Preparation method of nitrogen-containing fused ring compound

Abstract

The invention provides a preparation method of a nitrogen-containing fused ring compound with anti-tumor activity. According to the method, the target product can be efficiently obtained under relatively mild reaction conditions, and compared with an original process, the yield is obviously improved, the material cost is greatly reduced, and process amplification is more facilitated.

Description

Preparation method of nitrogen-containing fused ring compound

[0001] This application is based on the application with CN application number 202310025425.7 and application date January 9, 2023, and claims its priority. The disclosed content of the CN application is hereby introduced as a whole into this application. Technical Field

[0002] The present application relates to the field of pharmaceutical chemicals, and specifically to a method for preparing a nitrogen-containing fused ring compound. Background Art

[0003] Camptothecin (CPT) is a pentacyclic quinoline compound isolated from the plant Camptotheca acuminata (Davidia involucrata). It consists of a quinoline ring AB, a pyrrole ring C, a pyridone ring D, and an α-hydroxylactone ring E, with the 20-position in the S configuration. It was introduced into clinical practice in the early 1970s due to its excellent anticancer activity. However, clinical trials were subsequently discontinued due to severe side effects such as diarrhea and hemorrhagic cystitis.

[0004] Research data indicates that camptothecin can form a three-membered ring complex with cellular DNA topoisomerase I, thereby inhibiting DNA unwinding, leading to blocked DNA replication and, subsequently, cell death (Cancer Res. 1989, 49, 6365). Camptothecin and its derivatives have demonstrated potent antitumor activity in animal models of lung, breast, colorectal, and ovarian cancers (Nature Review Cancer. 2006, 6, 789).

[0005] Currently, several camptothecin drugs have been approved for marketing for tumor treatment, for example, topotecan is used to treat ovarian cancer, and belotecan is used to treat ovarian cancer and small cell lung cancer. Dxd developed by Daiichi Sankyo was approved by the FDA on August 11, 2022, becoming the world's first HER2-targeted antibody-drug conjugate dextratinib (T-DXd, DS-8201). Currently, this drug has achieved outstanding "results" in common solid tumors such as non-small cell lung cancer, breast cancer, gastric cancer, and colorectal cancer.

[0006] The synthesis process of camptothecin analogs has a significant impact on the commercialization of anti-tumor drugs. For example, the control of impurities and the scale-up of camptothecin analog production can significantly affect the production cost of anti-tumor drugs.

[0007] Daiichi Sankyo disclosed a synthesis route for camptothecin analogs in patent application CN111065621A. However, this synthesis method leaves much to be desired. For example, the two-step high-temperature reaction requires high equipment requirements, the reaction time is long, the yield of the target product is low (43% total yield for the two steps), isomer recycling is difficult, isomer control is difficult after process scale-up, and the synthesis efficiency is low, ultimately leading to high costs for scale-up production.

[0008] Summary of the Invention

[0009] In order to solve the above technical problems, the present application provides a method for preparing a single-configuration exitecan and its analogs shown in formula (I), wherein R1 and R2 are independently selected from hydrogen, halogen, C 1-6 Alkyl, C 1-6 Hydroxyalkyl, C 1-6 Alkoxyalkyl, C 1-6 Alkoxy, C 1-4 or R1 and R2 are linked to adjacent carbon atoms to form a 5-6 membered carbon ring or oxygen-containing heterocycle. In some embodiments, R1 and R2 are independently selected from halogen and C 1-6 In some embodiments, R1 and R2 are independently selected from F, Cl, Br, I and C 1-2 In some embodiments, R1 and R2 are independently selected from Cl and methyl. In some embodiments, R1 is Cl and R2 is methyl.

[0010] The method involves obtaining the parent nucleus structure (III) under mild conditions, then flipping the isomer under acidic conditions to the target configuration (IV), followed by deprotection and salt formation, to obtain the target compound (I) in a single configuration in three steps with an overall yield exceeding 75%. This method is highly versatile and can be applied to the synthesis of other isoforms of isoforms. It features a simple process, easy control of isomers, high synthesis efficiency, low cost, greater scalability, and enhanced practicality.

[0011] Specifically, the present application provides a method for synthesizing exitecan and its analogs suitable for large-scale preparation of a single configuration. The synthetic route is as follows:

[0012] wherein R1 and R2 are independently selected from hydrogen, halogen, C 1-6 Alkyl, C 1-6 Hydroxyalkyl, C 1-6 Alkoxyalkyl, C 1-6 Alkoxy, C 1-4 or R1 and R2 are connected with adjacent carbon atoms to form a 5-6 membered carbocyclic ring or oxygen-containing heterocyclic ring; preferably, R1 and R2 are independently selected from halogen and C 1-6Alkyl; preferably, R1 and R2 are independently selected from F, Cl, Br, I and C 1-2 Alkyl; preferably, R1 and R2 are independently selected from Cl and methyl; preferably, R1 is Cl, R2 is methyl;

[0013] wherein R3 is an electron-withdrawing protecting group, for example, a substituted ethoxycarbonyl group (e.g., 2,2,2-trichloroethoxycarbonyl, 2-trimethylsilylethoxycarbonamide), formyl, acetyl, chloroacetyl, dichloroacetyl, trichloroacetyl, trifluoroacetyl, Fmoc, an Fmoc-like group, Troc, Cbz, Teoc, Alloc, phthaloyl (Pht), trifluoromethanesulfonyl, tert-butylsulfonyl, methylsulfonyl, benzylsulfonyl, p-toluenesulfonyl, benzylsulfonyl, 2-(trimethylsilyl)ethanesulfonyl, 4-nitrobenzenesulfonyl, (9H-9-pentyl)methylsulfonyl, 2 and 4 nitrobenzenesulfonyl, 2,4-dinitrobenzenesulfonyl, pivaloyl.

