Process for the preparation of dihydroxyborylphenylalanine and intermediates thereof

Abstract

The application provides a preparation method of dihydroxy boron phenylalanine and intermediates thereof. The method comprises the following steps: mixing 4-halogen-Boc-L-phenylalanine of formula (II) with an alkyl borate, and adding a Grignard reagent to obtain an intermediate compound of formula (I): (I) (II).

Description

Technical Field

[0001] This invention relates to the pharmaceutical field, specifically to a method for preparing dihydroxyboronylphenylalanine and its intermediates. Background Technology

[0002] Boron neutron capture therapy (BNCT) is a radiotherapy that uses boron-containing compounds to selectively kill tumor cells while preserving normal cells. 10 Botanicals (B) are neutral, non-radioactive elements. When exposed to low-energy thermal (0.025 eV) neutrons or ultrathermal neutrons (10000 eV), they undergo a fission reaction, producing alpha particles (α particles). 4 He) and recoiled lithium cores ( 7 Li), accompanied by highly linear energy transfer (LET). As shown below: 10 B+n→ 11 B→ 7 Li+ 4 He+2.79MeV 6.3% 10 B+n→ 11 B→ 7 Li+ 4 He+2.31MeV 93.7% These particles have the characteristics of high energy and short path length. The linear energy transfer in the unit path exceeds 100 keV / µm, which means that a few alpha particles can have a lethal effect on tumor cells. Since their range in tissue is about 5-9µm, which is equivalent to the diameter of a cell, they have a very small destructive effect on the surrounding normal cells.

[0003] L-BPA and BSH are both considered second-generation compounds that emerged in the 1960s. They exhibit significantly lower toxicity and better pharmacokinetic (PK) and biodistribution. L-BPA (dihydroxyboronylphenylalanine) is currently the only approved boron-containing drug for BNCT (benzylcholine agonist) and its structural formula is as follows: The preparation method has been reported in numerous patents and literature both domestically and internationally. For example, in a patent published in 2023 by Stella Corporation of Japan (CN116113636A), a Grignard reagent was prepared using a stepwise method with the substrate 4-iodo-Boc-L-phenylalanine in the presence of isopropyl magnesium chloride and lithium chloride. This reagent was then reacted with tributyl borate to prepare boric acid, and finally, deprotecting was performed in an acetone / water solvent using concentrated hydrochloric acid to obtain dihydroxyboronphenylalanine. The Grignard reagent preparation step used a -30°C solution. o At low temperature, Grignard reagent was added dropwise. After the addition was complete, the reaction was kept at this temperature for 4 hours. Then, tributyl borate was added dropwise at the same temperature, and the reaction was continued for 1.5 hours.

[0004] Additionally, a patent published by Dongyangguang in 2019 (CN110498810A) reported the preparation of L-BPA using a reaction of 4-iodo-Boc-L-phenylalanine with isopropyl magnesium chloride Grignard reagent and tributyl borate. The Grignard reagent preparation step requires temperature control at -30°C. o C, slowly add isopropyl magnesium chloride dropwise, then reduce to -30°C after the addition is complete. o C reaction overnight, then at -30 o C to -25 o Tributyl borate was added dropwise between C and C, and the reaction was kept at a constant temperature after the addition was complete.

[0005] In the aforementioned published patent reports, whether using isopropyl magnesium chloride-lithium chloride solution or isopropyl magnesium chloride solution, the preparation methods are all staged. First, a Grignard reagent is prepared at low temperature, and then it is reacted with a borate ester to deprotect and obtain L-BPA. Low temperature requires a certain amount of energy, staged preparation is time-consuming, and the operation is relatively complex. Summary of the Invention

[0006] One object of the present invention is to provide a method for preparing dihydroxyboronylphenylalanine; Another object of the present invention is to provide a method for preparing an intermediate for preparing dihydroxyboronylalanine.

[0007] To achieve the above objectives, in one aspect, the present invention provides a method for preparing the compound shown in formula (I): The method includes mixing 4-halo-Boc-L-phenylalanine of formula (II) with alkyl borate ester, and then adding Grignard reagent to react and obtain compound (I). The temperature of the reaction system when adding Grignard reagent is -30~30℃, and the amount of alkyl borate ester is 0.9-3.0 eq of compound (II).

