Pyridostigmine bromide crystal and preparation method thereof

Abstract

The invention provides a pyridostigmine bromide crystal and a preparation method thereof, and belongs to the field of medicine preparation. The pyridostigmine bromide crystal prepared by utilizing the intermediate I is superior to a commercially available product in purity, high in yield, free of impurity detection and superior to the prior art in quality; meanwhile, the process is simple and convenient, can be completed by conventional test equipment, and is high in batch yield, low in cost, stable in crystal form of the obtained product and suitable for industrial mass production.

Description

A bright crystal of pyridostigmine and its preparation method Technical Field

[0001] This invention belongs to the field of pharmaceutical preparation, specifically relating to a pyridostigmine crystal and its preparation method. Background Technology

[0002] Pyridostigmine bromide is a cholinesterase inhibitor used to treat myasthenia gravis, and can also be used to treat postoperative abdominal distension and urinary retention.

[0003] Currently, industrial production processes for pyridostigmine bromide include continuous flow processes and batch reactors. Patent application CN114950299 A discloses an apparatus and method for preparing pyridostigmine bromide, which uses a continuous flow microchannel reactor. Microchannel reactors enable efficient mixing and rapid transfer of fluids, achieving high conversion and yield rates while controlling undesirable reactions. However, microchannel reactors have small batch processing capacities. Large-scale production would require a significantly increased number of microreactors, greatly increasing the complexity and cost of their detection and control, making them unsuitable for large-scale industrial production.

[0004] However, the current method of producing pyridostigmine bromide using a batch reactor suffers from problems such as poor quality and low yield.

[0005] According to the United States Pharmacopeia (USP) (official as of 01-MAY-2020), 3-hydroxy-1-methylpyridine bromide (CAS No.: 31034-86-3) is listed as a quality control impurity of pyridostigmine bromide, and its content needs to be controlled to ensure the purity and safety of the drug.

[0006] Therefore, developing a pyridostigmine bromide product that is high in purity, low in impurities, low in cost, and capable of large-scale production with stable crystal forms, suitable for industrial-scale production, is an urgent problem that pharmaceutical companies need to solve. Summary of the Invention

[0007] The purpose of this invention is to provide a pyridostigmine crystal and a method for its preparation.

[0008] This invention provides a clear crystal of pyridoxine bromide, wherein the crystal exhibits characteristic absorption peaks at 2θ diffraction angles of 10.8°±0.2°, 14.0°±0.2°, 16.3°±0.2°, 18.6°±0.2°, 21.2°±0.2°, 22.6°±0.2°, 25.1°±0.2°, 26.8°±0.2°, 28.3°±0.2°, and 29.5°±0.2° in X-ray powder diffraction.

[0009] Furthermore, in the X-ray powder diffraction of the crystal, the peak area percentage (%) of the characteristic peak at the 2θ diffraction angle is:

[0010]

[0011]

[0012] Furthermore, the X-ray powder diffraction pattern of the crystal is shown in Figure 1, Figure 2, or Figure 3.

[0013] The present invention also provides a method for preparing pyridostigmine crystals, the method comprising the following steps:

[0014]

[0015] (1) Methyl bromide reacts with intermediate I to obtain a reaction solution;

[0016] (2) Crystallize and dry to obtain clear crystals of pyridoxine bromide.

[0017] Further, in step (1), the molar ratio of bromomethane to intermediate I is 1 to 3:1; the reaction conditions are: bromomethane, intermediate I and organic solvent are mixed at -15 to 0°C and then reacted at 10 to 40°C for 4 to 25 hours.

[0018] Further, in step (1), the molar ratio of bromomethane to intermediate I is 2:1; after mixing bromomethane, intermediate I and organic solvent at -10 to 0°C, the mixture is reacted at 20 to 30°C for 6 to 20 hours; the organic solvent is selected from one or more of dichloromethane and acetone.

