Preparation method for synthesizing glutamic acid-1-tert-butyl ester

Abstract

The invention discloses a preparation method for synthesizing glutamic acid-1-tert-butyl ester, which comprises the following steps: carrying out 5-carboxyl methyl esterification on L-glutamic acid to obtain glutamic acid-5-methyl ester, carrying out phthaloyl protection on amino of the glutamic acid-5-methyl ester to obtain N-phthaloyl-L-glutamic acid-5-methyl ester, and carrying out 1-tert-butyl ester synthesis on the N-phthaloyl-L-glutamic acid-5-methyl ester to obtain the N-phthaloyl-L-glutamic acid-5-methyl ester. Carrying out carboxyl tert-butyl esterification on the N-phthaloyl-L-glutamic acid-5-methyl ester to obtain N-phthaloyl-L-glutamic acid-5-methyl ester-1-tert-butyl ester, and carrying out selective saponification on the N-phthaloyl-L-glutamic acid-5-methyl ester-1-tert-butyl ester to obtain the N-phthaloyl-L-glutamic acid-1-tert-butyl ester. The N, N-phthaloyl-L-glutamic acid-1-tert-butyl ester hydrazine hydrate is subjected to phthaloyl protection removal to obtain a glutamic acid-1-tert-butyl ester crude product, and the crude product is purified, refined and dried to obtain a glutamic acid-1-tert-butyl ester finished product. The method provided by the invention has the advantages of simple process scheme, cheap and easily available raw materials, good reaction selectivity, high single-step conversion rate, easy operation and mild reaction conditions, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of polypeptide drug synthesis, and in particular to a preparation method for synthesizing 1-tert-butyl glutamate. Background Art

[0002] 1-tert-Butyl Glutamate is one of the key intermediates in the synthesis of GLP-1 drugs such as semaglutide, tilportide, and retaglutide. Glutamate plays a crucial role in protein metabolism in living organisms and participates in many important chemical reactions in animals, plants, and microorganisms. It is also the most abundant excitatory neurotransmitter in the vertebrate nervous system. Glutamate is widely used in medicine, food, nutritional supplements, and daily chemicals. Because glutamate cannot be used directly in peptide synthesis, the corresponding active groups need to be protected, such as by forming various types of protected amino acids such as Fmoc-1-tert-butyl glutamate, 1-tert-butyl glutamate, Fmoc-5-tert-butyl glutamate, and 5-tert-butyl glutamate, to participate in subsequent solid-phase or liquid-phase peptide synthesis. The tert-butyl ester also facilitates removal and purification in subsequent reactions of peptide synthesis, making it easy to operate. This application describes a simple synthesis method for 1-tert-butyl L-glutamate.

[0003] The known synthetic schemes of 1-tert-butyl glutamate are generally as follows: Method 1: Hydrogenation For example, patents CN111704566 (Jill Biochemical), US6291469 (Eli Lily), and CN115504893 (Pukang) all involve L-glutamic acid, which is esterified with the 5-carboxyl group, protected with Cbz amino groups, and tert-butyl esterified with the 1-carboxyl group. The amino group and the benzyl ester protecting group at the 5-carboxyl group are then removed by palladium-carbon hydrogenation. The resulting crude product is purified to yield qualified 1-tert-butyl glutamate, as shown in Route 1 below. This route is a well-established and commonly used production route, ensuring product purity. However, its drawbacks are the low yield of the 5-carboxyl benzyl esterification, the use of expensive heavy metal palladium-carbon hydrogenation, and the high cost and potential for heavy metal residues. These unique process conditions restrict large-scale, commercial mass production, raising the market entry barrier for this product.

[0004] Route 1: Method 2: Trifluoroacetyl Scheme For example, patent CN116178214A describes a method for preparing Fmoc-L-glutamic acid-1-tert-butyl ester. Starting from L-glutamic acid, the 5-carboxyl group is methylated, the amino group is protected with Tfa, and the 1-carboxyl group is tert-butylated. The methyl ester protecting groups of the amino group and the γ-carboxyl group are then simultaneously removed by alkaline saponification. The crude L-glutamic acid-1-tert-butyl ester obtained after treatment is directly protected with an Fmoc protecting group to obtain Fmoc-L-glutamic acid-1-tert-butyl ester, as shown in Route 2 below. This route cleverly uses a trifluoroacetyl group to protect the amino group and a methyl ester to protect the 5-carboxyl group. The methyl ester and trifluoroacetyl groups are easily removed under alkaline conditions, while the tert-butyl ester is relatively stable. However, experimental verification found that under the described conditions, the saponification reaction progressed slowly, and because the rate of trifluoroacetyl removal was faster than the rate of methyl ester hydrolysis, pyrolysis by-products were inevitably produced, accompanied by partial hydrolysis products of tert-butyl ester. The reaction was relatively complex, and no solid product was precipitated after adjusting the isoelectric point and standing, and the reaction reproducibility was poor.

