Preparation and purification process of oxytetracycline hydrochloride

Abstract

The invention discloses an oxytetracycline hydrochloride preparation and purification process, and relates to the technical field of medical chemistry. The preparation and purification process comprises the following steps: catalyzing a compound a serving as an initial raw material and a compound b through piperidine to obtain a compound c; reacting the compound c with a compound d to obtain a compound e; reacting the compound e with a compound f to obtain a compound g; performing photochemical isomerization on the compound g to obtain a compound h oxytetracycline hydrochloride crude product; and purifying the compound h oxytetracycline hydrochloride crude product by using a choline-lactic acid eutectic solvent to obtain oxytetracycline hydrochloride. According to the micro-channel reactor, precise control over the three-dimensional configuration is achieved in the micro-channel reactor through a 365 nm UV light source, 365 nm photon energy is precisely matched with trans-configuration pi-to-pi electron transition energy, trans-configuration pi electrons can freely rotate, and a cis-structure is formed. The problem of stereoisomerization in chemical synthesis is solved, and the isomerization yield is increased to 90% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of pharmaceutical chemistry, and in particular to a preparation and purification process of oxytetracycline hydrochloride. Background Art

[0002] Oxytetracycline hydrochloride is a broad-spectrum antibiotic whose antibacterial spectrum, antibacterial principle and application are basically the same as those of tetracycline.

[0003] Oxytetracycline hydrochloride is currently produced primarily through fermentation and chemical synthesis. The fermentation method relies on Streptomyces aureus, which carries the risk of strain degeneration. Fermentation also offers a low yield of approximately 1.5% to 4.0%, produces numerous byproducts, and requires complex separation and purification processes. Traditional chemical synthesis routes, such as the Woodward route, require more than 20 reaction steps, resulting in a long reaction path and low overall yield. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation and purification process of oxytetracycline hydrochloride to solve the problems of low yield and complex process in traditional process.

[0005] The technical solutions of the present invention are as follows:

[0006] A preparation and purification process of oxytetracycline hydrochloride, comprising the following synthesis and purification steps:

[0007] (1) Compound a is used as a starting material and reacted with compound b under piperidine catalysis to obtain compound c;

[0008] (2) Compound c reacts with compound d to obtain compound e;

[0009] (3) Compound e reacts with compound f under the catalysis of titanium tetrachloride to obtain compound g;

[0010] (4) Compound g is photoisomerized to obtain crude oxytetracycline hydrochloride compound h;

[0011] (5) The crude product of compound h, oxytetracycline hydrochloride, was purified using a choline-lactic acid deep eutectic solvent to obtain oxytetracycline hydrochloride;

[0012] The specific reactions are as follows:

[0013]

[0014] Furthermore, the reaction conditions in step (1) are as follows: dissolving compound a and 1.3 times the weight of compound b in 10 times the weight of anhydrous ethanol, adding 0.1 times the weight of piperidine, reflux for 6 hours, distilling off 2 / 3 of the anhydrous ethanol under reduced pressure, cooling to 0°C, filtering, and obtaining a solid which is recrystallized with anhydrous ethanol to obtain compound c;

[0015] The completion of the reaction in step (1) can be determined by conventional methods in the art, such as TLC technology.

[0016] Furthermore, the reaction conditions in step (2) are as follows: under argon protection, compound c and 1.8 times the mass of compound d are dissolved in 8 times the weight of dichloromethane, reacted at 5-20°C for 2 hours, filtered through a diatomaceous earth pad, the filtrate is washed twice with a saturated sodium bicarbonate solution, dried over anhydrous magnesium sulfate, and dichloromethane is evaporated under reduced pressure. The mixture is slurried with n-hexane and filtered to obtain compound e;

[0017] The completion of the reaction in step (2) can be determined by conventional methods in the art, such as TLC technology.

[0018] Furthermore, the reaction conditions in step (3) are as follows: diethyl malonate and 0.2 times the weight of NaH are stirred in THF at 0°C for 30 minutes to generate a carbon anion, and then 0.9 times the weight of BrCHOCH solution is added dropwise. After reacting at room temperature for 4 hours, the mixture is extracted with ethyl acetate, dried, and distilled to obtain an activated product containing a methoxy group and an ester group; compound e is reacted with 1 times the weight of L-cysteine ​​methyl ester hydrochloride, 1.2 times the weight of the activated product, 1.2 times the weight of triethylamine, and 2.6 times the weight of HATU in DMF at room temperature under the catalysis of titanium tetrachloride for 12 hours, extracted and concentrated with ethyl acetate, and the obtained product is refluxed with a NaOH aqueous solution for desulfurization, and then condensed with 0.1 times the weight of TsOH in toluene under reflux for 8 hours for cyclization, extracted and concentrated with ethyl acetate, hydrolyzed under reflux with a NaOH aqueous solution, and reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain compound g;

[0019] The reaction in step (3) can be judged to be complete according to conventional methods in the art, such as HPLC technology.

