RU2850645C1 - Method for obtaining 7-(4,7-diazaspir[2.5]octane-7-yl)-2-(2,8- dimethylimidazo [1,2-b]pyridazine-6-yl)pyrido[1,2-a]pyrimidine-4-ona - Google Patents

Abstract

FIELD: chemical and pharmaceutical industry.

SUBSTANCE: invention relates to a new improved method for producing 7-(4,7-diazaspir[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrid[1,2-a]pyrimidin-4-one (risdiplama) of formula (I) used for the treatment of spinal muscular atrophy. The method comprises the step of reacting 2,8-dimethyl-6-chlorimidazo[1,2-b]pyridazine with a diborane derivative in the presence of a palladium catalyst, followed by adding tert-butyl-7-[4-oxo-2-(para-tolylsulfonyl)pyrid[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) to obtain tert-butyl-7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrid[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (III). Next, the compound of formula (III) is treated with chloroform and recrystallised from dichloromethane, followed by treatment of the compound of formula (III) with a strong inorganic acid solution without the addition of organic solvents. The resulting solution is then neutralised, after which the precipitate of the compound of formula (I) is filtered off.

EFFECT: simplicity of implementation from an equipment and technological point of view, availability and stability of starting reagents, possibility of large-scale production, obtaining a final stable product with high yield and purity without additional purification stages, as well as reduction of the total process time and reduction of the amount of liquid waste. 10 cl, 2 tbl, 3 ex.

Description

Field of technology

The invention relates to the chemical-pharmaceutical industry, in particular to a new improved method for producing 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam), used for the treatment of spinal muscular atrophy.

State of the art

Spinal muscular atrophy (SMA) is a severe inherited disorder in which a mutation in the survival motor neuron gene (SMN1) causes loss of nerve cells in the spinal cord that control muscle movement.

According to the "Proximal Spinal Muscular Atrophy 5q" clinical guidelines (approved by the Russian Ministry of Health), although new cases are relatively rare, many people live with SMA. SMA affects approximately one in 6,000 to 10,000 children and is the leading genetic cause of death in children under two years of age worldwide. Regardless of its severity, all people with SMA experience motor loss.

The first registered drug intended for the pathogenetic treatment of SMA was nusinersen, manufactured by Biogen (USA). Nusinersen is administered intrathecally. Regular therapy slows the progression of the disease and improves patients' quality of life. The drug's proven efficacy is a positive aspect, while its intrathecal administration is a drawback, as this method is not suitable for patients with severe scoliosis, spinal rotation, or those with metal implants.

The second approved drug for the treatment of SMA was risdiplam, an orally administered drug. It was developed by PTC Therapeutics (USA) and is manufactured by Roche for the treatment of SMA. Risdiplam (Eurysdi®) is a splicing modifier for the survival motor neuron 2 (SMN2) gene, developed for the treatment of SMA caused by mutations on chromosome 5q, resulting in a deficiency of the SMN protein.

A third drug, onasemnogene abeparvovec, has been developed and approved by the FDA for the treatment of children under 2 years of age with SMA type 1. It is a gene therapy based on the adeno-associated virus (AAV) serotype 9, which delivers a fully functional copy of the human SMN1 gene to target motor neuron cells. A single intravenous injection of a dose of viral genomes per kilogram of body weight leads to increased survival and improved movement and muscle function. The rate of recovery of physiological function in patients depends on their age, body weight, and baseline condition.

Although more than a century has passed since the first clinical case of SMA was described, a treatment capable of slowing the disease's progression was discovered less than a decade ago. Currently, the aforementioned drugs nusinersen, risdiplam, and onasemnogene abeparvovec are widely used worldwide for the treatment of SMA. These medications have proven effective and safe in both pediatric and older patients. The pronounced clinical effects of these treatments offer patients of all ages the opportunity to increase life expectancy and improve their health-related quality of life.

Risdiplam is convenient for patients because it is administered orally, allowing them to adequately maintain their regimen without leaving their home. This is an advantage of this motor neuron survival gene 2 splicing modifier over two other known drugs. It is important to note that risdiplam requires lifelong administration at a frequency of once daily (Komarova E.A., Kotov A.S. Pathogenetic therapy in children with spinal muscular atrophy. RMJ. 2025; 4:26-30. DOI: 10.32364/2225-2282-2025-4-5).

