Preparation method of maxacalcitol impurity C

Abstract

The invention belongs to the technical field of chemical synthesis, and particularly relates to a preparation method, a detection method and application of a maxacalcitol 24-hydroxyl isomer impurity. The impurity is a maxacalcitol impurity C. The preparation method comprises the following steps: by taking (5E, 7E)-(1S, 3R, 20S)-1, 3-bis (tert-butyldimethylsiloxy)-9, 10-open-loop pregna-5, 7, 10 (19)-triene-20-ol (a compound shown as a formula 1) as a raw material, carrying out three-step chemical reaction of condensation, TBS protection removal and illumination overturning, and carrying out two-step purification of DAC preparation and column chromatography to obtain the maxacalcitol impurity C. The invention further discloses a preparation method of the maxacalcitol impurity C. The preparation method comprises the following steps: preparing the maxacalcitol impurity C. The preparation method is simple in process, low in equipment requirement and good in reaction selectivity, and has instructive significance on quality control of maxacalcitol bulk drugs.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and particularly relates to a preparation method, a detection method and an application of a maxacalcitol impurity C. Background Art

[0002] Menatetrenone, chemical name: (+)(5Z,7E)-(1S,3R,20S)-20-(3-hydroxy-3-methylbutyloxy)-9,10-opened pregnan-5,7,10(19)-triene-1,3-diol, structural formula:

[0003]

[0004] Maxacalcitol is a third-generation active vitamin D3 drug developed by Chugai Pharmaceutical Co., Ltd. of Japan. It was launched in Japan in 2000. Its injection (trade name: Oxarol) is used to treat secondary hyperparathyroidism (SHPT) in patients with renal dialysis; its ointment (trade name: Oxarol) is used to treat psoriasis and other psoriasis-like skin diseases.

[0005] Although maxacalcitol is only 1 / 10 of calcitriol in binding capacity with vitamin D3 receptor VDR, its effect in suppressing secretion of parathyroid hormone (PTH) is suitable with calcitriol. When treating secondary hyperparathyroidism (SHPT) of renal dialysis patients, due to its weak calcium metabolism, undesirable reactions such as hypercalcemia are less. The incidence of chronic renal failure is higher. According to expert estimates, there are about several million chronic renal failure patients in the whole country. The most common cause causing chronic renal failure is chronic nephritis, which accounted for 60% of the number of dialysis patients in the past. Because renal dialysis patients all have active vitamin D3 deficiency, and develop into secondary hyperparathyroidism, therefore develop active vitamin D3 class medicine maxacalcitol with less undesirable reaction, can satisfy the needs of treating secondary hyperparathyroidism (SHPT) of renal dialysis patients, can satisfy skin diseases such as psoriasis again, and market application prospect is also very broad.

[0006] However, the structure of maxacalcitol contains multiple double bonds and hydroxyl groups, which makes it easy to produce multiple isomers and other impurities during the chemical synthesis process. For example, the 24-hydroxy isomer, i.e., impurity C, is easily formed in the side chain ring-opening reaction of maxacalcitol. The structure and properties of these isomeric impurities are similar to those of maxacalcitol, and they are difficult to separate and purify, and may be introduced into the finished product to affect the safety and effectiveness of the product. Maxacalcitol impurity C is a known important impurity, which has been reported in many patents such as JP1994080626A and WO1990009991A1, and is a key indicator in drug quality control. Therefore, how to improve the quality control of isomeric impurities in maxacalcitol raw materials and preparations has become a problem to be solved urgently. Summary of the invention

[0007] In view of this, the present invention provides a preparation and detection method of maxacalcitol impurity C. The preparation method has simple process, low equipment requirements, and selective reaction, and the detection method has the advantages of strong specificity, high sensitivity, and simple and easy operation, which provides effective technical support for the quality control of maxacalcitol.

