Synthesis method of chiral Fmoc-alpha-methyl high phenylalanine

Abstract

The invention relates to a synthesis method of chiral Fmoc-a-methyl high phenylalanine. The method mainly solves the technical problems of long reaction steps, harsh conditions, high cost and unsuitability for large-scale production in the existing synthesis method. The method comprises the following steps: (1) reacting L-high phenylalanine ethyl ester hydrochloride with benzophenoneimine in dichloromethane to obtain a compound 1; (2) reacting with methyl iodide in tetrahydrofuran under the action of potassium tert-butoxide to obtain a compound 2; (3) hydrolyzing in diluted hydrochloric acid and dichloromethane to obtain a compound 3; (4) reacting the compound 3 with phenylacetyl chloride in tetrahydrofuran in triethylamine to obtain a compound 4; (5) hydrolyzing in a sodium hydroxide aqueous solution and methanol to obtain a compound 5; (6) synthesizing a chiral pure compound 6 and a chiral pure compound 7 by using immobilized penicillin G acylase; (7) carrying out Fmoc-protection on the compound 6 to obtain Fmoc-a-methyl-L-homophenylalanine; and (8) hydrolyzing phenylacetyl by using hydrochloric acid, and carrying out Fmoc protection to obtain Fmoc-a-methyl-D-homophenylalanine.

Description

Technical Field

[0001] The invention relates to a method for synthesizing chiral Fmoc-a-methyl homophenylalanine. Chiral Fmoc-a-methyl homophenylalanine is a raw material for synthesizing polypeptide drugs or medicines, and belongs to the technical field of drug synthesis chemical industry. Background Art

[0002] Due to its structural rigidity and metabolic stability, a-methyl amino acids have received extensive attention in peptide drugs. Chirally pure Fmoc-a-methyl-L-homophenylalanine (CAS: 2079062-43-2) and Fmoc-a-methyl-D-homophenylalanine (CAS: 960060-25-7) can be used as raw materials for solid phase synthesis of peptide drugs and are widely used in peptide drug screening. The synthesis methods of these two compounds are currently reported in the literature. The European Journal of Organic Chemistry (2017, 4, 846-860, Martin Hennum et al.) disclosed a method for synthesizing Fmoc-a-methyl-L-homophenylalanine, which uses (R,E)-4-methyl-6-phenyl-3-hexene-2-ol as a chiral raw material and undergoes rearrangement, oxidation and other steps to synthesize Fmoc-a-methyl-L-homophenylalanine. The raw materials of this method are not easy to obtain, and ozone oxidation is required. The reaction conditions are harsh and the operation is complicated, which is not suitable for industrial production.

[0003]

[0004] Fischer, Daniel F. et al. reported a method for synthesizing Fmoc-a-methyl-D-homophenylalanine in Angewandte Chemie-International Edition (2007, 40, 7704–7707) and Chemistry-A European Journal (2009, 35, 8722–8741). The method uses β-bromophenylethane as a raw material and undergoes three-step reactions to obtain 2,2,2-trifluoro-N-(4-methoxyphenyl)acetic acid-3-methyl-5-phenyl-2-pentenyl ester, which is rearranged enantioselectively under the catalysis of a chiral catalyst and silver trifluoromethanesulfonate to obtain a key chiral intermediate (R)-2,2,2-trifluoro-N-(4-methoxyphenyl)-N-(1-phenylethyl-1-methylallyl)acetamide, and then undergoes several steps of deprotection, protection and oxidation to obtain Fmoc-a-methyl-D-homophenylalanine. The method has a long route, harsh reaction conditions, and the chiral catalyst used in the enantioselective rearrangement reaction is very expensive. It also uses an ozone oxidation step, and is not suitable for large-scale production.

[0005] . Summary of the invention

[0006] The invention aims to provide a method for synthesizing chiral Fmoc-a-methylhomophenylalanine with mild reaction conditions and simple operation, which is suitable for large-scale production, and mainly solves the technical problems of long reaction steps, harsh conditions, complex operation and high cost in the current synthesis method.

