WO2022018625A1

WO2022018625A1 - Process for the preparation of an intermediate used in the synthesis of letermovir

Info

Publication number: WO2022018625A1
Application number: PCT/IB2021/056528
Authority: WO
Inventors: Stefania BERTUOLO; Mara Sada; Alberto Mazza; Aldo Bianchi; Lazzaro Feliciani; Giorgio Bertolini
Original assignee: Olon SpA
Current assignee: Olon SpA
Priority date: 2020-07-21
Filing date: 2021-07-20
Publication date: 2022-01-27
Anticipated expiration: 2023-01-21
Also published as: IT202000017617A1

Abstract

Disclosed is an enantioselective process for the preparation of letermovir of formula (I) which comprises enantioselective addition of (S)-1-(4-benzyl-2-thioxothiazolidin-3-yl)ethanone (IV), catalysed by TiCl4 on the imine of formula III, to give intermediate V, which is hydrolysed to the acid of formula VI and subsequently cyclised in the presence of organic bases to give intermediate VII, from which letermovir is obtained with good yields and a high degree of enantioselection.

Description

PROCESS FOR THE PREPARATION OF AN INTERMEDIATE USED IN THE

SYNTHESIS OF LETERMOVIR

The present invention relates to an enantioselective process for the preparation of letermovir.

Technical context

Letermovir ((4S)-2-{ 8-fluoro-2 - [4-( 3 -methoxypheny l)piperazin- 1 -y 1] - 3 - [2- methoxy-5-(trifluoromethyl)phenyl]-3 ,4-dihydroquinazolin-4-yl } acetic acid), of formula

1

was recently approved by the regulatory agencies of various countries, including tire USA, Canada, Japan and Europe, for the prevention of cytomegalovirus (CMV) infection reactivation and CMV disease in CMV-positive adults after an allogeneic haematopoietic stem cell transplant (HSCT). The medicament (tradename Prevymis®) has a novel action mechanism: it inhibits the CMV enzyme known as “terminase” involved in DNA packaging in the protein coatings of the virus. In this way the virus is prevented from developing correctly and infecting other cells.

Letermovir exhibits stereoisomerism due to the presence of a chiral centre with the S configuration on the C4 carbon atom of the dihydroquinazoline ring.

The penultimate step in the synthesis method disclosed in WO2006133822, WO2013127971 and WO2013127968 is resolution with chiral salts of (4R/S)-2-{8- fluoro-2-[4-(3-methoxyphenyl)piperazin-1-yl]-3-[2-methoxy-5-(trifluoromethyl)phenyl]- 3 ,4-dihy droquinazolin-4-yl } acetic acid in racemic form to give letermovir, leading to a reduction in the global yield of the process, and loss of the undesirable enantiomer.

Various studies designed to improve the synthesis of letermovir by introducing the stereocentre via an enantioselective reaction were later published.

Guy R Humphrey et al. described in Org. Process. Res. Dev. 2016, 20, 1097- 1103 an enantioselective aza-Michael reaction catalysed by chiral quaternary bisammonium salts. Said salts are unstable in a basic medium and are used in phase- transfer conditions, giving rise to a product with moderate enantioselectivity and not very high yields. The synthesis comprises the formation of guanidine salicylate (intermediate A), obtained after 5 steps, followed by enantioselective closure of the heterocyclic ring (intermediate B) by means of the aza-Michael reaction. To improve the low enantioselection, chiral enrichment of intermediate B was subsequently performed, using the formation of diastereoisomeric salts of a tartaric acid derivative. Letermovir is subsequently obtained by unblocking the salt and hydrolysing the methyl ester.

.

K. Chung et al. in J. Am. Chem. Soc. 2017, 139, 10637-10640 perfected the aza- Michael reaction by using chiral Bnansted acids, which are more efficient than quaternary amines in catalysing the closure of the 3,4-dihydroquinazoline ring, allowing a simpler scale-up and eliminating the enantiomeric enrichment step with the formation of diastereoisomeric salts.

The best results were obtained with chiral bi-naphthol and 1,2 diamine triflates, with enantiomeric excesses determined by HPLC at around 90:10 for naphthol and up to 93.8:6.2 for the most efficient diamine triflate derivative.

Wang et al. in Angew. Chem. Int. Ed. 2017, 56, 16032-16036 introduced the chiral carbon of letermovir via enantioselective closure of intermediate C, using an allylic animation reaction in the presence of a palladium complex with chiral ligands, preferably selected from phosphoramidites.

The allyl portion of intermediate D (closed intermediate) is subsequently oxidised in various steps to obtain the corresponding ester H, thereby increasing the number of reactions in the synthesis method.

The purpose of the invention is to find a novel enantiose!ective synthesis method that produces letermovir with high enantiomeric excesses and a higher yield, using cheaper intermediates.

It has surprisingly been found that by using enantioselective addition of (S)-1-(4- benzyl-2-thioxothiazolidin-3 -y l)ethanone (TV), catalysed by TiCl₄ on the imine of formula ΠΙ, intermediate V is obtained with a high degree of diastereoselection. Intermediate V is hydrolysed to the corresponding acid of formula VI and then cyclised in the presence of organic bases to give intermediate VII.

Letermovir is obtained from intermediate VII, via a series of reactions, with good yields (57%) and a high degree of enantioselection, with no need for enrichments with chiral salts or particular purifications of the intermediates using chromatography columns.

Brief description of drawings

Figure 1 : chromatogram relating to the compound of formula VII for determination of the enantiomeric ratio.

Figure 2: chromatogram relating to the compound of formula IX with R’= Bn for determination of the enantiomeric ratio.