[0008] To achieve the above object, the technical solution of the present invention is:

[0009] In a first aspect, the present invention provides a method for preparing a maxacalcitol impurity C, wherein the impurity has the following structural formula:

[0010]

[0011] The reaction route of the preparation method is as follows:

[0012]

[0013] The preparation method comprises the following steps:

[0014] (1) Add the compound of formula 1 as the starting material (which can be synthesized according to the method in patent WO2012122451A2) together with a base, a crown ether and toluene into a reaction bottle and stir to react, then add 1,2-epoxy-3-methylbutane into the reaction bottle, raise the temperature to 100° C. to react, monitor by TLC until the reaction of the raw materials is complete, wash, extract, dry, concentrate and purify by column chromatography to obtain the compound of formula 2,

[0015] The eluent used in the column chromatography separation is a n-hexane-ethyl acetate solution, n-hexane:ethyl acetate=40:1;

[0016] (2) The compound of formula 2 obtained in step (1) was dissolved in tetrahydrofuran, and a 1 mol / L tetrabutylammonium fluoride solution in tetrahydrofuran was added, and the temperature was raised to react. TLC was monitored until the reaction of the raw materials was completed, and the compound of formula 3 was obtained by extraction and column chromatography purification.

[0017] The eluent used in the column chromatography separation is a n-hexane-ethyl acetate solution, with n-hexane:ethyl acetate = 5:1 to elute impurities and 1:1 to elute the main product;

[0018] (3) The compound of formula 3 obtained in step (2) is dissolved in acetone, a photosensitizer is added, and an ultraviolet lamp is turned on for illumination. TLC is monitored until the reaction of the raw materials is completed, and the compound of formula 4 is obtained by extraction and column chromatography purification.

[0019] The eluent used in the column chromatography separation is a n-hexane-ethyl acetate solution, with n-hexane:ethyl acetate = 5:1 to elute impurities and 1:1 to elute products;

[0020] (4) dissolving the compound of formula 4 obtained in step (3) in acetonitrile, and preparing, separating and purifying the compound by dynamic axial compression (DAC) to obtain a crude impurity C;

[0021] (5) Purifying the crude impurity C obtained in step (4) by column chromatography to obtain the maxacalcitol impurity C.

[0022] According to an embodiment, the base used in step (1) is selected from one or more of sodium hydride, sodium methoxide, sodium ethoxide, potassium tert-butoxide, and potassium hydroxide, preferably sodium ethoxide and potassium tert-butoxide, and more preferably potassium tert-butoxide.

[0023] According to an embodiment, the crown ether used in step (1) is selected from one or more of 15-crown-5, 18-crown-6, and dibenzo-18-crown-6, preferably dibenzo-18-crown-6.

[0024] According to an embodiment, the photosensitizer used in step (3) may be a triplet photosensitizer, preferably anthracene and / or 9-acetylanthracene, more preferably 9-acetylanthracene.

[0025] According to an embodiment, the chromatographic conditions of DAC in step (4) include:

[0026] Chromatographic column: DAC50 dynamic preparation column, column inner diameter: 50mm, column length: 750mm, filler particle size: 10μm, filler material: C18;

[0027] Mobile phase: Mobile phase A is acetonitrile, mobile phase B is methanol;

[0028] Column temperature: 30±5℃;

[0029] Detection wavelength: 265nm;

[0030] Flow rate: 70 mL / min;

[0031] Injection volume: ≤5mL;

[0032] The following steps are involved:

[0033] (1) Chromatographic condition setting:

[0034] Chromatographic column: DAC50 dynamic preparation column, column inner diameter: 50mm, column length: 750mm, filler particle size: 10μm, filler material: C18;

[0035] Mobile phase: Mobile phase A is acetonitrile, mobile phase B is methanol;

[0036] Column temperature: 30±5℃;

[0037] Detection wavelength: 265nm;

[0038] Flow rate: 70 mL / min;

[0039] Injection volume: ≤5mL;

[0040] (2) Sample preparation: Dissolve the crude impurity C in 10 times the volume of acetonitrile, filter with a 0.45 μm organic filter membrane, and prepare the sample solution to be prepared;

[0041] (3) Sampling: Take the crude product to be prepared and inject the sample solution;

[0042] (4) Elution: mobile phase A / mobile phase B = 4 / 3 for elution;

[0043] (5) Collection: Collect the product solution according to the product peak, and concentrate the target solution to dryness under reduced pressure at a vacuum degree of ≤-0.09 MPa and a temperature of 30±5°C.

