Preparation method of milbemycin oxime A4

Abstract

The invention provides a preparation method of milbemycin oxime A4, which comprises the following steps: under an acidic condition, carrying out hydrolysis disaccharide removal reaction on tenvermectin B to obtain tenvermectin B aglycone; the preparation method comprises the following steps: carrying out silicon-based protection on tenvermectin B aglycone by adopting a silicon-based protection reagent to obtain 5-hydroxyl silicon-based tenvermectin B aglycone; the preparation method comprises the following steps: brominating 5-hydroxyl silicon-based tenvermectin B aglycone by adopting a brominating reagent to obtain 13-bromine-5-hydroxyl silicon-based protected tenvermectin B aglycone; the preparation method comprises the following steps: reducing 13-bromo-5-hydroxyl silicon group protected tenvermectin B aglycone by using a reducing agent to obtain 5-hydroxyl silicon group protected milbemycins A4; the milbemycins A4 protected by the 5-hydroxyl silicon group is subjected to desilicication protection treatment, and the milbemycins A4 is obtained; oxidizing milbemycins A4 by adopting an oxidizing agent to obtain 5-ketomilbemycins A4; the preparation method comprises the following steps: reacting 5-ketomilbemycins A4 with hydroxylamine hydrochloride to obtain milbemycins A4, and efficiently preparing the active component milbemycins A4 single component by taking tenvermectin B as a raw material.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical synthesis technology, and in particular to a method for preparing high-purity milbemime A4, which can prepare high-purity single-component milbemime A4. Background Technology

[0002] Microorganisms, the most widely distributed life form on Earth, have existed for approximately 3.5 billion years and have evolved the ability to efficiently synthesize complex and diverse secondary metabolites using biocatalysts such as enzymes. Among these, avermectins and milbemycins are typical secondary metabolites from Streptomyces, both possessing a sixteen-membered macrocyclic lactone skeleton. Various derivatives isolated from these two classes of compounds exhibit significant insecticidal, acaricidal, and antiparasitic activities, providing a crucial foundation for product development in pharmaceuticals, pesticides, veterinary drugs, and other related fields.

[0003] A series of products developed based on these two types of metabolites include: from Streptomyces avermectin ( Streptomyces avermitilisAvermectin (containing a sixteen-membered macrocyclic lactone skeleton and sugar structure) and its derivatives ivermectin, emamectin benzoate, doramectin, eprimectin, and selamectin are prepared from raw materials isolated and extracted from fermentation products. In addition, milbemycin and its structural analogues nemadectin, moxidectin, and lepimectin are prepared from raw materials isolated and extracted from fermentation products of Streptomyces hygroscopicus and Streptomyces griseochromogenes. These compounds (including the aforementioned parent compounds and derivatives) are mainly composed of C, H, and O elements. They are easily degraded in the environment and exhibit low toxicity and high safety to non-target organisms and mammals, leading to rapid industrialization and widespread application in pharmaceuticals, pesticides, and veterinary drugs. All of these compounds possess a similar sixteen-membered macrocyclic lactone skeleton, which is extremely complex, containing 11 chiral carbons, at least four carbon-carbon double bonds, and chiral spirocyclic ketals and lactone bonds. The 3,4-carbon double bonds readily migrate to the 2,3-position, simultaneously initiating racemization of the 2-carbon. In the artificial total synthesis of these compounds, it is often difficult to precisely control the configuration of the chiral carbons (easily racemizing) and the cis-trans configuration of the carbon-carbon double bonds (easily forming mixtures). Furthermore, the high ring strain of the spirocyclic ring makes molecular rearrangement easily induced by acid and base conditions, resulting in numerous side reactions and low product purity. Therefore, artificial total synthesis is not feasible for production. For a long time, the only feasible industrial route to obtain such raw materials has been microbial fermentation: microorganisms use a polyketide synthase (PKS) system to precisely construct single-configuration chiral carbons, trans double bonds, and stable ring systems under mild conditions, effectively circumventing the technical bottlenecks of artificial synthesis; the fermentation products can be purified by organic solvent extraction, multiple column chromatography, and other extraction steps to obtain products with a purity greater than 95%. Although the separation and purification of the products is costly, this method remains the only way to obtain such compounds on a large scale.

[0004] Milbemycin is a typical sixteen-membered macrocyclic lactone compound. The commercially available product is a mixture of milbemycin A3 and A4, possessing highly effective insecticidal, acaricidal, and antiparasitic activities. It exhibits no cross-resistance and high safety for non-target organisms, making it an important member of this class of compounds. The commercial application of milbemycin began relatively early: in the mid-1980s, a formulation of milbemycin A3 and A4 mixed in a 3:7 ratio was first approved for marketing, primarily for acar control. Since 2002, the U.S. Environmental Protection Agency (EPA) has classified it as a low-risk pesticide, approving its use on crops such as strawberries, watermelons, peaches, pears, eggplants, and ornamental plants. Japan and China have also approved its use for pest and disease control in tea. Currently, milbemycin has been registered in 43 countries and regions worldwide, widely covering pest control in crops, vegetables, fruit trees, and flowers, and is particularly suitable for controlling pests resistant to abamectin, fully demonstrating its broad international recognition and market potential.

[0005] Milbemime is produced from milbemycin (a mixture of A3 and A4) through oxidation and oximation derivatization of the 5-carbonyl group in its molecule, a product of microbial fermentation. This derivative inherits the molecular skeleton of a sixteen-membered macrocyclic lactone while fully retaining the core biological activity and environmentally friendly properties of milbemycin, and achieves breakthrough optimization in insecticidal spectrum and host toxicity control. Compared to milbemycin, milbemime exhibits stronger targeting selectivity (acting only on specific targets of pests), higher safety for humans and animals (low mammalian toxicity), and greater environmental friendliness (rapid degradation with no residue risk), meeting the development needs of organic agriculture and green veterinary drugs. In the market, milbemime monotherapy and compound formulations are widely used in the veterinary drug field, such as the tablet "Quanxin'an" for the prevention and treatment of canine heartworm disease and the drops "Ermanmie" for the treatment of canine and feline ear mites. It can also be used for integrated pest management in organic agriculture and has become a mainstream product in the field of insecticides and acaricides in some countries.

[0006] Chemically, the active ingredient of milbemime is a mixture of milbemime A4 and A3, with milbemime A4 exhibiting significantly higher bioactivity than A3. Commercially available milbemime has strict limitations on the ratio of the two components: according to current industry standards, the ratio of milbemime A3 to A4 in the product must not exceed 2:8, creating a high technological barrier to production.

