Method for preparing Boc-His (Trt)-Aib-OH

Abstract

The invention relates to the field of organic synthesis, in particular to a method for preparing Boc-His (Trt)-Aib-OH, which comprises the following steps: 1, adding 2-aminoisobutyric acid, a solvent and organic alkali into a reaction container, cooling, dropwise adding a silicon protection reagent, and heating for reaction after adding to obtain a 2-aminoisobutyric acid solution protected by bis (trialkylsilyl); 2, dissolving Boc-His (Trt)-OH and an activating agent in a solvent, dropwise adding a coupling reagent, and after the reaction is finished, obtaining a Boc-His (Trt)-OH activated ester solution which is directly used for the next step; and step 3, cooling the Boc-His (Trt)-OH activated ester solution obtained in the step 2, dropwise adding the bis-trialkylsilyl protected 2-aminoisobutyric acid solution obtained in the step 1, dropwise adding organic alkali after the dropwise adding is completed, slowly dropwise adding a quenching reagent for quenching after the reaction is completed, carrying out post-treatment on the reaction solution to obtain a Boc-His (Trt)-Aib-OH crude product, and drying to obtain the Boc-His (Trt)-Aib-OH. And crystallizing the crude product to obtain a pure product of Boc-His (Trt)-Aib-OH. According to the method, purification of an intermediate is avoided, the reaction process is relatively well controlled, and high-quality Fmoc-Ser (tBu)-OH can be efficiently and stably prepared.

Description

Technical Field

[0001] The invention relates to the field of organic chemical synthesis, and in particular to a method for preparing Boc-His(Trt)-Aib-OH. Background Art

[0002] Boc-His(Trt)-Aib-OH, Chinese name: N-Boc-N′-triphenylmethyl-L-histidyl-2-methylalanine

[0003] Molecular formula C 34 H 38 N4O5, molecular weight: 582.70.

[0004] Chemical structure:

[0005]

[0006] Boc-His(Trt)-Aib-OH is a dipeptide with two protective groups, wherein the two amino acids are histidine and 2-aminoisobutyric acid, and the two protective groups on histidine are Boc and Trt. Boc-His(Trt)-Aib-OH is an important intermediate for synthesizing peptides, especially for synthesizing peptides by solid phase method, and is often used in the synthesis of various drugs, especially in the synthesis of semaglutide.

[0007] US invention patent US2017 / 0008944A1 discloses a method for preparing Boc-His(Trt)-Aib-OH. The method uses 2-aminoisobutyric acid benzyl ester hydrochloride as the starting material, and removes the benzyl group by Pd / C catalytic hydrogenation in the last step of the synthesis to obtain the final product Boc-His(Trt)-Aib-OH. The method requires the use of flammable and explosive hydrogen, which has a great safety hazard. In addition, the method uses Pd / C as a catalyst, which is expensive, which will lead to high production costs during production.

[0008] WO2023 / 012829A1 also reports another method for synthesizing Boc-His(Trt)-Aib-OH, which first synthesizes 2-aminoisobutyric acid methyl ester hydrochloride, uses 2-aminoisobutyric acid methyl ester hydrochloride as an intermediate and couples with protected histidine, and finally converts the methyl ester into carboxylic acid by saponification to obtain the final product. The purity of the final product reported in this method is 99.27%, which does not meet the standard of 99.5% purity of high-purity products.

[0009] The domestic and foreign markets have a large demand for Boc-His (Trt) -Aib-OH. The current domestic production methods of this compound still have problems such as high manufacturing costs and low purity of the obtained products. The production capacity cannot meet the needs of high-end drug synthesis. Therefore, how to optimize the production process of Boc-His (Trt) -Aib-OH, reduce production costs, and obtain high-purity products is an urgent problem to be solved. Summary of the invention

[0010] In order to overcome the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing Boc-His(Trt)-Aib-OH.

[0011] In order to solve the above problems, the technical solution provided by the present invention is as follows:

[0012] A method for preparing Boc-His(Trt)-Aib-OH comprises the following steps:

[0013] (1) adding 2-aminoisobutyric acid, a solvent and an organic base to a reaction vessel, dropping a silicon protection reagent while cooling, and heating the reaction after the addition is complete to obtain a bistrialkylsilyl-protected 2-aminoisobutyric acid solution;

[0014] (2) Dissolve Boc-His(Trt)-OH and the activation reagent in a solvent, add the coupling reagent dropwise, and after the reaction, obtain a Boc-His(Trt)-OH activated ester solution, which is directly used in the next step;