[0014] In one aspect, the present application provides a method for preparing a compound of formula (III), comprising the steps of reacting a compound of formula (II) and compound 2 in the presence of a catalyst;

[0015] Wherein, R1 and R2 are independently selected from hydrogen, halogen, C 1-6 Alkyl, C 1-6 Hydroxyalkyl, C 1-6 Alkoxyalkyl, C 1-6 Alkoxy, C 1-4 or R1 and R2 are linked to the carbon atoms to which they are attached to form a 5-6 membered carbocyclic ring or an oxygen-containing heterocyclic ring; preferably, R1 and R2 are independently selected from halogen and C 1-6 Alkyl; preferably, R1 and R2 are independently selected from F, Cl, Br, I and C 1-2 Alkyl; preferably, R1 and R2 are independently selected from Cl and methyl; preferably, R1 is Cl, R2 is methyl;

[0016] R3 is an electron-withdrawing protecting group;

[0017] The catalyst is selected from one or more of PPTS, AcOH, TFA, H2SO4, proline, PPA, P2O5, CAN, T3P, KOH, I2, MgCl2 and TMSCl.

[0018] In some embodiments, the catalyst is PPA.

[0019] In some embodiments, the reaction of the compound of formula (II) and compound 2 is carried out in a solvent, wherein the solvent is selected from aromatic hydrocarbons (e.g., toluene, xylene, o-toluene, m-toluene), aliphatic hydrocarbons (e.g., hexane, n-heptane), alcohols (e.g., methanol, ethanol, isopropanol), organic acids (e.g., acetic acid, trifluoroacetic acid), phenols (e.g., phenol, o-cresol, m-cresol, p-cresol), ethers (e.g., diethyl ether, ethylene oxide, anisole), esters (e.g., methyl acetate, ethyl acetate, propyl acetate), ketones (e.g., acetone, butanone), amides (e.g., DMF, DMA), nitriles (e.g., acetonitrile), heterocyclics (e.g., NMP, 1,4-dioxane, 2-MeTHF), sulfur-containing organic solvents (e.g., DMSO), and any combination thereof.

[0020] In some embodiments, the solvent of the method is a combination of a phenolic solvent and a heterocyclic solvent.

[0021] In some embodiments, the organic solvent is a mixed solvent of o-cresol and 1,4-dioxane.

[0022] More specifically, in one aspect, the present application provides a method for preparing a compound of formula (III), comprising the steps of reacting a compound of formula (II) and compound 2 in the presence of PPA in a mixed solvent of o-cresol and 1,4-dioxane;

[0023] Wherein, R1, R2 and R3 are as defined above.

[0024] Studies have shown that the reaction reagents significantly influence the reaction rate, product selectivity, product stability, and impurities. In some embodiments, an acidic catalyst such as p-toluenesulfonic acid, PPTS, AcOH, TFA, H2SO4, proline, phosphoric acid, or other catalysts such as P2O5, CAN, T3P, KOH, I2, MgCl2, or TMSCl can be used in place of PPA, with PPA being more preferred.

[0025] At the same time, studies have found that the reaction solvent also has a significant impact on the reaction rate and reaction by-products. In some embodiments, the reaction solvent is PhMe, xylene, AcOH, TFA, phenol, o-toluene, m-toluene, p-cresol, EtOH, DMF, DMSO, DMA, NMP, anisole, ACN, butanone, n-heptane, ethyl acetate, 1,4-dioxane and 2-MeTHF, as well as mixed solvent systems of these solvents. However, a mixed solvent system of o-cresol and 1,4-dioxane is more preferred.

[0026] In some embodiments, the volume ratio of o-cresol:1,4-dioxane is (10:1) to (1:10), for example, (10:1) to (1:1), (9:1) to (1:1), (8:1) to (1:1), (7:1) to (1:1), (6:1) to (1:1), (5:1) to (1:1), (4:1) to (1:1), (3:1) to (1:1), (2:1) to (1:1), preferably 1:1.

[0027] In some embodiments, the molar ratio of the compound of formula (II) and compound 2 is (1:1) to (1:1.5), for example, (0.8:1) to (1:1.5), for example, (1:1) to (1:1.1), (1:1) to (1:1.2), (1:1) to (1:1.3), (1:1) to (1:1.4), preferably 1:1.2.