[0044] According to the embodiment, the eluent used for column chromatography separation in step (5) is a n-hexane-ethyl acetate solution, and the product is eluted in a ratio of n-hexane:ethyl acetate=1:1.

[0045] In a second aspect, the present invention provides a method for detecting an impurity C in maxacalcitol, which specifically comprises the following steps:

[0046] (1) Instrument and chromatographic conditions:

[0047] Chromatographic column: Octadecylsilane bonded silica as filler (Thermo Accucore XL C18, 4.6mm×250mm, 4μm or chromatographic column with equivalent performance)

[0048] Mobile phase: acetonitrile as mobile phase A, water as mobile phase B, gradient elution;

[0049] Column temperature: 30°C;

[0050] Flow rate: 1.0 mL / min;

[0051] Injection volume: 20 μL;

[0052] Detection wavelength: 265nm,

[0053] (2) Sample configuration:

[0054] Test solution: Take about 4 mg of Maxacalcitol sample, weigh accurately, place in a 10 mL volumetric flask, add 2 mL of methanol and shake to dissolve, dilute to the scale with solvent, and shake well;

[0055] Control solution: Accurately measure an appropriate amount of the test solution and quantitatively dilute it with solvent to make a solution containing approximately 0.4 μg per 1 mL;

[0056] System suitability solution: Take about 1 mg of impurity C reference substance, place it in the same 25 mL volumetric flask, add methanol, shake to dissolve and dilute to the mark, shake well, accurately measure 1.5 mL, place it in a 10 mL volumetric flask, dilute to the mark with solvent, shake well, as the impurity stock solution; take about 4 mg of maxacalcitol reference substance, place it in a 10 mL volumetric flask, add about 2 mL of methanol, shake to dissolve, add 1 mL of impurity stock solution, dilute to the mark with solvent, shake well;

[0057] The solvent is a mixed solution of acetonitrile and water, acetonitrile: water = 75:25,

[0058] (3) Detection and calculation:

[0059] Accurately measure 20 μL of system suitability solution, test solution and control solution, inject into liquid chromatograph, and record the chromatogram.

[0060] According to the embodiment, the mobile phase is acetonitrile and water, and gradient elution is performed as shown in the following table:

[0061] t(min) 0 30 35 50 51 60 A(％) 40 45 45 100 40 40 B(％) 60 55 55 0 60 60

[0062] According to the embodiment, the limit is: calculated according to the main component self-comparison method, the impurity C should not exceed 0.15%.

[0063] The beneficial effects of the present invention are:

[0064] (1) Improving impurity removal efficiency and product safety and effectiveness: The present invention provides a new method for preparing maxacalcitol impurity C, which can effectively prepare high-purity impurity C (purity 99.86%), reduce safety hazards in the product, and has significant significance for improving the safety and effectiveness of the final product.

[0065] (2) Optimizing the production process and ensuring quality control: The preparation method of the present invention is simple in process, has low requirements on equipment, and has good reaction selectivity, which provides a more efficient and economical production solution for the manufacturing process of maxacalcitol. By adopting this technology, product quality can be controlled more accurately, which has important practical and theoretical value in guiding and optimizing the overall production process of maxacalcitol.

[0066] (3) Strengthening drug monitoring and research: The present invention not only achieves structural confirmation of the impurity, but also discloses an HPLC detection method for detecting the content of impurity C in the raw material of maxacalcitol. The implementation of this method helps to more comprehensively control the quality of maxacalcitol and ensure the purity and efficacy of the drug. In addition, this technology has important research and practical value for studying and controlling quality problems that may occur in the drug production process and adverse reactions of drug receptors. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 HPLC spectrum for the detection of related substances of crude maxacalcitol.

[0068] Figure 2 The HPLC spectrum of the impurity C of maxacalcitol.

[0069] Figure 3 This is the H NMR spectrum of the impurity C of maxacalcitol.

[0070] Figure 4 This is the carbon spectrum of the impurity C of maxacalcitol.

[0071] Figure 5 This is a high-resolution mass spectrum of the impurity C of maxacalcitol.