Figure 3: chromatogram relating to the compound of formula IX with R'= Me for detennination of the enantiomeric ratio.

Figure 4: chromatogram relating to letermovir (I) for determination of the enantiomeric ratio.

Disclosure of the invention

The present invention relates to an enantioselective process for the preparation of letermovir of formula (I) which comprises: a) Reaction of compound of formula III, wherein R is a straight or branched C1- C4 alkyl, with (S)-1-(4-benzyl-2-thioxothiazolidin-3-yl)ethanone (IV), in the presence of TiCl₄ and an aliphatic amine;

b) Hydrolysis of compounds of formula V obtained in a) in the presence of bases to give compounds of formula VI;

c) Cyclisation of compounds of formula VI in the presence of organic bases

d) Esterification of compound of formula VII

e) Reaction of ester of formula VIII with N-(3-methoxyphenyl)piperazine or a salt thereof to give compound of formula IX in the presence of a chlorinating agent and an organic base

f) Hydrolysis of compound of fonnula IX to give letermovir I

In the formulas reported above, R represents a straight or branched C1-C4 alkyl, R^* represents a straight C1-C3 alkyl or a benzyl group, and X represents chlorine, bromine or a hydroxy group.

The term “organic base” refers to aliphatic or aromatic amines, alcoholates and carboxylates.

The term “base” refers to any basic organic or inorganic compound that has basicity according to Bransted definition.

The following commonly used acronyms will be used in the description and the examples, and their meanings are listed below.

THF = tetrahydrofuran

DCM = dichloromethane

DMF = dimethylfonnamide IPA = isopropanol RT = room temperature DBU - 1,8-diazabicyclo[5,4,0]undec-7-ene.

DMAP = dimethylaminopyridine.

GDI = carbonyldiimidazole.

DCC = dicyclohexylcarbodiimide.

EDC = 1 -ethyl-3-(3-dimethylaminopropyl)carbodiimide.

Intermediate III is obtained by condensing (2-fluaro-6-formylphenyl)carbamate with 2-methoxy-5-(trifluoromethyl)anilme in an organic solvent

Step a) is conducted in an aprotic solvent selected from toluene, methylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichloroethane, chloroform or mixtures thereof, preferably methylene chloride at a temperature ranging between -90°C and 0°C, and advantageously at -60°C.

The amine used in step a) is selected from triethylamine, diisopropylamine and tetramethylenediamine, sparteine, preferably triethylamine or diisopropylamine, and more preferably diisopropylamine. Crude (2-((S)-3-((S)-4-benzyl-2-thioxothiazolidin-3-yl)-1-((2-methoxy-5- (trifluoromethyl)phenyl)amino)-3-oxopropyl)-6-fluorophenyl)carbamate (V) is obtained at the end of the reaction, and used in the next step without any purification.

In step b), (2-((S)-3-((S)-4-benzyl-2-thioxothiazolidin-3-yl)-1-((2-methoxy-5- (trifluoromethyl)phenyl)ammo)-3-oxopropyl)-6-fluorophenyl)carbamate (V) IS hydrolysed in a mixture of solvents selected from tetrahydrofuran, dioxane, dimethoxyethane, dichloromethane and 1,2-dicycloethane in combination with water in tiie presence of bases selected from alkali hydroxides, potassium tert-butylate, sodium methylate, sodium ethylate, sodium and potassium carbonates and bicarbonates, and DMAP; the preferred conditions are tetrahydrofuran/ water with the addition of sodium hydroxide.

The resulting crude (S)-3-(2-((ethoxycarbonyl)amino)-3-fluorophenyl)-3-((2- methoxy-5-(trifluoromethyl)phenyl)amino)propanoic acid (VI) is isolated and used in the next reaction without further purification.

The heterocyclic ring closure reaction (step c) to give (5)-2-(8-fluoro-3-(2- methoxy-5-(trifluoromethyl)phenyl)-2-oxo-1,2,3,4-tetrahydroquinazolin-4-yl)acetic acid (VII) is conducted in a polar solvent selected from acetonitrile, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, dimethoxy ethane, ethanol and methanol, preferably acetonitrile in the presence of an organic base, preferably selected from DBU, DMAP, triethylamine, pyridine, potassium tert-butylate, sodium methylate and sodium ethylate, advantageously DBU.

Compound VII, isolated from the preceding reaction as a solid, has an enantiomeric ratio of 99.6: 0.4, calculated by chiral HPLC (Figure 1).

Esterification step d) can be conducted in various ways. Acid VII is reacted with alcohols selected from straight C1-C3 alcohols, benzyl alcohol in the presence of a condensing agent selected from DCC, EDC and GDI, preferably GDI, and an organic base selected from DBU, triethylamine and DMAP, advantageously DBU.

Alternatively, step d) is conducted in the presence of methyl bromide, ethyl bromide, benzyl bromide or chloride, preferably benzyl bromide, in a polar aprotic solvent selected from acetone, methyl ethyl ketone and acetonitrile, under reflux.

Step e), which gives rise to synthesis of compound IX, is conducted in the presence of a chlorinating agent selected from POCl₃ and PCl₅, preferably PCl₅, and N-(3- methoxyphenyI)piperazine or a salt thereof, with the addition of organic bases selected from DBU, DMAP and TEA, advantageously DBU. The reaction is conducted in a mixture of solvents selected from toluene, chlorobenzene, dioxane, DMF and TFE, preferably DMF and TFE, advantageously DMF. Step f), when R* is benzyl, is conducted in the presence of gaseous hydrogen and a metal catalyst, preferably palladium on carbon, to give letermovir with an enantiomeric ratio of 99.97: 0.03, calculated by chiral HPLC.