[0008] According to some specific embodiments of the present invention, X is Br or I.

[0009] According to some specific embodiments of the present invention, the alkyl group of the alkyl borate ester is C10. 1-6 alkyl.

[0010] According to some specific embodiments of the present invention, the alkyl borate ester is selected from one or more combinations of tri-n-butyl borate, triisobutyl borate, trimethyl borate, triisopropyl borate, and triethyl borate.

[0011] According to some specific embodiments of the present invention, the alkyl borate ester is selected from... 10 Tributyl borate, 10 Triisobutyl borate, 10 Trimethyl borate, 10 Triisopropyl borate and 10 One or more of triethyl borate.

[0012] According to some specific embodiments of the present invention, the Grignard reagent is isopropyl magnesium chloride, isopropyl magnesium chloride lithium chloride, or isopropyl magnesium bromide.

[0013] According to some specific embodiments of the present invention, the Grignard reagent is isopropyl magnesium chloride.

[0014] According to some specific embodiments of the present invention, the Grignard reagent is added dropwise.

[0015] According to some specific embodiments of the present invention, the Grignard reagent is added over a time of 10-30 minutes.

[0016] According to some specific embodiments of the present invention, the amount of Grignard reagent used is 5.0-8.0 eq of the compound of formula (II).

[0017] According to some specific embodiments of the present invention, the amount of Grignard reagent used is 6.0-8.0 eq of the compound of formula (II).

[0018] According to some specific embodiments of the present invention, the amount of Grignard reagent used is 7.0-8.0 eq of the compound of formula (II).

[0019] According to some specific embodiments of the present invention, the temperature of the reaction system is -10~10℃ when the Grignard reagent is added.

[0020] According to some specific embodiments of the present invention, the temperature of the reaction system is -5~5°C when the Grignard reagent is added.

[0021] According to some specific embodiments of the present invention, the method includes adding a Grignard reagent and maintaining the reaction system at the temperature at which the Grignard reagent was added, thereby obtaining a compound of formula (I).

[0022] According to some specific embodiments of the present invention, the method includes mixing 4-halo-Boc-L-phenylalanine of formula (II) with an alkyl ester of borate in an organic solvent, and then adding a Grignard reagent to react and obtain compound (I); wherein the organic solvent is selected from anhydrous tetrahydrofuran or anhydrous 2-methyltetrahydrofuran.

[0023] According to some specific embodiments of the present invention, the volume of the organic solvent used is 3-5 times the mass of 4-halo-Boc-L-phenylalanine.

[0024] According to some specific embodiments of the present invention, the volume of the organic solvent used is 4-5 times the mass of 4-halo-Boc-L-phenylalanine.

[0025] According to some specific embodiments of the present invention, the method includes dissolving 4-halo-Boc-L-phenylalanine in an organic solvent, then adding an alkyl borate ester under stirring, and then adding a Grignard reagent.

[0026] According to some specific embodiments of the present invention, the amount of alkyl borate ester used is 1.0-3.0 eq of the compound of formula (II).

[0027] According to some specific embodiments of the present invention, the amount of alkyl borate ester used is 1.3-3 eq of the compound of formula (II).

[0028] According to some specific embodiments of the present invention, the amount of alkyl borate ester used is 1.3-1.5 eq of the compound of formula (II).

[0029] According to some specific embodiments of the present invention, the amount of alkyl borate ester used is 2.1eq, 2.2eq, 2.3eq, 2.4eq, 2.5eq, 2.6eq, 2.7eq, 2.8eq or 2.9eq of the compound of formula (II).

[0030] According to some specific embodiments of the present invention, after the Grignard reagent is added, the reaction time of the system is 2-8 hours.

[0031] According to some specific embodiments of the present invention, after the Grignard reagent is completely added, the reaction time of the system is 2-6 hours.

[0032] According to some specific embodiments of the present invention, after the Grignard reagent is completely added, the reaction time of the system is 2-4 hours.

[0033] According to some specific embodiments of the present invention, after the Grignard reagent is added, the reaction time of the system is 2-3 hours.

[0034] According to some specific embodiments of the present invention, the reaction time of the system after the Grignard reagent is completely added is 2 hours.

[0035] According to some specific embodiments of the present invention, after the reaction is completed, the step of adjusting the pH of the reaction solution to 3-4 is further included.