[0020] Furthermore, the reaction conditions in step (4) are as follows: Compound g is dissolved in 20 times the mass of methanol, passed through a quartz microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m, and the setting conditions are 365 nm UV and a power density of 50 mW / cm 2 , control the flow rate to 2.0 ml / min, connect the reactor to an external circulating cooling system, maintain 20°C, and measure the temperature in real time with infrared; the effluent is directly passed into a -10°C cold well, and concentrated under reduced pressure to obtain the crude product of compound h oxytetracycline hydrochloride;

[0021] Furthermore, the crystallization conditions in step (5) are as follows: adding the crude compound h oxytetracycline hydrochloride to 10 times its weight of a choline-lactic acid low eutectic solvent, heating to 60°C, dissolving and clarifying; cooling to 15°C at a cooling rate of 0.5°C / min, applying a 10kHz electric field with a field strength of 50V / cm during the cooling process, and filtering after crystallization for 4 hours to obtain oxytetracycline hydrochloride.

[0022] Beneficial effects:

[0023] 1. The present invention achieves precise control of stereoisomerization in a microchannel reactor by using a 365nm UV light source. The 365nm photon energy precisely matches the π→π electron transition energy of the trans configuration, resulting in a reduction in the C-OH bond energy and a low energy barrier for excited-state single-bond rotation. This allows the trans-configured π electrons to rotate freely, rotate to 90°, and then relax to form a cis structure. This solves the problem of stereoisomerization in chemical synthesis, increases the isomerization yield to over 90%, and improves the isomeric purity of oxytetracycline hydrochloride.

[0024] 2. The present invention uses a choline-lactic acid low eutectic solvent and applies a 10kHz electric field to induce directional arrangement of oxytetracycline hydrochloride molecules, inhibit dendrite formation, improve the yield, and obtain crystals with uniform particle size distribution (D50 = 24 ± 2 μm). The particle size distribution is more uniform, which is more conducive to the bioavailability of the drug.

[0025] 3. The synthesis steps of the present invention are short, and the total yield of the four-step reaction and purification can reach 55% to 65%, which is significantly improved compared with the total yield of 1.5% to 4.0% of the traditional fermentation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The chemical structure of oxytetracycline hydrochloride.

[0027] Figure 2 This is the nuclear magnetic resonance image of oxytetracycline hydrochloride in Example 1 of the present invention.

[0028] Figure 3 This is the HPLC chart of oxytetracycline hydrochloride in Example 1 of the present invention.

[0029] Figure 4 This is the enantiomer spectrum of oxytetracycline hydrochloride in Example 1 of the present invention.

[0030] Figure 5 This is the particle size distribution diagram of oxytetracycline hydrochloride in Example 1 of the present invention.

[0031] Figure 6 This is the particle size distribution diagram of oxytetracycline hydrochloride in Comparative Example 2 of the present invention.

[0032] Figure 7 This is the particle size distribution diagram of oxytetracycline hydrochloride in Comparative Example 3 of the present invention.

[0033] Figure 8 This is the particle size distribution diagram of oxytetracycline hydrochloride in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the embodiments. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0035] Example 1 (1)

[0037]

[0038] 10 g of compound a and 13 g of compound b were dissolved in 100 g of anhydrous ethanol, 1 g of piperidine was added, and the reaction was refluxed for 6 hours. 66 g of anhydrous ethanol was evaporated under reduced pressure, the temperature was lowered to 0°C, and the reaction mixture was filtered. The obtained solid was dissolved in anhydrous ethanol by heating, the temperature was lowered to 0°C, and crystallization was carried out for 1 hour. The solid was filtered and dried in vacuo at 45°C to obtain 12.5 g of compound c with a yield of 87.7%. (2)

[0040]

[0041] Under argon protection, 10 g of compound c and 18 g of compound d were dissolved in 80 g of dichloromethane, reacted at 12 ° C for 2 hours, filtered through a celite pad, and the filtrate was washed twice with saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The dichloromethane was evaporated under reduced pressure, and the solid was slurried with n-hexane and filtered. The solid was dried in vacuo at 45 ° C to obtain 9.0 g of compound e in a yield of 91.9%. (3)

[0043]

