CN118355018A

CN118355018A - Process for the preparation of temozolomide

Info

Publication number: CN118355018A
Application number: CN202280080902.3A
Authority: CN
Inventors: O·D·C·帕切科; V·德西奥; M·马索尼; 马塞洛·塞卡托
Original assignee: Cristalia Produtos Quimicos e Farmaceuticos Ltda
Current assignee: Cristalia Produtos Quimicos e Farmaceuticos Ltda
Priority date: 2021-12-06
Filing date: 2022-12-05
Publication date: 2024-07-16
Also published as: AR127856A1; WO2023102627A1

Abstract

The present invention relates to a process for the industrial large scale preparation of temozolomide wherein the key intermediate 5-amino-N1-imidazole-1, 4-dicarboxamide (carbamoyl-AICA) is prepared using N-methylcarbamoylimidazole (NMCI) form I. Furthermore, the present invention relates to a process for preparing form I NMCI. Form NMCI I and temozolomide are purified by crystallization without the use of a chromatographic column or continuous extraction.

Description

Process for the preparation of temozolomide

Technical Field

The invention belongs to the field of chemical pharmacy, and relates to an improved method for preparing temozolomide on a large scale industrially, wherein N-methylcarbamoylimidazole (NMCI) I is used for preparing a key intermediate 5-amino-N1-imidazole-1, 4-dimethylformamide (carbamoyl-AICA). In addition, the invention relates to a process for the preparation of form NMCI I. Form NMCI I and temozolomide are purified by crystallization without the use of a chromatographic column or continuous extraction.

Background

Temozolomide, chemically known as 8-carbamoyl-3-methylimidazole [5,1-d ] -1,2,3, 5-tetrazin-4 (3H) -one, represented by structural formula I:

Temozolomide is a drug with antitumor activity and is described for the first time in patent US 5260291.

Several synthetic routes to temozolomide are reported in the literature. Document US5260291 describes a method represented by scheme 1, which comprises 2 steps: i) Diazotizing 5-aminoimidazole-4-carboxamide (AICA) with sodium nitrite (NaNO ₂) in an acidic medium to obtain an intermediate diazonium salt; ii) cyclizing the diazonium salt with methyl isocyanate (MeNCO) to obtain temozolomide.

Scheme 1

While this method represents an excellent example of quantitative cyclization, where all atoms of the starting material are incorporated into the final product, it was observed that the method had the following drawbacks: i) Isolation of unstable and potentially dangerous intermediate diazonium (5-diazonium-1H-imidazole-4-carboxamide); ii) the use of Methyl Isocyanate (MIC), which is an explosive compound that is extremely toxic when mixed with air and therefore very dangerous to handle, especially on an industrial scale; and iii) very long condensation reactions (about 20 days).

Alternative synthetic methods of temozolomide avoiding the use of MIC were described by Wang and Stevens in 1997 [ Wang, Y & Stevens, mfg.j. Org. Chem.1997,62,7288-7294]. Specifically, the key intermediate 5-amino-N1-imidazole-1, 4-dicarboxamide (carbamoyl-AICA) depicted in scheme 2 was converted to temozolomide in 45% yield by nitrosation cyclization (continuous diazotisation and cyclization) using sodium nitrite in aqueous tartaric acid at 0 to 5 ℃. carbamoyl-AICA can be prepared from AICA and 4-nitrophenylchloroformate in Dichloromethane (DCM) to provide 4-nitrophenylcarbamate, which is then treated with methylamine (MeNH ₂) or reacted directly with N-methylcarbamoyl chloride. Both processes are carried out in the presence of triethylamine (TEA or Et ₃ N) as catalyst base. TEA is a volatile liquid that is flammable and toxic to inhale, and thus is very dangerous to handle on a large scale, limiting its use on an industrial scale.

Scheme 2

Wang and Stevens also studied the effect of some nitrosation conditions such as temperature, nitrosating agent, solvents (polar and non-polar) and fatty and aromatic acids on product yields; and overall, aqueous conditions are preferred over non-aqueous conditions, and inorganic nitrites are preferred over organic nitrites. The use of phase transfer catalysts such as tetramethylammonium hydroxide, tetrabutylammonium bisulfate, and cetyltrimethylammonium bromide did not increase the yield; while the use of other potential cyclization regulators such as 15-crown-5, glyceraldehyde, succinimide, beta-cyclodextrin, benzenesulfonamide, potassium thiocyanate, zinc acetate or copper acetate and lithium chlorate also did not result in an increase in yield.

Meanwhile, according to Wang and Stevens, for nitrosation cyclisation of carbamoyl-AICA, sodium nitrite (1 molar equivalent), water and tartaric acid (1 molar equivalent) were used for 1 hour at a temperature of 0-5 ℃, wherein the weight/volume ratio of carbamoyl-AICA to water was 1:68. in the last step of nitrosylation cyclization of carbamoyl-AICA, azahydroxypurine (major impurity) is also formed, which is obtained in an amount approximately equal to temozolomide (50:50), resulting in low yield of this step. This method requires the use of chromatographic columns to isolate temozolomide, which limits its application on an industrial scale, especially when large quantities of product are required.

Document WO2008038031 describes the preparation of temozolomide by nitrosation cyclisation of carbamoyl-AICA in the presence of an excess of a metal halide (cyclisation promoter for temozolomide). In this document temozolomide is obtained in a high proportion with respect to azahydroxypurine, however the proportions obtained for each substance are not mentioned. Nitrosation cyclisation of carbamoyl-AICA is carried out in the presence of a metal halide (such as lithium chloride or lithium bromide), an acid and a nitrous acid source. The reaction was optimized by adding carbamoyl-AICA to the sodium nitrite solution to give a yield of 43% to 65% (based on the extraction method). According to example 4 of this document, nitrosation cyclisation is carried out in the presence of LiCl at room temperature (18 ℃ to 22 ℃) for 5 hours, with a weight/volume ratio of carbamoyl-AICA to water of 1:24, temozolomide is provided in 63% yield. The complete process is shown in scheme 3 below.