[0007] The fermentation, derivatization, synthesis, and quality analysis and control of milbemoxime still face multiple technical challenges, which have become the core technical bottlenecks restricting its expansion of export scale and international market development. These challenges are specifically manifested as follows: ① Difficulty in controlling the component ratio of key raw materials: Milbemycin A3 and A4 are key raw materials for the synthesis of milbemycin oxime, derived from microbial fermentation. However, microbial populations are prone to variation, and key parameters such as temperature, pH, and substrate concentration are easily fluctuated during fermentation, leading to an unstable ratio of milbemycin A3 to A4 in the fermentation product. Even after separation and purification, the ratio of the obtained A3 and A4 components is still difficult to precisely match the requirements of subsequent synthesis processes, often requiring the addition of additional milbemycin A3 or A4 for manual adjustment. This operation not only increases the production process and operational complexity but also easily leads to fluctuations in the quality of the final product, resulting in unstable drug efficacy, which in turn weakens international market trust in the product and is detrimental to the continuous acquisition of export orders and the steady increase of market share. ② Difficulty in Impurity Control and Quality Compliance: Both the key raw materials (milbemycin A3, A4) and the target products (milbemycin oxime A3, A4) are binary systems. Throughout the fermentation, purification, and subsequent derivatization of the key raw materials, various impurities are easily generated and introduced, including fermentation byproducts, unreacted raw materials, oxidation byproducts, and residual solvents from column chromatography. Furthermore, differences among companies in the sources of fermentation materials (e.g., strains, culture medium composition, reagent purity) and in the overall process control (e.g., fermentation parameters, reaction temperature, and time) further induce the generation of abnormal impurities. Because some impurities have highly similar physicochemical properties to the active ingredients (e.g., A3 oxime and A4 oxime have similar polarities), conventional analytical methods are insufficient for effective separation and accurate quantification, causing fluctuations in product purity, affecting bioactivity, and significantly increasing the difficulty of quality stability control. The international market has more stringent requirements for the quality indicators of veterinary drugs, such as limits on impurities, stability of component ratios, and solvent residues. Domestic products often fail to meet the regulatory requirements of core importing regions such as the EU, the US, and Japan due to issues such as excessive component ratios and the detection of abnormal impurities. This leads to the loss of export orders or the need to bear high testing and rectification costs, which weakens international market competitiveness and restricts further expansion in core markets.

[0008] ③ The purification of key raw materials and target products is technically challenging and costly: Both key raw materials (milbemycin A3, A4) and target products (milbemycin oxime A3, A4) are difficult to crystallize, requiring multiple column chromatography steps for purification. This results in a cumbersome production process, high initial equipment investment, and high energy and material consumption, leading to persistently high overall production costs. These high costs significantly limit the product's price adjustment space, weakening its cost-effectiveness advantage in the international market and hindering its ability to effectively capture high-end market share. Furthermore, it restricts its expansion into price-sensitive developing country markets, directly constraining further expansion of its overall market coverage.

[0009] Domestic patent CN106565740A discloses a technical solution for synthesizing milbemime analogs using avermectin as a starting material. However, experimental verification has revealed several technical flaws in this solution: In repeated verification experiments conducted according to the patent's method, the first step, the disaccharide hydrolysis reaction relying on glycoside hydrolase, failed to achieve the expected conversion. Subsequent attempts to use sulfoxide for dehydroxylation modification also failed to successfully prepare the target intermediate, raising doubts about the feasibility of the core conversion step. Furthermore, the patent's accompanying drawings contain significant discrepancies with the actual content of the drawings, and the structural formulas of some compounds disclosed in the document contain multiple structural characterization errors, potentially misleading the understanding and reproduction of the technical solution. Most importantly, the patent does not provide spectroscopic analysis data (such as NMR, MS, etc.) for the key intermediates and target products, lacking evidence for confirming the core structure, making it impossible to scientifically verify the authenticity and effectiveness of the disclosed technical solution.

[0010] Tenvermectin was developed by a domestic research team using large-fragment DNA seamless splicing technology to integrate the polyketide synthase (PKS) gene module of milbemycin into avermectin-producing bacteria. Streptomyces avermitilis Using the initial synthesis module of [unclear], a novel class of sixteen-membered macrocyclic lactone compounds was successfully constructed from engineered strains and obtained through fermentation. The main components are vitamins A and B. In terms of industrial application, vitamins possess two core advantages: "controllable single component" and "high fermentation potency." Significant breakthroughs have been achieved in the extraction and purification process of the key component, vitamins B, enabling the efficient preparation of high-purity single-component vitamins B through a low-cost process.

[0011] Currently, the fermentation potency of this engineered strain has reached 7000 mg / L, a level significantly superior to existing milbemycin-producing strains. Under strict control of the A3 and A4 ratios to meet subsequent synthesis requirements, the highest fermentation potency of milbemycin is only 3390 mg / L; even without considering the component ratio, the highest reported potency of milbemycin in the literature is only 6.37 g / L. Therefore, it is evident that astragalus not only possesses significant advantages in fermentation yield but also effectively overcomes the key technical bottlenecks in traditional milbemycin production regarding component uniformity.

[0012] In summary, existing milbemycin oxime products are mostly mixtures of A3 and A4, which suffer from problems such as insufficient proportion of the active A4 component, large fluctuations in fermentation components, and complex and difficult-to-control impurity profiles. Their synthesis requires multiple oxidation and oximation reactions, resulting in low yields. Furthermore, the two-component nature makes purification difficult, requiring column chromatography and incurring high costs. To address the challenges of industrial crystallization purification of milbemycin and its oximes (A3 and A4), the need for multiple column chromatography purifications, the manual adjustment required for fluctuations in the A3 and A4 composition ratios, and the instability in the types and amounts of impurities in the product due to the complex fermentation and synthesis processes, this study aims to provide solutions. Summary of the Invention

[0013] The purpose of this invention is to provide a method for preparing milbemoxime A4, which uses a single component, vitamins B, as raw material to efficiently prepare the active component milbemoxime A4. This method can effectively avoid the core problems of product quality fluctuations and complex quality control processes caused by traditional two-component systems, and provides key technical support for the development of safe, efficient, and quality-stable new veterinary drugs.

