3205-DELNP-2005-Petition-137-(26-12-2008).pdf