[0028] In some embodiments, based on the compound of formula (II), the feed equivalent of PPA is 0.2 to 5 equivalents, for example, 0.2 equivalents, 0.3 equivalents, 0.4 equivalents, 0.5 equivalents, 0.6 equivalents, 0.7 equivalents, 0.8 equivalents, 0.9 equivalents, 1.0 equivalents, 1.1 equivalents, 1.2 equivalents, 1.3 equivalents, 1.4 equivalents, 1.5 equivalents, 1.6 equivalents, 1.7 equivalents, 1.8 equivalents, 1.9 equivalents, 2.0 equivalents, 2.5 equivalents, 3.0 equivalents, 3.5 equivalents, 4.0 equivalents, 4.5 equivalents or 5.0 equivalents, preferably 1.0 equivalent.

[0029] In some embodiments, the compound of formula (II) and compound 2 are reacted at 60°C to 140°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C or 140°C, preferably 85-95°C.

[0030] In some embodiments, the compound of formula (II) and compound 2 are reacted for 6 to 48 hours, such as 6 to 24 hours, 6 to 18 hours, and preferably 12 to 18 hours.

[0031] In some embodiments, the reaction is carried out under no gas (such as nitrogen) protection, nitrogen protection, and argon protection, preferably under a nitrogen environment.

[0032] In some embodiments, after the reaction is completed, a post-treatment step is further included to obtain a crude product of the compound of formula (III).

[0033] In some embodiments, the post-treatment operation is to add water, sodium carbonate aqueous solution or sodium bicarbonate aqueous solution for quenching and then filtering, or to add DCM, DCM-IPA mixed solvent or 2-MeTHF for extraction, or to directly concentrate the reaction solution under reduced pressure to remove 1,4-dioxane and then add one or more solvents selected from isopropanol, ethyl acetate, acetone, MTBE, PhMe, n-heptane, ACN for dilution and then filter, preferably, after concentrating under reduced pressure to remove 1,4-dioxane, MTBE and n-heptane are added simultaneously or separately and then filtered to obtain a crude compound of formula (III).

[0034] In some embodiments, the crude compound of formula (III) does not need to be dried, and is preferably subjected to the next step after removing the residual solvent at 45-55° C. under vacuum or blowing conditions.

[0035] In some embodiments, after obtaining the crude compound of formula (III), the process further comprises the step of washing the crude compound of formula (III).

[0036] In some embodiments, the washing operation comprises dissolving the crude compound of formula (III) with an organic solvent to obtain an organic phase, washing the organic phase with water 1-5 times, and concentrating the organic phase. In some embodiments, the organic solvent is selected from DCM, DCM-IPA, DCM-EtOH, a DCM-MeOH mixed system, and 2-MeTHF, preferably 2-MeTHF.

[0037] In some embodiments, each aqueous phase is independently selected from water, aqueous NaCl solution, aqueous ammonium chloride solution, aqueous sodium carbonate solution, aqueous sodium bicarbonate solution, aqueous sodium hydroxide solution, aqueous sodium hydrogen phosphate solution, aqueous sodium sulfite solution, aqueous sodium thiosulfate solution, and any combination thereof.

[0038] In some embodiments, the organic phase is washed sequentially with an aqueous NaCl solution, a mixed solution of an aqueous sodium sulfite solution (e.g., a 2% aqueous sodium sulfite solution) and a saturated aqueous NaCl solution (e.g., a saturated aqueous NaCl solution) (e.g., the volume ratio of the sodium sulfate solution and the NaCl solution is 1:1), an aqueous sodium carbonate solution (e.g., a 2% aqueous sodium carbonate solution) and an aqueous NaCl solution (e.g., a saturated aqueous NaCl solution) (e.g., the volume ratio of the sodium carbonate solution and the NaCl solution is 1:1), and an aqueous NaCl solution.

[0039] In some embodiments, after washing the crude compound of formula (III), a recrystallization step is further included.

[0040] In some embodiments, the recrystallization operation is performed by dissolving the compound of formula (III) in 2-MeTHF and crystallizing with MTBE. In some specific embodiments, the compound of formula (III) is added to 2-MeTHF, heated to 40-60° C. to obtain a supersaturated solution of the compound of formula (III), 2-5 volumes of MTBE are added to the 2-MeTHF, the temperature is lowered to 20-30° C., and the compound of formula (III) is collected by filtration. Optionally, after the filtration, the steps of washing with MTBE and drying are further included.

[0041] The above preparation method reduces the reaction temperature, shortens the reaction time, improves the reaction stability and yield, simplifies the reaction post-treatment and purification methods, and improves the stability and scalability of the process by screening the types and equivalents of reaction reagents and reaction solvents, optimizing the reaction temperature, feed ratio, and post-treatment and purification methods.

[0042] In one aspect, the present application provides a method for preparing a compound of formula (IV), comprising the steps of converting a compound of formula (III) into a compound of formula (IV);

[0043] Wherein, R1, R2 and R3 are as described above.

[0044] In some embodiments, the conversion is carried out in an organic solvent selected from alcohols (e.g., methanol, ethanol, isopropanol, n-butanol), ketones (e.g., acetone, butanone, methyl isobutyl ketone), esters (e.g., ethyl acetate, isopropyl acetate), ethers (e.g., MTBE, isopropyl ether, anisole), aliphatic hydrocarbons (e.g., n-heptane), heterocycles (e.g., THF, 1,4-dioxane, 2-MeTHF, NMP), amides (e.g., DMF, DMA, sulfur-containing organic solvents (e.g., DMSO), halogenated aliphatic hydrocarbons (e.g., DCM), ammonium (e.g., CAN), aromatic hydrocarbons (e.g., toluene), and any combination thereof.

