CN113121640B

CN113121640B - Crystal of monomethyl auristatin E and preparation method thereof

Info

Publication number: CN113121640B
Application number: CN202110239973.0A
Authority: CN
Inventors: 毛声飞; 邵军; 潘昌明; 沙飞; 王贵涛; 黄保华
Original assignee: Tong Yi Medicine Suzhou Co ltd
Current assignee: Tong Yi Medicine Suzhou Co ltd
Priority date: 2021-03-04
Filing date: 2021-03-04
Publication date: 2022-10-28
Anticipated expiration: 2041-03-04
Also published as: CN113121640A

Abstract

The invention provides a methyl auristatin E crystal form A, a preparation method thereof, a pharmaceutical composition containing the crystal form A and application of the crystal form A in preparation of a pharmaceutical conjugate. The crystal form A has high purity, good stability and low hygroscopicity, is particularly suitable for industrial application, and overcomes the defects of low purity, poor stability, unsuitability for storage, high requirement on reaction equipment, complex operation and the like when amorphous MMAE is used for preparing a conjugate in the prior art; secondly, the preparation method of the MMAE crystal form A provided by the invention is simple to operate, the prepared crystal form is high in purity and uniform in particle size distribution, the production cost is reduced, and the preparation method is suitable for commercial production amplification.

Description

Crystal of monomethyl auristatin E and preparation method thereof

Technical Field

The invention belongs to the technical field of medicinal chemistry, and particularly relates to a methyl auristatin E crystal, a preparation method thereof, a medicinal composition containing the crystal, and application of the crystal forms in preparation of a medicinal conjugate.

Background

Methyl auristatin E (MMAE, structural formula is shown in formula (I)) is a synthetic derivative of palmatine 10, has very effective antimitotic effect, and can inhibit cell division by blocking polymerization of tubulin to realize antitumor purpose. Is as antimicrotubule like vinblastine, but is approximately 200 times as toxic as vinblastine. Because of the toxicity, it is too toxic to be used by direct intravenous drip, and therefore it can only exert its killing power in drug conjugates (ADC drugs). Among the ADC drugs that have been marketed so far, there are Bentuximab developed by Seattle Genetics, pontotuzumab developed by Genentech, and Ennocumab developed by Seattle Genetics and Astellas in combination, all of which use MMAE as a cytotoxin. At present, in ADC (antibody drug conjugate) and PDC (polypeptide drug conjugate) drugs, MMAE is used as cytotoxin for research.

However, currently commercially available monomethyl auristatin E is an amorphous solid, and no reports have been made on free monomethyl auristatin E crystals in any literature or patent. Amorphous MMAE is easy to deliquesce and poor in stability, and is not beneficial to long-term storage; in addition, amorphous MMAE also has the problem of low purity, resulting in more impurities in the drug conjugate prepared by using amorphous MMAE, difficult subsequent purification, and influence on the safety and effectiveness of the drug conjugate.

Purification methods using reverse phase liquid phase preparation in US2015/23989 and CN109200291A for MMAE purification have low yield, complex operation and high cost.

Therefore, the development of the MMAE crystal form which has good stability and high purity and is suitable for industrial application has very important significance.

Disclosure of Invention

In order to solve the above problems of the prior art, it is an object of the present invention to provide a high purity crystalline form of MMAE having a structure as shown in formula (I) and a method for preparing the same.

Firstly, the invention provides a new crystal form of MMAE, which is named as a crystal form A; specifically, the invention provides a crystal form A of a compound shown as a formula (I), wherein an X-ray powder diffraction pattern of the crystal form A has characteristic peaks at 2theta values of 3.8 degrees +/-0.2 degrees, 9.3 degrees +/-0.2 degrees, 9.9 degrees +/-0.2 degrees and 13.2 degrees +/-0.2 degrees,

further preferably, the X-ray powder diffraction pattern of form a also has diffraction peaks at one or more of 2 Θ values of 10.8 ° ± 0.2 °, 11.9 ° ± 0.2 °, 15.3 ° ± 0.2 ° and 16.3 ° ± 0.2 °, more preferably the X-ray powder diffraction pattern of form a also has diffraction peaks at one or two or three or four of 2 Θ values of 10.8 ° ± 0.2 °, 11.9 ° ± 0.2 °, 15.3 ° ± 0.2 ° and 16.3 ° ± 0.2 °.