Scheme 3

Temozolomide obtained by the process in WO2008038031 is isolated by countercurrent extraction with a continuous liquid-liquid extractor, which requires a large amount of solvent such as dichloromethane. The use of large amounts of metal halides, special equipment (extractors) and large amounts of methylene chloride makes the process generally expensive, uncompetitive and difficult to implement from an industrial and environmental point of view.

Document WO2018112589 describes scheme 4, a process for the preparation of temozolomide using N-methylcarbamoylimidazole (NMCI) as carbamoylating agent.

Scheme 4

NMCI can be purchased commercially or prepared by reacting N, N-Carbonyldiimidazole (CDI) with methylamine hydrochloride (MeNH ₂. HCl) in a mixture of acetonitrile and dimethylformamide according to the method described in Duspara et al J.org.chem.2012,77 (22), 10362-10368 and purified by chromatography. NMCI was reacted with AICA in acetonitrile or Tetrahydrofuran (THF) to afford carbamoyl-AICA, and isolated by filtration. Reacting carbamoyl-AICA with sodium nitrite added to the reaction medium in solid form in the presence of tartaric acid solution, wherein the weight/volume ratio of carbamoyl-AICA to water is 1:15. after the reaction was completed, the mixture was heated to 60 ℃ and filtered to provide 60: temozolomide and azahydroxypurine in a ratio of 40. Temozolomide is purified by chromatography and then crystallized.

NMCI carbamylating agents have the advantage of being non-hygroscopic, low toxic, non-explosive, easy to store and inexpensive crystalline solids. However, purification by chromatography columns makes its production difficult to implement on an industrial scale. Also, the use of chromatographic columns to isolate temozolomide limits the applicability of the process to large scale industrial production when large quantities of product are required.

Document WO2015057585 describes the preparation of intermediate NMCI (example 17; compound 32) from a coupling reaction of CDI and methylamine in dichloromethane and tetrahydrofuran. Characterization by ¹ HNMR, the resulting white to orange solid was NMCI: mixtures of imidazoles (1:1). NMCI was purified by partitioning between dichloromethane and saturated aqueous ammonium chloride (NH ₄ Cl) and separated. The aqueous layer was extracted with dichloromethane, the organic layers were combined, dried, filtered, and concentrated under reduced pressure to provide crystallized NMCI. Although the purification step does not involve the use of a chromatographic column which limits large-scale industrial application, the yield of the process is low, with a long chemical conversion step of 72 hours at a yield of about 50% (preliminary yield before purification). Furthermore, solutions of methylamine in tetrahydrofuran are limited by temperature and exposure to moisture in the air, requiring more careful handling and storage. This is because tetrahydrofuran and methylamine absorb moisture from the environment when exposed to air. Methylamine is very volatile at room temperature, which also affects the reproducibility of the process due to the varying concentration of methylamine dissolved in the organic solvent.

Clearly, there is a need to develop a safer, more efficient and industrially advantageous process to prepare temozolomide and NMCI on an industrial scale without the use of chromatographic columns or continuous extraction.

The process of the present invention meets the need in the art because it does not use hazardous reagents (e.g., methyl isocyanate), NMCI is purified by crystallization and isolated into a properly characterized crystalline form (referred to as form I); the temozolomide obtained is in a high proportion relative to the impurities, of about 90:10, wherein azahydroxypurine is the main impurity, facilitating purification by crystallization, and providing an improved process which is viable in industry on a larger scale (kilogram scale) and facilitates the preparation of temozolomide and NMCI in good overall yields and high purity.

Disclosure of Invention

The invention relates to a method for preparing temozolomide, comprising the following steps:

(a) Reacting N-methylcarbamoylimidazole (NMCI) form I with AICA in a polar aprotic organic solvent to provide carbamoyl-AICA;

(b) Reacting carbamoyl-AICA with an alkali metal or alkaline earth metal nitrite in an aqueous medium in the presence of an acid, wherein the weight/volume ratio of carbamoyl-AICA to water is 1: (5-7) w/v, the temperature of the diazotisation reaction being from-5 ℃ to 5 ℃, and the temperature of the cyclisation reaction being from 30 ℃ to 35 ℃, to provide a composition ratio of 90:10, wherein azahydroxypurine is the primary impurity;

(c) The inclusion ratio was set to 90:10 to a pH of 2-3, removing water from the medium to provide a concentrated suspension, and purifying the temozolomide by crystallization.

According to one aspect of the present invention there is provided a process for the preparation of temozolomide comprising the steps of:

(i) Reacting carbamoyl-AICA with an alkali metal or alkaline earth metal nitrite in an aqueous medium in the presence of an acid, wherein the weight/volume ratio of carbamoyl-AICA to water is 1: (5-7) w/v, the temperature of the diazotisation reaction being from-5 ℃ to 5 ℃, and the temperature of the cyclisation reaction being from 30 ℃ to 35 ℃, to provide a composition ratio of 90:10, wherein azahydroxypurine is the primary impurity;

(ii) The inclusion ratio was set to 90:10 to a pH of 2-3, removing water from the medium to provide a concentrated suspension, and purifying the temozolomide by crystallization.

