Preparation method of nefopam N-oxide

Abstract

The invention belongs to the technical field of medicinal chemistry, and particularly relates to a preparation method of nefopam N-oxide. Alkali, water and acetonitrile are stirred and dissolved, nefopam hydrochloride is added and stirred and dissolved, and a mixed solution is obtained; cooling the mixed solution, dropwise adding an oxidizing agent, and continuously carrying out heat preservation reaction after dropwise adding; after the heat preservation reaction is completed, adding a sodium thiosulfate solution to terminate the reaction, adding acid to adjust the pH value, and then adding a solvent for extraction to obtain an extracting solution; adding a drying agent into the extracting solution, drying, filtering, and concentrating under reduced pressure to obtain a concentrate; adding acetone into the concentrate for dissolving, cooling, crystallizing, filtering, washing and drying to obtain nefopam N-oxide. The nefopam N-oxide prepared by the invention has high purity, and can be used as a reference substance in the processes of process research, quality research, prescription research, metabolism research and the like of nefopam hydrochloride products.

Description

Technical Field

[0001] This invention belongs to the field of medicinal chemistry technology, specifically relating to a method for preparing nefopam N-oxide. Background Technology

[0002] Nefopam hydrochloride, chemically known as 5-methyl-1-phenyl-3,4,5,6-tetrahydro-1H-2,5-oxobenzoxine hydrochloride, is a novel non-narcotic analgesic with mild antipyretic and muscle relaxant effects. This drug blocks voltage-sensitive sodium channels (IC50 = 27 µM) and regulates glutamate transmission in rodents, therefore it does not possess the characteristics of nonsteroidal anti-inflammatory drugs (NSAIDs) and is not an opioid receptor agonist. Nefopam hydrochloride is effective in suppressing moderate to severe pain, has mild respiratory depression, no circulatory system depression, and no tolerance or dependence. Therefore, it is commonly used to suppress postoperative pain, cancer pain, acute traumatic pain, and visceral smooth muscle colic such as acute gastritis, biliary ascariasis, and ureteral stones.

[0003] The study *Pharmacokinetics, metabolism, and excretion of nefopam, a dualreuptake inhibitor in healthy male volunteers*, Madhu Sanga et al. *Xenobiotica* (2016), 46(11), 1001-1016, investigated the metabolism, excretion, and pharmacokinetics of nefopam in healthy male volunteers, focusing on the pharmacokinetics of its two main metabolites, nornefopam and nefopam N-oxide. The study *Biotransformation of nefopam (Ajan), I: Isolation and identification of the main metabolite and other metabolites*, Ebel, Siegfried et al. *Archiv der Pharmazie* (Weinheim, Germany) (1978), 311(6), 547-52, investigated how to isolate and characterize nefopam metabolites from urine. The study showed that isolating nefopam metabolites from urine is not only very difficult but also extremely labor-intensive.

[0004] To further investigate the metabolism of nefopam hydrochloride, it is necessary to study its metabolites. If nefopam hydrochloride metabolites can be prepared, they can serve as reference standards. On the one hand, this allows for better qualitative and quantitative studies of the various metabolic processes of nefopam hydrochloride; on the other hand, nefopam metabolites can play an important role in drug development, process improvement, and formulation research related to nefopam hydrochloride.

[0005] Currently, there are few reports on the preparation of nefopa N-oxide. Nefopa N-oxide reference standards are generally isolated and purified from excrement, but the price is extremely high. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing nefopam N-oxide. The nefopam N-oxide prepared by this method has high purity and can be used as a reference standard in the process research, quality research, formulation research and metabolism research of nefopam products. This method is economical and environmentally friendly, the process is stable and highly operable.

