Litamilast oxide impurity and control method thereof

Abstract

The invention belongs to the technical field of medicinal chemistry, and particularly discloses a ritamilast oxidation impurity and a control method thereof, the structural formula of the impurity disclosed by the invention is brand new and not disclosed, the impurity belongs to an oxidation impurity, and an intermediate compound 3 derived from ritamilast is unstable in structure and easy to oxidize to generate the oxidation impurity. Oxidized impurities react with the intermediates in the steps and are transferred into a final finished product all the time to form final derivative impurities; the invention provides the method for controlling the oxidation impurities, the intermediate 03 is washed and extracted, the oxidation impurities generated in the step are reduced, the content of the oxidation impurities in a finished product of litamilast is further reduced, API with stable quality is obtained, the method is simple to operate and easy to implement, and the product purity is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of pharmaceutical chemistry, relates to the study of impurities in the synthesis process of the raw material drug lifalast, and specifically relates to an oxidized impurity of lifalast and a control method thereof. Background Art

[0002] Lifitegrast, chemical name ((S)-2-[2-(Benzofuran-6-carbonyl)-5,7-dichloro-1,2,3,4-tetrahydroisoquinoline-6-carboxamido]-3-(3-methylsulfonylphenyl)propionic acid), CAS number is 1025967-78-5, molecular weight is 615.48, molecular formula is C 29 H 24 C l2 N 2 O 7 S, structural formula:

[0003]

[0004] Lifastat is a new inhibitor of intercellular adhesion factors, which can work by blocking the binding between intercellular adhesion molecule-1 and integrin protein lymphocyte function-associated antigen-1. The drug was approved by the US FDA in July 2016 and is marketed under the trade name Xiidra for the treatment of dry eye.

[0005] At present, the synthesis method of Litamistat is relatively mature, and the synthesis route is as follows:

[0006]

[0007] During the synthesis and storage process of Litamilast, multiple impurities are introduced. Currently, the impurities recorded in the literature are mainly:

[0008] Chinese patent CN111060629A discloses a method for detecting related substances of lifalast, using high performance liquid chromatography to determine 6 impurities (A, B, C, D, E, F) of lifalast; patent CN114689733A also discloses a method for detecting related substances of lifalast, using high performance liquid chromatography to determine 14 impurities (SM1, SM2, JP-Y-4, JP-Y-5, JP-Y-6, JP-Y-7, JP-Y-8, JP-Y-9, JP-Y-10, JP-Y-11, JP-Y-12, JP-Y-13, JP-Y-14, JP-Y-16) of lifalast; Chinese patent CN112592384A discloses new impurities of lifalast:

[0009]

[0010] Chinese patent CN111100118A also discloses a new impurity of Litamilast:

[0011]

[0012] Chinese patent CN115124592B also discloses a new impurity of Litamilast:

[0013]

[0014] With the advancement of the country's research on drug consistency, the study of impurities with novel structures produced during the synthesis process of lifastat is a dynamic and continuous process. This research can play a positive role in the quality control of lifastat. Summary of the invention

[0015] In view of the deficiencies of the prior art, the purpose of the present invention is to provide an oxidized impurity of Litamilast, the structural formula of which is completely new and undisclosed, and the impurity is an oxidized impurity derived from the intermediate compound 3 of Litamilast, which is structurally unstable and easily oxidized to produce oxidized impurities. The oxidized impurities will react with the intermediates of each step and be transferred to the final product to form the final derivative impurities; the second purpose of the present invention is to provide a control method for the oxidized impurities, by washing and extracting the intermediate 03, reducing the oxidized impurities produced in this step, and then reducing the content of oxidized impurities in the Litamilast product, to obtain API with stable quality, simple operation, easy to implement, and greatly improve the purity of the product.

[0016] The present invention is achieved through the following technical solutions:

[0017] A lifastat oxide impurity, the structural formula of which is shown below:

[0018]

[0019] A further improvement of the present invention is:

[0020] A method for controlling oxidized impurities in lifalast comprises the following steps: adding an ethyl acetate solution of a prepared lifalast intermediate compound 3 to an aqueous sodium bisulfite solution, stirring and dispersing the solution, standing the solution, separating the solution, retaining an organic phase, drying the organic phase by rotation, and removing the organic solvent to obtain the treated lifalast compound 3.

[0021] A further improvement of the present invention is:

[0022] Furthermore, the mass ratio of ethyl acetate to compound 3 is 4.5-8.5.

[0023] Furthermore, the mass concentration of the sodium bisulfite aqueous solution is 0.1%-1%.

[0024] Furthermore, the volume ratio of the sodium bisulfite aqueous solution to the ethyl acetate solution of compound 3 is 3-7:1.

[0025] Furthermore, the stirring and dispersing time is 10-40 minutes.

[0026] Furthermore, the standing time is 10-40 minutes.

[0027] Furthermore, the spin drying temperature is 30-50°C.