According to another aspect of the present invention there is provided a process for the preparation of N-methylcarbamoylimidazole (NMCI) form I comprising the steps of:

a) Reacting N, N-carbonyldiimidazole with methylamine hydrochloride in a mixture of acetonitrile and dimethylformamide to provide NMCI and imidazole hydrochloride by-products;

b) Distilling acetonitrile from the reaction medium under vacuum;

c) Ethyl acetate was added to the medium and the imidazole hydrochloride was removed by filtration and a solution containing crude NMCI was provided;

d) Acidifying the solution containing crude NMCI and discarding the aqueous phase;

e) The organic phase containing NMCI was concentrated by vacuum distillation of ethyl acetate;

f) Adding toluene to the organic phase and distilling an azeotropic mixture of toluene and N, N-dimethylformamide under vacuum;

g) Toluene was added and the mixture was cooled to provide NMCI I type crystals whose X-ray powder diffraction spectrum of NMCI I type crystals included characteristic peaks at 11.55, 13.77, 19.18, 20.11, 22.99, 26.27, 28.69, 29.58 and 32.66 expressed in 2θ° ±0.2.

Drawings

The drawings of the application are described below to illustrate the application.

Fig. 1: NMCI I type DRX.

Fig. 2: type NMCI I IR (ATR).

Fig. 3: type NMCI I DSC.

Fig. 4: DRX of purified temozolomide.

Fig. 5: IR (ATR) of purified temozolomide.

Fig. 6: DSC of purified temozolomide.

Fig. 7: NMCI III type DRX.

Fig. 8: type NMCI III IR (ATR).

Fig. 9: type NMCI III DSC.

Detailed Description

The present invention relates to an efficient and industrially advantageous process for the preparation of temozolomide as depicted in scheme 5.

Scheme 5

The method comprises the following steps:

(c) The inclusion ratio was 90:10 to a pH of 2-3, removing water from the medium to obtain a concentrated suspension, and purifying the temozolomide by crystallization.

AICA can be obtained from the reaction of AICA hydrochloride with an alkaline solution, such as a 20% aqueous sodium carbonate solution, to provide high purity (99.9% by HPLC) AICA. AICA is retained for use in the reaction step with N-methylcarbamoylimidazole (NMCI) in crystalline form (designated form I).

NMCI compounds can be prepared according to the method described in j.org.chem.2012,77 (22), 10362-10368 from N, N-Carbonyldiimidazole (CDI) and methylamine hydrochloride in the presence of a solvent mixture consisting of acetonitrile and dimethylformamide. NMCI is an important carbamoylating agent and its use in the preparation of key carbamoyl-AICA intermediates for the synthesis of temozolomide is disclosed in document WO 2018112589.

In addition to having several advantages as a carbamoylating agent, NMCI reacts with AICA to produce carbamoyl-AICA without the addition of tertiary amine bases such as triethylamine (TEA or Et ₃ N) or Diisopropylethylamine (DIPEA). This is because the imidazole formed in situ as a base drives the reaction towards the desired product in a safer and faster way than the processes described in the prior art for the preparation of temozolomide. TEA and DIPEA are considered dangerous compounds because they are highly flammable and inhaled toxic.

The procedure described in the literature for the preparation NMCI calls for purification by limited procedures such as chromatography [ JOC 2012,77 (22), 10362-10368 and WO2018112589]. Furthermore, the reported NCMI preparation scale is typically laboratory scale, and no conditions and information for industrial large scale (kilogram scale) applications are proposed.

To facilitate industrially viable production rates, the present invention discloses a production method of: the process advocates a typical single operation and is widely used in industry such as extraction, distillation and crystallization. These operations can promote efficient chemical conversions and can purify NMCI, in particular, by eliminating the imidazole hydrochloride byproduct.

According to one aspect of the invention, an intermediate of type NMCI I is obtained by a process comprising the steps of:

a1 Reacting N, N-carbonyldiimidazole with methylamine hydrochloride in a mixture of acetonitrile and dimethylformamide to provide NMCI and imidazole hydrochloride by-products;

a2 Under vacuum, distilling acetonitrile from the reaction medium;

a3 Ethyl acetate was added to the medium, filtered to remove the imidazole hydrochloride by-product, and provided a solution containing crude NMCI;

a4 Acidifying the solution containing crude NMCI and discarding the aqueous phase;

a5 Concentrating the organic phase containing NMCI by vacuum distillation of ethyl acetate;

a6 Toluene is added to the organic phase and an azeotropic mixture of toluene and N, N-dimethylformamide is distilled under vacuum;

a7 Toluene was added and the mixture was cooled to provide NMCI I form crystals.

In a mixture of acetonitrile and dimethylformamide, the coupling reaction of N, N-Carbonyldiimidazole (CDI) with methylamine hydrochloride produces imidazole hydrochloride as a by-product in addition to NMCI. In the first solvent exchange, acetonitrile was removed from the medium by distillation, ethyl acetate was added to crystallize the by-product, and the by-product was removed by filtration to provide a crude NMCI solution of 90% purity, which was treated with a 10% aqueous solution of citric acid, and the aqueous phase was discarded. In the second solvent exchange, the organic phase containing NMCI was concentrated under vacuum to remove ethyl acetate. Toluene is added to the medium and dimethylformamide still present in the reaction medium forms an azeotropic mixture with toluene, which is removed by distillation. Toluene was again added to the medium to crystallize NMCI I form, resulting in a yield of 82% and a chromatographic purity (HPLC) of 97.8%.

The X-ray powder diffraction (XRD) spectrum of the crystalline form known as form I obtained from NMCI includes characteristic peaks expressed in 2θ° ±0.2 at 11.55, 13.77, 19.18, 20.11, 22.99, 26.27, 28.69, 29.58 and 32.66 (fig. 1); its infrared absorption spectrum includes characteristic absorption peaks at 3199、3143、3109、3037、1712、1554、1514、1479、1421、1363、1330、1288、1251、1203、1192、1153、1109、1068、1045、979、908、881、837、806 and 710cm ^-1 (FIG. 2); and DSC (endothermic event) thereof: 115 ℃ -123 ℃ and 210 ℃ -234 ℃ (figure 3).

