A preparation method for effectively reducing impurities in seviratine

Abstract

The application relates to the technical field of medicine, and discloses a preparation method for effectively reducing impurities in selamectin, which comprises the following steps: S1, doramectin is oxidized under the action of a TEMPO catalytic system to obtain an oxidation product; S2, the oxidation product is dissolved in an organic solvent A, an ammonium chloride aqueous solution is added, a desugarization reaction is carried out, and a desugarization product is obtained; S3, the desugarization product is dissolved in an organic solvent B, a catalytic hydrogenation reaction occurs under the action of a Wilkinson catalyst, and a hydrogenation product is obtained; S4, the hydrogenation product is dissolved in isopropyl alcohol, an aqueous hydroxylamine hydrochloride solution is added, and a selamectin crude product is obtained; and S5, the selamectin crude product is recrystallized to obtain a selamectin finished product. Through the technical scheme, the problems of many process steps, high cost and many double desugarization impurity products in the preparation of selamectin in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical technology, specifically to a method for preparing selamectin that effectively reduces impurities. Background Technology

[0002] Selamectin, developed by Pfizer Pharmaceuticals in the United States, is used to treat and prevent flea and ear mite infestations, scabies, lice, roundworms, and heartworms in dogs and cats. Its wide range of applications and high safety profile have made it popular with consumers. Therefore, the industrial-scale production of qualified selamectin products has significant commercial value.

[0003] However, selamectin contains a specific impurity, namely impurity C. In commercially available products (such as Advantage), the content of impurity C is about 0.2% higher than other impurities, affecting the stability and efficacy of the drug. Therefore, many companies and research institutions use column chromatography or multiple recrystallizations of the finished product to remove it, greatly increasing costs and process steps. Therefore, reducing the content of impurity C is crucial for preparing qualified selamectin products. The cause of impurity C is an overreaction during the sugar removal reaction, resulting in the removal of two sugar ions.

[0004] Impurity C is a desaccharification product. Its chemical structural formula is as follows:

[0005] Selamectin is a monosaccharide-free product, and its chemical structural formula is as follows:

[0006] Currently, literature reports two methods for desugaring in the preparation of selamectin. One method uses hydroxylamine hydrochloride for simultaneous oxime and desugaring reactions, as shown in EP3150618A1 and CN1099394A. The other method uses strong acids such as sulfuric acid and hydrochloric acid for desugaring, as shown in CN107118247B and CN107021990A. The hydroxylamine hydrochloride method involves simultaneous oxime and desugaring, making process control difficult. The strong acid desugaring method uses sulfuric acid and hydrochloric acid, which, due to their high reactivity, easily leads to over-reaction, resulting in the removal of both sugars. These reasons necessitate the use of column chromatography purification and multiple recrystallizations of the finished product, indirectly causing problems such as more process steps and increased costs. Summary of the Invention

[0007] This invention proposes an effective preparation method for reducing impurities in selamectin, which solves the problems of multiple process steps, high cost, and numerous desugaring impurity products in the preparation of selamectin in related technologies.

[0008] The technical solution of the present invention is as follows: This invention proposes a method for preparing selamectin with effective reduction of impurities, comprising the following steps: S1, doramectin is oxidized in the TEMPO catalytic system to obtain the oxidation product; S2. After dissolving the oxidation product in organic solvent A, add an aqueous solution of ammonium chloride to carry out a desaccharification reaction to obtain the desaccharified product; S3. Dissolve the desugared product in organic solvent B, and under the action of Wilkinson catalyst, a catalytic hydrogenation reaction occurs to obtain the hydrogenated product. S4. Dissolve the hydrogenation product in isopropanol, then add an aqueous solution of hydroxylamine hydrochloride to obtain crude selamectin. S5. After recrystallization of crude selamectin, the finished selamectin product is obtained.

[0009] As a further technical solution, the volume ratio of organic solvent A to water in S2 is 15:1.

[0010] As a further technical solution, the organic solvent A in S2 includes one of ethanol, methanol, and isopropanol.

[0011] As a further technical solution, the temperature of the sugar removal reaction in S2 is 30~80℃, preferably 40~60℃.