[0045] In some embodiments, the conversion is carried out in an organic solvent selected from methanol, ethanol, isopropanol, n-butanol, acetone, butanone, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, MTBE, n-heptane, THF, 1,4-dioxane, 2-MeTHF, isopropyl ether, DMF, DMA, DMSO, NMP, anisole, DCM, CAN, toluene, and any combination thereof.

[0046] In some embodiments, the conversion is performed in the presence of an acid. In some embodiments, the acid is HCl.

[0047] In some embodiments, the conversion is carried out in HCl / 1,4-dioxane.

[0048] In some embodiments, the amount of the acid added is 2-20 equivalents based on the compound of formula (III).

[0049] In some embodiments, the present application provides a method for preparing a compound of formula (IV), comprising the step of converting a compound of formula (III) into a compound of formula (IV) in the presence of HCl;

[0050] Wherein, R1, R2 and R3 are as described above.

[0051] Studies have found that different acids have a significant effect on the stability of the raw materials and products, as well as the isomer ratio of the products. In some embodiments, acid reagents such as concentrated hydrochloric acid, dilute hydrochloric acid, HCl / organic solvent solution, hydrobromic acid, acetic acid, methanesulfonic acid, p-toluenesulfonic acid, benzoic acid, boron trifluoride ether solution, TFA, H2SO4 and H3PO4 can be added to carry out the conversion, preferably HCl / 1,4-dioxane solution.

[0052] In some embodiments, the HCl / 1,4-dioxane feed ratio is 2-20 equivalents, preferably 4-8 equivalents.

[0053] In some embodiments, the reaction solvent is methanol, ethanol, isopropanol, n-butanol, acetone, butanone, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, MTBE, n-heptane, THF, 1,4-dioxane, 2-MeTHF, isopropyl ether, DMF, DMA, DMSO, NMP, anisole, DCM, ACN and toluene, preferably 1,4-dioxane.

[0054] In some embodiments, the conversion is carried out at 25-100°C, preferably 40-50°C, such as 45°C.

[0055] In some embodiments, the conversion is performed for 1-24 hours, such as 4-24 hours, 1-20 hours, and preferably 6-10 hours.

[0056] In some embodiments, the reaction is stopped when the ratio of product:isomer in the reaction solution is (2:1) to (30:1), for example, (2:1) to (25:1), (2:1) to (20:1), (2:1) to (15:1), (5:1) to (30:1), (5:1) to (25:1), (5:1) to (20:1), (5:1) to (15:1), (10:1) to (30:1), (10:1) to (25:1), (10:1) to (20:1), (10:1) to (15:1), (15:1) to (30:1), (15:1) to (25:1), (15:1) to (20:1), preferably (10:1) to (25:1).

[0057] In some embodiments, after the conversion, a post-processing step is further included.

[0058] In some embodiments, the post-treatment is direct concentration under reduced pressure, or the addition of one or more anti-solvents of the reaction solvent, such as one or more of ethanol, isopropanol, n-butanol, acetone, butanone, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, MTBE, n-heptane, THF, 1,4-dioxane, isopropyl ether, anisole, DCM, ACN and toluene, to precipitate more solids and then filter, preferably adding MTBE and then filtering to obtain the target product.

[0059] In some embodiments, the method further comprises the step of preparing the compound of formula (III) according to any one of the methods described in the first aspect.

[0060] After reaction and treatment under the above reaction conditions, the ratio of the compound of formula (IV) and its isomers is increased from about 1:1 to 30-40:1, the purity of the product is further improved, the difficulty of subsequent removal of isomer impurities is reduced, the production cost is reduced, and the process is more suitable for scale-up production.

[0061] In another aspect, the present application provides a method for preparing a compound of formula (I) or a salt thereof, comprising the steps of removing the amino protecting group of the compound of formula (IV) to obtain a compound of formula (I);

[0062] wherein R1, R2 and R3 are as defined above.

[0063] A method known in the art can be selected to remove the amino protecting group. For example, when R3 is Fmoc, Et2NH can be added to carry out the deprotection reaction.

[0064] In some embodiments, after removing the amino protecting group of the compound of formula (IV), a post-treatment step is further included.

[0065] In some embodiments, the post-treatment operation is concentration, slurry washing and filtration 1-3 times to obtain a crude compound of formula (I).

[0066] In some embodiments, after concentrating to 1 / 4-1 / 2, preferably 1 / 3 of the original volume, acetonitrile is added for slurrying and the concentration is continued to be complete.

[0067] In some embodiments, the slurry washing is sequentially performed at a high temperature of 60-80°C (preferably 65-75°C) and a low temperature of 10-40°C (preferably 20-30°C), and then the solid is collected by filtration to obtain a crude compound of formula (IV).

[0068] In some embodiments, after the post-treatment, the step of salifying the compound of formula (I) is further included. In some embodiments, the salification refers to reacting the compound of formula (I) with an acid reagent to obtain a salt of the compound of formula (I).