[0028] Beneficial effects:

[0029] Compared with the prior art, the present invention has the following obvious advantages:

[0030] 1. The present invention provides a novel oxidized impurity of Litamilast that has not been disclosed in the prior art, and its structure has been confirmed. The oxidized impurity is formed by oxidation of the intermediate compound 3 of Litamilast, and then reacting with the intermediates of each step, and then being transferred to the final product;

[0031] Second, the present invention suppresses the content of oxidized impurities in the finished product of Litamilast by washing and extracting compound 3, so that the final finished product of Litamilast can reduce the derived impurities to less than 0.05% after one recrystallization, effectively improving the production efficiency, increasing the yield from 42% to more than 80%, and greatly reducing the production cost;

[0032] 3. The present invention uses ethyl acetate as the extractant in the extraction process of compound 3, without introducing other impurities, which can effectively reduce the generation of oxidative impurities, greatly improve the quality stability of the finished product of lifalast, and has no effect on the overall process;

[0033] Fourth, the present invention is simple to operate and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a graph showing the HPLC test results of the LT-26-240312-4 batch of Litamistat API;

[0035] Figure 2 This is a graph showing the HPLC test results of the LT-26-240313-4 batch of Litamistat API;

[0036] Figure 3 This is a graph showing the HPLC test results of the LT-26-240321-2 batch of Litamistat API;

[0037] Figure 4 is the mass spectrum of the separated lifalast oxidized impurity B;

[0038] Figure 5This is the H NMR spectrum of the separated Lifamide oxide impurity B;

[0039] Figure 6 This is a graph showing the HPLC test results of the lifalast compound 3 after washing in Example 2;

[0040] Figure 7 This is a graph showing the HPLC test results of the unwashed lifalast compound 3 of Comparative Example 1;

[0041] Figure 8 This is a graph showing the HPLC test results of the lifalast API prepared in Example 2;

[0042] Fig. 9 This is a graph showing the HPLC test results of Litamilast API obtained after washing three times in Comparative Example 1. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with specific embodiments.

[0044] Example 1: Confirmation of oxidized impurities in Litamilast

[0045] The synthesis of lifastat was carried out by the method recorded in the prior art, and the synthesis route is as follows:

[0046]

[0047] The process is briefly described as follows:

[0048] S1, using compounds 1 and 2 as starting materials, and obtaining compound 3 through condensation;

[0049] S2, removing BOC from compound 3 to obtain compound 4;

[0050] S3, condensing compound 4 and compound 5 to obtain compound 6;

[0051] S4. Compound 6 is hydrolyzed and crystallized to obtain a crude product of Lifalast, and the crude product is refined to obtain a finished product of Lifalast.

[0052] By performing HPLC analysis on multiple batches of lifastat (LT-26-240312-4, LT-26-240313-4, LT-26-240321-2) (see the spectrum Figure 1 , Figure 2 , Figure 3 ), and found 1 impurity that was difficult to remove.

[0053] 1. Detection of impurities

[0054] Detection method: HPLC

[0055] Chromatographic conditions: octadecylsilane bonded silica gel as filler (Waters Symmetry Shield RP18, 4.6×250mm, 5μm or a chromatographic column with equivalent performance); 0.01mol / L potassium dihydrogen phosphate solution (the pH value is adjusted to 2.0 with phosphoric acid) as mobile phase A, acetonitrile as mobile phase B, and gradient elution according to the table below; flow rate is 1.0ml per minute; column temperature is 25°C; detection wavelength is 220nm; injection volume is 10μl.

[0056] Table 1

[0057]

[0058] The results are shown in Table 2:

[0059] Table 2 HPLC test results of different batches of Litamistat API

[0060]

[0061] 2. Structural identification of impurities

[0062] The impurity is separated and purified by medium pressure Flash. The impurity is tested by mass spectrometry and nuclear magnetic resonance. The mass spectrum is as follows: Figure 4 Its H NMR spectrum is shown in Figure 5 shown.

[0063] Depend on Figure 4 It can be seen that the relative molecular weight of the impurity is 613.0570;

[0064] analyze Figure 5 , obtain the NMR data of the impurity and determine the structure of the impurity as follows:

[0065]

[0066] 3. Analyze the source of impurities

[0067] This impurity is an oxidized impurity. According to liquid phase tracing, it originates from compound 3. Oxidized impurity A is generated during the preparation of compound 3. Oxidized impurity A will react with intermediates in each step and be transferred to the final product to form oxidized impurity B. The transfer reaction process is as follows:

[0068]

[0069] Example 2: Control of Oxidative Impurities in Litamilast

[0070] Under nitrogen protection, DMF was added to the reactor, compound 1, triethylamine and HATU were added, and the mixture was stirred for 1 hour. Compound 2 was added at a temperature of 20-30°C, and after reacting for 4 hours, ethyl acetate was added, water was added, and the mixture was stirred for 30 minutes; the mixture was added at a temperature of 10-25°C, diluted hydrochloric acid aqueous solution was stirred for 30 minutes, and the mixture was allowed to stand for 30 minutes, and the liquid was separated, and the upper organic phase was retained; the mixture was added at a temperature of 10-25°C, sodium bisulfite aqueous solution was added to the mixture, and the mixture was stirred for 30 minutes, and the mixture was allowed to stand for 30 minutes, and the liquid was separated, and the upper organic phase was retained; the organic phase was distilled under reduced pressure, and the external bath temperature was controlled to be ≤50°C, and the mixture was concentrated to dryness under reduced pressure; the washed compound 3 was tested by HPLC, and the results are shown in the table. Figure 6 , the purity of compound 3 is 95.84%, and the content of oxidized impurity A is 1.92%.

