A new method for purifying methotrexate

Abstract

This invention relates to a novel method for purifying methotrexate. This invention is the first to utilize an alkaline ionic liquid as a catalyst in the methotrexate purification process, aligning with the trend towards green chemistry. The purification method of this invention features a simple post-processing procedure, eliminating the need for complex post-processing operations, thus saving operating costs and facilitating industrial production. The alkaline ionic liquid of this invention is readily available, its preparation method is mature, and the ionic liquid is easily separated and can be reused after simple activation, further saving production costs and facilitating industrial production. The purification method of this invention yields methotrexate with high purity, low C impurity content, and a significantly improved overall reaction yield compared to existing technologies.

Description

Technical Field

[0001] This invention relates to the field of medicinal chemistry, and specifically to a novel method for purifying methotrexate. Background Technology

[0002] Methotrexate is a folic acid antagonist that primarily works by inhibiting dihydrofolate reductase, preventing the reduction of dihydrofolate to its physiologically active form, tetrahydrofolate, thereby hindering tumor cell synthesis and inhibiting tumor cell growth and proliferation. Furthermore, methotrexate can also affect the activity of T cells and B cells, reducing the production of immune mediators, thus achieving anti-inflammatory and immunosuppressive effects. Clinically, methotrexate is used to treat various types of acute leukemia, especially acute lymphoblastic leukemia, malignant lymphoma, non-Hodgkin's lymphoma, testicular granuloma, and multiple myelopathy; it can also be used to treat head and neck cancer, lung cancer, various soft tissue sarcomas; as well as breast cancer, ovarian cancer, cervical cancer, malignant hydatidiform mole, choriocarcinoma, and testicular cancer. Methotrexate is also a cornerstone drug for the treatment of rheumatoid arthritis and can be used to treat juvenile idiopathic arthritis, psoriatic arthritis, systemic lupus erythematosus, vasculitis, inflammatory myopathy, systemic sclerosis, and multisystem sarcoidosis.

[0003] According to the Chinese Pharmacopoeia 2020 Edition, Part II, the purity requirement for methotrexate is: calculated on anhydrous basis, the methotrexate content should be 98.0%–102.0%. Currently, there are two main synthetic routes for methotrexate: 1. Patents US4080325, US422446, and US3989703 disclose a three-step synthetic method that synthesizes 6-hydroxypteridine from tetraaminopyrimidine and 1,3-dihydroxyacetone, followed by bromination or chlorination and docking with p-methylaminobenzoyl L-glutamic acid to obtain methotrexate; however, the yields of these methods are not high; 2. Patent US... 4374987 discloses a one-pot synthesis method for methotrexate, which synthesizes methotrexate by reacting tetraaminopyrimidine sulfate, p-methylaminobenzoyl L-glutamic acid, and tribromoacetone. After cooling, the reaction solution is adjusted to alkali with ammonia water, filtered, and the resulting filtrate needs to be repeatedly subjected to acid-base adjustments (two consecutive acid adjustments, followed by alternating alkali and acid adjustments). The resulting filter cake is then adjusted to alkali again, filtered, and the resulting filtrate is added to acetone to prepare the refined sodium methotrexate. Sulfuric acid is then added to crystallize the refined methotrexate. This method has good yield and purity, but the post-processing purification process is extremely cumbersome, and due to the repeated acid-base adjustments, it requires the use of large amounts of ammonia water and hydrochloric acid, which has a significant environmental impact.

[0004] Zhou Bei et al. (China Pharmaceutical Industry Magazine, 1990, 21(12), 535) disclosed an improved purification process for methotrexate. Their method involved adjusting the alkali of the methotrexate sample with ammonia, filtering, adjusting the acidity of the filtrate to crystallize, filtering again, adjusting the alkali of the filter cake, filtering again, and then using acetone to crystallize the filtrate. The filter cake was then crystallized with sulfuric acid to obtain pure methotrexate. This method still uses hydrochloric acid and ammonia for acid-base adjustment, requiring a large amount of ammonia and causing significant environmental pollution. WO2018028496A1 disclosed a purification method for methotrexate. This invention's purification process controls the pH and temperature of the reaction solution through a pretreatment step. This pretreatment step can synergistically control the solubility of methotrexate isomers in the reaction solution. Filtration is then performed to remove the methotrexate isomers. Although this method reduces the amount of ammonia used, it still requires a large amount of acetone, which is a controlled substance. Furthermore, the large-scale use of acetone generates a large amount of wastewater, which is detrimental to environmental protection requirements.

