Synthesis method of (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester

Abstract

The invention discloses a method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidine-1-yl)-2-oxo-ethyl] tert-butyl carbamate, wherein Fmoc-4,4-difluoro-L-proline and amino resin are used as starting materials, and (S)-[2-(2-cyano-4,4-difluoropyrrolidine-1-yl)-2-oxo-ethyl] tert-butyl carbamate (Boc-fapi-a) is prepared by solid phase synthesis. The method has short synthesis steps and simple process operation, avoids cumbersome post-processing steps, has high product yield and high purity, and is easy to industrialize.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester. Background Art

[0002] The multi-modal imaging system, which is a combination of positron emission tomography (PET) and computer tomography (CT), is the world's most advanced medical imaging equipment and also an imaging technology that can image at the molecular level. Fibroblast activation protein (FAP) is a type II transmembrane serine protease that belongs to the prolyl oligopeptidase family. It is highly expressed in many epithelial tumor-associated fibroblasts, such as liver cancer, colorectal cancer, pancreatic cancer, and ovarian cancer. It is also highly expressed in lesions characterized by interstitial tissue activation, such as infectious, inflammatory, fibrotic diseases, and healing wounds, but is not expressed or expressed at a low level in normal tissues and benign tumor stroma.

[0003] FAPI is a radioactive tracer, the full name of which is fibroblast activation protein inhibitor. It is a small molecule enzyme activity inhibitor. FAP inhibitor (FAPI) has a high affinity and specificity for FAP on the surface of CAF membranes and can be used for PET imaging. It has high sensitivity and is conducive to the non-invasive early diagnosis, staging, differential diagnosis and prognosis evaluation of FAP-positive diseases. By combining with FAP, FAPI can visualize the location and size of the tumor in PET-CT scans, thereby helping to determine the type and location of the tumor and guiding the choice of tumor treatment. FAPI is considered to be a new tumor imaging agent with potential application prospects, and a series of radioactive ligands related to FAP targeting are being further developed.

[0004] (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester (Boc-fapi-a) is an important intermediate for the synthesis of FAP targeting structure, and its structural formula is:

[0005]

[0006] Among the synthesis methods of Boc-fapi-a in the prior art, the synthesis method with patent publication number CN111991570A is that the starting material (2S)-1-(tert-butoxycarbonyl)-4-hydroxypyrrolidine-2-carboxylic acid is subjected to ester exchange, hydroxyl oxidation to generate carbonyl, carbonyl fluorination, carbamoyl dehydration to generate cyano, removal of Boc protecting group of pyrrolidine, Boc-Gly-OH amide condensation reaction, and removal of Boc protecting group to obtain the target product (S)-4,4-difluoro-1-glycylpyrrolidine-2-cyano.

[0007] The reaction route is as follows:

[0008]

[0009] The synthesis method of patent publication number CN112105354A is as follows: the starting material 1-(tert-butyl)-2-methyl-(S)-4-oxopyrrolidine-1,2-dicarboxylate is subjected to carbonyl fluorination, carbamoyl dehydration to generate cyano group, removal of Boc protecting group of pyrrolidine, Boc-Gly-OH amide condensation reaction, and removal of Boc protecting group to obtain the target product (S)-4,4-difluoro-1-glycylpyrrolidine-2-cyano.

[0010] The reaction route is as follows:

[0011]

[0012] The synthesis methods of these two patents are similar. The cyano group is obtained by first converting the carboxylic acid into an ester, the ester is amidated to obtain an amide, and the amide is dehydrated with trifluoroacetic anhydride to convert it into a cyano group. HATU / DIEA is used for coupling Boc-Gly-OH, and there are more reaction steps. Summary of the invention

[0013] The purpose of the present invention is to provide a method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester.

