WO2025176871A1 - Process for preparing pyrimido[6,1-a]isoquinoline-4-ones - Google Patents

Abstract

The present invention provides a straightforward process for preparing pyrimido[6,1- a]isoquinoline-4-ones of formula (I), or a pharmaceutically acceptable acid addition salt thereof, preferably ensifentrine, involving the reaction of a precursor with an advanced alkylating agent.

Description

PROCESS FOR PREPARING PYRIMIDO[6,1-A]ISOQUINOLINE-4-ONES

This application claims the benefit of European Patent Application EP24382199.8 filed 23 February 2024.

FIELD OF THE INVENTION

The present invention provides a straightforward process for preparing pyrimido[6,1- a]isoquinoline-4-ones of formula I, or a pharmaceutically acceptable acid addition salt thereof, preferably ensifentrine, involving the reaction of a precursor with an advanced alkylating agent.

BACKGROUND ART

Some pyrimido[6,1-a]isoquinoline-4-ones have been described as useful for respiratory disorders, as being bronchodilators with anti-inflammatory properties, such as trequinsin in GB1597717 A. 9,10-Dimethoxy-2-[(2,4,6-trimethylphenyl)imino]-3-(/\/- carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one, also known as ensifentrine, depicted below as compound (la), is a dual inhibitor of phosphodiesterase 3 (PDE3) and phosphodiesterase 4 (PDE4) with combined antiinflammatory and bronchodilator properties.. Ensifentrine is currently approved by the US Food and Drug Administration (FDA) for the treatment of chronic obstructive pulmonary disease (COPD) and available under the commercial name of OHTUVAYRE in the form of an inhalation suspension.

.0.

J CT

(la)

WO00/58308 A1 discloses ensifentrine, its preparation method and its use in the treatment of asthma or treatment of COPD. Particularly, ensifentrine is prepared in Example 1 (Scheme 1) which involves the alkylation of intermediate (Ila), wherein Ar is 2,4,6-trimethylphenyl, with /\/-(2-bromoethyl)phthalimide, followed by deprotection using hydrazine, and finally, the reaction of the obtained amino intermediate (VI) with sodium cyanate in the presence of hydrochloric acid. This method has several disadvantages, for instance the low yield of 13.5% of the alkylation reaction with the phthalimide derivative and the use of the genotoxic hydrazine in the deprotection step.

Scheme 1

WO2016128742 A1 discloses pharmaceutically acceptable acid addition salts of compound (la) with ethane-1 ,2-disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, phosphoric acid or sulfuric acid that have improved intrinsic dissolution rates suitable for pressurized metered dose and dry powder formulations.

WO2018/020249 A1 discloses an alternative method to manufacture ensifentrine which involves the /V-alkylation of intermediate (Ila), wherein Ar is 2,4,6-trimethylphenyl, with bromoacetonitrile to yield intermediate (VII), which is further hydrogenated to give the above amino intermediate (VI) which is further transformed to final ensifentrine (la) as mentioned above. This method has also the disadvantage of using several steps that increases the cost of final ensifentrine, thereby increasing the cost of the medicinal product containing it.

Scheme 2

Therefore, from what is known in the art there is still the need in developing an efficient method to manufacture ensifentrine at an industrial scale with low energy and cost- effective, avoiding the problems of the known processes. SUMMARY OF THE INVENTION

The prior art methods mentioned above provide ensifentrine in a very low yield along with several impurities associated therewith. Surprisingly, the present inventors have found that the precursor amino intermediate of formula (II) can directly react with an advanced alkylating agent of formula (III) (Scheme 3) in a moderate yield and high purity, thereby providing ensifentrine in a shorter sequence step. Thus, advantageously this process allows the obtention of ensifentrine with reduced number of steps avoiding the use of toxic reagents.

Scheme 3

Therefore, the present invention relates to a process for preparing a compound of formula (I), or a pharmaceutically acceptable acid addition salt, wherein R¹ and R² are the same or different and each is independently either a Ci-Ce alkyl group or a C2-C7 acyl group, or alternatively, R¹ and R² together form a Ci-Ce alkylene group; R³ and R⁴ are the same or different and each is independently selected from the group consisting of hydrogen, halogen, and a Ci-Ce alkyl group; R⁵ and R⁶ the same or different and each one is independently selected from the group consisting of hydrogen, halogen, and a Ci-Ce alkyl group; X is selected from the group consisting of CHR⁷, O, and NR⁷ R⁷ is either hydrogen or a Ci-Ce alkyl group; and Ar is 2,4,6- trimethylphenyl, which comprises the step of reacting a compound of formula (II)

(II) wherein R¹, R², R³, R⁴, R⁵, R⁶, X, and Ar is as defined for compound (I), with a compound of formula (III)

(HI) wherein Y is a leaving group selected from the group consisting of halogen, mesylate (OMs), tosylate (OTs), nosylate (ONs), acetate (OAc), and triflate (OTf), preferably Y is halogen such as Cl, Br and I, more preferably Y is Cl.

Particularly, the process of the invention provides the compound of formula I, wherein R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵ and R⁶ are hydrogen; and X is CH2, compound of formula (la), (i.e. ensifentrine) in an efficient manner involving the reaction of compound of formula (II), wherein R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵and R⁶ are hydrogen; and X is CH2, (compound of formula Ila) with advanced alkylating agent compound of formula (III) in a moderate yield and high purity.

The present invention also refers to a process wherein the compound of formula I thus obtained is combined with a pharmaceutically acceptable acid such as ethane-1 ,2- disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, p- toluenesulfonic acid, hydrochloric acid, hydrobromic acid, phosphoric acid, and sulfuric acid, to yield the corresponding pharmaceutically acceptable acid addition salt of compound of formula I.

DEFINITIONS

When describing the compounds and methods of the invention, the following terms have the following meanings, unless otherwise indicated.

As used herein, a Ci-Ce alkyl group or moiety is a linear or branched alkyl group or moiety containing from 1 to 6 carbon atoms. Typically, a Ci-Ce alkyl group or moiety is a C1-C4 alkyl group or moiety. A C1-C4 alkyl group or moiety is a linear or branched alkyl group or moiety containing from 1 to 4 carbon atoms. Examples of Ci-Ce alkyl groups and moieties include methyl, ethyl, n-propyl, /-propyl, n-butyl, /- butyl, f-butyl and 3-methylbutyl. Examples of C1-C4 alkyl groups and moieties include methyl, ethyl, n- propyl, /-propyl, n-butyl, /-butyl and t-butyl. For the avoidance of doubt, where two alkyl moieties are present in a group, the alkyl moieties may be the same or different.

As used herein, a Ci-Ce alkylene group or moiety is a linear or branched alkylene group or moiety. Examples include methylene, ethylene and n-propylene groups and moieties. As used herein, halide is typically chlorine, fluorine, bromine or iodine.

As used herein, a C2-C7 acyl group is typically a said Ci-Ce alkyl group attached to a - C(O)- group.

The terms “conventional isolation techniques” or “purification” as used herein refer to the process of rendering a product clean of foreign elements whereby a purified product can be obtained. The term industrial purification refers to purifications which can be carried out on an industrial scale such as solvent extraction, filtration, slurring, washing, phase separation, distillation, centrifugation or crystallization.

The term “crystallization” refers to any method known to a person skilled in the art such as crystallization from single solvent or combination of solvents by dissolving the compound, optionally at elevated temperature and precipitating the compound by cooling the solution or removing solvent from the solution or both. It further includes methods such as dissolving the compound in a solvent and precipitating it by addition of an “antisolvent” (i.e., a solvent in which the desired compound has low solubility or insolubility, and can be used to precipitate such compound by adding it to a solution in which the compound is dissolved).

As used herein the term “solvent” refers to either water or an organic molecule capable of at least partially dissolving another substance (i.e., the solute). Solvents may be liquids at room temperature. Suitable solvents may be, but are not limited to (C1- Ci2)hydrocarbon solvents such as n-pentane, n-hexane, n-heptane, n-octane, paraffin, cyclohexane, methylcyclohexane, decahydronaphthalene; (Ce-Ci4)aromatic hydrocarbon solvents such as toluene, o-xylene, m-xylene, and p-xylene; halogenated (Ci-Ci2)hydrocarbon solvents such as 1,2-dichloroethane, dichloromethane, chloroform; (Ci-Ci2)ether solvents such as diethyl ether, dipropyl ether, diphenyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4- dioxane; an ester solvent such as ethyl formate, methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, ethyl malonate; a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; (Ci-Ci2)alcohol solvents such as methanol, ethanol, isopropanol, 1-propanol, 2-methyl-1-propanol, 1-butanol, 2- butanol, 1-pentanol, 3-methyl-1 -butanol, tert-butanol, 1-octanol, benzyl alcohol, phenol, trifluoroethanol, glycerol, ethylene glycol, propylene glycol, m-cresol; a nitrile solvent such as acetonitrile; nitrobenzene; /V,/V-dimethylformamide; /V,/V, -dimethylacetamide; /V-methyl-2-pyrrolidone; or dimethyl carbonate. In some embodiments, the solvent may be formed by the combination of two or more solvents.

