Preparation method of (S)-3-methyl-(2-piperidinylphenyl)-1-butanamine acetylglutamate

Abstract

The present application discloses a preparation method of (S)-3-methyl-(2-piperidinylphenyl)-1-butanamine acetylglutamate, belonging to the field of pharmaceutical chemistry. In the present application, the commonly used solvent DMF in the condensation step is changed to acetonitrile or DMSO to avoid the generation of a large amount of o-dimethylaminobenzonitrile impurities. By changing the solvent of the Grignard addition reaction from toluene to a high-boiling ether solvent, the generation of benzyl impurities is avoided, thereby improving the purity and yield of (S)-3-methyl-(2-piperidinylphenyl)-1-butanamine acetylglutamate. At the same time, with the improvement of other process parameters, the overall yield and product quality of the present application are greatly improved, and the yield of the ragaglamide racemate is much higher than that of the currently reported processes.

Description

Technical Field

[0001] The present application relates to the field of medicinal chemistry, and particularly to a preparation method of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine acetylglutamate. Background Art

[0002] Repaglinide, chemically named (S)-2-ethoxy-4-[2-[[3-methyl-1-[2-(1-piperidinyl)phenyl]butyl]amino]-2-oxoethyl]benzoic acid, has the following structure:

[0003] ;

[0004] It is an oral hypoglycemic drug of methylbenzylamine benzoic acid (CBMA) jointly developed by Novo Nordisk and Boehringer Ingelheim. It was first launched in the United States in 1998 and is mainly used clinically for the treatment of type 2 diabetes. Repaglinide can promote insulin secretion. Its binding site to β-cells is different from that of sulfonylurea drugs such as glimepiride. It has the characteristics of fast absorption, fast onset, and short action time, a relatively high protein binding rate, will not accumulate in tissues, has good safety, and has a synergistic effect with biguanide drugs such as metformin. It can be used alone as a first-line anti-diabetic drug or in combination with other hypoglycemic drugs such as rosiglitazone to increase the efficacy, providing a new means for the treatment of type 2 diabetes.

[0005] (S)-3-Methyl-(2-piperidinophenyl)-1-butanamine glutamate (commonly known as regamine glutamate), as a key intermediate of repaglinide, is obtained by the reaction of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine and glutamate, and has a large market demand. Therefore, it is of great significance to develop a simple, safe, and inexpensive synthesis process. The main representative synthesis routes of regamine or regamine glutamate are as follows:

[0006] There is a method that uses o-chlorobenzaldehyde as a raw material, via an asymmetric allylation reaction, a halogenation reaction, and a configuration inversion reaction with an azide compound, and then obtains the final product regamine through hydrogenation reduction and piperidine substitution. The chiral auxiliary used in this route has a high price, the optical purity of the obtained product is low, and the use of azides is involved, with high danger and is not suitable for industrial production. The reaction route is as shown below:

[0007] .

[0008] There is a method that uses 2-fluorobenzaldehyde as a raw material, which is successively subjected to piperidine substitution, Grignard addition, and oxidation under the action of sodium dichromate and dilute sulfuric acid, and then undergoes reductive amination reaction with formamide and formic acid amide to obtain racemic regamine, with a yield of 28%. The yield of the reductive amination reaction in this method is relatively low. During the process from ketone to amine, a large amount of 3-methyl-1-(2-(1-piperidyl)phenyl)butene by-products are generated, reducing the quality and yield of the product, increasing the cost of separation and purification. The reaction route is as follows:

[0009] 。

[0010] There is a method that uses 2-chlorobenzonitrile as a raw material, condenses with piperidine to obtain an imine through Grignard addition, and then reduces it with sodium borohydride to obtain racemic regamine, and performs chiral resolution to obtain the target product regamine glutamate. Toluene is used as the solvent for Grignard addition. The reagents used in this route have low costs, the raw materials are easily available, and the operation is simple. However, 2-chlorobenzonitrile has low activity, requires high reaction temperature, long reaction time, and high impurities, and the total yield of regamine glutamate obtained is only 30.48%. The reaction route is as follows:

[0011] 。

[0012] In addition, the journal literature ("Synthesis of the Key Intermediate (S)-(+)-3-Methyl-1-[2-(1-piperidyl)phenyl]butylamine of Repaglinide", Chen Huilai et al., Journal of Shenyang Pharmaceutical University, No. 6, 2012) reported that using 2-fluorobenzaldehyde as a raw material, racemic regamine was prepared through 5-step reactions, and then the target product regamine glutamate was obtained through chiral resolution. DMF was used as the solvent for piperidine condensation, and toluene was used as the solvent for Grignard addition. This method also has many impurities and is difficult to remove, and the product yield and purity are relatively low. The reaction route is as follows:

[0013] 。

[0014] When the inventors repeated this method, they unexpectedly found that when DMF was used as the solvent for piperidine condensation, a large amount of 2-dimethylaminobenzonitrile impurities were contained in the product, and when toluene was used as the solvent for Grignard addition, a large amount of benzyl impurities were also generated. Based on this, it is necessary to further optimize the preparation process to avoid the generation of the above impurities, thereby improving the purity and yield of (S)-3-methyl-(2-piperidylphenyl)-1-butylamine acetylglutamate. Summary of the Invention

[0015] Based on this, it is necessary to provide a preparation method of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine acetylglutamate. By changing the commonly used solvent DMF in the condensation step to acetonitrile or DMSO, the generation of a large amount of o-dimethylaminobenzonitrile impurities is avoided. By changing the solvent of the Grignard addition reaction from toluene to a high-boiling ether solvent, the generation of benzyl impurities is avoided, thereby improving the purity and yield of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine acetylglutamate.

[0016] In one aspect of the present application, a preparation method of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine acetylglutamate is provided, including the following steps:

[0017] (1) 2-Fluorobenzonitrile and piperidine are condensed in a first solvent to form o-piperidinophenylbenzonitrile;

[0018] (2) The o-piperidinophenylbenzonitrile and isobutylmagnesium halide undergo a Grignard addition reaction in a second solvent to form regimine;

[0019] (3) The regimine reacts in the presence of a reducing agent to form a racemic mixture of regamine;

[0020] (4) The racemic mixture of regamine reacts with N-acetyl-L-glutamic acid to form (S)-3-methyl-(2-piperidinophenyl)-1-butanamine acetylglutamate;

[0021] The first solvent includes acetonitrile and / or DMSO; the second solvent includes a high-boiling ether solvent; the high-boiling ether solvent includes an ether solvent with a boiling point of 135-200 °C.

[0022] In some embodiments, the high-boiling ether solvent includes at least one of anisole, phenetole, n-butyl ether, isoamyl ether, and n-pentyl ether.

[0023] In some embodiments, the reaction route of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine acetylglutamate is as follows:

[0024] .

[0025] In some embodiments, the preparation of the isobutylmagnesium halide includes the following steps: magnesium, iodine granules, a third solvent, and isobutyl halide are mixed to prepare the isobutylmagnesium halide.

[0026] In some embodiments, the isobutyl halide includes at least one of isobutyl bromide and isobutyl chloride.

[0027] In some embodiments, the third solvent includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran, and methyl tert-butyl ether.

[0028] In some embodiments, in step (1), the temperature of the condensation reaction is 40-90 °C, and the time of the condensation reaction is 15-45 h.

[0029] In some embodiments, the molar ratio of the 2-fluorobenzonitrile to the piperidine is 1:(1.5-2.5).

[0030] In some embodiments, the halogen element in the isobutylmagnesium halide includes at least one of chlorine and bromine.

[0031] In some embodiments, the molar ratio of the o-piperidinylbenzonitrile to the isobutylmagnesium halide is 1:(2-5).

[0032] In some embodiments, the conditions of the Grignard addition reaction include: the reaction temperature is 80-120 °C, and the reaction time is 4-8 h.

[0033] In some embodiments, the reducing agent includes at least one of potassium borohydride, sodium borohydride, and lithium borohydride.

[0034] In some embodiments, the molar ratio of the Gramine and the reducing agent is 1:(2-5).

[0035] In some embodiments, the reaction conditions in step (3) include: the reaction temperature is 20-40 °C, and the reaction time is 1-5 h.

[0036] In some embodiments, the reaction solvent in step (3) includes at least one of methanol and ethanol.

[0037] In some embodiments, the molar ratio of the racemic Gramine to the N-acetyl-L-glutamic acid is 1:(0.8-1.2).

[0038] In some embodiments, after the reaction in step (4) is completed, it further includes a crystallization step; the crystallization temperature is 0-30 °C.

[0039] The beneficial effects of this application are:

[0040] 1. This application changes the commonly used solvent DMF in the condensation step to acetonitrile or DMSO, avoiding the generation of a large amount of o-dimethylaminobenzonitrile impurities, and greatly improving the quality and yield of this step.