Further, the X-ray powder diffraction pattern of the crystalline form a of the compound represented by the formula (I) has diffraction peaks at 2 θ values of 10.8 ° ± 0.2 °, 11.9 ° ± 0.2 °, 15.3 ° ± 0.2 ° and 16.3 ° ± 0.2 °.

Furthermore, the compound shown in the formula (I) in the invention has a crystal form A, and the X-ray powder diffraction pattern of the crystal form A has a 2theta value: characteristic diffraction peaks are provided at 3.8 degrees +/-0.2 degrees, 9.3 degrees +/-0.2 degrees, 9.9 degrees +/-0.2 degrees, 10.8 degrees +/-0.2 degrees, 11.9 degrees +/-0.2 degrees, 13.2 degrees +/-0.2 degrees, 15.1 degrees +/-0.2 degrees, 15.3 degrees +/-0.2 degrees, 16.3 degrees +/-0.2 degrees, 18.4 degrees +/-0.2 degrees, 18.6 degrees +/-0.2 degrees, 20.1 degrees +/-0.2 degrees, 21.6 degrees +/-0.2 degrees and 23.0 degrees +/-0.2 degrees.

According to a particular and preferred aspect of the present invention, said compound of formula (I) in crystalline form a has substantially the same X-ray powder diffraction pattern as shown in figure 1 or 2. Further, the X-ray powder diffraction pattern shows at least 14 diffraction peaks whose positions and intensities are shown in FIG. 1 or 2, in which the peak positions are varied within. + -. 0.2 ℃ and the peak intensities are appropriately varied depending on the specific detection conditions.

Preferably, the compound of formula (I) has a Differential Scanning Calorimetry (DSC) pattern with an endothermic peak at 112.81 ℃ + -2 ℃, wherein the DSC pattern is shown in figure 3.

Further, the crystal form A of the compound shown in the formula (I) contains 0-5% (w/w) of water; preferably, said form a contains 1-3% (w/w) water.

In a second aspect of the invention, there is provided a process for the preparation of form a of the compound of formula (I) comprising the steps of:

a) Adding a compound shown in a formula (I) into a first solvent, stirring for dissolving, and optionally adding water to obtain a first mixed system;

b) Stirring the first mixed system, and then adding a second solvent into the first mixed system to obtain a second mixed system; preferably, the stirring of the first mixed system is carried out at a temperature of-10 to 10 ℃;

c) Stirring the second mixed system, and then adding a third solvent into the second mixed system to obtain a third mixed system; preferably, the stirring of the second mixed system is carried out at a temperature of-10 to 10 ℃;

d) Stirring the third mixed system to separate out solid, thus obtaining the solid; preferably, the stirring of the third mixing system is carried out at a temperature of-10 to 10 ℃.

In the above method, preferably, the first solvent of step a) is selected from esters, isopropanol, DMF or any combination thereof; more preferably, the esters comprise methyl formate, methyl acetate, isopropyl acetate, ethyl acetate, propyl acetate, butyl acetate, or any combination thereof.

Step B) the second solvent is selected from diethyl ether, isopropyl ether, methyl tert-butyl ether, toluene or any combination thereof;

step C) the third solvent is selected from petroleum ether, n-hexane, cyclohexane, methylcyclohexane, n-heptane or any combination thereof.

Further, in the above method, the content of water in the step a) is 0.5 to 4% (w/w) based on the total amount of the first mixed system; preferably, the water content is 1% to 2% (w/w); more preferably the water content is 1-1.5% (w/w); preferably, for example, the water content is 1.1% (w/w), 1.2% (w/w), 1.3% (w/w), 1.4% (w/w), 1.5% (w/w), 1.6% (w/w), 1.7% (w/w), 1.8% (w/w), 1.9% (w/w), or 2% (w/w).

