A process for the preparation of acetylamino-avermectins

Abstract

The present invention relates to a preparation method of avermectin. The method comprises the following steps: using avermectin B1 as a raw material, preparing an avermectin crude product through protection reaction, oxidation reaction, imidization reaction, reduction and deprotection reaction, and acylation reaction; then subjecting the avermectin crude product to crystallization treatment by a nitric acid crystallization method, and drying the product to obtain an avermectin finished product; wherein the nitric acid crystallization method comprises the following steps: dissolving the avermectin crude product in ethyl acetate, adding pure water and 10% nitric acid solution at room temperature, adjusting the solution pH to 5-6, then standing and stratifying, discarding the ethyl acetate layer, adding an alkaline solution with a weight concentration of 20% to the aqueous layer, adjusting the pH to 7-8 for crystallization, then filtering, and washing the wet crystals with pure water. The method greatly improves product yield, product purity, and reduces the impurity content and solvent residue of the product, so that the product can not only meet the national standards of my country, but also meet the standards of the USP of the United States.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of acetylamino-avermectin preparation, in particular to a preparation method of acetylamino-avermectin. BACKGROUND

[0002] Acetylamino-avermectin is an acetylamino derivative of avermectin, which has the characteristics of high efficiency, low toxicity, broad spectrum and low residue, and is mainly used for preventing and treating various internal and external parasites such as parasites, lice, mites and flies of livestock (especially during lactation period). It acts on the nervous system of parasites, promotes the release of γ-aminobutyric acid, opens the chloride ion channel, prevents the excitation transmission to the muscle, and finally causes the paralysis and death of the parasites. It has a strong killing effect on most nematodes and arthropods.

[0003] At present, the synthesis route of acetylamino-avermectin is usually to first protect the C5-OH of AVMB1 in dichloromethane solvent, then oxidize the C4"-OH to a carbonyl group, replace it with isopropyl acetate, introduce an amino group on C4", remove the protecting group on C5, and then perform acetylation on C4" to obtain acetylamino-avermectin. Finally, acetonitrile method is used for crystallization to obtain the finished product. The existing defects are: 1) due to long process flow and complex reaction, more by-products are generated, and at least 3 times of acetonitrile crystallization or recrystallization operation is usually required to make the product related impurities meet the requirements of the Chinese Pharmacopoeia, but even if the number of acetonitrile crystallization is increased, it cannot meet the USP Pharmacopoeia standard; 2) the acetonitrile crystallization method has limited removal of residual solvents, and the solvent residue is high. Although it can meet the standard of the Chinese Pharmacopoeia, it cannot meet the solvent residue standard of the USP Pharmacopoeia no matter how the number of acetonitrile crystallization is increased; 4) solvent replacement is required during the reaction process. SUMMARY

[0004] The present application aims to overcome the defects of the prior art and provides a preparation method of acetylamino-avermectin, which greatly improves the product yield, the purity of the product, reduces the impurity content and solvent residue of the product, and meets not only the national standard of China but also the USP standard.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A preparation method of acetyl amino avermectin, which comprises the following steps: dissolving acetyl amino avermectin crude product in ethyl acetate, adding pure water and 10% nitric acid solution in mass concentration at normal temperature, adjusting the pH of the solution to 5-6, so that acetyl amino avermectin is converted into nitrate and dissolved in water, then standing and separating, discarding the ethyl acetate layer, adding 20% alkali solution in weight concentration to the water layer, adjusting the pH to 7-8 for crystallization, then centrifugal filtration, and washing the wet crystal with pure water.

[0007] As a further technical scheme, the acetyl amino avermectin crude product is treated once by acetonitrile crystallization method before being treated by the nitric acid crystallization method.

[0008] As a further technical scheme, the nitric acid crystallization method is used once.

[0009] The acetonitrile crystallization method comprises the following steps: adding acetyl amino avermectin crude product into acetonitrile, dissolving at 50℃, then cooling and crystallizing, and centrifugal filtration.

[0010] As a further technical scheme, the acetyl amino avermectin crude product is prepared from avermectin B1 by protection reaction, oxidation reaction, imination reaction, reduction and deprotection reaction, and acylation reaction.

[0011] As a further technical scheme, the protection reaction comprises the following steps: dissolving avermectin B1 in dichloromethane solvent, cooling to-15 to-20℃, then adding allyl chloroformate and dropping in acid-binding agent tetramethyl ethylenediamine, and reacting for 50-70 min under normal pressure to obtain the protection product of C5-OH, i.e. the protection product of avermectin B1, which is intermediate one.

[0012] As a further technical scheme, the oxidation reaction comprises the following steps: adding dimethyl sulfoxide solution and tetramethyl ethylenediamine solution to the reaction liquid of the protection product of avermectin B1 at-10℃, and reacting for 1.5-2.5 h at-10℃ to oxidize C4"-OH into C4"=O to obtain the oxidation product of avermectin B1, i.e. intermediate two, then adding water to the reaction liquid to terminate the reaction, standing and separating, and keeping the dichloromethane layer, i.e. the dichloromethane solution of the oxidation product of avermectin B1, for standby;

[0013] As a further technical scheme, the imination reaction comprises the following steps:

[0014] To the dichloromethane solution of the abamectin B1 oxidation product, add hexamethyldisilazane and a catalyst zinc trifluoroacetate, heat to 48-53℃, control the pressure of the reaction kettle to be slightly positive, and react for 110-130 min to introduce imino group at the C4" position of the abamectin oxidation product to generate the abamectin B1 imination product, i.e. intermediate three. Then add water to the reaction liquid to terminate the reaction, and leave the dichloromethane layer, i.e. the dichloromethane solution of the abamectin B1 imination product, for standby.

[0015] As a further technical solution, the pressure of the slightly positive pressure state is 0.01-0.05 mpa;

[0016] The addition amount of hexamethyldisilazane is 1.1-3 times, preferably (1.05-1.35) times, of the molar mass of abamectin B1.