Alternatively, the benzyl can be removed by using as hydrogen source formic acid or ammonium formate in water in the presence of a metal catalyst, preferably palladium on carbon.

If R^* is methyl or ethyl, step f) is conducted in the presence of alkali hydroxides, preferably sodium hydroxide.

The invention is described in greater detail in the examples below. Experimental conditions for determination of enantiomeric ratios by HPLC

Figure 1

HPLC analyses for determination of the enantiomeric ratio of (S)-2-(8-fluoro-3-(2- methoxy-5 -(trifluoromethy l)pheny l)-2-oxo- 1 ,2 , 3 ,4-tetrahy droquinazolin-4-y l)acetic acid

(VII)) were conducted with an Agilent Technologies 1260 Infinity II instrument under the following conditions:

• Column: Lux i-CelluIose-550 x 4.6 mm 3 pm

• Mobile phase: Isocratic, 850 ml Hexane + 150 ml IPA + 1 ml HCOOH

• Flow rate: 1 ml/min

■ Injection: 20 pL

• Temperature: 40°C

• UV (λ = 250 mn) Samples: 20 mg in 5 ml MeOH+ 5 ml IPA at 20 ml with hexane (1 mg/ml).

Figure 2

HPLC analyses for determination of the enantiomeric ratio of (S)-methyl 2-(8- fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3-methoxyphenyl)piperazin-1-yl)- 3,4-dihydroquinazolin-4-yl)acetate (IX) were conducted with an Agilent Technologies 1260 Infinity II instrument under the following conditions:

• Column: Lux Amylose 1 250*4.6 mm 3 pm

• Mobile phase: Isocratic, 1000 ml Hexane + 30 ml IPA 0.2% DBA

• Flow rate: 2 ml/min

• Injection: 20 pL

• Temperature: 40°C

• UV (λ = 250 nm)

Samples: 10 mg in 3 mL IPA at 10 ml with hexane 0.2% DBA (1 mg/ml).

Figure 3

HPLC analyses for determination of the enantiomeric ratio of (S)-benzyl 2-(8- fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-oxo- 1 ,2,3,4-tetrahydroquinazolin-4- yl)acetate (IX) were conducted with an Agilent Technologies 1260 Infinity II instrument under the following conditions:

• Column: Lux Cellulose-3 50 x 4.6 mm 3 pm

• Mobile phase: Isocratic, 900 ml Hexane + 100 ml IPA

• Flow rate: 1.5 ml/min

• Injection: 10 μL

• Temperature: 40°C

• UV (λ = 250 run)

Sample Preparation: 20 mg in 5 ml MeOH+ 5 ml IPA at 20 ml with hexane

(1 mg/ml).

Figure 4

HPLC analyses for determination of the enantiomeric ratio of letermovir were conducted with an Agilent Technologies 1260 Infinity II instrument under the following conditions:

• Column: Lux Amylose 1250*4.6 mm 3 mm

• Mobile phase: Isocratic, 850 ml Hexane + 150 ml IPA 0.2% DBA

• Flow rate: 1.0 ml/min

• Injection: 20 fiL

• Temperature: 45°C

• UV (λ = 250 nm)

Sauries: 10 mg in 1.5 mL IPA at 10 ml with hexane (1 mg/ml)

Example 1

Synthesis of ethyl (2-fluo ro-6-(((2-m ethoxy-5-(trifluorom ethyl)pheny l)imino)- methyl)phenyl)carbamate

a) 2-methoxy-5 -{trifluoromethy l)aniline (13.8 g) is added to a solution of (2- fluoro-6-formylphenyl)carbamate (15.2 g) in toluene (47 mL), and the mixture is stirred at room temperature for 24 hours. The solid is filtered, and dried at 65°C to obtain 18.3 g of crude product. The solid is dissolved in isopropanol (146 mL) at 60°C, left to cool at room temperature, and stirred for 2-3 h. The mixture is filtered and dried at 65°C. 14.0 g of ethyl (2-fluoro-6-(((2-methoxy-5-(trifluoromethyl)phenyl)imino)methyl)phenyl)- carbamate (yield 50.6%) is obtained as a pale yellow solid. b) 2-methoxy-5 -(trifluoromethy l)aniline (18.2 g) is added to a solution of (2- fluoro -6 -formylphenyl)carbamate (20.0 g) in toluene (60 mL), and the mixture is stirred at room temperature for 24 hours. The solvent is then distilled under vacuum to residue, to obtain 36.5 g of ethyl (2-fluoro-6-(((2-methoxy-5-(trifluoromethyl)phenyl)imino)- methyl)phenyl)carbamate as a crude solid.

¹H NMR (300 MHz, d₆-DMSO): δ=9.59 (s, 1H), 8.61 (s, 1H), 7.89-7.86 (d, ³J=7.1, 1H), 7.61-7.59 (d, ³J=8.4, 1H), 7.48-7.39 (m, 3H), 7.28-7.25 (d, ³J=8.5, 1H), 4.16- 4.08 (q, ³J=7.1, 2H), 3.90 (s, 3H), 1.24-1.19 (t, ³J=7.1, 3H).