[0014] To achieve the above objectives, this technical solution provides a method for preparing milbemoxime A4, comprising the following steps: S1: Under acidic conditions, vitamins B undergo a hydrolysis and disaccharide removal reaction to obtain vitamins B aglycone. S2: 5-hydroxysilyl vitamins B aglycone was obtained by silicon-based protection of vitamins B aglycone with silicon-based protection reagent. S3: 13-bromo-5-hydroxysilyl vitamin B aglycone was obtained by bromination of 5-hydroxysilyl vitamin B aglycone with a bromination reagent. S4: At a certain temperature, the 13-bromo-5-hydroxysilyl-protected stilbene aglycone is reduced with a reducing agent to obtain 5-hydroxysilyl-protected milbemycin A4. S5: Milbemycin A4 was obtained by desilication protection of 5-hydroxysilyl-protected milbemycin A4; S6: Milbemycin A4 was oxidized with an oxidizing agent to obtain 5-ketomilbemycin A4; S7: 5-Ketomilbemycin A4 is reacted with hydroxylamine hydrochloride to obtain milbemycin A4.

[0015] The preparation route for milbemime A4 in this scheme is as follows: .

[0016] This method uses a single compound, sennamycin B, as the starting material to synthesize milbemime A4, a single component, through a seven-step chemical reaction. Compared with existing synthetic routes, the method provided in this method has significant advantages: sennamycin B is a high-purity single component that can be obtained through fermentation with genetically engineered bacteria, ensuring stable and controllable source quality; moreover, this method directly synthesizes the highly active single component milbemime A4 with a purity of up to 95%, eliminating the need for proportion adjustment; and the entire process adopts a standard chemical synthesis route, with clear functional group protection and transformation at each step, resulting in relatively clear side reactions and impurities, simplifying quality control; the yield of each step is generally higher than 90%, with a theoretically higher cumulative yield, and the material utilization rate is superior to separation and purification routes.

[0017] In step S1, after the acidic solution and organic solvent are stirred and mixed under inert gas protection, vitamins B are added at room temperature and the mixture is stirred for a period of time to carry out the hydrolysis and disaccharide removal reaction.

[0018] In some embodiments, after the hydrolysis and disaccharide removal reaction is completed, saturated sodium bicarbonate solution is added to adjust the pH to neutral, water is added to precipitate a white solid, the filter cake is washed with water after filtration and collected, and then vacuum dried at room temperature to obtain taeniacin B aglycone.

[0019] In some embodiments, the organic solvent in step S1 is selected as one or a combination of two of methanol, ethanol, isopropanol, tetrahydrofuran, and water.

[0020] In some embodiments, the acidic solution includes at least one of sulfuric acid, hydrochloric acid, and methanesulfonic acid.

[0021] In some embodiments, tamarind B is added at room temperature and the mixture is stirred for 24-48 h to carry out the hydrolysis and disaccharide removal reaction.

[0022] In step S2, under inert protection and at room temperature, 5-hydroxysilyl vitamins B aglycone and acid-binding agent are added sequentially into a container and dissolved in an organic solvent. After cooling to 0 °C in an ice bath, a solution of a silicon-based protecting group reagent is slowly added dropwise. The mixture is stirred at room temperature for a period of time to obtain 5-hydroxysilyl vitamins B aglycone.

[0023] In some embodiments, the organic solvent in step S2 is selected as dichloromethane and... N , N - One or a combination of dimethylformamide (DMF), with the acid-binding agent selected as one or a combination of imidazole, pyridine, and triethylamine.

[0024] In some embodiments, the silicon-based protecting agent is selected from at least one of tert-butyldiphenylchlorosilane, trimethylchlorosilane, triethylchlorosilane, and tert-butyldimethylchlorosilane.

[0025] In some embodiments, after silicon-based protection, the reaction is quenched with water and the reaction solution is extracted with ethyl acetate. The organic phases are combined and washed sequentially with saturated sodium bicarbonate solution, hydrochloric acid aqueous solution, and saturated sodium chloride aqueous solution. The mixture is dried with anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to obtain 5-hydroxysilyl trastuzumab aglycone.

[0026] In step S3, under an inert gas and room temperature environment, the bromide reagent, acid-binding agent, and 5-hydroxysilyl vitamins B aglycone are added to an organic solvent and cooled to 0 °C. Then, a sulfonic anhydride solution dissolved in the solvent is slowly added dropwise. The mixture is stirred at 0 °C for a period of time and then stirred at room temperature for a period of time.

[0027] In some embodiments, the acid-binding agent is one or a combination of triethylamine (TEA), diisopropylethylamine (DIPEA), and piperidine.

[0028] In some embodiments, the dissolving solvent is one or a combination of dichloromethane or THF, and the sulfonic anhydride solution includes one or a combination of methanesulfonic anhydride, p-methanesulfonic anhydride, and o-nitromethanesulfonic anhydride.

[0029] In some embodiments, the organic solvent in step S3 is selected from at least one of dichloromethane, tetrahydrofuran, and toluene.

[0030] In some embodiments, the brominating agent is at least one selected from NBS, liquid bromine, sodium bromide, lithium bromide, and phosphorus tribromide.

[0031] In some embodiments, the residue is filtered after bromination and concentrated under reduced pressure. The residue is then subjected to silica gel rapid column chromatography to obtain 13-bromo-5-hydroxysilyl-protected trastuzumab B aglycone.

[0032] In step S4, under an inert gas and room temperature environment, 13-bromo-5-hydroxysilyl-protected vitamins B aglycone, a reducing agent, and azobisisobutyronitrile are added to an organic solvent, and the mixture is heated and stirred for a period of time.

[0033] In some embodiments, the reducing agent is one or a combination of Pd / C, Pt, Zn, and tri-n-butyltin hydride.

[0034] In some embodiments, the reaction temperature of the stirred reaction is between 0 and 100 °C. In some embodiments, the organic solvent in step S4 is one of toluene, benzene, methanol, acetic acid, etc.

[0035] Furthermore, after the reduction reaction was completed, water was added to the reaction system for lysis. The aqueous phase was extracted with ethyl acetate, the organic phases were combined, washed with saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered, dissolved under reduced pressure, concentrated under reduced pressure to obtain the residue, and the residue was subjected to silica gel rapid column chromatography to obtain 5-hydroxysilyl-protected milbemycin A4 as a yellow solid.

