A method for synthesizing a tridentate linker fragment useful for improving the hydrophilicity of antibody drug conjugates
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUHAN AOFEI TECH CO LTD
- Filing Date
- 2024-11-28
- Publication Date
- 2026-05-29
AI Technical Summary
聚集后的ADC很容易被免疫系统发现，当作异物被迅速清除，这会导致进入肿瘤细胞发挥作用的ADC数量减少，药效降低
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Figure CN122103196A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of organic synthesis, specifically to a method for synthesizing a linker fragment ({[5-amino-2-(3,3,4,4-tetramethyl-2-oxa-3-silazopent-1-yl)phenyl]methyl}(methyl)amino)methane-2-methylpropyl-2-yl ester) that can be used to improve the hydrophilicity of antibody-drug conjugates. Background Technology
[0002] ADC drugs, short for Antibody-Drug Conjugates, are a novel type of cancer treatment. They combine the targeting capabilities of monoclonal antibodies with the cytotoxicity of small molecule drugs, precisely delivering the drug to tumor cells while minimizing damage to normal cells and improving treatment efficacy. The structure of an ADC drug typically consists of three parts: 1) Monoclonal antibody: This antibody specifically recognizes and binds to specific antigens on the surface of tumor cells. The expression levels of these antigens on tumor cells are usually much higher than on normal cells, thus serving as a target carrier for the drug; 2) Linker: This connects the monoclonal antibody and the small molecule drug, controlling the release of the drug within the tumor cells; 3) Small molecule drug: Also known as a cytotoxic drug, this is the "warhead" of the ADC drug, responsible for killing cancer cells. This type of drug causes tumor cell death by interfering with DNA replication, mitosis, or other key biological processes in tumor cells (Nat. Rev. Clin. Oncol., 2021, 18, 327-344; J. Med. Chem., 2022, 65(6), 4496-4499; Pharmacol. Rev., 2024, 76(4), 579-598). Therefore, ADC drugs, as a novel precision medicine approach, have attracted attention and investment from traditional large pharmaceutical companies and emerging biotechnology companies, and several blockbuster drugs have been launched to date.
[0003] The higher the hydrophobicity of ADC drugs, the higher their clearance rate. This is because toxins are mostly hydrophobic, and the binding of hydrophobic linkers with hydrophobic toxins promotes ADC aggregation. Aggregated ADCs are easily detected by the immune system and rapidly cleared as foreign substances, which leads to a reduction in the number of ADCs that can enter tumor cells to exert their effects, thus reducing drug efficacy. Therefore, for classic hydrophobic enzyme-cleaved linkers Val-Cit-PAB-OH(1-amino-N-[(4S)-5-{[4-(hydroxymethyl)phenyl]amino}-4-{[(2S)-2-amino-3-methyl-1-oxylidene butyl]amino}-5-oxylidene pentyl]methaneamide) and Val-Ala-PAB-OH((2S)-N-[4-(hydroxymethyl)phenyl]-2-{[(2S)-2-amino-3-methyl-1-oxylidene butyl]amino}-5-oxylidene pentyl]methaneamide) For ADC drugs, if the terminal is a hydrophobic toxin such as Exatecan, the linker of the ADC drug must be modified to be hydrophilic, such as by introducing hydrophilic polyethylene glycol chains, polysarcosine chains, sugar chains and hydrophilic peptide chains, in order to reduce ADC drug aggregation, prolong the drug action time, thereby promoting the killing effect on tumor cells and broadening the therapeutic index of ADC (Chem. Sci., 2019, 10, 4048-4053; Cancer Discov., 2023, 13(4), 950-973; J. Med. Chem., 2024, 67(20), 18124-18138).