Example 2

Synthesis of ethyl (2-((S)-3-((S)-4-benzyl-2-thioxothiazolidin-3-yl)-1-{(2- methoxy-5-(trifluoromethyl)phenyl)amino)-3-oxopropyl)-6-fhiorophenyl)carbamate

A solution of titanium tetrachloride (3.6 mL) in dichloromethane (10 mL) is added to a solution of (S)- 1 -(4-benzyl-2-thioxothiazolidin-3 -yl)ethanone (7.2 g) in dichloromethane (86 mL) at 0°C and stirred for 15 minutes. The mixture is cooled to -60°C, a solution of Ν,Ν-diisopropyl ethylamine (5.4 mL) in dichloromethane (5.4 mL) is added slowly, and the mixture is stirred for 2 hours. A solution of ethyl (2-fluoro-6-(((2- methoxy-5-(trifluoromethyl)phenyl)imino)methyl)phenyl)carbamate (10.0 g) in dichloromethane (50 mL) is dripped in, and the mixture is stirred at -60°C for 8 hours. The mixture is left to stand until 0°C is reached, and a 10% w/w aqueous solution of NH₄CI (75 mL) is added, maintaining the temperature below 10°C; the mixture is left to stand at room temperature under stirring, and the organic phase is separated and concentrated to residue. 17.0 g of crude ethyl (2-((S)-3-((S)-4-benzyl-2-thioxothiazolidin- 3 -yl)- 1 -((2-methoxy-5 -(trifluoromethyl)phenyl)amino)-3-oxopropyl)-6-fluorophenyl) carbamate is obtained, and used in the next step without any purification.

¹H NMR (300 MHz, d₆-DMSO): δ=9.14 (br s, 1H), 7.33-7.15 (m, 9H), 6.96-6.85 (m, 2H), 6.60 (br s, 1H), 5.36-5.22 (m, 2H), 4.35-4.26 (dd, ²J=17.2, ³J=10.0, 1H), 4.25- 4.05 (m, 2H), 3.88 (s, 3H), 3.55-3.49 (dd, ²J=11.7, ³J=7.7, 1H), 3.32-3.18 (dd, ²J=17.2, ³J=2.3, 1H), 3.01-2.96 (m, 3H), 1.24-1.18 (m, 3H).

Example 3

Synthesis of (S)-3-(2-((ethoxycarbonyl)amino)-3-fluorophenyl)-3-((2-methoxy- 5-(trifIuoromethyl)phenyl)amino)propanoic add

A solution of crude ethyl (2 -((S)-3-((S)-4-benzyl-2-thioxothiazolidin-3 -yl)-1-((2- methoxy-5-(trifluoromethyl)phenyl)amino)-3-oxopropyl)-6-fluorophenyl)carbamate (17.0 g) in THF (32 mL) is added to a solution of NaOH (2.6 g), water (135 mL) and tetrahydrofuran (32 mL) at 0-5°C, maintaining the temperature at 0-5°C, after which the mixture is stirred for an hour. Toluene (120 mL) and 4N HCl_(aq) (21 mL) are added, maintaining the temperature below 10°C; the mixture is left to stand at room temperature, and the aqueous phase is removed. The mixture is extracted with 0.5N NaOH_(aq) (60 mL), dichloromethane (80 mL) is added to the aqueous phase, the mixture is acidified with HCl_(aq) concentrated to an acid pH, and the organic phase is concentrated to residue. 11.2 g of crude (S)-3-(2-((ethoxycarbonyl)amino)-3-fluorophenyl)-3-((2-methoxy-5-(trifluoro- methyl)phenyl)amino)propanoic acid is obtained, and used without further purification.

¹H NMR (300 MHz, d₆-DMSO): δ=12.31 (br s, 1H), 9.14 (br s, 1H), 7.29-7.09 (m, 3H), 6.96-6.93 (d, ³J=8.3, 1H), 6.86-6.84 (d, ³J=8.3, 1H), 6.61 (br s, 1H), 5.99-5.96 (d, ³J=8.4, 1H), 5.14-5.09 (m, 1H), 4.14-4.11 (m, 2H), 3.91 (s, 3H), 2.87-2.69 (m, 2H), 1.36- 1.15 (m, 3H). Example 4

Synthesis of (S)-2-(8-fluoro-3-(2-methoxy-5~(trifluoromethyl)phenyl)-2-oxo- 1 ,2,3 ,4-tetrahy dro quinazo Iin-4-yl)aceti c acid

DBU (5.6 mL) is added to a solution of crude (S)-3-(2-((ethoxycaibonyl)amino)- 3-fluorophenyl)-3-((2-methoxy-5-(trifluoromethyl)phenyl)ammo)propanoic acid (11.2 g) in acetonitrile (280 mL), and maintained under reflux for 22 hours. The mixture is cooled to room temperature below 30°C. The mixture is cooled to 0-5°C and stirred for 4 h, the solid is filtered, and the residue is dried at 65°C. 6.74 g (yield 65% in three steps) of (S)-2-(8- fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-oxo- 1,3,4-tetrahydroquinazolin-4- yl)acetic acid is obtained.

¹H NMR (300 MHz, d₆-DMSO): δ=12.34 (br s, 1H), 9.66 (br s, 1H), 7.71-7.68 (m, 2H), 7.32-7.29 (d, ³J=9, 1H), 7.15-7.09 (m, 1H), 7.00-6.89 (m, 2H), 5.08-5.04 (m, 1H), 3.82 (s, 3H), 2.75-2.69 (dd, J=3, J=15, 1H), 2.53-2.46 (m, 1H).

Example 5

Synthesis of (S)-benzyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)- 2-oxo- 1 ,2 ,3 ,4-tetrahydro quinazolin-4-yI) acetate

A suspension of 1,1’-carbonyldiimidazole (17.2 g) in DMF (30.5 mL) is added to a solution of (S)-2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-oxo-1, 2,3,4- tetrahydroquinazolin-4-yl)acetic acid (40 g) in DMF (120 mL), and left under stirring at room temperature for 3.5 hours. A solution of benzyl alcohol (112 g) and DBU (7.7 g) in DMF (11.2 mL) is then dripped in, and the mixture is maintained under stirring for 18 hours at room temperature. The mixture is diluted with toluene, and water is dripped in.