[0012] As a further technical solution, the molar ratio of the oxidation product in S2 to ammonium chloride in the ammonium chloride aqueous solution is 1:2~8, preferably 1:2~4.

[0013] As a further technical solution, the organic solvent B in S3 is one of acetone and toluene.

[0014] As a further technical solution, after the catalytic hydrogenation reaction in S3, an organic solvent C is added for recrystallization to obtain the hydrogenation product. The organic solvent C includes one of methanol, acetonitrile, and toluene.

[0015] As a further technical solution, the mass-to-volume ratio of organic solvent C to desaccharification product in S3 is 1g:1~4mL.

[0016] As a further technical solution, the molar ratio of the hydrogenation product in S4 to the hydroxylamine hydrochloride in the aqueous solution of hydroxylamine hydrochloride is 1:3~6, preferably 1:3~5.

[0017] As a further technical solution, the volume ratio of isopropanol to water in the aqueous solution of hydroxylamine hydrochloride in S4 is 5~10:1, preferably 1:3~5.

[0018] As a further technical solution, toluene is used for recrystallization in step S5.

[0019] As a further technical solution, the mass ratio of crude selamectin to toluene in S5 is 1:2~8, preferably 1:3~5.

[0020] As a further technical solution, recrystallization in S5 involves dissolving crude selamectin in toluene at 50-70°C, then cooling the solution to 20-40°C to allow for crystal growth, thereby obtaining the finished selamectin product.

[0021] As a further technical solution, the cooling rate is 5~15℃ / 30min, preferably 5~10℃ / 30min.

[0022] The working principle and beneficial effects of this invention are as follows: This invention employs a novel process route, using a one-pot method of oxidation, desaccharification, and hydrogenation to prepare selamectin. This reduces yield losses caused by intermediate purification and further lowers costs. The preparation of selamectin does not involve column chromatography purification; the finished product only undergoes recrystallization, simplifying the process and reducing production costs. The desaccharification reaction uses weakly acidic ammonium chloride, minimizing over-reaction and significantly reducing the pressure on recrystallization. Furthermore, the yield is further improved, and the amount of impurities from the double desaccharification process is further reduced. Process control is also more convenient. Attached Figure Description

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 This is an HPLC chromatogram of crude selamectin in Example 1 of the present invention; Figure 2 This is an HPLC chromatogram of the selamectin product in Example 1 of the present invention; Figure 3 This is an HPLC chromatogram of crude selamectin in Example 2 of the present invention; Figure 4 This is an HPLC chromatogram of the selamectin product in Example 2 of the present invention; Figure 5 This is an HPLC chromatogram of crude selamectin in Example 3 of the present invention; Figure 6 This is an HPLC chromatogram of the selamectin product in Example 3 of the present invention; Figure 7 This is an HPLC chromatogram of the crude selamectin in Comparative Example 1 of this invention; Figure 8 This is an HPLC chromatogram of the selamectin product in Comparative Example 1 of the present invention; Figure 9 This is an HPLC chromatogram of the crude selamectin in Comparative Example 2 of this invention; Figure 10 This is an HPLC chromatogram of the selamectin product in Comparative Example 2 of the present invention; Figure 11This is the HPLC detection chromatogram of the commercially available product, Da Chong Ai, in Comparative Example 3 of this invention; Figure 12 This is a synthetic route diagram of selamectin in Example 1 of the present invention; Wherein, I is doramectin; II is the oxidation product; III is the desugaring product; IV is the hydrogenation product; and V is seramectin. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 Table 1. Feed ratios for oxidation reaction

[0027] S1. According to the feeding ratio in Table 1, add doramectin, dichloromethane, and TEMPO to a 500mL reaction flask, then add an aqueous solution of sodium bicarbonate. Stir in an ice-water bath, maintaining the temperature at 0~10℃, and add 10% sodium hypochlorite solution dropwise at a uniform rate. The reaction is completed in 30min. Maintain the temperature at 0~10℃ and detect the reaction by TLC (DCM:MeOH=20:1). After the reaction is completed in 2.5h, allow the mixture to stand and separate into layers. Collect the organic layer and extract the aqueous layer with 50mL×2 of dichloromethane. Combine the organic phases and wash with 50mL×2 of saturated sodium sulfite solution. Dry with 20g of anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure at 35℃ in an external bath to obtain a pale yellow oily substance, which is the oxidation product.