[0005] Route 2: Other approaches, such as patent CN117865832, report a method for preparing 1-tert-butyl glutamate by ring-opening tert-butyl pyroglutamate with trifluoroacetic acid, but this is theoretically impractical. Patent US2004030177 describes a method for hydrolyzing di-tert-butyl glutamate followed by separation and purification. However, due to the poor selectivity and low yield of diester hydrolysis, separation and purification are difficult, making it unsuitable for large-scale application.

[0006] In summary, except for the hydrogenation scheme that can be applied on a large scale, the other methods are not highly operational. In addition, the hydrogenation scheme uses expensive heavy metal catalysts, and the hydrogenation process has strict restrictions on production conditions and is costly. To overcome the drawbacks of the existing technology, the present invention aims to provide a green, low-cost, and widely applicable non-hydrogenation route for synthesizing 1-tert-butyl glutamate. Summary of the Invention

[0007] The purpose of the present invention is to provide a preparation method for synthesizing 1-tert-butyl glutamate, so as to solve the technical problems of the prior art methods such as low operation efficiency, the need to use expensive heavy metal catalysts and harsh production conditions.

[0008] To achieve the above objectives, the present invention provides the following technical solutions: The present invention provides a method for preparing 1-tert-butyl glutamate, comprising the following steps: S1, L-glutamic acid 5-carboxyl methyl esterification to obtain glutamic acid-5-methyl ester; S2, phthaloyl protection of the amino group of 5-methyl glutamate to obtain N-phthaloyl-L-glutamate-5-methyl ester; S3, tert-butyl esterification of N-phthaloyl-L-glutamic acid-5-methyl ester carboxyl to obtain N-phthaloyl-L-glutamic acid-5-methyl ester-1-tert-butyl ester; S4, selective saponification of N-phthaloyl-L-glutamic acid-5-methyl ester-1-tert-butyl ester to obtain N-phthaloyl-L-glutamic acid-1-tert-butyl ester; S5, deprotecting the phthaloyl group of N-phthaloyl-L-glutamic acid-1-tert-butyl ester with hydrazine hydrate to obtain the target product, glutamic acid-1-tert-butyl ester; The route is as follows: .

[0009] Furthermore, the reaction process of S1 is as follows: L-glutamic acid and methanol are cooled to 0-5°C, 98% concentrated sulfuric acid is added dropwise, and the reaction is carried out at 20-25°C for 4-5h; Subsequent treatment: After the reaction is completed, the reaction solution is adjusted to pH = 8 with triethylamine, then cooled to 0℃ and beaten for 2-3h, filtered to obtain flaky white crystals of 5-methyl glutamate, and dried at 50℃.

[0010] Furthermore, the triethylamine can be replaced by other fatty amines, such as isopropylamine, monoethylamine, diethylamine, etc.

[0011] Furthermore, the reaction process of S2 is to heat L-glutamic acid-5-methyl ester, phthalic anhydride, toluene, and triethylamine under reflux and separate water, and react for 6-8 hours; Subsequent treatment: The solvent was removed by concentration under reduced pressure, and the resulting residue was dissolved in ethyl acetate (200 mL), washed with 1N dilute hydrochloric acid and saturated brine in sequence, and dried over anhydrous sodium sulfate.

[0012] Furthermore, the reaction process of S3 is as follows: N-Phth-L-glutamic acid-5-methyl ester, tert-butyl alcohol, DMAP, heating to 40-50 °C, adding BOC anhydride dropwise, and continuing to keep the temperature for 0.5 h after the addition is completed; The reaction process of S4 is to add water (200 ml), cool to 0-5°C, and add 2N sodium hydroxide solution in batches until the pH no longer decreases; Subsequent treatment: adjust the pH to weak acidity with dilute hydrochloric acid, concentrate to dryness to obtain a yellow oil, dissolve it in water and adjust the pH to weak alkalinity with sodium hydroxide solution, then extract the impurities twice with EA (100 ml*2), decolorize with alkaline activated carbon, cool the water solution to 0°C, adjust the pH to 2~3 with 2N hydrochloric acid, and precipitate a large amount of solid. The solid is dissolved and clarified by heating to 80°C with ethyl acetate-petroleum ether (1:1, 200 ml), and then cooled to 0~5°C to precipitate a large amount of solid, which is filtered, washed with water, and dried to obtain N-Phth-L-glutamic acid-1-tert-butyl ester.