[0004] Introducing hydrophilic polyethylene glycol and polysarcosine chains at the 3-position of the benzene ring in the self-cleaving structural unit PAB-OH (p-aminobenzyl alcohol) is a proven and widely used strategy (WO2020236841A2; WO2020236825A2; WO2022228495A1; WO2022115477A1; WO2022115451A1; WO2022225336A1; WO2023225320A1; WO2023225359A1; WO2023223097A1; WO2023104188A1; WO2024083162A1). Taking the ADC drug PRO-1184, currently in Phase 1 / 2 clinical trials, as an example, the introduction of a hydrophilic polysarcosine chain at the 3-position of the benzene ring of Val-Ala-PAB-OH((2S)-N-[4-(hydroxymethyl)phenyl]-2-{[(2S)-2-amino-3-methyl-1-oxoylidenebutyl]amino}propionamide) enhances the drug's hydrophobic shielding effect and stability, prolongs its duration of action, and overcomes multiple tumor drug resistance, thereby further improving the therapeutic window of existing ADC drugs. Figure 1, Cancer Discov., 2023, 13(4), 950-973. ), in which the 3-substituted PAB-OH ({4-amino-2-[(methylamino)methyl]phenyl}methanol) of the benzene ring plays a key role in linking the Val-Ala dipeptide, the polysarcosine chain and the small molecule drug Exatecan.
[0005] Literature review revealed that, to date, the only relevant fragments used in ADC drugs are as follows: Figure 2 The three fragments shown in figure a (intermediate I, intermediate II, and intermediate III) are reported, and only intermediate I has a synthetic route, such as Figure 2 As shown in b: Starting from commercially available 6-nitrotetrachlorophthalide (CAS: 610-93-5), an important intermediate I ({[5-amino-2-(4,4-dimethyl-3,3-diphenyl-2-oxa-3-silazopent-1-yl)phenyl]methyl}(methyl)amino)methane-9H-fluorene-9-ylmethyl ester (CAS: 2563870-49-3)(WO2020236841A2; WO2020236825A2)) was prepared via a five-step reaction involving ammonolysis, amide reduction, benzyl alcohol protection, amine protection, and nitro reduction.
[0006] Given the importance and application potential of the PAB-OH structural unit with special substitution at the 3-position of the benzene ring in ADC drugs and other fields, it is necessary to design novel routes and synthesize novel structures to meet the growing market demand. Summary of the Invention
[0007] The purpose of this invention is to provide a method for preparing a tripentate linker fragment ({[5-amino-2-(3,3,4,4-tetramethyl-2-oxa-3-silaxapran-1-yl)phenyl]methyl}(methyl)amino)methane-2-methylpropyl-2-yl ester, which can be used to improve the hydrophilicity of antibody-drug conjugates, relating to the field of organic synthesis. This ({[5-amino-2-(3,3,4,4-tetramethyl-2-oxa-3-silaxapran-1-yl)phenyl]methyl}(methyl)amino)methane-2-methylpropyl-2-yl ester) can be used to link hydrophobic dipeptides, hydrophilic chains, and small molecule drugs in ADC drugs, thereby prolonging the action time of the ADC drug. This invention uses the inexpensive and readily available commercial raw material 2-bromo-5-nitrobenzaldehyde as a starting material. Through seven conventional transformation steps including reductive amination, protection, coupling, ozonation, and nitro reduction, the target product was successfully prepared in a ~60% overall yield and on a 100-gram scale. This route utilizes inexpensive starting materials, is simple to operate, and operates under mild reaction conditions. It represents a novel synthetic route with significant economic benefits and market potential. Attached Figure Description
[0008] Figure 1Structure of ADC drug PRO-1184
[0009] Figure 2 Reported intermediates and related synthetic routes for PAB-OH with special substitution at the 3-position of the benzene ring. Detailed Implementation
[0010] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0011] Example 1
[0012]
[0013] [Step 1]
[0014] Compound 1 (450 mg, 2.0 mmol) was dissolved in ethanol (5 mL) at room temperature. Methylamine hydrochloride (2.0 eq., 261 mg) and potassium acetate (3.0 eq., 589 mg) were added sequentially. After stirring for 1 hour, sodium cyanoborohydride (3.0 eq., 367 mg) was added in portions, and the reaction was continued for 2 hours. After the reaction was completed, the reaction solution was extracted with ethyl acetate, the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, and dried under reduced pressure to obtain off-white solid 2 (464 mg, 98%), which was used directly in the next step without further purification.