The term “room temperature” in the context of the present invention refers to a temperature from 15°C to 30°C, preferably from 20°C to 25°C.

As used herein, the term “solvent extraction” refers to the process of separating components of a mixture by using a solvent which possesses greater affinity for one component and may, therefore, separate said one component from at least a second component which is less miscible than said one component with said solvent.

The term “filtration” refers to the act of removing solid particles greater than a predetermined size from a feed comprising a mixture of solid particles and liquid. The expression filtrate refers to the mixture less the solid particles removed by the filtration process. It will be appreciated that this mixture may contain solid particles smaller than the predetermined particle size. The expression filter cake refers to residual solid material remaining on a feed side of a filtration element.

The term “evaporation” refers to the change in state of solvent from liquid to gas and removal of that gas from the reactor. Various solvents may be evaporated during the processes disclosed herein. As known to those of skilled in the art, each solvent may have a different evaporation time and/or temperature.

The term “distillation” refers to the process of separating the component substances from a liquid mixture by selective evaporation and condensation. It may result in essentially complete separation (nearly pure components), or it may be a partial separation that increases the concentration of selected components of the mixture. In either case the process exploits differences in the volatility of mixture's components.

As used herein, the term “slurrying” refers to any process which employs a solvent to wash, suspend or disperse a crude solid product.

The term “phase separation” refers to a solution or mixture having at least two physically distinct regions. The term "solvate" refers to a crystalline form of a molecule that further comprises solvent molecule/s incorporated into the crystalline structure. When the solvent incorporated in the crystal is water, is called hydrate. The solvent molecules in the solvate may be present in a regular arrangement and/or a non-ordered arrangement. The solvate may comprise either a stoichiometric or nonstoichiometric amount of the solvent molecules. Solvates can exhibit polymorphism.

BRIEF DESCRIPTION OF THE FIGURES

Examples of the invention are illustrated with the following drawings:

FIG. 1 provides a representative X-ray Powder Diffraction (XRPD) pattern of crystal form 1 of ensifentrine benzenesulfonate acid addition salt in 1 :1 stoichiometry.

FIG. 2 provides a representative ¹H-RMN plot of crystal form 1 of ensifentrine benzenesulfonate acid addition salt in 1 :1 stoichiometry.

FIG. 3 provides a representative X-ray Powder Diffraction (XRPD) pattern of crystal form 1 of ensifentrine p-toluenesulfonate acid addition salt in 1:1 stoichiometry.

FIG. 4 provides a representative ¹H-RMN plot of crystal form 1 of ensifentrine p- toluenesulfonate acid addition salt in 1 :1 stoichiometry.

DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention for preparing a compound of formula (I), or a pharmaceutically acceptable acid addition salt comprises the step of reacting a compound of formula (II) with a compound of formula (III), each of the compounds being as defined above.

In compound of formula (III) Y is a leaving group selected from the group consisting of halogen, mesylate (OMs), tosylate (OTs), nosylate (ONs), acetate (OAc), and triflate (OTf). In another particular embodiment, Y is halogen such as Cl, Br and I, as the number of impurities is reduced.

In another particular embodiment of the process, the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II). In a particular embodiment, the amount of compound of formula (III) is from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II). In a particular embodiment, the amount of compound of formula (III) is from 1.0 to 5.0 equivalents with respect to an equivalent of the compound of formula (II). In another particular embodiment, the process is conducted in the presence of a base. In a particular embodiment, the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate, sodium acetate, and potassium acetate. In a more particular embodiment, the base is lithium carbonate as the yield is increased.

In another particular embodiment of the process, the base used is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II). In another particular embodiment of the process, the base used is in an amount in a range from 1.0 to 5.0 equivalents with respect to an equivalent of the compound of formula (II). In a particular embodiment, the amount of base is from 1.5 to 3.0 equivalents of the compound of formula (II) as the number of impurities is reduced.

In another particular embodiment of the process, consecutive additions of compound of formula (III) and base, wherein each addition is used in an amount of 1 to 3 equivalents to an equivalent of the compound of formula (II), can be made at 24, 48 and 72 h after the beginning of the reaction as the yield of the reaction is increased.

In another particular embodiment, the process of the present invention is conducted in the presence of a solvent. In an embodiment, suitable solvents are selected from the group consisting of a (Ci-Ci2)hydrocarbon solvent such as n-pentane, n-hexane, n- heptane, n-octane, paraffin, cyclohexane, methylcyclohexane, decahydronaphthalene; a (Ce-Ci4)aromatic hydrocarbon solvent such as toluene, o-xylene, m-xylene, and p- xylene; a halogenated (Ci-Ci2)hydrocarbon solvent such as 1,2-dichloroethane, dichloromethane, chloroform, an ester solvent such as ethyl formate, methyl acetate, ethyl acetate, isopropyl acetate, ethyl malonate; a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, diphenyl ether, isopropyl ether, tert-butyl methyl ether, tetra hydrofuran, 2-methyltetrahydrofuran, 1,4- dioxane; a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; a (Ci-Ci2)alcohol solvent such as methanol, ethanol, isopropanol, 1-propanol, 2-methyl-1-propanol, 1-butanol, 2- butanol, 1-pentanol, 3-methyl-1 -butanol, tert-butanol, 1-octanol, benzyl alcohol, phenol, trifluoroethanol, glycerol, ethylene glycol, propyleneglycol, m-cresol; a nitrile solvent such as acetonitrile; nitrobenzene; /V,/V-dimethylformamide (DMF); N,N- dimethylacetamide (DMA); dimethyl sulfoxide (DMSO); /V-methyl-2-pyrrolidone, dimethylcarbonate, and a combination thereof. In another particular embodiment, the process is conducted in the presence of a solvent selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetra hydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone. In a particular embodiment, the solvent is a nitrile solvent such as acetonitrile.

In another particular embodiment of the process, the reaction process is conducted at a temperature in a range from 50°C to 100°C. In an embodiment, the reaction process is conducted at a temperature in a range from 60°C to 95°C. In an embodiment, the reaction process is conducted at a temperature in a range from 70°C to 90°C. In a particular embodiment, the reaction process is conducted at reflux temperature of the solvent. In a more preferred embodiment, the reaction process is conducted at a temperature in a range from 70°C to 80°C as the degradation of compound of formula (III) over long periods of time is reduced.

In another particular embodiment of the process, the reaction process is maintained for at least 6 hours. In another particular embodiment of the process, the reaction process is maintained for at least 12 hours. In an embodiment, the reaction process is maintained for at least 24 hours, preferably at least 48 hours, more preferably at least 120 hours.

In another particular embodiment of the process, the reaction process is maintained for at least 72 hours, preferably for at least 120 hours, and consecutive additions of compound of formula (III) and base, wherein each addition is used in an amount of 1 to 3 equivalents to an equivalent of the compound of formula (II), can be made at 24, 48 and 72 h after the beginning of the reaction as the yield of the reaction is increased.

In another particular embodiment of the process, the reaction process is maintained for at least 120 hours, preferably for at least 168 hours, and consecutive additions of compound of formula (III) and base, wherein each addition is used in an amount of 1 to 3 equivalents to an equivalent of the compound of formula (II), can be made at 24, 48 and 72 h after the beginning of the reaction as the yield of the reaction is increased.

In another particular embodiment of the process, the reaction process is conducted in the presence of a source of iodide or bromide, preferably in the form of an inorganic salt such as sodium iodide, potassium iodide, and caesium iodide or sodium bromide, potassium bromide, and caesium bromide. In another particular embodiment, the reaction is conducted in the presence of sodium iodide, potassium iodide, caesium iodide, or a combination thereof. In another particular embodiment, the reaction is conducted in the presence of sodium bromide, potassium bromide, or a combination thereof.