[0036] In step S5, under an inert gas and room temperature environment, 5-hydroxysilyl-protected milbemycin A4 is added to an organic solvent and cooled to 0 °C, followed by the addition of p-benzenesulfonic acid and a reaction time. Alternatively, 5-hydroxysilyl-protected milbemycin A4 and a desilication protecting agent are added to an organic solvent and cooled to 0 °C and a reaction time is carried out.

[0037] In some embodiments, after the reaction is complete, saturated sodium bicarbonate is added to the reaction system, followed by extraction with dichloromethane. The filtrate is collected, the organic phases are combined, and the mixture is washed with water and a saturated sodium chloride aqueous solution, dried with anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to obtain milbemycin A4 as a yellow solid.

[0038] In some embodiments, the desilication protecting agent is a fluorine reagent, and the selected fluorine reagent is selected from at least one of hydrogen fluoride and tetra-n-butylammonium fluoride.

[0039] In step S6, under inert gas protection and at room temperature, the oxidant and milbemycin A4 are added to an organic solvent to react and obtain 5-ketomilbemycin A4.

[0040] In some embodiments, the oxidant is selected from at least one of Desmartin oxidant, Jones reagent, Sarret reagent, Coslin reagent, PDC, and IBX oxidant.

[0041] In some embodiments, after the reaction is complete, the mixture is filtered, the filtrate is collected, and the solution is concentrated under reduced pressure to obtain a yellow solid, 5-ketomilbemycin A4.

[0042] In step S7, 5-ketomilbemycin A4 is dissolved and reacted with hydroxylamine hydrochloride for a period of time under an inert gas atmosphere.

[0043] In some embodiments, after the reaction is complete, water is added, ethyl acetate is extracted, the organic phases are combined, washed with water and saturated sodium chloride solution respectively, dried with anhydrous sodium sulfate, filtered, concentrated under reduced pressure to obtain the residue, and the residue is separated by silica gel rapid column chromatography to obtain milbemime A4 as a white solid.

[0044] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects: This method uses bacitracin B as the starting material and synthesizes single components milbemycin A4 and milbemycin oxime A4 in high yield through a seven-step reaction, systematically eliminating the key technical bottlenecks in the production and application of existing milbemycin A3, A4 and milbemycin oxime A3, A4 mixtures. ① The target product, milbemoxime A4, has high purity, laying the foundation for the development of new drugs based on the active ingredient milbemoxime A4.

[0045] ② The high purity of intermediate milbemycin A4 can be obtained and used to adjust the component ratio of key raw materials for the production of milbemycin derivatives (milbemycin oxime, lepimectin, etc.).

[0046] ③ It does not rely on unstable A3 and A4 fermentation ratios, avoiding yield fluctuations caused by component fluctuations and manual adjustment processes, thus simplifying the production process; ④ The single-component system significantly simplifies the impurity profile, greatly reduces the difficulty of quality control, and effectively improves product purity and batch-to-batch consistency; ⑤ The components of the target product are clearly defined and the impurities are controllable. Attached Figure Description

[0047] Figure 1 This is the HPLC-UV chromatogram of the starting material Tianweimin B in this invention.

[0048] Figure 2 This is the ESI+ ion chromatogram of vitamins B, the starting material of this invention.

[0049] Figure 3 This is the 1H NMR spectrum of vitamins B, the starting material of this invention.

[0050] Figure 4 The 1H NMR spectrum of the 5-hydroxysilyl-protected sennamycin B aglycone, an intermediate of this invention.

[0051] Figure 5 The image shows the 1H NMR spectrum of milbemycin A4, an intermediate of this invention.

[0052] Figure 6 The photon NMR spectrum of 5-ketomilbemycin A4, an intermediate of this invention, is shown below.

[0053] Figure 7 The image shows the hydrogen nuclear magnetic resonance spectrum of the target compound of this invention, milbexime A4.

[0054] Figure 8 This is the HPLC-UV chromatogram of commercially available milbemoxime.

[0055] Figure 9 This is the HPLC-UV chromatogram of the target compound milbexime A4 obtained in this invention.

[0056] Figure 10 This is the ESI+ ion chromatogram of the target compound milbexime A4 obtained in this invention. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0058] Example 1: (1) Preparation of vitamins B aglycone (02)

[0059] Under nitrogen protection and at room temperature, methanol (49.5 mL) was mixed with H₂SO₄ (0.5 mL) and stirred until homogeneous. After returning to room temperature, compound 01 (5.00 g, 5.90 mmol) was added, and the reaction was stirred at room temperature for 24 h. TLC analysis: R f (02) = 0.50, R f (03) = 0.70, V EA : V PE =1:1. Adjust the pH of the reaction solution to neutral with saturated sodium bicarbonate solution, add water (100 mL), and a large amount of white solid precipitates out. Filter, wash the filter cake with water (50 mL), collect the filter cake, and vacuum dry at room temperature for 16 h to obtain white solid O2 (3.19 g, 97%).

[0060] 1 H NMR (500 MHz, CDCl3) δ 5.83 (dt, J = 11.0, 2.4 Hz, 1H), 5.79 – 5.69(m, 2H), 5.41 (t, J = 2.1 Hz, 1H), 5.35 – 5.28 (m, 2H), 4.73 –4.61 (m, 2H), 4.31– 4.27 (m, 1H), 4.12 (q, J = 7.2 Hz, 1H), 4.01 (s, 1H), 3.96 (d, J = 6.2 Hz, 1H), 3.68 (td, J = 11.0, 3.6 Hz, 1H), 3.25 (p, J = 2.4 Hz, 1H), 3.20 – 3.16 (m, 1H), 2.52 (ddd, J = 9.3, 7.1, 2.4 Hz, 1H), 2.34 – 2.25 (m, 2H), 2.04 (s, 1H), 1.98(ddd, J = 12.1, 5.1, 1.8 Hz, 1H), 1.87 (t, J = 2.1 Hz, 3H), 1.78 – 1.73 (m, 1H), 1.68 – 1.64 (m, 1H), 1.55 – 1.47 (m, 8H), 1.43 (q, J= 7.3 Hz, 2H), 1.35 – 1.30(m, 1H), 1.26 (t, J = 7.1 Hz, 2H), 1.17 (d, J = 7.0 Hz, 3H), 0.96 (t, J = 7.4 Hz, 2H), 0.85 (d, J = 6.8 Hz, 3H). HPLC-MS (ESI+) m / z: 581 [M+Na] + . HPLC conditions: R t(01) = 81.63 min. HPLC chromatographic conditions: Diamonsil C18 column (5 µm, 4.6 mm × 250 mm, Dima Corporation, USA); flow rate 0.8 mL / min; wavelength 254 nm; column temperature 30 ℃; injection volume 10 µL; gradient elution (min / %B) control: 0 / 5, 1 / 5, 100 / 100, 180 / 100; A is an aqueous solution containing 0.05% formic acid, and B is acetonitrile.