[0044] 12 g of diethyl malonate and 2.4 g of NaH were stirred in THF at 0°C for 30 minutes, and then 10.8 g of BrCHOCH solution was added dropwise. The mixture was reacted at room temperature for 4 hours, and then extracted with ethyl acetate, dried, and distilled to obtain an activated product. 10 g of compound e was reacted with 10 g of L-cysteine ​​methyl ester hydrochloride, 12 g of the activated product, 12 g of triethylamine, and 26 g of HATU in DMF at room temperature for 12 hours under the catalysis of titanium tetrachloride. The product was extracted and concentrated with ethyl acetate. The product was desulfurized by refluxing with a NaOH aqueous solution, and then condensed with 1 g of TsOH in toluene under refluxing for 8 hours for cyclization. The product was extracted and concentrated with ethyl acetate, hydrolyzed by refluxing with a NaOH aqueous solution, and then reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain 21.7 g of compound g with a yield of 83.0%. (4)

[0046]

[0047] 10 g of compound g was dissolved in 200 g of methanol and passed through a quartz microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m. The conditions were set at 365 nm UV and a power density of 50 mW / cm 2 , control the flow rate to 2.0 ml / min, connect the reactor to an external circulating cooling system, maintain 20°C, and measure the temperature in real time with infrared; the effluent is directly passed into a -10°C cold well, and after concentration under reduced pressure, 9.8 g of crude oxytetracycline hydrochloride of compound h is obtained, with a yield of 98%. (5)

[0049] 9.8 g of crude compound H oxytetracycline hydrochloride was added to 98 g of a choline-lactic acid deep eutectic solvent and heated to 60°C until dissolved and clarified. The mixture was then cooled to 15°C at a rate of 0.5°C / min. During the cooling process, a 10 kHz electric field with a field strength of 50 V / cm was applied. Crystallization occurred for 4 hours and then filtered to obtain 9.31 g of oxytetracycline hydrochloride, a yield of 93.1%. The total yield of the four-step reaction and purification was 62.2% based on the starting material. The product molecular formula is: C 22 H 25 ClN2O9, molecular weight: 496.89. Analysis results: HPLC purity analysis > 99.9%, elemental analysis: C53.17%, H5.03%, Cl 7.13%, N5.64%, O28.98%. The nuclear magnetic resonance, purity analysis, enantiomers, and particle size distribution of oxytetracycline hydrochloride are as follows: Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 shown.

[0050] Example 2 (1)

[0052]

[0053] 10 g of compound a and 13 g of compound b were dissolved in 100 g of anhydrous ethanol, 1 g of piperidine was added, and the reaction was refluxed for 6 hours. 66 g of anhydrous ethanol was evaporated under reduced pressure, the temperature was lowered to 0°C, and the reaction mixture was filtered. The obtained solid was dissolved in anhydrous ethanol by heating, the temperature was lowered to 0°C, and crystallization was carried out for 1 hour. The solid was filtered and dried in vacuo at 45°C to obtain 12.5 g of compound c with a yield of 87.7%. (2)

[0055]

[0056] Under argon protection, 10 g of compound c and 18 g of compound d were dissolved in 80 g of dichloromethane, reacted at 20°C for 2 hours, filtered through a celite pad, and the filtrate was washed twice with a saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The dichloromethane was evaporated under reduced pressure, the mixture was slurried with n-hexane, filtered, and the solid was dried in vacuo at 45°C to obtain 8.9 g of compound e in a yield of 90.9%. (3)

[0058]

[0059] 12 g of diethyl malonate and 2.4 g of NaH were stirred in THF at 0°C for 30 minutes, and then 10.8 g of BrCHOCH solution was added dropwise. The mixture was reacted at room temperature for 4 hours, and then extracted with ethyl acetate, dried, and distilled to obtain an activated product. 10 g of compound e was reacted with 10 g of L-cysteine ​​methyl ester hydrochloride, 12 g of the activated product, 12 g of triethylamine, and 26 g of HATU in DMF at room temperature for 12 hours under the catalysis of titanium tetrachloride. The product was extracted and concentrated with ethyl acetate. The product was desulfurized by refluxing with a NaOH aqueous solution, and then condensed with 1 g of TsOH in toluene under refluxing for 8 hours for cyclization. The product was extracted and concentrated with ethyl acetate, hydrolyzed by refluxing with a NaOH aqueous solution, and then reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain 22.0 g of compound g with a yield of 84.1%. (4)

[0061]

[0062] 10 g of compound g was dissolved in 200 g of methanol and passed through a quartz microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m. The conditions were set at 365 nm UV and a power density of 50 mW / cm 2 , control the flow rate to 2.0 ml / min, connect the reactor to an external circulating cooling system, maintain 20°C, and measure the temperature in real time with infrared; the effluent is directly passed into a -10°C cold well, and concentrated under reduced pressure to obtain 9.9 g of crude compound h oxytetracycline hydrochloride, with a yield of 99%. (5)

