A method for synthesizing a tofacitinib desmethyl impurity

Abstract

The application is a preparation method of tofacitinib demethylated impurity, comprising the following steps: dissolving free tofacitinib raw material in a solvent, adding N-iodosuccinimide, adding a base catalyst, heating to initiate the reaction, and then stirring and reacting after the reaction is initiated; the reaction is detected by TLC, and the target compound is obtained after post-treatment and purification; the impurity compound can be used as an impurity reference substance in the detection standard of tofacitinib finished product, and is used for the quality control link of impurity qualitative and quantitative analysis in the production process of tofacitinib; the preparation method is novel, raw materials are easy to obtain, operation is simple, and the cost is low.

Description

Technical Field

[0001] This invention belongs to the field of drug synthesis technology, and specifically relates to a method for preparing a tofacitinib demethylated impurity. Background Technology

[0002] Tofacitinib citrate, chemically named (3R,4R)-4-methyl-3-(methyl-7H-pyrrolo[2,3-d]pyrimidin-4-ylamino)-β-carbonyl-1-piperidinium propionitrile-2-hydroxy-1,2,3-propane tricarboxylate (1:1), is a novel oral JAK inhibitor developed by Pfizer Inc. It was approved by the FDA in November 2012 under the brand name Xel janz for the treatment of adult patients with moderate to severe active rheumatoid arthritis who have an inadequate response to or are intolerant of methotrexate. Its structural formula is as follows:

[0003] .

[0004] There are currently many reported methods for preparing tofacitinib, which can be summarized into two main steps. The first step is the synthesis of a piperidine ring intermediate containing a protecting group; the second step is the coupling reaction of this piperidine ring intermediate with a chloro-7H-pyrrolo[2,3-d]pyrimidin-4-yl group to obtain tofacitinib. For example, the original patent US6627754 and Chinese patent application CN1409712 report a method that uses benzyl-protected 4-methyl-piperidin-3-one as a starting material, first undergoes a reductive amination reaction of the ketone to add a methylamino group, and then proceeds to N-alkylation, hydrogen debenzylation, piperidine N-nitrile acetylation, and resolution to obtain tofacitinib.

[0005]

[0006] .

[0007] According to publicly reported synthetic routes, the demethylation byproduct (3R,4R)-1-benzyl-4-methyl-3-methylamino-piperidine during the synthesis of the key intermediate cis-1-benzyl-4-methyl-3-amine leads to the following structure of the tofacitinib demethylation impurity:

[0008] .

[0009] In the process of new drug research and development, drug quality is an important standard for measuring drug quality. Drug quality standards have relatively strict regulations on the purity of drug active ingredients and the limits of impurities. Generally speaking, drug impurities exceeding 0.1% should be identified and quantified by selective methods. For drug researchers, it is also very important to develop efficient impurity synthesis routes and directional synthesis processes to obtain impurity reference standards and ensure the quality testing of each batch of raw materials (such as impurity HPLC localization, impurity content determination, etc.).

[0010] With the advancement of national research on drug consistency evaluation, determining the preparation method of the demethylated impurity in tofacitinib and providing qualified reference standards can play a positive role in the quality control of tofacitinib. Currently, there are few publicly reported studies on this demethylated impurity; only one synthetic method is reported in *ChemMedChem 2014, 9, 2516-2527*, with the following route:

[0011] .

[0012] This route uses the initial starting materials (3R,4R)-1-benzyl-4-methyl-3-amine and 4-chloro-7-toluenesulfonyl-7H-pyrrole[2,3-D]pyrimidine via a substitution reaction, followed by hydrogenation to remove the benzyl group, condensation to attach cyanoacetic acid, and then removal of Tos to obtain the target impurity. This route is lengthy, and the starting material (3R,4R)-1-benzyl-4-methyl-3-amine requires chiral resolution, making the synthetic steps cumbersome, separation and purification difficult, and the cost high.

[0013] Therefore, finding a route that is shorter, easier to operate, and lower in cost to synthesize tofacitinib demethylation impurities remains a problem that needs to be solved. Summary of the Invention

[0014] To address the aforementioned problems, this invention discloses a method for synthesizing a tofacitinib demethylation impurity. This impurity compound can be used as an impurity reference standard in the tofacitinib finished product testing standard, and is employed in the quality control stage of qualitative and quantitative impurity analysis during the tofacitinib production process. The preparation method is novel, uses readily available raw materials, is simple to operate, and has low cost.

[0015] To achieve the above objectives, the technical solution of the present invention is as follows:

[0016] A method for synthesizing a tofacitinib demethylated impurity includes the following steps: dissolving free tofacitinib active pharmaceutical ingredient in a solvent, adding N-iodosuccinimide, adding base catalysis, heating, stirring and maintaining the temperature during the reaction, detecting the end of the reaction by TLC, and obtaining the tofacitinib demethylated impurity after post-processing.