[0069] Studies have found that the choice of acid reagent used has a significant impact on the stability of the product, the salt formation ratio, the filtration rate, and the isomer removal effect. In some embodiments, the acid used includes hydrochloric acid, hydrobromic acid, methanesulfonic acid, p-toluenesulfonic acid, camphorsulfonic acid, phosphoric acid, acetic acid, benzoic acid, sulfuric acid, and TFA, preferably methanesulfonic acid.

[0070] In some embodiments, the reaction solvent is one of water, methanol, ethanol, isopropanol, acetonitrile, THF and 1,4-dioxane or any combination thereof, preferably a mixed solvent system of methanol and water.

[0071] The study found that the order of adding materials has a great influence on reaction stirring and temperature control. When methanesulfonic acid or water is added last, the reaction liquid releases heat violently, which is difficult to control and difficult to stir. In the preferred experimental scheme, methanesulfonic acid is slowly added to a mixed solvent of water and MeOH, and the crude free base is added in batches at the end. The whole process is stirred well and the reaction temperature is easy to control.

[0072] In some embodiments, the reaction temperature is 20-80°C, preferably 40-55°C. Under this temperature condition, stirring is good, salt formation is complete, and the product is stable.

[0073] In some embodiments, after salt formation, a post-treatment step is further included.

[0074] In some embodiments, the post-reaction treatment is filtration, such as direct filtration, filtration after adding water, filtration after adding methanol, filtration after adding EtOH, filtration after adding isopropanol, filtration after adding acetone, or filtration after adding acetonitrile, preferably, filtration after crystallization by adding methanol.

[0075] In some embodiments, the method further comprises the step of preparing a compound of formula (IV) according to any of the aforementioned methods.

[0076] In some embodiments, the method further comprises the step of preparing the compound of formula (III) according to any of the methods described above.

[0077] In another aspect, the present application provides a method for preparing a drug-linker, which comprises preparing the compound of formula (I) or a salt thereof according to any of the methods described above, wherein the drug is a compound of formula (I) or a salt thereof.

[0078] In some embodiments, the method further comprises the step of preparing the compound of formula (IV) according to any of the aforementioned methods.

[0079] In some embodiments, the method further comprises the step of preparing the compound of formula (III) according to any of the methods described above.

[0080] In another aspect, the present application provides a method for preparing an antibody-drug conjugate, which is prepared by reacting the antibody and the drug-linker, and further preparing the drug-linker according to the method described above.

[0081] Advantageous Effects of the Invention

[0082] This application provides a method for preparing isomeric isomers and their derivatives. By optimizing the types and equivalents of reaction reagents, reaction solvents, and temperature, and developing isomer reversal conditions to avoid high temperatures and prolonged reactions, the three-step total yield is increased from 43% to over 75%, saving one-third of the material cost compared to the original process. Furthermore, the substrates for the reversal are widely applicable and can be used to synthesize multiple isomeric isomers and their analogs. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0084] FIG1 is a HPLC chart showing compound 8 prepared in Example 3. DETAILED DESCRIPTION

[0085] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0086] The abbreviations and English terms used in this document have the following meanings:

[0087] Example 1-1: Preparation of Compound 6

[0088] To a 2L glass reaction flask, add PPA (68.05g, 201.38mmol), o-cresol (360mL), and 1,4-dioxane (360mL) in sequence and start stirring. Add compound 5 (90.00g, 201.38mmol) and compound 2 (58.31mmol, 221.51mmol). After nitrogen replacement three times, continue stirring under N2 and start heating. Maintain the internal temperature at 85-95°C and continue stirring for 12-18h. Stop the reaction when the concentration of compound 5 by HPLC is less than 1.0%.

[0089] Post-treatment: The reaction mixture was cooled to <60°C, transferred, and concentrated under reduced pressure at 50-60°C until no more liquid was visible. The concentrate was transferred to a 10-L glass bottle, stirred, and MTBE (5 L) was slowly added, resulting in the precipitation of a large amount of solid. After addition, n-heptane (1.4 L) was slowly added. Stirring was continued for 1-2 hours. Filtered and drained. The filter cake was rinsed twice with MTBE (500 mL x 2) and drained until no more liquid was visible. The filter cake was collected and dried under vacuum at 40-50°C for 16-24 hours to yield 152.66 g of crude compound 6 (yield: 112.5%, HPLC: 96.44% (46.62% + 49.82%), qNMR: 88%).

[0090] Washing: Take 150 g of the crude product of compound 6, add 2-MeTHF (4500 mL), stir at room temperature to dissolve, continue to add NaCl aqueous solution (1500 mL), stir for 5-15 min, and let stand to separate; separate the organic phase, add 2% sodium sulfite aqueous solution (750 mL) and saturated brine (750 mL), stir for 5-10 min, and let stand to separate; separate the organic phase, add 2% sodium carbonate aqueous solution (750 mL) and saturated brine (750 mL), stir for 5-10 min, and let stand to separate; separate the organic phase, add water (750 mL) and saturated brine (750 mL), stir for 5-10 min, and let stand to separate; separate the organic phase, concentrate under reduced pressure at 35-45°C until no obvious droplets flow down to obtain the washed product of compound 6.