[0036] According to some specific embodiments of the present invention, after the reaction is completed, the reaction solution is further further comprising the steps of adjusting the pH of the reaction solution to 3-4, adjusting the pH of the reaction solution to 12-13, and adjusting the pH of the separated aqueous phase to 3-4, and finally obtaining compound (I).

[0037] According to some specific embodiments of the present invention, after the reaction is completed, the reaction further includes the steps of adjusting the pH of the reaction solution to 3-4 and separating the organic phase, adjusting the pH of the obtained organic phase to 12-13 and separating the aqueous phase, and adjusting the pH of the separated aqueous phase to 3-4, finally obtaining the compound of formula (I).

[0038] According to some specific embodiments of the present invention, after the reaction is completed, the following steps are further included: adjusting the pH of the reaction solution to 3-4, separating the organic phase, adjusting the pH of the organic phase to 12-13 and separating the aqueous phase, washing the separated aqueous phase with an organic solvent, adjusting the pH of the washed aqueous phase to 3-4, extracting it with an organic solvent, and adding an antisolvent to crystallize and obtain the compound of formula (I).

[0039] According to some specific embodiments of the present invention, after the reaction is completed, the pH of the reaction solution is adjusted to 3-4 using an aqueous acid solution.

[0040] According to some specific embodiments of the present invention, after the reaction is completed, the pH of the reaction solution is adjusted to 3-4 using an aqueous solution of a 4N-6N acid.

[0041] According to some specific embodiments of the present invention, the aqueous solution of the acid is selected from one or more of aqueous solutions of hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof.

[0042] According to some specific embodiments of the present invention, the pH of the separated aqueous phase is adjusted to 3-4 using a 4N-6N hydrochloric acid aqueous solution.

[0043] According to some specific embodiments of the present invention, the pH of the organic phase is adjusted to 12-13 by adding an aqueous solution of alkali.

[0044] According to some specific embodiments of the present invention, the alkali is an inorganic alkali.

[0045] According to some specific embodiments of the present invention, the alkali is selected from one or a mixture of two of sodium hydroxide and potassium hydroxide.

[0046] According to some specific embodiments of the present invention, the concentration of the alkali in the aqueous solution of the alkali is 1-3N; preferably 2N.

[0047] According to some specific embodiments of the present invention, the organic solvent used for washing the aqueous phase is selected from solvents that are immiscible with water.

[0048] According to some specific embodiments of the present invention, the organic solvent used for washing the aqueous phase is selected from one or more combinations of n-butanol, toluene, and methyl tert-butyl ether.

[0049] According to some specific embodiments of the present invention, the organic solvent used for extraction is selected from one or more combinations of ethyl acetate, isopropyl acetate, and dichloromethane.

[0050] According to some specific embodiments of the present invention, after the reaction is completed, the following steps are further included: quenching with water, adjusting the pH to 3-4 with hydrochloric acid aqueous solution, separating the organic phase, adding an aqueous solution of alkali to the organic phase and separating the aqueous phase, washing the separated aqueous phase with an organic solvent, adjusting the pH of the washed aqueous phase to 3-4 with hydrochloric acid aqueous solution, extracting with an organic solvent, and adding an antisolvent to crystallize and obtain compound of formula (I).

[0051] According to some specific embodiments of the present invention, the antisolvent is selected from one or more combinations of n-heptane, n-hexane, and cyclohexane.

[0052] According to some specific embodiments of the present invention, after adding the anti-solvent, the temperature is lowered to 0-10°C to crystallize, and then filtered.

[0053] According to some specific embodiments of the present invention, after adding the anti-solvent, stirring is continued for 1-3 hours, the temperature is lowered to 0-10°C and stirring is continued for 1-3 hours, and then the mixture is filtered.

[0054] According to some specific embodiments of the present invention, after adding the antisolvent, stirring is continued for 1.5-2 hours, then cooled to 0-10°C and stirring is continued for 1.5-2 hours, followed by filtration.

[0055] According to some specific embodiments of the present invention, the B element in formula (I) is a 10B isotope.

[0056] Furthermore, the present invention provides a method for preparing dihydroxyboronylphenylalanine of formula (III). (III) The method includes the steps of preparing the compound shown in formula (II) using the method described in any of the preceding claims of the present invention, and then preparing the dihydroxyboronylalanine shown in formula (III) using the compound shown in formula (II) as a raw material.