In another particular embodiment of the process, compound of formula (I) is selected from R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵ and R⁶ are hydrogen; and X is CH2, referred as compound (la).

In another particular embodiment, the process of the invention for preparing a compound of formula (I), or a pharmaceutically acceptable acid addition salt, is that wherein in compound of formula (I) R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵ and R⁶ are hydrogen; X is CH2, and Ar is 2,4,6-trimethylphenyl (i.e. compound of formula la), and comprises the step of reacting a compound of formula (Ila) wherein and Ar is as defined above, with a compound of formula (III)

(HI) wherein Y is a leaving group selected from the group consisting of halogen, mesylate (OMs), tosylate (OTs), nosylate (ONs), acetate (OAc), and triflate (OTf), preferably Y is halogen such as Cl, Br and I.

In another particular embodiment, the process for preparing a compound of formula (la), wherein R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵and R⁶ are hydrogen; X is CH2, and Ar is 2,4,6-trimethylphenyl, or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is as defined above, with a compound of formula (III) wherein Y is a leaving group selected from the group consisting of halogen, mesylate (OMs), tosylate (OTs), nosylate (ONs), acetate (OAc), and triflate (OTf), preferably Y is halogen such as Cl, Br and I, in the presence of a base and a solvent.

In another particular embodiment of the process, the base used is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate, sodium acetate, and potassium acetate.

In another particular embodiment of the process, the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2- methyltetrahydrofuran, 1 ,4-dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone.

In another particular embodiment, the process for preparing a compound of formula (la), is that wherein R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵and R⁶ are hydrogen; X is CH2, and Ar is 2,4,6-trimethylphenyl, or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is as defined above, with a compound (III)

(HI) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent, wherein the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate, sodium acetate, and potassium acetate, and wherein the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci- Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetra hydrofuran, 2-methyltetrahydrofuran, 1 ,4-dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone.

In another particular embodiment of the process, the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents, preferably from 1 .0 to 5.0 equivalents, with respect to an equivalent of the compound of formula (II).

In another particular embodiment, the process of the invention for preparing a compound of formula (la), wherein R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵ and R⁶ are hydrogen; X is CH2, and Ar is 2,4,6-trimethylphenyl, or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound (Ila) ed above, with a compound (III) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate, sodium acetate, and potassium acetate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2- methyltetrahydrofuran, 1 ,4-dioxane and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); and the base is in an amount in a range from 1.0 to 8.0 equivalents, preferably in an amount in a range from 1 .0 to 5.0 equivalents, with respect to an equivalent of the compound of formula (II).

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent, the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate, and the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4- dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2- pentanone, wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II), and wherein the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), and wherein the reaction is conducted at a temperature in a range from 50°C to 100°C.

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) (Ha) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III)

(HI) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, and wherein the reaction is maintained for at least 6 hours, preferably at least 12 hours.

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III)

(HI) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, and the reaction is maintained for at least 6 hours, preferably at least 12 hours, more preferably for at least 24 hours and wherein the reaction process is conducted in the presence of a source of iodide or bromide, preferably in the form of an inorganic salt sodium iodide, potassium iodide, and caesium iodide or sodium bromine and potassium bromine.

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, the reaction is maintained for at least 24 hours, preferably at least 48 hours, wherein the reaction process is conducted in the presence of a source of iodide or bromide, preferably in the form of an inorganic salt sodium iodide, potassium iodide, and caesium iodide or sodium bromine and potassium bromine, and wherein consecutive addition of compound of formula (III) and base are carried out, wherein each addition is used in an amount of 1 to 3 equivalents to an equivalent of the compound of formula (II), which can be made at 24 h after the beginning of the reaction.

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, the reaction is maintained for at least 48 hours, preferably at least 72 hours, wherein the reaction process is conducted in the presence of a source of iodine or bromine, preferably in the form of an inorganic salt sodium iodide, potassium iodide, and caesium iodide or sodium bromide and potassium bromide, and wherein consecutive addition of compound of formula (III) and base are carried out, wherein each addition is used in an amount of 1 to 3 equivalents to an equivalent of the compound of formula (II), which can be made at 24 h and 48 h after the beginning of the reaction.

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, the reaction is maintained for at least 72 hours, preferably at least 120 hours, wherein the reaction process is conducted in the presence of a source of iodide or bromide, preferably in the form of an inorganic salt sodium iodide, potassium iodide, and caesium iodide or sodium bromine and potassium bromine, and wherein consecutive additions of compound of formula (III) and base are carried out, wherein each addition is used in an amount of 1 to 3 equivalents to an equivalent of the compound of formula (II), which can be made at 24, 48 and 72 h after the beginning of the reaction.

In another particular embodiment, the process for preparing compound of formula (Ila) further comprises previously reacting a compound of formula (IVa) with 2,4,6- trimethylaniline to yield compound of formula (Ila).

In another particular embodiment of the process, the reaction of compound of formula (IVa) with 2,4,6-trimethylaniline is conducted in the presence of a (Ci-Ci2)alcohol solvent such as methanol, ethanol, isopropanol, 1-propanol, 2-methyl-1-propanol, 1- butanol, 2-butanol, 1-pentanol, 3-methyl-1 -butanol, tert-butanol, or mixtures thereof. In a particular embodiment, the reaction of compound of formula (IVa) with 2,4,6- trimethylaniline is conducted in the presence of isopropanol.

Compounds of formula (II) used in the process of the present invention can be prepared analogously to compound of formula (Ila) as described above.

In another particular embodiment, the process of the invention further comprises previously reacting compound of formula (Va) with a chlorinating agent such as phosphorous oxychloride to yield compound of formula (IVa).

In another particular embodiment of the process, the reaction between compound of formula (Va) with a chlorinating agent such as phosphorous oxychloride is conducted in the presence of a polar aprotic solvent such as sulfolane. In another particular embodiment of the process, the compound of formula (Va) may be obtained reacting /\/-[2-(3,4-dimethoxyphenyl)ethyl]urea with dimethyl malonate in the presence of sodium methoxide.

Compounds of formula (V) used in the present invention can be prepared analogously to compound of formula (Va).

In another particular embodiment, /\/-[2-(3,4-dimethoxyphenyl)ethyl]urea may be obtained by reacting 2-(3,4-dimethoxyphenyl)ethan-1 -amine or salt thereof, such as the commercially available hydrochloride salt, with sodium cyanate or potassium cyanate.

In another particular embodiment of the process, after the reaction of compound of formula (II) with compound (III) is completed, the obtained compound of formula (I) is isolated by conventional isolation techniques. It may then be further purified via acid addition salt formation to provide the compound (I) with even reduced amount of impurities. Optionally, the salt formed may be purified before recovering the compound (I).

In another particular embodiment of the process, the compound of formula (I) may be recovered following the process for preparing a compound of formula (I) by cooling the reaction mixture and filtering it, optionally at elevated temperature, followed by evaporation of the resulting solution to recover the compound of formula (I), preferably to yield the amorphous compound of formula (I). In another particular embodiment, the process for preparing the compound of formula (I) further comprises crystallizing the compound of formula (I) from a solvent to yield a crystalline form of compound of formula (I). For instance, known crystalline forms of compound of formula (la) are disclosed in WO2012/020016 A1 , such as Form I, Form II, Form III, Form IV, and Form V.

In another particular embodiment, the process of the invention comprises isolating the compound of formula (I), preferably isolating by evaporation. In a particular embodiment, the process comprises isolating the compound of formula (la) in amorphous form, preferably isolating by evaporation. In a particular embodiment, the process comprises isolating the compound of formula (la) in amorphous form, preferably isolating by evaporation.

In another particular embodiment, the process of the invention comprises dissolving the amorphous form of compound of formula (I), preferably compound of formula (la), obtained in a solvent selected from the group consisting of a (Ci-Ci2)hydrocarbon solvent such as n-pentane, n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohexane; a (C6-Ci4)aromatic hydrocarbon solvent such as toluene, o-xylene, m-xylene, and p-xylene; a halogenated (Ci-Ci2)hydrocarbon solvent such as 1 ,2- dichloroethane, dichloromethane, chloroform; an ester solvent such as ethyl formate, methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, ethyl malonate; a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2- pentanone; a (Ci-Ci2)alcohol solvent such as methanol, ethanol, isopropanol, 1- propanol, 2-methyl-1-propanol, 1-butanol, 2-butanol, 1-pentanol, 3-methyl-1 -butanol, tert-butanol; water and a combination thereof, and crystallizing crystalline compound of formula (I), preferably Form I of compound of formula (la), from said solvent or said mixture of solvents.