[0007] The method for preparing nefopam N-oxide according to the present invention includes the following steps: (1) Dissolve the alkali, water and acetonitrile by stirring, then add nefopam hydrochloride and stir to dissolve, to obtain a mixed solution; (2) After the mixture is cooled down, add the oxidant dropwise, and continue to keep the reaction at the temperature after the addition is complete; (3) After the heat preservation reaction is completed, sodium thiosulfate solution is added to terminate the reaction, acid is added to adjust the pH, and then solvent is added to extract the extract. (4) The extract was dried with a desiccant, filtered, and concentrated under reduced pressure to obtain the concentrate; (5) The concentrate was dissolved in acetone, cooled and crystallized, filtered, washed and dried to obtain nefopa N-oxide.

[0008] In step (1), the alkali is sodium hydroxide or potassium hydroxide.

[0009] In step (1), the molar ratio of nefopam hydrochloride to alkali is 1:2.0 to 3.0; the ratio of nefopam hydrochloride, water and acetonitrile is 1:2 to 4:4 to 8, where nefopam hydrochloride is expressed in g and water and acetonitrile are expressed in ml.

[0010] In step (2), the oxidant is sodium hypochlorite solution with a concentration of 0.092 g / ml. The molar ratio of sodium hypochlorite in the sodium hypochlorite solution to nefopam hydrochloride in step (1) is 1.05 to 1.15:1.

[0011] In step (2), the temperature is lowered to -10 to 5℃, the temperature at which the oxidant is added is -10 to 5℃, the temperature at which the reaction is kept warm is -10 to 5℃, and the reaction time is 1 to 2 hours.

[0012] In step (3), the concentration of sodium thiosulfate solution is 0.10 g / ml.

[0013] In step (3), the acid is acetic acid or hydrochloric acid, the solvent is dichloromethane or ethyl acetate, and the pH is adjusted to 7.0-8.0.

[0014] In step (4), the desiccant is anhydrous magnesium sulfate or anhydrous sodium sulfate.

[0015] The temperature for vacuum concentration in step (4) is 50-60℃.

[0016] In step (5), the ratio of acetone to nefopam hydrochloride in step (1) is 4 to 8:1, where nefopam hydrochloride is expressed in g and acetone in ml.

[0017] In step (5), the dissolution temperature is 50-55℃, the cooling temperature is 0-5℃, and the crystallization time is 1-2 hours.

[0018] The reaction route of this invention is as follows:

[0019] This invention uses nefopam hydrochloride as the starting material, oxidizes it under alkaline conditions, and then extracts, dries, concentrates and crystallizes it to obtain nefopam N-oxide.

[0020] The beneficial effects of this invention are as follows: (1) The nefopam N-oxide prepared by this invention has high purity and can be used as a reference for process research, quality research, formulation research and metabolism research of nefopam hydrochloride products.

[0021] (2) The raw materials and reagents used in this invention are commercially available and inexpensive, making it economical and environmentally friendly.

[0022] (3) The process of the present invention is stable and highly operable. Attached Figure Description

[0023] Figure 1 This is the HPLC spectrum of nefopa N-oxide from Example 1. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below with reference to examples.

[0025] Example 1 (1) Add 0.69g sodium hydroxide, 6ml water and 12ml acetonitrile to the reaction flask and stir to dissolve; then add 2.0g nefopam hydrochloride and stir to dissolve to obtain a mixture; (2) Cool the mixture to -5 to 0℃, and add 6.2 ml of sodium hypochlorite solution (concentration: 0.092 g / ml) dropwise while keeping it at -5 to 0℃. After the addition is complete, keep the mixture at -5 to 0℃ for 1 hour. (3) After the heat preservation reaction is completed, add 11.4 ml of sodium thiosulfate solution (concentration: 0.10 g / ml) and stir for 10 minutes; add acetic acid dropwise to adjust the pH to 7.0-8.0; add 20 ml of dichloromethane, stir, let stand to separate the layers, separate the organic layer, extract the aqueous layer twice with 20 ml × 2 dichloromethane, combine the organic layers, wash once with 20 ml of water to obtain the extract; (4) Add 6.0 g of anhydrous magnesium sulfate to the extract, stir and dry for 1 hour, filter to remove anhydrous magnesium sulfate, and obtain filtrate and filter cake. Wash the filter cake with a small amount of dichloromethane to obtain washing liquid. Combine the washing liquid and filtrate and concentrate under reduced pressure at 55°C until there is basically no distillate to obtain concentrate. (5) Add 12 ml of acetone to the concentrate, stir to dissolve at 50-55 °C, slowly cool to crystallize, cool to 0-5 °C and continue stirring to crystallize for 1.5 hours; filter, wash the filter cake with a small amount of cold acetone, and dry the filter cake under reduced pressure at 50 °C to obtain nefopam N-oxide with an HPLC purity of 95.19%. The HPLC results are shown in [Figure number missing]. Figure 1 See Table 1.

