A Preparation Method of High-Purity Pemetrexed Disodium Dimer Impurity

Abstract

The present invention provides a novel and simple preparation method for pemetrexed disodium dimer impurities. The method comprises: generating oxidation impurity I from pemetrexed disodium under oxidizing agent and alkaline conditions, and condensing oxidation impurity I with pemetrexed disodium under alkaline conditions to obtain dimer impurity B and impurity C.

Description

Technical Field

[0001] The present invention belongs to the technical field of drug synthesis, and particularly relates to a novel and concise method for preparing a high-purity pemetrexed disodium dimer impurity. Background Art

[0002] Pemetrexed disodium, chemically named disodium N-[4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamate, is a novel multi-target folic acid blocker developed by Eli Lilly and Company in the United States and launched in the United States in 2004 under the trade name Alimta. It entered China in December 2005 for the treatment of malignant pleural mesothelioma and so on.

[0003]

[0004] Regarding the impurities of pemetrexed disodium, the European Pharmacopoeia (EP 9.0) and the United States Pharmacopoeia (USP) have published the structures of five impurities, namely A, B, C, D, and E (where impurity B and impurity C are epimers of each other); at the same time, Patrick J. Jansen et al. (Journal of Pharmaceutical Sciences. 2016, 105(11): 3256-68) have disclosed two other impurities, oxidation impurity I and oxidation impurity II.

[0005]

[0006] In terms of the difficulty of impurity synthesis, the synthesis of the dimer impurities B / C is the most challenging.

[0007] The preparation method of the reference solution for dimer impurities B / C in the European Pharmacopoeia 9.0 is as follows: Dissolve 30 mg of pemetrexed disodium in 10.0 mL of a 4.0 g / L sodium hydroxide solution, heat to 70 °C for 40 min, cool, and the mother liquor is obtained. When in use, take 1.0 mL and dilute it to 10.0 mL with water to obtain the reference solution for dimer impurities B / C. The United States Pharmacopeia (USP40-NF35) uses the same method as the European Pharmacopoeia to prepare the system suitability stock solution of pemetrexed disodium, and states that this method can cause pemetrexed disodium to degrade to produce dimer impurities. Olga Michalak et al. (Molecules. 2015, 20(6): 10004-31) improved the pharmacopeia method. Dissolve pemetrexed disodium in 0.1 M NaOH solution, heat under reflux for 3 days. After the mixture cools, adjust the pH to 3 with 10% aqueous HCl solution to obtain a precipitate, filter, and purify by chromatography to obtain dimer impurities B / C. The time required for this preparation method is relatively long, and it has been proven that under these conditions for preparing impurities B / C, the total content of impurities B and C in the reaction solution is less than 3%, and extending the reaction time or adjusting the concentration of the base cannot further increase the total content of impurities B and C.

[0008] Patrick J. Jansen et al. (Journal of Pharmaceutical Sciences. 2016, 105(11): 3256-68) continuously purged a solution containing 5 mg / mL of pemetrexed disodium and 1.6 mg / mL of sodium bisulfite with air for 64 h. The resulting solution contained approximately 20% dimer impurities and other impurities, and subsequent reverse-phase preparative HPLC and freeze-drying were required to obtain the dimer impurity product. This method requires a long time and uses a variety of instrument and equipment such as HPLC and freeze-dryers, and has high requirements for equipment and process parameters.

[0009] In addition, when Anne Warner et al. (Journal of Pharmaceutical and Biomedical Analysis. 2015, 105: 46-54.) developed an analytical method for pemetrexed disodium, the preparation method of the system suitability stock solution was to heat a solution containing 2 mg / mL of pemetrexed disodium and 2.8 mg / mL of oxidant Vazo 52 with an acetonitrile aqueous solution (volume ratio of acetonitrile to water was 1:1) at 70 °C for 30 min; or heat a solution containing 2 mg / mL of pemetrexed disodium and hydrogen peroxide (0.3%, v / v) at 75 °C for 2 - 5 h, and dilute it 1:10 with water before detection; the HPLC chromatogram of the solution showed the presence of dimer impurities. This method was not for the preparation of impurities, and the resulting solution was a mixture. Judging from its HPLC chromatogram, the content of dimer impurities was low.

[0010] In view of the various defects existing in the above prior art, it is necessary to develop a more concise and efficient method for preparing dimer impurities. Summary of the Invention

[0011] The present invention provides a brand-new and concise method for preparing pemetrexed disodium dimer impurities, and the reaction route is as follows:

[0012]

[0013]

[0014] Among them, pemetrexed disodium generates a salt of oxidized impurity I under oxidant and alkaline conditions, and it can be optionally acidified to obtain oxidized impurity I or not acidified; oxidized impurity I or its salt condenses with pemetrexed disodium under alkaline conditions to obtain a salt of dimer impurities B / C, and acidification gives impurities B / C. Since there is no stereoselectivity when oxidized impurity I condenses with pemetrexed disodium, the ratio of impurity B to impurity C is 1:1.