[0028] Table 2. Feed ratios for the desugaring reaction Material Name molecular weight Feeding amount moles / mmol Feed ratio Oxidation products 897.11 19.95g 22.24 1 ammonium chloride 53.49 3.57g 66.74 3 water - 19.95mL - 1V / m Anhydrous ethanol - 299.25mL - 15V / m S2. According to the feed ratio in Table 2, dissolve the oxidation product (calculated based on 100% conversion rate) in anhydrous ethanol at room temperature, stir until dissolved, and place in a 500mL reaction flask. Add ammonium chloride aqueous solution to the reaction flask, and after the addition is complete, raise the temperature to 50℃. Maintain the reaction temperature and monitor the reaction by HPLC. The reaction endpoint is reached when the oxidation product is ≤1%. Cool down to 30℃, add 200mL of water to the reaction flask, and extract with 50mL×2 of dichloromethane. Combine the organic phases, dry with 20g of anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure at 40℃ in an external bath to obtain a pale yellow oily substance, which is the desugaring product.

[0029] Table 3. Feed ratios for the hydrogenation reaction Material Name Feeding amount Feed ratio Desugar products 16.75g 1 Wilkinson catalyst 0.5g 0.03 acetone 167.50mL 10V / m Toluene 16.75mL 1.5V / m S3. Take the desugaring product (calculated based on 100% conversion of oxidation products), Wilkinson catalyst, and acetone according to the feeding ratio in Table 3, and add them to a 500mL hydrogenation reactor. Open the nitrogen valve and purge with nitrogen to reach a pressure of 0.2MPa inside the reactor. After purging three times, close the nitrogen valve. Open the hydrogen valve and purge with hydrogen to reach a pressure of 0.2MPa inside the reactor. After purging three times, close the hydrogen valve and raise the pressure inside the reactor to 0.15MPa. Maintain the internal temperature at 25-30℃ and continue the pressure-maintaining reaction. Analyze the reaction using HPLC. When the desugaring product is ≤1%, it is considered the reaction endpoint. After the reaction is complete, open the vent valve.

[0030] The solution was concentrated under reduced pressure at 40°C in an external bath to obtain a pale yellow solid. 16.75 mL of toluene was added, and the mixture was stirred at 60°C until dissolved. The temperature was slowly lowered to 30°C, and crystallization was carried out with stirring for 3 hours. The solid was filtered to obtain an off-white solid, which was then transferred to a vacuum drying oven at 60°C for 8 hours to obtain 14.83 g of solid, the hydrogenated product, with a purity of 98.26%. Recrystallization of doramectin from the hydrogenated product yielded 88.33%.

[0031] Table 4. Feed ratios for oxime reaction Material Name molecular weight Feeding amount moles / mmol Feed ratio hydrogenation products 754.96 14.83g 19.64 1 Hydroxylamine hydrochloride 69.49 6.82g 98.14 5 water - 14.83mL - 1V / m Isopropanol - 118.64mL - 8V / m S4. According to the feeding ratio in Table 4, place the hydrogenation product and isopropanol in a 250mL reaction flask and stir until dissolved at 30℃. Add an aqueous solution of hydroxylamine hydrochloride to the reaction flask and maintain the internal temperature at 20-25℃ to carry out the reaction. Monitor the reaction by HPLC; the hydrogenation product ≤0.3% is the reaction endpoint. Add 100mL of water to the reaction flask and extract with 50mL×2 of dichloromethane. Combine the organic phases, dry with 20g of anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure at 40℃ in an external bath to obtain a pale yellow oily substance, which is crude selamectin. The purity of crude selamectin is 94.38%, and the content of impurity C is 0.51%. The HPLC detection results of crude selamectin are as follows: Figure 1 As shown in Table 5.