[0017] As a further technical solution, the addition amount of the catalyst zinc trifluoroacetate is (0.3-1.5) times, preferably (0.3-0.5) times, of the molar mass of abamectin B1.

[0018] As a further technical solution, the reduction and deprotection reaction comprises the following steps:

[0019] To the dichloromethane solution of the abamectin B1 imination product, add anhydrous ethanol, cool to -5 to -10℃, and then slowly add sodium borohydride. After reacting for 50-70 min, the C4"=NH of the abamectin B1 imination product is reduced to C4"-NH2 to generate the abamectin B1 reduction product, i.e. intermediate four.

[0020] After the reduction reaction is qualified, continue to add anhydrous ethanol, sodium borohydride and 4-triphenylphosphine palladium chloride to the reaction liquid, and perform deprotection reaction at -5 to 5℃ for 50-70 min to remove the protecting group of the abamectin C5-OH to generate amino abamectin, i.e. the abamectin B1 deprotection product, i.e. intermediate five. Then add 10% acetic acid aqueous solution below 0℃ dropwise until the material is neutral. After stirring until the aqueous solution is dissolved, stand for separation, and leave the dichloromethane layer, i.e. the dichloromethane solution of the amino abamectin, for standby.

[0021] As a further technical solution, in the deprotection reaction, the addition amount of sodium borohydride is 0.4-1.5 times, preferably 0.4-0.6 times, of the molar mass of abamectin B1.

[0022] As a further technical solution, the addition amount of 4-triphenylphosphine palladium chloride is 0.007-0.02 times, preferably 0.007-0.008 times, of the molar mass of abamectin B1.

[0023] As a further technical solution, the acylation reaction comprises the following steps:

[0024] The temperature of the dichloromethane solution of the amino-avermectin is controlled below 0°C, acetic anhydride is added, and the reaction is maintained for 25-35 min to acetylate the amino group on the amino-avermectin to generate acetylamino-avermectin. Then, 10% sodium hydroxide aqueous solution is added to the reaction solution to adjust the pH to neutral, the water layer is discarded, and the dichloromethane solution containing the acetylamino-avermectin is evaporated under reduced pressure at 60°C to remove the dichloromethane, thereby obtaining the crude acetylamino-avermectin.

[0025] As a further technical solution, a method for preparing acetylamino-avermectin comprises the following steps:

[0026] Step 1, protection reaction: avermectin B1 is dissolved in dichloromethane solvent, and the temperature is lowered to -15 to -20°C. Allyl chloroformate is added, and tetramethyl ethylenediamine is added dropwise as an acid-binding agent. The reaction is carried out under normal pressure for 50-70 min to obtain a protection product of C5-OH, i.e., an avermectin B1 protection product, which is intermediate one.

[0027] Step 2, oxidation reaction: at -10°C, dimethyl sulfoxide solution and tetramethyl ethylenediamine solution are added to the reaction solution of the avermectin B1 protection product obtained in step 1. The reaction is carried out at -10°C for 1.5-2.5 h to oxidize C4"-OH to C4"=O to obtain an oxidation product of avermectin B1, i.e., intermediate two. Then, water is added to the reaction solution to terminate the reaction, and the mixture is allowed to stand and separate into layers. The dichloromethane layer, i.e., a dichloromethane solution of the oxidation product of avermectin B1, is reserved for use.

[0028] Step 3, imination reaction: hexamethyl disilazane and a catalyst, zinc trifluoroacetate, are added to the dichloromethane solution of the oxidation product of avermectin B1. The reaction kettle is heated to 50°C, and the pressure is controlled to be slightly positive. The reaction is carried out for 110-130 min to introduce imino group at the C4" position of the oxidation product of avermectin to generate an imination product of avermectin B1, i.e., intermediate three. Then, water is added to the reaction solution to terminate the reaction, and the dichloromethane layer, i.e., a dichloromethane solution of the imination product of avermectin B1, is reserved for use.

[0029] Step 4, reduction and deprotection reaction: anhydrous ethanol is added to the dichloromethane solution of the imination product of avermectin B1. The temperature is lowered to -5 to -10°C, and sodium borohydride is slowly added. The reaction is carried out for 50-70 min to reduce C4"=NH of the imination product of avermectin B1 to C4"-NH2.

[0030] After the reduction reaction is qualified, continue to add anhydrous ethanol, sodium borohydride and 4-triphenylphosphine palladium chloride to the reaction solution, and react at -5℃ to 5℃ for 50-70 min to remove the protecting group of avermectin C5-OH to obtain amino avermectin (i.e. intermediate five); then drop 10% acetic acid aqueous solution below 0℃ to neutralize the material, and stir until the aqueous solution is dissolved, then stand and separate the layers, and the dichloromethane layer, i.e. the dichloromethane solution of amino avermectin, is reserved for later use;

[0031] Step 5, acylation:

[0032] The temperature of the dichloromethane solution of amino avermectin is controlled below 0℃, acetic anhydride is added, and the reaction is incubated for 25-35 min to acetylate the amino group on the amino avermectin to generate acetylamino avermectin; then 10% sodium hydroxide aqueous solution is added to the reaction solution to adjust the pH to neutral, the water layer is discarded, and the dichloromethane solution containing acetylamino avermectin is evaporated under reduced pressure at 60℃ to remove the dichloromethane to obtain acetylamino avermectin crude product;

[0033] Step 6, crystallization

[0034] The acetylamino avermectin crude product is crystallized by the nitric acid method or first crystallized by the acetonitrile crystallization method and then crystallized by the nitric acid crystallization method, and then dried to obtain acetylamino avermectin finished product;

[0035] The acetonitrile crystallization method comprises the following steps:

[0036] The acetylamino avermectin crude product is added to acetonitrile, dissolved by heating to 50℃, and then crystallized by cooling, and centrifuged and filtered to obtain acetylamino avermectin wet crystal;

[0037] The nitric acid crystallization method comprises the following steps:

[0038] The acetylamino avermectin crude product or acetylamino avermectin wet crystal is dissolved in ethyl acetate, and pure water and 10% nitric acid solution are added at room temperature to adjust the pH of the solution to 5-6, so that the acetylamino avermectin is converted into a nitrate salt dissolved in water, and then the solution is allowed to stand and separate the layers, the ethyl acetate layer is discarded, and a 20% alkali solution is added to the water layer to adjust the pH to 7-8 for crystallization, and then the wet crystal is centrifuged and washed with pure water.