[0019] Further, the crystallization in step (2) includes the following operations:

[0020] (a) Add an inert solvent and a clear seed of pyridoxine bromide to the reaction solution, crystallize, and filter to obtain a filter cake;

[0021] (b) After dissolving the filter cake from step (a), add an inert solvent and a clear seed of pyridoxine bromide, crystallize, and filter to obtain the filter cake; or, after dissolving the filter cake from step (a), add a stabilizer and an inert solvent in sequence, recrystallize, and filter to obtain the filter cake.

[0022] Further, in steps (a) and (b), the inert solvent is an organic solvent; the volume-to-mass ratio of the inert solvent to intermediate I is 1 to 3:1 (ml / g); and the amount of seed crystals added is 0.05% to 0.15% of the mass of intermediate I.

[0023] In step (a), the crystallization temperature is 5–25°C and the time is 5–20 min;

[0024] In step (b), the mass ratio of intermediate I to stabilizer is 100:1 to 5; the stabilizer is an inorganic acid; the solvent for dissolution is one or a mixture of two or more of dichloromethane, anhydrous ethanol, and ethyl acetate; the dissolution temperature is room temperature or the reflux temperature of the solvent; the temperature at which the stabilizer and inert solvent are added is 45 to 70°C; the recrystallization temperature is 10 to 25°C, and the time is 5 to 65 minutes.

[0025] Further, in steps (a) and (b), the inert solvent is one or a mixture of two or more of ethyl acetate, n-hexane, and methyl tert-butyl ether; the volume-to-mass ratio of the inert solvent to intermediate I is 1 to 3:1 (ml / g); and the amount of seed crystals added is 0.1% of the mass of intermediate I.

[0026] In step (a), the crystallization temperature is 10–20°C and the time is 5–15 min;

[0027] In step (b), the mass ratio of intermediate I to stabilizer is 100:3; the stabilizer is hydrobromic acid; the temperature when adding stabilizer and inert solvent is 50-65°C; the recrystallization temperature is 15-20°C and the time is 10-60 min.

[0028] Further, after step (2) is completed, the following steps are also included: washing the filter cake with a mixed solvent; the mixed solvent is a mixture of dichloromethane and ethyl acetate in a volume ratio of 3:1 to 3, preferably 3:2.

[0029] Experimental results show that the purity of the pyridostigmine crystals prepared by the present invention using intermediate I is superior to that of commercially available products, with high yield and no detectable impurities, and the quality is superior to existing technologies. At the same time, the process is simple and convenient, can be completed with conventional experimental equipment, has high batch production, low cost, and the obtained product has stable crystal form, making it suitable for large-scale industrial production.

[0030] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0031] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0032] Figure 1 shows the X-ray powder diffraction pattern of pyridostigmine bromide obtained in Example 1.

[0033] Figure 2 shows the X-ray powder diffraction pattern of pyridostigmine bromide obtained in Example 3.

[0034] Figure 3 shows the X-ray powder diffraction pattern of pyridostigmine bromide obtained in Example 5. Detailed Implementation

[0035] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0036] Seed crystal: Pyridostigmine bromide, purity ≥99.976%, source: Sichuan Tiandao Pharmaceutical Co., Ltd.;

[0037] Intermediate I, source: Sichuan Tiandao Pharmaceutical Co., Ltd.

[0038] In this invention, "v / m" refers to the ratio of volume to mass.

[0039] In this invention, "room temperature" means 25±5℃.

[0040] In this embodiment of the invention: all solvent volume-to-mass ratios (v / m) are the volume-to-mass ratios of solvent to intermediate 1.

[0041] The present invention describes the preparation of pyridostigmine crystals according to the following synthetic route:

[0042]

[0043] Example 1: Preparation of bright crystals of pyridostigmine bromide

[0044] S1. Reaction of bromomethane with intermediate I

[0045] Preparation of bromomethane and dichloromethane solution: Weigh 114.26g (1.20mol, 2.0eq) of bromomethane and add it to 171.39g (129ml, 1.29v / m) of dichloromethane at -10℃, mix well and dilute, and store temporarily at -10℃.

[0046] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 171 mL (1.71 v / m) of dichloromethane, cool to -10 °C, and add the above bromomethane-dichloromethane solution. After the addition is complete, heat to 25 °C and stir for 20 h. Perform TLC monitoring every 2 h until the reaction is complete.