[0041] 2. In the Grignard reactions reported in the literature, toluene was used as the material solvent, which reacted with the cyano group to produce a large amount of benzyl impurities that were difficult to remove, seriously affecting the quality and yield. In this application, the material solvent for this step was changed to a high-boiling ether solvent, and such impurities were no longer produced, greatly improving the quality and yield of this step. Further, with the improvement of other process parameters, the overall yield and product quality of this application were greatly improved. The yield of the racemic form of regabamine was much higher than that of the processes reported so far. Moreover, the starting materials selected were easily available and inexpensive, which was conducive to reducing the process cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Liquid chromatogram of o-piperidinobenzonitrile prepared in Basic Example 1;

[0043] Figure 2 Liquid chromatogram of pure (S)-3-methyl-(2-piperidinophenyl)-1-butylamine acetylglutamate prepared in Basic Example 1;

[0044] Figure 3 For Figure 1 Mass spectrum of the component at the retention time of 8.029 min in

[0045] Figure 4 For Figure 2 Mass spectrum of the component at the retention time of 17.454 min in

[0046] Figure 5 Liquid chromatogram of pure (S)-3-methyl-(2-piperidinophenyl)-1-butylamine acetylglutamate prepared in Example 14. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] To facilitate the understanding of this application, the following will describe this application more comprehensively in combination with specific embodiments. Preferred embodiments of this application are given below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of this application more thorough and comprehensive.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0049] In this article, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0050] In this text, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features.

[0051] In the description herein, the meaning of "at least one" is more than one, including one or more than two, such as one, two, three, etc., unless otherwise specifically defined.

[0052] In this text, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0053] In this text, regarding the units of data ranges, if there is only a unit after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 500 - 600 rpm means that the units of the left endpoint "500" and the right endpoint "600" are both rpm (revolutions per minute).

[0054] In this text, for the temperature parameters, unless otherwise specifically limited, both constant temperature treatment and treatment within a certain temperature range are allowed. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.

[0055] In one aspect of the present application, a method for preparing (S)-3-methyl-(2-piperidinylphenyl)-1-butylamine acetylglutamate is provided, comprising the following steps:

[0056] (1) 2-Fluorobenzonitrile is condensed with piperidine in a first solvent to form o-piperidinylbenzonitrile;

[0057] (2) The o-piperidinylbenzonitrile undergoes a Grignard addition reaction with isobutylmagnesium halide in a second solvent to form regimine;

[0058] (3) The regimine reacts in the presence of a reducing agent to form a racemic mixture of regamine;

[0059] (4) The racemic mixture of regamine reacts with N-acetyl-L-glutamic acid to form (S)-3-methyl-(2-piperidinylphenyl)-1-butylamine acetylglutamate;

[0060] The first solvent includes acetonitrile and / or DMSO; the second solvent includes a high-boiling ether solvent; the high-boiling ether solvent includes an ether solvent with a boiling point of 135 - 200 °C.

[0061] In some embodiments, the high-boiling ether solvent includes at least one of anisole, phenetole, n-butyl ether, isoamyl ether, and n-amyl ether.

[0062] It is understandable that the first solvent can be either a single solvent or a combination of different solvents, such as acetonitrile, DMSO, or a combination of acetonitrile and DMSO; similarly, the second solvent can be either a single solvent or a combination of different solvents, such as anisole, n-amyl ether, or a combination of anisole and n-amyl ether.

[0063] It is understandable that the dosages of the first solvent and the second solvent can be adjusted in combination with the reaction effect. For example, the volume-mass ratio of the first solvent to 2-fluorobenzonitrile can be (2-5) mL:1 g, specifically 2 mL:1 g, 2.5 mL:1 g, 3 mL:1 g, 3.4 mL:1 g, 4 mL:1 g, 4.5 mL:1 g, 5 mL:1 g, etc.; the volume-mass ratio of the second solvent to 2-(piperidin-1-yl)benzonitrile can be (5-20) mL:1 g, specifically 5 mL:1 g, 10 mL:1 g, 12 mL:1 g, 13 mL:1 g, 14 mL:1 g, 15 mL:1 g, 20 mL:1 g, etc.

[0064] It is understandable that a catalyst can also be used in step (1) to improve the reaction efficiency; the catalyst includes potassium carbonate, and the mass ratio of the catalyst to 2-fluorobenzonitrile is (1.5-3):1, specifically 1.5:1, 2:1, 2.5:1, 3:1, etc.