[0014] To achieve the above purpose, the technical solution provided by the present invention is:

[0015] The present invention is achieved through the following technical solutions:

[0016] A method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester comprises the following steps:

[0017] Step S1: coupling Fmoc-4,4-difluoro-L-proline with amino resin to obtain Fmoc-4,4-difluoro-L-proline-resin;

[0018] Step S2: coupling Fmoc-4,4-difluoro-L-proline-resin with Boc-Gly-OH to obtain Boc-Gly-4,4-difluoro-L-proline-resin;

[0019] Step S3: Boc-Gly-4,4-difluoro-L-proline-resin is cleaved and post-treated to obtain (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester.

[0020] To optimize the above technical solutions, the specific measures taken also include:

[0021] The amino resin is selected from at least one of Rink Amide Resin, Rink Amide-MBHA Resin or Sieber Amide Resin.

[0022] Preferably, the molar ratio of Fmoc-4,4-difluoro-L-proline to amino resin is 1.5:1.

[0023] Furthermore, in step S1, the amino resin is swollen with solvent N,N-dimethylformamide, and the amount of solvent used is 4.0-6.0 ml of solvent DMF per 1 g of amino resin.

[0024] Preferably, the molar ratio of the amino resin to Boc-Gly-OH is 1:1.5.

[0025] Furthermore, in step S1 and step S2, the coupling auxiliary agents are HBTU and DIPEA.

[0026] Preferably, the molar ratio of the amino resin to the HBTU and DIPEA added during coupling is 1:1.5:3.

[0027] Furthermore, in step S3, triethylamine, trifluoroacetic anhydride and solvent DCM are used for cleavage, and the amount of solvent DCM used is 3.0-5.0 ml solvent DCM per 1 g of the resin to be cleaved.

[0028] Preferably, the molar ratio of the amino resin to the triethylamine and trifluoroacetic anhydride added during cracking is 1:3:1.5.

[0029] Furthermore, the cracking conditions are as follows: Boc-Gly-4,4-difluoro-L-proline-resin, triethylamine and DCM are put into a reaction bottle, trifluoroacetic anhydride is added dropwise under stirring at room temperature 10-30°C, and the reaction is stirred at room temperature 10-30°C for 1.0h.

[0030] Further, in step S3, the post-treatment is filtering and collecting the filtrate; the filter cake is washed with DCM and the filtrate is combined; the filtrate is transferred to a separatory funnel, and the DCM layer of the filtrate is washed with an appropriate amount of saturated NaHCO3 solution and an aqueous solution in turn to obtain a DCM solution; the DCM solution is placed on a rotary evaporator, concentrated to dryness under reduced pressure in a water bath at 40-50°C, and the (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester product is obtained.

[0031] Taking Rink Amide Resin as an example, the reaction equation is as follows:

[0032]

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The invention uses Fmoc-4,4-difluoro-L-proline and amino resin as starting materials and prepares (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester (Boc-fapi-a) by solid phase synthesis.

[0035] The invention has short synthesis steps and simple process operation, avoids complicated post-processing steps, has high product yield and purity, and is easy for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 : Overall picture of the high performance liquid chromatography of Boc-fapi-a prepared in Example 1.

[0037] Figure 2 : A magnified image of the HPLC of Boc-fapi-a prepared in Example 1.

[0038] Figure 3 : Overall picture of the high performance liquid chromatography of Boc-fapi-a prepared in Example 2.

[0039] Figure 4 : A magnified image of the HPLC of Boc-fapi-a prepared in Example 2.

[0040] Figure 5 : Overall picture of the high performance liquid chromatography of Boc-fapi-a prepared in Example 3.

[0041] Figure 6 : A magnified image of the HPLC of Boc-fapi-a prepared in Example 3.

[0042] Figure 7 : H NMR spectrum of Boc-fapi-a prepared in Example 1.

[0043] Figure 8 : NMR carbon spectrum of Boc-fapi-a prepared in Example 1.

[0044] Fig. 9 : Mass spectrum of Boc-fapi-a prepared in Example 1.