[0047] S2. Crystallization occurs after the reaction is complete.

[0048] After the reaction was complete, 100 ml (1 v / m) of ethyl acetate and 0.10 g (0.1%) of seed crystals were added to the reaction solution, and 100 ml (1 v / m) of ethyl acetate was added dropwise while stirring. After the addition was complete, the mixture was stirred at 15 °C for 10 min to allow crystals to crystallize. The mixture was then filtered, and the filter cake was rinsed with a 100 ml (1 v / m) solution of dichloromethane:ethyl acetate = 3:2.

[0049] S3. Recrystallization after crystallization

[0050] The resulting filter cake was recrystallized using the following process:

[0051] The above filter cake was added to 300 ml (3 v / m) of dichloromethane and stirred at room temperature to dissolve. After dissolution, 100 ml (1 v / m) of ethyl acetate and 0.10 g (0.1%) of seed crystals were added, and 100 ml (1 v / m) of ethyl acetate was added dropwise while stirring. After the addition was complete, the mixture was stirred at 15 °C for 10 min to crystallize. The mixture was filtered, and the filter cake was washed with a 100 ml (1 v / m) solution of dichloromethane:ethyl acetate = 3:2. The filter cake was dried under reduced pressure at 45 °C for 3 h to obtain pyridostigmine crystals with a yield of 90% and a purity of 100.000%.

[0052] Example 2: Preparation of bright crystals of pyridostigmine bromide

[0053] S1. Reaction of bromomethane with intermediate I

[0054] Preparation of bromomethane and dichloromethane solution: Weigh 114.26g (1.20mol, 2.0eq) of bromomethane and add it to 171.39g (129ml, 1.29v / m) of dichloromethane at -10℃, mix well and dilute, and store temporarily at -10℃.

[0055] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 171 mL (1.71 v / m) of dichloromethane, cool to -10 °C, and add the above bromomethane-dichloromethane solution. After the addition is complete, heat to 30 °C and stir for 20 h. Perform TLC monitoring every 2 h until the reaction is complete.

[0056] S2. Crystallization occurs after the reaction is complete.

[0057] After the reaction was complete, 100 ml (1 v / m) of ethyl acetate and 0.10 g (0.1%) of seed crystals were added to the reaction solution, and 100 ml (1 v / m) of ethyl acetate was added dropwise while stirring. After the addition was complete, the mixture was stirred at 20 °C for 15 min to allow crystals to precipitate. The mixture was then filtered, and the filter cake was rinsed with a 100 ml (1 v / m) solution of dichloromethane:ethyl acetate = 3:2.

[0058] S3. Recrystallization after crystallization

[0059] The resulting filter cake was recrystallized using the following process:

[0060] The above filter cake was added to 300 ml (3 v / m) of dichloromethane and stirred at room temperature to dissolve. After dissolution, 100 ml (1 v / m) of ethyl acetate and 0.10 g (0.1%) of seed crystals were added, and 100 ml (1 v / m) of ethyl acetate was added dropwise while stirring. After the addition was complete, the mixture was stirred at 20 °C for 15 min to crystallize. The mixture was filtered, and the filter cake was washed with a 100 ml (1 v / m) solution of dichloromethane:ethyl acetate = 3:2. The filter cake was dried under reduced pressure at 50 °C for 3.5 h to obtain pyridostigmine crystals with a yield of 90% and a purity of over 99.98%.

[0061] Example 3: Preparation of bright crystals of pyridostigmine bromide

[0062] S1. Reaction of bromomethane with intermediate I

[0063] Preparation of bromomethane and dichloromethane solution: Weigh 114.26g (1.20mol, 2.0eq) of bromomethane and add it to 171.39g (129ml, 1.29v / m) of dichloromethane at 0℃, mix well and dilute, and store temporarily at 0℃.

[0064] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 171 ml (1.71 v / m) of dichloromethane, cool to 0 °C, and add the above bromomethane-dichloromethane solution. After the addition is complete, heat to 25 °C and stir for 6 h. Perform TLC monitoring every 2 h until the reaction is complete.