The process for the preparation of form NMCI I of the present invention facilitates robust and flexible applications from laboratory scale to industrial scale, as demonstrated in the examples, has a highly satisfactory yield and gives NMCI in a non-hygroscopic high purity crystalline form stable for up to 24 months when stored at temperatures up to 30 ℃.

The reaction of form NMCI I with AICA to synthesize carbamoyl-AICA is carried out in a polar aprotic organic solvent, preferably acetonitrile or tetrahydrofuran, more preferably acetonitrile. The reaction is carried out at a temperature between 55 ℃ and 60 ℃ for about 7 hours. The reaction mixture was then cooled to 25 ℃ and after 1 hour, the carbamoyl-AICA crystals were isolated by filtration without further purification. carbamoyl-AICA is obtained in high yields and high purity (87% yield, 99.2% chromatographic purity) on an industrial scale (kg scale).

In accordance with the present invention, the conversion reaction of carbamoyl-AICA to temozolomide is carried out in an aqueous medium in the presence of an alkali or alkaline earth metal nitrite and an acid, which covers an improvement over the prior art. Preferably, the alkali metal nitrite is sodium nitrite and the acid is tartaric acid.

The chemical reaction for the preparation of temozolomide involves intramolecular nitrosation cyclisation via a diazonium salt intermediate, wherein the formation of the diazonium salt intermediate is due to the reaction of carbamoyl-AICA with sodium nitrite in an aqueous medium under acidic conditions. Diazotized carbamoyl-AICA intermediates can cyclize in two different ways:

1. nucleophilic attack of the secondary amide moiety to form temozolomide; or (b)

2. Nucleophilic attack of the primary amide moiety results in the formation of azahydroxypurine impurities.

The possible chemical mechanism is shown in scheme 6.

Scheme 6

In general, the two cyclizations may occur virtually equally such that the ratio of temozolomide to azahydroxypurine is about 50:50[ J.org.chem.62,7288-7294 (1997) ], or a slightly higher enrichment value of temozolomide, as disclosed in WO2018112589 at 60:40. in physical state, the reaction mixture is a suspension of temozolomide and azahydroxypurine between a solid phase and a liquid phase. The best way to separate the two reaction products and obtain pure temozolomide according to the prior art is to completely dissolve the reaction mixture in water, followed by continuous extraction using a chromatographic column or an organic solvent. This predicts that large amounts of solvent will be used and greatly limits industrial productivity at significant volumes.

In order to separate the solid mixture consisting of temozolomide and azahydroxypurine for purification by crystallization, it is desirable to obtain an enriched temozolomide mixture, which is surprisingly achieved when increasing the concentration of the reaction medium and adjusting the temperature of the diazotisation and cyclization reactions to a specific range.

According to one aspect of the invention, a process for preparing temozolomide comprises: reacting carbamoyl-AICA with an alkali metal or alkaline earth metal nitrite in an aqueous medium in the presence of an acid, wherein the weight/volume ratio of carbamoyl-AICA to water is 1: (5-7) w/v, the temperature of the diazotization reaction is-5 ℃ to 5 ℃, and the temperature of the cyclization reaction is 30 ℃ to 35 ℃. Preferably, the weight/volume ratio of carbamoyl-AICA to water is 1:5w/v, the temperature of the diazotisation reaction was maintained at 5℃for 4 hours, and the temperature of the cyclization reaction was maintained at 30℃for 5 hours.

Surprisingly, the more concentrated reaction medium promotes a better ratio between temozolomide and impurities, correspondingly about 90:10, wherein azahydroxypurine is the major impurity. This result is due to the precipitation of temozolomide, which is more insoluble than azahydroxypurine, especially at higher concentrations. This condition creates a driving force to mainly result in cyclization of the diazonium salt intermediate to temozolomide (nucleophilic attack 1 in scheme 6). In addition, the intramolecular cyclization in which the secondary amide participates has a lower energy transition state because the secondary amide has a greater nucleophilicity than the primary amide, and in this regard, the higher the concentration of mediator, the easier it is to promote intramolecular cyclization in the secondary amide nucleophile.

Cyclization by secondary amide attack has also been found to be slightly energetically favorable. In this regard, cyclisation temperatures between 30 ℃ and 35 ℃ provide little energy to the system and therefore promote predominantly cyclisation of the diazonium salt to temozolomide.

The choice of both the concentration and the temperature surprisingly results in a suspension highly enriched in temozolomide, which enables purification by crystallization, also expands the possibilities of using the process for medium and large batches and increases the yield of the process.

According to one aspect of the invention, the inclusion ratio will be 90:10 with 30% to 35% hydrochloric acid to a pH of 2-3, wherein azahydroxypurine is the main impurity, and distilling off the water in the medium to obtain a concentrated suspension, and purifying the temozolomide by crystallization.

According to the present invention, a process for purifying temozolomide by crystallization comprises: temozolomide is dissolved in Dimethylsulfoxide (DMSO) preheated to 60 ℃, solid residue is removed by filtration, ethyl acetate is slowly added to the resulting filtrate, cooled to crystallization, filtered, the resulting crystals are washed with ethyl acetate, and dried to give purified temozolomide, wherein the w/v ratio of temozolomide (crude) to dimethylsulfoxide is 1:10, the w/v ratio of temozolomide (crude) to ethyl acetate is 1:4, the v/v ratio of dimethyl sulfoxide to ethyl acetate is 1: (0.4-0.5). Purified temozolomide was obtained in 62% yield and 98.7% chromatographic purity (HPLC).