[0045] Fig.10 : Absolute configuration analysis diagram of Boc-fapi-a prepared in Example 1. DETAILED DESCRIPTION

[0046] The above contents of the present invention are further described in detail below in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the above contents of the present invention belong to the scope of the present invention.

[0047] The experimental methods used in the following examples are all conventional methods unless otherwise specified, and the reagents, methods and equipment used are all conventional reagents, methods and equipment in the technical field unless otherwise specified.

[0048] Example 1: Preparation of Boc-fapi-a (using Rink Amide Resin)

[0049] Follow these steps:

[0050] Feeding amount:

[0051] Table 1 Example 1 Feeding amount

[0052]

[0053] Process Description:

[0054] Washing and swelling:

[0055] Weigh Rink Amide Resin and add it to the peptide solid phase synthesis tube. Measure N,N-dimethylformamide (DMF) and add it to the peptide solid phase synthesis tube (the amount of solvent is based on the uniform dispersion of the resin in the solvent. Generally, the amount of solvent is 4.0-6.0 ml / 1 g resin, the same below). Wash twice (N2 bubbling, 1 min each time, and remove after washing); Add DMF to the peptide solid phase synthesis tube, bubble N2 for 30 min, and drain the liquid after sufficient swelling;

[0056] Coupling of Fmoc-4,4-difluoro-L-proline:

[0057] Removal of Fmoc group and color development:

[0058] Add 20% piperidine solution to the peptide solid phase synthesis tube, remove Fmoc twice [N2 bubbling, time (5min, 7min), and drain the liquid after completion], and wash with DMF 6 times (N2 bubbling, 1min each time, and drain after washing);

[0059] Kaiser method (take a small amount of resin, wash with DMF, add 3-5 drops of ninhydrin solution, heat at 120℃ for 3min, and observe whether color develops) to detect the color change of the resin;

[0060] Activation, coupling, color development, washing:

[0061] Based on the synthesis scale N0, weigh the materials according to a certain feed ratio: Fmoc-4,4-difluoro-L-proline (1.5eq), HBTU (1.5eq); add them to a beaker, take an appropriate amount of DMF, stir to dissolve, add DIPEA (3.0eq), activate the reaction for 3 minutes, and then add it to the peptide solid phase synthesis tube; room temperature 20-35℃, coupling reaction 0.5~1.0 hour;

[0062] Kaiser method (take a small amount of resin, wash with DMF, add 3-5 drops of ninhydrin solution, heat at 120°C for 3 minutes; observe whether color is developed to determine whether the reaction is complete. If color is developed, continue coupling for 0.5 hours);

[0063] The reaction solution was drained and washed with DMF 3 times (N2 bubbling, 1 min each time, and then drained after washing);

[0064] According to the dosage in the material list, repeat the above (2) operation to couple the following Boc-Gly-OH fragment:

[0065] shrink:

[0066] Add appropriate amount of methanol to the peptide solid phase synthesis tube and shrink it 3 times [N2 bubbling, the time is (5min, 5min, 10min), and then drain the liquid after completion];

[0067] dry:

[0068] Dry with nitrogen flow for 4.0-5.0 h until the resin particles are no longer sticky and are in the form of quicksand, to obtain 61.85 g of Boc-Gly-4,4-difluoro-L-proline-resin, with a weight gain of 11.85 g.

[0069] Lysis:

[0070] Boc-Gly-4,4-difluoro-L-proline-resin, triethylamine and DCM (3.0-5.0 ml / 1 g resin) were placed in a reaction bottle. Trifluoroacetic anhydride was added dropwise at room temperature (10-30°C) with stirring. After the addition was completed, the mixture was stirred at room temperature (10-30°C) for 1.0 h.