[0039] In the present application,

[0040] The structural formula of avermectin B1 is:

[0041]

[0042] The structural formula of intermediate one (a protected product) is:

[0043]

[0044] Structure formula of intermediate two (oxidation product) :

[0045] Structure formula of intermediate three (imidization product) :

[0046]

[0047] Structure formula of intermediate four (reduction product) :

[0048]

[0049] Structure formula of intermediate five (deprotection product, that is, amino avermectin) :

[0050]

[0051] Structure formula of acetylamino avermectin:

[0052]

[0053] Compared with the prior art, the beneficial effects obtained by the present application are as follows:

[0054] In the amination reaction, the present application improves the atmospheric pressure reaction in the conventional process into a micro-positive pressure reaction, compared with the conventional process, the amination reaction does not replace the solvent, and it is possible to continue to use dichloromethane as the solvent in the protection reaction, avoiding a series of defects brought by solvent replacement, in addition, when the amination reaction is carried out with dichloromethane as the solvent, by optimizing the reaction conditions of the amination reaction, on the one hand, the amount of hexamethyldisilazane in the amination reaction and the amount of sodium borohydride in the deprotection reaction are greatly reduced, the material cost is saved, and in the deprotection reaction, the deprotection reaction time is also shortened, on the other hand, the purity of the final product is improved, the content of related impurities is reduced, and it can meet the requirements of Chinese Veterinary Pharmacopoeia (2020 edition).

[0055] The present application adopts nitric acid crystallization method to crystallize and purify acetylamino avermectin, which only needs one crystallization to meet the requirements of Chinese Veterinary Pharmacopoeia, and even in terms of solvent residue, it can meet the requirements of USP45 Pharmacopoeia; compared with the acetonitrile crystallization method in the conventional technology, acetonitrile is no longer used, solving a series of defects brought by the use of acetonitrile in the conventional technology, in addition, it also solves the problem that no matter how many times of crystallization is increased, the solvent residue cannot meet the USP Pharmacopoeia standard when acetonitrile is used for crystallization in the conventional technology;

[0056] The ammination reaction and the subsequent reaction in the application, although the reaction conditions of the ammination reaction are improved so that the end product can reach the provisions of the Chinese Veterinary Pharmacopoeia without replacing the solvent, compared with the traditional solvent replacement method, the total unknown impurities cannot meet the requirements of the USP Pharmacopoeia, and no matter how many times the acetonitrile crystallization is increased, it cannot meet the requirements of the USP Pharmacopoeia, and the problem is perfectly solved by using the nitric acid crystallization method for crystallization and purification, so that the related impurities of the end product not only meet the provisions of the Chinese Veterinary Pharmacopoeia but also meet the provisions of the USP Pharmacopoeia.

[0057] The acetylamino avermectin is first crystallized by the acetonitrile crystallization method, and then the acetylamino avermectin is crystallized by the nitric acid method, the combination of the two methods greatly improves the purity of the finished product and reduces the content of related impurities, and each crystallization method only needs to be crystallized once to meet the requirements of the USP Pharmacopoeia;

[0058] In summary, the ammination reaction is carried out under the condition of micro-positive pressure with dichloromethane as the solvent, and the crystallization technology of the nitric acid method or the combination of the acetonitrile method and the nitric acid method is used, which greatly improves the product yield, the purity of the product, reduces the impurity content of the product and the solvent residue, so that it not only meets the provisions of the Chinese Veterinary Pharmacopoeia but also meets the provisions of the USP Pharmacopoeia. DETAILED DESCRIPTION

[0059] The application will be further described in detail in combination with the following examples.

[0060] Example 1

[0061] A preparation method of acetylamino avermectin, comprising the following steps:

[0062] Step 1, protection reaction: 100g of avermectin B1 is dissolved in 500g of dichloromethane solvent, cooled to-15 to-20℃, then 14g of chloroformic acid allyl ester is added, and 19g of acid-binding agent tetramethyl ethylenediamine is added dropwise, and reacted for 1h under normal pressure to obtain the protection product of C5-OH, that is, the protection product of avermectin B1, that is, intermediate one;

[0063] Step 2, oxidation reaction: 22g of dimethyl sulfoxide solution and 15g of tetramethyl ethylenediamine solution are added to the reaction liquid of intermediate one obtained in step 1 at-10℃, and reacted for 2h at-10℃ to oxidize C4"-OH to C4"=O to obtain the oxidation product of avermectin B1, that is, intermediate two, then water is added to terminate the reaction, and the layers are separated after standing, and the dichloromethane layer is reserved, that is, the dichloromethane solution of intermediate two, for standby;

[0064] Step 3, imidization reaction: to the dichloromethane solution of intermediate two, 21 g of hexamethyldisilazane and 5 g of catalyst zinc trifluoroacetate are added, heated to 50 °C, the reaction kettle pressure is controlled to be a micro-positive pressure of 0.01-0.05 mpa, and the reaction is carried out for 2 h. At this time, the reaction liquid is qualified in quality control, the imino group is introduced at the C4" position of the abamectin oxidation product to generate the abamectin B1 imidization product, i.e. intermediate three. Then, water is added to the reaction liquid to terminate the reaction, and the dichloromethane layer is retained, i.e. the dichloromethane solution of intermediate three, which is ready for use;