The X-ray powder diffraction (XRD) spectrum of the resulting crystalline form of purified temozolomide included characteristic peaks at 7.34、8.61、10.75、12.78、13.07、13.98、14.62、16.01、16.69、17.72、18.91、19.37、20.13、20.68、21.41、22.84、23.75、24.38、24.99、25.56、26.28、28.07、28.58、29.43 and 30.97 expressed in 2θ° ±0.2 (fig. 4);IR(ATR,cm^-1)：3053、2920、2883、2804、1639、1580、1537、1492、1475、1440、1415、1365、1328、1278、1251、1186、1126、1107、1068、1024、1002、964、902、813、773、725、702、684( fig. 5); DSC: endothermic events 115 ℃ -123 ℃ (melting) and exothermic events 210 ℃ -234 ℃ (degradation) (fig. 6).

According to the present invention, the process for preparing temozolomide further comprises the steps of: suspending the purified temozolomide in acetonitrile and water (3:1), heating and cooling between 55 ℃ and 60 ℃ to provide temozolomide form III, whose X-ray powder diffraction (XRD) spectrum comprises characteristic peaks expressed in 2θ° ±0.2 at 5.5, 10.9, 13.3, 14.2, 14.7, 16.3, 16.8, 18.0, 19.1, 19.6, 20.7, 21.5, 23.8, 25.2, 26.2, 26.5, 27.2, 27.8, 28.8, 29.8 and 30.3 (fig. 7); IR (ATR, cm ^-1): 3419. 3386, 3185, 3116, 1758, 1732, 1676, 1452, 1354, 1266 (fig. 8); DSC: the exothermic event (degradation) was 204 ℃ -213 ℃ (figure 9).

According to another aspect of the invention, a process for preparing temozolomide comprises the steps of:

(ii) The inclusion ratio was 90:10 to a pH of 2-3, removing water from the medium to provide a concentrated suspension, and purifying the temozolomide by crystallization.

The conversion reaction of carbamoyl-AICA to temozolomide according to the present invention incorporates an improvement over the prior art, which surprisingly results in obtaining a mixture enriched in temozolomide. Preferably, the alkali metal nitrite is sodium nitrite added to the reaction medium in solid form, the acid is tartaric acid, and the weight/volume ratio of carbamoyl-AICA to water is 1:5w/v, the temperature of the diazotisation reaction was 5℃and the temperature of the cyclization reaction was 30 ℃.

In a preferred embodiment, the process for preparing temozolomide comprises: reacting carbamoyl-AICA with sodium nitrite in an aqueous medium in the presence of tartaric acid, wherein the weight/volume ratio of carbamoyl-AICA to water is 1:5w/v, the temperature of the diazotisation reaction was maintained at 5℃for 4 hours, and the temperature of the cyclization reaction was maintained at 30℃for 5 hours.

Surprisingly, a more concentrated reaction medium favors a significantly better ratio between temozolomide and impurities, correspondingly about 90:10, wherein azahydroxypurine is the major impurity. It was also verified that the cyclisation temperature between 30 ℃ and 35 ℃ provides little energy to the system and therefore is mainly beneficial for cyclisation of diazonium salts to temozolomide. The choice of the two parameters, concentration and temperature of the reaction medium, surprisingly makes it possible to obtain a highly enriched suspension of temozolomide, making purification by crystallization possible.

According to the invention, the hydrochloric acid is used in a proportion of 30% to 35% in order to make the content 90:10 (wherein azahydroxypurine is the main impurity) to a pH of 2-3, and removing water from the medium by distillation to give a concentrated suspension, and purifying the temozolomide by crystallization.

According to the invention, purifying temozolomide by crystallization comprises: temozolomide is dissolved in dimethyl sulfoxide preheated to 60 ℃, solid residues are removed by filtration, ethyl acetate is slowly added to the obtained filtrate, the obtained crystals are cooled to crystallization, filtered, washed with ethyl acetate, and dried to obtain purified temozolomide, wherein the w/v ratio of temozolomide (crude) to dimethyl sulfoxide is 1:10, the w/v ratio of temozolomide (crude) to ethyl acetate is 1:4, the v/v ratio of dimethyl sulfoxide to ethyl acetate is 1: (0.4-0.5).

According to the present invention, the process for preparing temozolomide further comprises the steps of: suspending the purified temozolomide in acetonitrile and water (3:1), heating between 55 ℃ and 60 ℃, and cooling to provide temozolomide form III, whose X-ray powder diffraction (XRD) spectrum comprises characteristic peaks expressed in 2θ° ±0.2 at 5.5, 10.9, 13.3, 14.2, 14.7, 16.3, 16.8, 18.0, 19.1, 19.6, 20.7, 21.5, 23.8, 25.2, 26.2, 26.5, 27.2, 27.8, 28.8, 29.8, and 30.3; IR (ATR, cm ^-1): 3419. 3386, 3185, 3116, 1758, 1732, 1676, 1452, 1354, 1266; DSC: exothermic events (degradation) 204 ℃ -213 ℃.

According to another aspect of the invention, a process for preparing N-methylcarbamoylimidazole (NMCI) form I comprises the steps of:

b) Distilling acetonitrile from the reaction medium under vacuum;

c) Filtering the imidazole hydrochloride by-product removed by adding ethyl acetate to the medium and providing a solution containing crude NMCI;

f) Toluene was added to the organic phase and the azeotropic mixture of toluene and N, N-dimethylformamide was distilled under vacuum;

g) Toluene was added and the mixture was cooled to provide NMCI I type crystals, and the X-ray powder diffraction spectrum of NMCI I type crystals included characteristic peaks, expressed in 2θ±0.2, at 11.55, 13.77, 19.18, 20.11, 22.99, 26.27, 28.69, 29.58 and 32.66.

