阅读说明：本技术 一种适合工业化生产的盐酸苯达莫司汀制备方法 (Preparation method of bendamustine hydrochloride suitable for industrial production ) 是由 罗名汉 侯常林 王长平 阳怡林 卓秋琪 于玉根 于 2020-12-30 设计创作，主要内容包括：本发明提供了一种盐酸苯达莫司汀的合成方法,该方法利用合适的溶剂去除氯化反应残余的氯化亚砜,水解反应完后蒸除部分反应液后加水析晶,能够明显减少杂质的生成,提升产品的纯度和改善产品的颜色。采用本发明方法无需精制步骤以及脱色操作就能够在实验室规模以及生产放大规模均能制备得到纯度达到99.6%以上,单杂在0.3%以内的纯白色盐酸苯达莫司汀产品,经重结晶精制后产品纯度能达到99.8%,单杂在0.1%以内,符合国家要求的化学原料药质量要求,能够为注射用盐酸苯达莫司汀研究和生产提供质量合格的原料药。该方法反应条件温和,操作安全、简便,适合工业化放大生产。(The invention provides a method for synthesizing bendamustine hydrochloride, which utilizes a proper solvent to remove residual thionyl chloride in chlorination reaction, evaporates and removes partial reaction liquid after hydrolysis reaction, and then adds water for crystallization, thus obviously reducing the generation of impurities, improving the purity of products and improving the color of products. By adopting the method, the pure white bendamustine hydrochloride product with the purity of more than 99.6 percent and the single impurity of within 0.3 percent can be prepared in a laboratory scale and a production scale without refining steps and decoloring operation, the purity of the product after recrystallization refining can reach 99.8 percent and the single impurity of within 0.1 percent, the product meets the quality requirement of national chemical raw material medicines, and the raw material medicines with qualified quality can be provided for the research and production of bendamustine hydrochloride for injection. The method has mild reaction conditions, safe and simple operation and is suitable for industrial scale-up production.)

1. The preparation method of bendamustine hydrochloride comprises the following steps:

the method is characterized by comprising the following steps:

1) reacting 5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate, namely a compound II, with ethylene oxide to prepare 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate, namely a compound III;

2) dissolving a compound III by using dichloromethane, dropwise adding thionyl chloride to react at room temperature, concentrating the reaction solution to be dry after the reaction is completed, adding a solvent for removing the thionyl chloride, stirring to separate out a solid, and filtering to obtain 4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate, namely a compound IV;

3)4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate is added with concentrated hydrochloric acid for reflux reaction until the reaction is finished, the mixture is cooled and filtered, partial reaction liquid is concentrated and distilled out, water is added for stirring and crystallization, the filtration is carried out, and acetone is washed, thus obtaining the bendamustine hydrochloride.

2. The process according to claim 1, wherein the molar ratio of [ 1-methyl-2 (4' -ethylbutyrate) -5-amino ] -1H-benzimidazole to ethylene oxide in step 1) is 1: 8-15, wherein the reaction solvent is water/glacial acetic acid in a ratio of 1-2: 1, the pH of the reaction solution is adjusted to 7.0-7.3 after the reaction is finished, dichloromethane is used for extraction, the organic phase is washed by water, dried, filtered, concentrated, and recrystallized by ethyl acetate.

3. The method as claimed in claim 1, wherein the solvent for removing thionyl chloride in step 2) is selected from the group consisting of ester solvents including methyl acetate, ethyl acetate, butyl acetate, ketones including acetone, methyl ethyl ketone, halogenated hydrocarbons including dichloromethane, chloroform, and toluene and tetrahydrofuran.

4. The method according to claim 1, wherein the solvent for removing thionyl chloride in step 2) is selected from the group consisting of ethyl acetate, dichloromethane, and acetone.

5. The method according to claim 1, wherein the solvent for removing thionyl chloride in step 2) is selected from ethyl acetate.

6. The method according to claim 1, wherein the solvent for removing thionyl chloride in step 2) is used in a volume of 3 to 8 times the mass of the compound III.