The volume ratio of the first solvent to the second solvent to the third solvent is 1 to 2; more preferably, the volume ratio of the first solvent to the second solvent to the third solvent is 1. In a specific preferred embodiment, the volume ratio of the first solvent to the second solvent to the third solvent is 1.

Further, the feeding ratio of the compound shown in the formula (I) to the first solvent is 1; more preferably, the feeding ratio of the compound represented by the formula (I) to the first solvent is 1.

Further, in the above method, preferably, the first mixed system is stirred in step B), the seed crystal is added to the first mixed system, the temperature is reduced to-10 to 10 ℃, and then the second solvent is added to obtain the second mixed system. In another more preferred embodiment of the present invention, there is provided a process for the preparation of form a of the compound of formula (I) comprising the steps of:

a) Adding a compound shown as a formula (I) into a first solvent, stirring and dissolving, and optionally adding water to obtain a first mixed system; wherein, calculated by the total amount of the first mixed system, the water content is 0.5-4% (w/w), and the feeding ratio of the compound shown in the formula (I) to the first solvent is 1;

b) Stirring the first mixed system, adding seed crystals, continuously stirring at-10 ℃, and then adding a second solvent to obtain a second mixed system; preferably, the volume ratio of the first solvent to the second solvent is 1;

c) Stirring the mixture at the temperature of between 10 ℃ below zero and 10 ℃, and then adding a third solvent into the second mixed system to obtain a third mixed system; preferably, the volume ratio of the first solvent to the third solvent is 1;

d) Stirring the third mixed system under the condition of stirring at the temperature of between 10 ℃ below zero and 10 ℃ to separate out solids, thus obtaining the solid; preferably, the precipitated solid is filtered, optionally rinsed with a third solvent, and then dried under vacuum to obtain the form a.

In the above process, it is further preferred that the first solvent is selected from methyl formate, methyl acetate, isopropyl acetate, ethyl acetate, propyl acetate, butyl acetate, isopropanol, DMF or any combination thereof;

the second solvent is selected from diethyl ether, isopropyl ether, methyl tert-butyl ether, toluene or any combination thereof;

the third solvent is selected from petroleum ether, n-hexane, cyclohexane, methylcyclohexane, n-heptane, or any combination thereof.

In a third aspect of the present invention, there is also provided a pharmaceutical composition comprising the compound of formula (I) provided herein in crystalline form a and a pharmaceutically acceptable carrier.

Preferably, said pharmaceutical composition contains said crystalline form a in an amount of not less than 85%, preferably not less than 90%, preferably not less than 95%, preferably not less than 99%, preferably not less than 99.5%, preferably not less than 99.9%, preferably not less than 99.99% by weight relative to the total amount of compound of formula (I) present in the composition.

In the fourth aspect of the invention, the invention also provides application of the crystal form A of the compound shown in the formula (I) and application thereof in preparing a drug conjugate. Wherein the drug conjugate comprises an antibody drug conjugate, a polypeptide drug conjugate or a small molecule drug conjugate which takes the crystal form A of the compound shown in the formula (I) as cytotoxin. Such as present-tuximab developed by Seattle Genetics, polotuzumab developed by Genentech, and enrobiumab developed in combination with Seattle Genetics and Astellas; also included are currently under-developed ADC (antibody drug conjugates) and PDC (polypeptide drug conjugates) drugs with MMAE as the cytotoxin. Methods for preparing ADC (antibody drug conjugate) and PDC (polypeptide drug conjugate) drugs using MMAE as cytotoxin using MMAE are known and have been reported in various documents, for example, WO2019183438A1 discloses a method for preparing the present rituximab using MMAE, and WO 2017/025057 Al describes a method for preparing polypeptide drug conjugate drugs using MMAE. The disclosures of these documents are incorporated herein by reference.