[0032] Table 5. HPLC detection results of crude selamectin in Example 1

[0033] Table 6. Feed ratios for recrystallization

[0034] S5. Take crude selamectin (calculated based on 100% conversion of hydrogenated products) and toluene, and place them in a 250mL reaction flask according to the feed ratio in Table 6. Heat to 80℃ and stir until dissolved. Using a programmed cooling method, reduce the temperature to 20℃ at a rate of 10℃ / 30min, precipitating a large amount of white solid. Filter, collect the solid, and vacuum dry at 60℃ to obtain 8.94g of white solid, which is the finished selamectin product. The purity of the finished selamectin product is 99.31%, and the content of impurity C is 0.08%, which is lower than the impurity C content in commercially available products (Advantage), showing a significant advantage. Recrystallization of the hydrogenated products yielded a finished product yield of 59.85%, and the overall yield was 52.86%. The HPLC results of the finished selamectin product are as follows: Figure 2 As shown in Table 7.

[0035] Table 7. HPLC detection results of the finished selamectin product in Example 1

[0036] Example 2 S1 is the same as step S1 in Example 1; Table 8. Feed ratios for the desugaring reaction

[0037] S2. According to the feed ratio in Table 8, dissolve the oxidation product (calculated based on 100% conversion rate) in isopropanol at room temperature, stir until dissolved, and place in a 500mL reaction flask. Add ammonium chloride aqueous solution to the reaction flask, and after the addition is complete, raise the temperature to 30℃. Maintain the reaction temperature and monitor the reaction with HPLC. The reaction endpoint is reached when the oxidation product is ≤1%. Cool down to 30℃, add 200mL of water to the reaction flask, and extract with 50mL×2 of dichloromethane. Combine the organic phases, dry with 20g of anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure at 40℃ in an external bath to obtain a pale yellow oily substance, which is the desugaring product. Table 9. Feed ratios for the hydrogenation reaction

[0038] S3. Take the desugared product (open the nitrogen valve according to the oxidation procedure, purge with nitrogen to reach a pressure of 0.2 MPa in the reactor, purge 3 times, then close the nitrogen valve. Open the hydrogen valve, purge with hydrogen to reach a pressure of 0.2 MPa in the reactor, purge 3 times, then close the hydrogen valve and raise the pressure in the reactor to 0.5 MPa, maintain the internal temperature at 30-35℃, and continue the pressure reaction. HPLC analysis of the reaction shows that a desugared product content ≤1% is considered the reaction endpoint. After the reaction is complete, open the vent valve; The solution was concentrated under reduced pressure at 40°C in an external bath to obtain a pale yellow solid. 16.75 mL of acetonitrile was added, and the mixture was stirred at 60°C until dissolved. The temperature was slowly lowered to 30°C, and crystallization was carried out with stirring for 3 hours. The solid was filtered to obtain an off-white solid, which was then transferred to a vacuum drying oven at 60°C for 8 hours to obtain 11.74 g of solid, the hydrogenated product, with a purity of 99.01%. Recrystallization of doramectin from the hydrogenated product yielded 69.92%. Table 10. Feed ratios for oxime reaction

[0039] S4. According to the feeding ratio in Table 10, place the hydrogenation product and isopropanol in a 250mL reaction flask and stir until dissolved at 30℃. Add an aqueous solution of hydroxylamine hydrochloride to the reaction flask and maintain the internal temperature at 25~30℃ to carry out the reaction. Monitor the reaction by HPLC; the hydrogenation product ≤0.3% is the reaction endpoint. Add 100mL of water to the reaction flask and extract with 50mL×2 of dichloromethane. Combine the organic phases, dry with 20g of anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure at 40℃ in an external bath to obtain a pale yellow oily substance, which is crude selamectin. The purity of crude selamectin is 94.47%, and the impurity C content is 0.7%. The HPLC detection results of crude selamectin are as follows: Figure 3 As shown in Table 11; Table 11 HPLC detection results of crude selamectin in Example 2

[0040] Table 12. Feed ratios for recrystallization

[0041] S5. Take crude selamectin (calculated based on 100% conversion of hydrogenated products) and toluene, and place them in a 250 mL reaction flask according to the feed ratio in Table 12. Heat to 80℃ and stir until dissolved. Using a programmed cooling method, reduce the temperature to 30℃ at a rate of 5℃ / 30 min, precipitating a large amount of white solid. Filter, collect the solid, and vacuum dry at 60℃ to obtain 7.72 g of white solid, which is the finished selamectin product. The purity of the finished selamectin product is 98.99%, the content of impurity C is 0.16%, and the yield of the finished product after recrystallization of the hydrogenated product is 64.47%. The overall yield is 45.08%. The HPLC results of the finished selamectin product are as follows: Figure 4 As shown in Table 13.