[0007] The technical scheme of the present invention is as follows: A method for synthesizing chiral Fmoc-a-methyl homophenylalanine comprises the following steps: (1): L-homophenylalanine ethyl ester hydrochloride and benzophenone imine react in dichloromethane to obtain compound 1; (2): Compound 1 is reacted with iodomethane in tetrahydrofuran under the action of potassium tert-butoxide to obtain compound 2; (3): Compound 2 is hydrolyzed in dilute hydrochloric acid and dichloromethane to obtain compound 3; (4): In the presence of triethylamine, compound 3 reacts with phenylacetyl chloride in tetrahydrofuran to obtain compound 4; (5): Compound 4 is hydrolyzed in aqueous sodium hydroxide solution and methanol to obtain compound 5; (6): Compound 5 was used to stereoselectively synthesize chirally pure compounds 6 and 7 using immobilized penicillin G acylase; (7): Compound 6 was subjected to Fmoc-protection to obtain chirally pure Fmoc-a-methyl-L-homophenylalanine; (8): Compound 7 was hydrolyzed with 6 N hydrochloric acid to remove the phenylacetyl group, and then Fmoc protection was performed to obtain Fmoc-a-methyl-D-homophenylalanine. The reaction formula is as follows:

[0008] In the above reaction, the reaction temperature of step (2) is 20°C to 30°C, preferably 25°C, and the reaction time is 6-8 hours, preferably 7 hours. The concentration of the dilute hydrochloric acid in step (3) is 6 N hydrochloric acid, and the amount used is 3-5 times the amount of compound 2. The reaction temperature of step (6) is controlled at 36-38°C, and the reaction pH is controlled at 7-9.

[0009] Beneficial effects of the present invention: The present invention has the advantages of high yield, low cost, simple operation and purification, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is the mass spectrum of Fmoc-a-methyl-L-homophenylalanine of the present invention.

[0011] Figure 2 It is the mass spectrum of Fmoc-a-methyl-D-homophenylalanine of the present invention.

[0012] Figure 3 It is the chiral liquid chromatogram of Fmoc-a-methyl-L-homophenylalanine of the present invention.

[0013] Figure 4 It is the chiral liquid chromatogram of Fmoc-a-methyl-D-homophenylalanine of the present invention.

[0014] Figure 5 The figure is the nuclear magnetic spectrum of Fmoc-a-methyl-L-homophenylalanine of the present invention.

[0015] Figure 6 The figure is the nuclear magnetic spectrum of Fmoc-a-methyl-D-homophenylalanine of the present invention. DETAILED DESCRIPTION

[0016] The present invention is further illustrated by the following examples, which should not be construed as limiting the present invention. Example

[0017] Step (1) In a 50 L reaction flask, L-homophenylalanine ethyl ester hydrochloride (2100 g, 8.62 mol) and 21 L of dichloromethane were added, and benzophenone imine (1561 g, 8.62 mol) was added under stirring, and the reaction solution was stirred at 25°C for 20 hours. The solid in the reaction solution was filtered off, the filtrate was evaporated to dryness, and the residue was dissolved in 20 L of isopropyl ether, and the insoluble matter was filtered off. The filtrate was washed with water (10 L), dried over anhydrous sodium sulfate, and concentrated to obtain compound 1 (2869 g, yield 89.6%).

[0018] Step (2) Compound 1 (2865 g, 7.71 mol) and 14 L of tetrahydrofuran were added to a 50 L reaction bottle, stirred, and cooled to 0°C. A 1 M THF solution of potassium tert-butoxide (9 L, 9.0 mol) was added dropwise, and the temperature in the bottle was kept below 5°C. After the addition, the mixture was stirred at 0°C for 30 minutes. Methyl iodide (2735 g, 19.27 mol) was added, and the temperature in the bottle was controlled to be below 5°C. After the addition, the reaction solution was heated to 25°C and stirred for 7 h. 15 L of water was added, and the mixture was extracted with ethyl acetate (2 x 10 L). The organic phases were combined and washed with 15% saline solution (2 x 15 L). Drying was performed over anhydrous sodium sulfate, and the mixture was concentrated to dryness to obtain compound 2 (2973 g).

[0019] Step (3) Compound 2 (2973 g, 7.71 mol) and dichloromethane (3 L) were added to a 20 L reaction flask. 6N hydrochloric acid (7.6 L) was added and stirred at room temperature for 24 hours. The solid in the reaction solution was filtered off and the filtrate was extracted with dichloromethane (3 x 5 L). The organic phases were combined, dried over anhydrous sodium sulfate, and concentrated. The residue was slurried with 10 L petroleum ether, the solid was collected by filtration, and compound 3 (955 g, yield 55.9%) was obtained after drying.