[0072] Figure 6 This is the HPLC spectrum of related substances in a mixed solution of maxacalcitol and impurities. DETAILED DESCRIPTION

[0073] The present invention is further described in detail below in conjunction with specific examples and drawings. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto. Unless otherwise specified, the raw materials used can be obtained from the market or homemade.

[0074] During the development of the synthesis of maxacalcitol, we found that in the process of constructing the side chain by the epoxy ring opening method, due to the low selectivity of the epoxy ring opening, it is inevitable to introduce 24-hydroxymaxacalcitol impurity, namely impurity C. The content of impurity C in the crude product of maxacalcitol is 2.719%. The HPLC test results of the crude product of maxacalcitol related substances are shown in Table 1, and the corresponding test spectrum is shown in Figure 1 .

[0075] Table 1

[0076] name batch number Impurity C(%) Retention time (min) Maxacalcitol MC-C1-23032101 2.719 35.941

[0077] The above impurities are difficult to remove through traditional purification methods such as column chromatography and recrystallization, and cannot be completely removed during the reaction process, which will pose a hidden danger to product safety and effectiveness.

[0078] The invention uses (5E,7E)-(1S,3R,20S)-1,3-di(tert-butyldimethylsilyloxy)-9,10-opened pregnane-5,7,10(19)-triene-20-ol (compound of formula 1) as a raw material, and obtains the impurity through three-step chemical reactions of condensation, TBS protection removal and light flipping, and two-step DAC preparation and column chromatography purification, and the structure of the impurity is confirmed by nuclear magnetic resonance and mass spectrometry.

[0079] The chemical name and structural formula of impurity C are as follows:

[0080] Chemical name: (5Z,7E)-(1S,3R,20S)-20-(2S-hydroxy-3-methylbutyloxy)-9,10-secoepregnane-5,7,10(19)-triene-1,3-diol.

[0081] The structural formula is:

[0082]

[0083] The present invention aims to protect the preparation method of impurity C, establish a detection method, analyze the impurity content, and determine a reasonable impurity limit to ensure the product quality and medication safety and effectiveness of maxacalcitol.

[0084] Example 1

[0085] (1) Preparation of compound of formula 2

[0086] Reaction:

[0087]

[0088] Weigh 6.5 g of the compound of formula 1, 3.0 g of dibenzo-18-crown-6 ether, 15.8 g of potassium tert-butoxide, and 360 mL of toluene into a 1.0 L three-necked reaction bottle, stir at room temperature for 0.5 h, then weigh 1,2-epoxy-3-methylbutane and slowly add it to the reaction solution, raise the temperature to 100 ° C for reaction after the addition, monitor by TLC until the reaction of the raw materials is complete, add 360 mL of purified water and stir for 3 to 5 min, let stand for 5 to 10 min, separate the liquids, collect the organic phase, extract the aqueous phase with 360 mL of n-hexane for 3 to 5 min, let stand for 5 to 10 min, separate the liquids, wash the organic phase with 360 mL of saturated brine, dry with 50.0 g of anhydrous sodium sulfate for half an hour, filter, and concentrate the filtrate to dryness under reduced pressure at 40 ° C and then concentrate for 20-30 min to obtain a black oil.

[0089] Column chromatography purification: 130 g of silica gel (200-300 mesh) was used to load the column, and the column was moistened with n-hexane. The oil was dissolved with n-hexane / ethyl acetate = 10 / 1, and the sample was loaded by wet method. The product was eluted with n-hexane / ethyl acetate = 40 / 1. The eluate was concentrated to dryness under reduced pressure at 40°C to obtain 6.01 g of compound of formula 2, with a yield of 80.1%.

[0090] (2) Preparation of compound of formula 3

[0091] Reaction:

[0092]

[0093] 6.0g of the compound of formula 2 was dissolved in 60mL of tetrahydrofuran and added to a 500mL reaction bottle, and then 55mL of 1M tetrabutylammonium fluoride tetrahydrofuran solution was measured. After the addition, nitrogen was protected, the temperature was raised to 60°C for reaction, TLC was monitored until the reaction of the raw materials was completed, the temperature was lowered to room temperature, the reaction solution was concentrated to dryness under reduced pressure at 40°C, the obtained residue was stirred with 120mL of ethyl acetate and 120mL of purified water for 3-5min, allowed to stand for 5-10min, separated, the organic phase was collected, the aqueous phase was stirred and extracted with 60mL of ethyl acetate for 3-5min, allowed to stand for 5-10min, separated, the organic phase was combined, washed with 120mL of saturated brine, dried with 60.0g of anhydrous sodium sulfate for half an hour, filtered, and the filtrate was concentrated to dryness under reduced pressure at 40°C and then concentrated for 20-30min to obtain a gray-brown oil.

