Process for the preparation of sitagliptin

Abstract

The present invention relates to a process for the preparation of sitagliptin.

Description

[0001] PROCESS FOR THE PREPARATION OF SITAGLIPTIN

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for the preparation of sitagliptin.

[0004] BACKGROUND OF THE INVENTION

[0005] Sitagliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor used to treat type 2 diabetes. Its structural formula (I) is

[0006] Sitagliptin contains a chiral center and only R-enantiomer is used as an active substance. Sitagliptin and its pharmaceutically acceptable acid addition salts have been first described in W003004498. In particular, Example 7 W003004498 discloses the preparation of sitagliptin base and its hydrochloride salt. W02005003135 describes dihydrogenphosphate salt of sitagliptin and crystalline hydrates thereof, in particular a crystalline monohydrate. The crucial step in the synthesis of sitagliptin is preparation of pure enantiomer of sitagliptin or its intermediate. The processes disclosed in the prior art fall mainly into three types: asymmetric reductive amination, diastereomeric resolution and biocatalytic (enzymatic) transamination. For example, asymmetric reductive amination is disclosed in W02005097733, W02006081151, W02010078440, W02016055015, W02020121321 and J. Am. Chem. Soc. 2009, vol. 131, no. 32, 11316-11317; diastereomeric resolution is disclosed in W02010131025, WO2013114173, W02009085990, WO2010122578, W02016110750 and W02010009630; biocatalytic transamination is disclosed in W02010099501, W02011005477,

[0007] WO2014133960, Science 329, 305-309 (2010), W02019011236,

[0008] WO2021135886, WO2021077425, W02021250702, CN110951706,

[0009] CN112048485, CN108866021, CN113481254 and CN113121546.

[0010] Biocatalytic transamination with transaminase enzymes is arguably the shortest and simplest route to sitagliptin. The process was first disclosed in W02010099501, wherein ketoamide of formula (IV) was transaminated to sitagliptin.

[0011] Other possible pathways are longer regarding the number of reaction steps. In the case of asymmetric reductive amination the process is at least one step longer than the enzymatic process and in the case of diastereomeric resolution the process is at least two steps longer and also produces 50 % of undesired enantiomer which has to be recycled. Considering the number of steps, the synthesis time and also the amount of waste (solvents, excess reagents,...) produced, the enzymatic process is clearly the process of choice.

[0012] Enzymatic process itself can also be further optimized but not in a way to reduce the number of synthetic steps but in a way to reduce reaction times, to reduce the number of isolation steps, to reduce waste produced, to use minimal excess of reagents needed or to use regenerated solvent and / or second crops.

[0013] In W02010099501 the enantioselective enzymatic transamination process is described in detail. It is stated that for the successful transformation you need to add dimethyl sulfoxide (DMSO) solution of prochiral ketoamide (compound of formula (IV)) to alkaline buffered solution (pH above 8) of an enzyme, a cofactor (pyridoxal 5'-phosphate) and a nitrogen source (isopropylamine) in water and triethanolamine. The DMSO solution of ketoamide (IV) is prepared from isolated ketoamide, which is dissolved in DMSO. The alkaline buffered solution is prepared by partially neutralizing isopropylamine and triethanolamine with hydrochloric acid. It is imperative to perform the reaction under alkaline-buffered conditions, because of enzyme instability in acidic and neutral media and the fact that enantioselective transamination reaction is much slower or impossible to perform in acidic or neutral conditions. Also, it is very important that isopropylamine is added over the course of the reaction to ensure adequate amount of nitrogen source for transamination. The excess of isopropylamine in the reaction mixture is achieved with its continuous addition, which is important for two reasons; firstly, isopropylamine reacts during the enantioselective transformation, its concentration decreases and acetone is formed as a side product. Secondly, as acetone acts as an enzyme inhibitor and slows down the transamination, it needs to be removed from the reaction mixture with a nitrogen headspace sweep, which simultaneously removes nitrogen source isopropylamine. l-(3-(trifluoromethyl)-5,6-dihydro-[l,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl)-4- (2,4,5-trifluorophenyl)butane-l,3-dione (compound of formula (IV)) can be prepared according to processes disclosed in W02005003135 and W02004083212, which describe the synthesis of compound of formula (IV) by reacting a compound of formula (II) with a compound of formula (III) in a solvent and in the presence of an organic base, for example N,N- diisopropylethylamine (DIPEA). Compound of formula (II) is prepared from 2- (2,4,5-trifluorophenyl)acetic acid and Meldrum's acid.