[0065] Step 4, reduction and deprotection reaction: to the dichloromethane solution of intermediate three, 80 g of anhydrous ethanol is added, cooled to -5 to -10 °C, and then 5 g of sodium borohydride is slowly added. The reaction is carried out for 1 h, and the C4"-NH of the abamectin B1 imidization product is reduced to C4"-NH2;

[0066] After the reduction reaction is qualified, 40 g of anhydrous ethanol, 2 g of sodium borohydride and 1 g of 4-triphenylphosphine palladium chloride are continuously added to the reaction liquid, and the reaction is carried out at -5 to 5 °C for 1 h. The reaction liquid is qualified in quality control, the protecting group of abamectin C5-OH is removed, and amino abamectin (i.e. intermediate five) is obtained. Then, 10% acetic acid aqueous solution below 0 °C is added dropwise until the material becomes neutral. After stirring until the aqueous solution is dissolved, the reaction liquid is allowed to stand and separate into layers. The dichloromethane layer, i.e. the dichloromethane solution of amino abamectin, is retained and ready for use;

[0067] Step 5, acylation:

[0068] The temperature of the dichloromethane solution of amino abamectin is controlled to be below 0 °C, and 12 g of acetic anhydride is added. The reaction is carried out for 30 min, the amino group on the amino abamectin is acetylated to generate acetylamino abamectin, and then 10% sodium hydroxide aqueous solution is added to the reaction liquid to adjust the pH to neutral. The aqueous layer is discarded, and the dichloromethane solution containing acetylamino abamectin is evaporated under reduced pressure at 60 °C to remove dichloromethane, and acetylamino abamectin crude product is obtained;

[0069] Step 6, crystallization

[0070] The acetylamino abamectin crude product is crystallized once by acetonitrile method and then crystallized by nitric acid method, and dried to obtain acetylamino abamectin finished product;

[0071] The acetonitrile method comprises the following steps:

[0072] The acetylamino abamectin crude product is added to 500 g of acetonitrile, dissolved by heating to 50 °C, and then crystallized by cooling. The product is centrifuged and filtered to obtain acetylamino abamectin wet crystal;

[0073] The nitric acid method comprises the following steps:

[0074] Dissolve acetylamino-avermectin wet crystal in 500 g ethyl acetate, add pure water and 10% nitric acid solution at room temperature, adjust the pH of the solution to 5-6, convert acetylamino-avermectin into nitrate dissolved in water, then stand to separate layers, discard the ethyl acetate layer, and add a 20% alkali solution to the water layer, adjust the pH to 7-8 to crystallize, then filter, wash the wet crystal with pure water, and it is ready;

[0075] Example 2

[0076] A method for preparing acetylamino-avermectin, comprising the following steps:

[0077] Step 1, protection reaction: dissolve 50 g of avermectin B1 in 200 g of dichloromethane solvent, cool to -15 to -20 °C, then add 7 g of allyl chloroformate and 9 g of acid-binding agent tetramethyl ethylenediamine, react at normal pressure for 1 h to obtain the protection product of C5-OH, i.e. intermediate one;

[0078] Step 2, oxidation reaction: at -10 °C, add 11 g of dimethyl sulfoxide solution and 9 g of tetramethyl ethylenediamine solution to the reaction solution of intermediate one obtained in step 1, react at -10 °C for 2 h to oxidize C4"-OH to C4"=O to obtain the oxidation product of avermectin B1, i.e. intermediate two, then add water to terminate the reaction, stand to separate layers, and keep the dichloromethane layer, i.e. the dichloromethane solution of intermediate two, for standby;

[0079] Step 3, imination reaction: add 11 g of hexamethyldisilazane and 3 g of catalyst zinc trifluoroacetate to the dichloromethane solution of intermediate two, heat to 50 °C, control the pressure of the reaction kettle to be 0.01-0.05 mpa of micro-positive pressure, and react for 2 h, at which time the reaction solution is qualified in quality control, introduce imino group at the C4" position of the oxidation product of avermectin to generate the imination product of avermectin B1, i.e. intermediate three, then add water to terminate the reaction, keep the dichloromethane layer, i.e. the dichloromethane solution of intermediate three, for standby;

[0080] Step 4, reduction and deprotection reaction: add 40 g of anhydrous ethanol to the dichloromethane solution of intermediate three, cool to -5 to -10 °C, then slowly add 2 g of sodium borohydride, and react for 1 h to reduce C4"=NH of the imination product of avermectin B1 to C4"-NH2;

[0081] After the reduction reaction is qualified, 20 g of anhydrous ethanol, 1 g of sodium borohydride and 0.5 g of 4-triphenylphosphine palladium chloride are continuously added to the reaction solution, and the reaction is carried out at -5°C to 5°C for 1 h. At this time, the reaction solution is qualified in quality control, the protecting group of avermectin C5-OH is removed, and amino avermectin (i.e. intermediate five) is obtained. Then, 10% aqueous acetic acid below 0°C is added dropwise until the material is neutral. After stirring until the aqueous solution is dissolved, it is left to separate into layers, and the dichloromethane layer, i.e. the dichloromethane solution of amino avermectin, is retained for standby;

[0082] Step 5, acylation:

[0083] The temperature of the dichloromethane solution of amino avermectin is controlled below 0°C, 6 g of acetic anhydride is added, and the reaction is carried out at 60°C for 30 min to acetylate the amino group on the amino avermectin to generate acetylamino avermectin. Then, 10% aqueous sodium hydroxide solution is added to the reaction solution to adjust the pH to neutral. The water layer is discarded, and the dichloromethane solution containing acetylamino avermectin is evaporated under reduced pressure at 60°C to remove the dichloromethane, thereby obtaining the crude acetylamino avermectin.