[0065] S2. Crystallization occurs after the reaction is complete.

[0066] After the reaction was complete, 50 ml (0.5 v / m) of ethyl acetate and 0.10 g (0.1%) of seed crystals were added to the reaction solution, and 150 ml (1.5 v / m) of ethyl acetate was added dropwise while stirring. After the addition was complete, the mixture was stirred at 15 °C for 10 min to allow crystals to precipitate. The mixture was then filtered, and the filter cake was rinsed with 100 ml (1 v / m) of dichloromethane:ethyl acetate = 3:2 solution.

[0067] S3. Recrystallization after crystallization

[0068] The resulting filter cake was recrystallized using the following process:

[0069] The above filter cake was dissolved in 150 ml (1.5 v / m) anhydrous ethanol and 300 ml (3 v / m) ethyl acetate by heating to reflux at 72 °C. After dissolution, the internal temperature was lowered to 65 °C and 3.00 g (3.0%) hydrobromic acid was added, and the mixture was stirred for 5 min. The internal temperature was then lowered to 55 °C and 450 ml (4.5 v / m) ethyl acetate was added dropwise while maintaining the temperature. After the addition was complete, the internal temperature was lowered to 20 °C and the mixture was stirred for 60 min to induce crystallization. The crystals were filtered, and the filter cake was dried under reduced pressure at an external temperature of 40 °C for 3 h to obtain pyridostigmine crystals with a yield of 76% and a purity of 99.984%.

[0070] Example 4: Preparation of bright crystals of pyridostigmine bromide

[0071] S1. Reaction of bromomethane with intermediate I

[0072] Preparation of bromomethane and dichloromethane solution: Weigh 114.26g (1.20mol, 2.0eq) of bromomethane and add it to 171.39g (129ml, 1.29v / m) of dichloromethane at 0℃, mix well and dilute, and store temporarily at 0℃.

[0073] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 171 mL (1.71 v / m) of dichloromethane, cool to 0 °C, and add the above bromomethane-dichloromethane solution. After the addition is complete, heat to 20 °C and stir for 6 h. Perform TLC monitoring every 2 h until the reaction is complete.

[0074] S2. Crystallization occurs after the reaction is complete.

[0075] After the reaction was complete, 50 ml (0.5 v / m) of ethyl acetate and 0.10 g (0.1%) of seed crystals were added to the reaction solution, and 150 ml (1.5 v / m) of ethyl acetate was added dropwise while stirring. After the addition was complete, the mixture was stirred at 10 °C for 5 min to allow crystals to precipitate. The mixture was then filtered, and the filter cake was rinsed with 100 ml (1 v / m) of dichloromethane:ethyl acetate = 3:2 solution.

[0076] S3. Recrystallization after crystallization

[0077] The resulting filter cake was recrystallized using the following process:

[0078] The above filter cake was dissolved in 150 ml (1.5 v / m) anhydrous ethanol and 300 ml (3 v / m) ethyl acetate under reflux. After dissolution, the internal temperature was lowered to 60°C, and 3.00 g (3.0%) hydrobromic acid was added and stirred for 5 min. The internal temperature was lowered to 50°C, and 450 ml (4.5 v / m) ethyl acetate was added dropwise while maintaining the temperature. After the addition was complete, the internal temperature was lowered to 15°C, and the mixture was stirred for 50 min to induce crystallization. The mixture was filtered, and the filter cake was dried under reduced pressure at an external temperature of 35°C for 2.5 h to obtain pyridostigmine crystals with a yield of 76% and a purity of over 99.98%.

[0079] Example 5: Preparation of bright crystals of pyridostigmine bromide

[0080] S1. Reaction of bromomethane with intermediate I

[0081] Preparation of bromomethane and dichloromethane solution: After purging the reaction vessel with nitrogen, weigh 12.94 kg (136 mol, 2.1 eq) of bromomethane and add it to 18.46 kg (13.88 L, 1.30 v / m) of dichloromethane at a temperature not exceeding 0℃. Mix well and dilute. Store temporarily below 0℃.