[0065] This application changes the commonly used solvent DMF in the condensation step to acetonitrile or DMSO, avoiding the generation of a large amount of 2-(dimethylamino)benzonitrile impurities (prepared according to the literature, the impurity content is as high as 27%), and greatly improving the quality and yield of this step.

[0066] The reported Grignard reactions in the literature all use toluene as the material solvent, which reacts with the cyano group to produce a large amount of benzyl impurities (prepared according to the literature, the impurity content is as high as 10%), and it is difficult to remove, seriously affecting the quality and yield. This application changes the material solvent in this step to a high-boiling ether solvent, and no such impurities are generated, greatly improving the quality and yield of this step.

[0067] It is understandable that the replacement of the solvent in the above reaction steps not only avoids the generation of 2-(dimethylamino)benzonitrile impurities and benzyl impurities, but also promotes the synthesis of the reaction raw materials into the target product. Therefore, not only the purity is improved, but also the yield can be increased.

[0068] In some embodiments, the total yield of (S)-3-methyl-(2-piperidin-1-ylphenyl)butan-1-amine acetylglutamate can reach 61.22%, and the purity can reach 99.77%.

[0069] In some embodiments, the reaction route of (S)-3-methyl-(2-piperidinylphenyl)-1-butanamine acetylglutamate is as follows:

[0070] 。

[0071] It is understandable that isobutylmagnesium halide can be either a commercially available product or synthesized by itself, and there is no limitation here.

[0072] In some embodiments, the preparation of the isobutylmagnesium halide comprises the following steps: mixing magnesium, iodine grains, a third solvent and isobutyl halide to prepare the isobutylmagnesium halide.

[0073] It is understandable that the dosage ratios of magnesium, iodine grains, the third solvent and isobutyl halide can be adjusted conventionally, and there is no special limitation in this application. For example, the dosage ratio of magnesium to isobutyl halide can be (8-15):1, the volume-mass ratio of the third solvent to magnesium can be (3-5) mL:1 g, and the dosage ratio of iodine to magnesium can be (0.1-1):100.

[0074] In some embodiments, the isobutyl halide includes at least one of isobutyl bromide and isobutyl chloride.

[0075] In some embodiments, the third solvent includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran and methyl tert-butyl ether.

[0076] It is understandable that during the preparation of isobutylmagnesium halide, toluene is not used as a solvent, which can avoid the reaction of introduced toluene with the cyano group in the Grignard addition reaction step to generate benzyl impurities.

[0077] In some embodiments, in step (1), the temperature of the condensation reaction is 40-90 °C, and the time of the condensation reaction is 15-45 h. It can be understood that the temperature and time of the condensation reaction can be adjusted according to the reaction efficiency. Generally, when the reaction temperature is higher, the required reaction time is shortened. The specific temperature of the condensation reaction can be 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, etc.; the time of the condensation reaction can be 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, etc.

[0078] In some embodiments, the molar ratio of the 2-fluorobenzonitrile to the piperidine is 1:(1.5-2.5), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc.

[0079] In some embodiments, the halogen element in the isobutylmagnesium halide includes at least one of chlorine and bromine.

[0080] In some embodiments, the molar ratio of the o-piperidinylbenzonitrile to the isobutylmagnesium halide is 1:(2 - 5), and for example, it can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, etc.

[0081] In some embodiments, the conditions for the Grignard addition reaction include: the reaction temperature is 80 - 120°C, and the reaction time is 4 - 8 h. Among them, the reaction temperature can specifically be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, etc.; the reaction time can be 4 h, 5 h, 6 h, 7 h, 8 h, etc.

[0082] In some embodiments, the reducing agent includes at least one of potassium borohydride, sodium borohydride, and lithium borohydride.

[0083] In some embodiments, the molar ratio of the Grignard imine to the reducing agent is 1:(2 - 5), and specifically it can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, etc.

[0084] In some embodiments, the reaction conditions in step (3) include: the reaction temperature is 20 - 40°C, and the reaction time is 1 - 5 h. Among them, the reaction temperature can specifically be 20°C, 25°C, 30°C, 45°C, 40°C, etc.; the reaction time can be 1 h, 2 h, 3 h, 4 h, 5 h, etc.

[0085] In some embodiments, the reaction solvent in step (3) includes at least one of methanol and ethanol.

[0086] In some embodiments, the molar ratio of the racemic form of the regamine to the N-acetyl-L-glutamic acid is 1:(0.8 - 1.2), and for example, it can be 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc.

[0087] In some embodiments, after the reaction in step (4) is completed, it further includes a crystallization step; the crystallization temperature is 0 - 30°C, and for example, it can be 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, etc.