[0091] Purification: Dissolve the washed product in 2-MeTHF (450 mL), heat to 40-60°C (gradually dissolve, then some solid precipitates), and stir for 10-20 min. Slowly add MTBE (1800 mL) and, upon completion, slowly cool to 20-30°C and continue stirring for 1-3 h. Filter and drain. Rinse once with MTBE (300 mL) and drain. Collect the filter cake and vacuum dry at 40-50°C for 16-24 h to yield 120 g of compound 6 (89% overall yield, HPLC: 99.17% (48.75%, 50.42%), QNMR: 96%).

[0092] Example 1-2: Preparation of Compound 6

[0093] To a glass reaction flask, add PPA (227 mg, 1.5 eq) and 1,4-dioxane (2 ml) sequentially and initiate stirring. Add compound 5 (200 mg) and compound 2 (140 mg). After nitrogen replacement three times, continue stirring under a nitrogen atmosphere and heat. Maintain the internal temperature at 85-95°C and continue stirring for 12-18 hours. Stop the reaction when the concentration of compound 5 is less than 1.0% by HPLC.

[0094] Post-treatment: Cool the reaction mixture to <60°C, transfer, and concentrate under reduced pressure at 50-60°C until no more liquid drips out. Slowly add 10 mL of MTBE and 3 mL of n-heptane, and continue stirring for 1-2 hours. Filter and drain; rinse the filter cake twice with MTBE and drain until no more liquid drips out. Collect the filter cake and dry it in a vacuum at 40-50°C for 16-24 hours to obtain 370 mg of crude compound 6 (approximately 75% content).

[0095] Example 2: Preparation of Compound 7

[0096] To a 5L glass bottle, add compound 6 (114.00 g, 169.10 mmol) and 1,4-dioxane (2280 mL) sequentially and start stirring. Add HCl / 1,4-dioxane (274 mL, 1096 mmol, 4 M) and begin heating. Maintain the internal temperature at 40-50°C and stir for 6-10 h. Stop the reaction when the compound 6:isomer ratio reaches 10:1 to 25:1 as determined by HPLC.

[0097] Post-treatment: Cool the reaction mixture to 20-30°C and slowly add MTBE (2600 mL). After addition, cool to 15-20°C and continue stirring for 1-3 hours. Filter and drain; rinse three times with MTBE (330 mL x 3) and drain. Collect the filter cake and dry it under vacuum at 40-50°C for 16-24 hours. 108.3 g of product was obtained (yield: 95%, HPLC: 97.18% compound 7 and 2.12% isomers, QNMR: 99%).

[0098] Example 3: Preparation of Compound 8

[0099] To a 1 L glass bottle, compound 7 (104.44 g, 154.92 mmol) and 1,4-dioxane (627 mL) were added sequentially and stirred. Et2NH (56.65 g, 774.62 mmol) was slowly added, maintaining the internal temperature at 20-30°C. After addition, stirring was continued at this temperature for 18-24 h. The reaction was stopped when the content of compound 7 was less than 1% by HPLC.

[0100] Post-treatment: Transfer the reaction solution, concentrate under reduced pressure at 40-50°C to about 1 / 3 of the reaction solution volume, add acetonitrile (530mL) and beat at room temperature for 1-2h, then continue to concentrate under reduced pressure until no obvious droplets flow down, and end the concentration. Add acetonitrile (1060mL) and heat to 65-75°C and beat for 2h; slowly cool to 20-30°C and continue stirring for 8-16h. Filter, drain, and rinse the filter cake once with acetonitrile (200mL). Collect the filter cake, add acetonitrile (1060mL) and beat at 65-75°C for 2h; slowly cool to 20-30°C and continue stirring for 3-5h. Filter, drain, and rinse the filter cake once with acetonitrile (200mL). Collect the filter cake and dry it in a vacuum at 40-50°C for 16-24h; collect the material to obtain 67g of crude free base.

[0101] Salt Formation: Add water (255 mL) and methanol (126 mL) to a 3 L glass bottle and start stirring. Slowly add methanesulfonic acid (255 mL), maintaining the internal temperature at 20-30°C. After addition, add the crude free base (60 g, 132.77 mmol) in three batches, heat to 40-50°C, and stir for 1-2.5 hours. Slowly add a mixed solution of methanesulfonic acid (126 mL) and methanol (126 mL), and continue stirring for 1-2 hours. Slowly add methanol (1070 mL) to precipitate a large amount of solid. After addition, continue stirring for 1-2 hours. Cool to 20-30°C and continue stirring for 3-5 hours.

[0102] The mixture was filtered and drained; the filter cake was rinsed once with methanol (300 mL) and drained; the filter cake was collected and dried under vacuum at 40-50°C for 18-24 h to give 65.12 g of product (90% yield, HPLC: 99.58% compound 8 and 0.08% isomer, QNMR: 98%).

[0103] The HPLC analysis of compound 8 is shown in FIG1 .

[0104] Example 4: Screening test of first step cyclization reaction reagent

[0105] Compound 9 was used as the model substrate. 100 mg of the material and 1 ml of solvent were added to each reaction to react with compound 2 to prepare the target compound 10. The reaction progress was monitored by HPLC. The statistical results of the reaction after 4 h are shown in Table 1.