[0082] After nitrogen purging, 10.70 kg (64 mol, 1.0 eq) of intermediate I and 24.23 kg (18.22 L, 1.70 v / m) of dichloromethane were weighed and added to the reactor. The temperature was lowered to below 0 °C, and the above-mentioned bromomethane-dichloromethane solution was added. After the addition was complete, the temperature was raised to 25 °C and the mixture was stirred for 6 h. TLC was performed every 2 h until the reaction was complete.

[0083] S2. Crystallization occurs after the reaction is complete.

[0084] After the reaction was complete, 4.80 kg (5.33 L, 0.5 v / m) of ethyl acetate and 10.70 g (0.1%) of seed crystals were added to the reaction solution. Then, 14.40 kg (16.00 L, 1.5 v / m) of ethyl acetate was added dropwise while stirring. After the addition was complete, the mixture was stirred at 15 °C for 10 min to allow crystals to precipitate. The mixture was then filtered, and the filter cake was rinsed with a 3:2 solution of dichloromethane and ethyl acetate (11.47 kg (10.70 L, 1 v / m)).

[0085] S3. Recrystallization after crystallization

[0086] The resulting filter cake was recrystallized using the following process:

[0087] After nitrogen purging, the filter cake was transferred to a reaction vessel, and 12.60 kg (16.15 L, 1.5 v / m) of anhydrous ethanol and 28.89 kg (32.10 L, 3.0 v / m) of ethyl acetate were added. The mixture was then refluxed at 72 °C to dissolve the ethanol. After dissolution, the internal temperature was lowered to 65 °C, and 321.00 g (3.0%) of hydrobromic acid was added and stirred for 5 min. The internal temperature was then lowered to 55 °C, and 43.34 kg (48.16 L, 4.5 v / m) of ethyl acetate was added dropwise while maintaining the temperature. After the addition was complete, under nitrogen protection, the internal temperature was lowered to 20 °C, and the mixture was stirred for 60 min to induce crystallization. The mixture was then filtered, and the filter cake was dried under reduced pressure at an external temperature of 40 °C for 3 h to obtain 13.24 kg of pyridostigmine crystals, with a yield of 78% and a purity of over 99.987%.

[0088] Example 6: Preparation of bright crystals of pyridostigmine bromide

[0089] S1. Reaction of bromomethane with intermediate I

[0090] Preparation of bromomethane-acetone solution: Weigh 114.26g (1.20mol, 2.0eq) of bromomethane and add it to 171.39g (217ml, 2.17v / m) of acetone at 0℃. Mix well and dilute. Store temporarily at 0℃.

[0091] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 65.57 g (83 ml, 0.83 v / m) of acetone, cool to 0 °C, and add the above bromomethane-acetone solution. After the addition is complete, heat to 20 °C and stir for 6 h. Perform TLC monitoring every 2 h until the reaction is complete.

[0092] S2. Crystallization occurs after the reaction is complete.

[0093] Same as described in Example 1.

[0094] S3. Recrystallization after crystallization

[0095] Same as described in Example 1.

[0096] Example 7: Preparation of bright crystals of pyridostigmine bromide

[0097] S1. Reaction of bromomethane with intermediate I

[0098] Preparation of bromomethane-acetone solution: Weigh 114.26g (1.20mol, 2.0eq) of bromomethane and add it to 171.39g (217ml, 2.17v / m) of acetone at 0℃. Mix well and dilute. Store temporarily at 0℃.

[0099] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 65.57 g (83 ml, 0.83 v / m) of acetone, cool to 0 °C, and add the above bromomethane-acetone solution. After the addition is complete, heat to 25 °C and stir for 6 h. Perform TLC monitoring every 2 h until the reaction is complete.

[0100] S2. Crystallization occurs after the reaction is complete.

[0101] Same as described in Example 1.

[0102] S3. Recrystallization after crystallization

[0103] Same as described in Example 1.

[0104] The above experimental results show that the mass of the products obtained in Examples 1 and 2 is greater than 141g; the mass of the products obtained in Examples 3 and 4 is greater than 119g; and the mass of the product obtained in Example 5 is 13.24kg. It can be seen that the method of the present invention can produce pyridostigmine bromide in large quantities, with a batch yield of up to 13.24kg. The cost is low and it is suitable for industrial mass production.