[0088] It can be understood that in steps (1)-(4), after the reaction is completed, it may further include steps such as solid-liquid separation, washing, and drying. The conditions for the above-mentioned solid-liquid separation, drying, and washing are not particularly limited, and common solid-liquid separation methods (such as centrifugation, filtration, liquid separation, etc.), common drying methods (such as heating drying, vacuum drying, freeze drying, natural drying, etc.), and common washing methods can be used.

[0089] The following are specific embodiments:

[0090] Basic Example 1

[0091] According to the method described in the journal literature ("Synthesis of the Key Intermediate of Repaglinide (S)-(+)-3-Methyl-1-[2-(1-piperidinyl)phenyl]butanamine", Chen Huilai et al., Journal of Shenyang Pharmaceutical University, No. 6, 2012), using o-fluorobenzene and piperidine as starting materials to prepare (S)-3-methyl-(2-piperidinylphenyl)-1-butanamine acetylglutamate, the specific process is as follows:

[0092] 1) Dissolve 20 g (0.165 mol) of o-fluorobenzene and 18.2 g (0.214 mol) of piperidine in 150 mL of DMF. After stirring evenly, add 46 g (0.34 mol) of potassium carbonate and react at 90 °C for 10 h. Cool the reaction solution to room temperature, pour it into 400 mL of water, extract with ethyl acetate (200 mL × 2), combine the organic layers, wash with water, wash with saturated brine, dry with anhydrous sodium sulfate, and evaporate the ethyl acetate to obtain o-piperidinylbenzonitrile.

[0093] 2) Add 13.8 g (0.575 mol) of magnesium chips, 54 mL of THF, and a small grain of iodine (about 0.126 g) to the reaction flask. Under nitrogen protection, add 10 drops of bromoisobutane dropwise at 35 - 40 °C to initiate the reaction. After the reaction is initiated, add 160 mL of toluene to the three-necked flask, and add a mixture of 85 g (0.62 mmol) of bromoisobutane and 56 mL of toluene from the dropping funnel dropwise over 1.5 h. After the addition is complete, stir for 2 h to prepare the Grignard reagent.

[0094] Add 26 g (0.214 mol) of o-piperidinylbenzonitrile to a mixture of THF (84 mL) and toluene (336 mL), and dropwise add the above Grignard reagent from the dropping funnel while controlling the temperature within 35 - 40 °C. Complete the addition in 0.5 h. Reflux and stir for 4 h, and let it stand overnight at room temperature. Add the reaction solution to a mixture of saturated ammonium chloride (600 mL) and concentrated ammonia water (600 mL) at -15 °C, stir for 10 min, and filter. Separate the organic layer, extract the aqueous layer with ethyl acetate 2 times (200 mL × 2), combine the organic phases, wash with water, wash with saturated brine, and dry. Evaporate the organic solvent to obtain Gramine.

[0095] 3) Add 32 g of gramine and 140 mL of methanol to a three-necked flask equipped with a thermometer. Cool to -2 to 0 °C, and slowly add 20 g of solid sodium borohydride. Finish adding in about 1 h, stir at the same temperature for 1 h, and detect by thin layer chromatography that the reaction is complete. Evaporate methanol. Under an ice-water bath, slowly add 500 mL of 10% hydrochloric acid by mass, continue to stir for 1 h, extract the reaction solution with dichloromethane (200 mL × 3). Discard the organic layer. Alkalize the aqueous layer with 5% NaOH by mass, extract with dichloromethane (200 mL × 2), dry over anhydrous sodium sulfate, and rotary evaporate to obtain 3-methyl-1-[2-(1-piperidinyl)phenyl]butylamine (i.e., the racemate of regamine).

[0096] 4) Dissolve the regamine racemate prepared in step 3) in 200 mL of acetone, add 24.7 g of N-acetyl-L-glutamic acid, and reflux for 1 h. Cool, filter by suction to obtain the crude product of N-acetyl-L-glutamate salt of 3-methyl-1-[2-(1-piperidinyl)phenyl]butylamine (i.e., (S)-3-methyl-(2-piperidinylphenyl)-1-butylamine acetylglutamate).

[0097] Dissolve 40 g of the crude product of (S)-3-methyl-(2-piperidinylphenyl)-1-butylamine acetylglutamate in a mixed solution of 240 mL of methanol and acetone (the volume ratio of methanol to acetone is 8:1), heat until completely dissolved. Slowly cool to crystallize, filter by suction to obtain the pure product of (S)-3-methyl-(2-piperidinylphenyl)-1-butylamine acetylglutamate.