When developing drugs, it's important that the active agent be readily available and meet quality requirements. The most optimal way to increase the availability and quality control of the active agent is to develop a unique synthetic protocol. Active agent synthesis allows for the control of properties such as the active agent's form (e.g., crystalline, amorphous, or the ratio of the two); chemical purity, specifically the amount of related impurities or reagents used in chemical transformations; and the stereoisomeric purity of the active agent.

Chemical purity is of great importance in the production of substances. It is known that the degree of purity of substances potentially affects their safety and efficacy in both human and veterinary medicine. Increasing the chemical purity of a substance improves its original biological properties and reduces potential side effects associated with the presence of impurities.

According to the ICH (International Council on Harmonization) Tripartite Guideline on Impurities in New Drug Substances, an impurity present in a drug substance is not considered a component of the drug product. Furthermore, the safety of a drug product depends largely on the quantity and nature of impurities contained in the drug product. Furthermore, impurities are known to play a key role in the observed toxicological properties of the drug product.

In the production of substances and medicinal products, it is necessary to minimize the presence of various impurities in the final product, since they have a negative impact on both the preparation process and the quality of the final product.

To meet the stringent requirements for the form of active agents in drugs in this field, it is still necessary to develop new efficient methods for the synthesis and purification of the active agent and intermediates.

The development of new approaches to active agent synthesis opens up opportunities to improve the physicochemical and technological characteristics of pharmaceutical products. This expands the range of active agents available to drug developers when developing a new drug with an enhanced safety profile. Furthermore, the sustainable development of modern approaches to active agent synthesis enables the introduction of environmentally friendly, resource-efficient innovative technologies into production, which contribute to economic development and minimize environmental impact.

Thus, there is currently a continuing need to develop new, improved methods for synthesizing the survival motor neuron 2 (SMN2) gene pre-mRNA splicing modifier, risdiplam, intended for the treatment of spinal muscular atrophy (SMA).

In accordance with the Decree of the President of the Russian Federation dated May 7, 2018 No. 204 "On the national goals and strategic objectives of the development of the Russian Federation through 2024" within the framework of the import substitution program "Pharma-2030", the main tasks to ensure sustainable socio-economic development of the Russian Federation are the development, implementation and use of drugs for medical use, as well as acceleration of the scientific and technological development of the pharmaceutical industry of the Russian Federation. In this regard, the authors of the present invention have made efforts to create an innovative method for producing the compound 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam, compound of formula (I)).

The method for synthesizing risdiplam was first disclosed by F. Hoffmann-La Roche and PTC Therapeutics Inc. in international application WO2015173181. The method for preparing the compound of formula (I) involves an aromatic nucleophilic substitution reaction:

The main drawback of this method is the use of column chromatography to purify the intermediates and risdiplam, which is difficult to achieve when synthesizing the compound on an industrial scale. The achievable yield of risdiplam is 18%.

A method for producing risdiplam (variants) and a method for purifying it (WO2024003798) are known, consisting of dissolving risdiplam in one or more suitable solvents, passing the resulting solution through a quartz column, collecting all fractions, removing the solvent, dissolving the resulting residue in a mixture of water and ascorbic acid, followed by adjusting the pH of the aqueous layer to 9-10, removing the solvents. One or more solvents are added to the resulting solid residue, then the solvent is distilled off. One or more solvents are again added to the resulting solid residue, the reaction mixture is heated for 5-6 hours at 80-85 °C, then the reaction mixture is cooled to room temperature and pure risdiplam with a total impurity content of less than 1.0%. The confirmed achievable purity of risdiplam is 99.8%, while the yield of the purification stage is no more than 50%.

A known method for purifying risdiplam involves mixing 90% pure risdiplam with a mixture of acid and alcohol, stirring the resulting mixture at a temperature of 27 to 35°C until a homogeneous suspension is obtained (WO2025057179). The suspension is filtered and washed with a suitable solvent to obtain a wet product. Water is added to the wet product, the resulting mixture is stirred and held for 30-35 minutes, and after settling, the mixture is separated. The pH of the resulting solution is adjusted to 10-12. The solid is filtered and washed with water, after which it is recrystallized from a lower alcohol with stirring at a temperature of 30-40°C for approximately one hour, followed by filtration and washing the solid with alcohol to obtain risdiplam with a purity of >97.0%. The resulting risdiplam is repeatedly purified as described above to obtain risdiplam with an HPLC purity of >99.5%. To achieve the required purity, several purification steps are required, which results in compound loss. Furthermore, the disposal of the large number of solvents used (alcohol, acid) presents a challenge during industrial production of the compound.