[0105] The product yield obtained by the preparation method of this invention can reach a minimum of 76% and a maximum of 95%; the purity is above 99.98%.

[0106] The typical crystal forms of the pyridostigmine bromide crystals obtained in Examples 1, 3, and 5 are shown in Figures 1-3. The crystal forms of the obtained pyridostigmine bromide crystals have characteristic peaks in the range of 10.8°±0.2°, 14.0°±0.2°, 16.3°±0.2°, 18.6°±0.2°, 21.2°±0.2°, 22.6°±0.2°, 25.1°±0.2°, 26.8°±0.2°, 28.3°±0.2°, and 29.5°±0.2°.

[0107] The percentage of peak area (%) of the characteristic peak at the 2θ diffraction angle in the X-ray powder diffraction of the pyridoxine crystals obtained in the examples is as follows:

[0108]

[0109] The method of the present invention can produce crystalline pyridostigmine bromide in large quantities.

[0110] The following is the preparation method for the comparative example.

[0111] Comparative Example 1: S1. Reaction of bromomethane with intermediate I

[0112] Preparation of methyl bromide in ethyl acetate solution: Weigh 114.26 g (1.20 mol, 2.0 eq) of methyl bromide and add it to 171.39 g (154 ml, 1.54 v / m) of ethyl acetate at -10℃. Mix well and dilute. Store temporarily at -10℃.

[0113] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 146 mL (1.71 v / m) of ethyl acetate, cool to -10 °C, and add the above methyl bromide ethyl acetate solution. After the addition is complete, heat to 25 °C and stir for 20 h, then perform TLC analysis every 2 h.

[0114] Comparative Example 2: S1. Reaction of bromomethane with intermediate I

[0115] Preparation of methyl bromide in ethyl acetate solution: Weigh 114.26 g (1.20 mol, 2.0 eq) of methyl bromide and add it to 190 ml (1.90 v / m) of ethyl acetate at 0℃. Mix well and dilute. Store temporarily at 0℃.

[0116] Weigh 100.00 g (0.60 mol, 1.0 eq) of intermediate I, add 150 mL (1.50 v / m) of anhydrous ethanol and 110 mL (1.10 v / m) of ethyl acetate, cool to 0 °C, and add the above methyl bromide-ethyl acetate solution. After the addition is complete, heat to 20 °C and stir for 20 h, then perform TLC analysis every 2 h.

[0117] The effect of the solvent on step S1 of the preparation method was verified by comparing Examples 1 and 2 and Examples 6 and 7.

[0118] The method for determining the reaction endpoint using TLC detection is as follows:

[0119] The reaction endpoint is indicated when the color of the intermediate spot in 1 μl of reaction solution is lighter than that in 1 μl of 1% intermediate I standard solution (2 mg / ml).

[0120] Developing solvent: ethyl acetate;

[0121] Color development: Iodine.

[0122] The result of the TLC point panel monitoring endpoint determination is:

[0123] Comparative Example 1 Results: TLC of 20h reaction solution showed that the intermediate spot in 1μl of reaction solution was darker than that in 1μl of 1% intermediate standard solution (2mg / ml). The reaction endpoint was not reached even after the reaction time was extended.

[0124] Comparative Example 2 Results: TLC of 20h reaction solution showed that the intermediate spot in 1μl of reaction solution was darker than that in 1μl of 1% intermediate standard solution (2mg / ml). The reaction endpoint was not reached even after the reaction time was extended.

[0125] Examples 1-7 of the present invention: Under the same reaction conditions (reagents, reaction temperature, etc. are all the same), reaction solutions with the same reaction time were subjected to TLC. The color of the intermediate spot in 1 μl of reaction solution was lighter than that in 1 μl of 1% intermediate standard solution (2 mg / ml), indicating that the reaction endpoint was reached. This step of the reaction can reach the reaction endpoint.