[0005]

[0006] Zhu Haixi et al. (Pharmaceutical and Clinical Research, 2023, 31(2), 136-139) disclosed a synthetic process for methotrexate. This process involves crystallizing (2S)-2-[[4-[[(2,4-diaminopterin-6-yl)methyl]methylamino]benzoyl]amino]glutaric acid diethyl ester with an aqueous solution of p-toluenesulfonic acid to obtain its p-toluenesulfonate. The p-toluenesulfonate is then deethylated in an aqueous solution of sodium hydroxide to obtain disodium methotrexate. Methotrexate can be precipitated by adjusting the pH. CN114249731A discloses a purification method for methotrexate intermediates. Using p-toluenesulfonic acid, the intermediate Int1 of methotrexate is salted and then precipitated, resulting in a significantly reduced content of impurity C in the methotrexate precursor. The precursor is then hydrolyzed to obtain methotrexate raw material with a lower impurity C content. The above route effectively reduces the content of impurity C. However, this requires adding a salt-forming step for intermediates, which lengthens the process and increases costs.

[0007]

[0008] Therefore, developing an economical, environmentally friendly, and commercially viable methotrexate purification process has significant economic and social value. Summary of the Invention

[0009] To address the aforementioned technical problems in the existing technology, this invention provides a novel method for purifying methotrexate. The method of this invention uses mild conditions, readily available and simple reagents, and yields high product purity, making it more suitable for industrial production.

[0010] In a first aspect, the present invention provides a novel method for purifying methotrexate, characterized by comprising the following steps:

[0011] 1) In the presence of an alkaline ionic liquid, compound I and compound II react to give intermediate compound III;

[0012] 2) Under alkaline conditions, intermediate III undergoes ester hydrolysis to yield intermediate IV;

[0013] 3) Adjust the pH value of intermediate IV to obtain the final product V, namely methotrexate;

[0014] The reaction pathway is as follows:

[0015]

[0016] Where: X is a halogen, and M is an alkali metal or alkaline earth metal;

[0017] The alkaline ionic liquid in step 1) is [Nbmm]OH, with the structural formula as follows: .

[0018] Preferably, X is bromine;

[0019] Preferably, M is Na or K;

[0020] Preferably, the reaction temperature in step 1) is 50°C to 150°C, more preferably 100°C to 120°C.

[0021] Preferably, the reaction time in step 1) is 4 to 24 hours, more preferably 6 to 12 hours, and most preferably 8 to 10 hours.

[0022] Preferably, the molar ratio of compound I to compound II in step 1) is 1:0.8~1.5, more preferably 1:1.0~1.2.

[0023] Preferably, in step 1), the mass ratio of compound I to alkaline ionic liquid is 1:1~20, more preferably 1:6~12.

[0024] Preferably, the alkali used in the alkaline conditions in step 2) is sodium hydroxide or potassium hydroxide.

[0025] Preferably, the reaction temperature in step 2) is room temperature.

[0026] Preferably, the reaction time in step 2) is 1 to 3 hours, more preferably 1.5 to 2 hours.

[0027] Preferably, the acid used in step 3) is hydrochloric acid or sulfuric acid;

[0028] Preferably, the reaction temperature in step 3) is room temperature.

[0029] Preferably, step 3) involves dissolving compound IV in water, adding acid, and adjusting the pH of the reaction solution to 4.0-4.5.

[0030] In recent years, the unique solvent properties of ionic liquids have led to their widespread application in synthesis and catalysis. However, the economic and potential environmental concerns surrounding ionic liquids have drawn increasing attention to their catalytic properties. Various functionalized ionic liquids with specific catalytic properties have been designed by modifying their structures. Functionalized ionic liquids have found considerable application in catalyzing carbon-nitrogen bond formation reactions. The structures of functionalized ionic liquids typically contain functional groups that enable them to exhibit catalytic activity. These specific functional groups allow functionalized ionic liquids to activate reactants in specific ways. Yetkin GOK et al. (Journal of Catalysis, 2007, 28(6), 489-491) disclosed the use of ionic liquids as solvents / catalysts for the selective alkylation of amines by haloalkanes, and studied the selective alkylation of amino groups in amine compounds by various haloalkanes in the presence of triethylamine in ionic liquids ([bmim]I) and ([bmim]PF6).