[0061] (2) Preparation of 5-hydroxysilyl-protected vitamins B aglycone (03)

[0062] Under nitrogen protection at room temperature, compound O2 (3.10 g, 5.55 mmol) and imidazole (0.60 g, 8.77 mmol) were added sequentially to a 100 mL round-bottom flask, dissolved in dichloromethane (20 mL), and cooled to 0 °C in an ice bath. Finally, a DCM solution of TBSCl (1.10 g, 7.01 mmol) in 10 mL was slowly added dropwise, and the mixture was stirred at room temperature for 5 h. TLC analysis: R f (02) = 0.20, R f (03) = 0.8, V EA : V PE The ratio of compound O2 to compound O2 was 1:5. The reaction was essentially complete. The reaction was quenched with water (200 mL). The reaction solution was extracted with ethyl acetate (200 mL × 3). The organic phases were combined and washed successively with saturated sodium bicarbonate solution (20 mL × 1), hydrochloric acid aqueous solution (20 mL × 2, 1 M), and saturated sodium chloride aqueous solution (20 mL × 1). The mixture was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to obtain a white solid O3 (3.58 g, 96%). 1 H NMR (500 MHz, CDCl3) δ 5.81 – 5.66 (m, 4H), 5.54 (dd, J = 9.9, 2.6Hz, 1H), 5.34 – 5.32 (m, 1H), 4.68 (dd, J = 14.4, 2.1 Hz, 1H), 4.58 (dd, J =14.4, 2.0 Hz, 1H), 4.43 (ddt, J = 5.5, 2.7, 1.3 Hz, 1H), 4.00 (d, J = 2.4 Hz,1H), 3.90 – 3.83 (m, 1H), 3.81 (d, J = 5.5 Hz, 1H), 3.46 (dd, J = 9.9, 1.8 Hz, 1H), 3.36 (h, J = 2.6 Hz, 1H), 2.52 (ddd, J = 9.6, 7.0, 2.6 Hz, 1H), 2.33 – 2.23(m, 3H), 2.04 – 2.00 (m, 1H), 1.78 (dq, J = 4.2, 2.1 Hz, 3H), 1.77 – 1.71 (m,1H), 1.59 (qd, J = 6.9, 1.8 Hz, 2H), 1.53 (s, 3H), 1.51 – 1.42 (m, 3H), 1.28 –1.23 (m, 1H), 1.16 (d, J = 6.9 Hz, 3H), 0.96 (t, J = 7.4 Hz, 3H), 0.92 (d, J = 3.2Hz, 9H), 0.91 (d, J = 2.5 Hz, 3H), 0.90 (d, J = 1.6 Hz, 3H), 0.13 (s, 6H). HPLC-MS (ESI+) m / z: 695 [M+Na] + . (3) Preparation of 13-bromo-5-hydroxysilyl-protected vitamins B aglycone (04)

[0063] Under nitrogen protection at room temperature, compound O3 (3.50 g, 5.20 mmol), TEA (1.57 g, 15.60 mmol), and LiBr (4.70 g, 57.27 mmol) were added sequentially to THF (30 mL). The mixture was cooled to 0 °C, and a solution of methanesulfonic anhydride (1.0 g, 5.93 mmol) dissolved in THF (10 mL) was slowly added dropwise. The mixture was stirred at 0 °C for 1 h, followed by stirring at room temperature for 1 h. TLC showed that compound O3 reacted completely. TLC analysis: R f (03) = 0.3, R f (04) = 0.50, V EA : V PE =1:5. Filter, concentrate under reduced pressure to obtain the residue, and then perform high-speed column chromatography on silica gel (…). V EA : V PE =1:5), to obtain yellow solid O4 (3.52 g, 92%).

[0064] 1 H NMR (500 MHz, CDCl3) δ 6.58 – 6.49 (m, 1H), 5.83 (d, J = 11.4 Hz,2H), 5.45 – 5.32 (m, 3H), 4.82 – 4.67 (m, 2H), 4.09 (d, J = 10.5 Hz, 1H), 3.86(s, 1H), 3.61 – 3.53 (m, 2H), 3.07 (td, J = 9.4, 2.7 Hz, 1H), 2.57 (td, J = 10.5,6.4 Hz, 1H), 2.32 – 2.29 (m, 1H), 2.06 – 2.02 (m, 1H), 1.93 – 1.87 (m, 3H), 1.72 – 1.67 (m, 2H), 1.65 (s, 3H), 1.51 (dd, J = 13.8, 9.4 Hz, 3H), 1.41 – 1.33(m, 3H), 1.29 – 1.24 (m, 2H), 1.21 (d, J = 6.5 Hz, 3H), 0.99 (t, J= 7.3 Hz, 3H), 0.97 – 0.91 (m, 10H), 0.84 (d, J = 6.5 Hz, 3H). HPLC-MS (ESI+) m / z: 758 [M+Na] + . (4) Preparation of 5-hydroxysilyl-protected milbemycin A4 (05)

[0065] Under nitrogen protection at room temperature, compound O4 (3.5 g, 4.76 mmol), tri-n-butyltin hydride (6.92 g, 23.80 mmol), and azobisisobutyronitrile (80 mg, 0.52 mmol) were sequentially added to anhydrous toluene (30 mL), and the mixture was heated to 85 °C and stirred for 2 h. TLC monitoring showed that compound O4 reacted completely. TLC analysis: R f (04) = 0.50, R f (05) = 0.55, V EA : V PE =1:5, UV colorimetric assay. Add water (30 mL) to the reaction solution and separate the phases. Extract the aqueous phase with ethyl acetate (30 mL × 2). Combine the organic phases, wash with saturated sodium chloride aqueous solution (50 mL), dry to anhydrous sodium sulfate, filter, remove solvent under reduced pressure, concentrate under reduced pressure to obtain the residue, and then perform rapid silica gel column chromatography (…). V EA : V PE =1:5), to obtain yellow solid 05 (2.81 g, 90%).