[0126] In step S1 of the preparation method of the present invention, dichloromethane and acetone are selected as the first solvents, and the reaction can proceed completely; however, if the first solvent is changed to ethyl acetate or ethyl acetate / ethanol, the reaction will not be complete, indicating that the choice of solvent is crucial in this step. The first solvent directly affects the subsequent steps and thus affects the quality and yield of the final product.

[0127] The following experimental examples demonstrate the beneficial effects of the present invention.

[0128] Experimental Example 1: Impurity Test of Pyridoxine Bromide Crystals

[0129] Impurity tests were performed on commercially available pyridostigmine bromide products 1 and 2, and the pyridostigmine bromide crystals obtained in Example 1 of this invention. The results are shown in Table 1 below. Stability tests were performed on the pyridostigmine bromide crystals obtained in Example 1 of this invention. The test results are shown in Table 2 below.

[0130] The determination method for related substances was as follows: HPLC was used, with octadecyl bonded silica gel as the stationary phase and a mixture of sodium dodecyl sulfate solution and acetonitrile as the mobile phase; the flow rate was 1.0 ml per min; the column temperature was 30 ℃; the detection wavelength was 220 nm; and the injection volume was 20 μl.

[0131] The concentration of the test solution is 1 mg / ml. Each 1 ml of the reference solution contains approximately 0.6 μg each of impurity A, impurity B, and pyridostigmine bromide.

[0132] Accurately measure the sample solution, inject it into the liquid chromatograph, and record the chromatogram.

[0133] If the chromatogram of the test solution contains a peak with the same retention time as impurity A and impurity B, the peak area should be calculated using the external standard method. Impurity A should not exceed 0.06%, impurity B should not exceed 0.06%, and other individual impurities should not exceed 0.06% based on the peak area of ​​pyridost using the external standard method. The total amount of impurities should not exceed 0.5%. Bromide ion peaks and chromatographic peaks with areas smaller than the main peak area of ​​the sensitivity solution should be ignored.

[0134] According to the USP (official as of 01-MAY-2020), the limit of detection for impurities is approximately 0.02%, and the limits of detection for impurities A (3-(N,N-dimethylcarbamoyloxy)pyridine), B (3-hydroxy-1-methylpyridine bromide), and pyridostigmine bromide are all 0.002%.

[0135] Table 1. Information on Impurities in Commercially Available Products

[0136] Sample Information: Batch No. Impurity A Impurity B Other Individual Impurities Total Impurity Commercially Available Product 1HBW231102 Not Detected 0.02% 0.04% 0.06% Commercially Available Product 2Z094B Not Detected 0.96% 0.04% 1.0% surface

[0137] No obvious impurities (as per the test items in Table 1) were detected in the pyridostigmine bromide of this invention, while impurity B in commercially available products, especially product 2, was 0.96%, and the total impurity was 1.0%. The purity of the product of this invention is above 99.98%, while the purity of commercially available product HBW231102 is 99.56%, and the purity of commercially available reference batch number Z094B is 99.0%.

[0138] Table 2. Stability of the product obtained in Example 1

[0139]

[0140] As shown in Table 2, no impurities were detected in the product prepared by the method of the present invention after long-term storage for 3 months or accelerated testing for 3 months, indicating that the crystalline form of pyridoxine bromide obtained by the present invention is stable.

[0141] In summary, this invention provides a clear pyridostigmine crystal and its preparation method. The clear pyridostigmine crystal prepared by this invention using intermediate I has a higher purity than commercially available products, a higher yield, and no detectable impurities, resulting in superior quality compared to existing technologies. Furthermore, the process is simple and convenient, can be completed with conventional experimental equipment, has high batch yield (up to 13.24 kg), low cost, and the obtained product has a stable crystal form, making it suitable for large-scale industrial production.

Claims

1. A pyridostigmine crystal, characterized in that, In the X-ray powder diffraction of the crystal, characteristic absorption peaks are observed at 2θ diffraction angles of 10.8°±0.2°, 14.0°±0.2°, 16.3°±0.2°, 18.6°±0.2°, 21.2°±0.2°, 22.6°±0.2°, 25.1°±0.2°, 26.8°±0.2°, 28.3°±0.2°, and 29.5°±0.2°.