[0094] Column chromatography purification: 100 g of silica gel (100-200 mesh) was loaded into the column, the column was moistened with n-hexane, the oil was dissolved with ethyl acetate, the sample was loaded by wet method, the impurities were eluted with n-hexane / ethyl acetate = 5 / 1, and the product was eluted with n-hexane / ethyl acetate = 1 / 1. The eluate was concentrated to dryness under reduced pressure at 40°C to give 3.2 g of white foamy solid compound of formula 3, with a yield of 83.0%.

[0095] (3) Preparation of compound of formula 4

[0096] Reaction:

[0097]

[0098] 3.0 g of the compound of formula 3 was dissolved in 300 mL of acetone and added to a photochemical reactor, and then 0.3 g of 9-acetylanthracene (9-AA) was added. After the addition was completed, nitrogen was protected, the temperature was lowered to -5 to 5°C, a 500 W ultraviolet lamp was turned on, cooling water was turned on, and TLC was monitored until the reaction of the raw materials was completed. The reaction solution was concentrated to dryness under reduced pressure at 35°C and then concentrated for 20-30 min to obtain a yellow oil.

[0099] Column chromatography purification: 60 g of silica gel (100-200 mesh) was loaded into the column, the column was moistened with n-hexane, the oil was dissolved with ethyl acetate, the sample was loaded by wet method, the impurities were eluted with n-hexane / ethyl acetate = 5 / 1, and the product was eluted with n-hexane / ethyl acetate = 1 / 1. The eluate was concentrated to dryness under reduced pressure at 40°C to obtain 2.75 g of compound 4, with a yield of 91.7%.

[0100] (4) Preparation of crude impurity C

[0101] Reaction:

[0102]

[0103] A DAC50 dynamic preparative column was used for preparative separation. The chromatographic column information was as follows: inner diameter of the column: 50 mm, column length: 750 mm, filler particle size: 10 μm, filler material: C18. 3.0 g of compound 4 was dissolved in 30 mL of acetonitrile, filtered with a 0.45 μm organic filter membrane, and prepared into a sample solution to be prepared. The sample solution to be prepared was injected, and the maximum injection volume per needle was ≤5 mL. Mobile phase A was acetonitrile, mobile phase B was methanol, the flow rate was set to 70 mL / min, the detection wavelength was 265 nm, and mobile phase A / mobile phase B = 4 / 3 for elution. The product segment solution was collected according to the product peak. The target solution was concentrated to dryness under reduced pressure under vacuum degree ≤-0.09 MPa and temperature of 30±5°C to obtain 1.35 g of white foamy solid with a yield of 85.0%.

[0104] (5) Preparation of impurity C

[0105] Reaction:

[0106]

[0107] Column chromatography purification: 50 g silica gel (100-200 mesh) was loaded into the column, the column was moistened with n-hexane, and the crude impurity C was dissolved in ethyl acetate. The product was eluted with n-hexane / ethyl acetate = 1 / 1, monitored by TLC, and developed with phosphomolybdic acid. The product spots were collected, and the eluate was concentrated to dryness under reduced pressure at 40°C to obtain 1.05 g of compound 4, with a yield of 74.8%. HPLC purity: 99.86%, HPLC spectrum: Figure 2 , H NMR spectrum see Figure 3 , carbon spectrum Figure 4 , [M+H-H2O] + The m / z is 401.30, and the high-resolution mass spectrum is shown in Figure 5 , the data are shown in Table 2 and Table 3.

