WO2006082228A1 - Method for synthesising cysteine derivatives, in particular thio carbaesters used in the form of intermediate products in drug synthesis - Google Patents

Abstract

The invention relates to a method for synthesising cysteine derivatives of formula I, wherein R<SUB>1</SUB> is an alkyl radical, R<SUB>2</SUB> is a radical selected from a group consisting of alkyl or aryl radicals and r<SUB>3</SUB> is a radical selected from a group consisting of alkyl, aryl and arylalkyl radicals. Said invention relates, in particular to a method for synthesising thio carabaesters, in particular N-nenzyloxycarbonyl-S-phenyl-L-casteine methyl ester. The use of the compound of formula I obtainable by the inventive method in the form of an intermediate product for a drug synthesis is also disclosed.

Description

 Process for the synthesis of cysteine derivatives, especially thiocarbaester, useful as intermediates in drug synthesis

The invention relates to a new process for the preparation of cysteine derivatives, in particular thiocarbaester derivatives, in particular N-benzyloxycarbonyl-S-phenyl-L-cysteine methyl ester.

The cysteine derivatives are useful as intermediates in the synthesis of several pharmaceutically active compounds. In particular, thiocarbaester is involved in the synthesis of nelfmavir, an active anti-AIDS product of the class of HIV protease inhibitors (WO96 / 23756 and EP 604 185).

In the prior art, the methods for synthesizing cysteine derivatives use three synthetic routes using, as raw materials, an esterified serine derivative whose amino function is protected by an appropriate radical (Z-Ser-OMe), a derivative of cysteine whose amino function is protected by a suitable radical and the thiol function is substituted by a phenyl radical (Z-Cys (Ph) -OH), or an esterified cysteine derivative whose amino function is protected by an appropriate radical (Z-Cys (H) -OMe).

The derivatives mentioned above and corresponding to the formulas Z-Cys (Ph) -OH, Z-Cys (Ph) -OMe and Z-Cys (H) -OMe respectively correspond to formulas a, b or c:

dans lesquelles Z représente un groupement protecteur de la fonction aminé, notamment le radical benzyloxycarbonyle.

in which Z represents a protective group for the amine function, in particular the benzyloxycarbonyl radical.

dans lesquelles Z représente un groupement protecteur de la fonction aminé, notamment le radical benzyloxycarbonyle.The derivatives mentioned above and corresponding to the formulas Z-Ser-OH and Z-Ser-OMe respectively correspond to formulas d or e:

in which Z represents a protective group for the amine function, in particular the benzyloxycarbonyl radical.

The first synthetic route described involves a derivative of serine as a raw material: Z-Ser-OMe. The alcohol function of serine is then activated as a mesylate derivative in the presence of mesyl chloride before reacting with sodium thiophenate to yield thiocarbaester. This chemical route has been described for the first time by the team of the University of Nottingham in J. Chem. Soc; Perkin Trans. 1, 15, (1997), 2179-2187 and Tetrahedron Letters, 34 (41), (1993), 6607-6610.

Patent applications EP 0 897 911 and US2002 / 008688 describe the synthesis of thiocarbaester from derivatives of serine Z-Ser-OMe. Processes displacing hydroxyl from serine, substitution of the hydroxyl radical or a leaving group by a thiophenyl radical, are of little economic interest because they employ elaborate reagents such as methanesulfonyl chloride. (US2002 / 008688) and they are also difficult to control, because of significant risks of elimination of the desired product in dehydroalanine and the risks of racemization.

The second synthetic route described involves a derivative of cysteine as raw material: Z-Cys (Ph) -OH. The carboxylic acid function of the cysteine is then esterified. The protective group of the amino function Z is generally introduced under the Schotten-Bauman conditions carried out in an aqueous medium, which implies a careful isolation and drying of the intermediate product Z-

Cys (Ph) -OH for carrying out esterification which requires anhydrous conditions.

The patent application EP 1 054 000, which describes this second synthetic route, teaches that it is preferable to carry out the protection of the amine function followed by the esterification reaction of the carboxylic function, in particular to avoid the formation of impurities such as N-benzyl-phenylcysteine methyl ester or dehydroalanine. The third route of synthesis described involves a derivative of cysteine as a raw material: Z-Cys (H) -OMe. The fhiol function of the cysteine derivative is then substituted with a phenyl radical. Methods for introducing a phenyl group onto cysteine are known methods such as the reaction of cysteine with a phenyldiazonium salt (J. Org. Chem., 23, (1958), 1251) or the reaction of bromo or iodobenzene with cysteine or a cysteine derivative (Australian J. Chem., 38, (1985), 38 and EP 0 968 997). This type of process gives poor yields and purities.