[0017] .

[0018] Further, the molar ratio of tofacitinib to N-iodosuccinimide is 1.0:1.0-2.0, preferably, the molar ratio of tofacitinib to N-iodosuccinimide is 1.0:1.1.

[0019] Further, the volume ratio of tofacitinib to solvent is 1.0:10.0-30.0, preferably, the volume ratio of tofacitinib to solvent is 1.0:20.0.

[0020] Further, the molar ratio of tofacitinib to the base is 1.0:1.0-2.0, preferably, the molar ratio of tofacitinib to the base is 1.0:1.5.

[0021] Further, the alkali is one or more selected from sodium acetate, potassium acetate, triethylamine, potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, and lithium hydroxide; preferably, the alkali is sodium acetate.

[0022] Further, the solvent is one or more selected from acetonitrile, acetone, tetrahydrofuran, dioxane, water, isopropanol, and N,N-dimethylformamide; preferably, the solvent is acetonitrile.

[0023] Further, the temperature of the heat-insulating and stirring reaction is 20–60°C. Preferably, the temperature of the heat-insulating and stirring reaction is 55–60°C.

[0024] Furthermore, the heat preservation and stirring reaction time is 1 to 6 hours; preferably, the heat preservation and stirring reaction time is 2 to 3 hours.

[0025] Further, the post-processing specifically includes the following steps: after the TLC detection reaction is completed, sodium thiosulfate is added and stirred for 0.5-1 hours to quench the reaction, the reaction solution is concentrated to dryness, water is added for dilution, then ethyl acetate is added for extraction, the organic phases are combined, saturated sodium chloride solution is added for washing, the organic phases are separated by separation, anhydrous sodium sulfate is added for drying, salt is removed by filtration, and the product is dried, concentrated, and obtained by column chromatography to obtain the tofacitinib demethylated impurity.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention provides a one-step reaction method for preparing tofacitinib demethylated impurities. Compared with previously published literature, this method is simpler, easier to operate, and less expensive. The prepared high-purity tofacitinib demethylated impurity can be used as a tofacitinib impurity reference standard, which is of great significance for quality control in the production process of active pharmaceutical ingredients. Attached Figure Description

[0028] Figure 1 The HPLC spectrum of the product obtained in Example 1 of this invention;

[0029] Figure 2 The mass spectrum of the product obtained in Example 1 of this invention;

[0030] Figure 3 The hydrogen NMR spectrum of the product obtained in Example 1 of this invention;

[0031] Figure 4 This is the synthesis process route of the present invention. Implementation

[0032] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Example

[0033] 10.0 g (0.032 mol) of initial material was added to a 500 ml three-necked flask, followed by 200 ml of acetonitrile, 7.9 g (0.035 mol) of N-iodosuccinimide, and 6.5 g (0.048 mol) of sodium acetate. The mixture was heated to 55-60 °C to initiate the reaction, which gradually turned brown from colorless. After initiation, the reaction was maintained at 55-60 °C for 2 hours, and TLC analysis confirmed complete reaction. 1.0 g (0.006 mol) of sodium thiosulfate was added and stirred for 0.5 hours to quench the reaction. The reaction solution was concentrated to dryness, dissolved in 100 ml of water, and extracted with 100 ml of ethyl acetate (2 x 100 ml). The organic phases were separated and combined. The mixture was washed with 50 ml of saturated brine, and the organic phase was dried with 10 g of anhydrous sodium sulfate. The organic phase was filtered to remove salts and concentrated to dryness. Column chromatography was used to purify the organic phase, yielding 5.6 g of the target compound. Yield: 76.2%, purity: 98.3%.

[0034] The obtained target compound was analyzed by HPLC, and the results are as follows: Figure 1 As shown, the mass spectrometry and proton nuclear magnetic resonance (NMR) detection results are as follows: Figure 2 , Figure 3 As shown.

[0035] Process route and chemical structure of target compound, such as Figure 4 As shown. Example

[0036] 10.0 g (0.032 mol) of initial material was added to a 500 ml three-necked flask, followed by 100 ml of acetone, 8.6 g (0.038 mol) of N-iodosuccinimide, and 8.8 g (0.064 mol) of potassium carbonate. The mixture was heated to 55-60 °C until initiation, at which point the system gradually changed from colorless to brown. After initiation, the reaction was maintained at 55-60 °C for 3 hours, and TLC analysis confirmed complete reaction. 1.6 g (0.01 mol) of sodium thiosulfate was added and stirred for 0.5 hours to quench the reaction. The reaction solution was concentrated to dryness, dissolved in 100 ml of water, and extracted with 100 ml of ethyl acetate (2 x 100 ml). The organic phases were separated and combined. The mixture was washed with 50 ml of saturated brine, and the organic phase was dried with 10 g of anhydrous sodium sulfate. The organic phase was filtered to remove salts and concentrated to dryness. Column chromatography was used to purify the organic phase, yielding 5.3 g of the target compound. Yield: 72.3%, purity: 97.0%. Example