[0014] The main role of the organic base is to neutralize hydrogen chloride, which is present in the compound (III). After the reaction is completed, volatile components are evaporated and ketoamide (IV), the organic base and / or its hydrochloride salt are the main components that are left in the residue after evaporation. To isolate pure solid ketoamide (IV) the residue is dissolved in a mixture of water immiscible organic solvent and water to perform an extraction and to remove the organic base. After the extraction volatile components are evaporated again to crystallize ketoamide (IV) from appropriate solvent.

[0015] The inventors of the present invention have surprisingly found that crude ketoamide (IV) can be used in the next step of enzymatic transamination without purification. The organic base and its hydrochloride salt present in the crude ketoamide (IV) can act as a buffer and therefore less organic base is used to buffer the transamination reaction. This solution has two positive consequences which are shorter synthesis of sitagliptin in terms of reaction time and greener synthesis due to less waste produced.

[0016] DETAILED DESCRIPTION OF THE INVENTION

[0017] The object of the present invention is a process for the preparation of sitagliptin of formula (I) comprising the following steps: a) reacting a compound of formula (II) with a compound of formula (III) in a solvent and in the presence of an organic base to obtain a compound of formula (IV) in a reaction mixture b) optionally removing the solvent from the reaction mixture; and c) subjecting the compound of formula (IV) in the reaction mixture to enzymatic transamination to form sitagliptin, wherein the organic base is not removed from the reaction mixture.

[0018] The organic base can be any suitable organic base, preferably the organic base is selected from the group consisting of N,N-diisopropylethylamine, triethylamine, diisopropylamine, triethanolamine, 2,4,6-collidine, imidazole, pyridine, lutidine, 4-Dimethylaminopyridine, l,4-diazabicyclo[2.2.2]octane, and / or l,8-Diazabicyclo[5.4.0]undec-7-ene. Preferably, the organic base is N,N-diisopropylethylamine, triethylamine and / or diisopropylamine. Most preferably, the organic base is N,N-diisopropylethylamine. The term "the group consisting of N,N-diisopropylethylamine, triethylamine, diisopropylamine, triethanolamine, 2,4,6-collidine, imidazole, pyridine, lutidine, 4-Dimethylaminopyridine, l,4-diazabicyclo[2.2.2]octane, and / or 1,8- Diazabicyclo[5.4.0]undec-7-ene" can be used in the present application interchangeably with the term "the group consisting of N,N- diisopropylethylamine, triethylamine, diisopropylamine, triethanolamine, 2,4,6-collidine, imidazole, pyridine, lutidine, 4-Dimethylaminopyridine, 1,4- diazabicyclo[2.2.2]octane, l,8-Diazabicyclo[5.4.0]undec-7-ene, and mixtures thereof".

[0019] The solvent can be any suitable solvent. Preferably the solvent is an organic solvent. More preferably, the solvent is selected from the group consisting of acetonitrile, tetrahydrofuran, dimethoxymethane, dimethylether, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, isopropyl acetate, ethyl acetate, methyl tertiary-butyl ether (MTBE), and / or toluene. The term "the group consisting of acetonitrile, tetrahydrofuran, dimethoxymethane, dimethylether, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, isopropyl acetate, ethyl acetate, methyl tertiary- butyl ether (MTBE), and / or toluene" can be used in the present application interchangeably with the term "the group consisting of acetonitrile, tetrahydrofuran, dimethoxymethane, dimethylether, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, isopropyl acetate, ethyl acetate, methyl tertiary-butyl ether (MTBE), toluene, and mixtures thereof". Especially, the solvent can comprise acetonitrile or can be a mixture comprising acetonitrile and one or more of tetrahydrofuran, dimethoxymethane, dimethylether, dimethylformamide, dimethylacetamide, N-methyl-2- pyrrolidone, isopropyl acetate, ethyl acetate, methyl tertiary-butyl ether (MTBE), and toluene. Most preferably, the solvent is acetonitrile.

[0020] In a preferred aspect of the present invention the solvent is acetonitrile and the organic base is N,N-diisopropylethylamine.