[0071] Post-treatment: Filter and collect the filtrate. Wash the filter cake once with a small amount of DCM. Combine the DCM filtrates; transfer the DCM filtrates to a separatory funnel, wash the DCM layer with an appropriate amount of saturated NaHCO3 solution and an aqueous solution in turn, and place the DCM solution on a rotary evaporator, and concentrate to dryness under reduced pressure in a water bath at 40-50°C to obtain a white solid, which is the product Boc-fapi-a, weighing 9.03g, with a yield of 96.05%. The purity of the product is: 99.503%

[0072] The overall HPLC diagram and enlarged diagram of the product in Example 1 are shown in Figure 1 , Figure 2 , NMR hydrogen spectrum see Figure 7 , NMR carbon spectrum see Figure 8 , mass spectrum see Fig. 9 , absolute configuration analysis diagram see Fig.10 .

[0073] Example 2

[0074] Preparation of Boc-fapi-a (using Rink Amide-MBHA Resin)

[0075]

[0076] Follow these steps:

[0077] Feeding amount:

[0078] Table 2 Example 2 Feeding amount

[0079]

[0080] Process Description:

[0081] Washing and swelling:

[0082] Weigh Rink Amide MBHA Resin and add it to a peptide solid phase synthesis tube. Measure N,N-dimethylformamide (DMF) and add it to the peptide solid phase synthesis tube (the amount of solvent is based on the uniform dispersion of the resin in the solvent. Generally, the amount of solvent is 4.0-6.0 ml / 1 g of resin, the same below). Wash twice (N2 bubbling, 1 min each time, and remove after washing); Add DMF to the peptide solid phase synthesis tube, bubble with N2 for 30 min, and drain the liquid after sufficient swelling;

[0083] Coupling of Fmoc-4,4-difluoro-L-proline:

[0084] Removal of Fmoc group and color development:

[0085] Add 20% piperidine solution to the peptide solid phase synthesis tube, remove Fmoc twice [N2 bubbling, time (5min, 7min), and drain the liquid after completion], and wash with DMF 6 times (N2 bubbling, 1min each time, and drain after washing);

[0086] Kaiser method (take a small amount of resin, wash with DMF, add 3-5 drops of ninhydrin solution, heat at 120℃ for 3min, and observe whether color develops) to detect the color change of the resin;

[0087] Activation, coupling, color development, washing:

[0088] Based on the synthesis scale N0, weigh the materials according to a certain feed ratio: Fmoc-4,4-difluoro-L-proline (1.5eq), HBTU (1.5eq); add them to a beaker, take an appropriate amount of DMF, stir to dissolve, add DIPEA (3.0eq), activate the reaction for 3 minutes, and then add it to the peptide solid phase synthesis tube; room temperature 20-35℃, coupling reaction 0.5~1.0 hour;

[0089] Kaiser method (take a small amount of resin, wash with DMF, add 3-5 drops of ninhydrin solution, heat at 120°C for 3 minutes; observe whether color is developed to determine whether the reaction is complete. If color is developed, continue coupling for 0.5 hours);

[0090] The reaction solution was drained and washed with DMF 3 times (N2 bubbling, 1 min each time, and then drained after washing);

[0091] According to the dosage in the material list, repeat the above (2) operation to couple the following Boc-Gly-OH fragment:

[0092] shrink:

[0093] Add appropriate amount of methanol to the peptide solid phase synthesis tube and shrink it 3 times [N2 bubbling, the time is (5min, 5min, 10min), and then drain the liquid after completion];

[0094] dry:

[0095] Dry with nitrogen flow for 4.0-5.0 h until the resin particles are no longer sticky and are in the form of quicksand, to obtain 62.49 g of Boc-Gly-4,4-difluoro-L-proline-resin, with a weight gain of 12.49 g.

[0096] Lysis:

[0097] Boc-Gly-4,4-difluoro-L-proline-resin, triethylamine and DCM (3.0-5.0 ml / 1 g resin) were placed in a reaction bottle. Trifluoroacetic anhydride was added dropwise at room temperature (10-30°C) with stirring. After the addition was completed, the mixture was stirred at room temperature (10-30°C) for 1.0 h.