[0057] According to some specific embodiments of the present invention, the step of preparing dihydroxyboronylphenylalanine of formula (III) from the compound shown in formula (II) includes hydrolyzing the compound shown in formula (II) to obtain dihydroxyboronylphenylalanine of formula (III).

[0058] According to some specific embodiments of the present invention, the reaction temperature of the hydrolysis is 20-95°C.

[0059] According to some specific embodiments of the present invention, the hydrolysis is carried out under acidic conditions.

[0060] According to some specific embodiments of the present invention, the hydrolysis is carried out in a 2M-6M hydrochloric acid aqueous solution.

[0061] According to some specific embodiments of the present invention, the hydrolysis is carried out in a 2M aqueous solution of hydrochloric acid at a reaction temperature of 85-95°C.

[0062] According to some specific embodiments of the present invention, the hydrolysis is carried out in a 6M aqueous hydrochloric acid solution at a reaction temperature of 40-60°C.

[0063] According to some specific embodiments of the present invention, the hydrolysis is carried out in a dichloromethane solution of 30%-70% (preferably 50%) trifluoroacetic acid at a temperature of 20-30°C.

[0064] According to some specific embodiments of the present invention, the B element in formula (III) is a 10B isotope.

[0065] According to some specific embodiments of the present invention, the B element is a 10B isotope.

[0066] In summary, this invention provides a method for preparing dihydroxyboronylphenylalanine and its intermediates. The method of this invention has the following advantages: This invention can further optimize commercially viable production processes, improve safety, and reduce costs. Market research shows that the price of high-abundance (99%) boron-10 acid is approximately RMB 100,000 / kg. This invention can reduce the amount of boron ester used, which will greatly reduce material input costs and help control the cost of raw materials.

[0067] The in-situ preparation method for synthesizing L-BPA simplifies the operation, eliminates the need for an ultra-low temperature environment, reduces energy consumption, shortens the reaction process, and is more conducive to industrial production. Detailed Implementation

[0068] The following detailed embodiments illustrate the implementation process and beneficial effects of the present invention, aiming to help readers better understand the essence and characteristics of the present invention, and are not intended to limit the scope of implementation of this case.

[0069] Example 1: Preparation of L-BPA Under a nitrogen atmosphere, 2.0 g of 4-iodo-Boc-L-phenylalanine was added to a 250 mL three-necked flask and dissolved in anhydrous THF (5V). Then, 1.5 eq. of tri-n-butyl borate was added with stirring, and the temperature of the reaction system was controlled at 0±5 °C. o Within the range of C, add a tetrahydrofuran solution of isopropyl magnesium chloride and lithium chloride (1.3M, 8 eq.) dropwise over 30 min, then maintain the reaction temperature for 5 hours. Take samples for testing; if the starting material is completely converted (or NMT 5 Area%), maintain the temperature at -5 to 0°C. o C. Quench with 5 volumes of water (based on substrate), adjust pH to 3-4 with 6N hydrochloric acid, allow to stand and separate, extract the aqueous phase once with ethyl acetate, combine the organic phases, concentrate the organic phase, and separate by column chromatography (DCM / MeOH (V / V) = 50 / 1 to 20 / 1) to give a pale yellow solid with an in-situ yield of 75%. 1 H NMR (DMSO-d6) δ 12.58 (s, 1H), 7.94 (s, 2H), 7.70-7.68 (d, J =8Hz, 2H), 7.21-7.19 (d, J = 8Hz, 2H), 7.08-7.06 (d, J =8Hz, 1H), 4.11-4.06 (m, 1H), 3.03-2.99 (dd, J =4Hz, 8Hz1H), 2.85-2.79 (dd, J =4Hz, 8Hz 1H), 1.32 (s,9H). MS(ESI, pos.) m / z calcd forC 14 H 20 BNO6 ([M+H)) + ): 310.10.