[0037] 10.0 g (0.032 mol) of initial material was added to a 500 ml three-necked flask, followed by 300 ml of dioxane, 10.8 g (0.048 mol) of N-iodosuccinimide, and 1.2 g (0.048 mol) of lithium hydroxide. The mixture was heated to 55-60 °C until initiation, at which point the system gradually changed from colorless to brown. After initiation, the reaction was carried out at 50-55 °C for 4 hours, and TLC analysis confirmed complete reaction. 3.3 g (0.02 mol) of sodium thiosulfate was added and stirred for 0.5 hours to quench the reaction. The reaction mixture was concentrated to dryness, dissolved in 100 ml of water, and extracted with 100 ml of ethyl acetate (2 x 100 ml). The organic phases were separated and combined, washed with 50 ml of saturated brine, and dried with 10 g of anhydrous sodium sulfate. The organic phase was filtered to remove salts and concentrated to dryness. Column chromatography was used to purify the organic phase, yielding 5.0 g of the target compound. Yield: 67.3%, purity: 96.1%. Example

[0038] 10.0 g (0.032 mol) of initial material was added to a 500 ml three-necked flask, followed by 100 ml of acetonitrile, 14.4 g (0.064 mol) of N-iodosuccinimide, and 4.7 g (0.048 mol) of potassium acetate. The mixture was heated to 60 °C to initiate the reaction, which gradually turned brown from colorless. After initiation, the reaction was maintained at 45-50 °C for 5 hours, and TLC was used to confirm complete reaction. 5.5 g (0.035 mol) of sodium thiosulfate was added and stirred for 0.5 hours to quench the reaction. The reaction solution was concentrated to dryness, dissolved in 100 ml of water, and extracted with 100 ml of ethyl acetate (2 x 100 ml). The organic phases were separated and combined, washed with 50 ml of saturated brine, and dried with 10 g of anhydrous sodium sulfate. The organic phase was filtered to remove salts and concentrated to dryness. Column chromatography was used to purify the organic phase, yielding 4.9 g of the target compound. Yield: 66.1%, purity: 95.5%. Example

[0039] 10.0 g (0.032 mol) of initial material was added to a 500 ml three-necked flask, followed by 200 ml of acetonitrile, 7.9 g (0.035 mol) of N-iodosuccinimide, and 5.1 g (0.048 mol) of sodium carbonate. The mixture was heated to 55-60 °C to initiate the reaction, which gradually turned brown from colorless. After initiation, the reaction was maintained at 40-45 °C for 6 hours, and TLC analysis confirmed complete reaction. 1.0 g (0.006 mol) of sodium thiosulfate was added and stirred for 0.5 hours to quench the reaction. The reaction solution was concentrated to dryness, dissolved in 100 ml of water, and extracted with 100 ml of ethyl acetate (2 x 100 ml). The organic phases were separated and combined. The mixture was washed with 50 ml of saturated brine, and the organic phase was dried with 10 g of anhydrous sodium sulfate. The organic phase was filtered to remove salts and concentrated to dryness. Column chromatography was used to purify the organic phase, yielding 4.7 g of the target compound. Yield: 63.3%, purity: 94.3%.

[0040] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A method for synthesizing a tofacitinib demethylated impurity, characterized in that, Includes the following steps: The free tofacitinib active pharmaceutical ingredient was dissolved in a solvent, N-iodosuccinimide was added, and the mixture was catalyzed with a base, heated, and stirred while maintaining the temperature. The reaction was monitored by TLC until completion. Post-processing yielded the tofacitinib demethylated impurity. ； The base is one or more selected from sodium acetate, potassium acetate, triethylamine, potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, and lithium hydroxide. The temperature of the heat-preserving and stirring reaction is 20–60°C; The heat preservation and stirring reaction time is 1 to 6 hours; The molar ratio of tofacitinib to N-iodosuccinimide is 1.0:1.0-2.0; The volume ratio of tofacitinib to solvent is 1.0:10.0-30.0; The molar ratio of tofacitinib to the base is 1.0:1.0-2.0; The solvent is one or more selected from acetonitrile, acetone, tetrahydrofuran, dioxane, water, isopropanol, and N,N-dimethylformamide; The post-processing specifically includes the following steps: after the TLC detection reaction is completed, sodium thiosulfate is added and stirred for 0.5-1.0 hours to quench the reaction, the reaction solution is concentrated to dryness, water is added for dilution, then ethyl acetate is added for extraction, the aqueous phase is separated, the organic phases are combined, saturated sodium chloride solution is added for washing, the organic phases are separated by separation, anhydrous sodium sulfate is added for drying, salt is removed by filtration, and the product is dried and concentrated before column chromatography to obtain the tofacitinib demethylated impurity.

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