[0108] Table 2 Results of H NMR spectroscopy

[0109]

[0110] Table 3 Results of carbon NMR spectrometry

[0111]

[0112]

[0113] Example 2

[0114] A method for detecting impurity C in maxacalcitol can effectively separate impurity C and other impurities, and specifically comprises the following steps:

[0115] (1) Instrument and chromatographic conditions:

[0116] Chromatographic column: Octadecylsilane bonded silica as filler (Thermo Accucore XL C18, 4.6mm×250mm, 4μm or chromatographic column with equivalent performance)

[0117] Mobile phase: acetonitrile as mobile phase A, water as mobile phase B, gradient elution as shown in the table below:

[0118] t(min) 0 30 35 50 51 60 A(％) 40 45 45 100 40 40 B(％) 60 55 55 0 60 60

[0119] Column temperature: 30°C;

[0120] Flow rate: 1.0 mL / min;

[0121] Injection volume: 20 μL;

[0122] Detection wavelength: 265nm,

[0123] (2) Sample configuration:

[0124] Test solution: Take about 4 mg of Maxacalcitol sample, weigh accurately, place in a 10 mL volumetric flask, add 2 mL of methanol and shake to dissolve, dilute to the scale with solvent, and shake well;

[0125] Control solution: Accurately measure an appropriate amount of the test solution and quantitatively dilute it with solvent to make a solution containing approximately 0.4 μg per 1 mL;

[0126] System suitability solution: Take about 1 mg of impurity C reference substance, place it in the same 25 mL volumetric flask, add methanol, shake to dissolve and dilute to the mark, shake well, accurately measure 1.5 mL, place it in a 10 mL volumetric flask, dilute to the mark with solvent, shake well, as the impurity stock solution; take about 4 mg of maxacalcitol reference substance, place it in a 10 mL volumetric flask, add about 2 mL of methanol, shake to dissolve, add 1 mL of impurity stock solution, dilute to the mark with solvent, shake well;

[0127] The solvent is a mixed solution of acetonitrile and water, acetonitrile: water = 75:25,

[0128] (3) Detection and calculation:

[0129] Accurately measure 20 μL of system suitability solution, test solution and control solution, inject into liquid chromatograph, and record the chromatogram.

[0130] The results are as follows Figure 6 It showed that the test sample PZC was well separated from the main peak and other impurities, and had good sensitivity and response.

Claims

1. A method for preparing a maxacalcitol impurity C, wherein the impurity is a maxacalcitol impurity C, and the structural formula thereof is as follows: It is characterized in that The reaction route of the preparation method is as follows: The preparation method steps are as follows: (1) Add the compound of formula 1 as the starting material, a base, a crown ether, and toluene into a reaction flask and stir to react, then add 1,2-epoxy-3-methylbutane into the reaction flask, raise the temperature to 100° C. to react, monitor by TLC until the reaction of the raw materials is complete, wash, extract, dry, concentrate, and then purify by column chromatography to obtain the compound of formula 2, The eluent used in the column chromatography separation is a n-hexane-ethyl acetate solution, n-hexane:ethyl acetate=40:1; (2) The compound of formula 2 obtained in step (1) was dissolved in tetrahydrofuran, and a 1 mol / L tetrabutylammonium fluoride solution in tetrahydrofuran was added, and the temperature was raised to react. TLC was monitored until the reaction of the raw materials was completed, and the compound of formula 3 was obtained by extraction and column chromatography purification. The eluent used in the column chromatography separation is a n-hexane-ethyl acetate solution, with n-hexane:ethyl acetate = 5:1 to elute impurities and 1:1 to elute the main product; (3) The compound of formula 3 obtained in step (2) is dissolved in acetone, a photosensitizer is added, and an ultraviolet lamp is turned on for illumination. TLC is monitored until the reaction of the raw materials is completed, and the compound of formula 4 is obtained by extraction and column chromatography purification. The eluent used in the column chromatography separation is a n-hexane-ethyl acetate solution, with n-hexane:ethyl acetate = 5:1 to elute impurities and 1:1 to elute products; (4) dissolving the compound of formula 4 obtained in step (3) in acetonitrile, and preparing, separating and purifying the compound by dynamic axial compression (DAC) to obtain a crude impurity C; (5) Purifying the crude impurity C obtained in step (4) by column chromatography to obtain the maxacalcitol impurity C.

