Method for preparing N-methyl-N-carbobenzoxy-L-aspartic acid-4-tert-butyl ester
The one-pot method of preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester solves the problems of low safety, difficulty in purification, and inability to produce in large quantities in the existing technology, and achieves The product has high purity and high chiral purity, which is suitable for industrial production.
Patent Information
- Application Number
- CN202411471062.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-22
- Publication Date
- 2025-01-24
AI Technical Summary
In the prior art, the preparation of N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester has problems such as low safety, difficulty in purifying and inability to mass production.
It is prepared by a one-pot method, using L-aspartate tert-butyl ester and formaldehyde as raw materials, and performs reductive amination in the presence of zinc powder in a buffer system and hexafluoroisopropanol solvent, and then reacts with Cbz protecting group in an alkaline solution. Under protective conditions, N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester was obtained.
The method is simple to operate and uses a buffer system to prevent racemization of the product. The reaction solution has high purity and is easier to solidify. It is suitable for industrial-scale production and has a chiral purity of up to 99.5%.
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Figure CN119350189A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester, belonging to the technical field of organic synthesis. Background Art
[0002] Amino acid materials have the advantages of chirality, biocompatibility, multifunctional groups, and rich secondary structures. L-aspartic acid is one of the important acidic amino acids. After modification, N-methyl amino acids are important raw materials for peptide drugs. They have biological activities such as antiviral, antibacterial, and antitumor. They are widely present in natural peptides and have important applications in peptide biopharmaceuticals and food additives. N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester is a very important natural amino acid derivative and an important chiral intermediate for the synthesis of peptide drugs.
[0003] At present, there are few reports on the synthesis route of N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester. Among them, the literature [Journal of Antibiotics 2001, Vol.54No.1] uses Cbz-L-aspartic acid-4-tert-butyl ester as raw material and uses sodium hydride and iodomethane to react to obtain N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester. This synthetic route reacts with iodomethane, which is easy to form methyl ester at the carboxyl group, thereby increasing impurities and being not conducive to purification; and the use of sodium hydride has low safety and is not conducive to industrial production and expansion; the reaction equation is expressed as follows:
[0004]
[0005] In order to solve the defects of the prior art in preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester in terms of safety, difficulty in purification, and inability to produce in large quantities, the present invention provides a one-pot method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester. The preparation method is simple to operate, a buffer system is used to prevent the racemization of the product, the reaction solution has high purity, is easier to solidify, and is suitable for industrial-scale production. Summary of the invention
[0006] In order to overcome the defects of the above-mentioned technology, the present invention discloses a method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester. L-aspartic acid-tert-butyl ester and formaldehyde are used as raw materials, and reductive amination is carried out in a buffer system and a hexafluoroisopropanol solvent in the presence of zinc powder, and then the Cbz protecting group is protected under alkaline conditions to obtain N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester. The present invention is a one-pot operation, and a buffer system is used to prevent the racemization of the product, and the reaction selectivity is high. The final product obtained has high purity, and the chiral purity is as high as 99.5%.
[0007] The method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester of the present invention comprises the following operations: mixing L-aspartic acid-4-tert-butyl ester, a high polarity solvent, a buffer salt, a formaldehyde solution and water, cooling the mixture to 0-5°C, adding zinc powder in batches, filtering the mixture, and adding alkali and a Cbz protecting reagent to the filtrate to react and obtain N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester.
[0008] Furthermore, in the above technical solution, the buffer salt is selected from sodium dihydrogen phosphate or disodium hydrogen phosphate, or a mixture of sodium acetate and sodium dihydrogen phosphate or disodium hydrogen phosphate.
[0009] Furthermore, in the above technical solution, the highly polar solvent is selected from trifluoroethanol or hexafluoroisopropanol. During the experimental optimization, it was found that the use of hexafluoroethanol solvent and the batch addition of zinc powder are the key to the monomethyl group on N. Without the addition of the solvent or when the zinc powder is added at once, monomethyl and dimethyl groups coexist.
[0010] Furthermore, in the above technical solution, the base is selected from potassium carbonate, sodium carbonate, sodium bicarbonate or sodium hydroxide.