[0031] Based on this, the inventors, through extensive research, discovered that in the presence of the functionalized ionic liquid of this invention, the selective alkylation reaction of 6-halomethyl-2,4-pteridinediamine can be achieved under relatively mild conditions, with high yield and purity of the product. Since no inorganic base is used in this step and no water is generated during the reaction, hydrolysis of the amino group at the tip of the pteridine ring is avoided, resulting in a significant reduction in the content of impurity C in the final methotrexate. Furthermore, in subsequent purification steps, there is no need to perform a salt-forming reaction on intermediate compound III, reducing reaction steps, increasing the purity of the intermediate, and thus improving the purity of the product and reducing the formation of subsequent impurities. In this process, selecting a suitable ionic liquid is crucial. Because compound II has an amino group on its pteridine ring, if the catalytic activity of the ionic liquid is too high, compound II may undergo a reaction between its own haloalkane and the amino group, generating undesirable impurities; if the catalytic activity of the ionic liquid is too low, the reaction will be incomplete or even fail, thus affecting the yield and purity of the final product.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. This invention is the first to use alkaline ionic liquid as a catalyst in the purification process of methotrexate, which is in line with the development trend of green chemistry.

[0034] 2. The purification method of the present invention has a simple post-processing procedure, which does not require complicated post-processing operations, saves operating costs, and is conducive to industrial production.

[0035] 3. The catalyst of the present invention is simple and readily available, and the preparation method is mature. Furthermore, the ionic liquid of the present invention is easy to separate and can be reused after simple activation, saving production costs and facilitating industrial production.

[0036] 4. The purification method of the present invention produces methotrexate with high purity and low content of impurity C, and the overall reaction yield is also significantly improved compared with the prior art. Detailed Implementation

[0037] The present invention will be specifically illustrated below through examples. In this invention, the following examples are provided to better illustrate the invention and are not intended to limit the scope of the invention. Unless otherwise specified, the materials, reagents, etc., used in the following examples are commercially available.

[0038] Synthesis Example 1: Preparation of Alkaline Ionic Liquid Catalysts

[0039] The alkaline ionic liquid used in this invention is [Nbmm]OH, with the structural formula as follows: It was prepared according to the method in Example 2 of Patent Document CN 109796406 A. The specific steps are as follows:

[0040] 2 mol of n-butane bromide was slowly added to a three-necked flask containing 2 mol of N-methylmorpholine. The mixture was stirred and heated to reflux for 5 h. After removing unreacted N-methylmorpholine and n-butane by vacuum filtration, the product was dried in a vacuum oven at 70 °C for 24 h to obtain a yellow solid intermediate, N-methyl-N-butylmorpholine bromide. Then, 2 mol of N-methyl-N-butylmorpholine bromide and potassium hydroxide were dissolved in a certain volume of anhydrous ethanol, and the mixture was stirred for 24 h. The insoluble KBr was removed by centrifugation, and the resulting liquid mixture was distilled under reduced pressure to remove anhydrous ethanol. The remaining solid was dried under vacuum at 70 °C to constant weight and recrystallized from anhydrous ethanol to obtain a white solid, which was the target product, the basic ionic liquid [Nbmm]OH.

[0041] Example 1

[0042] Step 1): 3000 g of basic ionic liquid [Nbmm]OH was added sequentially to the reaction vessel, and the temperature was raised while stirring. Once the internal temperature reached 110 °C, compound I (336.4 g, 1 mol) was added, and stirring continued for 15 min. Then, compound II (255 g, 1.0 mol) was added, and the reaction was maintained at 110 °C for 9 h. After the reaction was complete, purified water (8 L) was added dropwise after the reaction solution cooled to 70 °C, and crystallization was carried out by stirring for 1 h. After centrifugation and drying, a brown solid compound III (463.8 g, yield 90.9%) was obtained, mp 178~179 °C. The HPLC purity was 98.43%, and the content of impurity C precursor was 0.08%.

[0043] After filtration, most of the water in the filtrate is removed by vacuum distillation. The residue is then dried in an oven to recover the ionic liquid, which can be reused. Alternatively, the residue can be filtered and purified by activated carbon adsorption before reuse.

[0044] Step 2): 500 mL of purified water and 100 g of intermediate 3 were added sequentially to the reaction flask. 250 mL of sodium hydroxide (25 g) aqueous solution was added dropwise while stirring. After the addition was complete, the reaction was allowed to proceed at room temperature for 1.5 h. After the reaction was complete, the mixture was filtered, and the filtrate was collected. 1500 mL of acetone was added dropwise while stirring to induce crystallization. After filtration and drying, a yellow solid compound IV (88.6 g, yield 88.3%) was obtained with an HPLC purity of 99.82%, containing approximately 0.02% impurity C. 1 H NMR (400 MHz, CDCl3) δ: 8.59 (s, 1H), 7.80-7.83 (t, J =7.5 Hz, 2H), 6.85-6.89 (m, 2H), 4.84 (s, 2H), 4.41-4.45 (m, 1H), 3.26 (s, 3H), 2.31-2.36 (m, 1H), 2.22-2.26 (m, 2H), 2.18-2.20 (m, 1H).