2. The crystalline form of pyridostigmine according to claim 1, characterized in that, In the X-ray powder diffraction of the crystal, the percentage of peak area of ​​the characteristic peak at the 2θ diffraction angle is as follows: 2θ peak area percentage % 10.8°±0.2° 19.6~30.6 14.0°±0.2° 14.6~24.1 16.3°±0.2° 72.8~100 18.6°±0.2° 23.2~30.1 21.2°±0.2° 51.0~100 22.6°±0.2° 36.2~44.8 25.1°±0.2° 30.4~51.3 26.8°±0.2° 19.3~23.3 28.3°±0.2° 75.9~100 29.5°±0.2° 37.6~48.0 。 3. The clear crystalline form of pyridostigmine according to claim 1, characterized in that, The X-ray powder diffraction pattern of the crystal is shown in Figure 1, Figure 2, or Figure 3.

4. A method for preparing pyridostigmine crystals, characterized in that, The method Includes the following steps: (1) Methyl bromide reacts with intermediate I to obtain a reaction solution; (2) Crystallize and dry to obtain clear crystals of pyridoxine bromide.

5. The method according to claim 4, characterized in that, In step (1), the molar ratio of bromomethane to intermediate I is 1 to 3:1; the reaction conditions are: bromomethane, intermediate I and organic solvent are mixed at -15 to 0°C and then reacted at 10 to 40°C for 4 to 25 hours.

6. The method according to claim 5, characterized in that, In step (1), the molar ratio of bromomethane to intermediate I is 2:1; after mixing bromomethane, intermediate I and organic solvent at -10 to 0°C, the mixture is reacted at 20 to 30°C for 6 to 20 hours; the organic solvent is selected from one or more of dichloromethane and acetone.

7. The method according to claim 4, characterized in that, The crystallization in step (2) includes the following operations: (a) adding an inert solvent and a clear seed of pyridoxine bromide to the reaction solution, crystallizing, and filtering to obtain a filter cake; (b) dissolving the filter cake from step (a), adding an inert solvent and a clear seed of pyridoxine bromide, crystallizing, and filtering to obtain a filter cake; or, dissolving the filter cake from step (a), adding a stabilizer and an inert solvent in sequence, recrystallizing, and filtering to obtain a filter cake.

8. The method according to claim 7, characterized in that, In steps (a) and (b), the inert solvent is an organic solvent; the volume-to-mass ratio of the inert solvent to intermediate I is 1–3:1 (ml / g); the amount of seed crystals added is 0.05%–0.15% of the mass of intermediate I; in step (a), the crystallization temperature is 5–25°C and the time is 5–20 min; in step (b), the mass ratio of intermediate I to stabilizer is 100:1–5; the stabilizer is an inorganic acid; the solvent for dissolution is one or a mixture of two or more of dichloromethane, anhydrous ethanol, and ethyl acetate, and the dissolution temperature is room temperature or the reflux temperature of the solvent; the temperature at which the stabilizer and inert solvent are added is 45–70°C; the recrystallization temperature is 10–25°C and the time is 5–65 min.

9. The method according to claim 8, characterized in that, In steps (a) and (b), the inert solvent is one or a mixture of two or more of ethyl acetate, n-hexane, and methyl tert-butyl ether; the volume-to-mass ratio of the inert solvent to intermediate I is 1–3:1 (ml / g); the amount of seed crystals added is 0.1% of the mass of intermediate I; in step (a), the crystallization temperature is 10–20°C and the time is 5–15 min; in step (b), the mass ratio of intermediate I to stabilizer is 100:3; the stabilizer is hydrobromic acid; the temperature at which the stabilizer and inert solvent are added is 50–65°C; the recrystallization temperature is 15–20°C and the time is 10–60 min.

10. The method according to claim 7, characterized in that, After step (2) is completed, the following steps are also included: washing the filter cake with a mixed solvent; the mixed solvent is a mixture of dichloromethane and ethyl acetate in a volume ratio of 3:1 to 3, preferably 3:2.

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