[0098] Perform component separation and analysis on the 2-(piperidin-1-yl)benzonitrile prepared in step 1) and the pure product of (S)-3-methyl-(2-piperidinylphenyl)-1-butylamine acetylglutamate in step 4) by liquid chromatography-mass spectrometry (LC-MS, where the liquid chromatography model is Waters e2695 and the mass spectrometry is Waters Acquity). The chromatographic conditions (the HPLC purity chromatographic conditions in this application are the same) are as follows:

[0099] Chromatographic column: Octadecylsilyl-bonded silica gel as the filler;

[0100] Mobile phase: Use phosphate buffer solution (dissolve 6.8 g of potassium dihydrogen phosphate in 900 ml of water, adjust the pH to 7.5 with sodium hydroxide test solution, and add water to 1000 ml) as mobile phase A, and acetonitrile as mobile phase B. The gradient elution program is as follows:

[0101]

[0102] Flow rate: 1.0 mL / min; Column temperature: 30 °C; Detection wavelength: 225 nm; Injection volume: 20 μL.

[0103] Preparation of solution:

[0104] Solvent: Mobile phase A: Mobile phase B (45:55)

[0105] Test solution: Weigh accurately about 50 mg of the test substance, place it in a 25 mL volumetric flask, dissolve it with the solvent and dilute to the mark, shake well, and use it as the test solution.

[0106] The liquid chromatogram of o-piperidinylbenzonitrile is as shown in Figure 1 , and the liquid chromatogram of the pure product of (S)-3-methyl-(2-piperidinylphenyl)-1-butylamine acetylglutamate is as shown in Figure 2 .

[0107] For the component at the retention time of 8.029 min in Figure 1 and the component at the retention time of 17.454 min in Figure 2 , mass spectrometry analysis was carried out, and the results are shown in Figure 3 and Figure 4 respectively. The mass spectrometry results show that the molecular weight of the component at the retention time of 8.029 min in Figure 1 is 147.00, and the molecular weight of the component at the retention time of 17.454 min in Figure 2 is 281.18.

[0108] The structural formula of o-dimethylaminobenzonitrile is as follows:

[0109] ;

[0110] Its [M + H] + theoretical molecular formula is C9H 11 N2, [M + H] + theoretical exact molecular weight is 147.09. It can be seen that the component at the retention time of 8.029 min in Figure 1 is consistent with o-dimethylaminobenzonitrile, and the test value and the theoretical value meet the required error range. It can be known from this that the o-piperidinylbenzonitrile prepared in step 1) contains the impurity o-dimethylaminobenzonitrile, and its content is 26.96%. The reaction formula of the speculated impurity o-dimethylaminobenzonitrile is as follows:

[0111] .

[0112] The structure of the benzyl impurity is as shown below:

[0113] ;

[0114] Its [M + H] + theoretical molecular formula is C 19 H 25 N2, [M + H] + theoretical exact molecular weight is 281.20; the mass spectrometry results show thatFigure 2 The component at 17.454 min in the retention time was [M+H] + The measured molecular weight was 281.18, and the test value and the theoretical value met the required error range. The test value of 264.14 was the molecular weight of the fragment peak with the amino group bombarded off. The above results confirmed that the pure product of (S)-3-methyl-(2-piperidinophenyl)-1-butyramine acetylglutamate in step 4) of Basic Example 1 contained benzyl impurities with a content of 9.98%. The speculated reaction formula of the benzyl impurities was as follows:

[0115] 。

[0116] As can be seen from Basic Example 1, DMF was used as the solvent during piperidine condensation, and a large amount of o-dimethylaminobenzonitrile impurities (26.96%) were contained in the product. Also, when using toluene as the solvent for Grignard addition, a large amount of benzyl impurities (9.98%) were generated. Therefore, the inventor further optimized the preparation process to avoid the generation of the above impurities, thereby improving the purity and yield of (S)-3-methyl-(2-piperidinophenyl)-1-butyramine acetylglutamate. See Examples 1-14 for details.

[0117] Example 1

[0118] Preparation of o-piperidinobenzonitrile

[0119] 88.00 g of 2-fluorobenzonitrile and 124.00 g of piperidine were dissolved in 300.00 ml of acetonitrile. After stirring evenly, 200.00 g of potassium carbonate was added, and the reaction was carried out at 80 °C for 40 hours. After the reaction was completed, it was cooled to room temperature. It was poured into water, extracted with ethyl acetate, the organic layers were combined, washed with water and saturated brine, dried over anhydrous sodium sulfate, and the organic solvent was evaporated to obtain 133 g of a yellow oily liquid, yield: 98.27%, HPLC purity: 98.78%.

