Preparation method of arfamarin

Abstract

The invention discloses a preparation method of arfamarana, which belongs to the technical field of medicine, and comprises the following steps: step 1, taking Sm1 as an initial raw material, and carrying out amidation reaction on Sm1 and Sm2 to generate Int-1; step 2, carrying out aldol condensation reaction on the Int-1 and Sm3 to obtain Int-2; and step 3, carrying out cyclization reaction on the Int-2 and hydroxylamine hydrochloride to obtain the final product arfamparin. According to the invention, the reaction conditions are mild, the harsh process conditions (high-risk reagents, diazotization reaction operation and Grignard reaction operation) are avoided, and the use of complex Oldershaw rectification water removal equipment is also avoided. The method disclosed by the invention is short in synthesis step and high in yield, in terms of Sm1, the total molar yield is up to 67.37%, the product purity is 99% or above, and the maximum single impurity is 0.1% or below.

Description

Technical Field

[0001] The invention relates to the technical field of medicines, in particular to a method for preparing afollana. Background Art

[0002] Afolaner belongs to the isoxazoline family and is a new generation of isoxazoline external anthelmintics. It inhibits GABA chloride channels, causing arthropod nerves to become highly excited and cause death, making it a revolutionary and powerful insecticide. Its oral preparation has the characteristics of rapid onset, high safety, convenient oral administration, and delicious taste. It can kill fleas quickly and has a longer-lasting effect. At the same time, it is relatively safe for mammals and can be widely used to kill external parasites of pets (cats and dogs).

[0003]

[0004] At present, there are many existing methods for preparing afollana, among which the more commonly used methods are the olefin method and the ketone method, and the ketone method has more advantages. In patent CN115433140B, the reaction route is as follows:

[0005]

[0006] After intermediate II or key intermediate V is subjected to formylation reaction to obtain key intermediate III, key intermediate III is oxidized and condensed with 2-amino-N-(2,2,2-trifluoroethyl)acetamide hydrochloride to obtain afoxolane. However, the DMF / POCl3 method in steps II to III is violent and environmentally unfriendly, with heavy pollution, and POCl3 is highly corrosive. The Grignard reaction is used in steps V to III, which is not easy to initiate and is highly dangerous, and the reaction conditions require anhydrous and oxygen-free conditions.

[0007] The PCT patent WO2013021949A1 uses the ketone method for preparation. First, the reaction route is relatively long, involving eight steps. Second, the reagents used, iodine chloride, are highly oxidizing and corrosive, thionyl chloride is highly corrosive, and are dangerous and harmful. The reagent 2-amino-N-(2,2,2-trifluoroethyl)acetamide is easy to absorb moisture and difficult to store. The reagent hydroxylamine sulfate is not as economical as the cheaper domestic hydroxylamine hydrochloride. Third, the diazotization reaction is a hazardous chemical process that is subject to key supervision in my country, and the Grignard reaction is an anhydrous and oxygen-free reaction with demanding reaction conditions. Finally, the dehydration step uses a more complex Oldershaw distillation device to remove water. This device is a laboratory-level device and has certain advantages in small quantities, but it is troublesome to transform the equipment during industrialization and is not easy to operate in production.

[0008] Therefore a more effective and gentler approach is needed. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a method for synthesizing afoxolone with high yield and high purity.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is:

[0011] A method for preparing afollana comprises the following steps:

[0012] Step 1: Using Sm1 as the starting material, Sm1 and Sm2 undergo an amidation reaction to generate Int-1.

[0013] Step 2: Int-1 and Sm3 undergo aldol condensation reaction to obtain Int-2.

[0014] Step 3: Int-2 and hydroxylamine hydrochloride undergo a cyclization reaction to obtain the final product, afoxolamide. The reaction equation is as follows:

[0015]

[0016] The further improvement of the technical solution of the present invention is that: the specific steps of step one are: adding Sm1 to an organic solvent, the organic solvent is one or a mixed solution of acetonitrile, DMF, DMSO, adding carbonyldiimidazole CDI to react for a period of time, adding N,N-diisopropylethylamine or triethylamine, adding Sm2, stirring the reaction, and monitoring the reaction until the reaction is completed.