[0015] [Step 2]
[0016] Compound 2 (464 mg, 1.9 mmol) was dissolved in dichloromethane (DCM, 3 mL) at room temperature, followed by the addition of triethylamine (TEA, 2.0 eq., 0.5 mL) and di-tert-butyl dicarbonate (1.1 eq., 456 mg). The mixture was stirred for 12 hours and monitored by TLC. After the reaction was complete, the reaction solution was extracted with ethyl acetate. The organic phases were combined, washed with water, saturated citric acid, and saturated brine, and dried over sodium sulfate. The mixture was filtered, concentrated, and the residue was slurried with hexane / ethyl acetate. The residue was filtered and dried to obtain a white solid 3 (525 mg, 80%), which was used directly in the next step without further purification.
[0017] [Step 3]
[0018] Compound 3 (525 mg, 1.5 mmol) was dissolved in a mixed solvent of 1,4-dioxane and water (6 mL, volume ratio 2:1) at room temperature and under a nitrogen atmosphere. Potassium vinyltrifluoroborate (3.0 eq., 603 mg), sodium phosphate (3.0 eq., 738 mg), and tetrakis(triphenylphosphine)palladium (0.1 eq., 173 mg) were added sequentially. The mixture was heated to 110 °C and stirred for 16 hours under TLC monitoring. After the reaction was completed, the mixture was filtered through diatomaceous earth. The filtrate was extracted with ethyl acetate, and the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was purified by rapid column chromatography to give yellow solid 4 (395 mg, 90%).
[0019] [Step 4]
[0020] Compound 4 (395 mg, 1.4 mmol) was dissolved in methanol (20 mL) at room temperature, cooled to -50 °C, and O3 was continuously introduced into the system until the raw materials were consumed. The reaction solution was purged with nitrogen for 15 minutes, and sodium borohydride (10.0 eq., 530 mg) was added at -60 °C. The mixture was stirred for 15 minutes and monitored by TLC. After the reaction was completed, the reaction solution was extracted with ethyl acetate, the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was purified by rapid column chromatography to obtain off-white solid 5 (406 mg, 98%).
[0021] [Step 5]
[0022] Compound 5 (406 mg, 1.4 mmol) was dissolved in dichloromethane (3 mL) at room temperature, and triethylamine (TEA, 2.0 eq., 0.4 mL) was added. The mixture was cooled to 0 °C, and tert-butyldimethylchlorosilane (1.2 eq., 253 mg) was added. The mixture was then heated to room temperature and stirred for 1 hour. The reaction was monitored by TLC. After the reaction was complete, the reaction solution was extracted with ethyl acetate, and the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was purified by rapid column chromatography to give a white solid 6 (563 mg, 98%).
[0023] [Step 6]
[0024] Compound 6 (563 mg, 1.4 mmol) was dissolved in ethyl acetate (5 mL) at room temperature, and 10% palladium on carbon (0.1 eq., 48 mg) was added. The mixture was evacuated three times with a hydrogen balloon, and the reaction was continued to be stirred for 12 hours under a hydrogen atmosphere (1 atm). The reaction was monitored by TLC. After the reaction was completed, the reaction solution was diluted with ethyl acetate and filtered through diatomaceous earth. The filtrate was directly concentrated to obtain a yellow oily substance 7 (522 mg, 98%), which could be used directly in the next step without further purification.
[0025] Example 2
[0026]
[0027] [Step 1]
[0028] Compound 1 (15 g, 65 mmol) was dissolved in methanol (120 mL) at room temperature. Methylamine hydrochloride (2.0 eq., 8.7 g) and sodium acetate (3.0 eq., 16 g) were added sequentially. After stirring for 1 hour, sodium cyanoborohydride (2.5 eq., 10 g) was added in portions, and the reaction was continued for 2 hours. After the reaction was completed, the reaction solution was extracted with ethyl acetate, the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, and dried under reduced pressure to obtain off-white solid 2 (15 g, 93%). No further purification was required, and it was used directly in the next step.