[0084] Step 6, crystallization

[0085] The crude acetylamino avermectin is crystallized once using the acetonitrile method and then crystallized using the nitric acid method, and dried to obtain the finished acetylamino avermectin.

[0086] The acetonitrile method includes the following steps:

[0087] The crude acetylamino avermectin is added to 240 g of acetonitrile, dissolved by heating to 50°C, and then crystallized by cooling. The wet crystal is obtained by centrifugal filtration.

[0088] The nitric acid method includes the following steps:

[0089] The wet crystal of acetylamino avermectin is dissolved in 300 g of ethyl acetate, and pure water and 10% nitric acid solution are added at room temperature to adjust the pH of the solution to 5-6, so that the acetylamino avermectin is converted into a nitrate salt dissolved in water. Then, it is left to separate into layers, and the ethyl acetate layer is discarded. A 20% alkali solution is added to the water layer to adjust the pH to 7-8 for crystallization, and then the wet crystal is washed with pure water.

[0090] Example 3

[0091] A method for preparing acetylamino avermectin includes the following steps:

[0092] Step 1, protection reaction: 150g of abamectin B1 is dissolved in 620g of dichloromethane solvent, cooled to -15 to -20℃, then 21g of allyl chloroformate is added, while 27g of acid binding agent tetramethyl ethylenediamine is added dropwise, and the reaction is carried out under normal pressure for 1h to obtain the protection product of C5-OH, i.e. intermediate one;

[0093] Step 2, oxidation reaction: at -10℃, 33g of dimethyl sulfoxide solution and 21g of tetramethyl ethylenediamine solution are added to the reaction solution of intermediate one obtained in step 1, and the reaction is carried out at -10℃ for 2h to oxidize C4"-OH to C4"=O to obtain the oxidation product of abamectin B1, i.e. intermediate two, then water is added to terminate the reaction, and the layers are separated after standing, and the dichloromethane layer, i.e. the dichloromethane solution of intermediate two, is reserved for use;

[0094] Step 3, imination reaction: 32g of hexamethyldisilazane and 10g of catalyst zinc trifluoroacetate are added to the dichloromethane solution of intermediate two, heated to 50℃, and the pressure of the reaction kettle is controlled to be a micro-positive pressure of 0.01-0.05mpa, and the reaction is carried out for 2h, at which time the reaction solution is qualified in quality control, and imino group is introduced at the C4" position of the oxidation product of abamectin to generate the imination product of abamectin B1, i.e. intermediate three, then water is added to terminate the reaction, and the dichloromethane layer, i.e. the dichloromethane solution of intermediate three, is reserved for use;

[0095] Step 4, reduction and deprotection reaction: 100g of anhydrous ethanol is added to the dichloromethane solution of intermediate three, cooled to -5 to -10℃, then 6g of sodium borohydride is slowly added, and the reaction is carried out for 1h to reduce C4"=NH of the imination product of abamectin B1 to C4"-NH2;

[0096] After the reduction reaction is qualified, 50g of anhydrous ethanol, 3g of sodium borohydride and 1.5g of 4-triphenylphosphine palladium chloride are continuously added to the reaction solution, and the reaction is carried out at -5 to 5℃ for 1h, at which time the reaction solution is qualified in quality control, and the protection group of C5-OH of abamectin is removed to obtain amino abamectin (i.e. intermediate five); then 10% aqueous acetic acid below 0℃ is added dropwise until the material becomes neutral, and after stirring until the aqueous solution is dissolved, the layers are separated after standing, and the dichloromethane layer, i.e. the dichloromethane solution of amino abamectin, is reserved for use;

[0097] Step 5, acylation:

[0098] The temperature of the dichloromethane solution of amino abamectin is controlled below 0℃, 17g of acetic anhydride is added, and the reaction is carried out for 30min to acetylate the amino group on amino abamectin to generate acetylamino abamectin, then 10% aqueous sodium hydroxide solution is added to the reaction solution to adjust the pH to neutral, the aqueous layer is discarded, and the dichloromethane solution containing acetylamino abamectin is evaporated under reduced pressure at 60℃ to remove dichloromethane to obtain acetylamino abamectin crude product;

[0099] Step 6, crystallization

[0100] The acetylamino-avermectin crude product is crystallized by acetonitrile method and nitric acid method in sequence, dried, and acetylamino-avermectin finished product is obtained.

[0101] The acetonitrile method comprises the following steps:

[0102] The acetylamino-avermectin crude product is added into 500g acetonitrile, dissolved at 50℃, then cooled to crystallize, centrifuged and filtered, and acetylamino-avermectin wet crystal is obtained.

[0103] The nitric acid method comprises the following steps:

[0104] The acetylamino-avermectin wet crystal is dissolved in 600g ethyl acetate, pure water and 10% nitric acid solution are added at room temperature, the solution pH is adjusted to 5-6, acetylamino-avermectin is converted into nitrate salt dissolved in water, then it is left to stand and stratified, the ethyl acetate layer is discarded, a 20% alkali solution is added to the water layer, the pH is adjusted to 7-8 for crystallization, then it is centrifuged and filtered, and the wet crystal is washed with pure water.

[0105] Example 4

[0106] A preparation method of acetylamino-avermectin comprises the following steps:

[0107] Step 1, protection reaction: same as example 1;

[0108] Step 2, oxidation reaction: same as example 1;

[0109] Step 3, amination reaction: same as example 1;

[0110] Step 4, reduction and deprotection reaction: same as example 1;

[0111] Step 5, acylation: same as example 1;

[0112] Step 6, crystallization

[0113] The acetylamino-avermectin crude product is crystallized by nitric acid method, dried, and acetylamino-avermectin finished product is obtained.