Another process for the synthesis of cysteine derivatives uses as raw material an alkyl derivative of cysteine (S-methylcysteine, S-hepylecysteine, S-hexyl cysteine). This alkyl derivative of cysteine is first esterified in the presence of methanol and an acid (HCl gas or SOCl ₂ ). The esterification reaction is carried out at room temperature or at cold temperature (-10 ^° C.). The hydrochloride of the S-alkyl-cysteine methyl ester (alkyl = methyl, hexyl, heptyl) resulting from this esterification step is then isolated. The amine function is then protected by a suitable protecting group. To do this, said isolated hydrochloride is reacted in a second reactor with said appropriate protective group.

Such a method is for example described in the following publications: CH.

Levenson, design and synthesis of tetrahedral intermediate analogs as potential dihydroorotase inhibitors, J. Med. Chem., 1984, 27, 228-232; LEON A.G.M. VAN DEN

BROEK et al., Lipophilic analogues of sparsomycin as strong inhibitors of protein synthesis and tumor growth: a structure-activity relationship study, J Med. Chem, 1989, 32, 2002-

2015 and G. DESIMONI et al., Copper (II) in organic synthesis. XI. Evaluation of the ligand architecture on the efficiency of a copper (II) catalyst for enantioselective Michael reactions, Tetrahedron vol. 51, No. 14, pp. 4131-4144, 1995.

This process requires the isolation of the hydochloride from the S-S-alkyl-cysteine methyl ester (alkyl = methyl, hexyl, heptyl). It is therefore a two-step process, carried out in two different reactors.

In addition, this process requires the completion of the esterification reaction at a temperature below or equal to room temperature. There is also a need for a more economical process for obtaining derivatives of cysteine, especially thiocarbaester, with good chemical and chiral purity.

However, the inventors have discovered, surprisingly, that it is possible to carry out the "one pot" synthesis of cysteine derivatives, in particular thiocarbaester, using as starting material cysteine, the thiol function of which is substituted with an alkyl or aryl radical.

The subject of the invention is therefore a process for the synthesis of cysteine derivatives of formula 1

dans laquelle Ri représente un radical alkyle, R₂ représente un radical choisi dans le groupe constitué par les radicaux alkyles, aryles et R₃ représente un radical choisi dans le groupe constitué par les radicaux alkyles, aryles et arylalkyles, caractérisé en ce qu'il comprend les étapes successives suivantes : a) estérification du composé de formule II

in which R 1 represents an alkyl radical, R ₂ represents a radical chosen from the group consisting of alkyl and aryl radicals, and R ₃ represents a radical chosen from the group consisting of alkyl, aryl and arylalkyl radicals, characterized in that comprises the following successive steps: a) esterification of the compound of formula II

avec un alcool de formule III

with an alcohol of formula III

R 1 -OH to form the compound of formula IV

les radicaux Ri et R₂ ayant la même signification que pour le composé de formule I, b) puis, fonctionnalisation du groupement amino (du composé de formule IV) pour donner le composé de formule I, les étapes a) et b) étant réalisées dans un seul et même réacteur. Dans le cadre de la présente invention, le terme « alkyle » désigne un résidu hydrocarboné à chaîne droite ou ramifiée contenant de 1 à 10 atomes de carbone, avantageusement de 1 à 6 atomes de carbone, encore plus avantageusement de 1 à 4 atomes de carbone, tel que le méthyle, l'éthyle, le propyle, Pisopropyle et le butyle, plus avantageusement l'éthyle, le propyle, Pisopropyle et le butyle.

the radicals R 1 and R ₂ having the same meaning as for the compound of formula I, b) and then functionalization of the amino group (of the compound of formula IV) to give the compound of formula I, the steps a) and b) being carried out in one and the same reactor. In the context of the present invention, the term "alkyl" denotes a hydrocarbon residue with a straight or branched chain containing from 1 to 10 carbon atoms, advantageously from 1 to 6 carbon atoms, more advantageously from 1 to 4 carbon atoms. such as methyl, ethyl, propyl, isopropyl and butyl, more preferably ethyl, propyl, isopropyl and butyl.