2. The preparation method according to claim 1, characterized in that: The base used in step (1) is selected from one or more of sodium hydride, sodium methoxide, sodium ethoxide, potassium tert-butoxide, and potassium hydroxide, preferably potassium tert-butoxide.

3. The preparation method according to claim 1, characterized in that: The crown ether used in step (1) is selected from one or more of 15-crown-5, 18-crown-6, and dibenzo-18-crown-6, preferably dibenzo-18-crown-6.

4. The preparation method according to claim 1, characterized in that: The photosensitizer used in step (3) may be a triplet photosensitizer, preferably anthracene and / or 9-acetylanthracene, more preferably 9-acetylanthracene.

5. The preparation method according to claim 1, characterized in that: The chromatographic conditions of DAC in step (4) include: Chromatographic column: DAC50 dynamic preparation column, packing material: C18; Mobile phase: Mobile phase A is acetonitrile, mobile phase B is methanol; Column temperature: 30±5℃; Detection wavelength: 265nm; Flow rate: 70 mL / min; Injection volume: ≤5mL; The following steps are involved: (1) Chromatographic condition setting: Chromatographic column: DAC50 dynamic preparation column, packing material: C18; Mobile phase: Mobile phase A is acetonitrile, mobile phase B is methanol; Column temperature: 30±5℃; Detection wavelength: 265nm; Flow rate: 70 mL / min; Injection volume: ≤5mL; (2) Sample preparation: Dissolve the crude impurity C in 10 times the volume of acetonitrile, filter with a 0.45 μm organic filter membrane, and prepare the sample solution to be prepared; (3) Sampling: Take the crude product to be prepared and inject the sample solution; (4) Elution: mobile phase A / mobile phase B = 4 / 3 for elution; (5) Collection: Collect the product solution according to the product peak, and concentrate the target solution to dryness under reduced pressure at a vacuum degree of ≤-0.09 MPa and a temperature of 30±5°C.

6. The preparation method according to claim 1, characterized in that: In step (5), the eluent used for column chromatography separation is n-hexane-ethyl acetate solution, and the product is eluted with n-hexane:ethyl acetate=1:1.

37.

7. Use of the preparation method according to any one of claims 1 to 6 in pharmaceutical process research, which can be used for the study of maxacalcitol impurities.

8. A method for detecting impurity C in maxacalcitol raw material drug, comprising the following steps: (1) Instrument and chromatographic conditions: Chromatographic column: ThermoAccucore XL C18, specification: 4.6mm×250mm, 4μm Mobile phase: acetonitrile as mobile phase A, water as mobile phase B, gradient elution; Column temperature: 30°C; Flow rate: 1.0 mL / min; Injection volume: 20 μL; Detection wavelength: 265nm, (2) Sample configuration: Test solution: Take about 4 mg of Maxacalcitol sample, weigh accurately, place in a 10 mL volumetric flask, add 2 mL of methanol and shake to dissolve, dilute to the scale with solvent, and shake well; Control solution: Accurately measure an appropriate amount of the test solution and quantitatively dilute it with solvent to make a solution containing approximately 0.4 μg per 1 mL; System suitability solution: Take about 1 mg of impurity C reference substance, place it in the same 25 mL volumetric flask, add methanol, shake to dissolve and dilute to the mark, shake well, accurately measure 1.5 mL, place it in a 10 mL volumetric flask, dilute to the mark with solvent, shake well, as the impurity stock solution; take about 4 mg of maxacalcitol reference substance, place it in a 10 mL volumetric flask, add about 2 mL of methanol, shake to dissolve, add 1 mL of impurity stock solution, dilute to the mark with solvent, shake well; The solvent is a mixed solution of acetonitrile and water, acetonitrile: water = 75:25, (3) Detection and calculation: Accurately measure 20 μL of system suitability solution, test solution and control solution, inject into liquid chromatograph, and record the chromatogram.

9. The method according to claim 8, characterized in that The mobile phase is acetonitrile and water, and gradient elution is performed as shown in the table below:

10. The method according to claim 8, characterized in that The limit is: calculated according to the main component self-comparison method, impurity C should not exceed 0.15%.

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