In another particular embodiment, the process of the invention comprises crystallizing or slurrying the compound of formula (la) in a (Ci-Ci2)alcohol solvent such as methanol, ethanol, isopropanol, 1-propanol, 2-methyl-1-propanol, 1-butanol, 2-butanol, 1-pentanol, 3-methyl-1 -butanol, tert-butanol, and a combination thereof, preferably in methanol. In another particular embodiment, the process of the invention comprises crystallizing the compound of formula (la) in a mixture of (Ci-Ci2)alcohol solvent and water in an amount of 1 :1 v/v to 6:1 v/v, wherein the (Ci-Ci2)alcohol is selected from the group consisting of methanol, ethanol, isopropanol, 1-propanol.

In another particular embodiment of the process, the compound of formula (I) may be isolated by the addition of an antisolvent to precipitate it from the reaction medium. Suitable antisolvents may be an organic solvent, water or an aqueous or organic acid solution to precipitate compound of formula (I) in the form of a free base or an acid addition salt.

In another particular embodiment, the process of the invention comprises reacting the compound of formula I, preferably compound of formula (la), with an acid selected from the group consisting of ethane-1 ,2-disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, phosphoric acid, and sulfuric acid, to yield the corresponding pharmaceutically acceptable acid addition salt of compound of formula I. In a particular embodiment, the pharmaceutically acceptable acid addition salt is ethane-1 ,2- disulfonate acid addition salt.

In another particular embodiment, the process further comprises a purification process of the compound (I), preferably compound (la), which comprises the steps of: a) converting compound (I), preferably compound (la), into a pharmaceutically acceptable acid addition salt of: (i) compound (I, preferably la) and (ii) an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p- toluenesulfonic acid, wherein the stoichiometry of the compound (I), preferably la) to the counter ion is 1 :1 by ¹H-NMR; b) optionally, purifying the acid addition salt obtained in step a); and c) converting the pharmaceutically acceptable acid addition salt obtained in step a) or b) into compound (I), preferably (la).

The inventors of the present invention found that the use of specific aryl sulfonic acid salts, specifically, benzenesulfonic acid or p-toluensulfonic acid salts, in the purification of compound (la) significantly enhances the purity levels achievable compared to other acids tested such as phosphoric, HBr, HCI, methanesulfonic, maleic, L-aspartic and sulfuric. The aryl sulfonic acid salts, such as benzenesulfonic acid and p-toluensulfonic acid addition salts, are particularly effective due to their unique chemical properties that facilitate the removal of impurities during the purification process. The compound (I), preferably compound (la), thus obtained has a purity equal to or higher than 99.0% a/a by HPLC, preferably equal to or higher than 99.5% a/a by HPLC, more preferably equal to or higher than 99.7% a/a by HPLC, even more preferably equal to or higher than 99.9% a/a by HPLC.

In another particular embodiment of the process, the aryl sulfonic acid used in step (a) (ii) is in an amount from 1.0 to 1.5 equivalents, preferably from 1.0 to 1.2 equivalents, with respect to an equivalent of the compound of formula (I), preferably compound (la).

In another particular embodiment, the process step (a) may be carried out in the presence of a solvent selected from group consisting of an ester solvent such as ethyl formate, methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, ethyl malonate; a (Ci-Ci2)alcohol solvent such as methanol, ethanol, isopropanol, 1-propanol, 2-methyl-1-propanol, 1-butanol, 2-butanol, 1-pentanol, 3- methyl-1 -butanol, tert-butanol, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane; a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2- pentanone, a nitrile solvent such as acetonitrile, and a combinations thereof. In another particular embodiment of the process, the amount of solvent used in step a) is from 5 V to 25 V (i.e. 1 V = 1 mL / g), preferably 10 V to 20 V, with respect to compound of formula (I), preferably (la).

In another particular embodiment of the process, step a) is conducted at a temperature in a range from 50°C to 100°C, preferably in a range from 50°C to 95°C, more preferably in a range from 75°C to 95°C. In a particular embodiment, the reaction process is conducted at reflux temperature of the solvent or mixture of solvents.

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the benzesulfonic acid at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution thereby crystallizing compound (la) benzenesulfonate.

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the benzesulfonic acid at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution crystallizing compound (la) benzenesulfonate, wherein the amount of the benzesulfonic acid is from 1.0 to 1.5 equivalents with respect to compound (I), preferably (la).

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the benzesulfonic acid at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution crystallizing compound (la) benzenesulfonate, wherein the amount of the benzesulfonic acid is from 1.0 to 1.5 equivalents with respect to compound (I), preferably (la), and wherein the solvent is n-propanol (1 -propanol).

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the benzesulfonic acid at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution crystallizing compound (la) benzenesulfonate, wherein the amount of the benzesulfonic acid is from 1.0 to 1.5 equivalents with respect to compound (I), preferably (la), wherein the solvent is n-propanol in an amount of 10 V to 20 V with respect to the compound (la).

In an embodiment of the process, the molar ratio of compound (la) to the benzesulfonic acid is about 1:1 by ¹H-NMR.

In an embodiment of the process, the invention relates to the acid addition salt of compound (la) with benzesulfonic acid, wherein the stoichiometry of the compound (la) to the counter ion is 1:1 by ¹H-NMR, referred as crystal form 1 , having an X-ray powder diffraction pattern comprising peaks at 2theta values of 5.2°±0.2°, 13.1 °±0.2°, 21.6°±0.2° and 24.3°±0.2°, measured with Ka radiation of copper having an X-ray wavelength of 1.5406 A at room temperature.

In an embodiment of the process, the crystal form 1 of ensifentrine benzenesulfonic acid addition salt is characterized by an XRPD pattern which matches the pattern exhibited in FIG. 1. In an embodiment, the crystal form 1 is characterized by an XRPD pattern having at least 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, or 20 peaks matching peaks in the representative crystal form 1 pattern provided in Table 1.

Table 1. XRPD Main Peak List for Benzenesulfonate salt.

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the p-toluenesulfonic acid (p-TSA) at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution crystallizing compound (la) p-toluenesulfonate.

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the p-toluenesulfonic acid (p-TSA) at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution crystallizing compound (la) p-toluenesulfonate, wherein the amount of the p- toluenesulfonic acid is from 1.0 to 1.5 equivalents with respect to compound (la).

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the p-toluenesulfonic acid (p-TSA) at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution crystallizing compound (la) p-toluenesulfonate, wherein the amount of the p- toluenesulfonic acid is from 1.0 to 1.5 equivalents with respect to compound (la), and wherein the solvent is methyl ethyl ketone (MEK).

In a particular embodiment of the process, step a) is conducted by heating the compound (la) and the p-toluenesulfonic acid (p-TSA) at a temperature comprised in a range from 50 to 95°C until complete dissolution and cooling down the solution crystallizing compound (la) p-toluenesulfonate, wherein the amount of the p- toluenesulfonic acid is from 1.0 to 1.5 equivalents with respect to compound (la), wherein the solvent is methyl ethyl ketone (MEK) in an amount of 10 V to 20 V with respect to the compound (la).

In an embodiment of the process, the molar ratio of compound (la) to the p- toluenesulfonic acid is about 1:1 by ¹H-NMR.

In an embodiment of the process, the invention relates to the acid addition salt of compound (la) with p-toluenesulfonic acid, wherein the stoichiometry of the compound (la) to the counter ion is 1:1 by ¹H-NMR, referred as crystal form 1 , having an X-ray powder diffraction pattern comprising peaks at 2theta values of 5.0°±0.2°, 8.8°±0.2°, 17.0 °±0.2°, and 24.2°±0.2°, measured with Ka radiation of copper having an X-ray wavelength of 1.5406 A at room temperature.

In an embodiment of the process, the crystal 1 of ensifentrine p-toluenesulfonic acid addition salt is characterized by an XRPD pattern which matches the pattern exhibited in FIG. 3. In an embodiment, the crystal form 1 is characterized by an XRPD pattern having at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18 peaks matching peaks in the representative crystal form 1 pattern provided in Table 2.

Table 2. XRPD Main Peak List for p-toluenesulfonate salt. In another embodiment of the process, the acid addition salts of compound (la) with an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p- toluenesulfonic acid contain water in the crystal lattice or water admixed with other organic solvent in the crystal lattice.