[0098] Post-treatment: Filter and collect the filtrate. Wash the filter cake once with a small amount of DCM. Combine the DCM filtrates; transfer the DCM filtrates to a separatory funnel, wash the DCM layer with an appropriate amount of saturated NaHCO3 solution and an aqueous solution in turn, and place the DCM solution on a rotary evaporator, and concentrate to dryness under reduced pressure in a water bath at 40-50°C to obtain a white solid, which is the product Boc-fapi-a, weighing 9.63 g, with a yield of 95.11%. The purity of the product is: 99.479%.

[0099] The overall HPLC diagram and enlarged diagram of the product in Example 2 are shown in Figure 3 , Figure 4 .

[0100] Example 3: Preparation of Boc-fapi-a (using Sieber Amide Resin)

[0101]

[0102] Follow these steps:

[0103] Feeding amount:

[0104] Table 3 Feeding amount of Example 3

[0105]

[0106] Process Description:

[0107] Washing and swelling:

[0108] Weigh Sieber Amide Resin and add it to a peptide solid phase synthesis tube. Measure N,N-dimethylformamide (DMF) and add it to the peptide solid phase synthesis tube (the amount of solvent is based on the uniform dispersion of the resin in the solvent. Generally, the amount of solvent is 4.0-6.0 ml / 1 g of resin, the same below). Wash twice (N2 bubbling, 1 min each time, and remove after washing); Add DMF to the peptide solid phase synthesis tube, bubble N2 for 30 min, and drain the liquid after sufficient swelling;

[0109] Coupling of Fmoc-4,4-difluoro-L-proline:

[0110] Removal of Fmoc group and color development:

[0111] Add 20% piperidine solution to the peptide solid phase synthesis tube, remove Fmoc twice [N2 bubbling, time (5min, 7min), and drain the liquid after completion], and wash with DMF 6 times (N2 bubbling, 1min each time, and drain after washing);

[0112] Kaiser method (take a small amount of resin, wash with DMF, add 3-5 drops of ninhydrin solution, heat at 120℃ for 3min, and observe whether color develops) to detect the color change of the resin;

[0113] Activation, coupling, color development, washing:

[0114] Based on the synthesis scale N0, weigh the materials according to a certain feed ratio: Fmoc-4,4-difluoro-L-proline (1.5eq), HBTU (1.5eq); add them to a beaker, take an appropriate amount of DMF, stir to dissolve, add DIPEA (3.0eq), activate the reaction for 3 minutes, and then add it to the peptide solid phase synthesis tube; room temperature 20-35℃, coupling reaction 0.5~1.0 hour;

[0115] Kaiser method (take a small amount of resin, wash with DMF, add 3-5 drops of ninhydrin solution, heat at 120℃ for 3min; observe whether color appears to determine whether the reaction is complete. If color appears, continue coupling for 0.5 hours);

[0116] The reaction solution was drained and washed with DMF 3 times (N2 bubbling, 1 min each time, and then drained after washing);

[0117] According to the dosage in the material list, repeat the above (2) operation to couple the following Boc-Gly-OH fragment:

[0118] shrink:

[0119] Add appropriate amount of methanol to the peptide solid phase synthesis tube and shrink it 3 times [N2 bubbling, the time is (5min, 5min, 10min), and then drain the liquid after completion];

[0120] dry:

[0121] Dry with nitrogen flow for 4.0-5.0 h until the resin particles are no longer sticky and are in the form of quicksand, to obtain 62.88 g of Boc-Gly-4,4-difluoro-L-proline-resin, with a weight gain of 12.88 g.

[0122] Lysis:

[0123] Boc-Gly-4,4-difluoro-L-proline-resin, triethylamine and DCM (3.0-5.0 ml / 1 g resin) were placed in a reaction bottle. Trifluoroacetic anhydride was added dropwise at room temperature (10-30°C) with stirring. After the addition was completed, the mixture was stirred at room temperature (10-30°C) for 1.0 h.