[0029] [Step 2]
[0030] Compound 2 (15 g, 61 mmol) was dissolved in dichloromethane (130 mL) at room temperature, followed by the addition of triethylamine (2.0 eq., 17 mL) and di-tert-butyl dicarbonate (1.3 eq., 13 g). The mixture was stirred for 12 hours and monitored by TLC. After the reaction was complete, the reaction solution was extracted with ethyl acetate. The organic phases were combined, washed with water, saturated citric acid, and saturated brine, and dried over sodium sulfate. The mixture was filtered, concentrated, and the residue was slurried with hexane / ethyl acetate. The residue was filtered and dried to obtain a white solid 3 (19 g, 91%), which was used directly in the next step without further purification.
[0031] [Step 3]
[0032] Compound 3 (19 g, 55 mmol) was dissolved in a mixed solvent of 1,4-dioxane and water (160 mL, volume ratio 3:1) at room temperature and under a nitrogen atmosphere. Potassium vinyltrifluoroborate (3.0 eq., 22 g), potassium phosphate (4.0 eq., 47 g), and tetrakis(triphenylphosphine)palladium (0.05 eq., 3 g) were added sequentially. The mixture was heated to 110 °C and stirred for 12 hours under TLC monitoring. After the reaction was complete, the mixture was filtered through diatomaceous earth. The filtrate was extracted with ethyl acetate, and the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was crystallized from n-hexane / ethyl acetate. The crystals were filtered and dried to obtain a yellow solid 4 (14 g, 86%), which was used directly in the next step without further purification.
[0033] [Step 4]
[0034] Compound 4 (14 g, 47 mmol) was dissolved in methanol (200 mL) at room temperature, cooled to -40 °C, and O3 was continuously introduced into the system until the raw materials were consumed. After the reaction solution was purged with nitrogen for 15 minutes, sodium borohydride (10.0 eq., 18 g) was added in batches at -40 °C, and the reaction was stirred for half an hour. The reaction was monitored by TLC. After the reaction was completed, the reaction solution was extracted with ethyl acetate, the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was slurried with n-hexane / ethyl acetate, filtered and dried to obtain off-white solid 5 (13 g, 94%), which did not require further purification and was used directly in the next step.
[0035] [Step 5]
[0036] Compound 5 (13 g, 45 mmol) was dissolved in dichloromethane (80 mL) at room temperature, and imidazole (2.0 eq., 6 g) was added. The mixture was cooled to 0 °C, and tert-butyldimethylchlorosilane (1.2 eq., 8 g) was added in portions. The mixture was then stirred at room temperature for 3 hours and monitored by TLC. After the reaction was complete, the reaction solution was extracted with ethyl acetate, and the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was slurried with n-hexane / ethyl acetate. The residue was filtered and dried to obtain off-white solid 6 (17 g, 93%), which did not require further purification and was used directly in the next step.
[0037] [Step 6]
[0038] Compound 6 (17 g, 41 mmol) and copper sulfate pentahydrate (0.2 eq., 2 g) were dissolved in a mixed solvent of dichloromethane and methanol (100 mL) at 0 °C. Sodium borohydride solid (3.0 eq., 5 g) was added in multiple batches. After the addition was complete, the mixture was brought to room temperature and stirred for 6 hours. The reaction was monitored by TLC. After the reaction was completed, the reaction solution was extracted with ethyl acetate. The organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and dried under vacuum to obtain a yellow oily substance 7 (15 g, 97%). No further purification was required, and it could be used directly in the next step.
[0039] Example 3
[0040]
[0041] [Step 1]
[0042] Compound 1 (150 g, 652 mmol) was dissolved in methanol (1500 mL) at room temperature. Methylamine hydrochloride (2.0 eq., 87 g) and sodium acetate (3.0 eq., 160 g) were added sequentially. After stirring for 1 hour, sodium cyanoborohydride (2.5 eq., 102 g) was added in portions, and the reaction was continued for 2 hours. After the reaction was completed, the reaction solution was extracted with ethyl acetate, the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, and dried under reduced pressure to obtain off-white solid 2 (150 g, 94%). No further purification was required, and it was used directly in the next step.