[0021] Optionally, step a) can comprise combining a compound of formula (II) with a compound of formula (III) in a solvent and in the presence of an organic base, and heating the so obtained mixture to a temperature in the range of 60 to 66°C.

[0022] The removing of the solvent (in step b)) can be partially or completely removing the solvent. Optionally, in step b) of the process according to present invention, the solvent can be removed from the reaction mixture and the obtained residue can be redissolved in another solvent. Preferably, said "another solvent" is dimethylsulfoxide (DMSO) or a mixture of solvents comprising DMSO. The term "another solvent" can encompass a solvent different from the solvent removed in step b), as well as can encompass mixtures of solvents, which mixtures of solvents comprise one or more (especially two or more) solvents different from the solvent removed in step b). Said mixtures of solvents can be optionally free of the solvent removed in step b) or can optionally comprise the solvent removed in step b) (in addition to one or more solvents different from the solvent removed in step b)). The removing of the solvent can be carried out e.g. by evaporating the solvent, optionally at a pressure reduced below ambient pressure. For example, after the reaction is completed, acetonitrile as the most preferred solvent can be removed and obtained residue redissolved in dimethylsulfoxide.

[0023] The enzymatic transamination is preferably performed by adding the compound of formula (IV) in the reaction mixture to a buffered solution comprising an alkaline buffer, an enzyme (transaminase enzyme for providing transaminase activity), a cofactor (preferably a cofactor for transaminase, especially selected from vitamin B6 family compounds pyridoxal 5'-phosphate (PLP), pyridoxine, pyridoxal, pyridoxamine, pyridoxine 5'-phosphate, and / or pyridoxamine 5'-phosphate) and a nitrogen source (preferably isopropylamine). Especially, the enzymatic transamination can be performed by adding the compound of formula (IV) in the reaction mixture to a buffered solution comprising an alkaline buffer, a transaminase, a cofactor for transaminase (especially selected from vitamin B6 family compounds pyridoxal 5'-phosphate (PLP), pyridoxine, pyridoxal, pyridoxamine, pyridoxine 5'- phosphate, and / or pyridoxamine 5'-phosphate), and a nitrogen source (preferably isopropylamine).

[0024] Optionally, the reaction mixture obtained after adding the compound of formula (IV) in the reaction mixture to a buffered solution comprising an alkaline buffer, an enzyme, a cofactor and a nitrogen source, can be heated to a temperature in the temperature range of 40 to 46°C.

[0025] The term "alkaline buffer" as used herein refers to an aqueous solution having a pH above 7.0 and comprising a weak base and its conjugate acid. The alkaline buffer can be any suitable buffer, most preferably the alkaline buffer is triethanolamine buffer. Triethanolamine buffer can be an aqueous solution having a pH above 7.0 and comprising triethanolamine and its conjugate acid.

[0026] The pH of the buffered solution is preferably more than 8.0, more preferably more than 8.5 and most preferably more than 9.0. The pH of the buffered solution is preferably in the range of more than 8.0 to 12, more preferably in the range of more than 8.5 to 11.5, and most preferably in the range of more than 9.0 to 11.0.

[0027] The enzyme can be any suitable transaminase enzyme capable of converting the compound of formula (IV) to sitagliptin. For example, the enzyme disclosed in W02010099501, W02011005477 or WO2014133960 can be used. Alternatively, commercial enzymes can be used such as an enzyme designated as CDX-036, which is commercially available and can be obtained from the company Codexis (Codexis, Inc., Redwood City, United States).

[0028] The cofactor can be any suitable cofactor, preferably the cofactor is selected from vitamin B6 family compounds pyridoxal 5'-phosphate (PLP), pyridoxine, pyridoxal, pyridoxamine, pyridoxine 5'-phosphate, and / or pyridoxamine 5'- phosphate. Most preferably, the cofactor is pyridoxal 5'-phosphate. The term "pyridoxal 5'-phosphate (PLP), pyridoxine, pyridoxal, pyridoxamine, pyridoxine 5'-phosphate, and / or pyridoxamine 5'-phosphate" can be used herein interchangeably with the term "pyridoxal 5'-phosphate (PLP), pyridoxine, pyridoxal, pyridoxamine, pyridoxine 5'-phosphate, pyridoxamine 5'-phosphate, and mixtures thereof".