[0071] At room temperature, the washed compound 3 was dissolved in dioxane, and a dioxane solution of HCl (4N, excess) was added to react for 8 hours, and ether was added, and the solid product compound 4 was separated by filtration. The dichloromethane solution of benzofuran carboxylic acid was added with oxalyl chloride and a catalytic amount of DMF, and stirred at room temperature for 5.5 hours until a clear solution was obtained. Compound 5 was obtained by concentration under reduced pressure. The dichloromethane solution of compound 5 was slowly added to the dichloromethane solution of compound 4 and DIPEA cooled to 0-5°C. The reaction temperature must not exceed 5°C. After the addition was completed, it was stirred at 5°C for another 0.5 hours. After aqueous post-treatment and extraction with dichloromethane, compound 6 was separated. Tetrahydrofuran and water were mixed with compound 6, 2N sodium hydroxide was slowly added within 1 hour, methyl tert-butyl ether and ethyl acetate were added, and 4N hydrochloric acid aqueous solution was added to pH~2, and the filter cake was separated by filtration. The wet cake was suspended in acetone and water (about 2 / 1). Seed crystals were added and stirred for 12 hours. The product was collected by filtration and dried at 45 to 55° C. under vacuum to obtain Litamilast API. The API was tested by HPLC. The results are shown in Figure 8 , no oxidative impurity B was detected in the finished product.

[0072] Comparative Example 1: Original process, without washing and separation of compound 3

[0073] Under nitrogen protection, DMF, compound 1, triethylamine and HATU were added to the reaction kettle, and the mixture was stirred for 1 hour. Compound 2 was added at a temperature of 20-30°C, and after reacting for 4 hours, ethyl acetate and water were added, and the mixture was stirred for 30 minutes; the mixture was added at a temperature of 10-25°C, and a dilute hydrochloric acid solution was stirred for 30 minutes, and the mixture was allowed to stand for 30 minutes, and the liquid was separated, and the upper organic phase was retained; the organic phase was distilled under reduced pressure, and the external bath temperature was controlled to be ≤50°C, and the mixture was concentrated under reduced pressure to dryness; the obtained compound 3 was tested by HPLC, and the results are shown in FIG. Figure 7 , the purity of compound 3 is 90.93%, and the content of oxidized impurity A is 7.02%.

[0074] The above compound 3 was used to continue the synthesis of lifalast using the existing process. In this comparative example, the filter cake crystals were washed 3 times to obtain lifalast API. The other operations were basically the same as those in Example 2. The API was tested by HPLC. The results are shown in FIG. Fig. 9 .

[0075] The HPLC results of the lifalast compound 3 in Example 2 and Comparative Example 2 before and after washing were compared, and the results are shown in Table 3 below:

[0076] Table 3 HPLC purity comparison of Litamilast compound 3 before and after washing

[0077]

[0078] The HPLC purity, yield and process of lifalast API in Example 2 and Comparative Example 2 were compared, and the results are shown in Table 4.

[0079] Table 4 HPLC purity, yield and process comparison of Litamilast API and impurity B before and after washing

[0080]

[0081] By comparison, it can be seen that compared with the original process, the new process provided by the present invention can effectively control the limit of oxidative impurities in the synthesis of lisdenafil, reduce the number of times of recrystallization and purification of the final product, and improve the yield.

[0082] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lifalast oxidized impurity, characterized in that: The structural formula is as follows:

2. The method for controlling oxidized impurities of Litamilast according to claim 1, characterized in that: The method comprises the following steps: adding the prepared ethyl acetate solution of the lifalast intermediate compound 3 to a sodium bisulfite aqueous solution, stirring and dispersing, standing, separating the liquids, retaining the organic phase, and drying the organic phase to remove the organic solvent to obtain the treated lifalast compound 3.

3. The method for controlling oxidized impurities of Litamilast according to claim 2, characterized in that: The mass ratio of the ethyl acetate to the compound 3 is 4.5-8.5:

1.

4. The method for controlling oxidized impurities of Litamilast according to claim 2, characterized in that: The mass concentration of the sodium bisulfite aqueous solution is 0.5%-5%.

5. The method for controlling oxidized impurities of Litamilast according to claim 4, characterized in that: The volume ratio of the sodium bisulfite aqueous solution to the ethyl acetate solution of compound 3 is 3-7:

1.

6. The method for controlling oxidized impurities of Litamilast according to claim 2, characterized in that: The stirring and dispersing time is 10-40 minutes.

7. The method for controlling oxidized impurities of Litamilast according to claim 2, characterized in that: The standing time is 10-40 minutes.

8. The method for controlling oxidized impurities of Litamilast according to claim 2, characterized in that: The spin drying temperature is 30-50°C.

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