[0043] [Step 2]
[0044] Compound 2 (150 g, 612 mmol) was dissolved in dichloromethane (DCM, 1500 mL) at room temperature, followed by the addition of triethylamine (2.0 eq., 169 mL) and di-tert-butyl dicarbonate (1.3 eq., 134 g). The mixture was stirred for 16 hours and monitored by TLC. After the reaction was complete, the reaction solution was extracted with ethyl acetate. The organic phases were combined, washed with water, saturated citric acid, and saturated brine, and dried over sodium sulfate. The mixture was filtered, concentrated, and the residue was slurried with hexane / ethyl acetate. The residue was filtered and dried to obtain a white solid 3 (188 g, 90%), which was used directly in the next step without further purification.
[0045] [Step 3]
[0046] Compound 3 (188 g, 551 mmol) was dissolved in a mixed solvent of 1,4-dioxane and water (1600 mL, volume ratio 3:1) at room temperature and under a nitrogen atmosphere. Potassium vinyltrifluoroborate (3.0 eq., 221 g), potassium phosphate (4.0 eq., 468 g), and tetrakis(triphenylphosphine)palladium (0.05 eq., 32 g) were added sequentially. The mixture was heated to 110 °C and stirred for 16 hours under TLC monitoring. After the reaction was complete, the mixture was filtered through diatomaceous earth. The filtrate was extracted with ethyl acetate, and the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was crystallized from hexane / ethyl acetate. The crystals were filtered and dried to obtain a yellow solid 4 (137 g, 85%), which was used directly in the next step without further purification.
[0047] [Step 4]
[0048] Compound 4 (137 g, 469 mmol) was dissolved in methanol (2000 mL) at room temperature, cooled to -40 °C, and O3 was continuously bubbled into the system until the raw materials were consumed. The reaction solution was purged with nitrogen for 15 minutes, and sodium borohydride (10.0 eq., 178 g) was added in batches at -40 °C. The mixture was stirred for half an hour and monitored by TLC. After the reaction was completed, the reaction solution was extracted with ethyl acetate, the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was slurried with n-hexane / ethyl acetate. The residue was filtered and dried to obtain off-white solid 5 (132 g, 95%), which did not require further purification and was used directly in the next step.
[0049] [Step 5]
[0050] Compound 5 (132 g, 446 mmol) was dissolved in dichloromethane (750 mL) at room temperature, and imidazole (2.0 eq., 61 g) was added. The mixture was cooled to 0 °C, and tert-butyldimethylchlorosilane (1.2 eq., 81 g) was added in portions. The mixture was then stirred at room temperature for 3 hours and monitored by TLC. After the reaction was complete, the reaction solution was extracted with ethyl acetate, and the organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and the residue was slurried with n-hexane / ethyl acetate. The residue was filtered and dried to obtain off-white solid 6 (168 g, 92%), which did not require further purification and was used directly in the next step.
[0051] [Step 6]
[0052] Compound 6 (168 g, 410 mmol) and copper sulfate pentahydrate (0.2 eq., 21 g) were dissolved in a mixed solvent of dichloromethane and methanol (1000 mL) at 0 °C. Sodium borohydride solid (3.0 eq., 47 g) was added in multiple batches. After the addition was complete, the mixture was brought to room temperature and stirred for 6 hours. The reaction was monitored by TLC. After the reaction was completed, the reaction solution was extracted with ethyl acetate. The organic phases were combined, washed with water and saturated brine, dried over sodium sulfate, filtered, concentrated, and dried under vacuum to obtain a yellow oily substance 7 (153 g, 98%). No further purification was required, and it could be used directly in the next step.
[0053] 1 H NMR (400MHz, CDCl3, ppm): δ7.12(s,1H),6.57-6.48(m,2H),4.60(s,2H),4.45(s,2H),2.84-2.75(m,3H),1.49(s,9H),0.90(s,9H),0.05(s,6H);
[0054] MS(ESI)m / z calculated for C 20 H 37N₂O₃Si[M+H] + :381.26,found:381.37.