[0026] Table 1 Chromatographic Peak Results

[0027] Example 2 (1) Add 0.55g sodium hydroxide, 4ml water and 8ml acetonitrile to the reaction flask and stir to dissolve; then add 2.0g nefopam hydrochloride and stir to dissolve to obtain a mixture; (2) Cool the mixture to -5 to 0℃, and add 5.9 ml of sodium hypochlorite solution (concentration: 0.092 g / ml) dropwise while keeping it at -5 to 0℃. After the addition is complete, keep the mixture at -5 to 0℃ for 1.5 hours. (3) After the heat preservation reaction is completed, add 11.4 ml of sodium thiosulfate solution (concentration: 0.10 g / ml) and stir for 10 minutes; add acetic acid dropwise to adjust the pH to 7.0-8.0; add 20 ml of dichloromethane, stir, let stand to separate the layers, separate the organic layer, extract the aqueous layer twice with 20 ml × 2 dichloromethane, combine the organic layers, wash once with 20 ml of water to obtain the extract; (4) Add 6.0 g of anhydrous magnesium sulfate to the extract, stir and dry for 1 hour, filter to remove anhydrous magnesium sulfate, and obtain filtrate and filter cake. Wash the filter cake with a small amount of dichloromethane to obtain washing liquid. Combine the washing liquid and filtrate and concentrate under reduced pressure at 60°C until there is basically no distillate to obtain concentrate. (5) Add 8 ml of acetone to the concentrate, stir to dissolve at 50-55℃, slowly cool down to crystallize, cool to 0-5℃ and continue stirring to crystallize for 1 hour; filter, wash the filter cake with a small amount of cold acetone, dry the filter cake under reduced pressure at 50℃ to obtain nefopam N-oxide with HPLC purity of 95.05%.

[0028] Example 3 (1) Add 0.83g sodium hydroxide, 8ml water and 16ml acetonitrile to the reaction flask and stir to dissolve; then add 2.0g nefopam hydrochloride and stir to dissolve to obtain a mixture; (2) Cool the mixture to -5 to 0℃, and add 6.4 ml of sodium hypochlorite solution (concentration: 0.092 g / ml) dropwise while keeping it at -5 to 0℃. After the addition is complete, keep it at -5 to 0℃ for 1.5 hours. (3) After the heat preservation reaction is completed, add 11.4 ml of sodium thiosulfate solution (concentration: 0.10 g / ml) and stir for 10 minutes; add acetic acid dropwise to adjust the pH to 7.0-8.0; add 20 ml of dichloromethane, stir, let stand to separate the layers, separate the organic layer, extract the aqueous layer twice with 20 ml × 2 dichloromethane, combine the organic layers, wash once with 20 ml of water to obtain the extract; (4) Add 6.0 g of anhydrous magnesium sulfate to the extract, stir and dry for 1 hour, filter to remove anhydrous magnesium sulfate, and obtain filtrate and filter cake. Wash the filter cake with a small amount of dichloromethane to obtain washing liquid. Combine the washing liquid and filtrate and concentrate under reduced pressure at 55°C until there is basically no distillate to obtain concentrate. (5) Add 16 ml of acetone to the concentrate, stir to dissolve at 50-55°C, slowly cool down to crystallize, cool to 0-5°C and continue stirring to crystallize for 1.5 hours; filter, wash the filter cake with a small amount of cold acetone, dry the filter cake under reduced pressure at 50°C to obtain nefopam N-oxide with HPLC purity of 95.38%.