A method for obtaining risdiplam by reacting a compound of formula (III) is known

with a strong acid, in particular HCl, in situ in the presence of propanol-1 and acetyl chloride (WO2019057740). In this case, the synthesis of the compound of formula (III) includes a cross-coupling reaction of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine with tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II)

The obtained compound of formula (III) is purified by chromatography on silica gel (eluent: dichloromethane/ethyl acetate in dichloromethane/methanol). After chromatography, the product as a yellow solid is precrystallized as follows: 15 g of this solid is dissolved in toluene (135 ml) and ethanol (15 ml). The solution is slowly cooled to room temperature, stirred for 16 hours at room temperature, then cooled to 0°C and stirred at 0°C for 4 hours. The precipitate is filtered off, washed with cold toluene and dried under high vacuum at 55°C. The yield of the product at this stage is 79.5%. Then, the protecting groups are removed to obtain risdiplam as a yellowish solid.

However, as noted above, the use of chromatography in the method of purifying intermediate compounds makes it difficult to carry out the synthesis of the compound on an industrial scale.

Since risdiplam requires lifelong use, there is an unmet need for an efficient, easily scalable, and simple method for the preparation of 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam) with high purity and high yield of the target product. This technical problem has not been solved in the prior art.

Brief disclosure of the invention

The authors of the present invention have developed a method for producing 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam) with a high yield of up to 75% in all stages and high purity of up to 99.9% of the target product without the need for an additional purification step.

The present invention relates to a process for the preparation of 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam) of formula (I)

including:

(a) reaction of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine with a diborane derivative in the presence of a palladium catalyst;

followed by adding tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) to the resulting product

to obtain tert -butyl 7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (III)

(b) treating the compound of formula (III) with an organochlorine solvent and recrystallizing the compound of formula (III) from the organochlorine solvent;

(c) treating the compound of formula (III) with an aqueous solution of a strong inorganic acid without adding organic solvents to obtain a compound of formula (I).

According to one embodiment of the present invention, step (a) is carried out in an inert gas atmosphere without intermediate isolation of the boron derivative in acetonitrile in the presence of a base under reflux for 6-12 hours.

According to one embodiment of the present invention, in step (a), one or more palladium compounds Pd(0) or Pd(II) with ligands selected from:

phosphine ligands, including triphenylphosphine (PPh ₃ ), tricyclohexylphosphine (PCy ₃ ), tri- tert -butylphosphine (t-Bu ₃ P);

N- heterocyclic carbenes, including 1,3-bis(2,6-diisopropylphenyl)imidazolinium (IPr) and 1,3-bis(2,4,6-trimethylphenyl)imidazolinium (IMes);

bidentate ligands, including 1,1'-bis(diphenylphosphino)ferrocene dppf, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl BINAP.

According to one embodiment of the present invention, [1,1`bis(diphenylphosphino)ferrocene]palladium(II) dichloride is used as the palladium catalyst.

According to one embodiment of the present invention, in step (a), esters of diboric acid ((R'O) ₂ BB(OR') ₂ ) are used as the diborane derivative.

According to one embodiment of the present invention, in step (a), bis(pinacolato)diboron is used as the boron agent.

According to one embodiment of the present invention, in step (b), treating the compound of formula (III) with an organochlorine solvent comprises: dissolving the compound of formula (III) in chloroform in an amount selected from 5-20 ml of chloroform per 1 g of compound of formula (III); subsequently separating undissolved impurities; removing chloroform; and drying the compound of formula (III) to constant weight.

According to one embodiment of the present invention, in step (b), recrystallizing the compound of formula (III) comprises dissolving the compound of formula (III) in boiling dichloromethane at 40-42°C, then cooling the resulting suspension to 20-25°C and separating the precipitate.

According to one embodiment of the present invention, in step (c), an aqueous solution of hydrochloric acid is used as an aqueous solution of a strong acid.

According to one embodiment of the present invention, in step (c), after treating the compound of formula (III) with an aqueous solution of hydrochloric acid, the resulting solution is neutralized with a solution of sodium hydroxide, the pH is adjusted to 12-13, after which the precipitate of the compound of formula (I) is filtered off and dried to constant weight.