[0011] Furthermore, in the above technical solution, the Cbz protecting agent is selected from benzyloxycarbonyl succinimide (Cbz-OSu) or benzyl chloroformate (Cbz-Cl).
[0012] Furthermore, in the above preferred technical scheme, when the Cbz protecting agent is benzyloxycarbonyl succinimide, the corresponding base is selected from potassium carbonate, sodium carbonate or sodium bicarbonate; when the Cbz protecting agent is benzyl chloroformate, the base is selected from sodium hydroxide or potassium carbonate.
[0013] Furthermore, in the above technical solution, the molar ratio of L-aspartic acid tert-butyl ester, formaldehyde, zinc powder, buffer salt, inorganic base and Cbz protective reagent is 1:1.1-1.5:1.9-2.0:2.0-2.5:2.5-3.5:1.05-1.20.
[0014] Furthermore, in the above technical scheme, the crude N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester obtained by the reaction is purified and crystallized using ethyl acetate and n-heptane in a volume ratio of 1 / 5-1 / 7.
[0015] Advantageous Effects of the Invention
[0016] 1. The highly polar solvent hexafluoroisopropanol is used. Its strong hydrogen bonding combined with the batch addition of zinc powder ensures highly selective monomethylation on N. N-methyl-L-aspartic acid-4-tert-butyl ester can be used as a product alone, or other different protecting groups can be connected to it. The buffer system makes it in a weakly alkaline state, ensuring that the compound does not undergo racemization.
[0017] 2. In the selection of Cbz protection reagents, CbzOSu reacts faster and has higher purity, while CbzCl is cheaper. By optimizing the solidification method, the best solution is to use reagents with cheaper raw materials. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 This is the HNMR spectrum of N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester obtained in Example 1. DETAILED DESCRIPTION
[0019] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.
[0020] Example 1
[0021]
[0022] Into a 500mL jacketed reaction bottle, 18.9g (0.1mol) of L-tert-butyl 4-aspartate, 95mL of hexafluoroisopropanol, 24g (0.2mol) of sodium dihydrogen phosphate, 10.6g (0.13mol) of 37% formaldehyde solution and 95mL of purified water were added in sequence, the temperature was lowered to 0-5°C, 13.1g (0.2mol) of zinc powder was added in 5-6 batches, and the temperature was slowly raised to room temperature for reaction for 2 hours. Celite was spread and filtered, the filter cake was rinsed with a small amount of water, the filtrate was retained, the filtrate was re-put into the reaction bottle, 27.4 g (0.11 mol) of CbzOSu was added, and 45% potassium carbonate aqueous solution was added dropwise to maintain the pH of the system at 8.5-9.5. No amino acid was detected by TLC. The low boiling point solvent was evaporated under reduced pressure at 20-30°C, and impurities were extracted with ethyl acetate. Then the aqueous phase was adjusted to pH = 4-4.5 with 3N hydrochloric acid, extracted with ethyl acetate, Su alcohol was washed off with water, and then concentrated under reduced pressure until no liquid flowed, and ethyl acetate was used to carry water to a moisture content of <0.5%. 20 mL of ethyl acetate was added, the temperature was raised to 70°C, 140 mL of n-heptane was added dropwise, 0.1 g of seed crystals was added, the temperature was slowly lowered to 10-15°C, filtered, the filter cake was rinsed with n-heptane, and dried to obtain 27 g of N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester, with a yield of 80%, HPLC 99.8%, and chiral purity 99.6%. 1 H NMR (400MHz, DMSO-d6):7.39-7.29(m,5H),5.13-5.07(m,2H),4.83-4.78(m,1H),2.87-2.81(m,4H),2.70-2.64(m,1H),1.36(s,9H).