In another embodiment of the process, the acid addition salts of compound (la) with an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p- toluenesulfonic acid contain an organic solvent in the crystal lattice such as n-propanol or MEK.

In a particular embodiment of the process, step b) is conducted by reacting the pharmaceutically acceptable acid addition salt with ammonia in methanol as solvent.

Generally, step b) is conducted at a temperature in a range from 30 to 45°C. In a particular embodiment, step b) is conducted at a temperature in a range from 35 to 40 °C. Generally, the salt is isolated at room temperature (20-25 °C). A pharmaceutically acceptable acid addition salt of: (i) a compound (la) and (ii) an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p-toluenesulfonic acid, wherein the stoichiometry by ¹HNMR of the compound (la) to the counter ion is 1:1 is part of the invention.

The crystal form 1 of compound (la) and benzesulfonic acid may be characterized by proton nuclear magnetic resonance (¹H-NMR) as shown in FIG. 2. The stoichiometry of compound (la) to the benzesulfonic acid is about 1:1 by ¹H-NMR. It also may be characterized by an X-ray powder diffraction pattern comprising peaks at 2theta values of 5.2°±0.2°, 13.1°±0.2°, 21.6°±0.2° and 24.3°±0.2°, measured with Ka radiation of copper having an X-ray wavelength of 1.5406 A at room temperature, more particularly it is characterized by having an X-ray powder diffraction pattern comprising the peaks at 2theta values included in Table 1 above.

The crystal form 1 of compound (la) and the p-toluenesulfonic acid may be characterized by proton nuclear magnetic resonance (¹H-NMR) as shown in FIG. 4. The stoichiometry of the compound (la) to the counter ion is 1:1 by ¹H-NMR. It also may be characterized by an X-ray powder diffraction pattern comprising peaks at 2theta values of 5.0°±0.2°, 8.8°±0.2°, 17.0 °±0.2°, and 24.2°±0.2°, measured with Ka radiation of copper having an X-ray wavelength of 1.5406 A at room temperature, more particularly, it is characterized by having an X-ray powder diffraction pattern comprising the peaks at 2theta values included in Table 2 above.

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, the reaction is maintained for at least 6 hours, preferably at least 12 hours, more preferably for at least 24 hours, even more preferably for at least 72 hours, wherein the reaction process is conducted in the presence of a source of iodide or bromide, preferably in the form of an inorganic salt sodium iodide, potassium iodide, and caesium iodide or sodium bromine and potassium bromine, and wherein the process further comprises a purification process of the compound (la), which comprises the steps of: a) converting compound (I), preferably compound (la), into a pharmaceutically acceptable acid addition salt of: (i) compound (I, preferably la) and (ii) an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p- toluenesulfonic acid, wherein the stoichiometry of the compound (I, preferably la) to the counter ion is 1 :1 by ¹H-NMR; b) optionally, purifying the acid addition salt obtained in step a); and c) converting the pharmaceutically acceptable acid addition salt obtained in step a) or b) into compound (la).

In another particular embodiment, the process for preparing a compound of formula (la), or a pharmaceutically acceptable acid addition salt, comprises the step of reacting a compound of formula (Ila) wherein Ar is 2,4,6-trimethylphenyl, with a compound of formula (III) wherein Y is a leaving group selected from the group consisting of halogen such as Cl, Br and I, in the presence of a base and a solvent; the base is selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate; the solvent is selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone; wherein the compound of formula (III) used is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II); the base is in an amount in a range from 1.0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II), wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, the reaction is maintained for at least 72 hours, preferably at least 120 hours, more preferably for at least 168 hours, wherein the reaction process is conducted in the presence of a source of iodide or bromide, preferably in the form of an inorganic salt sodium iodide, potassium iodide, and caesium iodide or sodium bromine and potassium bromine, wherein consecutive additions of compound of formula (III) and base are carried out, wherein each addition is used in an amount of 1 to 3 equivalents to an equivalent of the compound of formula (II), which can be made at 24, 48 and 72 h after the beginning of the reaction, and wherein the process further comprises a purification process of the compound (la), which comprises the steps of: d) converting compound (I), preferably compound (la), into a pharmaceutically acceptable acid addition salt of: (i) compound (I, preferably la) and (ii) an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p- toluenesulfonic acid, wherein the stoichiometry of the compound (I, preferably la) to the counter ion is 1 :1 by ¹H-NMR; e) optionally, purifying the acid addition salt obtained in step a); and f) converting the pharmaceutically acceptable acid addition salt obtained in step a) or b) into compound (la).

Finally, it also forms part of the invention a pharmaceutical composition comprising the compound of formula I thus obtained or a pharmaceutically acceptable acid addition salt, preferably compound of formula (la), (i.e. ensifentrine), with one or more pharmaceutically acceptable carriers, or excipients.

CLAUSES

Clause 1. A process for preparing a compound of formula (I), or a pharmaceutically acceptable acid addition salt,

(I) wherein: R¹ and R² are the same or different and each is independently either a Ci-Ce alkyl group or a C2-C7 acyl group, or alternatively, R¹ and R² together form a Ci-Ce alkylene group; R³ and R⁴ are the same or different and each is independently selected from the group consisting of hydrogen, halogen, and a Ci-Ce alkyl group; R⁵ and R⁶ the same or different and each one is independently selected from the group consisting of hydrogen, halogen, and a Ci-Ce alkyl group; X is selected from the group consisting of CHR⁷, O, and NR⁷; R⁷ is either hydrogen or a Ci-Ce alkyl group; and Ar is 2,4,6- trimethylphenyl; which comprises the step of reacting a compound of formula (II) ⁴, R⁵, R⁶, X, and Ar is as defined for compound (I), with a compound wherein Y is a leaving group selected from the group consisting of halogen, mesylate (OMs), tosylate (OTs), nosylate (ONs), acetate (OAc), and triflate (OTf).

Clause 2. The process according to clause 1 , wherein the compound of formula (III) is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II).

Clause 3. The process according to any one of clauses 1 to 2, wherein the process is conducted in the presence of a base selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate, sodium acetate, and potassium acetate.

Clause 4. The process according to clause 3, wherein the base is in an amount in a range from 1 .0 to 5.0 equivalents with respect to an equivalent of the compound of formula (II).

Clause 5. The process according to any one of clauses 1 to 4, wherein the process is conducted in the presence of a solvent selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, and 1 ,4-dioxane, and a combination thereof.

Clause 6. The process according to any one of clauses 1 to 5, wherein the reaction is conducted at a temperature in a range from 50°C to 100°C.

Clause 7. The process according to any one of clauses 1 to 6, wherein the reaction is maintained for at least 6 hours.

Clause 8. The process according to any one of clauses 1 to 7, wherein the reaction is conducted in the presence of a source of iodine.

Clause 9. The process according to any one of clauses 1 to 8, wherein R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵ and R⁶ are hydrogen; and X is CH2, referred as compound of formula (la) and compound of formula (Ila).

Clause 10. The process according to any one of clauses 1 to 9, wherein the process further comprises previously reacting a compound of formula (IVa) with 2,4,6- trimethylaniline to yield compound of formula (Ila).

Clause 11 . The process according to any one of clauses 1 to 10, wherein the process further comprises previously reacting compound of formula (Va) with a chlorinating agent such as phosphorous oxychloride to yield compound of formula (IVa).

Clause 12. The process according to any one of clauses 1 to 11 , wherein the process comprises isolating the compound of formula (I) in amorphous form, preferably isolating by evaporation.

Clause 13. The process according to clauses 12, wherein the process comprises dissolving the amorphous form obtained in claim 12 in a solvent selected from the group consisting of a (Ci-Ci2)hydrocarbon solvent such as n-pentane, n-hexane, n- heptane, n-octane, cyclohexane, methylcyclohexane; a (Ce-Ci4)aromatic hydrocarbon solvent such as toluene, o-xylene, m-xylene, and p-xylene; a halogenated (C1- Ci2)hydrocarbon solvent such as 1 ,2-dichloroethane, dichloromethane, chloroform; an ester solvent such as ethyl formate, methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, ethyl malonate; a (Ci-Ci2)alcohol solvent such as methanol, ethanol, isopropanol, 1-propanol, 2-methyl-1-propanol, 1-butanol, 2-butanol, 1 -pentanol, 3-methyl-1 -butanol, tert-butanol, and a combination thereof, and crystallizing crystalline form from said solvent or said mixture of solvents. Clause 14. The process according to any one of clauses 1 to 13, wherein the process comprises reacting the compound of formula I with an acid selected from the group consisting of ethane-1 ,2-disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, phosphoric acid, and sulfuric acid, to yield the corresponding pharmaceutically acceptable acid addition salt of compound of formula I.