[0029] Example 4 (1) Add 0.69g sodium hydroxide, 6ml water and 12ml acetonitrile to the reaction flask and stir to dissolve; then add 2.0g nefopam hydrochloride and stir to dissolve to obtain a mixture; (2) Cool the mixture to -10 to -5℃, and add 6.2 ml of sodium hypochlorite solution (concentration: 0.092 g / ml) dropwise while keeping it at -10 to -5℃. After the addition is complete, keep the mixture at -10 to -5℃ for 2 hours. (3) After the heat preservation reaction is completed, add 11.4 ml of sodium thiosulfate solution (concentration: 0.10 g / ml) and stir for 10 minutes; add acetic acid dropwise to adjust the pH to 7.0-8.0; add 20 ml of dichloromethane, stir, let stand to separate the layers, separate the organic layer, extract the aqueous layer twice with 20 ml × 2 dichloromethane, combine the organic layers, wash once with 20 ml of water to obtain the extract; (4) Add 6.0 g of anhydrous sodium sulfate to the extract, stir and dry for 1 hour, filter to remove anhydrous magnesium sulfate, and obtain filtrate and filter cake. Wash the filter cake with a small amount of dichloromethane to obtain washing liquid. Combine the washing liquid and filtrate and concentrate under reduced pressure at 50°C until there is basically no distillate to obtain concentrate. (5) Add 12 ml of acetone to the concentrate, stir to dissolve at 50-55℃, slowly cool down to crystallize, cool to 0-5℃ and continue stirring to crystallize for 2 hours; filter, wash the filter cake with a small amount of cold acetone, dry the filter cake under reduced pressure at 50℃ to obtain nefopam N-oxide with HPLC purity of 95.29%.

[0030] Example 5 (1) Add 0.69g sodium hydroxide, 6ml water and 12ml acetonitrile to the reaction flask and stir to dissolve; then add 2.0g nefopam hydrochloride and stir to dissolve to obtain a mixture; (2) Cool the mixture to 0-5℃, keep it at 0-5℃ and add 6.2ml of sodium hypochlorite solution (concentration: 0.092g / ml) dropwise. After adding, keep it at 0-5℃ and react for 1 hour. (3) After the heat preservation reaction is completed, add 11.4 ml of sodium thiosulfate solution (concentration: 0.10 g / ml) and stir for 10 minutes; add hydrochloric acid solution dropwise to adjust the pH to 7.0-8.0; add 20 ml of dichloromethane, stir, let stand to separate the layers, separate the organic layer, extract the aqueous layer twice with 20 ml × 2 dichloromethane, combine the organic layers, wash once with 20 ml of water to obtain the extract; (4) Add 6.0 g of anhydrous sodium sulfate to the extract, stir and dry for 1 hour, filter to remove anhydrous magnesium sulfate, and obtain filtrate and filter cake. Wash the filter cake with a small amount of dichloromethane to obtain washing liquid. Combine the washing liquid and filtrate and concentrate under reduced pressure at 50°C until there is basically no distillate to obtain concentrate. (5) Add 8 ml of acetone to the concentrate, stir to dissolve at 50-55℃, slowly cool down to crystallize, cool to 0-5℃ and continue stirring to crystallize for 1.5 hours; filter, wash the filter cake with a small amount of cold acetone, dry the filter cake under reduced pressure at 50℃ to obtain nefopam N-oxide with HPLC purity of 95.06%.

