Preparation method of amino acid derivative with protected main chain carboxyl

Abstract

The invention discloses a preparation method of an amino acid derivative with a protected main chain carboxyl group, and relates to the technical field of polypeptide synthesis. Comprising the following steps: dissolving benzyl alcohol in anhydrous dichloromethane, adding amino acid until the system is turbid at the moment, and dropwise adding trimethylchlorosilane; according to the route, benzyl alcohol is protected by trimethylsilane to generate trimethylsilyl ester, the trimethylsilyl ester is active and is subjected to transesterification with amino acid, and meanwhile, HCl generated by the trimethylsilane and the benzyl alcohol and generated amino acid benzyl ester form hydrochloride. Compared with a traditional esterification reaction, trimethylchlorosilane is used as an HCl donor, environmental hazard is reduced, trimethylchlorosilane and benzyl alcohol can form trimethylsilyl ester, benzyl alcohol is activated in a phase change mode, the reaction rate is increased, the reaction yield is increased, and the method is suitable for industrial production. The invention relates to all common amino acids except tryptophan, serine and other amino acids containing side chain alcoholic hydroxyl groups and aspartic acid, glutamic acid and other amino acids containing side face carboxyl groups.

Description

Technical Field

[0001] The present invention relates to the technical field of polypeptide synthesis, and specifically relates to a method for preparing an amino acid derivative with a protected main-chain carboxyl group. Background Art

[0002] The synthesis of polypeptides is controlled by the synthesis of different amino acids in a certain order, and such control is achieved by the selective protection of amino acids. By protecting the amino group of one amino acid and the carboxyl group of another amino acid (the influence of side-chain functional groups is not considered here for the time being), selective peptide bonding can be achieved.

[0003] The protection of carboxyl groups is generally esterification protection, and commonly used ones include methyl ester, ethyl ester, benzyl ester, etc. Compared with methyl ester and ethyl ester, the amino acid protected by benzyl ester is very stable, stable in most reactions and will not be removed, and high-purity products can be obtained efficiently only through hydrogenolysis, while methyl ester and ethyl ester need to be removed by saponification, and many amino acids are prone to impurities that are difficult to remove during the saponification process, affecting the purity.

[0004] In the synthesis of benzyl ester, it is generally prepared by reacting benzyl bromide or benzyl chloride under the action of a base in a benign organic solvent such as DMF, DCM and acetonitrile. Both benzyl bromide and benzyl chloride have extremely strong tear gas properties, are very unfriendly to the human body, and are unstable under alkaline conditions, easily hydrolyzed into benzyl alcohol, reducing the reaction activity or even not reacting, so it is required that the reaction must be carried out quickly and under anhydrous conditions as much as possible, and the conditions are relatively harsh. Summary of the Invention

[0005] Aiming at the above technical problems, the present application solves the problems of environmental unfriendliness, high cost and high requirements of the prior art for the amino acid carboxyl protection technology.

[0006] In order to achieve the above purpose, the technical solution adopted in the present application is: a method for preparing an amino acid derivative with a protected main-chain carboxyl group, the amino acid derivative is 2-aminoisobutyric acid benzyl ester hydrochloride, and the preparation method includes the following steps:

[0007] Step 1: Obtain benzyl alcohol and dichloromethane, and dissolve benzyl alcohol in dichloromethane to obtain a mixed solution.

[0008] Step 2: Obtain 2-aminoisobutyric acid, and add 2-aminoisobutyric acid to the mixed solution in Step 1.

[0009] Step 3: Obtain trimethylchlorosilane, and use a dropping funnel to drop it into the mixed solution in Step 2. After dropping and reacting for a period of time, 2-aminoisobutyric acid benzyl ester hydrochloride is obtained, and after treatment, a qualified product is obtained.

[0010] To better implement this application, further, in the first and second steps, the ratio of 2-aminoisobutyric acid to benzyl alcohol is equal.

[0011] To better implement this application, further, in the second and third steps, the ratio of 2-aminoisobutyric acid to trimethylchlorosilane is equal.

[0012] To better implement this application, further, when adding trimethylchlorosilane dropwise in the third step, the system temperature must be maintained in the range of 20 - 30 °C.