[0017] The further improvement of the technical solution of the present invention is that the specific steps of step 2 are: adding Int-1 and Sm3 to an organic solvent, wherein the organic solvent is a mixed solution of one or more of acetonitrile, tetrahydrofuran, and toluene, adding DBU, triethylamine or anhydrous sodium carbonate, heating to 60-65°C, and reacting until Int-1 reacts completely.

[0018] The further improvement of the technical solution of the present invention is that: the specific steps of step three are: dissolving sodium hydroxide in purified water, cooling to 0-5°C, adding hydroxylamine hydrochloride, and stirring until all dissolved to obtain a hydroxylamine solution; Int-2 and tetrabutylammonium bromide are dissolved in tetrahydrofuran or dichloromethane, stirring evenly, adding the hydroxylamine solution, reacting at room temperature, and monitoring by TLC until the reaction is completed.

[0019] A further improvement of the technical solution of the present invention is that after the reaction in step 1 is completed, purified water is added dropwise to the reaction liquid for crystallization, the temperature is slowly lowered, stirring is continued for 1 hour at room temperature to fully crystallize, filtered, and washed with purified water to obtain a white to off-white solid Int-1.

[0020] A further improvement of the technical solution of the present invention is that after the reaction in step 2 is completed, the solvent is evaporated under reduced pressure, ethyl acetate and water are added, stirred and washed, the aqueous phase is extracted again with ethyl acetate, the organic phases are combined and concentrated, the concentrated residue is slurried with a mixture of ethyl acetate and petroleum ether, filtered, and the filter cake is air-dried to constant weight to obtain a light yellow to off-white solid Int-2.

[0021] A further improvement of the technical solution of the present invention is that after the reaction in step 3 is completed, the organic phase is washed with purified water, the solvent is evaporated under reduced pressure to obtain a crude product, acetonitrile is added, stirred, heated to dissolve the crude product, cooled to -10 to 10°C, stirred to grow crystals, filtered, rinsed, and dried to constant weight to obtain a finished product of afoxol, a white crystalline powder.

[0022] A further improvement of the technical solution of the present invention is that the molar ratio of Sm1, CDI, alkali and Sm2 is 1:1-1.3:2-3:1.0-1.5.

[0023] A further improvement of the technical solution of the present invention is that the molar ratio of Int-1, Sm3 and alkali is 1:1-1.5:0.1.

[0024] The further improvement of the technical solution of the present invention is that the molar ratio of NaOH to hydroxylamine hydrochloride in the hydroxylamine solution is 1-1.5:1, and the molar ratio of Int-2, tetrabutylammonium bromide and hydroxylamine hydrochloride is 1:0.05:1-3.

[0025] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0026] The method has mild reaction conditions, avoids harsh process conditions (highly dangerous reagents, diazotization reaction operation, Grignard reaction operation), and avoids the use of complex Oldershaw distillation and water removal equipment. The patented method of the present invention has short synthesis steps and high yield. The total molar yield is up to 67.37% based on Sm1, the product purity is above 99%, and the maximum single impurity is below 0.1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the liquid phase spectrum of the Afoxlan reference substance;

[0028] Figure 2 This is the liquid phase spectrum of Afollana obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with embodiments:

[0030] Example 1

[0031] Step 1: Preparation of Int-1

[0032] Acetonitrile (440 g) and Sm1 (110 g, 1.0 eq.) were added into the reaction bottle with stirring. After dissolution, CDI (87.4 g, 1.05 eq.) was added. Gas was obviously generated (to prevent material impact). The reaction was carried out at room temperature for 0.5 hour. Triethylamine (103.8 g, 2.0 eq.) was added, followed by Sm2 (108.8 g, 1.1 eq.). After the addition was completed, the reaction was kept at 50-60°C and monitored by TLC until the reaction was completed.

[0033] After the reaction was completed, purified water was added dropwise to the reaction liquid for crystallization, the temperature was slowly lowered, and stirring was continued for 1 hour at room temperature for complete crystallization. The mixture was filtered with suction, washed with purified water, and the filter cake was collected and air-dried to constant weight to obtain 159.1 g of a white to off-white solid with a molar yield of 87.95%.