[0031] Example 6 (1) Add 0.97g potassium hydroxide, 6ml water and 12ml acetonitrile to the reaction flask and stir to dissolve; then add 2.0g nefopam hydrochloride and stir to dissolve to obtain a mixture; (2) Cool the mixture to -5 to 0℃, and add 6.2 ml of sodium hypochlorite solution (concentration: 0.092 g / ml) dropwise while keeping it at -5 to 0℃. After the addition is complete, keep the mixture at -5 to 0℃ for 1.5 hours. (3) After the heat preservation reaction is completed, add 11.4 ml of sodium thiosulfate solution (concentration: 0.10 g / ml) and stir for 10 minutes; add acetic acid dropwise to adjust the pH to 7.0-8.0; add 20 ml of ethyl acetate, stir, let stand to separate the layers, separate the organic layer, extract the aqueous layer twice with 20 ml × 2 ethyl acetate, combine the organic layers, wash once with 20 ml of water to obtain the extract; (4) Add 6.0 g of anhydrous magnesium sulfate to the extract, stir and dry for 1 hour, filter to remove anhydrous magnesium sulfate, and obtain filtrate and filter cake. Wash the filter cake with a small amount of dichloromethane to obtain washing liquid. Combine the washing liquid and filtrate and concentrate under reduced pressure at 60°C until there is basically no distillate to obtain concentrate. (5) Add 12 ml of acetone to the concentrate, stir to dissolve at 50-55℃, slowly cool down to crystallize, cool to 0-5℃ and continue stirring to crystallize for 1 hour; filter, wash the filter cake with a small amount of cold acetone, dry the filter cake under reduced pressure at 50℃ to obtain nefopam N-oxide with HPLC purity of 95.09%.

[0032] Example 7 (1) Add 1.01g potassium hydroxide, 8ml water and 16ml acetonitrile to the reaction flask and stir to dissolve; then add 2.0g nefopam hydrochloride and stir to dissolve to obtain a mixture; (2) Cool the mixture to 0-5℃, keep it at 0-5℃ and add 6.4ml of sodium hypochlorite solution (concentration: 0.092g / ml) dropwise. After adding, keep it at 0-5℃ and react for 1 hour. (3) After the heat preservation reaction is completed, add 11.4 ml of sodium thiosulfate solution (concentration: 0.10 g / ml) and stir for 10 minutes; add acetic acid dropwise to adjust the pH to 7.0-8.0; add 20 ml of ethyl acetate, stir, let stand to separate the layers, separate the organic layer, extract the aqueous layer twice with 20 ml × 2 ethyl acetate, combine the organic layers, wash once with 20 ml of water to obtain the extract; (4) Add 6.0 g of anhydrous magnesium sulfate to the extract, stir and dry for 1 hour, filter to remove anhydrous magnesium sulfate, and obtain filtrate and filter cake. Wash the filter cake with a small amount of dichloromethane to obtain washing liquid. Combine the washing liquid and filtrate and concentrate under reduced pressure at 60°C until there is basically no distillate to obtain concentrate. (5) Add 16 ml of acetone to the concentrate, stir to dissolve at 50-55°C, slowly cool down to crystallize, cool to 0-5°C and continue stirring to crystallize for 2 hours; filter, wash the filter cake with a small amount of cold acetone, and dry the filter cake under reduced pressure at 50°C to obtain nefopam N-oxide with an HPLC purity of 95.07%.

[0033] Detection of degradation impurities, nefopam N-oxide, in nefopam hydrochloride injection: Using the nefopa N-oxide prepared in Example 1 as a reference, the content of degradation impurity nefopa N-oxide in nefopa hydrochloride injection was detected.

[0034] Detection method: Determined according to high performance liquid chromatography (Chinese Pharmacopoeia 2020 Edition, Part IV, General Chapter 0512).