7. The method according to claim 1, wherein the concentrated hydrochloric acid used in the hydrolysis reaction in step 3) is 7 to 10 times the mass of the compound IV.

8. The method according to claim 1, wherein the distilling out of the part of the reaction solution in the step 3) is carried out until the residual volume of the reaction solution is 4-6 times of the mass of the compound IV.

9. The method according to claim 1, wherein the volume of the water added for crystallization in the step 3) is 4-6 times of the volume of the residual reaction solution, and the crystallization temperature is 10-20 ℃.

10. The method of claim 1, further comprising the following refining steps: dissolving the product obtained in the step 3) with 4-8N hydrochloric acid solution at room temperature, adding water, crystallizing at 10-20 ℃ to obtain a product, filtering, washing with acetone, and drying.

Technical Field

The invention relates to the field of pharmaceutical chemistry, in particular to a preparation method of bendamustine hydrochloride raw material medicine.

Background

Bendamustine hydrochloride is a bifunctional alkylating agent with a new action mechanism, and has the effects of resisting tumors and killing cells. It was first developed by Ozegowski and coworkers at the society for testing microorganisms at yera university, germany in the early 60 s of the 19 th century. The main mechanism is that the single strand and the double strand of DNA are crosslinked through alkylation, the function of the DNA and the synthesis of the DNA are disturbed, and the crosslinking between the DNA and the protein and between the protein and the protein are generated, thereby playing the role of anti-tumor. The bendamustine hydrochloride injection is used for treating malignant tumors such as Hodgkin's disease, non-Hodgkin's lymphoma, plasmacytoma (multiple myeloma), Chronic Lymphocytic Leukemia (CLL), breast cancer and the like by alone or in combination with other anti-tumor drugs.

Chemical name of bendamustine hydrochloride: 4- [5- [ bis (2-chloroethyl) amino]-1-methylbenzimidazol-2-yl]Butyric acid hydrochloride of formula C₁₆H₂₂Cl₃N₃O₂The structural formula is as follows:

the Chinese New drug journal (2007, 16 vol 23, 1960-:

the synthesis route of bendamustine hydrochloride disclosed in the prior art mostly takes the intermediate 5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate in the route as a starting material, and the starting material reacts with oxirane ring, and the obtained product is subjected to chlorination reaction with a chlorinating reagent and then is hydrolyzed by hydrochloric acid to generate the bendamustine hydrochloride.

For example, CN 101691359B discloses a method for preparing bendamustine hydrochloride by performing substitution reaction of 5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate with ethylene oxide and phosphorus oxychloride in sequence, hydrolysis to form salt, and refining. CN101948436B discloses a method for preparing a bendamustine hydrochloride crude product by reacting 5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate with oxirane ring, purifying an intermediate by using a C1-4 alkyl acetate solution and C5-8 hydrocarbon, performing chlorination reaction with thionyl chloride, hydrolyzing concentrated hydrochloric acid to form salt and purifying.

However, when the chlorinating agent is phosphorus oxychloride, the chlorination reaction of the phosphorus oxychloride is characterized by high-temperature induced reaction, so that a sudden violent reaction occurs in the reaction process, danger is easy to occur, particularly, when the workshop is used for large-scale production, the danger is increased, and the requirement on equipment is high, so that the method is not suitable for large-scale production.

Most of chlorination reactions in the prior art use thionyl chloride as a chlorinating agent, and the post-treatment method is to directly concentrate and remove the thionyl chloride. However, tests show that when thionyl chloride is used as a chlorinating agent, the reaction solution is concentrated and dried, and then the product is easily darkened or even carbonized and blackened when exposed to air, so that the color of subsequent products is deepened, more impurities are generated, and the quality of raw material medicine products is affected. Since the concentrated product is oily, the residual thionyl chloride is encapsulated, and the thionyl chloride cannot be completely removed by the concentration method. When the preparation method is used for laboratory scale preparation, the feeding amount is small, most of redundant thionyl chloride is easily removed by a reduced-pressure rotary evaporation method, and the influence of residual trace thionyl chloride on subsequent reaction is small. However, as the amount of the residual thionyl chloride after concentration increases with the increase of the feeding amount and the concentration equipment, the color deepening and the generation of the impurity a inevitably occur, and the more the residual thionyl chloride, the darker the product color, and the larger the generated impurity a. The structure of the impurity a is confirmed to be:

from the structural analysis, the impurity a may be thionyl chloride and derivatives thereof which are generated as byproducts in the subsequent hydrolysis reaction and react with the product at high temperature.