[0070] The above-mentioned pale yellow solid was added to 10 ml of 2M hydrochloric acid. The reaction solution was slowly heated to 90±5℃ and reacted for 2 h until intermediate C was completely reacted. The temperature was then lowered to 45±5℃, and sodium hydroxide solution (2M) was added dropwise to adjust the pH to 4-5. The temperature was then lowered to 20-30℃ and stirred for 0.5 h. The mixture was filtered, washed with 2V of purified water, and the filter cake was dried under vacuum at 65±5℃ for 4 h. 535 mg of off-white solid with a purity of 94.6% was obtained, with an overall yield of 50% for both steps. 1H NMR (DMSO-d6 + a few drops of CF3COOH) δ 12.58 (s, 1H), 7.94 (s, 2H), 7.70-7.68 (d, J =8Hz, 2H), 7.21-7.19 (d, J =8Hz, 2H), 4.11-4.06 (m, 1H), 3.03-2.99 (dd, J =4Hz, 8Hz1H), 2.85-2.79(dd, J =4Hz, 8Hz1H). MS(ESI, pos.) m / z calcd for C9H 12 BNO4 ([M+H) + ): 210.10.

[0071] Example 2: Preparation of key intermediates for L-BPA Under a nitrogen atmosphere, 2.0 g of 4-iodo-Boc-L-phenylalanine was added to a 250 mL three-necked flask and dissolved in anhydrous THF (5V). Then, 1.5 eq. of tri-n-butyl borate was added with stirring, and the temperature of the reaction system was controlled at 0±5 °C. o Within the temperature range C, add a 1.3M, 5 eq. solution of isopropyl magnesium chloride in tetrahydrofuran dropwise over 30 minutes, then maintain the reaction temperature for 5 hours. Take a sample for testing; the remaining raw material should not exceed 10%. Control the temperature to -5 to 0°C. o C. Quench with 5 volumes of water (based on substrate), adjust pH to 3-4 with 6N hydrochloric acid, allow to stand and separate, extract the aqueous phase once with ethyl acetate, combine the organic phases, concentrate the organic phase, and separate by column chromatography (DCM / MeOH (V / V) = 50 / 1 to 20 / 1) to obtain a pale yellow solid with a purity of 93.8% and a yield of 40%.

[0072] Example 3: Preparation of key intermediates for L-BPA Under a nitrogen atmosphere, 5.0 g of 4-iodo-Boc-L-phenylalanine was added to a 250 mL three-necked flask and dissolved in anhydrous THF (5V). Then, 1.5 eq. of tri-n-butyl borate was added with stirring, and the reaction temperature was controlled at 0±5 °C. o Within the range of C, add a 1.3M tetrahydrofuran solution of isopropyl magnesium chloride dropwise over 30 minutes, then maintain the reaction temperature for 2 hours. Take a sample for analysis; the starting material should be completely converted (or NMT 5 Area%). Control the temperature at -5 to 0°C. o C. Quench with 5 volumes of water (based on substrate), adjust pH to 3-4 with 6M hydrochloric acid, allow to stand and separate. Extract the aqueous phase once with ethyl acetate, combine the organic phases, and reflux the organic phase at 0-10 °C.o Slowly add 2M NaOH aq. to the pH range of 12.1-12.6, allow to stand, and separate the liquids. Collect the aqueous phase. Wash the aqueous phase once with n-butanol, and adjust the pH of the washed aqueous phase to 3-4 with 2M hydrochloric acid aqueous solution. Extract twice with EtOAc, combine the organic phases, and rotary evaporate ethyl acetate under reduced pressure until viscous. Add 2.5V n-heptane, stir and slurry at 20-30℃ for 2 hours, then cool to 0-10℃ and slurry for 2 hours. Filter under nitrogen protection and wash with n-heptane. Dry the filter cake in a vacuum drying oven at 65±5℃ for 3 hours. Obtain crude dihydroxyboron-Boc-L-phenylalanine (yield 60%, purity 98.3%). Add the crude product to a mixed solution of 3V purified water and 3V acetonitrile, heat to reflux, and then reflux until clear. First, the temperature was lowered to 40-50℃ using circulating water, then switched to refrigerant and lowered to 20-30℃, with stirring for 2 hours; then lowered to 0-10℃ and stirred for 2 hours; filtered, and washed with a mixture of acetonitrile and water. The filter cake was vacuum dried at 65±5℃ for 4 hours to obtain dihydroxyboron-Boc-L-phenylalanine with a purity of 98.7% and a yield of 56.7%.