[0045] Step 3) Add compound IV (50 g) and 500 mL of purified water to the reaction flask, stir until dissolved, and adjust the pH to 4.0-4.5 with 8% hydrochloric acid solution. After filtration and drying, obtain yellow solid methotrexate (42.2 g, yield 92.5%), mp 194-195℃, purity 99.79%, impurity C content 0.01%.

[0046] Example 2

[0047] Step 1): 4000 g of basic ionic liquid [Nbmm]OH was added sequentially to the reaction vessel, and the temperature was raised while stirring. Once the internal temperature reached 120 °C, compound I (336.4 g, 1 mol) was added, and stirring continued for 15 min. Then, compound II (280.5 g, 1.1 mol) was added, and the reaction was maintained at 120 °C for 8 h. After the reaction was complete, purified water (8 L) was added dropwise after the reaction solution cooled to 70 °C, and crystallization was carried out by stirring for 1 h. After centrifugation and drying, a brown solid compound III (442.7 g, yield 86.7%) was obtained, mp 178~179 °C. The HPLC purity was 98.58%, and the content of impurity C precursor was 0.07%.

[0048] After filtration, most of the water in the filtrate is removed by vacuum distillation. The residue is then dried in an oven to recover the ionic liquid, which can be reused. Alternatively, the residue can be filtered and purified by activated carbon adsorption before reuse.

[0049] Example 3

[0050] Step 1): 2800 g of basic ionic liquid [Nbmm]OH was added sequentially to the reaction vessel, and the mixture was heated while stirring. Once the internal temperature reached 100 °C, compound I (336.4 g, 1 mol) was added, and stirring continued for 15 min. Then, compound II (280.5 g, 1.1 mol) was added, and the mixture was kept at 100 °C for 10 h. After the reaction was complete, purified water (8 L) was added dropwise after the reaction solution cooled to 70 °C, and crystallization was carried out by stirring for 1 h. After centrifugation and drying, a brown solid compound III (452.3 g, yield 88.6%) was obtained, mp 178~179 °C. The HPLC purity was 97.43%, and the content of impurity C precursor was 0.10%.

[0051] After filtration, most of the water in the filtrate is removed by vacuum distillation. The residue is then dried in an oven to recover the ionic liquid, which can be reused. Alternatively, the residue can be filtered and purified by activated carbon adsorption before reuse.

[0052] Comparative Example 1

[0053] Using the same method as in Example 1, except that 3000g of alkaline ionic liquid [Bmim]OH was used instead of the alkaline ionic liquid in Example 1, the target product was not obtained.

Claims

1. A method for purifying methotrexate, characterized in that... Includes the following steps: 1) In the presence of an alkaline ionic liquid, compound I and compound II react to yield intermediate compound III; 2) Under alkaline conditions, intermediate III undergoes ester hydrolysis to yield intermediate IV; 3) Adjust the pH value of intermediate IV to obtain the final product V, namely methotrexate; The reaction pathway is as follows: Where: X is a halogen, and M is an alkali metal or alkaline earth metal; The alkaline ionic liquid in step 1) is [Nbmm]OH, with the structural formula as follows: .

2. The method for purifying methotrexate according to claim 1, characterized in that: X is bromine; M is Na or K.

3. The method for purifying methotrexate according to claim 1 or 2, characterized in that: The reaction temperature for step 1) is 100℃~120℃.

4. The method for purifying methotrexate according to claim 1 or 2, characterized in that: The reaction time for step 1) is 8 to 10 hours.

5. The method for purifying methotrexate according to claim 1 or 2, characterized in that: In step 1), the molar ratio of compound I to compound II is 1:0.8~1.

5.

6. The method for purifying methotrexate according to claim 1 or 2, characterized in that: In step 1), the molar ratio of compound I to compound II is 1:1.0~1.

2.

7. The method for purifying methotrexate according to claim 1 or 2, characterized in that: In step 1), the mass ratio of carbon tetrachloride to the diacidic ionic liquid is 1:6~12.

8. The method for purifying methotrexate according to claim 1 or 2, characterized in that: In step 2), the base used for the alkaline conditions is sodium hydroxide or potassium hydroxide.

9. The method for purifying methotrexate according to claim 1 or 2, characterized in that: The reaction temperature in step 2) is room temperature, and the reaction time is 1 to 3 hours.

10. The method for purifying methotrexate according to claim 1 or 2, characterized in that: Step 3) uses either hydrochloric acid or sulfuric acid.

11. The method for purifying methotrexate according to claim 1 or 2, characterized in that: Step 3) involves dissolving compound IV in water, adding acid, and adjusting the pH of the reaction solution to 4.0-4.5.

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