The aqueous phase is separated, and the organic phase is washed with 5% HCl_(aq) and water. The organic phase is concentrated to residue, and 49.1 g of crude (S)-benzyl 2-(8- fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-oxo-l,2,3,4-tetrahydroquinazolin-4- yl)acetate is obtained, and used without further purification.

¹H NMR (300 MHz, d₆-DMSO): δ=9.72 (s, 1H), 7.72 (m, 2H), 7.32 (m, 4H), 7.20 - 7.10 (m, 3H), 7.00 - 6.89 (m, 2H), 5.17 (m, 1H), 4.95 (d, J=12.4, 1H), 4.87 (d, 1=12.4, 1H), 3.82 (s, 3H), 2.84 (dd, J=15.1, 5.2, 1H), 2.67 (dd, J=15.1, 6.4, 1H)

Example 6

Synthesis of (S)-methyl 2-(8-flaoro-3-(2-methoxy-5-(trifluoromethyI)phenyl)- 2-oxo-1,2,3,4-tetrahydroquinazolm-4-yl)acetate

A suspension of 1,1’-carbonyldiimidazole (5.9 g) in DMF (11 mL) is added to a solution of (S)-2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-oxo-l ,2,3,4- tetrahydroquinazolin-4-yl)acetic acid (12 g) in DMF (36 mL), and left under stirring at room temperature for 3.5 hours. A solution of methanol (4 mL) and DBU (2.3 g) in DMF (6 mL) is then dripped in, and the mixture is maintained under stirring for 18 hours at room temperature. The mixture is diluted with toluene, and water is dripped in. The aqueous phase is separated, and the organic phase is washed with 5% HCl(iq) and water. The organic phase is concentrated to residue, and 15.9 g of crude (S)-niethyl 2-(8-fluoro- · 3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-oxo-1,2,3,4-tetrahydroquinazolin-4-yl)acetate is obtained, and used without further purification.

¹H NMR (300 MHz, d₆-DMSO): δ=9.72 (s, 1H), 7.72 (m, 2H), 7.32 (d, 1H), 7.18 - 7.11 (m, 1H), 7.03 - 6.92 (m, 2H), 5.15 (t, J=6.0, 1H), 3.84 (s, 3H), 3.41 (s, 3H), 2.81 (dd, J=15, 6, 1H), 2.58 (dd, J=15, 6, 1H)

Example 7

Synthesis of (S)-benzyl 2-(8-flnoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)- 2-oxo-l ,2 ,3,4-tetrahy droqui n azolin-4-yl)acetate

Solid potassium carbonate (1.5 g) is added to a suspension of (S)-2-(8-fluoro-3-(2- methoxy-5 -(trifluoromethyl)pheny l)-2-oxo- 1 ,2,3 ,4-tetrahy droquinazolin-4-yl)acetic acid (4.0 g) in acetone (80 mL), and stirred at room temperature for 5 min. Benzyl bromide

(1.3 mL) is added, and the mixture is heated to reflux and stirred for 2-3 h. The mixture is cooled to room temperature, ethyl acetate (80 mL) and water (80 mL) are added, and the aqueous phase is removed. The organic phase is washed with water (40 mL) and concentrated to residue. 4.9 g of crude (S)-benzyl 2-(8-fluoro-3-(2-methoxy-5- (trifluoromethyl)phenyl)-2-oxo-1,2,3,4-tetrahydroqmnazolin-4-yl)acetate is obtained, and used without further purification.

¹H NMR (300 MHz, d₆-DMSO): δ=9.72 (s, 1H), 7.72 (m, 2H), 7.32 (m, 4H), 7.20 - 7.10 (m, 3H), 7.00 - 6.89 (m, 2H), 5.17 (m, 1H), 4.95 (d, J=12.4, 1H), 4.87 (d, J=12.4, 1H), 3.82 (s, 3H), 2.84 (dd, J-15.1, 5.2, 1H), 2.67 (dd, J=15.1, 6.4, 1H) Example 8

Synthesis of (S)-methyl 2-(8-fluoro-3-(2-m ethoxy-5-(trifluoromethyl)pheny I)- 2-οχο-1,2,3,4-tetrahydroquinazolin-4-yl)acetate

Solid potassium carbonate (0.75 g) is added to a suspension of (S)-2-(8-fluoro-3- (2-methoxy-5-(trifluoromethyl)phenyl)-2-oxo- 1 ,2,3,4-tetrahydroquinazolin-4-yl)acetic acid (2.0 g) in acetone (40 mL), and stirred at room temperature for 5 min. A solution of acetone containing methyl bromide (0.5 g) is added, and the mixture is heated to reflux and stirred for 2-3 h. The mixture is cooled to room temperature, ethyl acetate (40 mL) and water (40 mL) are added, and the aqueous phase is removed. The organic phase is washed with water (20 mL) and concentrated to residue. 1.9 g of crude (S)-methyl 2-(8- fluoro-3 -(2 -methoxy- 5 -(trifIuoromethyl)pheny l)-2-oxo- 1 ,2,3 ,4-tetrahydroquinazolin-4- yl)acetate is obtained, and used without further purification.