Disclosure of the essence of the invention

The present inventors have developed a method for producing 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam) in high yield and purity of the target product without the need for an additional step of purification of the target product in accordance with the following scheme:

To do this, a diborane derivative is added to 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine in the presence of a palladium catalyst and a base. Then, tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) is added to the resulting product. The reaction yields tert -butyl 7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (III). The subsequent removal of the tert -butylcarbonyl protecting group (the so-called BOC protection) is carried out in an acidic environment.

The authors of the present invention significantly optimized each stage of the synthesis. For example, the cross-coupling reaction (Miyaura reaction) utilized a one-pot process without intermediate isolation of the corresponding boron derivative. This results in a single catalyst loading and single degassing of the reaction mixture, representing a significant technological improvement in the claimed production method.

The yield of risdiplam, the purity of the product, and the potential for scaling up the synthesis are significantly affected by intermediate purification of the compound of formula (III) by recrystallization from an organochlorine solvent. The present inventors have found that treatment of the compound of formula (III) with an organochlorine solvent (e.g., chloroform) and recrystallization of the compound of formula (III) from an organochlorine solvent (e.g., dichloromethane) yields the final target product with increased yield and purity, and enables scaling up the synthesis. Furthermore, in the case of this intermediate purification of the compound of formula (III), subsequent purification of the target compound of formula (I) is not required.

Unlike prototype WO2019057740, subsequent removal of the tert -butylcarbonyl protecting group (BOC protection) can be performed in an aqueous medium without the addition of an organic solvent, significantly reducing the amount of associated impurities and simplifying the isolation and washing of the final product. The amount of liquid organic waste is significantly reduced, ensuring an environmentally friendly overall process. The improved method preserves the biological properties of the target compound and reduces potential side effects.

Thus, the technical result, which the present invention is aimed at achieving, is the production of 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam), wherein the method is characterized by simplicity of implementation from the hardware and technological points of view, availability and stability of the initial reagents, as well as more favorable profitability due to a reduction in the overall time of the process, a decrease in the amount of liquid waste, with the production of a final stable product with a high yield and purity without additional purification steps.

Method for obtaining risdiplam

The present technical problem is solved and the said technical result is achieved thanks to the method for obtaining 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam) of formula (I)

including:

(a) reaction of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine with a diborane derivative in the presence of a palladium catalyst;

followed by adding tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) to the resulting product

to obtain tert -butyl 7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (III)

(b) treating the compound of formula (III) with an organochlorine solvent and recrystallizing the compound of formula (III) from the organochlorine solvent;

(c) treating the compound of formula (III) with an aqueous solution of a strong inorganic acid without adding organic solvents to obtain a compound of formula (I).

Step (a) of the process for obtaining risdiplam

Step (a) of the process for preparing risdiplam involves reacting 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine with a diborane derivative in the presence of a palladium catalyst, followed by adding tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) to the resulting product according to the following scheme:

As a diborane derivative, a diboric acid ester ((R'O) ₂ BB(OR') ₂ ) is preferably selected, and even more preferably bis(pinacolato)diboron (B ₂ pin ₂ ).

As a palladium catalyst, one or more palladium compounds Pd(0) or Pd(II) with ligands are preferably used. The ligands can be selected from phosphine ligands, including triphenylphosphine ( _PPh3 ), tricyclohexylphosphine ( _PCy3 ), tri- tert -butylphosphine (t- _Bu3P ); from N- heterocyclic carbenes, including 1,3-bis(2,6-diisopropylphenyl)imidazolinium (IPr) and 1,3-bis(2,4,6-trimethylphenyl)imidazolinium (IMes); and from bidentate ligands, including 1,1′-bis(diphenylphosphino)ferrocene (dppf), 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP). In a preferred embodiment, the catalyst is [1,1`bis(diphenylphosphino)ferrocene]palladium(II) dichloride.

The cross-coupling reaction (Miyaura reaction) underlying this step also involves the addition of a base selected, for example, from potassium phosphate (K ₃ PO ₄ ), but others can also be used, such as triethylamine (Et ₃ N), potassium acetate (AcOK), cesium acetate (AcOCs), etc.

The reaction is carried out in an organic solvent suitable for cross-coupling, such as toluene, acetonitrile, or isopropanol. The reaction can also be carried out in water or in aqueous-organic systems, such as tetrahydrofuran/water, 1,4-dioxane/water, dimethyl sulfoxide/water, or dimethylformamide/water. Preferably, the reaction is carried out in acetonitrile.