[0106] Table 1 Results of cyclization reaction reagent screening

[0107] Note: * Product 10 diastereomers, i.e., the ratio of (1S,9S)-product 10 to (1R,9S)-product 10.

[0108] The data in the above table show that reaction 23 (PPA, o-crestol) has the fastest reaction, produces fewer impurities, and has a greater price advantage than the combination of PPA and m-crestol (reaction 21), and can be further optimized as the optimal condition.

[0109] Example 5: Screening test of solvent for the first step of cyclization reaction

[0110] Compound 11 was used as a model substrate. 100 mg of the material was added to each reaction, and 1 equivalent of PPA was added to react with compound 2 to prepare the target compound 12. The reaction progress was monitored by HPLC. The results of the reaction at 95°C for 11 h are shown in Table 2.

[0111] Table 2 First step cyclization reaction solvent screening results

[0112] Note: * Product 12 diastereomers, i.e., the ratio of (1S,9S)-product 12 to (1R,9S)-product 12.

[0113] The data in the above table show that compared with a single solvent, the mixed system of o-cresol and 1,4-dioxane has the best reaction.

[0114] Example 6: Second step configuration reversal condition screening test

[0115] Using compound 13 as a model substrate, each reaction was charged with 50 mg of material and 1 ml of solvent to screen the changes in the ratio of products 14 and 15 under different conditions. The results are statistically shown below:

[0116] The above data show that under the conditions of HCl / dioxane and reaction at 45°C, the ratio of target compound 14 is the best.

[0117] Although the specific embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications and substitutions may be made to those details based on all the teachings disclosed, and these changes are all within the scope of protection of the present invention. The full scope of the present invention is given by the appended claims and any equivalents thereof.

Claims

1. A method for preparing a compound of formula (III), comprising the step of reacting a compound of formula (II) and compound 2 in the presence of a catalyst; in, R1 and R2 are independently selected from hydrogen, halogen, C 1-6 Alkyl, C 1-6 Hydroxyalkyl, C 1-6 Alkoxyalkyl, C 1-6 Alkoxy, C 1-4 Haloalkyl, hydroxyl and cyano; or R1 and R2 are linked to the carbon atoms to which they are attached to form a 5-6 membered carbocyclic ring or an oxygen-containing heterocyclic ring; R3 is an electron-withdrawing protecting group; The catalyst is selected from one or more of PPTS, AcOH, TFA, H2SO4, proline, PPA, P2O5, CAN, T3P, KOH, I2, MgCl2 and TMSCl.

2. The method of claim 1, wherein: The catalyst is PPA.

3. The method of claim 1, wherein: The reaction is carried out in a solvent with the compound of formula (II) and compound 2, wherein the solvent is selected from aromatic hydrocarbons (e.g., toluene, xylene, o-toluene, m-toluene), aliphatic hydrocarbons (e.g., hexane, n-heptane), alcohols (e.g., methanol, ethanol, isopropanol), organic acids (e.g., acetic acid, trifluoroacetic acid), phenols (e.g., phenol, o-cresol, m-cresol, p-cresol), ethers (e.g., ethyl ether, ethylene oxide, anisole), esters (e.g., methyl acetate, ethyl acetate, propyl acetate), ketones (e.g., acetone, butanone), amides (e.g., DMF, DMA), nitriles (e.g., acetonitrile), heterocyclics (e.g., NMP, 1,4-dioxane, 2-MeTHF), sulfur-containing organic solvents (e.g., DMSO), and any combination thereof.

4. The method of claim 3, wherein: The solvent is a combination of a phenolic solvent and a heterocyclic solvent.

5. The method of claim 4, wherein: The solvent is a mixed solvent of o-cresol and 1,4-dioxane.

6. The method according to any one of claims 1 to 5, characterized in that One or more of the following: (1-1) The volume ratio of o-cresol to 1,4-dioxane is (10:1) to (1:10); (1-2) The molar ratio of the compound of formula (II) and compound 2 is (1:1) to (1:1.5); (1-3) Based on the compound of formula (II), the feed equivalent of PPA is 0.2 to 5 equivalents; (1-4) The compound of formula (II) and compound 2 are reacted at 60°C to 140°C; (1-5) reacting the compound of formula (II) with compound 2 for 6 to 48 hours; (1-6) The reaction is carried out under no gas protection, nitrogen protection and argon protection; (1-7) After the reaction is completed, it also includes a post-treatment step to obtain a crude product of the compound of formula (III); (1-8) After obtaining the crude compound of formula (III) described in item (1-7), the step of washing the crude compound of formula (III) is also included; (1-9) After the washing operation described in item (1-8), a recrystallization step is also included.

7. The method of claim 6, wherein: The volume ratio of o-cresol to 1,4-dioxane is (10:1) to (1:1); and / or The molar ratio of the compound of formula (II) and compound 2 is (0.8:1) to (1:1.5).