[0015] (3) cooling the activated ester solution of Boc-His(Trt)-OH obtained in the second step, adding dropwise the bistrialkylsilyl protected 2-aminoisobutyric acid solution obtained in the first step, adding dropwise an organic base after the addition is complete, slowly adding dropwise a quenching reagent after the reaction is completed for quenching, and the reaction solution is post-treated to obtain a crude product of Boc-His(Trt)-Aib-OH, and the crude product is crystallized to obtain a pure product of Boc-His(Trt)-Aib-OH;

[0016] The specific reaction formula is as follows:

[0017]

[0018] R1 is a C1-C3 alkyl group; R2 is a benzotriazolyl group, a 7-azabenzotriazolyl group, a succinimide group or a pentafluorophenyl group.

[0019] Preferably, the silicon protecting agent in step (1) is selected from trimethylsilyl chloride, triethylsilyl chloride, hexamethyldisilazane, hexamethyldisilazane or N,O-bis(trimethylsilyl)acetamide.

[0020] Preferably, the organic base in step (1) is selected from triethylamine, N,N-diisopropylethylamine, n-tributylamine, pyridine or DBU.

[0021] Preferably, the solvent in step (1) is selected from tetrahydrofuran, dichloromethane or ethylene glycol dimethyl ether. The amount of the solvent used is 3 to 10 times that of 2-aminoisobutyric acid.

[0022] Preferably, the molar ratio of 2-aminoisobutyric acid to silicon protective agent in step (1) is 1:1.5-2.5.

[0023] Preferably, the coupling reagent in step (2) is selected from DCC, DIC or EDCI.

[0024] Preferably, the activation reagent in step (2) is selected from HOBt, HOAt, HOSu or pentafluorophenol.

[0025] Preferably, the solvent in step (2) is selected from tetrahydrofuran, dichloromethane or ethylene glycol dimethyl ether. The amount of the solvent used is 3 to 10 times that of Boc-His(Trt)-OH.

[0026] Preferably, the organic base in step (3) is selected from triethylamine, N,N-diisopropylethylamine, n-tributylamine, pyridine and DBU.

[0027] Preferably, the quenching reagent in step (3) is water, methanol, ethanol or isopropanol.

[0028] Preferably, the molar ratio of the bistrialkylsilyl protected 2-aminoisobutyric acid to the activated ester of Boc-His(Trt)-OH in step (3) is 0.8 to 3.0:1, and the more preferred molar ratio is 2 to 3.0:1. The molar ratio of the organic base in step (3) to the Boc-His(Trt)-OH in step (2) is 0.8 to 2.0:1.

[0029] Preferably, the target product in step (3) is purified by recrystallization, and the solvent used for the recrystallization purification is ethanol, methanol, isopropanol, tetrahydrofuran, ethyl acetate, diethyl ether, isopropyl ether, methyl tert-butyl ether or petroleum ether.

[0030] If there is a conflict between the Chinese name and the structural formula of the compound in the present invention, the structural formula shall prevail, unless there is an obvious error in the structural formula.

[0031] The preparation method of Boc-His(Trt)-Aib-OH provided by the present invention can efficiently and stably synthesize high-quality Boc-His(Trt)-Aib-OH with a purity greater than 99.5% and a single impurity less than 0.1%, thereby avoiding the purification of intermediates, and the reaction process is relatively easy to control, and is suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the HNMR spectrum of Boc-His(Trt)-Aib-OH obtained in the specific implementation mode 1 of the present invention. DETAILED DESCRIPTION

[0033] The present invention is described below with reference to examples, but the present invention is not limited thereto. In the art, simple replacement or improvement made by technicians in the field to the present invention belongs to the technical solution protected by the present invention.

[0034] Embodiment 1:

[0035] 1. Synthesis of 2-aminoisobutyric acid protected by bis-silyl group

[0036] Add 400g of tetrahydrofuran to a dry and clean 1000mL reaction bottle, then add 50g of 2-aminoisobutyric acid (molecular weight 103.12g / mol, molar number 485mmol), 122g of triethylamine (molecular weight 101.19g / mol, molar number 1206mmol), cool to 15-20℃ in an ice-water bath, and drop 110.7g of trimethylchlorosilane (molecular weight 108.64g / mol, molar number 1019mmol) for 0.5 hours. After the addition is complete, heat the oil bath to 60℃ and keep the reaction for 5.0 hours until all the solids are dissolved, and the final reaction solution is a red clear solution. Cool the reaction solution to 25℃ and keep it in nitrogen for standby use.