The invention provides a new crystal form of monomethyl auristatin E and a preparation method thereof, the crystal form has high purity, good stability and low hygroscopicity, is particularly suitable for industrial application, and overcomes the defects of low purity, poor stability, unsuitability for storage, high requirement on reaction equipment, complex operation and the like when amorphous MMAE is used for preparing a conjugate in the prior art; secondly, the preparation method of the MMAE crystal form A provided by the invention is simple to operate, the prepared crystal form is high in purity and uniform in particle size distribution, the production cost is reduced, and the method is suitable for commercial production amplification, and the purity of the MMAE can be improved to more than 99.5%.

The MMAE and the monomethyl auristatin E have the same meanings, and all refer to compounds with the structures shown in the formula (I):

the term "w/w" as used herein means a weight ratio unless otherwise specified.

Drawings

The technical solution of the present application is further explained below with reference to the drawings and the embodiments.

Figure 1 is an X-ray powder diffraction (XRPD) pattern of form a of the compound of formula (I) prepared in example 2;

figure 2 XRPD pattern of form a of the compound of formula (I) prepared in example 3;

FIG. 3 is a DSC of form A of the compound of formula (I);

FIG. 4 is a TGA profile of crystalline form A of the compound of formula (I);

FIG. 5 is an HPLC plot of form A of the compound of formula (I);

FIG. 6 is an XRPD pattern for commercially available sample 1;

FIG. 7 is an XRPD pattern for commercially available sample 2;

FIG. 8 is an XRPD pattern for commercially available sample 3;

FIG. 9 is an HPLC chart of commercial sample 1;

FIG. 10 is an HPLC chart of commercial sample 2;

FIG. 11 is an HPLC chart of commercially available sample 3.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the present invention is not limited to the following examples; it should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. Conditions not indicated in the examples are conventional experimental conditions. The starting material (i.e. MMAE) used in the present invention is an amorphous white powder obtained commercially or synthesized by a synthetic route known in the art, for example, from CN 109200291A.

The moisture content, unless otherwise specified, was calculated by coulometry.

The seed crystals used in examples 2 to 6 below were crystals A prepared by the method of example 1.

Example 1 preparation of crystalline form A of Monomethylauristatin E

Adding ethyl acetate (2.6 mL) into methyl auristatin E (0.65g, HPLC.

Example 2 preparation of Monomethylauristatin E form A

Adding ethyl acetate (2.6 mL) into methyl auristatin E (0.65g, HPLC, 98.8%) and stirring until the ethyl acetate is dissolved, adding purified water (28.0 mg), stirring uniformly, detecting the water content to be 1.03% by a coulometry method, adding seed crystals (25.0 mg), cooling to 2.5 ℃, stirring for 15-20 h, precipitating a large amount of solid, dropwise adding methyl tert-butyl ether (2.6 mL), stirring for 1-2 h, dropwise adding n-heptane (13.0 mL), continuously stirring for 2-4 h, filtering, leaching the solid with n-heptane (0.6 mL), and drying in vacuum at 40 ℃ to obtain a methyl auristatin E crystal, HPLC:99.4 percent.

Example 3 preparation of Monomethylauristatin E form A

Adding isopropyl acetate (4.0 mL) into methyl auristatin E (1.00g, HPLC (high performance liquid chromatography): 99.5 percent.

Example 4 preparation of Monomethylauristatin E form A

Adding a mixture (4.0 mL) of ethyl acetate and propyl acetate into methyl auristatin E (1.00g, HPLC (high performance liquid chromatography).

Example 5 preparation of crystalline form A of Monomethylauristatin E

Adding butyl acetate (3.0 mL) into monomethyl auristatin E (1.00g, HPLC, 94.9%) and stirring until the mixture is dissolved, adding purified water (51.1 mg) and stirring uniformly, detecting the water content to be 2% by using a coulometry method, adding seed crystals (40.0 mg), cooling to 2.5 ℃, stirring for 15-20 h, precipitating a large amount of solid, adding methyl tert-butyl ether (6.0 mL) dropwise, stirring for 1-2 h, adding n-heptane (15.0 mL), continuing stirring for 2-4 h, filtering, leaching the solid with n-heptane (1.0 mL), and drying in vacuum at 40 ℃ to obtain monomethyl auristatin E crystals.

Example 6 preparation of Monomethylauristatin E form A

Methyl formate (4.0 mL) is added into monomethyl auristatin E (1.00g, HPLC.