[0064] 9.9g of crude compound H oxytetracycline hydrochloride was added to 99g of choline-lactic acid deep eutectic solvent, heated to 60°C, dissolved and clarified; cooled to 15°C at a cooling rate of 0.5°C / min, and a 10kHz electric field with a field strength of 50V / cm was applied during the cooling process. After crystallization for 4 hours, filtration was performed to obtain 9.30g of oxytetracycline hydrochloride, with a yield of 93.0%. Based on the starting material, the total yield of the four-step reaction and purification was 62.4%.

[0065] Example 3 (1)

[0067]

[0068] 10 g of compound a and 13 g of compound b were dissolved in 100 g of anhydrous ethanol, 1 g of piperidine was added, and the reaction was refluxed for 6 hours. 66 g of anhydrous ethanol was evaporated under reduced pressure, the temperature was lowered to 0°C, and the reaction mixture was filtered to obtain a solid which was dissolved in anhydrous ethanol by heating, the temperature was lowered to 0°C, crystallized for 1 hour, filtered, and the solid was dried in vacuo at 45°C to obtain 12.3 g of compound c with a yield of 86.3%. (2)

[0070]

[0071] Under argon protection, 10 g of compound c and 18 g of compound d were dissolved in 80 g of dichloromethane, reacted at 20°C for 2 hours, filtered through a celite pad, and the filtrate was washed twice with saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The dichloromethane was evaporated under reduced pressure, and the solid was slurried with n-hexane and filtered. The solid was dried in vacuo at 45°C to obtain 8.8 g of compound e in a yield of 89.9%. (3)

[0073]

[0074] 12 g of diethyl malonate and 2.4 g of NaH were stirred in THF at 0°C for 30 minutes, and then 10.8 g of BrCHOCH solution was added dropwise. After reaction at room temperature for 4 hours, the mixture was extracted with ethyl acetate, dried, and distilled to obtain an activated product. 10 g of compound e was reacted with 10 g of L-cysteine ​​methyl ester hydrochloride, 12 g of the activated product, 12 g of triethylamine, and 26 g of HATU in DMF at room temperature for 12 hours under the catalysis of titanium tetrachloride. The product was extracted and concentrated with ethyl acetate. The product was desulfurized by refluxing with a NaOH aqueous solution, and then condensed with 1 g of TsOH in toluene under refluxing for 8 hours for cyclization. The product was extracted and concentrated with ethyl acetate. After hydrolysis by refluxing with a NaOH aqueous solution, the product was reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain 22.4 g of compound g with a yield of 85.7%. (4)

[0076]

[0077] 10 g of compound g was dissolved in 200 g of methanol and passed through a quartz microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m. The conditions were set at 365 nm UV and a power density of 50 mW / cm 2 , control the flow rate to 2.0 ml / min, connect the reactor to an external circulating cooling system, maintain 20°C, and measure the temperature in real time with infrared; the effluent is directly passed into a -10°C cold well, and concentrated under reduced pressure to obtain 9.9 g of crude compound h oxytetracycline hydrochloride, with a yield of 99%. (5)

[0079] 9.9 g of crude compound H oxytetracycline hydrochloride was added to 99 g of choline-lactic acid deep eutectic solvent, heated to 60°C, dissolved and clarified; cooled to 15°C at a cooling rate of 0.5°C / min, and a 10 kHz electric field with a field strength of 50 V / cm was applied during the cooling process. After crystallization for 4 hours, filtration was performed to obtain 9.33 g of oxytetracycline hydrochloride, with a yield of 93.3%. Based on the starting material, the total yield of the four-step reaction and purification was 62.0%.

[0080] Comparative Example 1 (1)

[0082]

[0083] 10 g of compound a and 13 g of compound b were dissolved in 100 g of anhydrous ethanol, 1 g of piperidine was added, and the reaction was refluxed for 6 hours. 66 g of anhydrous ethanol was evaporated under reduced pressure, the temperature was lowered to 0°C, and the reaction mixture was filtered. The obtained solid was dissolved in anhydrous ethanol by heating, the temperature was lowered to 0°C, and crystallization was carried out for 1 hour. The solid was filtered and dried in vacuo at 45°C to obtain 12.0 g of compound c with a yield of 84.2%. (2)

[0085]