[0029] The nitrogen source can be any suitable nitrogen source, preferably the nitrogen source is selected from isopropylamine, alanine, 3-aminobutyric acid, and / or methylbenzylamine. Most preferably, the nitrogen source is isopropylamine.

[0030] In a preferred aspect of the present invention the buffered solution comprises an enzyme, pyridoxal 5'-phosphate as a cofactor, isopropylamine as a nitrogen source and triethanolamine buffer as an alkaline buffer.

[0031] In a more preferred aspect of the present invention the buffered solution comprises an enzyme, pyridoxal 5'-phosphate as a cofactor, isopropylamine as a nitrogen source and triethanolamine buffer as a buffer, wherein the pH of the buffered solution is more than 9.0. In another aspect of the present invention the solvent is acetonitrile, the organic base is N,N-diisopropylethylamine and the buffered solution comprises triethanolamine buffer as an alkaline buffer.

[0032] In a preferred aspect of the present invention the solvent is acetonitrile, the organic base is N,N-diisopropylethylamine and the enzymatic transamination is performed by subjecting the compound of formula (IV) in the reaction mixture to enzymatic transamination by adding the compound of formula (IV) in the reaction mixture to a buffered solution comprising pyridoxal 5'- phosphate as a cofactor, isopropylamine as a nitrogen source and triethanolamine buffer as an alkaline buffer.

[0033] In a most preferred aspect of the present invention the solvent is acetonitrile, the organic base is N,N-diisopropylethylamine, and the enzymatic transamination is performed by subjecting the compound of formula (IV) in the reaction mixture to enzymatic transamination by adding the compound of formula (IV) in the reaction mixture to a buffered solution comprising an enzyme, pyridoxal 5'-phosphate as a cofactor, isopropylamine as a nitrogen source and triethanolamine buffer as an alkaline buffer, wherein the pH of the buffered solution is more than 9.0.

[0034] Compound of formula (II) can optionally be prepared in situ from 2-(2,4,5- trifluorophenyl)acetic acid and Meldrum's acid (2,2-dimethyl-l,3-dioxane-4,6- dione) in the presence of pivaloyl chloride and a base and used directly in the next step according to the present invention without isolation and / or purification.

[0035] The process of the present invention for the preparation of sitagliptin thus can comprise, before step a), a step of reacting 2-(2,4,5-trifluorophenyl)acetic acid and Meldrum's acid in the presence of pivaloyl chloride and a base to obtain a reaction product being or comprising compound of formula (II), the reaction product being or comprising compound of formula (II) being used without isolation and / or purification in step a).

[0036] Step c) can be in particular subjecting the compound of formula (IV) in the reaction mixture obtained in step a) to enzymatic transamination to form sitagliptin, wherein the organic base is not removed from the reaction mixture.

[0037] Step c) can be in particular subjecting the compound of formula (IV) in the reaction mixture obtained in step b) to enzymatic transamination to form sitagliptin, wherein the organic base is not removed from the reaction mixture.

[0038] The process of the present invention can further comprise (after step c)) step d) of isolating sitagliptin formed in step c), optionally further followed by purifying the isolated sitagliptin. In an embodiment, the process of the present invention can further comprise step d) of isolating sitagliptin formed in step c), optionally further followed by reacting the isolated sitagliptin with an acid (preferably hydrochloric acid) to prepare a sitagliptin acid addition salt (preferably sitagliptin hydrochloride).

[0039] If not explicitly otherwise indicated, pH values can be determined at 20°C, especially at 20°C and 1 atm.

[0040] The present invention is illustrated in more detail below by the following non-limiting examples:

[0041] EXAMPLES

[0042] Example 1:

[0043] To the mixture of 25.0 g of 5-(l-hydroxy-2-(2,4,5-trifluorophenyl)ethylidene)- 2, 2-dimethyl-l,3-dioxane-4, 6-dione and 18.8 g of 3-(trifluoromethyl)- 5,6,7,8-tetrahydro-[l,2,4]triazolo[4,3-a]pyrazine hydrochloride in 175 mL of acetonitrile, 14.8 mL of N,N-diisopropylethylamine was added. The reaction mixture was heated to 65 °C until complete conversion. The volatile compounds were evaporated or partially evaporated. Residue was dissolved in 45 mL of DMSO to obtain a solution of ketoamide substrate (IV).