X-ray powder diffraction analysis (XRP D) was performed on the samples prepared in examples 2 to 6; and the sample prepared in example 2 was subjected to Differential Scanning Calorimetry (DSC) and simultaneous thermal analysis (TGA), in which,

x-ray powder diffraction analysis (XRPD) was collected on Bruker D8 ADVANCE, cuka radiation. The method parameters are as follows:

a test mode: wide angle;

scanning range: 2-50 °;

step length of test: 0.01 degree/step;

integration time: 0.1 s/step.

XRPD tests show that the samples 1 to 6 prepared in the examples 1 to 6 are all crystals and are named as the crystal form A.

The XRPD pattern of the MMAE crystalline form prepared in example 2 is shown in fig. 1, wherein a total of 39 peaks are shown, the specific diffraction data are shown in table 1, and the 2theta values are determined by considering various factors such as d value, low angle, intensity, characteristic line and complete peak shape, and the diffraction peaks at the positions of 3.8 ° ± 0.2 °, 9.3 ° ± 0.2 °, 9.9 ° ± 0.2 ° and 13.2 ° ± 0.2 ° are characteristic peaks. Diffraction peaks at 2theta values of 10.8 ° ± 0.2 °, 11.9 ° ± 0.2 °, 15.3 ° ± 0.2 ° and 16.3 ° ± 0.2 ° are important peaks. The diffraction peaks at 2theta values of 15.1 DEG +/-0.2 DEG, 18.4 DEG +/-0.2 DEG, 18.6 DEG +/-0.2 DEG, 20.1 DEG +/-0.2 DEG, 21.6 DEG +/-0.2 DEG and 23.0 DEG +/-0.2 DEG are the secondary important peaks.

TABLE 1

The XRPD pattern of the MMAE crystalline form prepared in example 3 is shown in fig. 2, the specific diffraction data is determined by considering various factors such as d value, low angle, intensity, characteristic line and complete peak shape, referring to table 2, the 2theta value is 3.8 ° ± 0.2 °, 9.3 ° ± 0.2 °, 9.9 ° ± 0.2 ° and the diffraction peak at 13.2 ° ± 0.2 ° is the characteristic peak. Diffraction peaks at 2theta values of 10.8 ° ± 0.2 °, 11.9 ° ± 0.2 °, 15.3 ° ± 0.2 ° and 16.3 ° ± 0.2 ° are important peaks. The diffraction peaks at 2theta values of 15.1 DEG +/-0.2 DEG, 18.4 DEG +/-0.2 DEG, 18.6 DEG +/-0.2 DEG, 20.1 DEG +/-0.2 DEG, 21.6 DEG +/-0.2 DEG and 23.0 DEG +/-0.2 DEG are the secondary important peaks.

TABLE 2

The XRPD patterns of the MMAE crystalline forms prepared in examples 4-6 are essentially the same as shown in fig. 1-2.

The Differential Scanning Calorimetry (DSC) chart of the invention is collected on a TADICOMOVERY DSC25, and the method parameters are as follows:

sample pan: aluminum plate and gland

Temperature range: 25-268 deg.C

Scanning speed: 10 ℃/min

Protective gas: and (4) nitrogen.

A DSC diagram as shown in figure 3, showing that form a prepared in example 2 shows an endothermic peak at 112.81 ℃.

Simultaneous thermal analysis (TGA) plots were collected on METTLER TGA/DSC3+/1100F with the following process parameters:

sample pan: alumina oxide

Temperature range: 25-550 deg.C

Scanning rate: 10 ℃/min

Protective gas: nitrogen gas

A TGA profile as shown in figure 4, wherein form a prepared in example 2 is shown to begin with a weight loss at about 305 ℃.

Example 7 hygroscopicity test

Respectively measuring the moisture content of the MMAE crystal form prepared in the embodiment 2 of the invention and 500mg of the purchased amorphous MMAE, and recording the moisture content as the moisture content of the initial condition; then, the sample was placed at 25 ℃ and humidity of 92.5% for 24 hours, and then the moisture content was measured by coulometry, and the measurement results are shown in Table 3.