[0066] 1 H NMR (500 MHz, CDCl3) δ 6.59 – 6.44 (m, 1H), 5.88 (dt, J = 11.2, 2.5Hz, 1H), 5.74 (dd, J = 14.7, 11.3 Hz, 1H), 5.44 (ddd, J = 14.6, 8.3, 4.8 Hz, 2H),5.00 – 4.93 (m, 1H), 4.79 – 4.66 (m, 2H), 3.86 (s, 1H), 3.59 (t, J = 8.8 Hz, 1H), 3.56 (q,J = 2.5 Hz, 1H), 3.08 (td, J = 9.3, 2.6 Hz, 1H), 2.44 (t, J = 5.7 Hz,1H), 2.29 – 2.18 (m, 3H), 2.02 (ddd, J = 12.1, 5.0, 1.9 Hz, 1H), 1.92 – 1.85(m, 4H), 1.85 – 1.81 (m, 1H), 1.68 (tdd, J = 6.9, 5.3, 2.5 Hz, 2H), 1.53 (s,3H), 1.52 – 1.47 (m, 2H), 1.44 – 1.32 (m, 4H), 1.00 (t, J = 6.9 Hz, 6H), 0.93(s, 9H) 0.88 (d, J = 4.4 Hz, 2H), 0.83 (d, J = 6.5 Hz, 3H). HPLC-MS (ESI+) m / z: 679 [M+Na] + . (5) Preparation of milbemycin A4 (06)

[0067] Compound 05 (2.75 g, 4.18 mol) was added to MeOH (30 mL) under nitrogen protection at room temperature. The mixture was cooled to 0 °C, and p-benzenesulfonic acid (1.46 g, 8.36 mmol) was added. The mixture was stirred at 0 °C for 2 h. TLC monitoring showed that compound 05 reacted completely. TLC analysis: R f (05) = 0.7, R f (06) = 0.2, V EA : V PE =1:5, UV color development. Add saturated sodium bicarbonate (50 mL), extract with dichloromethane (20 mL × 3), collect the filtrate, combine the organic phases, wash with water (50 mL) and saturated sodium chloride aqueous solution (50 mL) respectively, dry with anhydrous sodium sulfate, filter, concentrate under reduced pressure to obtain yellow solid O6 (2.20 g, 97%).

[0068] 1H NMR (500 MHz, CDCl3) δ 5.83 – 5.71 (m, 2H), 5.39 (ddt, J = 9.7, 7.1,4.9 Hz, 2H), 4.99 – 4.92 (m, 1H), 4.75 – 4.60 (m, 2H), 4.31 – 4.27 (m, 1H), 3.96 (d, J = 6.2 Hz, 1H), 3.62 – 3.52 (m, 1H), 3.30 – 3.23 (m, 1H), 3.07 (td, J =9.3, 2.7 Hz, 1H), 2.41 (td, J = 12.5, 5.1 Hz, 1H), 2.22 (t, J = 9.1 Hz, 2H), 2.00(ddd, J = 12.2, 5.0, 1.9 Hz, 1H), 1.90 – 1.88 (m, 1H), 1.87 (t, J = 2.1 Hz, 3H), 1.81 (dq, J = 10.6, 2.4 Hz, 1H), 1.71 – 1.61 (m, 4H), 1.53 (s, 3H), 1.51 – 1.47(m, 2H), 1.39 – 1.26 (m, 6H), 1.09 – 1.02 (m, 1H), 1.01 – 0.99 (m, 3H), 0.95– 0.85 (m, 3H), 0.82 (dd, J = 7.1, 4.0 Hz, 3H). HPLC-MS (ESI+) m / z: 565 [M+Na] + . (6) Preparation of 5-ketomilbemycin A4 (07)

[0069] Under nitrogen protection at room temperature, compound 06 (2.10 g, 3.88 mmol) and MnO2 (3.38 g, 38.82 mmol) were added sequentially to DCM (30 mL) and stirred at room temperature for 1 h. TLC monitoring showed that compound 06 reacted completely. TLC analysis: R f (06) = 0.3, R f (07) = 0.50,V EA : V PE =1:3. Filter, collect the filtrate, and concentrate under reduced pressure to obtain a yellow solid 07 (1.99 g, 95%).

[0070] 1 H NMR (500 MHz, CDCl3) δ 6.59 – 6.44 (m, 1H), 5.88 (dt, J = 11.2, 2.5Hz, 1H), 5.74 (dd, J = 14.7, 11.3 Hz, 1H), 5.44 (ddd, J = 14.6, 8.3, 4.8 Hz, 2H),5.00 – 4.93 (m, 1H), 4.79 – 4.66 (m, 2H), 3.86 (s, 1H), 3.59 (t, J = 8.8 Hz, 1H), 3.56 (q, J = 2.5 Hz, 1H), 3.08 (td, J = 9.3, 2.6 Hz, 1H), 2.44 (t, J = 5.7 Hz,1H), 2.29 – 2.18 (m, 3H), 2.02 (ddd, J = 12.1, 5.0, 1.9 Hz, 1H), 1.92 – 1.85(m, 4H), 1.85 – 1.81 (m, 1H), 1.68 (tdd, J = 6.9, 5.3, 2.5 Hz, 2H), 1.53 (s,3H), 1.52 – 1.47 (m, 2H), 1.44 – 1.32 (m, 4H), 1.00 (t, J = 6.9 Hz, 6H), 0.88(d, J = 4.4 Hz, 2H), 0.83 (d, J = 6.5 Hz, 3H). HPLC-MS (ESI+) m / z: 563 [M+Na] + . (7) Preparation of milbemime A4 (08)

[0071] Under nitrogen protection at room temperature, compound 07 (1.90 g, 3.51 mmol) and hydroxylamine hydrochloride (1.30 g, 18.90 mmol) were added sequentially to a 50 mL round-bottom flask, dissolved in 25 mL of tert-butanol, and stirred at 30 °C for 24 h. TLC monitoring showed that compound 07 reacted completely. TLC analysis: R f (05) = 0.7, R f (06) = 0.30, V EA : V PE =1:3. Add water (50 mL), extract with ethyl acetate (20 mL × 3), combine the organic phases, wash with water (20 mL) and saturated sodium chloride solution (20 mL × 2), dry to anhydrous sodium sulfate, filter, concentrate under reduced pressure to obtain the residue, and then perform rapid silica gel column chromatography (…). V EA : V PE (1:5~1:2) Separation yielded a white solid 08 (1.81 g, 93%).