In addition, during the hydrolysis reaction, bendamustine hydrochloride is generated by the hydrolysis reaction of concentrated hydrochloric acid, and bendamustine easily generates an impurity of halogenated hydrocarbon group hydrolysis under alkaline conditions, so the bendamustine cannot be separated and purified by a neutralization extraction mode, and the treatment method for removing the concentrated hydrochloric acid in the prior art mainly adopts a method of concentrating under reduced pressure to be dry. However, it was found experimentally that bendamustine hydrochloride is less stable at high temperatures, and is more unstable especially in the absence of protection from acidic solutions. During the process of concentrating and removing concentrated hydrochloric acid, the product in the reaction solution is easy to react with the impurities of halohydrocarbon hydrolysis at high temperature to generate a dimer impurity b, and the dimer impurity is generated as follows:

the dimer impurity b has poor water solubility, and bendamustine hydrochloride is precipitated simultaneously when water is added for crystallization, so that the removal is difficult, and the product is unqualified. Particularly, in large-scale production, the heating and concentration time is long, and the generated dimer has more impurities, so that qualified products are difficult to obtain after the large-scale production.

Therefore, the prior art is not suitable for production from enlargement to workshops, reaction process conditions need to be further optimized, and the bendamustine hydrochloride raw material medicine with purity and impurities meeting quality standards and qualified color can be prepared on a production scale, so as to further prepare a bendamustine hydrochloride preparation product which can ensure safe use of patients.

Disclosure of Invention

The invention provides a method for synthesizing bendamustine hydrochloride, which can prepare a bendamustine hydrochloride raw material drug with the purity of 99.8 percent and the single impurity content within 0.1 percent under an industrial amplification condition, and has the advantages of mild reaction process conditions, safety, simple and convenient operation and suitability for industrial production.

The preparation method of bendamustine hydrochloride provided by the invention comprises the following steps:

the method is characterized by comprising the following steps:

1) reacting 5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate, namely a compound II, with ethylene oxide to prepare 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate, namely a compound III;

2) dissolving a compound III by using dichloromethane, dropwise adding thionyl chloride to react at room temperature, concentrating the reaction solution to be dry after the reaction is completed, adding a solvent for removing the thionyl chloride, stirring to separate out a solid, and filtering to obtain 4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate, namely a compound IV;

3)4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate is added with concentrated hydrochloric acid for reflux reaction until the reaction is finished, the mixture is cooled and filtered, partial reaction liquid is concentrated and distilled out, water is added for stirring and crystallization, the filtration is carried out, and acetone is washed, thus obtaining the bendamustine hydrochloride.

Wherein, the mol ratio of the [ 1-methyl-2 (4' -ethyl butyrate) -5-amino ] -1H-benzimidazole to the ethylene oxide in the step 1) is 1: 8-15, wherein the reaction solvent is water/glacial acetic acid in a ratio of 1-2: 1, after the reaction is finished, the pH of the reaction solution is adjusted to 7.0-7.3 by using a saturated potassium carbonate solution, the reaction solution is extracted by using dichloromethane, an organic phase is washed by water and then dried, filtered, concentrated, and the concentrate is recrystallized by using ethyl acetate.

The solvent for removing the thionyl chloride in the step 2) is selected from ester solvents including methyl acetate, ethyl acetate and butyl acetate, ketones including acetone and methyl ethyl ketone, and halogenated hydrocarbons including dichloromethane, chloroform, toluene and tetrahydrofuran. Ethyl acetate is the least toxic of the above solvents and is therefore preferred for industrial scale-up production.