[0086] Under argon protection, 10 g of compound c and 18 g of compound d were dissolved in 80 g of dichloromethane, reacted at 5°C for 2 hours, filtered through a celite pad, and the filtrate was washed twice with saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The dichloromethane was evaporated under reduced pressure, the mixture was slurried with n-hexane, filtered, and the solid was dried in vacuo at 45°C to obtain 8.6 g of compound e with a yield of 87.8%. (3)

[0088]

[0089] 12 g of diethyl malonate and 2.4 g of NaH were stirred in THF at 0°C for 30 minutes, and then 10.8 g of BrCHOCH solution was added dropwise. The mixture was reacted at room temperature for 4 hours, and then extracted with ethyl acetate, dried, and distilled to obtain an activated product. 10 g of compound e was reacted with 10 g of L-cysteine ​​methyl ester hydrochloride, 12 g of the activated product, 12 g of triethylamine, and 26 g of HATU in DMF at room temperature for 12 hours under the catalysis of titanium tetrachloride. The product was extracted and concentrated with ethyl acetate. The product was desulfurized by refluxing with a NaOH aqueous solution, and then condensed with 1 g of TsOH in toluene under refluxing for 8 hours for cyclization. The product was extracted and concentrated with ethyl acetate, hydrolyzed by refluxing with a NaOH aqueous solution, and then reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain 22.0 g of compound g with a yield of 84.1%. (4)

[0091]

[0092] 10g of compound g was dissolved in 100g of a methanol / water mixture (7 / 3). 1.1g of p-toluenesulfonic acid was added and the mixture was reacted at 70°C under argon for 5 hours. The reaction solution was cooled to 10°C and the pH was adjusted to 4.0 by slowly adding 10% sodium hydroxide solution. The precipitated solid was filtered to obtain 8.8g of solid. The solid was dissolved in 88g of 0.1M hydrochloric acid solution at 60°C. After the solution was clear, the pH was adjusted to 4.8 with aqueous ammonia. The solution was slowly cooled to 0°C and allowed to crystallize for 4 hours. The solution was then filtered to obtain 7.2g of crude compound h, oxytetracycline hydrochloride. The yield was 72%. (5)

[0094] 7.2 g of crude compound H oxytetracycline hydrochloride was added to 72 g of choline-lactic acid deep eutectic solvent, heated to 60°C, dissolved and clarified; cooled to 15°C at a cooling rate of 0.5°C / min, and a 10 kHz electric field with a field strength of 50 V / cm was applied during the cooling process. After crystallization for 4 hours, filtration was performed to obtain 6.8 g of oxytetracycline hydrochloride, with a yield of 68.0%. The total yield of the four-step reaction and purification was 42.3% based on the starting material.

[0095] Comparative Example 2 (1)

[0097]

[0098] 10 g of compound a and 13 g of compound b were dissolved in 100 g of anhydrous ethanol, 1 g of piperidine was added, and the reaction was refluxed for 6 hours. 66 g of anhydrous ethanol was evaporated under reduced pressure, the temperature was lowered to 0°C, and the reaction mixture was filtered to obtain a solid which was dissolved in anhydrous ethanol by heating, the temperature was lowered to 0°C, crystallized for 1 hour, filtered, and the solid was dried in vacuo at 45°C to obtain 12.3 g of compound c with a yield of 86.3%. (2)

[0100]

[0101] Under argon protection, 10 g of compound c and 18 g of compound d were dissolved in 80 g of dichloromethane, reacted at 5°C for 2 hours, filtered through a celite pad, and the filtrate was washed twice with saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The dichloromethane was evaporated under reduced pressure, and the solid was slurried with n-hexane and filtered. The solid was dried in vacuo at 45°C to obtain 9.1 g of compound e in a yield of 92.9%. (3)

[0103]

[0104] 12 g of diethyl malonate and 2.4 g of NaH were stirred in THF at 0°C for 30 minutes, and then 10.8 g of BrCHOCH solution was added dropwise. The mixture was reacted at room temperature for 4 hours, and then extracted with ethyl acetate, dried, and distilled to obtain an activated product. 10 g of compound e was reacted with 10 g of L-cysteine ​​methyl ester hydrochloride, 12 g of the activated product, 12 g of triethylamine, and 26 g of HATU in DMF at room temperature for 12 hours using titanium tetrachloride as a catalyst. The product was extracted and concentrated with ethyl acetate. The product was desulfurized by refluxing with a NaOH aqueous solution, and then condensed with 1 g of TsOH in toluene under refluxing for 8 hours for cyclization. The product was extracted and concentrated with ethyl acetate, hydrolyzed by refluxing with a NaOH aqueous solution, and then reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain 21.9 g of compound g with a yield of 83.7%. (4)