TABLE 3, 25 ℃,92.5% humidity examination results

Example 8 MMAE form a versus amorphous MMAE solubility contrast test

Comparing the solubility of the MMAE crystal form A prepared in the embodiment 2 of the invention with that of amorphous MMAE; the MMAE crystal form A and amorphous MMAE prepared in the embodiment 2 of the invention are respectively added into methyl tert-butyl ether at 20-25 ℃ to prepare saturated solution, and then the content of the MMAE in the saturated solution is determined by a high performance liquid chromatography after 1 hour and 2 hours. The results of the experiment are shown in table 4.

TABLE 4 solubility contrast test results for MMAE form A and amorphous MMAE

Example 9 stability study of MMAE form A

The MMAE crystal form A prepared in the embodiment 2 of the invention is placed at 40 ℃, and the purity and the moisture are respectively detected by a high performance liquid chromatography and a coulometry method in 1 month and 2 months. The results of the experiment are shown in Table 5.

TABLE 5 stability study results of MMAE form A

Time	Purity of	Moisture content
			Initiation of	99.42％	2.7％
1 month	99.45％	2.2％
			2 months old	99.42％	2.2％

Example 10 comparison of MMAE form A to MMAE amorphous purity

The MMAE solid prepared in example 2 of the present invention and the crystal form of the sample purchased from 3 different manufacturers were tested by XRPD and the purity of the sample was determined by HPLC method, the results are shown in table 6.

TABLE 6 comparison of amorphous purity of MMAE crystal form A and MMAE

The MMAE crystal forms prepared in examples 3-6 and the MMAE crystal form prepared in example 2 have similar properties in stability, solubility, and hygroscopicity, and the purity is also improved to different degrees compared to amorphous powder.

In light of the foregoing description of the preferred embodiments according to the present application, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims

1. Form a of a compound of formula (I) having an X-ray powder diffraction pattern at 2 Θ: characteristic peaks are present at 3.8 DEG +/-0.2 DEG, 9.3 DEG +/-0.2 DEG, 9.9 DEG +/-0.2 DEG, 10.8 DEG +/-0.2 DEG, 11.9 DEG +/-0.2 DEG, 13.2 DEG +/-0.2 DEG, 15.3 DEG +/-0.2 DEG and 16.3 DEG +/-0.2 DEG,

2. form a of the compound of formula (I) according to claim 1, characterized in that it has an X-ray powder diffraction pattern at 2 Θ values: diffraction peaks are present at positions of 3.8 degrees +/-0.2 degrees, 9.3 degrees +/-0.2 degrees, 9.9 degrees +/-0.2 degrees, 10.8 degrees +/-0.2 degrees, 11.9 degrees +/-0.2 degrees, 13.2 degrees +/-0.2 degrees, 15.1 degrees +/-0.2 degrees, 15.3 degrees +/-0.2 degrees, 16.3 degrees +/-0.2 degrees, 18.4 degrees +/-0.2 degrees, 18.6 degrees +/-0.2 degrees, 20.1 degrees +/-0.2 degrees, 21.6 degrees +/-0.2 degrees and 23.0 degrees +/-0.2 degrees.

3. Form a of the compound of formula (I) according to claim 1, characterized in that it has substantially the same X-ray powder diffraction pattern as shown in figure 1 or figure 2.

4. Form A of the compound of formula (I) according to claim 1 or 2, characterized in that its Differential Scanning Calorimetry (DSC) pattern comprises an endothermic peak at 112.81 ℃ ± 2 ℃.

5. Form a of the compound of formula (I) according to claim 1 or 2, characterized in that it has a DSC profile substantially the same as shown in figure 3.

6. Form a of the compound of formula (I) according to claim 1 or 2, characterized in that it contains 0-5% (w/w) water.

7. Form A of the compound of formula (I) according to claim 6, characterized in that it contains 1-3%

(w/w) water.