Preferably, in step d), the solution containing crude NMCI is acidified with a 10% aqueous solution of citric acid.

The process of the present invention overcomes the problems of the prior art by providing a simple, economical, robust and industrially advantageous synthetic route to temozolomide and N-methylcarbamoylimidazole (NMCI) form I, which can be used to prepare the key intermediate carbamoyl-AICA, in high yields and purity.

The following examples are merely illustrative and should be used to better understand the claimed methods, however, they should not be used to limit the scope of the invention.

Example 1

Preparation of N-methylcarbamoylimidazole form I

To a 500L reactor with mechanical stirring, 180.0L of acetonitrile, 36.2L of N, N dimethylformamide, 75.0kg of N, N-carbonyldiimidazole (0.463 mmol) were added, and then the obtained suspension was cooled to 10 ℃. 25.8kg of methylamine hydrochloride (0.385 mmol) was added to the suspension so that the temperature did not exceed 25 ℃. The reaction was stirred at 25℃for 2 hours. Then, all acetonitrile was distilled off under vacuum to give a viscous yellow liquid containing the product N-methylcarbamoylimidazole (NMCI) and imidazole hydrochloride by-product. For purification NMCI, 385.0L of ethyl acetate was added to the medium, stirring was maintained for 30 minutes, and the crystallized imidazole hydrochloride was filtered and then washed with ethyl acetate to give a solution containing crude NMCI with a purity of 90%. The solution containing NMCI was treated by adding 10% aqueous citric acid, the phases were separated and the aqueous solution was discarded, and then the organic solution containing the product was concentrated by vacuum distillation of all ethyl acetate. Then, 360.0L of toluene was added to the organic phase, and an azeotropic mixture of toluene and N, N-dimethylformamide was distilled under vacuum. 360.0L of toluene was again added and the system was cooled to 0℃with stirring for 2 hours. After NMCI crystallization, the suspension is filtered, the product is washed with toluene and dried under vacuum at 55℃for 5 hours to give 39.5kg of N-methylcarbamoylimidazole form I (as a white crystalline solid). The yield was 82% and the purity was 97.8% (HPLC). The crystalline form obtained from NMCI, designated form I, has an X-ray powder diffraction (XRD) spectrum comprising characteristic peaks expressed in 2θ° ±0.2 at 11.55, 13.77, 19.18, 20.11, 22.99, 26.27, 28.69, 29.58 and 32.66 (fig. 1); the infrared absorption spectrum includes characteristic absorption peaks at 3199、3143、3109、3037、1712、1554、1514、1479、1421、1363、1330、1288、1251、1203、1192、1153、1109、1068、1045、979、908、881、837、806 and 710cm ^-1 (FIG. 2); DSC (endothermic event): 115 ℃ -123 ℃ and 210 ℃ -234 ℃ (figure 3).

Example 2

Preparation of AICA

To a 500L reactor with mechanical stirring, 164.0L of pure water, 41.0kg of AICA. HCl (0.252 mmol) were added. To the resulting clear solution, a 20% aqueous sodium carbonate solution (16.0 kg of sodium carbonate (0.151 mmol) in 82.0L of pure water) was slowly added. The AICA suspension was then cooled to 5℃and kept stirring for 4 hours. The suspension was filtered and the product was washed with cold water and then dried under vacuum at 55 ℃ for 8 hours to give 27.4kg of AICA (as green fine powder). Yield 87% and purity 99.9% (HPLC).

Example 3

Preparation of carbamoyl-AICA

To a 200L reactor with mechanical agitation, 75.0L of acetonitrile, 30.0kg of AICA (0.238 mmol) and 38.0kg of NMCI (0.304 mmol) were added. The resulting suspension was heated to 60℃and kept stirring for 7 hours. The suspension was then cooled to 25 ℃ and kept stirring for 1 hour. The suspension was filtered and the product was washed with acetonitrile and dried under vacuum at 55 ℃ for 5 hours to give 34.9kg of carbamoyl-AICA (as light grey fine powder). Yield 87% and purity 99.2% (HPLC). The analysis method comprises the following steps: zorbax Eclipse XDB column 4.6X105 mm 5 μm 25 ℃; eluent a:0.05% trifluoroacetic acid in water; eluent B: acetonitrile solution of 0.05% trifluoroacetic acid; gradient: eluent A and eluent B (95:05) for 0.0-6.0 min; eluent A and eluent B (40:60) for 6.1-12.0 min; 12.1-13.0 minutes of eluent A and eluent B (95:05); eluent A and eluent B (95:05) for 13.1-20.0 min. Mobile phase flow rate: 1.0mL/min. UV-VIS detector: 292nm. Retention time: carbamoyl-AICA about 5.6 minutes .IR(ATR,cm^-1)：3458、3404、3348、3320、3131、3069、2949、1715、1645、1557、1530、1503、1460、1452、1420、1298、1248、1221、1173、1076、955、828、745、698.¹³C NMR(125MHz,DMSO,ppm)：δ27.0;δ39.3-40.5(DMSO);δ111.6;δ126.5;δ143.8;δ151.1;δ166.7.¹H NMR(500MHz,DMSO,ppm)：δ2.50-2.51(DMSO);δ2.80(d,3H);δ3.34( water );δ6.38(sl,2H);δ6.85(d,2H);δ7.61(sl,1H);δ8.43(q,1H).HRMS,[C₆H₉N₅O₂+Na]⁺m/z＝206.0654;M/z test value = 206.0653. Error: 1ppm.