[0114] The nitric acid method comprises the following steps:

[0115] The acetylamino-avermectin crude product is dissolved in 500g ethyl acetate, pure water and 10% nitric acid solution are added at room temperature, the solution pH is adjusted to 5-6, acetylamino-avermectin is converted into nitrate salt dissolved in water, then it is left to stand and stratified, the ethyl acetate layer is discarded, a 20% alkali solution is added to the water layer, the pH is adjusted to 7-8 for crystallization, then it is centrifuged and filtered, and the wet crystal is washed with pure water.

[0116] Comparative Example 1

[0117] A method for preparing acetylamino-avermectin, comprising the following steps:

[0118] Step 1, protection reaction: same as Example 1;

[0119] Step 2, oxidation reaction: same as Example 1;

[0120] Step 3, amination reaction: same as Example 1;

[0121] Step 4, reduction and deprotection reaction: same as Example 1;

[0122] Step 5, acylation: same as Example 1;

[0123] Step 6, crystallization

[0124] The acetylamino-avermectin crude product is crystallized 4 times by acetonitrile method, and dried to obtain acetylamino-avermectin finished product;

[0125] The acetonitrile method comprises the following steps:

[0126] The acetylamino-avermectin crude product or acetylamino-avermectin wet crystal obtained from the last crystallization is added into 500 g of acetonitrile, dissolved by heating to 50°C, and then crystallized by cooling, and centrifuged and filtered to obtain acetylamino-avermectin wet crystal;

[0127] Comparative Example 2

[0128] A method for preparing acetylamino-avermectin, comprising the following steps:

[0129] Step 1, protection reaction: same as Example 1;

[0130] Step 2, oxidation reaction: same as Example 1;

[0131] Step 3, amination reaction: 42 g of hexamethyldisilazane and 10 g of catalyst zinc trifluoroacetate are added into a dichloromethane solution of intermediate two, heated to 50°C, and controlled to be in a micro-positive pressure state (inert gas nitrogen is introduced for pressure control) with a pressure of 2-3 mpa in the reaction kettle, reacted for 2 h, at this time the reaction liquid is qualified in quality control, imino is introduced at the C4" position of the avemectin oxidation product to generate avemectin B1 imine product, i.e. intermediate three, then water is added into the reaction liquid to terminate the reaction, and the dichloromethane layer is reserved, i.e. the dichloromethane solution of intermediate three, for standby use; in the amination reaction of this comparative example, when the amount of hexamethyldisilazane is less than 42 g, the reaction will be incomplete, and when the amount of catalyst is less than 10 g, the reaction rate will be reduced and the reaction time will be prolonged, and the reaction cannot be completed in 2 h;

[0132] Step 4, reduction and deprotection reaction: 80 g of anhydrous ethanol was added to a dichloromethane solution of the intermediate three, and after cooling to -5 to -10 °C, 5 g of sodium borohydride was slowly added, and the reaction was carried out for 1 h to reduce the C4"=NH of the avermectin B1 imine product to C4"-NH2;

[0133] After the reduction reaction was qualified, 40 g of anhydrous ethanol, 4 g of sodium borohydride and 2.0 g of 4-triphenylphosphine palladium chloride were continuously added to the reaction solution, and the reaction was carried out at -5 to 5 °C to remove the protecting group of avermectin C5-OH. When the reaction was carried out for 1 h, the reaction solution was quality controlled, and it was found that the reaction was not complete, so the reaction was continued until the reaction was carried out for 3.8 h, the reaction solution was quality controlled, and amino avermectin (i.e. intermediate five) was obtained. Then 10% acetic acid aqueous solution below 0 °C was added dropwise until the material was neutral, and after stirring until the aqueous solution material was dissolved, it was left to separate into layers, and the dichloromethane layer, i.e. the dichloromethane solution of amino avermectin, was obtained. It was ready for use. In the deprotection reaction of the present comparative example, when the amount of sodium borohydride was less than 4 g, the reaction was not complete. When the amount of catalyst 4-triphenylphosphine palladium chloride was less than 2.0 g, the reaction rate was slow, and the reaction was still not complete after 3.8 h;

[0134] Step 5, acylation: same as example 1;

[0135] Step 6, crystallization: the crude acetylamino avermectin was crystallized by acetonitrile method for 4 times, and dried to obtain acetylamino avermectin finished product;

[0136] The acetonitrile method comprises the following steps:

[0137] The crude acetylamino avermectin or the acetylamino avermectin wet crystal obtained from the last crystallization was added to 500 g of acetonitrile, and then dissolved by heating to 50 °C. Then, the temperature was lowered to induce crystallization, and the filter was centrifuged to obtain acetylamino avermectin wet crystal.

[0138] Comparative example 3

[0139] A method for preparing acetylamino avermectin, comprising the following steps:

[0140] Step 1, protection reaction: same as example 1;

[0141] Step 2, oxidation reaction: same as example 1;

[0142] Step 3, amination reaction: to the dichloromethane solution of intermediate two, 42 g of hexamethyldisilazane and 10 g of catalyst zinc trifluoroacetate were added, heated to 50 °C, and refluxed for 2 h. At this time, the reaction solution was quality controlled. The imino group was introduced at the C4" position of the abamectin oxidation product to generate the abamectin B1 imination product, i.e. intermediate three. Then, water was added to the reaction solution to terminate the reaction, and the dichloromethane layer was retained, i.e. the dichloromethane solution of intermediate three, which was ready for use. In the amination reaction of the present comparative example, when the amount of hexamethyldisilazane was less than 42 g, the reaction was incomplete. When the amount of catalyst was less than 10 g, the reaction rate was reduced, and the reaction time was prolonged, and the reaction could not be completed in 2 h.

[0143] Step 4, reduction and deprotection reaction: to the dichloromethane solution of intermediate three, 80 g of anhydrous ethanol was added, and the temperature was lowered to -5 to -10 °C. Then, 5 g of sodium borohydride was slowly added, and the reaction was carried out for 1 h. The C4"-NH of the abamectin B1 imination product was reduced to C4"-NH2.