[0035] Test solution: Accurately measure an appropriate amount of nefopam hydrochloride injection and quantitatively dilute it with the mobile phase to prepare a solution containing approximately 1 mg of nefopam hydrochloride per 1 ml, which is used as the test solution.

[0036] Impurity reference solution: Accurately weigh an appropriate amount of nefopam N-oxide prepared in Example 1, dissolve it in the mobile phase and quantitatively dilute it to prepare a solution containing approximately 2 μg of nefopam N-oxide per 1 ml, which is used as the impurity reference solution.

[0037] Chromatographic conditions: Agilent ZORBAX Eclipse XDB-C18, 4.6 mm × 250 mm, 5 μm or equivalent column; octadecylsilane-bonded silica gel as packing material; methanol-water-triethylamine [(38:62:0.5), pH adjusted to 4.2 with glacial acetic acid] as mobile phase; detection wavelength 267 nm; injection volume 20 μl.

[0038] Determination method: Accurately measure the test solution and impurity reference solution, inject them separately into the liquid chromatograph, and record the chromatograms.

[0039] Test results: The content of nefopa N-oxide, a degradation impurity, was calculated using the external standard method. Six test solutions were tested in parallel, and the content of nefopa N-oxide ranged from 0.00% to 0.02%.

[0040] The method for preparing nefopam N-oxide provided by this invention is economical and environmentally friendly, with stable process. The prepared nefopam N-oxide can be used as a reference standard to achieve effective detection of nefopam N-oxide in nefopam hydrochloride, further strengthening the quality control of nefopam hydrochloride.

[0041] The present invention has been described in detail above with reference to the embodiments, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing nefopa N-oxide, characterized in that... Includes the following steps: (1) Dissolve the alkali, water and acetonitrile by stirring, then add nefopam hydrochloride and stir to dissolve, to obtain a mixed solution; (2) After the mixture is cooled down, add the oxidant dropwise, and continue to keep the reaction at the temperature after the addition is complete; (3) After the heat preservation reaction is completed, sodium thiosulfate solution is added to terminate the reaction, acid is added to adjust the pH, and then solvent is added to extract the extract. (4) The extract was dried with a desiccant, filtered, and concentrated under reduced pressure to obtain the concentrate; (5) The concentrate was dissolved in acetone, cooled and crystallized, filtered, washed and dried to obtain nefopa N-oxide.

2. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (1), the alkali is sodium hydroxide or potassium hydroxide.

3. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (1), the molar ratio of nefopam hydrochloride to alkali is 1:2.0 to 3.0; the ratio of nefopam hydrochloride, water and acetonitrile is 1:2 to 4:4 to 8, where nefopam hydrochloride is expressed in g and water and acetonitrile are expressed in ml.

4. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (2), the oxidant is sodium hypochlorite solution with a concentration of 0.092 g / ml. The molar ratio of sodium hypochlorite in the sodium hypochlorite solution to nefopam hydrochloride in step (1) is 1.05 to 1.15:

1.

5. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (2), the temperature is lowered to -10 to 5℃, the temperature at which the oxidant is added is -10 to 5℃, the temperature at which the reaction is kept warm is -10 to 5℃, and the reaction time is 1 to 2 hours.

6. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (3), the acid is acetic acid or hydrochloric acid, the solvent is dichloromethane or ethyl acetate, and the pH is adjusted to 7.0-8.

0.

7. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (4), the desiccant is anhydrous magnesium sulfate or anhydrous sodium sulfate.

8. The method for preparing nefopam N-oxide according to claim 1, characterized in that, The temperature for vacuum concentration in step (4) is 50-60℃.

9. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (5), the ratio of acetone to nefopam hydrochloride in step (1) is 4 to 8:1, where nefopam hydrochloride is expressed in g and acetone in ml.

10. The method for preparing nefopam N-oxide according to claim 1, characterized in that, In step (5), the dissolution temperature is 50-55℃, the cooling temperature is 0-5℃, and the crystallization time is 1-2 hours.

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