In the prior art, when thionyl chloride is used for chlorination reaction, the post-treatment usually adopts a method for removing thionyl chloride by concentration under reduced pressure, and the inventor unexpectedly finds that the product of the step 2) and thionyl chloride can be sufficiently separated by a solvent. The solvent for removing the thionyl chloride in the step 2) of the invention is a solvent which can be mutually soluble with the thionyl chloride, and simultaneously meets the conditions that the solvent does not react with other reaction reagents and products and is mutually insoluble with the reaction products. The inventors have experimentally found that ester solvents including methyl acetate, ethyl acetate and butyl acetate, ketones including acetone and methyl ethyl ketone, halogenated hydrocarbons including dichloromethane and chloroform, and toluene and tetrahydrofuran remove the thionyl chloride remaining after the reaction of step 2). The specific operation is to add the solvent into the reaction concentrate and fully stir the mixture to dissolve the residual thionyl chloride in the solvent, simultaneously separate out a compound IV solid, and filter the mixture to remove the thionyl chloride. The solid precipitation effect and the precipitated solid weight yield of different solvents (the volume of the solvent is 5 times of the mass of the compound III) and the influence on the content of the impurity a in the bendamustine hydrochloride product are examined on a 60g feeding scale, and the experimental results are as follows:

solvent(s)	Whether or not to precipitate a solid	Yield of Compound IV	Product color	The content of impurity a in the product
					N-hexane	Whether or not	-	-	-
Pyridine compound	Whether or not	-	-	-
					DMF	Whether or not	-	-	-
Ethyl acetate	Is that	90.5％	White colour	Not detected out
					Methylene dichloride	Is that	90％	White colour	Not detected out
Acetone (II)	Is that	89％	White colour	Not detected out
					Ethanol	Is that	63％	White colour	Not detected out
Without the use of solvents	-	-	Off-white color	0.25％

According to the results in the table, the crude bendamustine hydrochloride product obtained by continuous synthesis after removing the thionyl chloride by using the solvent does not contain the impurity a, which indicates that the residual thionyl chloride is a main factor influencing the amount and the color depth of the impurity a in the product.

The volume of the solvent for removing the thionyl chloride is 3-8 times, preferably 5 times of the mass of the compound III.

The use volume of the concentrated hydrochloric acid for hydrolysis reaction in the step 3) is 5-20 times, preferably 7-10 times of the mass of the compound IV.

After the hydrolysis reaction, hydrochloric acid in the reaction liquid needs to be concentrated and removed under reduced pressure, and in order to reduce the generation of impurities, particularly dimer impurity b, the method adopts a method for reducing the concentration time, namely a method for removing part of the reaction liquid by reduced pressure distillation and concentration. Since experiments show that the reaction for generating the dimer impurity is reversible, the dimer impurity is generated after the product and the halogenated hydrocarbon hydrolysis impurity in the reaction liquid are higher than a certain concentration at a certain temperature, so that the longer the concentration time is, the less the solvent in the reaction liquid is, and the more the dimer impurity is generated. Therefore, it is considered that the concentration of the reaction solution is stopped when the reaction solution is concentrated to a certain volume. The influence of the residual volume of the concentrated reaction solution (related to the concentration of the concentrated reaction solution and the concentration time) on the dimer impurity b in the reaction solution, the product yield purity and the impurity b content in the product is examined on a 60g feeding scale, and the results are shown in the following table:

according to the experimental results, under the laboratory bench scale, the content of the dimer impurity b in the reaction liquid increases along with the lengthening of the concentration time and the reduction of the volume of the solution left after the concentration, particularly when the reaction liquid is concentrated under reduced pressure and steamed until the residual volume is less than 4 times of the mass of the compound IV, the dimer impurity b in the reaction liquid is greatly increased, and the content of the impurity b in the product obtained by treating and crystallizing the reaction liquid is also greatly increased. If the reaction solution is only concentrated under reduced pressure and steamed until the residual volume is more than 6 times of the mass of the compound IV, the crystallization yield is obviously lower by adding water and the requirement of production cost is not met. The above criteria for concentrating the volume of different solutions on a production scale (600g batch size) were further examined according to the bench test results, which are shown in the following table:

from the above results, it can be seen that when the feed scale is enlarged, the dimer impurity b generated in the reaction solution is more significant than that generated in the lab bench scale under the condition of the same ratio of the concentration volume to the feed amount. However, similarly, when the reaction solution is concentrated and distilled under reduced pressure until the residual volume is 4 times of the mass of the compound IV, the dimer impurity b in the reaction solution and the product is greatly increased, and when the reaction solution is concentrated and distilled under reduced pressure until the residual volume is more than 6 times of the mass of the compound IV, the crystallization yield by adding water is obviously lower. Therefore, under the amplification scale of 600g, when the mass ratio of the residual volume of the reaction solution after reduced pressure concentration to the compound IV is 4-6 times, the purity of the prepared product can still reach more than 99.6%, the content of the impurity b in the product is below 0.25%, and the yield reaches more than 75%.

Therefore, the part of the reaction liquid distilled off in the step 3) is specifically distilled off until the residual volume of the reaction liquid is 4-6 times of the mass of the compound IV. And after concentration, adding water into the reaction solution for crystallization, wherein the volume of the water added for crystallization is 4-6 times of the volume of the residual reaction solution, and the crystallization temperature is 10-20 ℃.

The preparation method of the moxidectin hydrochloride can also comprise a refining step, and the product can be refined by a refining method in the prior art, such as a hydrochloric acid-water solvent system or a crystallization method, so that the purity and the impurity content of the product reach higher quality standards. The preferred refining method is as follows: dissolving the product obtained in the step 3) with 4-8N hydrochloric acid solution at room temperature, adding water, crystallizing at 10-20 ℃ to obtain a product, filtering, washing with acetone, and drying.

The invention provides a method for synthesizing bendamustine hydrochloride, which utilizes a proper solvent to remove residual thionyl chloride in chlorination reaction, evaporates and removes partial reaction liquid after hydrolysis reaction, and then adds water for crystallization, thus obviously reducing the generation of impurities, improving the purity of products and improving the color of products. By adopting the method, the pure white bendamustine hydrochloride product with the purity of more than 99.6 percent and single impurity of less than 0.3 percent can be prepared in a laboratory scale and a production scale without refining steps and decoloring operation, the purity of the product after recrystallization refining can reach more than 99.8 percent and the single impurity of less than 0.1 percent, the product meets the quality requirement of national chemical raw material medicines, and qualified raw material medicines can be provided for the research and production of bendamustine hydrochloride for injection. The method has mild reaction conditions, safe and simple operation and is suitable for industrial scale-up production.

The invention is further illustrated by the following examples of specific embodiments.

Detailed Description

Example 1 preparation and refinement of bendamustine hydrochloride (60g Scale)

1) Preparation of ethyl 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } butanoate

Dissolving 5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate (60g, 0.23mol), 600mL of water and 300mL of glacial acetic acid in a 2L reaction bottle by stirring, cooling to-5-0 ℃, adding 120mL of ethylene oxide, and controlling the temperature to react completely. Adjusting pH to 7.0-7.3 with potassium carbonate solution, extracting with dichloromethane (300 mL × 3), combining organic phases, washing with purified water (200 mL × 3), drying over anhydrous magnesium sulfate, filtering, and concentrating to obtain brown solid. And adding 1200mL of ethyl acetate, heating to 70-80 ℃ for dissolution, cooling to room temperature for crystallization, filtering and drying to obtain 63g of light brown solid with the purity of 99.3%. The yield thereof was found to be 78.5%.

2) Preparation of ethyl 4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } butanoate

Dissolving 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate (60g, 0.17mol) in 600mL of dichloromethane in a 2L reaction bottle, cooling to-5-0 ℃, dropwise adding 30mL of thionyl chloride, reacting for 2h at room temperature after finishing dripping, performing vacuum rotary evaporation and concentration on the reaction liquid after complete reaction until the reaction liquid is dried to obtain a brown yellow oily substance, adding 240mL of ethyl acetate, stirring to separate out a solid, filtering, and performing vacuum drying to obtain 60g of a light gray solid. The yield thereof was found to be 90.5%.