In the context of the present invention, the term "aryl" denotes an aromatic carbocyclic residue containing from 6 to 10 carbon atoms. As an example of an aryl radical, there may be mentioned phenyl and naphthyl, advantageously phenyl. In the context of the present invention, the term "aralkyl" denotes a hydrocarbon residue containing from 1 to 6 carbon atoms bonded to an aryl radical, as defined above. As an example of an aralkyl radical, there may be mentioned in particular benzyl and phenethyl.

Steps a) and b) are carried out in one and the same reactor. This means that the compound of formula IV is not isolated. This is called "one pot" synthesis.

The reagents, solvents and potential byproducts present in the first stage were considered to be removed for good yield and purity of the final product. However, performing steps a) and b) in the same reactor (without isolation of the compound of formula IV and thus without removal of impurities, solvents, unreacted starting reagents) does not affect the total yield of the process (It is indeed comparable to the yield obtained when compound IV is isolated) nor the purity of the final product.

Ri preferably represents an alkyl radical, linear or branched Ci -C _O, even more preferably methyl. R ₂ preferably represents an aryl radical C ₆ -C _O, still more preferably phenyl.

R ₃ advantageously represents the benzyl radical.

dans laquelle Ri et R₂ ont la même signification que pour le composé de formule I.According to an advantageous variant of the invention the compound of formula I represents the compound of formula Ia below:

in which R 1 and R ₂ have the same meaning as for the compound of formula I.

The process according to the invention advantageously makes it possible to conserve the enantiomer of the starting compound, more particularly of cysteine. Thus, when the compound of formula II is in enantiomerically pure form (R or S), the compound of formula I is obtained in the same enantiomeric form.

The process according to the invention thus makes it possible to obtain derivatives of cysteine, in particular thiocarbaester, with good chiral purity. If the starting compound is in enantiomerically pure form, the desired product is obtained with an enantiomeric excess greater than 90%, advantageously greater than 95%, still more preferably greater than 97%, still more preferably greater than 98%.

The process according to the invention also makes it possible to obtain derivatives of cysteine, in particular thiocarbaester, with good chemical purity

The desired product is obtained with a chemical purity greater than 90% by weight, advantageously greater than 95% by weight, and even more advantageously greater than 97% by weight, relative to the total weight of the compounds present.

The esterification reaction of step a) can advantageously be carried out under anhydrous conditions, to promote the shift of equilibrium from the esterification reaction to the formation of the ester. The reaction of step a) can be catalyzed (acid catalysis): it can then be carried out in the presence of an acid, such as hydrochloric acid gas, or an acid chloride, such as thionyl. The alcohol of formula III is advantageously also used as a solvent for the esterification reaction of step a).

During the esterification reaction of step a), following the addition of the reagents, the medium is advantageously heated to a temperature of between 40 ^° C. and the reflux temperature of the solvent (156 ° C. for hexanol). ), more advantageously between 40 ⁰ C and at a temperature located 5 ⁰ C below the reflux temperature of the solvent, more advantageously between 50 and 60 ⁰ C. The heating time of the medium of step a) varies from 2 to 36 hours, advantageously the medium is heated for 2 to 10 hours, even more advantageously for 3 to 5 hours. The medium is then cooled to room temperature, advantageously at 20 ^° C.

Following step a), excess acid and solvent are advantageously removed and the resulting residue is solubilized in water.

During step b), the amino group may be functionalized by any method known to those skilled in the art. In the context of the present invention, the term "functionalization of the amino group" means that the amine function of the compound of formula IV is substituted, under appropriate operating conditions well known to those skilled in the art, to form the compound of formula I.

Step b) is advantageously carried out in an aqueous and basic medium by adding a compound R ₃ OC (O) -X (formula V), in which X represents a halogen atom. In the context of the present invention, the term "halogen" denotes chlorine, bromine, fluorine or iodine, advantageously fluorine or chlorine.

The aqueous medium of step b) may also comprise a solvent selected from the group consisting of toluene, ethyl acetate (AcOEt), isopropyl acetate (AcOiPr) and dichloromethane (CH ₂ Cl ₂ ). According to an advantageous variant of the invention, the functionalization of the amino group is carried out under Schotten-Bauman conditions, that is to say by reaction of an acid chloride in the presence of alkali and water ( J. March, Advanced Organic Chemistry, p. 392).

The medium of step b) is advantageously made basic by addition of a strong base such as sodium hydroxide. The medium of step b) is advantageously buffered by addition of a weak base, advantageously sodium hydrogencarbonate and / or potassium hydrogen carbonate.