[0072] 1 H NMR (500 MHz, CDCl3) δ 5.88 (dt, J = 11.3, 2.5 Hz, 1H), 5.80 (dd, J =2.4, 1.4 Hz, 1H), 5.76 (dd, J = 14.7, 11.3 Hz, 1H), 5.47 – 5.36 (m, 2H), 4.96(t, J = 7.8 Hz, 1H), 4.80 – 4.68 (m, 2H), 4.67 (s, 1H), 3.63 – 3.51 (m, 1H), 3.38 (t, J = 2.4 Hz, 1H), 3.08 (td, J = 9.4, 2.6 Hz, 1H), 2.43 (dq, J = 10.3, 5.0Hz, 1H), 2.22 (dt, J = 13.7, 9.2 Hz, 3H), 2.00 (ddd, J = 12.1, 4.9, 1.8 Hz, 1H),1.94 (dd, J= 2.5, 1.4 Hz, 3H), 1.87 (s, 1H), 1.85 – 1.80 (m, 1H), 1.72 – 1.64(m, 2H), 1.55 – 1.52 (m, 3H), 1.52 – 1.46 (m, 2H), 1.40 – 1.25 (m, 4H), 1.00(dd, J = 8.3, 6.9 Hz, 6H), 0.93 – 0.85 (m, 1H), 0.83 (d, J = 6.5 Hz, 3H). The obtained sample (08): HPLC-MS (ESI+) m / z: 578 [M+Na] + The HPLC retention time (16.231 min) of the sample (08) obtained in this application is similar to that of commercially available milbexime A4 (see...). Figure 8 R t =16.251 min) consistent.

[0073] HPLC chromatographic conditions: Diamonsil C18 column (5 µm, 4.6 mm × 250 mm, Dima Corporation, USA); flow rate 0.8 mL / min; wavelength 254 nm; column temperature 30 ℃; injection volume 10 µL; gradient elution (min / %B) control: 0 / 70, 1 / 70, 13 / 100, 20 / 100; A was an aqueous solution containing 0.05% formic acid, and B was acetonitrile.

[0074] In summary, and drawing on the literature (Tsukamoto Y, Sato K, Mio S, et al . Synthesis of 5-keto-5-oxime derivatives of milbemycins and their activities against microfilariae [J]. Agric. Biol. Chem (1991, 55 (10): 2615-2621) By comparison, the white solid 08 was confirmed to be the target compound milbexime A4.

[0075] Example 2: (1) Preparation of vitamins B aglycone (02): Under nitrogen protection and at room temperature, methanol (495 mL) and H₂SO₄ (5 mL) were mixed and stirred until homogeneous. After returning to room temperature, compound 01 (50.00 g, 59.03 mmol) was added, and the reaction was stirred at room temperature for 24 h. TLC analysis: R f(02) = 0.50, R f (03) = 0.70, V EA : V PE =1:1. Adjust the pH of the reaction solution to neutral with saturated sodium bicarbonate solution, add water (1000 mL), and a large amount of white solid precipitates. Filter, wash the filter cake with water (100 mL), collect the filter cake, and vacuum dry at room temperature for 16 h to obtain white solid O2 (32.65 g, 99%).

[0076] (2) Preparation of 5-hydroxysilyl-protected vitamins B aglycone (03): Under nitrogen protection at room temperature, compound O2 (32.50 g, 58.16 mmol) and imidazole (6.0 g, 87.66 mmol) were added sequentially to a 1000 mL round-bottom flask, dissolved in dichloromethane (200 mL), and cooled to 0 °C in an ice bath. Finally, a DCM solution of TBSCl (10.6 g, 70.13 mmol) in 100 mL was slowly added dropwise, and the mixture was stirred at room temperature for 5 h. TLC analysis: R f (02) = 0.20, R f (03) = 0.8, V EA : V PE The ratio of compound O2 to compound O2 was 1:5. The reaction was basically complete. The reaction was quenched with water (200 mL). The reaction solution was extracted with ethyl acetate (200 mL × 3). The organic phases were combined and washed successively with saturated sodium bicarbonate solution (200 mL × 1), hydrochloric acid aqueous solution (1 M, 200 mL × 2), and saturated sodium chloride aqueous solution (200 mL × 1). The solution was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to obtain white solid O3 (38.36 g, 98%).

[0077] (3) Preparation of 13-bromo-5-hydroxysilyl-protected vitamins B aglycone (04): Under nitrogen protection at room temperature, compound O3 (38.30 g, 56.91 mmol), TEA (17.4 g, 171.81 mmol), and LiBr (47.5 g, 572.70 mmol) were sequentially added to THF (300 mL). The mixture was cooled to 0 °C, and a solution of o-methanesulfonic anhydride (10.3 g, 59.28 mmol) dissolved in THF (100 mL) was slowly added dropwise. The mixture was stirred at 0 °C for 1 h, followed by stirring at room temperature for 1 h. TLC showed that compound O3 reacted completely. TLC analysis:R f (03) = 0.3, R f (04) = 0.50, V EA : V PE =1:5. Filter, concentrate under reduced pressure to obtain the residue, and then perform high-speed column chromatography on silica gel (…). V EA : V PE =1:5), yielding a yellow solid 04 (37.69 g, 90%).

[0078] (4) Preparation of 5-hydroxysilyl-protected milbemycin A4(05): Under nitrogen protection at room temperature, compound O4 (37.60 g, 51.10 mmol), tri-n-butyltin hydride (7.5 g, 257.70 mmol), and azobisisobutyronitrile (0.8 g, 5.15 mmol) were sequentially added to anhydrous toluene (300 mL), and the mixture was heated to 85 °C and stirred for 2 h. TLC monitoring showed that compound O4 reacted completely. TLC analysis: R f (04) = 0.50, R f (05) = 0.55, V EA : V PE =1:5, UV colorimetric assay. Water (300 mL) was added to the reaction solution and the mixture was separated. The aqueous phase was extracted with ethyl acetate (300 mL × 2). The organic phases were combined, washed with saturated sodium chloride aqueous solution (500 mL), dried over anhydrous sodium sulfate, filtered, dissolved under reduced pressure, and concentrated under reduced pressure to obtain the residue. The residue was then subjected to silica gel rapid column chromatography (…). V EA : V PE =1:5), to obtain yellow solid 05 (30.21g, 90%).