[0013] Furthermore, the dilute hydrochloric acid and sodium hydroxide used to adjust the pH value can be replaced by other commonly used and cost-effective acids and bases.

[0014] Furthermore, the reaction process of S5 is to react N-Phth-L-glutamic acid-1-tert-butyl ester, ethanol, and 80% hydrazine hydrate at room temperature for 3-4 hours, during which a white solid suspension will gradually precipitate; Subsequent Treatment: After the reaction is complete, filter the filtrate and add an appropriate amount of benzaldehyde dropwise to the filtrate. Stir on a plate until the hydrazine hydrate disappears completely. Continue stirring. A white solid will gradually precipitate during the reaction. Continue stirring for 6-8 hours, at which point a large amount of white solid will precipitate. Filter the filter cake, wash it with anhydrous ethanol, dry it, and recrystallize it from anhydrous ethanol to completely remove any residual phthalhydrazide and phenylhydrazone. Filter and dry to obtain L-glutamic acid-1-tert-butyl ester as a white solid.

[0015] Based on the above technical solution, the embodiments of the present invention can produce at least the following technical effects: (1) The starting material L-glutamic acid and other reaction materials of the present invention are cheap and readily available, and the cost is low; (2) The synthesis method of the present invention is simple to operate and does not require expensive precious metal catalysts or harsh production conditions such as high-pressure hydrogenation. The reaction conditions are mild, the requirements for process equipment are low, and it is easy to produce on an industrial scale. (3) The method for synthesizing L-glutamic acid-1-tert-butyl ester provided by the present invention has a simple process, a short production cycle, high production efficiency, and a green and environmentally friendly production method, and is suitable for industrial large-scale production. DETAILED DESCRIPTION

[0016] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0017] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0018] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0019] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0020] Example 1 A preparation method for synthesizing 1-tert-butyl glutamate, specifically comprising: L-glutamic acid (73.5 g, 0.5 mol, 1 eq) and methanol (1176 ml, 16 V) were added to the reaction flask, and the temperature was lowered to 0-5 ° C. 98% concentrated sulfuric acid (37 ml, 0.68 mol, 1.36 eq) was added dropwise. After the addition, the reaction was carried out at 20-25 ° C for 4-5 h. The reaction was completed on a plate (411, ninhydrin). The reaction was stopped and the pH of the reaction solution was adjusted to 8 with triethylamine (about 150 ml of triethylamine). The temperature was then lowered to 0 ° C and slurried for 2-3 h. The flaky white crystals of 5-methyl glutamate were obtained by filtration. After drying at 50 ° C, 69 g of white solid was obtained with a yield of 85%.

[0021] To a reaction flask, add L-glutamic acid 5-methyl ester (40.5 g, 0.25 mol, 1 eq), phthalic anhydride (37 g, 0.25 mol, 1 eq), toluene (160 mL, 4V), and triethylamine (10 g, 0.1 mol). Heat under reflux to remove water and allow the reaction to proceed for 6-8 hours. After completion of the reaction, monitor the reaction by TLC and concentrate under reduced pressure to remove the solvent. The resulting residue is dissolved in ethyl acetate (200 mL), washed sequentially with 1N dilute hydrochloric acid and saturated brine, and dried over anhydrous sodium sulfate. After concentration and drying, 65 g of N-Phth-L-glutamic acid 5-methyl ester is obtained as a white solid powder, yielding 90%.