[0055] This invention uses the inexpensive and readily available commercial raw material 2-bromo-5-nitrobenzaldehyde (CAS: 84459-32-5, 100g / 860 yuan) as the starting material. Through seven conventional transformation steps including reductive amination, protection, coupling, ozonolysis, and nitro reduction, a tridentate linker fragment ({[5-amino-2-(3,3,4,4-tetramethyl-2-oxa-3-silazopent-1-yl)phenyl]methyl}(methyl)amino)methane-2-methylpropyl-2-yl ester) that can be used to improve the hydrophilicity of antibody-drug conjugates was successfully prepared in a ~60% overall yield and on a 100g scale. This route uses inexpensive starting materials, is easy to operate and process, and has mild reaction conditions. It is a novel synthetic route with good economic benefits and market prospects.
[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a tripentate linker fragment ({[5-amino-2-(3,3,4,4-tetramethyl-2-oxa-3-silazopent-1-yl)phenyl]methyl}(methyl)amino)methane-2-methylpropyl-2-yl ester) that can be used to improve the hydrophilicity of antibody-drug conjugates, the reaction formula of which is as follows:
2. The preparation method according to claim 1, characterized in that: The specific method for synthesizing compound 2 is as follows: compound 1 is dissolved in methanol, methylamine hydrochloride and sodium acetate are added sequentially, and the reaction is carried out at room temperature. After the reaction is completed, the reaction solution is extracted and the solvent is removed to obtain compound 2. No further purification is required, and it can be directly used for the next reaction. The specific method for synthesizing compound 3 is as follows: under room temperature conditions, compound 2 is dissolved in tetrahydrofuran, and triethylamine and ditert-butyl dicarbonate are added sequentially. The reaction is carried out at room temperature. After the reaction is completed, the reaction solution is extracted, desolventized, and pulped to obtain compound 3. No further purification is required, and it can be directly used for the next reaction. The specific method for synthesizing compound 4 is as follows: under room temperature conditions, compound 3 is dissolved in a mixed solvent of 1,4-dioxane and water, potassium vinyltrifluoroborate, potassium phosphate and tetra(triphenylphosphine)palladium are added in sequence, the temperature is raised and the reaction is carried out. After the reaction is completed, the reaction solution is filtered through diatomaceous earth, the filtrate is extracted, the solvent is removed, and the solution is crystallized to obtain compound 4. No further purification is required and it can be directly used in the next reaction. The specific method for synthesizing compound 5 is as follows: under room temperature conditions, compound 4 is dissolved in methanol, the temperature is lowered, ozone is continuously introduced into the system until the raw materials are consumed, the reaction solution is purged with nitrogen, sodium borohydride is added in batches, and after the reaction is completed, the reaction solution is extracted, solvent is removed, and pulped to obtain compound 5, which does not require further purification and can be directly used in the next reaction. The specific method for synthesizing compound 6 is as follows: under room temperature conditions, compound 5 is dissolved in dichloromethane, imidazole is added, the temperature is lowered, and tert-butyldimethylchlorosilane is added in batches. After the reaction is completed, the reaction solution is extracted, solvent is removed, and the mixture is pulped to obtain compound 6. No further purification is required, and it can be directly used in the next reaction. The specific method for synthesizing compound 7 is as follows: under room temperature conditions, compound 5 is dissolved in a mixed solvent of dichloromethane and methanol, copper sulfate pentahydrate is added, the temperature is lowered, and sodium borohydride solid is added in batches. After the reaction is completed, the reaction solution is extracted and the solvent is removed to obtain compound 7, which can be directly used for the next reaction without further purification.
3. The preparation method according to claim 2, characterized in that: The organic base used in steps 2 and 5 is one of triethylamine, N,N-diisopropylethylamine, imidazole, and pyridine.
4. The preparation method according to claim 2, characterized in that: The inorganic base used in step 3 is one of potassium phosphate, sodium phosphate, potassium carbonate, sodium carbonate, and cesium carbonate.
5. The preparation method according to claim 2, characterized in that: The solvent used in steps 1 and 4 is one of methanol, ethanol, isopropanol, and tert-butanol.
6. The preparation method according to claim 2, characterized in that: The reducing agent used in steps 1, 4 and 6 is one of sodium borohydride, sodium cyanoborohydride, hydrogen, or sodium triacetoxyborohydride.
7. The preparation method according to claim 2, characterized in that: The reaction temperatures in steps 3 and 4 are one of 80–150°C and 0–-80°C, respectively.