¹H NMR (300 MHz, d₆-DMSO): δ=9.72 (s, 1H), 7.72 (m, 2H), 7.32 (d, 1H), 7.18 - 7.11 (m, 1H), 7.03 - 6.92 (m, 2H), 5.15 (t, J=6.0, 1H), 3.84 (s, 3H), 3.41 (s, 3H), 2.81 (dd, J=15, 6, 1H), 2.58 (dd, J=15, 6, 1H) Example 9

Synthesis of (S)-benzyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)- 2-(4-(3-methoxyphenyl)pipenizin-1-yl)-3,4-dihydroquinazolin-4-yl)acetate

A solution of (S)-benzyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2- oxo- 1 ,2,3 ,4-tetrahydroquinazolin-4-yl)acetate (36.7 g) in chlorobenzene (220 mL) is heated to reflux and dried azeotropically. Phosphorus oxychloride (34.6 g) is dripped in, and the mixture is maintained under reflux for 3.5 h. The mixture is heated to 115-120°C, DBU (22.9 g) is dripped in, and the mixture is maintained under reflux for 18 h. The mixture is cooled to room temperature and the reaction mixture is dripped into water (240 mL), maintaining the temperature at between 40 and 50°C. The mixture is cooled to room temperature and diluted with dichloromethane (240 mL), and the organic phase is separated, then washed once with water and once with a saturated solution of NaCl(iq). The dichloromethane is distilled under atmospheric pressure. After cooling to room temperature, 1-(3-methoxyphenyl)piperazine hydrochloride (18.1 g) and 1,4-dioxane (80 mL) are added, and DBU (23.5 g) is then dripped in. The mixture is then heated under reflux for 2 h. The mixture is cooled to room temperature, diluted with dichloromethane (250 mL) and washed with water, a 5% solution of NaHCO_3(aq) and a saturated solution of NaCl_(aq). The solvent is distilled under vacuum to a small volume, after which isopropanol (300 mL) is added, and the mixture is heated until dissolution and left to stand at room temperature. The mixture is cooled at 0-5°C for 1.5 hours; the solid is filtered and the residue is dried at 65°C to obtain 32 g (yield 64%) of (S)-benzyl 2-(8-fluoro-3-(2- methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3-methoxyphenyl)piperazin-1-yl)-3,4- dihydroquinazolm-4-yl)acetate as a white solid.

¹H NMR (300 MHz, d₆-DMSO): δ=7.54 (m, 1H), 7.37 - 7.23 (m, 7H), 7.10 - 7.01 (m, 2H), 6.89 - 6.81 (m, 2H), 6.38 (m, 3H), 5.17 (d, J=12.3, 1H), 5.10 (d, J=12.3, 1H), 4.94 (t, J=7.0, 1H), 3.80 (s, 3H), 3.69 (s, 3H), 3.34 (hr m, 4H), 2.94-2.73 (hr m, 5H), 2.58

(dd, 1=14.5, 7.0, 1H)

Example 10

Synthesis of (S)-benzyI 2-(8-fluoro-3-(2-methoxy~5-(trifluoromethyI)phenyI)- 2-(4-(3-m eth oxyph enyl)p ip erazin- 1 -yl)-3,4-dihyd roquinazolin-4-yI) acetate

Phosphorus pentachloride (17 g) is added to a solution of crude (S)-benzyl 2-(8- fluoro-3 -(2-methoxy-5 -{trifluoromethy l)pheny l)-2-oxo-1,2,3,4 -tetrahydroquinazolin-4- yl)acetate (8.0 g) in dichloromethane (100 mL), heated to reflux and stirred for 2 hours. The mixture is left to cool at room temperature, water (50 mL) is added, the reflux reached is maintained for 15 min, the mixture is cooled to room temperature, and the aqueous phase is removed. The organic phase is washed with a saturated solution of NaHCO_3(aq) and NaCl_(aq), then concentrated to residue. The residue is taken up with DMF (50 mL), and a solution of 1 -(3 -methoxyphenyl)piperazme (15 g) in DMF (50 mL) is added. The solution is heated to 120-130°C and stirred for 3 h. The solution is cooled to room temperature, toluene is added, and the organic phase is washed with water and distilled to a small volume. Isopropanol (76 mL) is added, the suspension is stirred at room temperature for 18 h, the solid is filtered and the residue is dried at 65°C to obtain 7.2 g of (S)-benzyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3- methoxyphenyl)piperazin-1-yl)-3,4-dihydroquinazolin-4-yl)acetate as a white solid (yield 66%).

¹H NMR (300 MHz, d₆-DMSO): δ=7.54 (m, 1H), 7.37 - 7.23 (m, 7H), 7.10 - 7.01 (m, 2H), 6.89 - 6.81 (m, 2H), 6.38 (m, 3H), 5.17 (d, J=12.3, 1H), 5.10 (d, J=12.3, 1H),

4.94 (t, J=7.0, 1H), 3.80 (s, 3H), 3.69 (s, 3H), 3.34 (hr m, 4H), 2.94-2.73 (br m, 5H), 2.58 (dd, J=14.5, 7.0, 1H).

Example 11

Synthesis of (S)-methyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)- 2-(4-(3-methoxyphenyl)piperazin-1-yl)-3,4-dihydroquinazolin-4-yl)acetate

A solution of (S)-metiiyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2- oxo-1 ,2,3, 4-tetrahydroquinazolin-4-yl)acetaie (34 mg, 0.0825 mmol) in 12 ml of anhydrous toluene is heated to 100°C.