[0106]

[0107] 10 g of compound g was dissolved in 200 g of methanol and passed through a quartz microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m. The conditions were set at 365 nm UV and a power density of 50 mW / cm 2 , control the flow rate to 2.0 ml / min, connect the reactor to an external circulating cooling system, maintain 20°C, and measure the temperature in real time with infrared; the effluent is directly passed into a -10°C cold well, and after concentration under reduced pressure, 9.8 g of crude oxytetracycline hydrochloride of compound h is obtained, with a yield of 98%. (5)

[0109] 9.8g of crude compound h oxytetracycline hydrochloride was added to 98g of methanol / acetone mixed solvent (methanol / acetone = 3 / 7), heated to 55°C, dissolved and clarified; cooled to 5°C at a cooling rate of 1°C / min, crystallized for 4 hours, and filtered to obtain 8.02g of oxytetracycline hydrochloride with a yield of 80.2%. Based on the starting material, the total yield of the four-step reaction and purification was 53.8%. The particle size distribution of oxytetracycline hydrochloride obtained in this comparative example is shown in Figure 2. Figure 6 shown.

[0110] Comparative Example 3 (1)

[0112]

[0113] 10 g of compound a and 13 g of compound b were dissolved in 100 g of anhydrous ethanol, 1 g of piperidine was added, and the reaction was refluxed for 6 hours. 66 g of anhydrous ethanol was evaporated under reduced pressure, the temperature was lowered to 0°C, and the reaction mixture was filtered. The obtained solid was dissolved in anhydrous ethanol by heating, the temperature was lowered to 0°C, and crystallization was carried out for 1 hour. The solid was filtered and dried in vacuo at 45°C to obtain 12.4 g of compound c with a yield of 87.0%. (2)

[0115]

[0116] Under argon protection, 10 g of compound c and 18 g of compound d were dissolved in 80 g of dichloromethane, reacted at 5°C for 2 hours, filtered through a celite pad, and the filtrate was washed twice with a saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The dichloromethane was evaporated under reduced pressure, the mixture was slurried with n-hexane, filtered, and the solid was dried in vacuo at 45°C to obtain 8.9 g of compound e in a yield of 90.9%. (3)

[0118]

[0119] 12 g of diethyl malonate and 2.4 g of NaH were stirred in THF at 0°C for 30 minutes, and then 10.8 g of BrCHOCH solution was added dropwise. After reaction at room temperature for 4 hours, the mixture was extracted with ethyl acetate, dried, and distilled to obtain an activated product. 10 g of compound e was reacted with 10 g of L-cysteine ​​methyl ester hydrochloride, 12 g of the activated product, 12 g of triethylamine, and 26 g of HATU in DMF at room temperature for 12 hours under the catalysis of titanium tetrachloride. The product was extracted and concentrated with ethyl acetate. The product was desulfurized by refluxing with a NaOH aqueous solution, and then condensed with 1 g of TsOH in toluene under refluxing for 8 hours for cyclization. The product was extracted and concentrated with ethyl acetate, hydrolyzed by refluxing with a NaOH aqueous solution, and then reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain 22.1 g of compound g with a yield of 84.5%. (4)

[0121]

[0122] 10 g of compound g was dissolved in 200 g of methanol and passed through a quartz microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m. The conditions were set at 365 nm UV and a power density of 50 mW / cm 2 , control the flow rate to 2.0 ml / min, connect the reactor to an external circulating cooling system, maintain 20°C, and measure the temperature in real time with infrared; the effluent is directly passed into a -10°C cold well, and after concentration under reduced pressure, 9.8 g of crude oxytetracycline hydrochloride of compound h is obtained, with a yield of 98%. (5)

[0124] 9.8g of crude compound h oxytetracycline hydrochloride was added to 98g of methanol / acetone mixed solvent (methanol / acetone = 3 / 7), heated to 55°C, dissolved and clarified; cooled to 5°C at a cooling rate of 1°C / min, applied a 10kHz electric field with a field strength of 50V / cm during the cooling process, and filtered after crystallization for 4 hours to obtain 7.97g of oxytetracycline hydrochloride with a yield of 79.7%. Based on the starting material, the total yield of the four-step reaction and purification was 53.3%. The particle size distribution of oxytetracycline hydrochloride obtained in this comparative example is shown in FIG. Figure 7 shown.