3) Preparation of bendamustine hydrochloride

And adding 60g of solid obtained in the last step and 600mL of concentrated hydrochloric acid into a reaction bottle with tail gas absorption, heating and refluxing for reaction for 4h, cooling to room temperature after the reaction is finished, filtering to obtain light yellow reaction liquid, concentrating under reduced pressure until the volume of the reaction liquid is about 360mL, stopping concentrating, adding water with the volume 4 times of the residual volume, crystallizing at 10-20 ℃, filtering, washing with 300mL of acetone, filtering and drying to obtain 46.6g of white solid with the yield of 76%. The purity is 99.9 percent, the maximum single impurity content is 0.05 percent, and the impurities a and b are not detected by High Performance Liquid Chromatography (HPLC).

4) Recrystallization refining

Adding 40g of the crude product into 80mL of 6N hydrochloric acid solution, stirring and dissolving at room temperature, filtering, adding 400mL of water, stirring and crystallizing at 10-20 ℃ for 1-3h, filtering, washing with 200mL of acetone, filtering, and drying to obtain 33g of white bendamustine hydrochloride finished product with the yield of 82.5%. The purity is 99.96 percent and the maximum single impurity content is 0.02 percent by High Performance Liquid Chromatography (HPLC) detection.

Example 2 preparation of bendamustine hydrochloride (60g scale)

1) Preparation of ethyl 4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } butanoate

Dissolving 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate (60g, 0.17mol) prepared by the method in the step (1) in the embodiment 1 in a 2L reaction bottle by using 600mL of dichloromethane, cooling to-5-0 ℃, dropwise adding 30mL of thionyl chloride, reacting at room temperature for 2 hours after dropwise adding, performing vacuum rotary evaporation and concentration on the reaction liquid after complete reaction until the reaction liquid is dried to obtain a brown yellow oily substance, adding 300mL of dichloromethane, stirring to separate out a solid, and performing vacuum drying to obtain 61g of a light gray solid. The yield thereof was found to be 92%.

2) Preparation of bendamustine hydrochloride

And adding 60g of solid obtained in the last step and 600mL of concentrated hydrochloric acid into a reaction bottle with tail gas absorption, heating and refluxing for reaction for 4h, cooling to room temperature after the reaction is finished, filtering to obtain light yellow reaction liquid, concentrating under reduced pressure until the volume of the reaction liquid is about 300mL, stopping concentrating, adding water with the volume 5 times of the residual volume, crystallizing at 10-20 ℃, filtering, washing with acetone, filtering and drying to obtain 48.5g of white solid, wherein the yield is 79.1%. The purity is 99.87% by High Performance Liquid Chromatography (HPLC), the maximum single impurity content is 0.08% of impurity b, and impurity a is not detected.

Example 3 preparation of bendamustine hydrochloride (60g scale)

1) Preparation of ethyl 4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } butanoate

Dissolving 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate (60g, 0.17mol) prepared by the method in the step (1) in the embodiment 1 in a 2L reaction bottle by using 600mL of dichloromethane, cooling to-5-0 ℃, dropwise adding 30mL of thionyl chloride, reacting at room temperature for 2 hours after dropwise adding, performing vacuum rotary evaporation and concentration on the reaction liquid after complete reaction until the reaction liquid is dried to obtain a brown yellow oily substance, adding 360mL of acetone, stirring to separate out a solid, and performing vacuum drying to obtain 59g of a light gray solid. The yield thereof was found to be 89.5%.

2) Preparation of bendamustine hydrochloride

And adding 59g of solid obtained in the previous step and 600mL of concentrated hydrochloric acid into a reaction bottle with tail gas absorption, heating and refluxing for reaction for 4 hours, cooling to room temperature after the reaction is finished, filtering to obtain light yellow reaction liquid, concentrating under reduced pressure until the volume of the reaction liquid is about 240mL, stopping concentrating, adding water with the volume 5 times of the residual volume, crystallizing at 10-20 ℃, filtering, washing with acetone, filtering and drying to obtain 50g of white solid with the yield of 83%. The purity is 99.78% by High Performance Liquid Chromatography (HPLC), the maximum single impurity, namely the content of the impurity b is 0.11%, and the impurity a is not detected.