Preferably, the reaction is carried out in the absence of oxygen, i.e., in an inert, degassed environment. The reaction can also be carried out in nitrogen or argon.

Step (a) can be carried out without intermediate isolation of the corresponding boron derivative and without additional catalyst loading (one-pot mode). To obtain the intermediate boron derivative, 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine is dissolved in an organic solvent suitable for cross-coupling, for example, acetonitrile. A palladium catalyst (e.g., [1,1`bis(diphenylphosphino)ferrocene]palladium(II) dichloride), a base (e.g., potassium acetate), and an organoboron reagent, which is a diborane derivative (e.g., bis(pinacolato)diboron), are added to the solution. The reaction mixture is degassed, for example, by filling the system with argon as an inert gas. The mixture is then stirred with heating until the formation of the corresponding boron derivative is complete. The temperature range depends on the chosen solvent, for example, from 30 to 100°C, from 40 to 90°C, from 50 to 85°C, or at reflux. The reaction time can be determined by thin-layer chromatography based on the disappearance of the starting compound spot. The reaction time can range from 2 to 24 hours, preferably 6-12 hours, depending on the amount of starting compound used.

The molar ratio of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine to bis(pinacolato)diboron is from 1:1 to 1:5, preferably from 1:1 to 1:1.5. The palladium catalyst is taken in catalytic amounts of 0.5 to 5 mol.%, preferably 2.5 mol.%, of the amount of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine.

After completion of the reaction, the resulting solution is separated from the precipitate, if necessary (e.g., by filtering off the precipitate). Tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) and a base (e.g., potassium phosphate) are added to the filtrate containing the required boron derivative. The mixture is heated with stirring until completion of the reaction for 2-24 hours at a temperature of 30-100°C, preferably for 6-12 hours at a temperature of 55-85°C or while boiling the solvent.

The molar ratio of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine to tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) is from 2:1 to 1:1, preferably from 1.5:1 to 1:1, even more preferably 1.25:1.

The reaction time can be determined by thin-layer chromatography based on the disappearance of the starting compound spot. After completion of the reaction, the precipitate is separated from the reaction medium and, if necessary, washed and dried, yielding the target compound tert -butyl 7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate (compound of formula (III)).

A single loading of the catalyst eliminates the need to re-inert the heated reaction mixture, which is a significant technical improvement of the proposed method.

Step (b) of the process for obtaining risdiplam

Step (b) is aimed at purifying tert -butyl 7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate (compound of formula (III)) from impurities.

Step (b) comprises treating the compound of formula (III) with an organochlorine solvent and recrystallizing the compound of formula (III) from the organochlorine solvent.

Chloroform (CHCl ₃ ), dichloroethane (methylene chloride, CH ₂ Cl ₂ ), 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, 1,2,3-trichloropropane, carbon tetrachloride (carbon tetrachloride, CCl ₄ ) can be selected as organochlorine solvents. Chloroform and methylene chloride are preferably used.

The treatment of a compound of formula (III) with an organochlorine solvent comprises dissolving the compound of formula (III) in an organochlorine solvent in an amount selected at a rate of 5-20 ml of organochlorine solvent per 1 g of compound of formula (III); subsequent separation of undissolved impurities, for example, by filtering the solution on a porous filter; removal of the organochlorine solvent, for example, under vacuum; and, if necessary, drying to constant weight. If necessary, the porous filter is additionally washed with an organochlorine solvent at the stage of removing insoluble impurities.

The preferred solvent for the stage of treating the compound of formula (III) with an organochlorine solvent is chloroform. The product is purified from impurities of inorganic salts and palladium particles.

Recrystallization of a compound of formula (III) from an organochlorine solvent involves dissolving the compound of formula (III) in a minimum amount of boiling organochlorine solvent, followed by cooling the solution and separating the precipitate. In a preferred embodiment, recrystallization of a compound of formula (III) involves dissolving the compound of formula (III) in boiling dichloromethane at 40-42°C, followed by cooling to 20-25°C and separating the precipitate.

At this stage, the product is purified of organic impurities. The resulting product is dried to a constant weight.

Step (c) of the process for obtaining risdiplam

Step (c) of the process for producing risdiplam involves treating a compound of formula (III) with an aqueous solution of a strong inorganic acid to obtain a compound of formula (I). A key feature of this step is the use of water as the solvent. Organic solvents are not used. Hydrochloric acid is preferably used as the inorganic acid.