[0125] Comparative Example 4 (1)

[0127]

[0128] 10 g of compound a and 13 g of compound b were dissolved in 100 g of anhydrous ethanol, 1 g of piperidine was added, and the reaction was refluxed for 6 hours. 66 g of anhydrous ethanol was evaporated under reduced pressure, the temperature was lowered to 0°C, and the reaction mixture was filtered. The obtained solid was dissolved in anhydrous ethanol by heating, the temperature was lowered to 0°C, and crystallization was carried out for 1 hour. The solid was filtered and dried in vacuo at 45°C to obtain 12.2 g of compound c with a yield of 85.6%. (2)

[0130]

[0131] Under argon protection, 10 g of compound c and 18 g of compound d were dissolved in 80 g of dichloromethane, reacted at 5°C for 2 hours, filtered through a celite pad, and the filtrate was washed twice with a saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The dichloromethane was evaporated under reduced pressure, the mixture was slurried with n-hexane, filtered, and the solid was dried in vacuo at 45°C to obtain 9.0 g of compound e in a yield of 91.9%. (3)

[0133]

[0134] 12 g of diethyl malonate and 2.4 g of NaH were stirred in THF at 0°C for 30 minutes, and then 10.8 g of BrCHOCH solution was added dropwise. The mixture was reacted at room temperature for 4 hours, and then extracted with ethyl acetate, dried, and distilled to obtain an activated product. 10 g of compound e was reacted with 10 g of L-cysteine ​​methyl ester hydrochloride, 12 g of the activated product, 12 g of triethylamine, and 26 g of HATU in DMF at room temperature for 12 hours under the catalysis of titanium tetrachloride. The product was extracted and concentrated with ethyl acetate. The product was desulfurized by refluxing with a NaOH aqueous solution, and then condensed with 1 g of TsOH in toluene under refluxing for 8 hours for cyclization. The product was extracted and concentrated with ethyl acetate, hydrolyzed by refluxing with a NaOH aqueous solution, and then reacted with an ethanolic solution of NH3 at room temperature to generate a carbamoyl group to obtain 22.0 g of compound g with a yield of 84.1%. (4)

[0136]

[0137] 10 g of compound g was dissolved in 200 g of methanol and passed through a quartz microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m. The conditions were set at 365 nm UV and a power density of 50 mW / cm 2The flow rate was controlled at 2.0 ml / min. The reactor was connected to an external circulating cooling system to maintain 20°C, and infrared temperature was measured in real time. The effluent was directly passed into a -10°C cold well and concentrated under reduced pressure to obtain 9.8 g of crude compound H, oxytetracycline hydrochloride. The yield was 98%. (5)

[0139] 9.8g of crude compound h oxytetracycline hydrochloride was added to 98g of choline-lactic acid low eutectic solvent, heated to 60°C, dissolved and clarified; cooled to 15°C at a cooling rate of 0.5°C / min, crystallized for 4 hours and filtered to obtain 9.31g of oxytetracycline hydrochloride with a yield of 93.1%. Based on the starting material, the total yield of the four-step reaction and purification was 61.2%. The particle size distribution of oxytetracycline hydrochloride obtained in this comparative example is shown in FIG. Figure 8 shown.

[0140] Comparative Example 5

[0141] (1) Slant activation

[0142] Take the spores of Streptomyces fissiliflorus, streak inoculate them on oat slant medium, and culture them at -28℃ for 7 days until the slant is covered with gray spores.

[0143] (2) Seed solution preparation

[0144] Take one slant and add 50 mL of sterile water, shake with glass beads to prepare a spore suspension, inoculate it into a 500 mL conical flask at a 5% inoculum volume, fill it with 100 mL, and culture it at -28°C and 220 rpm for 48 hours.

[0145] (3) Secondary seeds

[0146] 3 L of liquid was added to 5 L of seed tank, sterilized at 121 °C for 30 minutes, and the first-grade seeds were inoculated at a 10% inoculum rate. The stirring speed was 200 rpm and the pH was controlled at 6.0.

[0147] (4) Fermentation production

[0148] A 10L fermenter was filled with 6L of material containing 360g of total sugar, sterilized at 121°C for 45 minutes, cooled to 28°C, and then filtered and sterilized with 0.01g / L CoCl2 solution. 1.5L of secondary seeds was inoculated, the temperature was 28°C, the speed was adjusted to 300rpm, and the pH naturally dropped to 6.2. After fermentation for 48 hours, 50ml of 0.1% sodium bromoacetate and 50ml of 50% glucose solution were added every 12 hours for 120 hours.

[0149] (5) Fermentation broth pretreatment

[0150] The fermentation broth was cooled to 15°C, 10% oxalic acid solution was slowly added to pH 2.0, 200 g of diatomaceous earth pad was added for filtration, and the filtrate was extracted with 5 L of ethyl acetate. 0.1 M Na2HPO4 buffer was added to the ethyl acetate layer to pH = 4.5, and the temperature was lowered to 10°C. Concentrated hydrochloric acid was slowly added dropwise to pH = 2.9. The mixture was stirred at 40°C for 2 hours to crystallize and filtered to obtain 13.2 g of a crude product.