Example 4 preparation and refinement of bendamustine hydrochloride (600g Scale)

1) Preparation of ethyl 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } butanoate

Stirring and dissolving 5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate (600g,2.3mol), 6L of water and 3L of glacial acetic acid in a 20L reaction bottle, cooling to-5-0 ℃, adding 1200mL of ethylene oxide, and controlling the temperature to react completely. Adjusting pH to 7.0-7.3 with potassium carbonate solution, extracting with dichloromethane 3L × 3, mixing organic phases, washing with purified water 2L × 3, drying with anhydrous magnesium sulfate, filtering, and concentrating by rotary evaporation to obtain brown solid. Then adding 12L of ethyl acetate, heating to 70-80 ℃ for dissolution, cooling to room temperature for crystallization, filtering and drying to obtain 615g of light brown solid with the purity of 99.2% and the yield of 76.6%.

2) Preparation of ethyl 4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } butanoate

Dissolving 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate (600g, 1.7mol) in 6.0L of dichloromethane in a 10L reaction bottle, cooling to-5-0 ℃, dropwise adding 300mL of thionyl chloride, reacting at room temperature for 2h after dropwise addition, performing vacuum rotary evaporation and concentration on the reaction liquid until the reaction liquid is dried to obtain a brown yellow oily substance, adding 3L of ethyl acetate, stirring to separate out a solid, filtering, and performing vacuum drying to obtain 590g of a light gray solid, wherein the yield is 89%.

3) Preparation of bendamustine hydrochloride

And adding the 590 solid obtained in the last step and 5.9L of concentrated hydrochloric acid into a 10L reaction bottle with tail gas absorption, heating and refluxing for reaction for 4 hours, cooling to room temperature after the reaction is finished, filtering to obtain a light yellow reaction liquid, concentrating under reduced pressure until the volume of the reaction liquid is about 3.54L, stopping concentrating, adding water with the volume of 4 times of the residual volume, crystallizing at 10-20 ℃, filtering, washing with acetone, filtering and drying to obtain 481g of a white solid, wherein the yield is 79.8%. HPLC detection shows that the purity is 99.80%, the maximum single impurity, namely the impurity b content is 0.12%, and the impurity a is not detected.

4) Recrystallization refining

Adding 900mL of 6N hydrochloric acid solution into 450g of crude product, stirring and dissolving at room temperature, performing membrane filtration, adding 4.5L of water, stirring and crystallizing at 10-20 ℃ for 1-3h, filtering to obtain a product, washing with 2.5L of acetone, filtering and drying to obtain 372.5g of white bendamustine hydrochloride finished product, wherein the total yield is 81%. The purity is 99.91% and the maximum single impurity content is 0.04% by High Performance Liquid Chromatography (HPLC) detection.

Example 5 preparation and refinement of bendamustine hydrochloride (6kg scale)

1) Preparation of ethyl 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } butanoate

5-amino-1-methyl-1H-2-benzimidazole ethyl butyrate (6.0kg, 23mol), 60L of water and 30L of glacial acetic acid are stirred and dissolved in a 200L reaction kettle, cooled to-5-0 ℃, added with 12.0L of ethylene oxide, and subjected to temperature control reaction until the reaction is complete. Adjusting pH to 7.0-7.3 with potassium carbonate solution, extracting with dichloromethane (30L × 3), mixing organic phases, washing with purified water (20L × 3), drying with anhydrous magnesium sulfate, filtering, and concentrating by rotary evaporation to obtain brown solid. Then adding 120L ethyl acetate, heating to 70-80 ℃ for dissolution, cooling to room temperature for crystallization, filtering and drying to obtain 5960g of light brown solid with the purity of 99.0% and the yield of 74.3%.