DMAP (20.13 mg, 0.165 mmol) and POCh (506 mg, 3.3 mmol) are added in sequence. The mixture is maintained under reflux for about 10-12 h. The solvent is removed under vacuum, and the residue is taken up with ethyl ether (10 ml) and water (10 ml). The organic phase is separated, and the aqueous phase is extracted 3 times with 5 ml of ethyl ether. The combined organic phases are washed in sequence with a saturated aqueous solution of NaHCO₃, and with a saturated solution of NaCl, then dried with Na₂SO₄. The solution is then filtered and concentrated under vacuum to residue. 3 ml of TFE and 1 -(3-methoxyphenyl)piperazine (31.7 mg, 0.165 mmol) are added. The reaction mixture is heated at 100°C for 24 h. The solvent is removed under vacuum until a residue is obtained, and the crude product is purified on silica to obtain 27 mg of (S)-methyl 2-(8- fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3 -methoxypheny l)piperazin- 1 -yl)- 3,4-dihydroquinazolin-4-l)acetate as a white solid.

Example 12

Synthesis of (S)-2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3- methoxyphenyl)piperazin-1-yI)-3,4-dihydroqainazolm-4-yl) acetic acid

5% Pd/C, 50% wet (1.0 g), suspended in H₂O (15 mL), is added to a solution of (S)-benzyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3-methoxy phenyl)- piperazin- 1 -yl)-3,4-dihydroquinazolin-4-yl)acetate (10.0 g) in THF (165 mL). The mixture is placed in a hydrogen atmosphere (3 bars) and left under stirring at 25 °C for 2 hours. The catalyst is filtered through cellulose, and the solution is concentrated to residue. Acetone (26 mL) is added, the mixture is filtered through cellulose, and the solution is dripped into in 232 mL of water. The mixture is left under stirring for 18 hours, and the solid is filtered and stove-dried at 55°C under vacuum. 7.5 g (87% yield) of (S)-2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3- methoxyphenyl)piperazin- 1 -y I)-3 ,4-dihydroquinazolin-4-y 1) acetic acid is obtained as a white solid.

¹H NMR (300 MHz, d₆-DMSO): δ=12.54 (br s, 1H), 7.54 (dd, J=8.6, 1.2, 1H), 7.40 (br s, 1H), 7.23 (d, J=8.6, 1H), 7.10 - 6.99 (m, 2H), 6.86 (m, 2H), 6.46 - 6.34 (m,

3H), 4.88 (m, 1H), 3.80 (s, 3H), 3.68 (s, 3H), 3.43 (br m, 4H), 2.97 - 2.75 (m, 5H), 2.44 (m, 1H). Example 13

Synthesis of (S)-2 -(8 -flu oro-3-(2 -m ethoxy-5-(t rifluorom ethy I)pheny l)-2-(4-(3- methoxyphenyl)piperazin-1-yl)-3,4-dihydroqumazolin-4-yl) acetic acid

5% Pd/C, 50% wet (0.13 g), and formic acid (0.37 mL) are added to a solution of

(S)-benzyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3- methoxyphenyl)piperarin-1-yl)-3,4-dihydroquinazolin-4-yl)acetate (1.3 g) in THF (15 mL). The mixture is stirred at 50°C for 1 h. The mixture is cooled to room temperature, and the catalyst is filtered through cellulose. Part of the THF is removed, H₂O is added, tiie pH is corrected to 5-6, and the product is extracted with MIBK. The organic phase is concentrated to residue, the residue is taken up with acetone (3.6 mL), and the solution is dripped into water (32.4 mL). The mixture is left under stirring for 18 hours, and the solid is filtered and stove-dried at 55°C under vacuum. 0.9 g (80.3% yield) of (S)-2-(8-fluoro- 3-(2-methoxy-5-(trifluorometiiyl)phenyl)-2-(4-(3-methoxyphenyl)piperazin-1-yl)-3,4- dihydroquinazolin-4-yl) acetic acid is obtained as a white solid.

¹H NMR (300 MHz, ( d₆-DMSO): δ=12.54 (hr s, 1H), 7.54 (dd, J=8.6, 1.2, 1H), 7.40 (hr s, 1H), 7.23 (d, J=8.6, 1H), 7.10 - 6.99 (m, 2H), 6.86 (m, 2H), 6.46 - 6.34 (m, 3H), 4.88 (m, 1H), 3.80 (s, 3H), 3.68 (s, 3H), 3.43 (hr m, 4H), 2.97 - 2.75 (m, 5H), 2.44 (m, 1H). Example 14

Synthesis of (S)-2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyI)-2-(4-(3- methoxyphenyl)piperazin-1-yl)-3,4-dihydroquinazolin-4-yl) acetic acid

5% Pd/C, 50% wet (0.33 g), water (6 mL) and ammonium formate (1.1 g) are added to a solution of (S)-benzyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2- (4-(3-methoxyphenyl)piperazin- 1 -yl)-3 ,4 -dihy droquinazolin-4-yl)acetate (3.3 g) in THF (32 mL). The mixture is stirred at 50°C for 1.5 h. The mixture is cooled to room temperature, and the catalyst is filtered through cellulose. Part of the THF is removed, H₂O is added, the pH is corrected to 5-6, and the product is extracted with MIBK. The organic phase is concentrated to residue, the residue is taken up with acetone (8.6 mL), and the solution is dripped into water (77 mL). The mixture is left under stirring for 18 hours, and the solid is filtered and stove-dried at 55°C under vacuum. 2.4 g (84.2% yield) of (S)-2-(8-fluoro-3 -(2 -methoxy-5 -(trifluoromethyl)pheny l)-2-(4-(3 -methoxy- phenyl)piperazin- 1 -yl)-3,4-dihydroquinazolin-4-yl) acetic acid is obtained as a white solid.