[0144] After the reduction reaction was qualified, 40 g of anhydrous ethanol, 4 g of sodium borohydride and 2 g of 4-triphenylphosphine palladium chloride were continuously added to the reaction solution, and the reaction was carried out at -5 to 5 °C. The protecting group of the abamectin C5-OH was removed. When the reaction was carried out for 1 h, the reaction solution was quality controlled, and it was found that the reaction was incomplete. Therefore, the reaction was continuously carried out until the reaction was carried out for 4 h. The reaction solution was quality controlled, and the amino abamectin (i.e. intermediate five) was obtained. Then, 10% acetic acid aqueous solution below 0 °C was added dropwise until the material was neutral. After stirring until the aqueous solution was dissolved, the reaction solution was separated into layers, and the dichloromethane layer was retained, i.e. the dichloromethane solution of amino abamectin, which was ready for use. In the deprotection reaction of the present comparative example, when the amount of sodium borohydride was less than 4 g, the reaction was incomplete. When the amount of catalyst 4-triphenylphosphine palladium chloride was less than 2.0 g, the reaction rate was reduced, and the reaction could not be completed in 3.8 h.

[0145] Step 5, acylation: the same as example 1.

[0146] Step 6, crystallization: the acetylamino abamectin crude product was crystallized by the acetonitrile method for 4 times, and dried to obtain the acetylamino abamectin finished product.

[0147] The acetonitrile method comprises the following steps:

[0148] The acetylamino abamectin crude product or the acetylamino abamectin wet crystal obtained from the last crystallization was added to 500 g of acetonitrile, and dissolved by heating to 50 °C. Then, the temperature was lowered to induce crystallization, and the filter was shaken by centrifugation to obtain the acetylamino abamectin wet crystal.

[0149] Comparative example 4

[0150] A preparation method of acetylamino abamectin comprises the following steps:

[0151] Step 1, protection reaction: same as Example 1;

[0152] Step 2, oxidation reaction: same as Example 1;

[0153] Step 3, amination reaction: first, the solvent in the dichloromethane solution of intermediate two was evaporated, then 400 g of isopropyl acetate solvent was added, followed by the addition of 50 g of hexamethyldisilazane and 10 g of catalyst zinc trifluoroacetate, heated to 50°C, reacted for 2 h, at this time the reaction liquid was qualified by quality control, the imino group was introduced at the C4" position of the avermectin oxidation product to generate the avermectin B1 imination product, i.e. intermediate three, then water was added to the reaction liquid to terminate the reaction, and the dichloromethane layer, i.e. the dichloromethane solution of intermediate three, was reserved for use; in the amination reaction of this comparative example, when the amount of hexamethyldisilazane was less than 50 g, the reaction was incomplete, and when the amount of catalyst was less than 10 g, the reaction rate decreased and the reaction time was prolonged, and the reaction could not be completed in 2 h;

[0154] Step 4, reduction and deprotection reaction: 80 g of anhydrous ethanol was added to the dichloromethane solution of intermediate three, cooled to -5 to -10°C, and then 5 g of sodium borohydride was slowly added, reacted for 1 h, and the C4" = NH of the avermectin B1 imination product was reduced to C4" - NH2;

[0155] After the reduction reaction was qualified, 40 g of anhydrous ethanol, 4 g of sodium borohydride and 2 g of 4-triphenylphosphine palladium chloride were continuously added to the reaction liquid, reacted at -5 to 5°C, and when the reaction liquid was not completely reacted after 1 h of reaction, the reaction was continuously carried out, and when the reaction liquid was qualified by quality control after 3.5 h of reaction, the protecting group of avermectin C5-OH was removed to obtain amino avermectin (i.e. intermediate five); then 10% aqueous acetic acid below 0°C was added dropwise until the material became neutral, stirred until the aqueous solution was dissolved, and then separated by standing, and the dichloromethane layer, i.e. the dichloromethane solution of amino avermectin, was reserved for use; in the deprotection reaction of this comparative example, when the amount of sodium borohydride was less than 4 g, the reaction was incomplete, and when the amount of catalyst 4-triphenylphosphine palladium chloride was less than 2.0 g, the reaction rate decreased and the reaction could not be completed in 3.5 h;

[0156] Step 5, acylation:

[0157] The temperature of the dichloromethane solution of amino avermectin was controlled below 0°C, 12 g of acetic anhydride was added, and the reaction was carried out for 30 min to acetylate the amino group on the amino avermectin to generate acetylamino avermectin, then 10% aqueous sodium hydroxide solution was added to the reaction liquid to adjust the pH to neutral, the aqueous layer was discarded, and the dichloromethane solution containing acetylamino avermectin was evaporated under reduced pressure at 60°C to remove dichloromethane to obtain acetylamino avermectin crude product;

[0158] Step 6, crystallization: same as Example 1.

[0159] Comparative Example 5

[0160] A preparation method of acetylamino-avermectin, comprising the following steps:

[0161] Step 1, protection reaction: same as Comparative Example 4;

[0162] Step 2, oxidation reaction: same as Comparative Example 4;

[0163] Step 3, amination reaction: same as Comparative Example 4;

[0164] Step 4, reduction and deprotection reaction: same as Comparative Example 4;

[0165] Step 5, acylation: same as Comparative Example 4;

[0166] Step 6, crystallization: after the acetylamino-avermectin crude product is crystallized 4 times by acetonitrile method, drying, acetylamino-avermectin finished product is obtained;

[0167] The acetonitrile method comprises the following steps:

[0168] The acetylamino-avermectin crude product or the acetylamino-avermectin wet crystal obtained last time is added into 500 acetonitrile, dissolved by heating to 50°C, then cooled to crystallize, centrifuged and filtered, and acetylamino-avermectin wet crystal is obtained;

[0169] Effect example:

[0170] The total yield of each example and each comparative example is calculated, and the acetylamino-avermectin finished product is detected according to Chinese Veterinary Pharmacopoeia (2020 edition) and USP Pharmacopoeia (USP45) respectively, and the results are shown in Tables 1-2;

[0171] Table 1

[0172]

[0173]

[0174] Table 2

[0175]

[0176]

[0177] Table 3

[0178]

[0179] Table 4

[0180]

[0181]

[0182] The above-described embodiments are merely preferred examples of the present application, and are not intended to limit the implementable scope of the present application. Any obvious modifications made by those skilled in the art to the present application without departing from the principles and spirit of the present application should be considered to fall within the scope of the claims of the present application.