2) Preparation of ethyl 4- {5- [ bis- (2-chloroethyl) amino ] -1-methyl-2-benzimidazole } butanoate

Dissolving 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate (5900g,16.88mol) in 59L dichloromethane in a 100L reaction kettle, cooling to-5-0 ℃, dropwise adding 2950mL of thionyl chloride, reacting for 2h at room temperature after dropwise adding, performing vacuum rotary evaporation and concentration on the reaction liquid until the reaction liquid is dried to obtain a brown yellow oily substance, adding 30L ethyl acetate, stirring to separate out a solid, and filtering to obtain 5800g of a light gray solid with the yield of 89%.

3) Preparation of bendamustine hydrochloride

Adding 5800g of solid obtained in the previous step and 58L of concentrated hydrochloric acid into a 100L reaction kettle with tail gas absorption, heating and refluxing for 4h, cooling to room temperature after the reaction is finished, filtering to obtain light yellow reaction liquid, concentrating under reduced pressure until the volume of the reaction liquid is about 34.8L, stopping concentrating, adding water with the volume of 4 times of the residual volume, crystallizing at 10-20 ℃, filtering, washing with 30L of acetone, filtering and drying to obtain 4669g of white solid with the yield of 78.8%. HPLC detection shows that the purity is 99.60%, the maximum single impurity, namely the content of the impurity b is 0.2%, and the content of the impurity a is 0.12%.

4) Recrystallization refining

4500g of the crude product is added with 9000mL of 6N hydrochloric acid solution, stirred and dissolved at room temperature, filtered, added with 45L of water, stirred and crystallized at 10-20 ℃ for 1-3h, centrifugally filtered, washed with 25L of acetone, and dried to obtain 3689g of white bendamustine hydrochloride finished product with yield of 80.2%. The purity is 99.85% and the maximum single impurity content is 0.08% by High Performance Liquid Chromatography (HPLC) detection.

COMPARATIVE EXAMPLE 1 CN101948436B preparation of bendamustine hydrochloride (60g Scale)

Dissolving 4- {5- [ bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate (60g, 0.17mol) prepared by the method in the step (1) in the embodiment 1 in a 5L reaction bottle by using 1000mL of dichloromethane, cooling to-5-0 ℃, dropwise adding 30mL of thionyl chloride, reacting at room temperature for 2h after dropwise adding, and performing vacuum rotary evaporation and concentration on the reaction liquid until the reaction liquid is dried to obtain a brown yellow oily substance. Adding 600mL of concentrated hydrochloric acid, heating and refluxing for reaction for 4h, cooling to room temperature, adding a proper amount of activated carbon for decolorization, filtering, concentrating under reduced pressure to obtain a reddish brown oily substance, adding 3L of water, crystallizing at 10-20 ℃, filtering, washing with 300mL of acetone, filtering and drying to obtain 52g of off-white solid with the yield of 76.7%. The purity is 98.2 percent, the maximum single impurity b content is 0.95 percent, and the impurity a content is 0.25 percent by High Performance Liquid Chromatography (HPLC) detection.

Comparative example 2 CN101948436B Process Scale preparation of bendamustine hydrochloride (6kg Scale)

Dissolving 4- {5- [ -bis- (2-hydroxyethyl) amino ] -1-methyl-2-benzimidazole } ethyl butyrate (6000g, 17mol) prepared by the method of the step 1) in a 100L reaction kettle by using 60L dichloromethane, cooling to-5-0 ℃, dropwise adding 3000mL of thionyl chloride, reacting at room temperature for 2h after dropwise adding, and concentrating the reaction liquid in vacuum until the reaction liquid is dried to obtain a brown yellow oily substance. Adding 60L of concentrated hydrochloric acid, heating and refluxing for reaction for 4h, cooling to room temperature, adding a proper amount of activated carbon for decolorization, filtering, concentrating under reduced pressure to obtain a reddish brown oily substance, adding 30L of water, crystallizing at 10-20 ℃, centrifuging, filtering, washing with 30L of acetone, filtering and drying to obtain 4500g of off-white solid, wherein the yield is 66.4%. The purity is 95.4 percent, the maximum single impurity, namely the content of the impurity b is 2.3 percent, and the content of the impurity a is 1.5 percent through High Performance Liquid Chromatography (HPLC) detection.