[0042] Table 13 HPLC detection results of the finished selamectin product in Example 2

[0043] Example 3 S1 is the same as step S1 in Example 1; Table 14. Feed ratios for the sugar removal reaction

[0044] S2. According to the feed ratio in Table 14, dissolve the oxidation product (calculated based on 100% conversion rate) in methanol at room temperature, stir until dissolved, and place in a 500mL reaction flask. Add ammonium chloride aqueous solution to the reaction flask, and after the addition is complete, raise the temperature to 80℃. Maintain the reaction temperature for 3 hours, monitor the reaction by HPLC, and the reaction endpoint is reached when the oxidation product is ≤1%. Cool down to 30℃, add 200mL of water to the reaction flask, and extract with 50mL×2 of dichloromethane. Combine the organic phases, dry with 20g of anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure at 40℃ in an external bath to obtain a pale yellow oily substance, which is the desugaring product.

[0045] Table 15. Feed ratios for the hydrogenation reaction

[0046] S3. Take the desugaring product (calculated based on 100% conversion of oxidation products), Wilkinson catalyst, and acetone according to the feeding ratio in Table 15, and add them to a 500mL hydrogenation reactor. Open the nitrogen valve and purge with nitrogen to reach a pressure of 0.2MPa inside the reactor. After purging three times, close the nitrogen valve. Open the hydrogen valve and purge with hydrogen to reach a pressure of 0.2MPa inside the reactor. After purging three times, increase the pressure inside the reactor to 0.15MPa, maintain the internal temperature at 25-30℃, and continue the pressure reaction. Analyze the reaction using HPLC. A desugaring product ≤1% is considered the reaction endpoint. After the reaction is complete, open the vent valve.

[0047] The solution was concentrated under reduced pressure in an external bath at 40°C to obtain a pale yellow solid. 67 mL of methanol was added, and the mixture was stirred at 60°C until dissolved. The temperature was slowly lowered to 30°C, and crystallization was carried out with stirring for 3 hours. The mixture was then filtered to obtain a white solid, which was transferred to a vacuum drying oven at 60°C for 8 hours to obtain 10.26 g of solid, the hydrogenated product, with a purity of 99.31%. The yield of doramectin recrystallized from the hydrogenated product was 61.11%.

[0048] Table 16. Feed ratios for oxime reaction

[0049] S4. According to the feeding ratio in Table 16, place the hydrogenation product and isopropanol into a 250mL reaction flask and stir until dissolved at 30℃. Add an aqueous solution of hydroxylamine hydrochloride to the reaction flask and maintain the internal temperature at 25~30℃ to carry out the reaction. Monitor the reaction by HPLC; the hydrogenation product ≤0.3% is the reaction endpoint. Add 100mL of water to the reaction flask and extract with 50mL×2 of dichloromethane. Combine the organic phases, dry with 20g of anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure at 40℃ in an external bath to obtain a pale yellow oily substance, i.e., crude selamectin. HPLC: 95.82%, impurity C: 0.82%. The HPLC detection results of crude selamectin are as follows: Figure 5As shown in Table 17.

[0050] Table 17 HPLC Detection Results of Crude Seramucin in Example 3

[0051] Table 18. Feed ratios for recrystallization

[0052] S5. Take crude selamectin (calculated based on 100% conversion of hydrogenated product) and toluene, and place them in a 250mL reaction flask according to the feed ratio in Table 18. Heat to 80℃ and stir until dissolved. Using a programmed cooling method, reduce the temperature to 40℃ at a rate of 15℃ / 30min, precipitating a large amount of white solid. Filter, collect the solid, and vacuum dry at 60℃ to obtain 6.81g of white solid, which is the selamectin product. The purity of the selamectin product is 99.21%, with impurity C of 0.16%. The yield of the product after recrystallization of the hydrogenated product is 65.08%. The overall yield is 39.77%. The HPLC results of the selamectin product are as follows: Figure 6 As shown in Table 19.