Claims

1. A method for preparing avermectin, characterized in that: A crude avermectin product is crystallized by a nitric acid crystallization method and then dried to obtain a finished avermectin product. The nitric acid crystallization method comprises the following steps: dissolving the crude avermectin product in ethyl acetate, adding pure water and a 10% nitric acid solution at room temperature, adjusting the pH of the solution to 5-6, converting the avermectin into a nitrate and dissolving it in water, then allowing the solution to stand for stratification, discarding the ethyl acetate layer, adding a 20% alkaline solution by weight to the aqueous layer, adjusting the pH to 7-8 for crystallization, then filtering, and washing the wet crystals with pure water. The crude avermectin is prepared from avermectin B1 as a raw material through protection reaction, oxidation reaction, imidization reaction, reduction and deprotection reaction, and acylation reaction; Wherein, the imidization reaction comprises the following steps: Hexamethyldisilazane and a catalyst, zinc trifluoroacetate, are added to a dichloromethane solution of the avermectin B1 oxidation product. The mixture is heated to 48-53° C. The pressure in the reactor is controlled to be slightly positive, and the reaction is carried out for 110-130 minutes. An imino group is introduced at the C4" position of the avermectin oxidation product to generate an avermectin B1 imidization product. Water is then added to the reaction solution to terminate the reaction, leaving a dichloromethane layer, i.e., a dichloromethane solution of the avermectin B1 imidization product, for later use.

2. The method for preparing avermectin according to claim 1, wherein The crude product of avermectin was treated once with acetonitrile crystallization before being treated with nitric acid crystallization.

3. The preparation method of avermectin according to claim 2, wherein The number of crystallization treatments by the nitric acid crystallization method is 1; The acetonitrile crystallization method comprises the following steps: adding crude avermectin to acetonitrile, heating to 50° C. to dissolve, then cooling to crystallize, and centrifuging and filtering.

4. The preparation method of avermectin according to claim 1, wherein The protection reaction comprises the following steps: dissolving avermectin B1 in dichloromethane solvent, cooling to -15 to -20°C, adding allyl chloroformate, and simultaneously adding tetramethylethylenediamine as an acid-binding agent dropwise, reacting for 50 to 70 minutes at normal pressure to obtain a C5-OH protection product, i.e., the avermectin B1 protection product; The oxidation reaction comprises the following steps: adding a dimethyl sulfoxide solution and a tetramethylethylenediamine solution to a reaction solution of an avermectin B1 protected product at -10°C, reacting at -10°C for 1.5-2.5 hours to oxidize C4"-OH to C4"=O to obtain an avermectin B1 oxidation product, then adding water to the reaction solution to terminate the reaction, allowing the solution to stand for stratification, and retaining a dichloromethane layer, i.e., a dichloromethane solution of the avermectin B1 oxidation product, for standby use.

5. The preparation method of avermectin according to claim 1, wherein The pressure in the slightly positive pressure state is 0.01-0.05 MPa; The amount of hexamethyldisilazane added is 1.1-3 times the molar mass of avermectin B1; The added amount of the catalyst zinc trifluoroacetate is (0.3-1.5) times the molar mass of avermectin B1.

6. The method for preparing avermectin according to claim 1, wherein The reduction and deprotection reaction comprises the following steps: Anhydrous ethanol is added to a dichloromethane solution of the imidization product of avermectin B1, and after cooling to -5 to -10°C, sodium borohydride is slowly added and reacted for 50-70 minutes to reduce the C4"=NH of the imidization product of avermectin B1 to C4"-NH2, thereby obtaining the reduction product of avermectin B1; After the reduction reaction is qualified, anhydrous ethanol, sodium borohydride and 4-triphenylphosphine palladium chloride are added to the reaction solution, and a deprotection reaction is carried out at -5°C to 5°C for 50-70min to remove the protecting group of C5-OH of avermectin to obtain aminoavermectin; then, an acetic acid aqueous solution with a mass concentration of 10% below 0°C is added dropwise until the material becomes neutral, stirred until the aqueous solution is dissolved, and allowed to stand for stratification, leaving a dichloromethane layer, i.e., a dichloromethane solution of aminoavermectin; set aside.

7. The method for preparing avermectin according to claim 6, wherein In the deprotection reaction, the amount of sodium borohydride added is 0.4-1.5 times the molar mass of avermectin B1; The added amount of 4-triphenylphosphine palladium chloride is 0.007-0.02 times the molar mass of avermectin B1.

8. A method for preparing avermectin according to claim 1, characterized in that, The acylation reaction comprises the following steps: The temperature of the dichloromethane solution of aminoavermectin is controlled below 0°C, acetic anhydride is added, and the reaction is kept warm for 25-35 minutes to acetylate the amino group on the aminoavermectin to generate acetylaminoavermectin. Then, a 10% sodium hydroxide aqueous solution is added to the reaction solution, the pH is adjusted to neutral, the water layer is discarded, and the dichloromethane containing acetylaminoavermectin is evaporated under reduced pressure at 60°C to obtain crude acetylaminoavermectin.

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