The pH of the aqueous medium of step b) is thus advantageously adjusted to values between 4 and 7, more advantageously between 5.5 and 6.5, still more advantageously at a value of 6 ± 0.2.

The addition of the compound of formula V is advantageously carried out at a temperature of between 0 and 20 ^° C., advantageously between 0 and 10 ^° C., and even more advantageously between 3 and 70 ^° C. Then, the medium is advantageously stirred at this temperature for a time varying from 5 minutes to 1 hour, advantageously from 15 to 45 minutes, even more advantageously for about 30 minutes. Finally, the medium is advantageously stirred at ambient temperature (advantageously 20 ^° C.) for a time varying from 5 minutes to 1 hour, advantageously from 15 to 45 minutes, even more advantageously for about 30 minutes.

The compound of formula V is advantageously benzyl chloroformate. According to an advantageous variant of the invention, step b) is carried out by adding benzyl chloroformate in a basic medium in the presence of a weak base, such as sodium hydrogencarbonate and / or potassium hydrogencarbonate.

The desired product can then be recovered by conventional methods known to those skilled in the art.

According to an advantageous variant of the invention, the first step a) consists of preparing the H-Cys (Ph) -OMe, HCl by esterification reaction of the cysteine derivative H-Cys (Ph) -OH in methanol in the presence an acid chloride such as thionyl chloride or an acid such as hydrochloric acid gas. After removing the excess acid and the synthesis solvent, the residue is solubilized in water. The functionalization of the amino group (step b)) is carried out by adding benzyl chloroformate in a basic medium in the presence of sodium hydrogen carbonate and / or potassium hydrogen carbonate.

According to an even more advantageous variant of the invention, the process is characterized in that 1 part of H-Cys (Ph) -OH is reacted with 1.2 parts of thionyl chloride in 4 to 10 volumes of methanol. . After concentration, the medium is dissolved in water in the presence of a solvent (AcOEt, AcOiPr, CH ₂ Cl ₂ ) to which soda is added until pH = 6 followed by 2 parts of sodium hydrogencarbonate and 1 part of benzyl chloroformate. After reaction, the product is obtained in the organic phase after decantation and precipitation by adding 3 to 5 volumes of heptane and cooling.

The process according to the invention is characterized by the use of a weak base, during step b), making it possible to work in a buffered medium so as to avoid the secondary reaction of saponification, a reaction generally observed when using a strong base like soda or potash. Thus, the process according to the invention by the pH conditions and the selected temperature conditions avoid the decomposition of the chloroformate which is at the origin of the impurity N-benzyl-phenylcysteine methyl ester. The pH and temperature conditions of the process also make it possible to avoid the elimination reaction of thiophenol and thus to avoid the formation of the dehydroalanine impurity.

Performing the esterification, prior to the functionalization of the amine function, keeps the product in the same reactor because it is sufficient to remove the excess alcohol R] -OH by evaporation before the implementation of the benzyloxycarbonylation. The synthesis "one pot" therefore mobilizes only one reactor, it thus makes it possible to manufacture the desired product in a minimum of manipulations and unit operations, for example a single filtration, a single drying of isolated product, less cleaning of equipment therefore less solvents and fewer discharges.

The carrying out of the esterification, prior to the functionalization of the amine function, also makes it possible to avoid the formation of dipeptide impurities, which can be obtained during the benzyloxycarbonylation reaction of the amino acids, whose carboxylic acid function is free.

The methods for introducing a phenyl group on cysteine yielding poor yields and purities, it is advantageous to place these reactions at the beginning of synthesis to reduce the impact on the cost and control impurities from the beginning of the synthesis.

The starting compound is advantageously S-phenyl cysteine

qui permet d'accéder au thiocarbaester, (2R)-2-[(benzyloxycarbonyl)amino]-3- (phénylthio) propanoïque acide méthyl ester, de formule IaI

which makes it possible to access thiocarbaester, (2R) -2 - [(benzyloxycarbonyl) amino] -3- (phenylthio) propanoic acid methyl ester, of formula IaI

avec conservation de l'excès énantiomérique de la cystéine de départ, ledit thiocarbaester étant ensuite utilisé dans la synthèse de médicaments, notamment le Nelfïnavir.

with retention of the enantiomeric excess of the starting cysteine, said thiocarbaester being then used in the synthesis of drugs, especially Nelfinavir.