[0044] In a separate reactor, 0.22 g of pyridoxal 5'-phosphate hydrate was dissolved in 150 mL of triethanolamine buffer solution with pH > 8. 0.78 g of enzyme CDX-036 (commercially available from the company Codexis (Codexis, Inc., Redwood City, United States)) in 22 mL of DMSO was slowly added and the mixture was heated to about 45 °C. The pH was controlled above 9 using aqueous solution of isopropylamine. The solution of ketoamide substrate (IV) was slowly added. During and after addition, pH was controlled above 9 using aqueous solution of isopropylamine and light nitrogen flow was established above the reaction mixture. Ketoamide was consumed in 22 hours.

[0045] Reaction mixture was diluted and acidified using HCI(aq) to pH ~ 2. Enzyme was denaturated and removed from reaction mixture by filtration through randalite pad (randalite being a commercially available filtration aid; randalite comprises inorganic material, e.g. perlites).

[0046] Randalite pad was washed with water. To the combined filtrate, 310 mL of isopropyl acetate is added, the mixture is alkalized using sodium hydroxide solution, agitated, settled and separated. Aqueous phase is extracted once more with isopropyl acetate. Brine is added if necessary for better phase separation. Combined organic phases are washed with brine solution, volatile compounds are evaporated and crude sitagliptin is isolated.

[0047] To purge impurities, 200 mL of isopropanol and 7.3 mL of concentrated hydrochloric acid were added to crude sitagliptin, the mixture was heated until clear solution was obtained and then sitagliptin hydrochloride was isolated by crystallization having purity above 99 % and enantiomeric purity above 99.8 %.

Claims

CLAIMS1. A process for the preparation of sitagliptin of formula (I)comprising the following steps: a) reacting a compound of formula (II) with a compound of formula (III) in a solvent and in the presence of an organic base to obtain a compound of formula (IV) in a reaction mixtureb) optionally removing the solvent from the reaction mixture; and c) subjecting the compound of formula (IV) in the reaction mixture to enzymatic transamination to form sitagliptin,wherein the organic base is not removed from the reaction mixture. The process according to claim 1, wherein the organic base is selected from the group consisting of N,N-diisopropylethylamine, triethylamine, diisopropylamine, triethanolamine, 2,4,6-collidine, imidazole, pyridine, lutidine, 4-Dimethylaminopyridine, l,4-diazabicyclo[2.2.2]octane, and / or l,8-Diazabicyclo[5.4.0]undec-7-ene. The process according to claim 2, wherein the organic base is N,N- diisopropylethylamine, triethylamine and / or diisopropylamine. The process according to claim 3, wherein the organic base is N,N- diisopropyl ethylamine. The process according to any one of the preceding claims, wherein the solvent is selected from the group consisting of acetonitrile, tetrahydrofuran, dimethoxymethane, dimethylether, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, isopropyl acetate, ethyl acetate, methyl tertiary- butyl ether and / or toluene. The process according to any one of the preceding claims, wherein the solvent is acetonitrile. The process according to any one of the preceding claims, wherein the solvent is acetonitrile and the organic base is N,N- diisopropyl ethylamine.The process according to any one of the preceding claims, wherein the enzymatic transamination is performed by adding the compound of formula (IV) in the reaction mixture to a buffered solution comprising an alkaline buffer, an enzyme, a cofactor and a nitrogen source. The process according to claim 8, wherein the cofactor is pyridoxal 5'- phosphate. The process according to any one of claims 8 to 9, wherein the nitrogen source is isopropylamine. The process according to any one of claims 8 to 10, wherein the alkaline buffer is triethanolamine buffer. The process according to any one of claims 8 to 11, wherein the buffered solution comprises an enzyme, pyridoxal 5'-phosphate as a cofactor, isopropylamine as a nitrogen source and triethanolamine buffer as an alkaline buffer. The process according to any one of claims 8 to 12, wherein the pH of the buffered solution is more than 9.

0. The process according to claim 1, wherein the solvent is acetonitrile, the organic base is N,N-diisopropylethylamine and the enzymatic transamination is performed by subjecting the compound of formula (IV) in the reaction mixture to enzymatic transamination by adding the reaction mixture to a buffered solution comprising an enzyme, pyridoxal 5'-phosphate as a cofactor, isopropylamine as a nitrogen source and triethanolamine buffer as an alkaline buffer.

15. The process according to claim 14, wherein the pH of the buffered solution is more than 9.0.

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