[0151] (6) Decolorization and purification

[0152] 13.2 g of the crude product was dissolved in 132 g of a 3 / 7 methanol / acetone mixture. The mixture was heated to 60°C, 0.4 g of activated carbon was added, and decolorization was carried out for 30 minutes. The mixture was then filtered while hot. The filtrate was cooled to 5°C at a rate of 1°C / min, crystallized for 4 hours, filtered, and dried under vacuum to yield 9.5 g of oxytetracycline hydrochloride. The yield based on total sugars was 2.64%.

[0153] By comparing Example 1 with Comparative Example 1, the present invention achieves precise control of stereo configuration in a microchannel reactor by using a 365 nm UV light source, and increases the isomerization yield to more than 90% compared with the traditional acid-catalyzed isomerization yield of 72.0%.

[0154] By comparing Example 1 with Comparative Examples 2, 3, and 4, by using a choline-lactic acid deep eutectic solvent and applying a 10kHz electric field, oxytetracycline hydrochloride molecules were induced to align in a directional manner, and crystals with D50 = 23.98 μm and D50 = 24.01 μm were obtained, with a yield of 93.1%. Compared with the crystals with D50 = 20.89 μm and D50 = 26.87 obtained by recrystallization without applying a 10kHz electric field, the particle size distribution was more uniform. Compared with the recrystallization yields of 80.2% and 79.7% using a traditional methanol / acetone system, the yield was significantly improved.

[0155] By comparing Example 1 with Comparative Example 5, the traditional fermentation method takes a long time to prepare and the yield is only 2.64%, while the total yield of Example 1 can reach 62.2%, which is significantly improved.

[0156] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A process for preparing and purifying oxytetracycline hydrochloride, characterized in that: The following synthesis and purification steps are included: S1, using compound a as a starting material and reacting it with compound b under piperidine catalysis to obtain compound c; S2, compound c reacts with compound d to obtain compound e; S3, compound e and compound f react under the catalysis of titanium tetrachloride to obtain compound g; S4. Compound g is photoisomerized to obtain crude oxytetracycline hydrochloride compound h; S5. Purifying the crude product of compound h oxytetracycline hydrochloride with a choline-lactic acid deep eutectic solvent to obtain oxytetracycline hydrochloride; The specific reactions are as follows:

2. The process for preparing and purifying oxytetracycline hydrochloride according to claim 1, wherein: Compound a and compound b react under the catalytic action of piperidine, specifically: compound a and compound b are dissolved in anhydrous ethanol, piperidine is added, and the mixture is refluxed to obtain compound c.

3. The process for preparing and purifying oxytetracycline hydrochloride according to claim 1, wherein: Compound c reacts with compound d, specifically, dissolving compound c and compound d in dichloromethane and reacting at 5-20° C. to obtain compound e.

4. The process for preparing and purifying oxytetracycline hydrochloride according to claim 1, wherein: Compound e and compound f are reacted together in activated diethyl malonate, specifically: diethyl malonate is reacted with NaH and BrCH2OCH3 in THF for activation, and then reacted with compound e, L-cysteine ​​methyl ester hydrochloride, triethylamine, and HATU in DMF using titanium tetrachloride as a catalyst to obtain a product, which is refluxed in a NaOH aqueous solution for desulfurization, and then refluxed with TsOH in toluene for condensation and cyclization. The product is then hydrolyzed with NaOH and reacted with NH3 to form a carbamoyl group to obtain compound g.

5. The process for preparing and purifying oxytetracycline hydrochloride according to claim 1, wherein: Compound g is photoisomerized to obtain compound h by passing compound g through a microchannel reactor with an inner diameter of 1.0 mm and a length of 15 m, with the setting conditions of 365 nm UV and a power density of 50 mW / cm 2 , to obtain compound h oxytetracycline hydrochloride crude product.

6. The process for preparing and purifying oxytetracycline hydrochloride according to claim 1, wherein: The purification method of step S5 is as follows: the purification solvent is choline-lactic acid low eutectic solvent, the amount of solvent used is 10 times the weight of the crude product of compound h oxytetracycline hydrochloride, dissolved and clarified at 60°C, cooled to 15°C at a cooling rate of 0.5°C / min, and a 10kHz electric field is applied at the same time. Crystallization is carried out for 4 hours, and oxytetracycline hydrochloride is obtained by filtration.

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