To do this, place a compound of formula (III) in a reactor and add an aqueous solution of hydrochloric acid, preferably hydrochloric acid with a concentration of 20-38%, more preferably concentrated hydrochloric acid with a concentration of 35-38%. The mixture is held for 1-6 hours until the reaction is complete. The reaction mixture is then filtered, and the filtrate is neutralized with a 15% aqueous sodium hydroxide solution to a pH of 12-13. A precipitate is observed.

The method according to the prototype was reproduced by the inventors. According to WO2019057740, the product is isolated from a water-toluene-alcohol mixture, resulting in a paste-like product that is difficult to isolate, filter, wash, and dry.

The product according to the present invention was obtained as a coarse precipitate. The precipitate is easily separated and then dried to a constant weight without the need for additional purification, achieving a yield of 75% across all stages and a target product purity of up to 99.9%.

Implementation of the invention

The present invention is further illustrated by the following illustrative examples.

Example 1. Preparation of tert-butyl 7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate (compound of formula (III))

Tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) and 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine were prepared according to WO2019057740 (examples 7 and 20).

To a solution of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine (534.4 g, 2.94 mol) in 2500 mL of anhydrous, degassed acetonitrile were added [1,1`bis(diphenylphosphino)ferrocene]palladium(II) dichloride (60.0 g, 2.5% mol), anhydrous potassium acetate (576.2 g, 5.88 mol) and bis(pinacolato)diboron (933.2 g, 3.68 mol). The mixture was argonized and heated under an inert gas atmosphere with vigorous stirring at 60°C for 2 h, then refluxed for 8 h. The reaction mixture was then left without stirring for 10 h at room temperature. The resulting precipitate was filtered and washed with acetonitrile (500 ml x 2 . Tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) (1240.0 g, 2.36 mol) and 2M potassium orthophosphate solution (700 ml) were added to the obtained filtrate. The solution was degassed, the reaction mixture was boiled under argon atmosphere, cooled, the solvent was removed, the precipitate was transferred to a filter, washed with water (500 ml x 3), acetonitrile (500 ml x 2), dried, obtaining the target compound (III) in yield 1089.1 g (92%). Purity 95-97% (HPLC).

Example 2. Purification of the compound of formula (III)

6.6 l of chloroform were poured into a reactor with a working volume of 20 l, then 700 g of a thoroughly ground compound of formula (III) was loaded, the stirrer was turned on at 180 rpm and the mixture was kept at a temperature of 22-27°C with stirring until completely dissolved.

Kieselguhr (Celite 545) was poured into a 1-liter Schott filter with a porosity of 40 pores. A deashed filter paper was then placed on the vacuum-compacted kieselguhr layer, and the solution of compound (III) was filtered. After filtration, the kieselguhr layer was washed with chloroform (2 x 0.8 L each), and the washing solution was added to the main filtrate. The combined filtrate was evaporated, and the residue was dried under vacuum. The mass of the dried intermediate product was 680±10 g.

8 L of dichloromethane were loaded into the reactor, heated to boiling, and 680 g of compound of formula (III) were added to the boiling dichloromethane over 30-40 minutes (in ten portions). The resulting suspension was boiled for 2-3 hours, the mass in the reactor was filtered through a 1 L Schott filter with a porosity of 40 pores, washed with dichloromethane and dried in a drying oven at a temperature of 45-50 °C under vacuum. The mass of the dried compound of formula (III) purified was 580.7 g (83%). Purity greater than 99% (HPLC).

Example 3. Synthesis of risdiplam (compound of formula (I))

A reactor was charged with 0.50 liters of purified water and 1.50 liters of concentrated hydrochloric acid. Then, 510 g of purified compound of formula (III) was added in small portions (20-25 grams) over 10-15 minutes. The reaction mixture was then maintained with stirring for 1.5 hours. At the same time, 4 liters of a 20% aqueous sodium hydroxide solution were prepared.

Stirring was initiated (180 rpm), the solution was cooled to 15-20°C, and the previously prepared 15% sodium hydroxide solution was added to the reactor contents until a pH of 13.0-14.0 was reached. A precipitate was observed. The mixture was then stirred for 45-60 minutes. The resulting precipitate was filtered on a 2-liter, 40-pore Schott filter. The risdiplam precipitate was washed with purified water (1000 ml). The procedure was repeated until the filtrate reached a neutral pH (7.0 ± 0.5).