The subject of the invention is also the use of the compounds of formula (I), obtained by the process according to the invention, as intermediates in the synthesis of medicinal products, in particular in the synthesis of active anti-AIDS products of the class of HIV protease inhibitors. In particular, the invention relates to the use of thiocarbaester IaI, obtained by the process according to the invention, as an intermediate product in the synthesis of active anti-AIDS products of the class of HIV protease inhibitors, in particular Nelfinavir. .

The following examples illustrate the invention without limiting it.

Example 1 Synthesis of Thiocarbaester IaI

a) Procedure:

In a 2-liter reactor equipped, 100 g of L- (R) -S-phenyl cysteine (H-Cys (Ph) -OH; S-phenyl cysteine levorotatory, configuration R) and 400 ml of methanol are introduced. The medium is heated at 55 ° C. and then 70.8 g of thionyl chloride are added while maintaining the temperature below 60 ^° C. A 4 hour run at 60 ^° C. is then carried out, the medium is cooled to 20 ^° C. and then concentrated under reduced vacuum. 100 ml of toluene are added and the medium is again concentrated under reduced vacuum. 300 ml of toluene and 300 ml of water are added, the pH of the aqueous phase is adjusted to pH = 6 by addition of aqueous sodium hydroxide, then 96 g of sodium hydrogencarbonate are added. 82 g of benzyl chloroformate are added at 5 ° C. The medium is stirred for 30 min at 5 ° C. and then 30 min at 20 ^° C.

The pH of the aqueous phase is adjusted to pH = 3 by addition of 35% hydrochloric acid. After decantation of the medium, the phases are separated. The toluene phase is washed twice with water and then concentrated by half.

420 ml of heptane are added and then the mixture is cooled to 10 ° C. After a plateau of 2 h at 10 ^° C., the precipitate is filtered and washed with heptane.

After drying, 130 g of thiocarbaester are obtained in the form of a white solid, ie a mass yield of 80%.

b) analysis

The results of the thiocarbaester analysis synthesized previously are given in Table 1 below.

Tableau 1

Table 1

¹ High Performance Liquid Chromatography = High Performance Liquid Chromatography

² Infrared

³ titration according to the Karl Fischer method

The process according to the invention makes it possible to obtain thiocarbaester IaI with a good yield, a chiral purity of 99.8% and a chemical purity of 99.4%.

Claims

1. Process for the synthesis of cysteine derivatives of formula I

in which R 1 represents an alkyl radical, R ₂ represents a radical chosen from the group consisting of alkyl or aryl radicals, and R ₃ represents a radical chosen from the group consisting of alkyl, aryl and arylalkyl radicals, characterized in that it comprises the following successive steps: a) esterification of the compound of formula II

with an alcohol of formula III R1-OH to form the compound of formula IV

the radicals R 1 and R ₂ having the same meaning as for the compound of formula I, b) then functionalization of the amino group to give the compound of formula I, steps a) and b) being carried out in a single reactor. 2. Process according to claim 1, characterized in that R 1 represents a linear or branched C ₁ -C ₆ alkyl radical, advantageously the methyl radical. 3. Method according to claim 1 or 2, characterized in that R ₂ represents the phenyl radical. 4. Method according to any one of the preceding claims, characterized in that R ₃ represents the benzyl radical. 5. Process according to any one of the preceding claims, characterized in that the esterification reaction of step a) is carried out in the presence of an acid or an acid chloride. 6. Process according to any one of the preceding claims, characterized in that, during step a), heating is carried out at a temperature of between 40 ^° C. and the boiling point of the solvent, for 2 to 36 hours. 7. Method according to any one of the preceding claims, characterized in that following step a) and prior to step b), excess acid and solvent are removed. 8. Process according to any one of the preceding claims, characterized in that step b) is carried out in an aqueous and basic medium by adding a compound R ₃ OC (O) -X (formula V), in which X represents a halogen atom. 9. Process according to claim 8, characterized in that the medium is buffered by addition of a weak base, advantageously sodium hydrogencarbonate and / or potassium hydrogencarbonate. 10. The method of claim 8 or 9, characterized in that the pH of the aqueous medium is adjusted to a value between 4 and 7. 11. A method according to any one of claims 8 to 10, characterized in that the addition of the compound of formula V is carried out at a temperature between 0 and 2O ⁰ C. 12. Process according to any one of claims 8 to 10, characterized in that the compound of formula V is benzyl chloroformate.