[0079] (5) Preparation of milbemycin A4 (06): Compound 05 (30.10 g, 45.82 mol) was added to MeOH (300 mL) under nitrogen protection at room temperature. The mixture was cooled to 0 °C, and p-benzenesulfonic acid (16.3 g, 92.77 mmol) was added. The mixture was stirred at 0 °C for 2 h. TLC monitoring showed that compound 05 reacted completely. TLC analysis: R f (05) = 0.7, Rf (06) = 0.2, V EA : V PE =1:5, UV color development. Add saturated sodium bicarbonate (500 mL), extract with dichloromethane (200 mL × 3), collect the filtrate, combine the organic phases, wash with water (500 mL) and saturated sodium chloride aqueous solution (500 mL) respectively, dry with anhydrous sodium sulfate, filter, concentrate under reduced pressure to obtain yellow solid O6 (23.54 g, 97%).

[0080] (6) Preparation of 5-ketomilbemycin A4 (07): Under nitrogen protection at room temperature, compound 06 (23.50 g, 44.36 mmol) and MnO2 (39.1 g, 450.00 mmol) were added sequentially to DCM (300 mL) and stirred at room temperature for 1 h. TLC monitoring showed that compound 06 reacted completely. TLC analysis: R f (06) = 0.3, R f (07) = 0.50, V EA : V PE =1:3. Filter, collect the filtrate, and concentrate under reduced pressure to obtain a yellow solid 07 (23.04 g, 96%).

[0081] (7) Preparation of milbemoxime A4 (08): Under nitrogen protection at room temperature, compound 07 (23.00 g, 42.51 mmol) and hydroxylamine hydrochloride (15.1 g, 217.30 mmol) were added sequentially to a 500 mL round-bottom flask, dissolved in 250 mL of tert-butanol, and stirred at 30 °C for 24 h. TLC monitoring showed that compound 07 reacted completely. TLC analysis: R f (05) = 0.7, R f (06) = 0.30, V EA : V PE =1:3. Add water (500 mL), extract with ethyl acetate (200 mL × 3), combine the organic phases, wash with water (200 mL) and saturated sodium chloride solution (200 mL × 2), dry to anhydrous sodium sulfate, filter, concentrate under reduced pressure to obtain the residue, and then perform rapid silica gel column chromatography (…). V EA : V PE(1:5~1:2) Separation yielded a white solid 08 (21.75 g, 92%).

[0082] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A process for the preparation of milbemycin A4, characterized in that, The method comprises the following steps: S1: hydrolysis of milbemycin B to obtain aglycone under acidic conditions; S2: silicon-based protection of the aglycone to obtain 5-hydroxyl silicon-based milbemycin B aglycone; S3: bromination of the 5-hydroxyl silicon-based milbemycin B aglycone to obtain 13-bromo-5-hydroxyl silicon-based protected milbemycin B aglycone; S4: reduction of the 13-bromo-5-hydroxyl silicon-based protected milbemycin B aglycone to obtain 5-hydroxyl silicon-based protected milbemycin A4 under a certain temperature; S5: desilicon-based protection of the 5-hydroxyl silicon-based protected milbemycin A4 to obtain milbemycin A4; S6: oxidation of the milbemycin A4 to obtain 5-ketone milbemycin A4; S7: reaction of the 5-ketone milbemycin A4 with hydroxylamine hydrochloride to obtain milbemycin oxime A4.

2. The process for the preparation of milbemycin A4 according to claim 1, characterized in that, In step S1, after the acid solution and the organic solvent are stirred and uniformly mixed under inert gas protection, milbemycin B is added at room temperature and stirred for a period of time to perform the hydrolysis and disaccharide removal reaction.

3. The process for the preparation of milbemycin A4 according to claim 1, characterized in that, Under inert protection and at room temperature, the aglycone of milbemycin B and the acid binding agent are sequentially added to the container and dissolved in the organic solvent, cooled to 0 DEG C in an ice bath, and then slowly added with a solution of the silicon-based protection group reagent, and stirred at room temperature for a period of time to obtain the 5-hydroxyl silicon-based milbemycin B aglycone.

4. The process for the preparation of milbemycin A4 according to claim 1, characterized in that, Under inert gas and at room temperature, the bromination reagent, the acid binding agent, and the 5-hydroxyl silicon-based milbemycin B aglycone are added to the organic solvent and cooled to 0 DEG C, and then slowly added with a solution of the sulfonic anhydride dissolved in the dissolving solvent, stirred at 0 DEG C for a period of time, and then stirred at room temperature for a period of time.

5. The process for the preparation of milbemycin A4 as claimed in claim 1, wherein, Under inert gas and at room temperature, the 13-bromo-5-hydroxyl silicon-based protected milbemycin B aglycone, the reducing agent, and the azobisisobutyronitrile are added to the organic solvent and stirred for a period of time.

6. The process for the preparation of milbemycin A4 as claimed in claim 1, wherein, Under inert gas and at room temperature, the 5-hydroxyl silicon-based protected milbemycin A4 is added to the organic solvent and cooled to 0 DEG C, and then reacted for a period of time after adding p-toluene sulfonic acid, or the 5-hydroxyl silicon-based protected milbemycin A4 and the desilicon-based protection reagent are added to the organic solvent and cooled to 0 DEG C and reacted for a period of time, wherein the desilicon-based protection reagent is a fluorine reagent selected from at least one of hydrogen fluoride and tetra-n-butylammonium fluoride. Under inert gas protection and at room temperature, the oxidizing agent and the milbemycin A4 are added to the organic solvent to obtain the 5-ketone milbemycin A4.

7. The process for the preparation of milbemycin A4 as claimed in claim 1, wherein, Under inert gas atmosphere, the 5-ketone milbemycin A4 is dissolved with hydroxylamine hydrochloride and reacted for a period of time.

8. The process for the preparation of milbemycin A4 as claimed in claim 1, wherein, The silicon-based protection reagent is selected from at least one of tert-butyl diphenyl chlorosilane, trimethyl chlorosilane, triethyl chlorosilane, and tert-butyl dimethyl chlorosilane.

9. The process for the preparation of milbemycin A4 as claimed in claim 1, wherein, The bromination reagent is at least one of NBS, liquid bromine, sodium bromide, lithium bromide, and phosphorus tribromide; the reducing agent is one of Pd / C, Pt, Zn, and tri-n-butyl tin hydride; and the oxidizing agent is at least one of the following: des Martin oxidizing agent, Jones reagent, Shaw reagent, Collins reagent, PDC, and IBX oxidizing agent.

10. The process for the preparation of milbemycin A4 as claimed in claim 1, wherein, ​

Images