Example 4

Preparation of purified temozolomide

To a 1000L reactor with mechanical stirring, 120.0L of pure water, 15.1kg of sodium nitrite (0.219 mmol) and 40.0kg of carbamoyl-AICA (0.218 mmol) were added. The resulting suspension was cooled to 0 ℃ and the system was inertized with nitrogen. To the suspension was slowly added 45% aqueous tartaric acid (34.6 kg of tartaric acid (0.231 mmol) in 80.0L of pure water). After the addition of tartaric acid solution was completed, the suspension was maintained at 5 ℃ for 4 hours with stirring. The system was then slowly heated to 30 ℃ and the suspension was maintained at 30 ℃ for 5 hours with stirring to give a suspension containing 89.0% temozolomide, 7.6% azahydroxypurine, and 3.4% impurities. To purify temozolomide, 35.0L of 30% to 35% hydrochloric acid is added to the suspension, and about 120L of water in the system is distilled off at a temperature of 50 ℃ and 60 ℃ under vacuum. Then, 300.0L of dimethyl sulfoxide preheated to 60℃was added to the concentrated suspension, and the medium was stirred for 10 minutes. The suspension was filtered and the solid residue was washed with 80.0L of dimethyl sulfoxide preheated to 60 ℃. 160.0L of ethyl acetate was slowly added to a 1000L reactor with mechanical agitation and containing the filtered product solution at 60 ℃. The medium was then slowly cooled to 5 ℃ and kept under stirring for 4 hours. The suspension was filtered and the product was then washed with 60.0L of ethyl acetate and dried under vacuum at 55 ℃ for 5 hours to give 26.3kg of purified temozolomide (as a white to micro-coloured crystalline solid). Yield 62% and purity 98.7% (HPLC). The resulting X-ray powder diffraction (XRD) spectrum of the crystalline form of purified temozolomide included characteristic peaks at 7.34、8.61、10.75、12.78、13.07、13.98、14.62、16.01、16.69、17.72、18.91、19.37、20.13、20.68、21.41、22.84、23.75、24.38、24.99、25.56、26.28、28.07、28.58、29.43 and 30.97 expressed in 2θ° ±0.2 (fig. 4);IR(ATR,cm^-1)：3418、3386、3290、3167、3115、1753、1729、1676、1601、1566、1452、1402、1354、1300、1263、1217、1111、1044、1005、946、801、735、711、634、563、510( fig. 5); DSC: endothermic events 115 ℃ -123 ℃ (melting) and exothermic events 210 ℃ -234 ℃ (degradation) (fig. 6).

Example 5

Preparation of temozolomide form III

To a 200L reactor with mechanical stirring, 60.0L of acetone, 20.0L of pure water, 26.3kg of purified temozolomide prepared according to example 4 were added and the suspension was heated to 55-60 ℃ with stirring. After 1 hour, the suspension was cooled to 5 ℃ and held under these conditions for 2 hours. The suspension was filtered, the product was washed with acetone and dried under vacuum at 55 ℃ for 8 hours. The product was then triturated to give 24.0kg of temozolomide form III (as a white crystalline powder). Yield was 81% and purity was 100% (HPLC). The X-ray powder diffraction (XRD) spectrum of temozolomide form III includes characteristic peaks expressed in 2θ° ±0.2 at 5.5, 10.9, 13.3, 14.2, 14.7, 16.3, 16.8, 18.0, 19.1, 19.6, 20.7, 21.5, 23.8, 25.2, 26.2, 26.5, 27.2, 27.8, 28.8, 29.8 and 30.3 (fig. 7); IR (ATR, cm ^-1): 3419. 3386, 3185, 3116, 1758, 1732, 1676, 1452, 1354, 1266 (fig. 8); DSC: exothermic events 204 ℃ -213 ℃ (degradation) (fig. 9).

Claims

1. A process for the preparation of temozolomide, comprising the steps of:

(b) Reacting carbamoyl-AICA with an alkali metal or alkaline earth metal nitrite in an aqueous medium in the presence of an acid, wherein the weight/volume ratio of carbamoyl-AICA to water is 1: (5-7) w/v, the temperature of the diazotisation reaction being from-5 ℃ to 5 ℃, and the temperature of the cyclization reaction being from 30 ℃ to 35 ℃, to give a composition ratio of 90:10, wherein azahydroxypurine is the primary impurity;

(c) The inclusion ratio was set to 90:10 to a pH of 2-3, removing water from the medium to obtain a concentrated suspension, and purifying the temozolomide by crystallization.

2. The method according to claim 1, wherein AICA is obtainable from the reaction of AICA hydrochloride with a 20% aqueous sodium carbonate solution.

3. The process according to claim 1, characterized in that the intermediate N-methylcarbamoylimidazole (NMCI) in crystalline form I is obtained by a process comprising the steps of:

a2 Under vacuum, distilling acetonitrile of the reaction medium;

a3 Ethyl acetate into the medium, filtering to remove the imidazole hydrochloride by-product, and providing a solution containing crude NMCI;

a7 Toluene and cooling the mixture to provide NMCI I form crystals, the X-ray powder diffraction spectrum of the NMCI I form crystals including characteristic peaks, expressed in 2θ° ±0.2, at 11.55, 13.77, 19.18, 20.11, 22.99, 26.27, 28.69, 29.58 and 32.66.

4. The process according to claim 1, wherein the polar aprotic organic solvent in step (a) is acetonitrile or tetrahydrofuran.

5. The process of claim 1, wherein the alkali metal nitrite in step (b) is sodium nitrite added to the reaction medium in solid form.

6. The process of claim 1 wherein the acid in step (b) is tartaric acid.

7. The method of claim 1, wherein in step (b), the weight/volume ratio of carbamoyl-AICA to water is 1:5w/v, the temperature of the diazotisation reaction is maintained at 5 ℃ for 4 hours, and the temperature of the cyclization reaction is maintained at 30 ℃ for 5 hours.