[0037] 2. Synthesis of Boc-His(Trt)-OH activated ester

[0038] Add Boc-His(Trt)-OH 120.7g (molecular weight 497.60g / mol, molar number 242.5mmol), 1-hydroxybenzotriazole (HOBt) 36.0g (molecular weight 135.13g / mol, molar number 266.8mmol), and tetrahydrofuran 600g to a dry and clean 500mL reaction bottle, stir to dissolve the solid at 25℃, and cool to 15℃. Keep the internal temperature at 15-20℃, add dicyclohexylcarbodiimide (DCC) 60.0g (molecular weight 206.33g / mol, molar number 291mmol) in batches, keep the temperature at 15-20℃ after addition, continue to react for 0.5 hours, and naturally heat to room temperature (28-32℃) for 4 hours. HPLC control shows that Boc-His(Trt)-OH <0.5% and the reaction is over, and nitrogen protection is used for standby;

[0039] 3. Synthesis of Boc-His(Trt)-Aib-OH

[0040] The whole reaction solution of Boc-His (Trt) -OH activated ester obtained in the second step was cooled to 5-10°C, and the 2-aminoisobutyric acid solution protected by the double silicon group obtained in the first step was slowly added under nitrogen protection and the internal temperature was maintained at 5-10°C, and then 49.1g of triethylamine (molecular weight 101.19g / mol, molar number 485mmol) was added. After the addition, the reaction was continued for 0.5 hours, and the temperature was naturally raised to room temperature (30°C ± 2) for 6 hours. The HPLC control showed that Boc-His (Trt) -OH activated ester <1.0% was over. Slowly add 200g of methanol to the reaction solution and stir for 2 hours. The reaction solution was concentrated under reduced pressure in a 40-45°C water bath until no fraction was distilled out. The residual oil was dissolved by adding 800g of ethyl acetate, and then washed twice with 400g of 10% saline solution. The organic phase was concentrated under reduced pressure to dryness to obtain a residual oil. The residual oil was recrystallized with 500 g of ethyl acetate / petroleum ether (1:1) to obtain a wet product, which was dried in vacuo at 50°C to obtain 115.9 g of a dry product with a yield of 82.0%, HPLC ≥ 99.5%, and a maximum single impurity ≤ 0.1%.

[0041] Embodiment 2:

[0042] 1. Synthesis of 2-aminoisobutyric acid protected by bis-silyl group

[0043] Add 400g of tetrahydrofuran to a dry and clean 1000mL reaction bottle, then add 50g of 2-aminoisobutyric acid (molecular weight 103.12g / mol, molar number 485mmol), 98.2g of triethylamine (molecular weight 101.19g / mol, molar number 970mmol), cool to 15-20℃ in an ice-water bath, and drop 105.4g of trimethylsilyl chloride (molecular weight 108.64g / mol, molar number 970mmol) for 0.5 hours. After the addition is complete, heat the oil bath to 60℃ and keep the reaction for 5.0 hours until all the solids are dissolved, and the final reaction solution is a red clear solution. Cool the reaction solution to 25℃ and keep it in nitrogen for standby use.

[0044] 2. Synthesis of Boc-His(Trt)-OH activated ester

[0045] Add Boc-His(Trt)-OH 120.7g (molecular weight 497.60g / mol, molar number 242.5mmol), 1-hydroxybenzotriazole (HOBt) 34.4g (molecular weight 135.13g / mol, molar number 254.6mmol), and tetrahydrofuran 600g to a dry and clean 500mL reaction bottle, stir to dissolve the solid at 25℃, and cool to 15℃. Keep the internal temperature at 15-20℃, add dicyclohexylcarbodiimide (DCC) 55.0g (molecular weight 206.33g / mol, molar number 266.8mmol) in batches, keep the temperature at 15-20℃ after addition, continue to react for 0.5 hours, and naturally heat to room temperature (28-32℃) for 4 hours. HPLC control shows that Boc-His(Trt)-OH <0.5% and the reaction is over, and nitrogen protection is used for standby;

[0046] 3. Synthesis of Boc-His(Trt)-Aib-OH

[0047] The whole reaction solution of Boc-His (Trt) -OH activated ester obtained in the second step was cooled to 5-10°C, and the 2-aminoisobutyric acid solution protected by the double silicon group obtained in the first step was slowly added under nitrogen protection and the internal temperature was maintained at 5-10°C, and then 49.1g of triethylamine (molecular weight 101.19g / mol, molar number 485mmol) was added. After the addition, the reaction was continued for 0.5 hours, and the temperature was naturally raised to room temperature (30°C ± 2) for 6 hours. The HPLC control showed that Boc-His (Trt) -OH activated ester <1.0% was over. Slowly add 200g of methanol to the reaction solution and stir for 2 hours. The reaction solution was concentrated under reduced pressure in a 40-45°C water bath until no fraction was distilled out. The residual oil was dissolved by adding 800g of ethyl acetate, and then washed twice with 400g of 10% saline solution. The organic phase was concentrated under reduced pressure to dryness to obtain a residual oil. The residual oil was recrystallized with 500g ethyl acetate / petroleum ether (1:1) to obtain a wet product. The wet product was vacuum dried at 50°C to obtain 119.0g of dry product, with a yield of 84.2%, HPLC ≥ 99.5%, and a maximum single impurity

[0048] ≤0.1%.