[0120] Example 2

[0121] Preparation of o-piperidinobenzonitrile

[0122] The same preparation method as in Example 1 was adopted, except that acetonitrile was changed to DMSO, yield: 97.54%, HPLC purity: 98.47%.

[0123] Example 3

[0124] Preparation of regimine

[0125] Add 55.20 g of magnesium chips, 216.00 ml of tetrahydrofuran and a small grain of iodine (about 0.126 g) into the reaction flask. Under nitrogen protection, add 5 g of isobutyl bromide at 35 - 45 °C to initiate the reaction. After the reaction is initiated, dropwise add a mixture of 340.00 g of isobutyl bromide and 336.00 ml of tetrahydrofuran from the dropping funnel, and control the temperature at 35 - 45 °C. After the addition is completed, keep the temperature and stir for 2 h to obtain the Grignard reagent.

[0126] Add 105.72 g of o-piperidinobenzonitrile (prepared in Example 1) into 1344.00 ml of anisole, and dropwise add it into the above-mentioned Grignard reagent. Control the temperature within 35 - 45 °C. After the addition is completed, raise the temperature to 100 °C and stir for 6 hours. After the reaction is completed, cool it to room temperature. Add the reaction solution into a mixed solution of saturated ammonium chloride and concentrated ammonia water at -10 °C, add ethyl acetate, separate the layers, wash with water and saturated brine, and dry with anhydrous sodium sulfate. Evaporate the organic solvent to obtain 137 g of a brown oily substance, yield: 98.77%, HPLC purity: 86.27%.

[0127] Example 4

[0128] Preparation of regimine

[0129] Adopt the same preparation method as in Example 3, except that isobutyl bromide is replaced by isobutyl chloride, yield: 94.72%, HPLC purity: 85.78%.

[0130] Example 5

[0131] Preparation of regimine

[0132] Adopt the same preparation method as in Example 3, except that tetrahydrofuran is replaced by 2-methyltetrahydrofuran, yield: 97.60%, HPLC purity: 86.02%.

[0133] Example 6

[0134] Preparation of regimine

[0135] Adopt the same preparation method as in Example 3, except that tetrahydrofuran is replaced by methyl tert-butyl ether, yield: 96.54%, HPLC purity: 84.75%.

[0136] Example 7

[0137] Preparation of regimine

[0138] Adopt the same preparation method as in Example 3, except that anisole is replaced by phenetole, yield: 98.63%, HPLC purity: 86.14%.

[0139] Example 8

[0140] Preparation of Regimine

[0141] Using the same preparation method as in Example 3, except that anisole is replaced with n-butyl ether, yield: 95.32%, HPLC purity: 84.58%.

[0142] Example 9

[0143] Preparation of Regimine

[0144] Using the same preparation method as in Example 3, except that anisole is replaced with isoamyl ether, yield: 98.04%, HPLC purity: 85.33%.

[0145] Example 10

[0146] Preparation of Regimine

[0147] Using the same preparation method as in Example 3, except that anisole is replaced with n-pentyl ether, yield: 97.93%, HPLC purity: 85.97%.

[0148] Example 11

[0149] Preparation of Racemic Regamine

[0150] Add 137.00 g of Regimine (prepared in Example 3) and 600.00 ml of methanol to the reaction flask, cool to -5 to 5 °C, and slowly add 121.00 g of potassium borohydride solid in batches. After addition, raise the temperature to 25 to 35 °C and react for 3 hours. After the reaction is completed, distill off methanol. At -5 to 5 °C, slowly add water and stir to disperse. Extract with ethyl acetate, separate the layers, wash with water. Add water to the organic phase and slowly add concentrated hydrochloric acid to acidify to pH = 2 - 3. Separate the layers, discard the organic layer, basify the aqueous layer with ammonia water to pH = 8 - 10, extract with ethyl acetate, dry over anhydrous sodium sulfate, and distill off the organic solvent to obtain 134 g of an orange oil, yield: 97.01%.

[0151] Example 12

[0152] Preparation of Racemic Regamine

[0153] Using the same preparation method as in Example 11, except that potassium borohydride is replaced with sodium borohydride, yield: 96.89%.

[0154] Example 13

[0155] Preparation of Racemic Regamine

[0156] Using the same preparation method as in Example 11, except that potassium borohydride is replaced with lithium borohydride, yield: 94.37%.