[0023] Example 2
[0024]
[0025] Into a 500mL jacketed reaction bottle, 18.9g (0.1mol) of L-tert-butyl 4-aspartate, 95mL of hexafluoroisopropanol, 18g (0.15mol) of sodium dihydrogen phosphate, 8.2g (0.1mol) of sodium acetate, 12.2g (0.15mol) of 37% formaldehyde solution and 135mL of purified water were added in sequence, the temperature was lowered to 0-5°C, 13.1g (0.2mol) of zinc powder were added in batches, and the temperature was slowly raised to room temperature for reaction for 1.5 hours. The mixture was filtered on diatomaceous earth, and the filter cake was rinsed with a small amount of water. The filtrate was retained and put back into the reaction bottle. 27.4 g (0.11 mol) of CbzOSu was added and 30% aqueous sodium carbonate solution was added dropwise to maintain the pH of the system at 8.5-9.5. No amino acid was detected by TLC. The low boiling point solvent was evaporated under reduced pressure at 20-30°C, and impurities were extracted with ethyl acetate. The aqueous phase was then adjusted to pH 4-4.5 with 3N hydrochloric acid, extracted with ethyl acetate, and Su alcohol was washed off with water. The mixture was then concentrated under reduced pressure until no liquid flowed, and ethyl acetate was used to remove water until the water content was <0.5%. Ethyl acetate and n-heptane were added for recrystallization to obtain 27.4 g of N-methyl-N-(benzyloxycarbonyl)-L-aspartic acid-4-tert-butyl ester with a yield of 81.2%, HPLC 99.7%, and chiral purity 99.8%.
[0026] Example 3
[0027]
[0028] To a 500mL jacketed reaction bottle, 18.9g (0.1mol) of L-aspartic acid-4-tert-butyl ester, 95mL of hexafluoroisopropanol, 32.7g (0.23mol) of disodium hydrogen phosphate, 12.2g (0.15mol) of 37% formaldehyde solution and 130mL of purified water were added in sequence, the temperature was lowered to 0-5°C, 13.1g (0.2mol) of zinc powder was added in 5-6 batches, and then the temperature was slowly raised to room temperature for reaction for 2.5 hours, diatomaceous earth was spread for filtration, the filter cake was rinsed with a small amount of water, the filtrate was retained, the filtrate was re-introduced into the reaction bottle, 200mL of toluene was added, the temperature was lowered to 0°C, 10% sodium hydroxide aqueous solution was added dropwise to adjust the pH to 11-12, and 20.5g (0.12mol) of CbzCl was added dropwise at the same time, and 10% sodium hydroxide was used to maintain the pH of the system at 11.0-12.0 for reaction for 3 hours. TLC detection showed that no amino acid remained. The product was allowed to stand and separate into layers. The aqueous phase was retained. The pH of the aqueous phase was adjusted to 4-4.5 with 3N hydrochloric acid at 0°C, extracted with ethyl acetate, washed with water, and then concentrated under reduced pressure until no liquid flowed. Ethyl acetate was used to remove water until the water content was <0.1%. Ethyl acetate and n-heptane were added for recrystallization to obtain 29.8 g of N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester with a yield of 88.4%, HPLC 99.8%, and chiral purity 99.5%.
[0029] Example 4
[0030]
[0031] To a 500mL jacketed reaction bottle, 18.9g (0.1mol) of L-aspartic acid-4-tert-butyl ester, 95mL of hexafluoroisopropanol, 24g (0.2mol) of sodium dihydrogen phosphate, 12.2g (0.15mol) of 37% formaldehyde solution and 95mL of purified water were added in sequence, the temperature was lowered to 0-5°C, 13.1g (0.2mol) of zinc powder was added in 5-6 batches, and then the temperature was slowly raised to room temperature for reaction for 2 hours, diatomaceous earth was spread for filtration, the filter cake was rinsed with a small amount of water, the filtrate was retained, the filtrate was re-introduced into the reaction bottle, 200mL of toluene was added, the temperature was lowered to 0°C, 30% potassium bicarbonate aqueous solution was added dropwise to adjust the pH to 11-12, and 20.5g (0.12mol) of CbzCl was added dropwise at the same time, and 30% potassium bicarbonate was used to maintain the pH of the system at 11.0-12.0 for reaction for 4.5 hours. TLC detection showed that no amino acid remained. The product was allowed to stand and separate into layers. The aqueous phase was retained. The pH of the aqueous phase was adjusted to 4-4.5 with 3N hydrochloric acid at 0°C, extracted with ethyl acetate, washed with water, and then concentrated under reduced pressure until no liquid flowed. Ethyl acetate was used to remove water until the water content was <0.1%. Ethyl acetate and n-heptane were added for recrystallization to obtain 29.4 g of N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester with a yield of 87.1%, HPLC 99.8%, and chiral purity 99.6%.