[0020] Step (4) Compound 3 (955 g, 4.31 mol) and tetrahydrofuran (9.5 L) were added to a 20 L reaction bottle, followed by triethylamine (1088 g, 10.78 mol), and then phenylacetyl chloride (799 g, 5.17 mol) was added dropwise. After the addition, the mixture was stirred at room temperature overnight. The next day, the solid in the reaction solution was filtered out, and the filtrate was evaporated to dryness to obtain compound 4 (1463 g).

[0021] Step (5) Compound 4 (1463 g, 4.31 mol), tetrahydrofuran (4.5 L) and methanol (1.5 L) were added to a 20 L reaction bottle and stirred to dissolve. A 2M aqueous sodium hydroxide solution (6465 mL) was added. After the addition, the mixture was stirred at room temperature overnight. The next day, the reaction solution was extracted with 6 L of a mixture of petroleum ether and ethyl acetate (volume ratio 3:1) to extract impurities, and the aqueous phase was adjusted to pH 2-3 with 3N hydrochloric acid. A large amount of solid precipitated, and the solid was collected by filtration and dried to obtain compound 5 (1190 g, yield 88.7%).

[0022] Step (6) Compound 5 (940 g, 3.02 mol) and water (15 L) were added to a 20 L three-necked flask, and the pH value was adjusted to 8.5 with 1 M sodium hydroxide aqueous solution. Heat to 37 °C, add immobilized penicillin G acylase (200 g, purchased from Zhejiang Shunfeng Haider Co., Ltd.), keep the pH value to 8-9, and stir at 37 °C for 16 hours. Adjust pH = 2 with 3 N hydrochloric acid, filter and collect the solid, and dry to obtain compound 7 (462 g, yield 98.3%). The filtrate was extracted with ethyl acetate (5 L), and the aqueous phase was adjusted to pH 6 with 1 M sodium hydroxide aqueous solution and concentrated to a small volume. The precipitated solid was collected by filtration, washed with anhydrous ethanol, and dried to obtain compound 6 (241 g, yield 82.6%).

[0023] Step (7) Compound 6 (240 g, 1.24 mol) and water (2.4 L) were added to a 10 L reaction flask, followed by sodium carbonate (197 g, 1.86 mol). Stir to dissolve, and add acetone (2.4 L) and Fmoc-OSu (398 g, 1.18 mol). After addition, stir at room temperature overnight. The next day, the solid in the reaction solution was filtered out, and the filtrate was washed three times with 3 L of a mixture of petroleum ether and ethyl acetate (volume ratio 3:1), and the pH value of the aqueous phase was adjusted to 2-3 with 3N hydrochloric acid. A large amount of solid precipitated, and the solid was collected by filtration and dried to obtain Fmoc-a-methyl-L-homophenylalanine (416 g, 100% ee, yield 84.9%), [a] D = +17.5 (C=1.0, CHCl 3 ), MS (ESI) M / Z: 416.2 [M+H] + . 1 H NMR (400 MHz, DMSO- d 6 ): d 2.76 (s,12.5), 7.90 (d, J = 7.6 Hz, 2H), 7.74 (d, J = 7.2 Hz, 2H), 7.56 (s, 1H), 7.43-7.17 (m, 9H), 4.31-4.24 (m, 3H), 2.50 (m, 2H), 2.09-1.95 (m, 2H), 1.42 (s,3H). The mass spectrum of the product is shown in Figure 1 , chiral liquid chromatography is shown in Figure 3 , NMR spectrum see Figure 5 .