[0053] Table 19 HPLC Detection Results of Seramucin Product in Example 3

[0054] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is the procedure. Following the method described in EP3150618A1, a weakly acidic hydroxylamine hydrochloride solution was used to simultaneously carry out the oxime and desaccharification reactions. The specific steps are as follows: 20g of doramectin was dissolved in 100mL of acetone. The solution was transferred to a 500mL hydrogenation reactor, and 0.38g of Wilkinson's catalyst was added. The nitrogen valve was opened, and nitrogen was introduced to pressurize the reactor to 0.2MPa. After three purgings, the nitrogen valve was closed. The hydrogen valve was then opened, and hydrogen was introduced to pressurize the reactor to 0.2MPa. After three purgings, the pressure was increased to 0.34MPa, and the reaction was maintained at room temperature for 8 hours. After the reaction was complete, the reaction solution was concentrated under reduced pressure at 40°C in an external bath to obtain a brown oily substance. This substance was washed with acetonitrile for 3 hours, filtered, and the solid was transferred to a 50°C vacuum oven and dried for 4 hours to obtain 16.64g of a paste-like solid (hydrogenation product).

[0055] 16.64 g of the hydrogenation product was dissolved in 133 mL of acetone, and 40.19 g of active manganese dioxide was added. The mixture was stirred at room temperature for 1.5 h. After the reaction was complete, the mixture was filtered, and the solid and liquid were separated. The filtrate was collected. The filtrate was concentrated to obtain a yellow oily substance. 58.24 mL of isopropanol was added to the oily substance, the temperature was raised to 82 °C, 5.82 mL of water was added, and the temperature was slowly lowered to room temperature. A solid gradually precipitated out. The mixture was stirred at room temperature overnight, and the solid was collected. The solid was transferred to a vacuum oven at 50 °C and dried for 4 h to obtain 12.64 g of a pale yellow solid (oxidation product).

[0056] 12.64 g of the oxidation product was added to 101 mL of isopropanol and 12 mL of water, and stirred to form a yellow slurry. 5.18 g of hydroxylamine hydrochloride was added, and the reaction was heated to 45 °C to form a clear solution. After 14 h, the reaction was complete. The solution was cooled to room temperature, and 66 mL of methyl tert-butyl ether, 66 mL of toluene, and 33 mL of water were added, and the mixture was stirred thoroughly. The solution was allowed to stand for phase separation, and the organic phase was collected. The organic phase was washed with 66 mL of 5 wt% sodium bicarbonate and 20 mL of sodium chloride. The organic phase was concentrated to obtain a yellow concentrate. 133 mL of toluene was added, and the solution was refluxed to dissolve the concentrate. The solution was slowly cooled to room temperature, and a solid gradually precipitated. The solution was stirred overnight at room temperature, and the solid was collected. The solid was transferred to a 50 °C vacuum oven and dried for 8 h to obtain 7.06 g of selamectin.

[0057] Results: The HPLC detection results of crude selamectin are as follows: Figure 7 As shown in Table 20, the purity of crude selamectin was 73.7%, and the content of impurity C was 3.61%.

[0058] The results show that the comparative example involved simultaneous desugaring and oxime reactions, which made process control difficult and resulted in a high level of impurity C.

[0059] Table 20 HPLC Detection Results of Crude Seramectin

[0060] The HPLC test results of the finished selamectin product are as follows: Figure 8 As shown in Table 21, the purity of the finished selamectin product was 92.21%, and the impurity C content was 1.87%. The total yield was 56.34%.

[0061] The test results show that if the level of impurity C in commercially available products (Advantage) is to be reached, recrystallization is required, which will further reduce the yield.

[0062] Table 21 HPLC Detection Results of Seramectin Product

[0063] Comparative Example 2 The only difference between this comparative example and Example 1 is that step S2 is performed using the strongly acidic sulfuric acid desugaring method described in Example 3 of CN107021990A.