[0034] Step 2: Preparation of Int-2

[0035] Under stirring at room temperature, acetonitrile (1000 g), Int-1 (150 g, 1.0 eq.), Sm3 (135.4 g, 1.15 eq.), and DBU (5.63 g, 0.1 eq.) were added into the reaction kettle, and the temperature was raised to 60-65°C for reaction, and the reaction was monitored by TLC until the end of the reaction.

[0036] After the reaction, acetonitrile was evaporated under reduced pressure, ethyl acetate and water were added, stirred and washed, and then allowed to stand and separated. Ethyl acetate was added to the aqueous phase for extraction again, the organic phases were combined, washed with water, dried over anhydrous sodium sulfate, filtered, and concentrated. The concentrated residue was slurried with a mixture of ethyl acetate and petroleum ether, filtered, rinsed, and dried. The filter cake was air-dried to constant weight to obtain 231.7 g of a light yellow to off-white solid with a molar yield of 89.09%.

[0037] Step 3: Preparation of the finished Afollana product

[0038] Sodium hydroxide (36.0 g, 2.5 eq.) was dissolved in 440 ml of purified water. Exotherm was evident. After cooling to 0-5°C, hydroxylamine hydrochloride (50.05 g, 2.0 eq.) was added and stirred until all dissolved to obtain a hydroxylamine solution for later use.

[0039] Tetrahydrofuran (4.4 L), Int-2 (220 g, 1.0 eq.) and tetrabutylammonium bromide (5.8 g, 0.05 eq.) were added to the reaction bottle under stirring at room temperature. After stirring, the hydroxylamine solution was added. After the addition was complete, the reaction was continued at room temperature and monitored by TLC until the reaction was completed.

[0040] After the reaction, the organic phase was washed with purified water, and the solvent was evaporated under reduced pressure to obtain a crude product. Acetonitrile was added, stirring was started, and the crude product was dissolved by heating. The temperature was then slowly lowered to -10 to 10°C, and stirring was continued to grow the crystals. The mixture was filtered and rinsed. The filter cake was air-dried to constant weight to obtain 193.8 g of afoxolane finished product as a white crystalline powder with a molar yield of 85.98%.

[0041] Taking Sm1 as the starting material, the total molar yield was 67.37%.

[0042] Example 2

[0043] Step 1: Preparation of Int-1

[0044] DMSO (550 g) and Sm1 (110 g, 1.0 eq.) were added into the reaction bottle with stirring. After dissolution, CDI (91.6 g, 1.1 eq.) was added. Gas was obviously generated (to prevent material impact). The reaction was carried out at room temperature for 0.5 hour. N,N-diisopropylethylamine (165.9 g, 2.5 eq.) was added, followed by Sm2 (128.6 g, 1.3 eq.). After the addition was completed, the reaction was kept at 50-60°C and monitored by TLC until the reaction was completed.

[0045] After the reaction was completed, purified water was added dropwise to the reaction liquid for crystallization, the temperature was slowly lowered, and stirring was continued for 1 hour at room temperature for complete crystallization. The mixture was filtered with suction, washed with purified water, and the filter cake was collected and air-dried to constant weight to obtain 157.15 g of a white to off-white solid with a molar yield of 86.87%.

[0046] Step 2: Preparation of Int-2

[0047] Under stirring at room temperature, tetrahydrofuran (1000 g), Int-1 (150 g, 1.0 eq.), Sm3 (176.6 g, 1.5 eq.) and potassium carbonate (5.88 g, 0.1 eq.) were added into the reaction kettle, and the temperature was raised to 60-65°C for reaction, and the reaction was monitored by TLC until the end of the reaction.

[0048] After the reaction, tetrahydrofuran was evaporated under reduced pressure, ethyl acetate and water were added, stirred and washed, and then allowed to stand and separated, the aqueous phase was extracted again with ethyl acetate, the organic phases were combined, washed with water, dried over anhydrous sodium sulfate, filtered, and concentrated, the concentrated residue was slurried with a mixture of ethyl acetate and petroleum ether, filtered, rinsed, and dried, and the filter cake was air-dried to constant weight to obtain 227.8 g of light yellow to off-white solid, with a molar yield of 87.59%.