The risdiplam precipitate was dried in a drying oven at 60-65°C under vacuum for 18-24 hours. The mass of the dried risdiplam precipitate was 400.7 g (98%). Purity was greater than 99% (HPLC).

For the purpose of correct assignment of signals in the NMR spectra, the numbering of atoms in the risdiplam molecule is given in Table 1 below.

Table 1 . NMR spectra of risdiplam

Designation Chemical shift ¹ H,
δ _H , m.d. Chemical shift ( ¹³ WITH),
δ _WITH , m.d. Note C ¹ H ₃ 2.19
(3H, singlet) 11.22 The signals of the 1-methyl group appear in the ¹ H NMR spectrum as a singlet, in addition, cross peaks with the H ⁴ proton are visible in the NOESY and COSY spectra. C ² H ₃ 2.22
(3H, singlet) 15.60 The signals of the 2-methyl group appear in the ¹ H NMR spectrum as a singlet, in addition, cross peaks with the H ⁵ proton are visible in the NOESY and COSY spectra. C ³ - 141.60 The HMBC and HSQC spectra contain cross peaks with C ¹ H ₃ protons. C ⁴ H 7.45
(1H, singlet) 115.33 The NOESY spectrum shows a cross peak with protons of C ¹ H ₃ C ⁵ H 7.39
(1H, singlet) 118.67 The NOESY spectrum has a cross peak with the H ⁹ proton. C ⁶ - 135.93 In the HMBC spectrum, cross peaks of the carbon atom with the H ^{4 5} protons are observed. From ⁷ - 133.84 The HMBC spectrum contains cross-peaks of the carbon atom with signals of the C ² H ₃ protons. From ⁸ - 149.16 The HMBC spectrum contains cross-peaks of the carbon atom with signals of the ^H2,5,9 protons. C ⁹ H 6.16
(1H, singlet) 97.53 In the HMBC spectrum, cross-peaks of the proton signal with signals of carbon atoms C ^8,10,12 are observed From ¹⁰ - 157.54 The HMBC spectrum contains cross-peaks of the carbon atom with protons H ^9,13,16 From ¹¹ - 145.29 The HMBC spectrum contains cross peaks of the C ¹¹ atom with the H ^14,16 protons. From ¹² - 152.44 The HMBC spectrum contains cross peaks of carbon with the H ⁵ proton. C ¹³ H 7.14
(1H, doublet) 126.12 The ¹ H spectrum shows a characteristic doublet with KCCB J 9.0 Hz due to interaction with the H ¹⁴ proton C ¹⁴ H 7.62
(1H, doublet) 131.50 The ¹ H spectrum shows a characteristic doublet with KCCB J 9.0 Hz due to interaction with the H ¹³ proton. However, unlike the C ¹³ atom, the NOESY spectrum contains cross peaks with the H ¹⁹ protons. From ¹⁵ - 138.20 The HMBC spectrum contains cross peaks with H ¹⁴ protons. C ¹⁶ H 7.63
(1H, singlet) 108.59 The HMBC spectrum contains cross peaks with the signal of the C ¹⁰ atom. C ¹⁷ H ₂ 3.47
(2H, singlet) 44.26 The HMBC spectrum contains cross peaks between the H ¹³ proton and the C ¹⁸ atom. C ¹⁸ H ₂ 3.47
(2H, singlet) 42.80 The HSQC spectrum contains cross-peaks of protons with the signal of the C ¹⁸ atom, and the NOESY spectrum contains cross-peaks of H ¹⁸ protons with H ¹⁴ protons. C ¹⁹ H ₂ 3.34
(2H, singlet) 52.06 The NOESY spectrum contains cross peaks of H ¹⁹ protons with H ^21,22 protons. From ²⁰ - 37.27 The HMBC spectrum contains a cross peak with H ¹⁹ protons C ²¹ H ₂ 1.19
(2H, singlet) 9.52 The HSQC spectrum contains cross peaks of H ²¹ protons with the C ²¹ carbon atom, as well as H ²² protons with the C ²² carbon atom. C ²² H ₂ 0.98
(2H, singlet)

Table 2 presents a comparative analysis of the proposed method and the method according to the prototype.