Clause 15. The process according to claim any one of clauses 1 to 14, wherein the pharmaceutically acceptable acid addition salt is ethane-1 ,2-disulfonate acid addition salt.

In the following, the present invention is further illustrated by examples. They should in no case be interpreted as a limitation of the scope of the invention as defined in the claims. Unless indicated otherwise, all indications of percentage are by weight and temperatures are in degrees Celsius.

GENERAL METHODS

Proton nuclear magnetic resonance (¹H-NMR)

Sample preparation: Approximately 2-5 mg of sample were dissolved in 0.5-0.7 mL of deuterated solvent (CDCh or DMSO). Data acquisition: Proton nuclear magnetic resonance analyses were recorded in a Bruker Avance III HD 400 NMR spectrometer, equipped with a z gradient 5 mm BBO (Broadband Observe) probe with ATM and an automatic autosampler. Measurement conditions: The samples were analyzed at room temperature.

X-Ray Powder Diffraction (XPRD)

Diffraction data was collected using a PANanalytical EMPYREAN vs. 8.2 20201404 diffractometer with a Cu-Ka radiation (A = 1.541874 A) source operating at 45 kV and 40 mA in transmission theta-theta configuration. Samples were scanned from 2 to 40 °2theta with a step size of 0.013 °2theta and a time per step of 78.795 sec. Data collection was performed with DATA COLLECTOR vs. 7.1.

Differential Scanning Calorimetry (DSC)

DSC analyses were performed using a Thermal Analysis (TA) Discovery instrument model DSC 25. The samples, typically weighing 1-3 mg, were heated in a sealed standard Tzero aluminum pan at a heating rate of 5°C/min under a nitrogen glass flow of 50 ml/min. A sealed empty Tzero aluminum pan was used as a reference. Data collection was performed with TRIOS software. Thermoqravimetric analisis (TGA)

TGA analyses were conducted in a Thermal Analysis (TA) Discovery instrument model TGA 550 using a nitrogen atmosphere with a gas flow of 60 mL/min and a heating rate of 10°C/min. Approximately 1 to 5 mg of sample was used. Data collection was performed with TRIOS software.

Balances

A RAGWAG analytical balance model AS.220 R2 PLUS and a TA microbalance from TA Discovery TGA 550 instruments were used.

High Pressure Liquid Chromatography (HPLC)

HPLC analyses were performed on an Agilent 1220 Infinity II LC system, equipped with a high-pressure binary pump, an auto-injector, a thermostatically controlled column compartment and a variable wavelength detector. For data processing and acquisition, OpenLab CDS software was used. Samples were prepared in glass vials, dissolved first in DCM:MeOH 1 :1 v:v and later diluted at 1/10 in MeCN to target 0.1 mg/ml for solid samples. Samples were filtered prior to injection in the HPLC system.

Chromatographic separations were achieved in a C18 column (Xbridge Shield RP18 3,5 pm 4,6 x 100 mm; 30 °C) and ammonium formate buffer (pH=5.0) and acetonitrile (ACN) as mobile phase. The gradient indicated in Table 24 was used. The run time was 60.1 min plus a 5 minutes conditioning step between injections. The detector wavelength was 360 nm.

HPLC parameters

Column: Xbridge Shield RP18 3,5 pm 4,6 x 100 mm;

Column temperature: 30 °C Flow rate: 0.8 mL/min

Mobile phase A: Ammonium Formate Buffer pH = 5.0

Mobile phase B: MeCN

Injection volume: 5 pL (Needle Wash with ACN)

Detection wavelength: 360 nm

Diluent: MeCN

Sample Preparation: 0.1 mg/mL

Table 3. HPLC gradient

EXAMPLES

Example 1. Preparation of 1-(3,4-dimethoxyphenethyl)barbituric acid (compound of formula Va)

A mixture of /\/-[2-(3,4-dimethoxyphenyl)ethyl]urea (195.0 g, 869.6 mmol, 1 ,0 equiv.) and dimethyl malonate (149.4 g, 1130.5 mmol, 1.30 equiv.) in methanol (780 mL) was stirred at 20-25°C. Then, sodium methoxide 25% (259 mL, 1130.5 mmol, 1.30 equiv.) were slowly added. The resulting yellow suspension was stirred at reflux temperature for 30 hours and one hour at 20-25°C. A mixture of HCI 1 N (1257 mL) and water (878 mL) was slowly added, and the resulting suspension was stirred at 20-25 °C for one hour. The solid was filtered and washed twice with water (200 mL). The obtained wet solid was dried at 40-45°C, recrystallized from acetonitrile (1544 mL) and dried. An off- white solid was obtained (202.7 g, 693.5 mmol, yield: 80%).

Example 2. Preparation of 2-chloro-9,10-dimethoxy-6,7-dihvdro-4H-pyrimidinof6,1- alisoquinolin-4-one (compound of formula IVa)

1-(3,4-Dimethoxyphenethyl)barbituric acid, obtained in Example 1, (46.2 mg, 158 mmol, 1.0 equiv.) and sulfolane (92 mL) were stirred at 20-25°C. Then, phosphorus oxychloride (44.2 mL, 474 mmol, 3.0 equiv.) were added at 20-25°C. The resulting suspension was stirred at 120-125°C for 2 hours. Afterwards, the reaction was cooled down to 5-10°C, dichloromethane (462 mL) and water (277 mL) were slowly added, keeping the temperature below 10°C. Next, 20% aqueous solution of sodium hydroxide was added at a temperature below 10°C until neutralization. The reaction was warmed to 35-40°C, and phases were separated. The organic phase was extracted twice with dichloromethane (120 mL) at 35-40°C. The organic phases were joined and washed twice with water (120 mL) at 35-40°C. The solvent of the organic phase was distilled-off and the residue obtained was stirred with water (924 mL) at 40-45°C for one hour. The resulting suspension was cooled down to 20-25°C and filtered at this temperature. The obtained solid was stirred with acetone (176 mL) at 40-45 °C for one hour, cooled down to 20-25°C and filtered. A yellow solid was obtained (32.8 g, 112 mmol, yield: 71 %; HPLC: 97,2%)

Example 3. Preparation of (E)-2-(mesitylimino)-9,10-dimethoxy-2,3,6,7-tetrahydro-4H- pyrimidinof6,1-a1isoquinolin-4-one (compound of formula Ila)

A mixture of 2-chloro-9,10-dimethoxy-6,7-dihydro-4H-pyrimidino[6,1-a]isoquinolin-4- one, obtained in Example 2, (60 g, 205 mmol, 1.0 equiv.), 2,4,6-trimethyaniline (58.2 g 430 mmol, 2.1 equiv.) and isopropanol (180 mL) were stirred at reflux temperature for 3 hours. The resulting reaction mixture was cooled down to 0-5°C and further stirred for one hour at this temperature. The obtained solid was filtered and washed twice with ice-cooled isopropanol. The obtained solid was recrystallized from isopropanol. A yellow solid was obtained (78.6 g, 201 mmol, yield: 98%).

Example 4. Preparation of ensifentrine (compound of formula la)

A mixture of (E)-2-(mesitylimino)-9,10-dimethoxy-2,3,6,7-tetrahydro-4H-pyrimidino[6,1- a]isoquinolin-4-one, obtained in Example 3, (398 mg 1.0 mmol, 1.0 equiv.), N-(2- chloroethyl)urea (compound of formula III, wherein Y is Cl) (623 mg, 5.1 mmol, 5.0 equiv.), U2CO3 (225 mg 3.1 mmol, 3.0 equiv.), and potassium iodide (84 mg, 0.5 mmol, 0.5 equiv.) in acetonitrile (2 mL) were stirred at reflux temperature for 4 days. The resulting reaction mixture was cooled down at 20-25°C, dichloromethane (10 mL) and aqueous saturated ammonium chloride (10 mL) were added. The phases were separated, and the aqueous phase was extracted with dichloromethane (5 mL). The organic phases were joined and washed with aqueous saturated ammonium chloride (5 mL). The solvent of the organic phase was distilled off at reduced pressure and the obtained residue was purified by column chromatography. A fraction of 200 mg of ensifentrine was obtained (yield: 40%).