[0015] In the method of the present invention described above, the oxidant is preferably hydrogen peroxide, m-chloroperoxybenzoic acid or sodium hypochlorite.

[0016] In the method of the present invention described above, the alkaline condition is preferably pH greater than or equal to 13.

[0017] In the method of the present invention described above, the reaction is carried out in a solution, and the solvent is preferably water, ethanol or methanol.

[0018] In the method of the present invention described above, the reaction temperature is 25 °C - 100 °C.

[0019] In the method of the present invention described above, the salt is preferably an alkali metal salt.

[0020] In the method of the present invention described above, when pemetrexed disodium is used to prepare oxidation impurity I under oxidizing agent and alkaline conditions, the molar ratio of pemetrexed disodium to the oxidizing agent is preferably 1:1 to 1:4.

[0021] In the method of the present invention described above, the oxidizing agent is preferably hydrogen peroxide, m-chloroperbenzoic acid or sodium hypochlorite.

[0022] In the method of the present invention described above, the molar ratio of the amount of pemetrexed disodium used to prepare impurity I or its salt to the amount of pemetrexed disodium used for condensation with impurity I or its salt to prepare impurity B / C is preferably 1:0.5 to 1:1.

[0023] The reaction mechanism of the present invention has been confirmed by the following comparative experiments:

[0024] A test conditions: 2.0 g of pemetrexed disodium was dissolved in 0.1 N aqueous sodium hydroxide solution (125 mL) and refluxed for 4 h;

[0025] B test conditions: 2.0 g of pemetrexed disodium was dissolved in 0.1 N aqueous sodium hydroxide solution (125 mL) and refluxed for 72 h;

[0026] C test conditions: 2.0 g of pemetrexed disodium was dissolved in 0.1 N aqueous sodium hydroxide solution (125 mL), 0.16 g of hydrogen peroxide (30%) was added and the mixture was refluxed for 4 h;

[0027] D test conditions: 2.0 g of pemetrexed disodium was dissolved in 0.1 N aqueous sodium hydroxide solution (125 mL), 0.14 g of hydrogen peroxide (30%) was added and the mixture was refluxed for 4 h, 1.0 g of pemetrexed disodium was added and the reaction was continued for 18 h.

[0028] High performance liquid chromatography (HPLC) test conditions: The HPLC method for pemetrexed disodium bulk drug published in the European Pharmacopoeia 9.0 was adopted. The test results are shown in Figure 1Under the condition of 0.1N sodium hydroxide (A test condition), there is basically no generation of impurities B / C (25.9 min; 26.1 min), and with the extension of the experiment (extended to 72 h, B test condition), there are about 10% amide bond hydrolysis products (36.1 min) and 3% impurities B / C appearing; under the conditions of alkalinity and the presence of oxidation (C test condition), the main products are oxidation impurities I at 19.3 min and 19.6 min (about 80%), and at the same time, there is about 5% of impurities B / C. At this time, pemetrexed disodium is added (D test condition), and reflux is continued for 18 h. The main components of the reaction solution are oxidation impurities I (about 20%) and impurities B / C (about 70%). It can be seen from this that the generation of impurities B / C must first experience the process of oxidation to the structure of oxidation impurity I and then polymerization with pemetrexed disodium. In this process, the presence of an oxidant is one of the core conditions. This also explains the reason why only 5% of impurities B / C can be obtained under a single alkaline condition (sodium hydroxide) (limited oxygen in the reaction system participates in the oxidation reaction, and as the oxygen is depleted, impurities B / C and oxidation impurity I are no longer generated).

[0029] After the reaction solution in which oxidation impurity I and pemetrexed disodium are condensed to obtain dimer impurity B / C by the method of the present invention, the pH of the system can be adjusted to 3 - 4, and then yellowish-green solid will precipitate. After filtration, ethanol is added, heated to reflux and then cooled to 0 °C, stirred for crystallization, suction filtered, and dried to obtain solid dimer impurity B / C. The present invention has a high yield in preparing dimer impurity B / C and a high HPLC purity.