[0032] Example 5
[0033]
[0034] To a 500mL jacketed reaction bottle, 18.9g (0.1mol) of L-aspartic acid-4-tert-butyl ester, 95mL of hexafluoroisopropanol, 18.5g (0.13mol) of disodium hydrogen phosphate, 8.2g (0.1mol) of sodium acetate, 12.2g (0.15mol) of 37% formaldehyde solution and 145mL of purified water were added in sequence, the temperature was lowered to 0-5°C, 13.1g (0.2mol) of zinc powder was added in 5-6 batches, and then the temperature was slowly raised to room temperature for reaction for 2.5 hours, diatomaceous earth was spread for filtration, the filter cake was rinsed with a small amount of water, the filtrate was retained, and the filtrate was put back into the reaction bottle, 27.4g (0.11mol) of CbzOSu was added at room temperature, and sodium bicarbonate was directly added at the same time. 5.2g (0.3mol) TLC detected no amino acid residue, low boiling point solvent was evaporated under reduced pressure at 20-30°C, impurities were extracted with ethyl acetate, and then the aqueous phase was adjusted to pH 4-4.5 with 3N hydrochloric acid, extracted with ethyl acetate, Su alcohol was washed off with water, and then concentrated under reduced pressure until no liquid flowed, and ethyl acetate was used to carry water until the water content was <0.5%, 20mL of ethyl acetate was added, the temperature was raised to 70°C, 140mL of n-heptane was added dropwise, 0.1g of seed crystals was added, the temperature was slowly lowered to 10-15°C, filtered, the filter cake was rinsed with n-heptane, and dried to obtain 27.5g of N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester, with a yield of 81.5%, HPLC 99.9%, and chiral purity 99.5%.
[0035] The above-described embodiments are only preferred embodiments of the present invention, and are not exhaustive of the feasible implementations of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.
Claims
1. A method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester, characterized in that: The method comprises the following steps: mixing L-aspartic acid-4-tert-butyl ester, a highly polar solvent, a buffer salt, a formaldehyde solution and water, cooling the mixture to 0-5°C, adding zinc powder in batches, filtering the mixture, and adding a base and a Cbz protecting reagent to the filtrate to react and obtain N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester.
2. The method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester according to claim 1, characterized in that: The buffer salt is selected from sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium acetate / sodium dihydrogen phosphate or sodium acetate / disodium hydrogen phosphate.
3. The method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester according to claim 1, characterized in that: The high polarity solvent is selected from trifluoroethanol or hexafluoroisopropanol.
4. The method for preparing N-methyl-N-(benzyloxycarbonyl)-L-aspartic acid-4-tert-butyl ester according to claim 1, characterized in that: The base is selected from potassium carbonate, sodium carbonate, sodium bicarbonate or sodium hydroxide.
5. The method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester according to claim 1, characterized in that: The Cbz protecting agent is selected from Cbz-OSu or Cbz-Cl.
6. The method for preparing N-methyl-N-(benzyloxycarbonyl)-L-aspartic acid-4-tert-butyl ester according to claim 5, characterized in that: When the Cbz protecting agent is Cbz-OSu, the base is selected from potassium carbonate, sodium carbonate or sodium bicarbonate; when the Cbz protecting agent is Cbz-Cl, the base is selected from sodium hydroxide or potassium carbonate.
7. The method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester according to claim 1, characterized in that: The molar ratio of L-aspartic acid tert-butyl ester, formaldehyde, zinc powder, buffer salt, inorganic base and Cbz protective reagent is 1:1.1-1.5:1.9-2.0:2.0-2.5:2.5-3.5:1.05-1.
20.
8. The method for preparing N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester according to claim 1, characterized in that: The crude N-methyl-N-benzyloxycarbonyl-L-aspartic acid-4-tert-butyl ester obtained by the reaction is purified and crystallized by using ethyl acetate and n-heptane in a volume ratio of 1 / 5 to 1 / 7.