[0049] Step 3: Preparation of the finished Afollana product

[0050] Dissolve sodium hydroxide (28.8 g, 2 eq.) in 440 ml of purified water. Exotherm is evident. After cooling to 0-5°C, add hydroxylamine hydrochloride (37.5 g, 1.5 eq.) and stir until all dissolved to obtain a hydroxylamine solution for later use.

[0051] Tetrahydrofuran (4.4 L), Int-2 (220 g, 1.0 eq.) and tetrabutylammonium bromide (5.8 g, 0.05 eq.) were added to the reaction bottle under stirring at room temperature. After stirring, the hydroxylamine solution was added. After the addition was complete, the reaction was continued at room temperature and monitored by TLC until the reaction was completed.

[0052] After the reaction, the organic phase was washed with purified water, and the solvent was evaporated under reduced pressure to obtain a crude product. Acetonitrile was added, stirring was started, and the crude product was dissolved by heating. The temperature was then slowly lowered to -10 to 10°C, and stirring was continued to grow the crystals. The mixture was filtered and washed, and the filter cake was air-dried to constant weight to obtain 196.4 g of afoxolane finished product as a white crystalline powder with a molar yield of 87.13%.

[0053] Taking Sm1 as the starting material, the total molar yield is 66.30%.

[0054] Example 3

[0055] Step 1: Preparation of Int-1

[0056] DMF (440 g) and Sm1 (110 g, 1.0 eq.) were added into the reaction bottle with stirring. After dissolution, CDI (87.4 g, 1.05 eq.) was added. Gas was obviously generated (to prevent material impact). The reaction was carried out at room temperature for 0.5 hour. Triethylamine (103.8 g, 2.0 eq.) was added, followed by Sm2 (108.8 g, 1.1 eq.). The reaction was kept at 50-60°C and monitored by TLC until the reaction was completed.

[0057] After the reaction was completed, purified water was added dropwise to the reaction liquid for crystallization, the temperature was slowly lowered, and stirring was continued for 1 hour at room temperature for complete crystallization. The mixture was filtered with suction, washed with purified water, and the filter cake was collected and air-dried to constant weight to obtain 153.1 g of a white to off-white solid with a molar yield of 84.63%.

[0058] Step 2: Preparation of Int-2

[0059] Under stirring at room temperature, toluene (1000 g), Int-1 (150 g, 1.0 eq.), Sm3 (135.4 g, 1.15 eq.) and anhydrous potassium carbonate (5.88 g, 0.1 eq.) were added into the reactor, and the temperature was raised to 60-65°C for reaction, and the reaction was monitored by TLC until the end of the reaction.

[0060] After the reaction, toluene was evaporated under reduced pressure, ethyl acetate and water were added, the mixture was stirred and washed, and then allowed to stand and separated. Ethyl acetate was added to the aqueous phase for extraction again, the organic phases were combined, washed with water, dried over anhydrous sodium sulfate, filtered, and concentrated. The concentrated residue was slurried with a mixture of ethyl acetate and petroleum ether, filtered, rinsed, and dried. The filter cake was air-dried to constant weight to obtain 231.2 g of a light yellow to off-white solid with a molar yield of 88.90%.

[0061] Step 3: Preparation of the finished Afollana product

[0062] Sodium hydroxide (31.7 g, 2.2 eq.) was dissolved in 440 ml of purified water. Exotherm was evident. After cooling to 0-5°C, hydroxylamine hydrochloride (50.05 g, 2.0 eq.) was added and stirred until all dissolved to obtain a hydroxylamine solution for later use.

[0063] Dichloromethane (4.4 L), Int-2 (220 g, 1.0 eq.) and tetrabutylammonium bromide (5.8 g, 0.05 eq.) were added to the reaction bottle under stirring at room temperature. After stirring evenly, hydroxylamine solution was added. After the addition was complete, the reaction was continued at room temperature and monitored by TLC until the reaction was completed. The reaction lasted for about 1 hour.

[0064] After the reaction, the organic phase was washed with purified water, and the solvent was evaporated under reduced pressure to obtain a crude product. Acetonitrile and ethanol were added, and stirring was started. The crude product was heated to dissolve, and then the temperature was slowly lowered to room temperature. After sufficient crystallization, the temperature was further lowered to 5-10°C, and the crystals were continued to be stirred, filtered, and washed. The filter cake was air-dried to constant weight to obtain 193.8 g of afoxolane finished product, a white crystalline powder, and a molar yield of 85.98%.