8. The method according to claim 6, characterized in that One or more of the following: 1-1) The post-treatment operation described in item (1-7) includes adding water, sodium carbonate aqueous solution or sodium bicarbonate aqueous solution for quenching and then filtering, or adding DCM, DCM-IPA mixed solvent or 2-MeTHF for extraction, or directly concentrating the reaction solution under reduced pressure to remove 1,4-dioxane and then adding one or more solvents selected from isopropanol, ethyl acetate, acetone, MTBE, PhMe, n-heptane, ACN to dilute and then filter; 1-2) The crude compound of formula (III) obtained in item (1-7) does not need to be dried; 1-3) The washing operation described in item (1-8) comprises dissolving the crude compound of formula (III) with an organic solvent to obtain an organic phase, washing the organic phase with water for 1 to 5 times, and concentrating the organic phase; 1-4) The recrystallization operation described in item (1-9) comprises dissolving the compound of formula (III) with 2-MeTHF and crystallizing with MTBE.

9. A method for preparing a compound of formula (IV), comprising the step of converting a compound of formula (III) into a compound of formula (IV); in, R1, R2 and R3 are as defined in claim 1.

10. The method of claim 9, wherein: The conversion is carried out in an organic solvent, and the organic solvent is selected from alcohols (e.g., methanol, ethanol, isopropanol, n-butanol), ketones (e.g., acetone, butanone, methyl isobutyl ketone), esters (e.g., ethyl acetate, isopropyl acetate), ethers (e.g., MTBE, isopropyl ether, anisole), aliphatic hydrocarbons (e.g., n-heptane), heterocyclics (e.g., THF, 1,4-dioxane, 2-MeTHF, NMP), amides (e.g., DMF, DMA, sulfur-containing organic solvents (e.g., DMSO), halogenated aliphatic hydrocarbons (e.g., DCM), ammoniums (e.g., CAN), aromatic hydrocarbons (e.g., toluene), and any combination thereof.

11. The method according to claim 9 or 10, wherein The conversion is carried out in the presence of an acid.

12. The method of claim 11, wherein: The acid is HCl.

13. The method according to any one of claims 9 to 12, characterized in that One or more of the following: (2-1) The conversion is carried out in HCl / 1,4-dioxane; (2-2) Based on the compound of formula (III), the acid feed is 2-20 equivalents; (2-3) The conversion is carried out at 25 to 100°C; (2-4) stopping the reaction when the ratio of the compound of formula (IV) to its isomer is (2:1) to (30:1); (2-5) the transformation is carried out for 1-24 hours; (2-6) After the conversion, the method further comprises a post-treatment step; (2-7) The method further comprises the step of preparing the compound of formula (III) according to any one of claims 1 to 8.

14. The method of claim 13, characterized in that One or more of the following: 2-1) The post-treatment operation described in item (2-7) is direct concentration under reduced pressure, or adding one or more anti-solvents of the organic solvent described in claim 10 to precipitate more solids and then filtering to obtain the target product; 2-2) The anti-solvent described in item 2-1) is selected from one or more of ethanol, isopropanol, n-butanol, acetone, butanone, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, MTBE, n-heptane, THF, 1,4-dioxane, isopropyl ether, anisole, DCM, ACN and toluene.

15. A method for preparing a compound of formula (I) or a salt thereof, comprising the step of removing the amino protecting group of a compound of formula (IV) to obtain a compound of formula (I); in, R1, R2 and R3 are as defined in claim 1.

16. The method of claim 15, characterized in that One or more of the following: (3-1) After removing the amino protecting group of the compound of formula (IV), the method further comprises a post-treatment step; (3-2) after the post-treatment described in item (3-1), further comprising the step of salifying the compound of formula (I); (3-3) After the salt formation described in item (3-2), a post-treatment step is also included; (3-4) The method further comprises the step of preparing the compound of formula (IV) according to any one of claims 9 to 14; (3-5) The method comprises the step of preparing the compound of formula (III) according to any one of claims 1 to 8.

17. The method of claim 16, characterized in that One or more of the following: 3-1) The post-treatment operation described in item (3-1) is concentration, slurry washing and filtration 1-3 times to obtain a crude product of the compound of formula (I); 3-2) The concentration described in item 3-1) refers to concentration to 1 / 4-1 / 2 of the volume of the original solution, followed by slurrying with acetonitrile and further concentration; 3-3) The slurry washing described in item 3-1) is carried out at a high temperature of 60-80°C and a low temperature of 10-40°C in sequence, and then the solid is collected by filtration to obtain a crude product of the compound of formula (I); 3-4) The salt formation described in item (3-2) comprises reacting the compound of formula (I) with an acid reagent to obtain a salt of the compound of formula (I); 3-5) The post-treatment operation described in item (3-3) is filtration, such as direct filtration, filtration after mixing with water, filtration after mixing with methanol, filtration after mixing with EtOH, filtration after mixing with isopropanol, filtration after mixing with acetone, or filtration after mixing with acetonitrile.

18. A method for preparing a drug-linker, comprising the step of preparing the compound of formula (I) or a salt thereof according to any one of claims 15 to 17, wherein: The drug is a compound of formula (I) or a salt thereof.

19. A method for preparing an antibody-drug conjugate, which is prepared by reacting the antibody and a drug-linker, and further comprising the step of preparing the drug-linker according to the method of claim 18.

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