¹H-NMR (400 MHz, CDCI3): 5 (ppm): 2.06 (6H, s), 2.28 (3H, s), 2.91 (2H, t, J=4 Hz), 3.54 (2H, m), 3.76 (3H, s), 3.90 (3H, s), 4.04 (2H, t, J=4 Hz), 4.40 (2H, t, J= 4 Hz), 5.35 (2 H, br. s), 5.45 (1 H, s), 6.67 (1 H, s), 6.70 (1 H, s), 6.88 (2H, s).

Example 5. Preparation of ensifentrine Form I by slurry in ethanol

A fraction of the solid obtained in above Example 4 (2.8 g) was suspended in ethanol (28 mL) and stirred at 50 °C for 16 h. The resulting suspension was cooled down to 20- 25 °C, filtered, washed with ethanol and dried at 20-25 under reduced pressure (yield: 90%; XPRD: Form I). Example 6. Preparation of ensifentrine Form I scale up

A mixture of (E)-2-(mesitylimino)-9,10-dimethoxy-2,3,6,7-tetrahydro-4H-pyrimidino[6,1- a]isoquinolin-4-one (125 g, 319 mmol, 1.0 equiv.), /\/-(2-chloroethyl)urea (78,3 g, 639 mmol, 2.0 equiv.), U2CO3 (70,8 g, 958 mmol, 3.0 equiv.), and potassium bromide (22,8 g , 192 mmol, 0.6 equiv.) in acetonitrile (1000 mL) were stirred at reflux temperature for 6 days, so that 3 consecutive additions of /\/-(2-chloroethyl)urea (78,3 g, 639 mmol, 2.0 equiv.), U2CO3 (23.6 g, 319 mmol, 1.0 equiv.) were made 1, 2 and 3 days after the beginning of the reactions. The resulting reaction mixture was cooled down to 20-25°C and the solvent was distilled-off at reduced pressure. A mixture of 2-MeTHF (1250 mL) and 1250 mL of water (1250 mL) were added to the yellow residue obtained. The mixture was stirred 15 min at 40°C, filtered and the phases were separated at 40°C.

The aqueous phase was extracted twice with 500 mL of 2-MeTHF. The organic phases were joined and washed twice with 500 mL of water and with 500 mL of brine. The solvent of the organic phase was distilled off at reduced pressure and the brownish residue obtained was solved in 500 mL of MeOH at 60°C. The brown solution was seeded and cooled to 20-25°C for 16 h. A yellow solid was filtered, washed twice with 125 mL of MeOH and purified by column chromatography means. A fraction of 63 g of ensifentrine was obtained (yield: 41%, purity 97.40% HPLC; XPRD: Form I).

Example 7. Purification of ensifentrine via conventional isolation methods

7.1. Ensifentrine (78,1 g; HPLC: 89,89%) was suspended in a mixture of dichloromethane (150 mL) and MeOH (1,5 mL) and stirred at 20-25 °C for 18 h. The resulting yellow solid was filtered off, washed with dichloromethane (2x75 mL) and dried at 40-45 °C (yield: 54,6 g; 70%; HPLC: 96,37%).

7.2. Ensifentrine (54,6 g) obtained in (7.1) was mixed with 1-propanol (550 mL) and heated at reflux temperature (93 °C). Water (130 mL) was added to the yellow suspension. The resulting yellow solution was cooled to 73 °C and seeded. The obtained suspension was cooled to 20-25 °C for 3 h and stirred at this temperature for 16 h. The yellow solid was filtered and washed twice with 1- propanokwater (4:1) (50 mL) (yield: 26,6 g; 49%; HPLC: 97,13%).

7.3. Ensifentrine (4,0 g) obtained in (7.2) was recrystallized from 50 mL of 1- propanol ater (4:1) (yield: 3,37 g; 84%; HPLC: 97,42%).

7.4. Ensifentrine (3,24 g) obtained in (7.3) was recrystallized from 40 mL of 1- propanol water (4:1) (yield: 2,87 g; 89%; HPLC: 97,49%). 7.5. Ensifentrine (2,69 g) obtained in (7.4) was recrystallized from 34 mL of 1- propanol water (4:1) (yield: 2,36 g; 88%; HPLC: 97,72%).

Example 8. Purification of ensifentrine via salt formation with an aryl sulfonic acid

Compound la (100 mg; 93.67% purity by HPLC) was mixed with 1.1 equiv. of an aryl sulfonic acid and the solvent (10, 15 and 20 V), as shown in Table 4. The resulting suspensions were heated to 75 °C and stirred at this temperature for 30 min. Then, samples were cooled down at 0.5°C/min to 25°C and stirred at that temperature for 16 h. Samples were vacuum-filtered and washed twice with the crystallization solvent (2V). The solids were dried at 40°C for 5-16 hours and analyzed by HPLC and XPRD. Table 4

Characterization of aryl sulfonic acid addition salts:

Acid addition salt of compound (la) and benzenesulfonic acid

XPRD (Fig. 1): Crystalline pattern.

¹H-NMR (Fig. 2; 400 MHz, DMSO): 5 11.53 (bs, 1H), 7.59 (dd, J = 7.3, 2.2 Hz, 2H), 7.38 - 7.22 (m, 3H), 7.10 (s, 2H), 7.08 (s, 1H), 6.80 (s, 1H), 6.54 (t, J = 4.5 Hz, 1 H), 6.03 (bs, 2H), 5.61 (s, 1 H), 4.26 (t, J = 6.8 Hz, 2H), 4.08 (t, J = 6.3 Hz, 2H), 3.85 (s, 3H), 3.65 (s, 3H), 3.41 - 3.24 (m, 4H), 3.00 (t, J = 6.2 Hz, 2H), 2.32 (s, 3H), 2.20 (s, 6H), 1.54 - 1.32 (m, 2H), 0.83 (t, J = 7.4 Hz, 3H).

DSC: Sharp endothermic peak with onset temperature at 131 °C (-96 J/g).

TGA: Weight loss of 8.65% between 105 °C and 150°C (probable loss of 1 equivalent of n-propanol). Decomposition starts at about 250°C.

Acid addition salt of compound (la) and p-toluensulfonic XPRD (Fig. 3): Crystalline pattern.

¹H-NMR (Fig. 4; 400 MHz, DMSO): 5 11.52 (bs, 1H), 7.47 (d, J = 8.0 Hz, 2H), 7.19 - 6.99 (m, J = 6.4 Hz, 5H), 6.80 (s, 1 H), 6.55 (t, J = 5.0 Hz, 1 H), 6.03 (bs, 2H), 5.61 (s, 1 H), 4.26 (t, J = 6.9 Hz, 2H), 4.08 (t, J = 6.3 Hz, 2H), 3.85 (s, 3H), 3.65 (s, 3H), 3.48 - 3.37 (m, 2H), 3.00 (t, J = 6.2 Hz, 2H), 2.43 (q, J = 7.3 Hz, 2H), 2.32 (s, 3H), 2.28 (s, 3H), 2.20 (s, 6H), 2.07 (s, 2H), 0.90 (t, J = 7.3 Hz, 2H).

DSC: Sharp endothermic peak with onset temperature at 114 °C (-53 J/g).

TGA: Weight loss of 6.9% between 50 °C and 170°C (probable loss of MEK). Decomposition starts at about 250°C.

Example 9. Purification of ensifentrine via formation of benzenesulfonate salt in propanol

Ensifentrine (2 g; 93.67% purity by HPLC) was mixed with 1.1 equiv. (744.4 mg) of benzenesulfonic acid and 10 V of n-propanol (20 mL). The resulting suspension was heated at 90 °C and stirred at this temperature for 30 min (solution was achieved). Then, sample was cooled down at 0.5°C/min to 25°C and stirred at this temperature for 16 h. Sample was vacuum-filtered and washed twice with n-propanol (4mL, 2V). Yield: 2.17 g (75%). HPLC: 99.90%

The obtained salt (50mg) was suspended in 10 V of n-propanol (0.5 mL), heated at 90 °C and stirred at this temperature for 30 min. Then, the resulting solution was cooled down to 0.5°C/min at 25°C and stirred for 4 h. Sample was vacuum-filtered and washed twice with n-propanol (2 V). Yield: 45mg (85%). HPLC: 100%

Example 10. Purification of ensifentrine via formation of p-toluensulfonate acid addition salt in ethanol

Ensifentrine (5,05 g; 96.37% purity by HPLC) was suspended in ethanol (30 mL) at 20- 25 °C. To the yellowish suspension formed a solution of p-toluensulfonic acid monohydrate (2,21 g, 11 ,6 mmol, 1,10 eq.) in ethanol (20 mL) was added at 20-25 °C. The obtained solution was heated at 80 °C. The obtained suspension was cooled to 20-25 °C and stirred 18 h at this temperature. The white solid was filtered and washed twice with ethanol (5 mL). Yield: 4,84 g (71%; HPLC: 99.17%).