[0030] The method of the present invention has a simple preparation process, the obtained dimer B / C impurity has a high purity, and the yield is much higher than that of the prior art. At the same time, the present invention has conducted a detailed and thorough study on the generation mechanism of this dimer impurity B / C, which is not only beneficial to preparing a high-purity dimer impurity B / C reference substance, but more importantly, has great practical significance for the quality control and storage condition selection in the production process of pemetrexed disodium raw material medicine, and better realizes the economic and social benefits of this drug. Description of the Drawings

[0031] Figure 1 HPLC chromatogram of the comparative test. Detailed Embodiments

[0032] The following examples are only representative to further clarify and understand the spiritual essence of the present invention, but do not limit the scope of the present invention. Any simple modification and variation carried out under the spiritual essence of the present invention belong to the scope of the present invention.

[0033] Example 1 Preparation of Oxidation Impurity I

[0034] In a 500 mL three-necked flask, pemetrexed disodium (2.0 g, 4.24 mmol) and aqueous sodium hydroxide solution (0.1 N, 125 mL) were added successively and stirred until dissolved clearly. Then, 30% aqueous hydrogen peroxide solution (0.16 g, 4.66 mmol) was added. The system was heated to reflux for 4 h. After cooling to room temperature, the system was adjusted to pH = 3 - 4 with 0.4 N HCl. After a grayish-white solid precipitated, it was stirred for 10 - 30 min and then filtered to obtain a filter cake. The filter cake was added to ethanol (20 mL), heated to reflux and then slowly cooled to 0 °C. After stirring for 1 h for crystallization, it was suction filtered and dried to obtain 1.5 g of a white solid, with a yield of 78.9% and an HPLC purity of 98.24%.

[0035] MS-EI: 444.2[M+H] + ;

[0036] 13 C-NMR(100MHz, d 6 - DMSO)δ(ppm): 179.85, 174.00, 73.57, 166.58, 164.67, 158.11(C3), 157.39, 145.64, 131.59, 128.30, 127.60, 90.38, 52.00, 48.68, 43.46, 31.54, 30.49, 26.01;

[0037] 1 H-NMR(400MHz, d 6 -DMSO)δ(ppm): 10.59(2H,s), 8.51(1H,m), 7.78(2H,s), 7.29(2H,s), 6.67(2H,d), 4.39(1H,m), 3.44(2H,dd), 3.30(1H,d), 2.72(2H,s), 2.35(2H,s), 2.07(2×2H,2s).

[0038] Example 2 Preparation of Pemetrexed Disodium Dimer Impurities B / C

[0039] In a 1000 mL three-necked flask, add pemetrexed disodium (8.0 g, 16.96 mmol) and aqueous sodium hydroxide solution (0.1 N, 500 mL) in sequence, stir until dissolved and clear, add 30% aqueous hydrogen peroxide solution (0.56 g, 16.96 mmol), and heat the system to reflux for 4 h. Add pemetrexed disodium (4.0 g, 8.48 mmol) and continue refluxing for 18 h. Cool the reaction solution to room temperature, adjust the system to pH = 3 - 4 with 0.4 N HCl. After the yellow-green solid precipitates, stir for 10 - 30 min, and filter to obtain the filter cake. Add the filter cake to ethanol (200 mL), heat to reflux for 15 min, then slowly cool to 0 °C, stir for crystallization for 1 h, then filter with suction and dry to obtain 9.6 g of yellow-green solid, with a yield of 65.1% and an HPLC purity of 97.4%.

[0040] MS-EI: 869.2[M+H]+;

[0041] 13C NMR(100MHz, d6-DMSO) δ(ppm): 179.59, 173.93, 173.90, 173.51, 173.48, 166.59, 166.41, 164.03, 159.08, 157.76, 157.63, 152.10, 150.29, 146.52, 145.00, 131.49, 131.39, 128.08, 127.97, 127.54, 127.42, 114.22, 99.51, 92.71, 51.91, 51.72, 37.76, 34.18, 30.44, 29.75, 28.08, 25.98

[0042] 1H NMR(400MHz, d6-DMSO) δ(ppm): 10.84(2H, s), 10.70(2H, m), 10.26(2H, s), 8.37(4H, d), 7.78(1H, d), 7.77(4H, m), 7.29(4H, d), 7.24(1H, s), 6.11(2H, s), 4.34(2H, s), 2.63(4H, s), 2.32(4H, m), 2.03 - 1.95(8H, d).