[0064] Results: The HPLC detection results of crude selamectin are as follows: Figure 9 As shown in Table 22, the purity of crude selamectin was 73.05%, and the content of impurity C was 4.04%.

[0065] Table 22 HPLC Detection Results of Crude Seramectin

[0066] The HPLC test results of the finished selamectin product are as follows: Figure 10 As shown in Table 23, the purity of the finished selamectin product was 99.16%, and the impurity C content was 0.22%. The total yield was 44%.

[0067] The test results show that although the content of impurity C is basically the same as that of commercially available products, the yield is low and the cost is significantly increased due to the three recrystallization processes.

[0068] Table 23 HPLC Detection Results of Seramectin Product

[0069] Comparative Example 3 The content of impurity C in the commercially available product, "Adventure," was determined by HPLC. The results are as follows: Figure 11 As shown in Table 24.

[0070] Table 24 HPLC Detection Results of Top-Tier Favorites

[0071] The detection methods for crude selamectin in Examples 1-3 and Comparative Examples 1-3 were performed according to the detection methods in European Pharmacopoeia EP10. in: Column: Waters Nova-Pak C18, 3.9 × 150 mm, 4 µm, catalog number WAT086344 Column temperature: 30℃; Detection wavelength: 243 nm; Injection volume: 20 μL Mobile phase A: Water; Mobile phase B: Acetonitrile; Flow rate: 2.0 mL / min Gradient elution procedure:

[0072] Mixed solvent: 60% acetonitrile (v / v) Test solution: Accurately weigh 25 mg of the test substance, dissolve and dilute it to 50 mL with a mixed solvent. Relative retention time: impurity C=0.5.

[0073] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing selamectin with effective reduction of impurities, characterized in that, Includes the following steps: S1, doramectin is oxidized in the TEMPO catalytic system to obtain the oxidation product; S2. After dissolving the oxidation product in organic solvent A, add an aqueous solution of ammonium chloride to carry out a desaccharification reaction to obtain the desaccharified product; S3. Dissolve the desugared product in organic solvent B, and under the action of Wilkinson catalyst, a catalytic hydrogenation reaction occurs to obtain the hydrogenated product. S4. Dissolve the hydrogenation product in isopropanol, then add an aqueous solution of hydroxylamine hydrochloride to obtain crude selamectin. S5. After recrystallization of crude selamectin, the finished selamectin product is obtained. The sugar removal reaction in S2 is carried out at a temperature of 30~80℃; The molar ratio of the oxidation product in S2 to the ammonium chloride in the ammonium chloride aqueous solution is 1:2~8.

2. The preparation method for effectively reducing impurities in selamectin according to claim 1, characterized in that, The organic solvent A in S2 includes one of ethanol, methanol, and isopropanol.

3. The preparation method for effectively reducing impurities in selamectin according to claim 1, characterized in that, After the catalytic hydrogenation reaction in S3, an organic solvent C is added for recrystallization to obtain the hydrogenated product. The organic solvent C includes one of methanol, acetonitrile, and toluene.

4. The preparation method for effectively reducing impurities in selamectin according to claim 1, characterized in that, The mass-to-volume ratio of organic solvent C to desaccharification product in S3 is 1g:1~4mL.

5. The preparation method for effectively reducing impurities in selamectin according to claim 1, characterized in that, The molar ratio of the hydrogenation product in S4 to hydroxylamine hydrochloride in the aqueous solution is 1:3~6.

6. The preparation method for effectively reducing impurities in selamectin according to claim 1, characterized in that, The volume ratio of isopropanol to water in the aqueous solution of hydroxylamine hydrochloride in S4 is 5~10:

1.

7. The preparation method for effectively reducing impurities in selamectin according to claim 1, characterized in that, In step S5, recrystallization involves dissolving crude selamectin in toluene at 50-70°C, then cooling the solution to 20-40°C to allow for crystal growth, thereby obtaining the finished selamectin product.

8. The preparation method for effectively reducing impurities in selamectin according to claim 7, characterized in that, The cooling rate is 5~15℃ / 30min.

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