[0013] To better implement this application, further, after the reaction is completed, the product can be directly obtained by filtration.

[0014] To better implement this application, further, the solvent used to process 2-aminoisobutyric acid is dichloromethane.

[0015] To better implement this application, further, throughout the entire reaction process, including the treatment process, the presence of water in the system must always be maintained.

[0016] The technical solution provided by the present invention has the following beneficial effects compared with the prior art:

[0017] 1. By using benzyl alcohol instead of benzyl bromide and benzyl chloride, the present invention reduces the harm to the human body and is environmentally friendly.

[0018] 2. By adding trimethylchlorosilane dropwise, the present invention makes benzyl alcohol generate the active intermediate trimethylsilyl ester. Trimethylsilyl ester is more reactive and selective than benzyl bromide and benzyl chloride used in traditional reactions. In addition, the trimethylsilanol generated after the reaction can also dissolve in common organic solvents and will not bring impurities.

[0019] 3. The present invention directly generates hydrochloride, which has poor solubility in the solvent DCM used and can be directly precipitated, eliminating the cumbersome impurity removal process. Only simple stirring and washing are required to obtain high-purity solids.

[0020] 4. Due to the high reaction selectivity of the present invention and the direct precipitation of hydrochloride solids, a high yield can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart for preparing amino acid benzyl ester hydrochloride according to the present invention;

[0022] Figure 2 is a schematic diagram of the HPLC detection result of Example 2 of the present invention;

[0023] Figure 3 is a schematic diagram of the HPLC detection result of Example 3 of the present invention;

[0024] Figure 4 Schematic diagram of the HPLC detection result of Example 4 of the present invention; Detailed implementation manners

[0025] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and illustrated herein can be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the present application claimed, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0027] Example 1:

[0028] As Figure 1 shown, a preparation method of an amino acid derivative with a protected main-chain carboxyl group, the amino acid derivative being 2-aminoisobutyric acid benzyl ester hydrochloride, the preparation method comprising the following steps:

[0029] Step 1: Obtain benzyl alcohol and dichloromethane, and dissolve the benzyl alcohol in dichloromethane to obtain a mixed solution.

[0030] Step 2: Obtain 2-aminoisobutyric acid, and add the 2-aminoisobutyric acid to the mixed solution in Step 1.

[0031] Step 3: Obtain trimethylchlorosilane, and use a dropping funnel to drop it into the mixed solution in Step 2. After dropping and reacting for a period of time, 2-aminoisobutyric acid benzyl ester hydrochloride is obtained, and after treatment, a qualified product is obtained.

[0032] In Step 1 and Step 2, the ratio of 2-aminoisobutyric acid to benzyl alcohol is an equal ratio.

[0033] In Step 2 and Step 3, the ratio of 2-aminoisobutyric acid to trimethylchlorosilane is an equal ratio.

[0034] In Step 3, the system temperature must be maintained in the range of 20-30°C when dropping trimethylchlorosilane.

[0035] After the reaction is completed, the product can be obtained directly by filtration.

[0036] The solvent used for treating 2-aminoisobutyric acid is any one of dichloromethane, ethyl acetate, tetrahydrofuran, chloroform, and acetone.

[0037] During the entire reaction process, including the processing, it is necessary to always ensure that there is no water in the system.

[0038] Example 2:

[0039] Weigh 1 mol (108 g) of benzyl alcohol and dissolve it in 1 L of dichloromethane. Then weigh 0.9 mol (93 g) of 2 - amino - isobutyric acid and dissolve it in the above - mentioned mixed solution. Then weigh 1 mol (108 g) of trimethylchlorosilane and slowly add it drop - by - drop using a dropping funnel over 1 h. During the dropping process, control the temperature at 25 °C. After the dropping is completed, react for another 1 h. During the reaction, solids continuously precipitate. When TLC shows that the reaction is complete, directly extract the solids, wash them twice with 1 L of dichloromethane, dry them, and send them for testing. 165 g of benzyl 2 - amino - isobutyrate hydrochloride is obtained, with a yield of 80.6%. As Figure 2 shown, the HPLC content is 98.43% and the titration content is 97.4%.