[0157] Example 14

[0158] Preparation of (S)-3-Methyl-(2-piperidinophenyl)-1-butanamine N-Acetylglutamate

[0159] Dissolve 134.00 g of the ragabalin racemate (prepared in Example 11) in 833.78 ml of acetone, add 102.88 g of N-acetyl-L-glutamic acid, heat to reflux, and stir for 1 hour. Cool to 20 - 30 °C, stir for crystallization for 2 hours, filter by suction, and wash with acetone to obtain 98 g of the crude product of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine N-acetylglutamate in the form of a white powder, with a yield of 82.75%. HPLC purity = 96.60%. Optical purity = 80.96%, isomer = 17.42%.

[0160] Purification: Add 98.00 g of the crude product to 98.00 ml of methanol and 196.00 ml of acetone, stir and heat to reflux for dissolution, add 588.00 ml of acetone, and stir at reflux for 1 hour. Cool to 20 - 30 °C, stir for crystallization for 2 hours, filter by suction, and wash with acetone to obtain 77 g of the pure product of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine N-acetylglutamate in the form of a white powder, with a yield of 78.57%. The liquid chromatogram of the pure product of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine N-acetylglutamate is shown in Figure 5 , with its HPLC purity = 99.77% and e.e. value of 99.80%. Total yield: 61.22%.

[0161] In summary, in Examples 1 - 14, by changing the commonly used solvent DMF in the condensation step to acetonitrile or DMSO, the generation of a large amount of o-dimethylaminobenzonitrile impurities is avoided, and by changing the solvent of the Grignard addition reaction from toluene to a high-boiling ether solvent, the generation of benzyl impurities is avoided, thereby improving the purity and yield of (S)-3-methyl-(2-piperidinophenyl)-1-butanamine N-acetylglutamate. The total yield can reach 61.22%, and the HPLC purity can reach 99.77%.

[0162] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0163] The above-described embodiments merely represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for preparing (S)-3-methyl-(2-piperidinylphenyl)-1-butanamine acetylglutamate, characterized in that, It includes the following steps: (1) 2-Fluorobenzonitrile and piperidine are condensed in a first solvent to form o-piperidinylbenzonitrile; (2) The o-piperidinylbenzonitrile undergoes a Grignard addition reaction with isobutylmagnesium halide in a second solvent to form regiimine; (3) The regiimine reacts in the presence of a reducing agent to form a racemic mixture of regiamine; (4) The racemic mixture of regiamine reacts with N-acetyl-L-glutamic acid to form (S)-3-methyl-(2-piperidinylphenyl)-1-butanamine acetylglutamate; The first solvent is acetonitrile and / or DMSO; the second solvent is a high-boiling ether solvent; the high-boiling ether solvent is at least one of anisole, phenetole, n-butyl ether, isoamyl ether, and n-pentyl ether; In step (1), the temperature of the condensation reaction is 40-90 °C, and the time of the condensation reaction is 15-45 h; The conditions for the Grignard addition reaction include: the reaction temperature is 80-120 °C, and the reaction time is 4-8 h; The preparation of the isobutylmagnesium halide includes the following steps: magnesium, iodine grains, a third solvent, and isobutyl halide are mixed to prepare the isobutylmagnesium halide; The third solvent is at least one of tetrahydrofuran, 2-methyltetrahydrofuran, and methyl tert-butyl ether.

2. The preparation method according to claim 1, characterized in that, The isobutyl halide includes at least one of isobutyl bromide and isobutyl chloride.

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of the 2-fluorobenzonitrile to the piperidine is 1:(1.5-2.5).

4. The preparation method according to claim 1, characterized in that, The halogen element in the isobutylmagnesium halide includes at least one of chlorine and bromine.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the o-piperidinylbenzonitrile to the isobutylmagnesium halide is 1:(2-5).

6. The preparation method according to claim 1, characterized in that, The reducing agent includes at least one of potassium borohydride, sodium borohydride, and lithium borohydride; and / or the molar ratio of the regiimine to the reducing agent is 1:(2-5).

7. The preparation method according to claim 1, characterized in that, The reaction conditions in step (3) include: the reaction temperature is 20-40 °C, and the reaction time is 1-5 h; and / or the reaction solvent in step (3) includes at least one of methanol and ethanol.

8. The preparation method according to claim 1, characterized in that, The molar ratio of the racemic mixture of regiamine to the N-acetyl-L-glutamic acid is 1:(0.8-1.2).

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