Table 2. Comparison of yields by stages of the present invention and the prototype

The present invention Prototype WO2019057740 Stage (a) 92% (Example 1) 85% (Example 11) Comparison of stages (a) One-time loading of the catalyst.
One-pot synthesis. The isolation of the boron derivative is performed as a separate step. Reloading of the catalyst is required. Stage (b) 83% (Example 2) 80% (Example 11) Comparison of stages (b) Double treatment with an organochlorine solvent allows obtaining the intermediate and final target product with increased yield and purity. Washing with an organochlorine solvent was not performed. Product yield and purity were reduced. Stage (c) 98% (Example 3) 95% (Example 15) Comparison of stages (c) The product was isolated from the aqueous solution. The product was obtained as a coarse precipitate, and isolation was accomplished by simple filtration of the precipitate. The intermediate in step (b) was initially dissolved in toluene, which is a toxic solvent and carcinogen.
The product was isolated from a complex water-toluene-alcohol mixture. A paste-like product or suspension was observed. Filtration and isolation of the product were difficult. General exit 75% 64%

Claims (22)

1. Method for preparing 7-(4,7-diazaspiro[2.5]octan-7-yl)-2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)pyrido[1,2-a]pyrimidin-4-one (risdiplam) of formula (I) including: (a) reaction of 2,8-dimethyl-6-chloroimidazo[1,2-b]pyridazine with a diborane derivative in the presence of a palladium catalyst; followed by adding tert -butyl 7-[4-oxo-2-( p- tolylsulfonyloxy)pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (II) to the resulting product to obtain tert -butyl 7-[2-(2,8-dimethylimidazo[1,2-b]pyridazin-6-yl)-4-oxo-pyrido[1,2-a]pyrimidin-7-yl]-4,7-diazaspiro[2.5]octane-4-carboxylate of formula (III) (b) treating the compound of formula (III) with chloroform and recrystallizing the compound of formula (III) from dichloromethane; (c) treating the compound of formula (III) with an aqueous solution of a strong inorganic acid without adding organic solvents, wherein the resulting solution is then neutralized, after which the precipitate of the compound of formula (I) is filtered off to obtain the compound of formula (I). 2. The method according to claim 1, characterized in that stage (a) is carried out in an atmosphere of inert gas without intermediate isolation of the boron derivative in acetonitrile in the presence of a base while boiling for 6-12 hours. 3. The method according to claim 1, characterized in that in stage (a) one or more palladium compounds Pd(0) or Pd(II) with ligands selected from: are used as the palladium catalyst: phosphine ligands, including triphenylphosphine (PPh ₃ ), tricyclohexylphosphine (PCy ₃ ), tri- tert -butylphosphine (t-Bu ₃ P); N- heterocyclic carbenes, including 1,3-bis(2,6-diisopropylphenyl)imidazolinium (IPr) and 1,3-bis(2,4,6-trimethylphenyl)imidazolinium (IMes); bidentate ligands, including 1,1'-bis(diphenylphosphino)ferrocene dppf, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl BINAP. 4. The method according to paragraph 3, characterized in that [1,1`bis(diphenylphosphino)ferrocene]palladium (II) dichloride is used as the palladium catalyst. 5. The method according to claim 1, characterized in that in stage (a) esters of diboric acid are used as the diborane derivative. 6. The method according to claim 5, characterized in that in stage (a) bis(pinacolato)diboron is used as the boron agent. 7. The method according to claim 1, characterized in that in step (b) treating the compound of formula (III) with an organochlorine solvent comprises: dissolving the compound of formula (III) in chloroform in an amount selected on the basis of 5-20 ml of chloroform per 1 g of the compound of formula (III); subsequent separation of undissolved impurities; removal of chloroform; and drying the compound of formula (III) to constant weight. 8. The method according to claim 1, characterized in that in step (b) the recrystallization of the compound of formula (III) comprises dissolving the compound of formula (III) in boiling dichloromethane at 40-42°C, subsequently cooling the resulting suspension to 20-25°C and separating the precipitate. 9. The method according to claim 1, characterized in that in step (c) an aqueous solution of hydrochloric acid is used as an aqueous solution of a strong acid. 10. The method according to claim 9, characterized in that in step (c), after treating the compound of formula (III) with an aqueous solution of hydrochloric acid, the resulting solution is neutralized with a solution of sodium hydroxide, the pH is adjusted to 12-13, after which the precipitate of the compound of formula (I) is filtered off and dried to a constant weight.