[0124] Post-treatment: Filter and collect the filtrate. Wash the filter cake once with a small amount of DCM. Combine the DCM filtrates; transfer the DCM filtrates to a separatory funnel, wash the DCM layer with an appropriate amount of saturated NaHCO3 solution and an aqueous solution in turn, and place the DCM solution on a rotary evaporator, and concentrate to dryness under reduced pressure in a water bath at 40-50°C to obtain a white solid, which is the product Boc-fapi-a, weighing 10.46 g, with a yield of 95.15%. The purity of the product is: 99.543%.

[0125] The overall HPLC diagram and enlarged diagram of the product in Example 3 are shown in Figure 5 , Figure 6 .

[0126] The synthesis results of Examples 1-3 are summarized in Table 4.

[0127] Table 4 Summary of results of synthesis of Boc-fapi-a in Example

[0128]

[0129] From the results in the above table, it can be seen that according to the methods of Examples 1-3, the Boc-fapi-a obtained by using amino resin as a carrier has a purity of >99%, the reaction operation is simple and efficient, and cumbersome intermediate processes are avoided. The reaction conditions are mild, the requirements for production equipment are low, and it is suitable for industrial production.

[0130] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester, characterized in that: The following steps are involved: Step S1: coupling Fmoc-4,4-difluoro-L-proline with amino resin to obtain Fmoc-4,4-difluoro-L-proline-resin; Step S2: coupling Fmoc-4,4-difluoro-L-proline-resin with Boc-Gly-OH to obtain Boc-Gly-4,4-difluoro-L-proline-resin; Step S3: cleaving and post-treating Boc-Gly-4,4-difluoro-L-proline-resin to obtain (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester; The amino resin is selected from at least one of Rink Amide Resin, Rink Amide-MBHA Resin or Sieber Amide Resin; in step S1 and step S2, the coupling auxiliary agent is HBTU and DIPEA; The molar ratio of Fmoc-4,4-difluoro-L-proline to amino resin is 1.5:1; the molar ratio of amino resin to Boc-Gly-OH is 1:1.5; the molar ratio of amino resin to HBTU and DIPEA added during coupling is 1:1.5:

3.

2. The method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester according to claim 1, characterized in that: In step S1, the amino resin is swollen with solvent N,N-dimethylformamide, and the amount of solvent used is 4.0-6.0 ml of solvent DMF per 1 g of amino resin.

3. The method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester according to claim 1, characterized in that: In step S3, triethylamine, trifluoroacetic anhydride and solvent DCM are used for cleavage, and the amount of solvent DCM is 3.0-5.0 ml of solvent DCM per 1 g of resin to be cleaved; the molar ratio of amino resin to triethylamine and trifluoroacetic anhydride added during cleavage is 1:3:1.

5.

4. The method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester according to claim 1, characterized in that: The cracking conditions are as follows: Boc-Gly-4,4-difluoro-L-proline-resin, triethylamine and DCM are put into a reaction bottle, trifluoroacetic anhydride is added dropwise under stirring at room temperature of 10-30°C, and the reaction is stirred at room temperature of 10-30°C for 1.0h.

5. The method for synthesizing (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester according to claim 1, characterized in that: In step S3, the post-treatment is filtering and collecting the filtrate; the filter cake is washed with DCM and the filtrate is combined; the filtrate is transferred to a separatory funnel, and the DCM layer of the filtrate is washed with an appropriate amount of saturated NaHCO3 solution and an aqueous solution in turn to obtain a DCM solution; the DCM solution is placed on a rotary evaporator, concentrated to dryness under reduced pressure in a water bath at 40-50°C, and the (S)-[2-(2-cyano-4,4-difluoropyrrolidin-1-yl)-2-oxo-ethyl]carbamic acid tert-butyl ester product is obtained.

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