[0049] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing Boc-His(Trt)-Aib-OH, characterized in that: The steps include: (1) adding 2-aminoisobutyric acid, a solvent and an organic base to a reaction vessel, dropping a silicon protection reagent while cooling, and heating the reaction after the addition is complete to obtain a bistrialkylsilyl-protected 2-aminoisobutyric acid solution; (2) Dissolve Boc-His(Trt)-OH and the activation reagent in a solvent, add the coupling reagent dropwise, and after the reaction, obtain a Boc-His(Trt)-OH activated ester solution, which is directly used in the next step; (3) cooling the activated ester solution of Boc-His(Trt)-OH obtained in the second step, adding dropwise the bistrialkylsilyl protected 2-aminoisobutyric acid solution obtained in the first step, adding dropwise an organic base after the addition is complete, slowly adding dropwise a quenching reagent after the reaction is completed for quenching, and the reaction solution is post-treated to obtain a crude product of Boc-His(Trt)-Aib-OH, and the crude product is crystallized to obtain a pure product of Boc-His(Trt)-Aib-OH; The specific reaction formula is as follows: R1 is a C1-C3 alkyl group; R2 is a benzotriazolyl group, a 7-azabenzotriazolyl group, a succinimide group or a pentafluorophenyl group.

2. The method according to claim 1, characterized in that The silicon protecting agent in step (1) is selected from trimethylsilyl chloride, triethylsilyl chloride, hexamethyldisilazane, hexamethyldisilazane or N,O-bis(trimethylsilyl)acetamide.

3. The method according to claim 1, characterized in that The organic base in step (1) is selected from triethylamine, N,N-diisopropylethylamine, n-tributylamine, pyridine or DBU.

4. The method according to claim 1, characterized in that The solvent in step (1) is selected from tetrahydrofuran, dichloromethane or ethylene glycol dimethyl ether; the amount of the solvent used is 3 to 10 times the mass of 2-aminoisobutyric acid.

5. The method according to claim 1, characterized in that The molar ratio of 2-aminoisobutyric acid to silicon protective agent in step (1) is 1:1.5-2.5, the molar ratio of 2-aminoisobutyric acid to organic base is 1:1.5-2.5, the cooling temperature in step (1) is 15-20°C, and the heating temperature is 55-60°C.

6. The method according to claim 1, characterized in that The coupling reagent in step (2) is selected from DCC, DIC or EDCI.

7. The method according to claim 1, characterized in that The activation reagent in step (2) is selected from HOBt, HOAt, HOSu or pentafluorophenol.

8. The method according to claim 1, characterized in that The solvent in step (2) is selected from tetrahydrofuran, dichloromethane or ethylene glycol dimethyl ether; the amount of the solvent is 3 to 10 times the mass of Boc-His(Trt)-OH, and the molar ratio of Boc-His(Trt)-OH to the activation reagent and the coupling reagent is 1:1.0 to 1.2:1.0 to 1.

5.

9. The method according to claim 1, characterized in that The organic base in step (3) is selected from triethylamine, N,N-diisopropylethylamine, n-tributylamine, pyridine and DBU; the molar ratio of the bistrialkylsilyl-protected 2-aminoisobutyric acid in step (3) to Boc-His(Trt)-OH in step (2) is 0.8-3.0:1, and the cooling temperature in step (3) is 5-10°C; the molar ratio of the organic base in step (3) to Boc-His(Trt)-OH in step (2) is 0.8-2.0:

1.

10. The method according to claim 1, characterized in that The quenching reagent in step (3) is water, methanol, ethanol or isopropanol; the crystallization is specifically: the crude product of Boc-His(Trt)-Aib-OH is purified by recrystallization, and the solvent used for the recrystallization purification is one or more of ethanol, methanol, isopropanol, tetrahydrofuran, ethyl acetate, ether, isopropyl ether, methyl tert-butyl ether or petroleum ether.

Images