8. A process for the preparation of crystalline form a of the compound of formula (I) according to any one of claims 1 to 7, comprising the steps of:

a) Adding a compound shown in a formula (I) into a first solvent, stirring and dissolving to obtain a first mixed system, wherein the first solvent is ethyl acetate;

b) Stirring the first mixed system, and then adding a second solvent into the first mixed system to obtain a second mixed system, wherein the second solvent is methyl tert-butyl ether;

c) Stirring the second mixed system, and then adding a third solvent into the second mixed system to obtain a third mixed system, wherein the third solvent is n-heptane;

d) And stirring the third mixed system to separate out a solid, thus obtaining the catalyst.

9. A process for the preparation of crystalline form a of the compound of formula (I) according to any one of claims 1 to 7, comprising the steps of:

a) Adding a compound shown in a formula (I) into a first solvent, stirring and dissolving to obtain a first mixed system, wherein the first solvent is selected from methyl formate, ethyl acetate, isopropyl acetate, butyl acetate or a mixed solution of ethyl acetate and propyl acetate;

b) Stirring the first mixed system, adding crystal seeds of a crystal form A of the compound shown in the formula (I), and adding a second solvent to obtain a second mixed system, wherein the second solvent is methyl tert-butyl ether;

d) And stirring the third mixed system to separate out solids to obtain the catalyst.

10. The method according to claim 8 or 9, wherein the compound represented by the formula (I) is added to the first solvent, dissolved with stirring, and added with water to obtain the first mixed system.

11. The method according to claim 8 or 9, wherein the stirring of the first mixed system in the step B) is performed at a temperature of-10 to 10 ℃;

the stirring second mixed system in the step C) is stirred at the temperature of-10 ℃;

and D), stirring the third mixed system at the temperature of-10 ℃.

12. The method according to claim 10, wherein the amount of water in step a) is 0.5% to 4% (w/w) based on the total amount of the first mixed system.

13. The method as set forth in claim 12, wherein the amount of water in step a) is 1% to 2% (w/w) based on the total amount of the first mixed system.

14. The method according to claim 12, wherein step a) is carried out in a water content of 1-1.5% (w/w) based on the total amount of the first mixed system.

15. The method according to claim 8 or 9, wherein the volume ratio of the first solvent to the second solvent to the third solvent is 1.

16. The method according to claim 15, wherein the volume ratio of the first solvent to the second solvent to the third solvent is 1.

17. The method according to claim 15, wherein the volume ratio of the first solvent to the second solvent to the third solvent is 1.

18. The method according to claim 8 or 9, wherein the dosage ratio of the compound of formula (I) to the first solvent is 1.

19. The method according to claim 18, wherein the ratio of the weight of the compound represented by formula (I) to the volume of the first solvent is 1.

20. The method as claimed in claim 9, wherein the step B) is carried out by stirring the first mixed system, adding the seed crystal, cooling to-10 to 10 ℃, and adding the second solvent to obtain the second mixed system.

21. A pharmaceutical composition comprising the crystalline form a of the compound of formula (I) according to any one of claims 1 to 7 and a pharmaceutically acceptable carrier.

22. The pharmaceutical composition according to claim 21, wherein the composition contains not less than 85% by weight of the compound of formula (I) in form a of the crystalline form a according to claim 1, relative to the total amount of the compound of formula (I) present in the composition.

23. The pharmaceutical composition according to claim 22, wherein the composition comprises not less than 90% by weight of the compound of formula (I) in form a according to claim 1.

24. Pharmaceutical composition according to claim 22, characterized in that it contains not less than 95% by weight of the compound of formula (I) in form a according to claim 1.

25. The pharmaceutical composition according to claim 22, wherein the composition comprises not less than 99% by weight of the compound of formula (I) in form a according to claim 1.

26. The pharmaceutical composition according to claim 22, wherein the composition comprises not less than 99.5% by weight of the compound of formula (I) in form a according to claim 1.

27. The pharmaceutical composition according to claim 22, wherein the composition comprises not less than 99.9% by weight of the compound of formula (I) in form a according to claim 1.

28. Use of crystalline form a of a compound of formula (I) according to any one of claims 1 to 7 for the preparation of a pharmaceutical conjugate.