[0073] Example 4: Preparation of key intermediates for L-BPA Under a nitrogen atmosphere, 50.0 g of 4-iodo-Boc-L-phenylalanine was added to a 2.5 L three-necked flask and dissolved in anhydrous THF (5V). Then, 1.5 eq. of tri-n-butyl borate was added with stirring, and the temperature of the reaction system was controlled at 0 ± 5 °C. o Within the temperature range C, add a 1.3M, 8 eq. solution of isopropyl magnesium chloride in tetrahydrofuran dropwise over 30 minutes, then maintain the reaction temperature for 2 hours. Samples are taken for analysis; the raw material conversion is complete. Temperature is controlled at -5 to -0. o C. Quench with 5 volumes of water (based on substrate), adjust pH to 3-4 with 6M hydrochloric acid, allow to stand and separate. Extract the aqueous phase once with ethyl acetate, combine the organic phases, and reflux the organic phase at 0-10 °C. oSlowly add 2M NaOH aq. to the pH range of 12.1-12.6, allow to stand, and separate the liquids. Collect the aqueous phase. Wash the aqueous phase once with n-butanol, and adjust the pH of the washed aqueous phase to 3-4 with 2M hydrochloric acid aqueous solution. Extract twice with EtOAc, combine the organic phases, and rotary evaporate ethyl acetate under reduced pressure until viscous. Add 2.5V n-heptane, stir and slurry at 20-30℃ for 2 hours, then cool to 0-10℃ and slurry for 2 hours. Filter under nitrogen protection and wash with n-heptane. Dry the filter cake in a vacuum drying oven at 65±5℃ for 3 hours. Obtain crude dihydroxyboron-Boc-L-phenylalanine (yield 75.2%, purity 97.5%). Add the crude dihydroxyboron-Boc-L-phenylalanine to a mixed solution of 3V purified water and 3V acetonitrile, heat to reflux, and then reflux until clear. First, the temperature was lowered to 40-50℃ using circulating water, then switched to refrigerant and lowered to 20-30℃, with stirring for 2 hours; then lowered to 0-10℃ and stirred for 2 hours; filtered, and washed with a mixture of acetonitrile and water. The filter cake was vacuum dried at 65±5℃ for 4 hours to obtain dihydroxyboron-Boc-L-phenylalanine with a purity of 98.9% and a yield of 70%.

[0074] Example 5: Study on different dosages of tributyl borate The synthesis method is the same as in Example 4, except that the amount of tributyl borate added is different. Example 6: Study of different reaction times The synthesis method is the same as in Example 4, except for the reaction time. Example 7: Study on reaction temperature The synthesis method is the same as in Example 4, except that the temperature at which the Grignard reagent is added (i.e., the reaction temperature) is different. Comparative Example 1 This comparative experiment simultaneously and in parallel carried out two feeding methods, repeating the methods of patent CN116113636 and the method of embodiment 4 of this invention. The specific parameters and results are shown in Tables 1 and 2 below: Table 1 Table 2 For the comparative example: "Temperature 1" refers to the temperature at which the Grignard reagent is prepared in the staged method, and "Temperature 2" refers to the temperature at which the borate ester is added and the reaction temperature.

[0075] The iodinated derivative is 4-iodo-Boc-L-phenylalanine; the borate ester is tributyl borate; and the Grignard reagent is isopropyl magnesium chloride and lithium chloride.

[0076] The comparative example, described in Stella's patent CN116113636, involves a step-by-step preparation process: first, a Grignard reagent is prepared, followed by boric acid. The preparation methods for items 1-3 are in-situ preparations.

[0077] The comparative experimental data in Tables 1 and 2 above show that: when conducting experiments with two feeding methods simultaneously and in parallel, repeating the method in CN116113636 did not yield ideal experimental results. After 2.5 hours, the remaining iodide was 26.83%, and the crude product yield was approximately 40%. However, using the in-situ preparation method of this invention, even with the equivalent of borate ester reduced to 1.5 eq., a better yield and purity can still be obtained, reducing the feeding cost and significantly shortening the reaction process.

[0078] Comparative Example 2 This comparative experiment simultaneously and in parallel carried out experiments with two feeding methods, repeating the methods of patent CN110498810 and Example 4 of this invention. The specific parameters and results are shown in Tables 3 and 4 below: Table 3 Table 4 For the comparative example: "Temperature 1" refers to the temperature at which the Grignard reagent is prepared in the staged method, and "Temperature 2" refers to the temperature at which the borate ester is added and the reaction temperature.