¹H NMR (300 MHz, d₆-DMSO): δ=12.54 (hr s, 1H), 7.54 (dd, J=8.6, 1.2, 1H), 7.40 (hr s, 1H), 7.23 (d, J=8.6, 1H), 7.10 - 6.99 (m, 2H), 6.86 (m, 2H), 6.46 - 6.34 (m, 3H), 4.88 (m, 1H), 3.80 (s, 3H), 3.68 (s, 3H), 3.43 (br m, 4H), 2.97 - 2.75 (m, 5H), 2.44

(m, 1H). Example 15

Synthesis of (S)-2-(8-fluoro-3-(2-meth oxy-5-(tr ifluo romethy 1) p heny l)-2-(4-(3 - metiioxyphenyl)piperazin-1-yl)-3,4-dihydroquinazolin-4-yl) acetic acid

0.22 mL of an aqueous solution of 1M NaOH is added to a solution of (S)-methyl 2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3-methoxyphenyl)piperazin- 1 -y l)-3 ,4-dihy droquinazolin-4-y l)acetate (26 mg, 0.0443 mmol) in THF 0.5 ml. The reaction mixture is stirred at room temperature for 15-20 minutes, then heated at 60°C for 10 hours. The mixture is cooled to room temperature, and H₂O (5 mL) and EtaO (5 mL) are added. The organic phase is eliminated and acidified with an aqueous solution of 0.5 M HC1 until pH 5-6 is reached. The aqueous phase is extracted with Et₂O (5 mLx3). The combined organic phases are washed with a saturated aqueous solution of NaCl and dried with Na₂SO₄. The drying agent is filtered and evaporated to residue to obtain 22 mg of

(S)-2-(8-fluoro-3-(2-methoxy-5-(trifluoromethyl)phenyl)-2-(4-(3-methoxy- phenyl)piperazin-1-yl)-3,4-dihydroquinazolin-4-yl) acetic acid as a ’white solid.

¹H NMR (300 MHz, d₆-DMSO): δ=12.54 (br s, 1H), 7.54 (dd, >8.6, 1.2, 1H), 7.40 (br s, 1H), 7.23 (d, >8.6, 1H), 7.10 - 6.99 (m, 2H), 6.86 (m, 2H), 6.46 - 6.34 (m, 3H), 4.88 (m, 1H), 3.80 (s, 3H), 3.68 (s, 3H), 3.43 (br m, 4H), 2.97 - 2.75 (m, 5H), 2.44 (m, 1H).

Claims

1. Process for the preparation of letermovir of formula I

comprising the sequence of the following steps: a) Reaction of compound of formula III, wherein R is a C1-C4 straight or branched alkyl group, with (S)-1-(4-benzyl-2-thioxothiazolidin-3-yl) ethanone (IV) in the presence of TiCl₄ and an aliphatic amine;

b) Hydrolysis of the compounds of formula V obtained in a) in the presence of bases to give the compounds of formula VI;

c) Cyclisation of the compounds of formula VI in the presence of organic bases

d) Esterification of the compound of formula VII

wherein R’ is a straight C1-C3 alkyl or a benzyl group e) Reaction of the ester of formula VIII with N-(3 -methoxyphenyl) piperazine or a salt thereof to give the compound of formula IX in the presence of a chlorinating agent and an organic base

f) Hydrolysis of the compound of formula IX to give letermovir I.

2. Process according to claim 1 wherein step a) is carried out at a temperature ranging between -90°C and 0°C.

3. Process according to claim 1 or 2 wherein the amine used in step a) is selected from triethylamine and diisopropylamine.

4. Process according to claims 1 to 3 wherein step a) is carried out in an aprotic solvent selected from toluene, methylene chloride, chlorobenzene, dichlorobenzene, 1,2- dichloroethane and chloroform or mixtures thereof.

5. Process according to claim 4 wherein the solvent is methylene chloride.

6. Process according to claim 1 wherein step b) is carried out in the presence of bases selected from alkali hydroxides, potassium tert-butylate, sodium methylate, sodium ethylate, sodium and potassium carbonates or bicarbonates and dimethylaminopyridine .

7. Process according to claim 1 wherein the organic base used in step c) is selected from DBU, DMAP, triethylamine, pyridine, potassium tert-butylate, sodium methylate and sodium ethylate.

8. Process according to claims 1 and 7 wherein step c) is carried out in a polar solvent selected from acetonitrile, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, dimethoxy ethane, ethanol and methanol.

9. Process according to claim 1 wherein step d) is carried out in the presence of alcohols selected from straight C1-C3 alcohols and benzyl alcohol.

10. Process according to claims 1 and 9 wherein step d) is carried out in the presence of a condensing agent selected from DCC, EDC and CDI.

11. Process according to claims 1, 9 and 10 wherein step d) is carried out in the presence of an organic base selected from DBU, DMAP and triethylamine.

12. Process according to claim 1 wherein step d) is carried out in the presence of methyl bromide, ethyl bromide, benzyl bromide or benzyl chloride.

13. Process according to claims 1 and 11 wherein step d) is carried out in an aprotic polar solvent selected from acetone, methyl ethyl ketone and acetonitrile.

14. Process according to claim 1 wherein step e) is carried out in the presence of a chlorinating agent selected from POCl₃ and PCl₅-

15. Process according to claims 1 and 13 wherein step e) is carried out in the presence of organic bases selected from DBU, DMAP and triethylamine.

16. Process according to claims 1, 14 and 15 wherein step e) is carried out in a mixture of solvents selected from toluene, chlorobenzene, dioxane, DMF, TFE and mixtures thereof.

17. Process according to claim 1 wherein step f) is carried out in the presence of gaseous hydrogen and a metal catalyst when R' is benzyl.

18. Process according to claims 1 and 17 wherein the metal catalyst used is palladium on carbon.

19. Process according to claim 1 wherein step f) is carried out in the presence of alkali hydroxides.