[0022] The intermediate N-Phth-L-glutamic acid-5-methyl ester (58.2 g, 0.2 mol, 1 eq) from the previous step, tert-butyl alcohol (580 ml, 10 V), DMAP (2.4 g, 0.02 mol, 0.1 eq) were added to the reaction flask, the temperature was raised to 40-50 ° C, and BOC anhydride (87.2 g, 0.4 mol, 2eq). After the addition was complete, the reaction was continued at this temperature for 0.5 h. The reaction was stopped after TLC monitoring of the reaction of the raw material. Water (200 ml) was added, the temperature was lowered to 0-5°C, and 2N sodium hydroxide solution was added in batches until the pH stopped decreasing. The reaction of the raw material on the plate was complete. The pH was adjusted to weak acidity with dilute hydrochloric acid and concentrated to dryness to obtain a yellow oil. Water (200 ml) was added to dissolve it and the pH was adjusted to weak alkalinity with sodium hydroxide solution. The impurities were extracted twice with EA (100 ml*2). After decolorization with alkaline activated carbon, the aqueous solution was cooled to 0°C and the pH was adjusted to 2-3 with 2N hydrochloric acid to precipitate a large amount of solid. The solid was dissolved and clarified in ethyl acetate-petroleum ether (1:1, 200 ml). The temperature was then lowered to 0-5°C to precipitate a large amount of solid. The solid was filtered, washed with water, and dried to obtain 56.6 g of N-Phth-L-glutamic acid-1-tert-butyl ester as a white solid with a yield of 85%.

[0023] To a reaction flask, add the intermediate N-Phth-L-glutamic acid-1-tert-butyl ester (50 g, 0.15 mol, 1 eq), ethanol (500 ml, 10 V), and 80% hydrazine hydrate (18.7 g, 0.3 mol, 2 eq) from the previous step. The reaction was allowed to proceed at room temperature for 3-4 hours. A white solid suspension gradually precipitated during the reaction, until the reaction was complete as monitored by TLC. After completion, the reaction was filtered, and an appropriate amount of benzaldehyde was added dropwise to the filtrate. The plate was aspirated until the hydrazine hydrate completely disappeared. Stirring was continued, and a white solid gradually precipitated during the reaction. Stirring was continued for 6-8 hours, at which point a large amount of white solid precipitated. The filter cake was filtered, washed with anhydrous ethanol, dried, and recrystallized from anhydrous ethanol to completely remove any residual phthaloyl hydrazide and phenylhydrazone. Filtration and drying yielded 22.8 g of L-glutamic acid-1-tert-butyl ester as a white solid, with a yield of 75%.

[0024] The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing 1-tert-butyl glutamate, characterized in that: The process includes five steps: S1, S2, S3, S4, and S5, and the preparation route is as follows: 。 2. The method for preparing synthetic 1-tert-butyl glutamate according to claim 1, wherein The S1 is a methyl esterification of the 5-carboxyl group of L-glutamic acid to obtain 5-methyl glutamic acid. The specific reagents and conditions are: L-glutamic acid, methanol, 98% concentrated sulfuric acid, triethylamine, reaction temperature 20-25°C, reaction time 4-5h, and subsequent treatment.

3. The preparation method of synthetic glutamic acid-1-tert-butyl ester according to claim 1, characterized in that, Said S2 is phthaloyl protected on the amino group of glutamic acid-5-methyl ester to obtain N-phthaloyl-L-glutamic acid-5-methyl ester. The specific reagents and conditions are: L-glutamic acid-5-methyl ester, phthalic anhydride, toluene, triethylamine, heating under reflux to separate water, and subsequent treatment after 6-8 hours of reaction.

4. The method for preparing the synthetic 1-tert-butyl glutamate according to claim 1, wherein The S3 is the carboxyl tert-butyl esterification of N-phthaloyl-L-glutamic acid-5-methyl ester to obtain N-phthaloyl-L-glutamic acid-5-methyl ester-1-tert-butyl ester. The specific reagents and conditions are: N-Phth-L-glutamic acid-5-methyl ester, tert-butanol, 4-dimethylaminopyridine, BOC anhydride, and the reaction is carried out at 40-50°C until the reaction is completed.

5. The method for preparing the synthetic 1-tert-butyl glutamate according to claim 4, wherein The S4 is N-phthaloyl-L-glutamic acid-5-methyl ester-1-tert-butyl ester selectively saponified to obtain N-phthaloyl-L-glutamic acid-1-tert-butyl ester, and the specific reagents and conditions are: sodium hydroxide solution and dilute hydrochloric acid.

6. The method for preparing synthetic 1-tert-butyl glutamate according to claim 1, wherein The S5 is N-phthaloyl-L-glutamic acid-1-tert-butyl ester hydrazine hydrate dephthaloyl protection to obtain the target product glutamic acid-1-tert-butyl ester. The specific reagents and conditions are: N-Phth-L-glutamic acid-1-tert-butyl ester, ethanol, 80% hydrazine hydrate, and the reaction is carried out at room temperature for 3-4 hours to complete the reaction before subsequent treatment.

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