[0040] Example 3:

[0041] Weigh 1 mol (108 g) of benzyl alcohol and dissolve it in 1 L of dichloromethane. Then weigh 1 mol (103 g) of 2 - amino - isobutyric acid and dissolve it in the above - mentioned mixed solution. Then weigh 1 mol (108 g) of trimethylchlorosilane and slowly add it drop - by - drop using a dropping funnel over 1 h. During the dropping process, control the temperature at 25 °C. After the dropping is completed, react for another 1 h. During the reaction, solids continuously precipitate. When TLC shows that the reaction is complete, directly extract the solids, wash them twice with 1 L of dichloromethane, dry them, and send them for testing. 198 g of benzyl 2 - amino - isobutyrate hydrochloride is obtained, with a yield of 87%. As Figure 3 shown, the HPLC content is 99.15% and the titration content is 99.9%.

[0042] Example 4:

[0043] Weigh 1 mol (108 g) of benzyl alcohol and dissolve it in 1 L of dichloromethane. Then weigh 1.1 mol (113 g) of 2 - amino - isobutyric acid and dissolve it in the above - mentioned mixed solution. Then weigh 1 mol (108 g) of trimethylchlorosilane and slowly add it drop - by - drop using a dropping funnel over 1 h. During the dropping process, control the temperature at 25 °C. After the dropping is completed, react for another 1 h. During the reaction, solids continuously precipitate. When TLC shows that the reaction is complete, directly extract the solids, wash them twice with 1 L of dichloromethane, dry them, and send them for testing. 201 g of benzyl 2 - amino - isobutyrate hydrochloride is obtained, with a yield of 80.3%. As Figure 4 shown, the HPLC content is 98.17% and the titration content is 97.9%.

[0044] The above are only the preferred examples of the present application, and only used as conditional comparisons. The impacts on products and quality do not represent that the patented technology has only been verified through three experiments.

[0045] Comparing Comparative Example 2, Example 3 and Example 4, during the experiment, the best addition ratio of benzyl alcohol to 2-aminoisobutyric acid is 1:1, and the best addition ratio of trimethylchlorosilane to 2-aminoisobutyric acid is 1:1. The experimental yield is the best and the detection results are also better.

[0046] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a main chain carboxyl-protected amino acid derivative, characterized in that: The amino acid derivative is 2-aminoisobutyric acid benzyl ester hydrochloride, and the preparation method comprises the following steps: Step 1: obtaining benzyl alcohol and dichloromethane, and dissolving benzyl alcohol in dichloromethane to obtain a mixed solution; Step 2: Obtain 2-aminoisobutyric acid, and add the 2-aminoisobutyric acid to the mixed solution in step 1; Step 3: obtain trimethylchlorosilane, and use a dropping funnel to drop it into the mixed solution of step 2. After the addition is completed and reacted for a period of time, 2-aminoisobutyric acid benzyl ester hydrochloride is obtained, and a qualified product is obtained after treatment.

2. The method for preparing a main chain carboxyl protected amino acid derivative according to claim 1, characterized in that: In the step 1 and the step 2, the ratio of 2-aminoisobutyric acid to benzyl alcohol is equal.

3. The method for preparing a main chain carboxyl protected amino acid derivative according to claim 1, characterized in that: In the step 2 and the step 3, the ratio of 2-aminoisobutyric acid to trimethylchlorosilane is equal.

4. The method for preparing a main chain carboxyl protected amino acid derivative according to claim 1, characterized in that: In the step 3, the system temperature must be maintained at 20-30° C. when trimethylchlorosilane is added dropwise.

5. The method for preparing a main chain carboxyl protected amino acid derivative according to claim 1, characterized in that: After the reaction is completed, the product can be obtained by direct filtration.

6. The method for preparing a main chain carboxyl protected amino acid derivative according to claim 1, characterized in that: The solvent used for treating 2-aminoisobutyric acid is dichloromethane.

7. The method for preparing a main chain carboxyl protected amino acid derivative according to claim 1, characterized in that: During the entire reaction process including the treatment process, it is always necessary to keep the system free of water.

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