[0079] The iodinated derivative in Table 3 is 4-iodo-Boc-L-phenylalanine; the borate ester is tributyl borate; and the Grignard reagent is isopropyl magnesium chloride.

[0080] The comparative example, Dongyangguang Patent CN110498810, describes a step-by-step preparation method, first preparing a Grignard reagent and then preparing boric acid. The preparation methods for items 1 to 10 are in-situ preparations.

[0081] The comparative experimental data in Tables 3 and 4 above show that: when the experiments with two feeding methods were carried out simultaneously and in parallel, using 6.0 eq. of Grignard reagent in the method of CN110498810, and controlled for 22 hours, approximately 20% of the raw material remained, and the crude product yield was approximately 38%. However, the method of this invention, by further reducing the amount of borate ester to 1.0 eq. or even 0.9 eq, still achieves the conversion of the raw material. The separated yield and purity after treatment are higher. In terms of reaction time, the staged method of CN110498810 takes more than 22 hours, while the reaction rate of the method of this invention can be controlled within 2-4 hours. After scaling up to a scale of 50g, the purity can be maintained stably, and the yield is significantly improved. Existing data shows that scaling up is more conducive to improving the yield.

Claims

1. A method for preparing the compound shown in formula (I): in, The method includes mixing 4-halo-Boc-L-phenylalanine of formula (II) with alkyl borate ester, and then adding Grignard reagent to react and obtain compound (I). The temperature of the reaction system when adding Grignard reagent is -30~30℃, and the amount of alkyl borate ester is 0.9-3.0 eq of compound (II).

2. The method according to claim 1, wherein, X is either Br or I.

3. The method according to claim 1 or 2, wherein, The alkyl group of the borate alkyl ester is C. 1-6 Alkyl group; preferably, the alkyl borate ester is selected from one or more combinations of tri-n-butyl borate, triisobutyl borate, trimethyl borate, triisopropyl borate and triethyl borate.

4. The method according to any one of claims 1 to 3, wherein, The Grignard reagent is isopropyl magnesium chloride, isopropyl magnesium chloride lithium chloride, or isopropyl magnesium bromide, preferably isopropyl magnesium chloride.

5. The method according to any one of claims 1 to 4, wherein, Grignard reagent is added dropwise over a period of 10-30 minutes.

6. The method according to any one of claims 1 to 5, wherein, The amount of Grignard reagent used is 5.0-8.0 eq of the compound of formula (II), preferably 6.0-8.0 eq, and more preferably 7.0-8.0 eq.

7. The method according to any one of claims 1 to 6, wherein, When the Grignard reagent is added, the temperature of the reaction system is -10~10℃, more preferably -5~5℃.

8. The method according to any one of claims 1 to 7, characterized in that... in, The amount of alkyl borate ester used is 1.0-3 eq of the compound of formula (II), more preferably 1.3-3 eq, and even more preferably 1.3-1.5 eq.

9. The method according to any one of claims 1 to 8, wherein, After the Grignard reagent is added, the reaction time of the system is 2-8 hours, preferably 2-4 hours, and more preferably 2-3 hours.

10. The method according to any one of claims 1 to 9, wherein, After the reaction was completed, the pH was adjusted to 3-4 with hydrochloric acid aqueous solution to remove the aqueous phase. An aqueous solution of alkali was added to the organic phase and the aqueous phase was separated. The separated aqueous phase was washed with an organic solvent. After the pH of the washed aqueous phase was adjusted to 3-4, it was extracted with an organic solvent and crystallized with an antisolvent to obtain compound (I).

11. A method for preparing dihydroxyboronylphenylalanine of formula (III), (III) in, The method includes the steps of preparing the compound of formula (II) using the method of any one of claims 1-10, and then preparing the dihydroxyboronylalanine of formula (III) using the compound of formula (II) as a raw material.

12. The method according to claim 11, wherein the step of preparing dihydroxyboronylphenylalanine of formula (III) from the compound shown in formula (II) comprises hydrolyzing the compound shown in formula (II) to obtain dihydroxyboronylphenylalanine of formula (III).

13. The method according to claim 1 or 11, wherein the B element refers to the 10B isotope.

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