Example 11. Preparation of purified ensifentrine

The ensifentrine benzenesulfonate salt (30 mg; 99.17%) was suspended in methanol (180pL) at 25°C. Ammonium hydroxide (12.6pL, cone 2 eq) were added. A change of color from white to yellow was observed. The suspension was heated to 35 °C and stirred at this temperature for 1 hour. The mixture was cooled at 0.5°C/min to 25°C and stirred at this temperature for 2 h. The mixture was filtered under vacuum, and the wet cake washed twice with Me0H:H20 3:5 (2 x 30 pL). Both the mother liquors and solid were analyzed by HPLC. Yield: 75%. Purity: 99.58% (HPLC). Example 12. Preparation of purified ensifentrine

Ensifentrine p-toluensulfonate acid addition salt (500 mg, 0,77 mmol, 1,00 equiv., 99.58%) obtained above was mixed with methanol (3,00 mL) at 20-25 °C. To the white suspension obtained 25% aqueous ammonia (0,10 mL, 1,92 equiv., 74,2 mmol) was added. The mixture was heated at 35-40 °C. The yellowish suspension obtained was stirred at this temperature for 1 h. Water (5 mL) was added at 35-40 °C and stirred at this temperature for 1 h. The mixture was cooled to 20-25 °C and stirred 1 h at this temperature. The yellow solid was filtered and washed twice with methanol (0,5 mL). Yield: 313 mg (85%). HPLC: 99.45%.

Claims

1. A process for preparing a compound of formula (I), or a pharmaceutically acceptable acid addition salt, wherein: R¹ and R² are the same or different and each is independently either a Ci-Ce alkyl group or a C2-C7 acyl group, or alternatively, R¹ and R² together form a Ci-Ce alkylene group; R³ and R⁴ are the same or different and each is independently selected from the group consisting of hydrogen, halogen, and a Ci-Ce alkyl group; R⁵ and R⁶ the same or different and each one is independently selected from the group consisting of hydrogen, halogen, and a Ci-Ce alkyl group; X is selected from the group consisting of CHR⁷, O, and NR⁷; R⁷ is either hydrogen or a Ci-Ce alkyl group; and Ar is 2,4,6- trimethylphenyl; which comprises the step of reacting a compound of formula (II)

(II) wherein R¹, R², R³, R⁴, R⁵, R⁶, X, and Ar is as defined for compound (I), with a compound of formula (III)

(HI) wherein Y is a leaving group selected from the group consisting of halogen, mesylate (OMs), tosylate (OTs), nosylate (ONs), acetate (OAc), and triflate (OTf).

2. The process according to claim 1 , wherein the compound of formula (III) is in an amount in a range from 0.5 to 10 equivalents with respect to an equivalent of the compound of formula (II).

3. The process according to any one of claims 1 to 2, wherein the process is conducted in the presence of a base selected from the group consisting of sodium carbonate, potassium carbonate, caesium carbonate, lithium carbonate, sodium acetate, and potassium acetate.

4. The process according to claim 3, wherein the base is in an amount in a range from 1 .0 to 8.0 equivalents with respect to an equivalent of the compound of formula (II).

5. The process according to any one of claims 1 to 4, wherein the process is conducted in the presence of a solvent selected from the group consisting of a nitrile solvent such as acetonitrile, a (Ci-Ci2)ether solvent such as diethyl ether, dipropyl ether, isopropyl ether, tert-butyl methyl ether, tetrahydrofuran, 1 ,4-dioxane, a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIK), ethyl isopropyl ketone, methyl isopropyl ketone, 3-methyl-2-pentanone, and a combination thereof.

6. The process according to any one of claims 1 to 5, wherein the reaction is conducted at a temperature in a range from 50°C to 100°C, preferably from 60 to 95°C.

7. The process according to any one of claims 1 to 6, wherein the reaction is maintained for at least 6 hours, preferably at least 12 hours, more preferably at least 24 hours, even more preferably 72 hours.

8. The process according to any one of claims 1 to 7, wherein the reaction is conducted in the presence of a source of iodide or bromide.

9. The process according to any one of claims 1 to 8, wherein the process comprises isolating the compound of formula (I), preferably isolating by evaporation.

10. The process according to any one of claims 1 to 9, wherein R¹ and R² are methyl; R³ and R⁴ are hydrogen; R⁵ and R⁶ are hydrogen; and X is CH2, referred as compound of formula (la) and compound of formula (Ila).

11 . The process according to claim 10, wherein the process further comprises previously reacting a compound of formula (IVa) with 2,4,6-trimethylaniline to yield compound of formula (Ila).

12. The process according to claim 11 , wherein the process further comprises previously reacting compound of formula (Va) with a chlorinating agent such as phosphorous oxychloride to yield compound of formula (I a).

13. The process according to any one of claims 10-12, further comprising a purification process of the compound (la) which comprises the steps of: a) converting compound (la) into a pharmaceutically acceptable acid addition salt of: (i) compound (la) and (ii) an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p-toluenesulfonic acid, wherein the stoichiometry of the compound (la) to the counter ion is 1 :1 by ¹H-NMR; b) optionally, purifying the acid addition salt obtained in step a), and c) converting the pharmaceutically acceptable acid addition salt obtained in step a) or b) into compound (la).

14. The process according to claim 13, wherein the pharmaceutically acceptable addition salt is the compound (la) benzenesulfonate and step a) is conducted in the presence of n-propanol as solvent.

15. The process according to claim 13, wherein the pharmaceutically acceptable addition salt is the compound (la) p-toluensulfonate and step a) is conducted in the presence of methyl ethyl ketone (MEK) as solvent.

16. The process according to any of the claims 13-15, wherein step c) is conducted by reacting the pharmaceutically acceptable acid addition salt with ammonia in methanol as solvent to provide purified compound (la).

17. The process according to any of the claims 9-16, wherein the process comprises dissolving the compound obtained in any of the claims 9-16 in a solvent selected from the group consisting of a (Ci-Ci2)alcohol solvent such as methanol, ethanol, isopropanol, 1-propanol, 2-methyl-1-propanol, 1-butanol, 2-butanol, 1-pentanol, 3- methyl-1 -butanol, tert-butanol, water and a combination thereof, and crystallizing crystalline form from said solvent or said mixture of solvents.

18. The process according to any one of claims 9 to 16, wherein the process comprises reacting the compound of formula I, preferably (la), with an acid selected from the group consisting of ethane-1 ,2-disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, phosphoric acid, and sulfuric acid, to yield the corresponding pharmaceutically acceptable acid addition salt of compound of formula I, preferably (la).

19. The process according to claim 18, wherein the pharmaceutically acceptable acid addition salt is ethane-1,2-disulfonate acid addition salt.

20. A pharmaceutically acceptable acid addition salt of: (i) a compound (la) and (ii) an aryl sulfonic acid selected from the group consisting of benzensulfonic acid and p- toluenesulfonic acid, wherein the stoichiometry by ¹HNMR of the compound (la) to the counter ion is 1 :1.

21. The pharmaceutically acceptable acid addition salt according to claim 20, which is the compound (la) benzenesulfonate and is characterized by having a powder X-ray diffraction that comprises characteristic peaks at approximately 5.2°±0.2°, 13.1 °±0.2°, 21.6°±0.2° and 24.3°±0.2°, degrees 2 theta using Cu Ka1 radiation (A = 1.54060 A).

22. The pharmaceutically acceptable acid addition salt according to claim 20, which is the compound (la) p-toluenesulfonate and is characterized by having a powder X-ray diffraction that comprises characteristic peaks at approximately 5.0°±0.2°, 8.8°±0.2°, 17.0 °±0.2°, and 24.2°±0.2°, degrees 2 theta using Cu Ka1 radiation (A = 1.54060 A).

23. The use of the pharmaceutically acceptable acid addition salt according to any one of claims 20 to 22, for the purification of compound of formula (la).