[0024] Step (8) Add compound 7 (462 g, 1.48 mol) and 6 N hydrochloric acid (3000 mL) to a 10 L reaction flask. Heat under reflux for 7 hours. Extract the reaction solution with dichloromethane. After concentrating the aqueous phase to dryness, α-methyl-D-homophenylalanine hydrochloride is obtained. Dissolve the obtained α-methyl-D-homophenylalanine hydrochloride in 2.6 L of water, adjust the pH to 8 - 9 with 2 M aqueous sodium hydroxide solution, and add sodium carbonate (235 g, 2.22 mol). Stir to dissolve. Add acetone (2.6 L) and Fmoc-OSu (476 g, 1.41 mol). After adding, stir at room temperature overnight. The next day, filter off the solid in the reaction solution. Wash the filtrate 3 times with a mixture of 3 L of petroleum ether and ethyl acetate (3:1). Adjust the pH of the aqueous phase to 2 - 3 with 3 N hydrochloric acid. A large amount of solid precipitates. Filter and collect the solid. After drying, Fmoc-α-methyl-D-homophenylalanine (526 g, 98.3% ee, yield 89.8%) is obtained, [α] D = -16.3 (C = 1.0, CHCl 3 ), MS (ESI) M / Z: 416.5 [M+H] + . 1 H NMR (400 MHz, DMSO- d 6 ): δ 2.76 (brs, 12.5), 7.90 (d, J = 7.6 Hz, 2H), 7.74 (d, J = 7.2 Hz, 2H), 7.61 (s, 1H), 7.44 - 7.17 (m, 9H), 4.31 - 4.23 (m, 3H), 2.51 (m, 2H), 2.09 - 1.91 (m, 2H), 1.42 (s, 3H). See the mass spectrum of the product in Figure 2 , see the chiral liquid chromatography in Figure 4 , and see the NMR spectrum in Figure 6 .

[0025] Example 2, step (2): The reaction temperature is 20 °C and the reaction time is 8 hours; step (3): The amount of 6 N hydrochloric acid used is 4 times the amount of compound 2; the rest is the same as in Example 1.

[0026] Example 3, step (2): The reaction temperature is 30 °C and the reaction time is 6 hours; step (3): The amount of 6 N hydrochloric acid used is 5 times the amount of compound 2; the rest is the same as in Example 1.

[0027] In Example 4, the reaction temperature in step (2) is 20°C and the reaction time is 8 hours; in step (3), the amount of 6 N hydrochloric acid used is 5 times that of compound 2; in step (6), the pH value is controlled at 7.5-8.5 and the temperature is controlled at 36°C; the rest is the same as in Example 1.

Claims

1. A method for synthesizing chiral Fmoc-a-methyl homophenylalanine, characterized in that: Including the following step: (1): L-homophenylalanine ethyl ester hydrochloride and benzophenone imine react in dichloromethane to obtain compound 1; (2): Compound 1 reacts with iodomethane in tetrahydrofuran under the action of potassium tert-butoxide to obtain compound 2; (3): Compound 2 is hydrolyzed in dilute hydrochloric acid and dichloromethane to obtain compound 3; (4): In the presence of triethylamine, compound 3 reacts with phenylacetyl chloride in tetrahydrofuran to obtain compound 4; (5): Compound 4 is hydrolyzed in aqueous sodium hydroxide solution and methanol to obtain compound 5; (6): Compound 5 was used to stereoselectively synthesize chirally pure compounds 6 and 7 using immobilized penicillin G acetylase; (7): Fmoc-protection of compound 6 gave chirally pure Fmoc-a-methyl-L-homophenylalanine; (8): Compound 7 is hydrolyzed with hydrochloric acid to remove the phenylacetyl group, and then Fmoc protection is performed to obtain Fmoc-a-methyl-D-homophenylalanine; the reaction formula is as follows: 。 2. A method for synthesizing chiral Fmoc-α-methyl homophenylalanine according to claim 1, characterized in that: The reaction temperature of step (2) is 20°C to 30°C, and the reaction time is 6-8 hours.

3. A method for synthesizing chiral Fmoc-α-methyl homophenylalanine according to claim 2, characterized in that: The reaction temperature of step (2) is 25°C and the reaction time is 7 hours.

4. A method for synthesizing chiral Fmoc-a-methylhomophenylalanine according to claim 1, characterized in that: The concentration of dilute hydrochloric acid in step (3) is 6 N, and the amount used is 3-5 times the amount of compound 2.

5. A method for synthesizing chiral Fmoc-α-methyl homophenylalanine according to claim 1, characterized in that: The reaction temperature in step (6) is controlled at 36-38°C.

6. A method for synthesizing chiral Fmoc-α-methyl homophenylalanine according to claim 1, characterized in that: The pH value of the reaction in step (6) is controlled at 7-9.

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