[0043] Example 3 Preparation of Pemetrexed Disodium Dimer Impurities B / C

[0044] In a 1000 mL three-necked flask, pemetrexed disodium (8.0 g, 16.96 mmol) and aqueous sodium hydroxide solution (0.2 N, 500 mL) were added successively and stirred until dissolved clearly. Then m-chloroperoxybenzoic acid (5.2 g, 30.42 mmol) was added, and the system was heated to reflux for 4 h. Pemetrexed disodium (4.0 g, 8.48 mmol) was added and reflux continued for 18 h. The reaction solution was cooled to room temperature, and the system was adjusted to pH = 3 - 4 with 0.4 N HCl. After the yellow-green solid precipitated, it was stirred for 10 - 30 min and then filtered to obtain the filter cake. The filter cake was added to ethanol (200 mL), heated to reflux for 15 min and then slowly cooled to 0 °C. After stirring for crystallization for 1 h, it was filtered with suction and dried to obtain 6.5 g of yellow-green solid, with a yield of 44.1% and an HPLC purity of 87.4%.

[0045] Example 4 Preparation of Pemetrexed Disodium Dimer Impurities B / C

[0046] In a 1000 mL three-necked flask, pemetrexed disodium (8.0 g, 16.96 mmol) and methanol (500 mL) were added successively. After stirring and dispersing, the temperature was cooled to 0 - 10 °C, and an aqueous sodium hypochlorite solution with an available chlorine content of 12% (19.4 g, 64.5 mmol) was added dropwise while maintaining the temperature. The system was heated to 25 - 35 °C and reacted for 5 h. Pemetrexed disodium (4.0 g, 8.48 mmol) was added and reflux continued for 18 h. The reaction solution was cooled to 10 - 15 °C, and the system was adjusted to pH = 3 - 4 with 0.4 N HCl. After the yellow-green solid precipitated, it was stirred for 10 - 30 min and then filtered to obtain the filter cake. The filter cake was added to ethanol (200 mL), heated to reflux for 15 min and then slowly cooled to 0 °C. After stirring for crystallization for 1 h, it was filtered with suction and dried to obtain 7.5 g of yellow-green solid, with a yield of 50.9% and an HPLC purity of 94.3%.

[0047] Example 5 Preparation of Pemetrexed Disodium Dimer Impurities B / C

[0048] In a 1000 mL three-necked flask, pemetrexed disodium (8.0 g, 16.96 mmol) and aqueous sodium hydroxide solution (0.1 N, 500 mL) were added successively and stirred until dissolved clearly. Then 30% aqueous hydrogen peroxide solution (0.56 g, 16.96 mmol) was added, and the system was heated to reflux for 4 h. Pemetrexed disodium (8.0 g, 16.96 mmol) was added and reflux continued for 18 h. The reaction solution was cooled to room temperature, and the system was adjusted to pH = 3 - 4 with 0.4 N HCl. After the yellow-green solid precipitated, it was stirred for 10 - 30 min and then filtered to obtain the filter cake. The filter cake was added to ethanol (200 mL), heated to reflux for 15 min and then slowly cooled to 0 °C. After stirring for crystallization for 1 h, it was filtered with suction and dried to obtain 6.1 g of yellow-green solid, with a yield of 41.4% and an HPLC purity of 95.4%.

Claims

1. A preparation method of pemetrexed disodium impurities B / C, and its reaction route is as follows: 。 2. According to the preparation method described in claim 1, the preparation method of the impurity I or its salt is as follows: ； The oxidant is hydrogen peroxide, m-chloroperbenzoic acid or sodium hypochlorite.

3. According to the preparation method described in claim 1 or 2, the salt is an alkali metal salt.

4. According to the preparation method described in claim 1 or 2, the alkaline condition is that the pH is greater than or equal to 13.

5. According to the preparation method described in claim 1 or 2, the reaction is carried out in a solution, and the solvent is water, ethanol or methanol.

6. According to the preparation method described in claim 1 or 2, It is characterized in that: The reaction temperature is 25°C to 100°C.

7. According to the preparation method described in claim 2, the molar ratio of pemetrexed disodium to the oxidant is 1:1 to 1:

4.

8. According to the preparation method described in claim 2, the molar ratio of the amount of pemetrexed disodium used to prepare the impurity I or its salt to the amount of pemetrexed disodium used to condense with the impurity I or its salt to prepare the impurity B / C is 1:0.5 to 1:

1.

9. According to the preparation method described in claim 1 or 2, It is characterized in that It comprises the following steps: 1) Pemetrexed disodium generates the salt of impurity I in a solution system of an oxidant and an alkaline condition, and the salt of impurity I condenses with pemetrexed disodium to obtain a reaction solution containing the salt of impurity B / C; 2) The reaction solution prepared in step 1) is cooled to room temperature, the pH is adjusted to 3 to 4, and after the solid precipitates, stirring is continued and filtration is carried out; 3) The solid filtered in step 2) is added to ethanol, heated to reflux and then slowly cooled to 0°C, and crystallization is carried out by stirring; 4) Filtration by suction and drying are carried out to obtain the solid of impurity B / C.

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