8. The process according to claim 1, wherein the suspension in step (c) is acidified with 30% to 35% hydrochloric acid.

9. The process according to claim 1, wherein in step (c), the purification of temozolomide by crystallization comprises: temozolomide is dissolved in preheated dimethylsulfoxide at 60 ℃, solid residues are removed by filtration, ethyl acetate is slowly added to the obtained filtrate, and the crystals obtained are cooled to crystallize, filtered, washed with ethyl acetate and dried to obtain purified temozolomide, wherein the w/v ratio of temozolomide (crude) to dimethylsulfoxide is 1:10, the w/v ratio of temozolomide (crude) to ethyl acetate is 1:4 and the v/v ratio of dimethyl sulfoxide to ethyl acetate is 1: (0.4-0.5); wherein the X-ray powder diffraction spectrum of purified temozolomide comprises characteristic peaks at 7.34、8.61、10.75、12.78、13.07、13.98、14.62、16.01、16.69、17.72、18.91、19.37、20.13、20.68、21.41、22.84、23.75、24.38、24.99、25.56、26.28、28.07、28.58、29.43 and 30.97, expressed in 2θ° ±0.2.

10. The method according to claim 1, characterized in that the method further comprises the steps of: suspending the purified temozolomide obtained in step (c) in acetonitrile and water (3:1), heating between 55 ℃ and 60 ℃, cooling to provide temozolomide form III, the X-ray powder diffraction profile of temozolomide form III comprising characteristic peaks at 5.5, 10.9, 13.3, 14.2, 14.7, 16.3, 16.8, 18.0, 19.1, 19.6, 20.7, 21.5, 23.8, 25.2, 26.2, 26.5, 27.2, 27.8, 28.8, 29.8 and 30.3 expressed in 2θ° ±0.2.

11. A process according to claim 3, characterized in that in step a 4) the solution containing crude NMCI is acidified with a 10% aqueous solution of citric acid.

12. A process for the preparation of temozolomide, comprising the steps of:

(i) Reacting carbamoyl-AICA with an alkali metal or alkaline earth metal nitrite in an aqueous medium in the presence of an acid, wherein the weight/volume ratio of carbamoyl-AICA to water is 1: (5-7) w/v, the temperature of the diazotisation reaction being from-5 ℃ to 5 ℃, and the temperature of the cyclization reaction being from 30 ℃ to 35 ℃, to give a composition ratio of 90:10, wherein azahydroxypurine is the primary impurity;

(ii) The inclusion ratio was set to 90:10 to a pH of 2-3, removing water from the medium to obtain a concentrated suspension, and purifying the temozolomide by crystallization.

13. The process of claim 12, wherein the alkali metal nitrite in step (i) is sodium nitrite added to the reaction medium in solid form.

14. The process of claim 12, wherein the acid in step (i) is tartaric acid.

15. The method of claim 12, wherein in step (i) the weight/volume ratio of carbamoyl-AICA to water is 1:5w/v, the temperature of the diazotisation reaction was maintained at 5 ℃ for 4 hours, and the temperature of the cyclization reaction was maintained at 30 ℃ for 5 hours.

16. The process according to claim 12, wherein the suspension in step (ii) is acidified with 30% to 35% hydrochloric acid.

17. The process according to claim 12, wherein in step (ii), the purification of temozolomide by crystallization comprises: temozolomide is dissolved in preheated dimethylsulfoxide at 60 ℃, solid residues are removed by filtration, ethyl acetate is slowly added to the obtained filtrate, and the crystals obtained are cooled to crystallize, filtered, washed with ethyl acetate and dried to obtain purified temozolomide, wherein the w/v ratio of temozolomide (crude) to dimethylsulfoxide is 1:10, the w/v ratio of temozolomide (crude) to ethyl acetate is 1:4 and the v/v ratio of dimethyl sulfoxide to ethyl acetate is 1: (0.4-0.5); wherein the X-ray powder diffraction spectrum of purified temozolomide comprises characteristic peaks at 7.34、8.61、10.75、12.78、13.07、13.98、14.62、16.01、16.69、17.72、18.91、19.37、20.13、20.68、21.41、22.84、23.75、24.38、24.99、25.56、26.28、28.07、28.58、29.43 and 30.97, expressed in 2θ° ±0.2.

18. The method according to claim 12, characterized in that the method further comprises the steps of: a step of suspending the purified temozolomide obtained in step (ii) in acetonitrile and water (3:1), heating between 55 ℃ and 60 ℃, cooling to provide temozolomide form III, the X-ray powder diffraction profile of which comprises characteristic peaks at 5.5, 10.9, 13.3, 14.2, 14.7, 16.3, 16.8, 18.0, 19.1, 19.6, 20.7, 21.5, 23.8, 25.2, 26.2, 26.5, 27.2, 27.8, 28.8, 29.8 and 30.3 expressed in 2θ° ±0.2.

19. A process for the preparation of N-methylcarbamoylimidazole (NMCI) form I comprising the steps of:

b) Distilling acetonitrile of the reaction medium under vacuum;

c) Adding ethyl acetate to the crystallization medium of imidazole hydrochloride removed by filtration and providing a solution containing crude NMCI;

g) Toluene was added and the mixture was cooled to provide form NMCI I, the X-ray powder diffraction spectrum of form NMCI I included characteristic peaks, expressed in 2θ° ±0.2, at 11.55, 13.77, 19.18, 20.11, 22.99, 26.27, 28.69, 29.58 and 32.66.

20. The method of claim 19, wherein in step d) the solution containing crude NMCI is acidified with a 10% aqueous solution of citric acid.