[0065] Taking Sm1 as the starting material, the total molar yield was 64.69%.

[0066] The finished products of Afollana obtained in Examples 1, 2 and 3 and the reference product were subjected to liquid phase testing. The test results are shown in Figure 1 and Figure 2 and the following table.

[0067] purity Yield Maximum single impurity Example 1 99.88％ 67.37％ 0.045％ Example 2 99.82％ 66.30％ 0.042％ Example 3 99.75％ 64.69％ 0.058％

Claims

1. A method for preparing afollana, characterized in that The following steps are involved: Step 1: Using Sm1 as the starting material, Sm1 and Sm2 undergo an amidation reaction to generate Int-1; Step 2: Int-1 and Sm3 undergo aldol condensation reaction to obtain Int-2; Step 3: Int-2 and hydroxylamine hydrochloride undergo a cyclization reaction to obtain the final product, afoxolamide. The reaction equation is as follows:

2. The method for preparing afollana according to claim 1, characterized in that: The specific steps of step 1 are: adding Sm1 to an organic solvent, which is a mixed solution of one or more of acetonitrile, DMF, and DMSO, adding carbonyldiimidazole CDI to react for a period of time, adding N,N-diisopropylethylamine or triethylamine, adding Sm2, stirring the reaction, and monitoring the reaction until the reaction is completed.

3. The method for preparing afollana according to claim 1, characterized in that: The specific steps of step 2 are: add Int-1 and Sm3 to an organic solvent, which is a mixed solution of one or more of acetonitrile, tetrahydrofuran, and toluene, add DBU, triethylamine or anhydrous sodium carbonate, raise the temperature to 60-65°C, and react until Int-1 reacts completely.

4. The method for preparing afollana according to claim 1, characterized in that: The specific steps of step 3 are as follows: dissolve sodium hydroxide in purified water, cool to 0-5°C, add hydroxylamine hydrochloride, and stir until completely dissolved to obtain a hydroxylamine solution; dissolve Int-2 and tetrabutylammonium bromide in tetrahydrofuran or dichloromethane, stir evenly, add the hydroxylamine solution, react at room temperature, and monitor by TLC until the reaction is completed.

5. The method for preparing afollana according to claim 2, characterized in that: After the reaction in step 1 is completed, purified water is added dropwise to the reaction solution for crystallization, and the temperature is slowly lowered to room temperature and stirring is continued for 1 hour to fully crystallize. The solution is filtered and washed with purified water to obtain a white to off-white solid Int-1.

6. The method for preparing afollana according to claim 3, characterized in that: After the reaction in step 2 is completed, the solvent is evaporated under reduced pressure, ethyl acetate and water are added, stirred and washed, the aqueous phase is extracted again with ethyl acetate, the organic phases are combined and concentrated, and the concentrated residue is slurried with a mixture of ethyl acetate and petroleum ether, filtered, and the filter cake is air-dried to constant weight to obtain a light yellow to off-white solid Int-2.

7. The method for preparing afollana according to claim 4, characterized in that: After the reaction in step 3 is completed, the organic phase is washed with purified water, and the solvent is evaporated under reduced pressure to obtain a crude product. Acetonitrile is added, stirred, and heated to dissolve the crude product. The temperature is lowered to -10 to 10°C, and the crystal is continued to be stirred, filtered, rinsed, and dried to constant weight to obtain the finished product of afoxolamide, a white crystalline powder.

8. The method for preparing afollana according to claim 2, characterized in that: The molar ratio of Sm1, CDI, alkali and Sm2 is 1:1-1.3:2-3:1.0-1.

5.

9. The method for preparing afollana according to claim 3, characterized in that: The molar ratio of Int-1, Sm3 and alkali is 1:1-1.5:0.

1.

10. The method for preparing afollana according to claim 4, characterized in that: The molar ratio of NaOH to hydroxylamine hydrochloride in the hydroxylamine solution is 1-1.5:1, and the molar ratio of Int-2, tetrabutylammonium bromide and hydroxylamine hydrochloride is 1:0.05:1-3.

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