A method for preparing ristatin
Patent Information
- Application Number
- CN202611468017.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-21
- Publication Date
- 2026-10-27
AI Technical Summary
即使进行重结晶提纯后，光学纯度也无法提高，不能达到原料药质量要求
[0046]本发明采用固相合成法，高效构建了立他司特结构中的酰胺键，反应位点指向性强，并且不影响手性构型，有效提升了立他司特的化学纯度和光学纯度，利于产物纯化。同时反应工序简短，操作更便捷，避免加氢脱保护以及手性拆分的复杂操作，还降低了副反应发生，提升了原料利用率，整体制备更高效易行，为立他司特高效制备提供了一种新的策略。
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Figure CN122978103A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a preparation method of lifitegrast, in particular to a preparation method of lifitegrast based on a solid-phase synthesis strategy, and belongs to the field of pharmacy. BACKGROUND
[0002] Lifitegrast is a small molecule integrin inhibitor, which plays an anti-inflammatory role by blocking the interaction of LFA-1 and ICAM-1, and is mainly used for treating the signs and symptoms of dry eye disease (DED), and is suitable for patients with moderate to severe dry eye disease.
[0003]
[0004] Lifitegrast
[0005] The conventional synthesis route of lifitegrast is as follows:
[0006] .
[0007] In the method, compound 6 is hydrolyzed by lithium hydroxide to remove the benzyl protecting group, wherein the ester bond is hydrolyzed under alkaline conditions, and the chiral carbon is partially racemized, so that the optical purity of the product is only about 96%~97%. Even after recrystallization purification, the optical purity cannot be improved, and the quality requirements of the raw material cannot be met. In addition, although the salt formation and separation using dicyclohexylamine can improve the optical purity, the salt formation and separation causes a loss of about 30% of the product, resulting in low utilization rate of the product. The commonly used method for removing the benzyl protecting group is catalytic hydrogenation to remove benzyl, which can reduce the racemization of chiral carbon, but the cost of noble metal palladium catalyst is high and the dechlorination impurity and furan ring hydrogenation impurity are easy to produce, and the purity of the obtained crude product is only about 85%, which also affects the yield and purity of the final product. SUMMARY
[0008] The present application aims to provide a preparation method of lifitegrast with high chemical purity and optical purity.
[0009] Technical scheme: The preparation method of lifitegrast provided by the present application comprises the following steps:
[0010] ,
[0011] (1) SMA and SMB are protected by Fmoc-Cl respectively, and after post-treatment, protected products compound A and compound B are obtained respectively;
[0012] (2) Compound A obtained in step (1) is fixed on resin compound C to obtain compound D, and then the Fmoc protection is removed to obtain compound E;
[0013] (3) reacting the compound E obtained in step (2) with compound B (Fmoc-protected compound SMB) to obtain compound F, and then removing the Fmoc protection to obtain compound G;
[0014] (4) reacting the compound G obtained in step (3) with SMC, then cleaving the resin compound C, and post-treatment to obtain Rilostazyme.
[0015] Preferably, in step (1), the SMA is protected by Fmoc-Cl under the catalysis of DIEA to obtain compound A, wherein the molar ratio of Fmoc-Cl to SMA is 1.5:1-2:1, and the molar ratio of DIEA to SMA is 2:1-3:1.
[0016] Further preferably, in step (1), the molar ratio of Fmoc-Cl to SMA is 1.5:1, and the molar ratio of DIEA to SMA is 2:1.
[0017] Preferably, in step (1), the SMB is protected by Fmoc-Cl under the catalysis of DIEA to obtain compound B, wherein the molar ratio of Fmoc-Cl to SMB is 1.5:1-2:1, and the molar ratio of DIEA to SMB is 2:1-3:1.
[0018] Further preferably, in step (1), the molar ratio of Fmoc-Cl to SMB is 1.5:1, and the molar ratio of DIEA to SMB is 2:1.
[0019] Preferably, the post-treatment in step (1) is washing the reaction solution with saturated sodium bicarbonate solution until neutral.
[0020] Preferably, in step (2), the resin compound C is selected from Wang resin or Rink amide resin.
[0021] Further preferably, in step (2), the resin compound C is Wang resin.
[0022] Preferably, the compound A obtained in step (1) is dissolved in DMF and fixed on the resin compound C to obtain compound D.
[0023] Preferably, in step (2), the mass ratio of the resin compound C to SMA is 2:1-4:1.
[0024] Further preferably, in step (2), the mass ratio of the resin compound C to SMA is 2 : 1.
[0025] Preferably, in step (2), the compound A is fixed on the resin compound C through a coupling agent and an organic base to obtain compound D.
[0026] Further preferably, the coupling agent in step (2) is selected from DIC, DCC, CDI, and the molar ratio of the coupling agent to SMA is 1.5:1 to 2:1.
[0027] Still further preferably, the coupling agent in step (2) is DIC, and the molar ratio of DIC to SMA is 1.5:1.
[0028] Further preferably, the organic base in step (2) is selected from DMAP, TEA, DIEA, and NMM, and the molar ratio of the organic base to SMA is 0.1:1 to 0.5:1.
[0029] Still further preferably, the organic base in step (2) is DMAP, and the molar ratio of DMAP to SMA is 0.1:1.
[0030] Preferably, in step (2), a 20% (m / v) piperidine / DMF solution is used to remove the Fmoc protecting group from compound D to obtain compound E.
[0031] Preferably, in step (3), compound E and compound B are subjected to condensation reaction catalyzed by a DIC / HOBT or HATU / DIEA system, and in step (4), compound G and SMC are subjected to condensation reaction catalyzed by a DIC / HOBT or HATU / DIEA system.
[0032] Further preferably, in steps (3) and (4), condensation reaction is catalyzed by a DIC / HOBT system, and the molar ratio of DIC to HOBT is 1:1.
[0033] Still further preferably, in step (3), condensation reaction is catalyzed by a DIC / HOBT system, and the molar ratio of DIC to HOBT is 1:1, and the molar ratio of DIC to SMB is 1.3:1 to 1.4:1.
[0034] Still further preferably, in step (4), condensation reaction is catalyzed by a DIC / HOBT system, and the molar ratio of DIC to HOBT is 1:1, and the molar ratio of DIC to SMC is 1.25:1 to 1.7:1.
[0035] Preferably, the molar ratio of SMA to SMB is 1:1.1 to 1:1.5.
[0036] Further preferably, the molar ratio of SMA to SMB is 1:1.1.
[0037] Preferably, the molar ratio of SMA to SMC is 1:1.2 to 1:1.5.
[0038] Further preferably, the molar ratio of SMA to SMC is 1:1.2.
[0039] Preferably, in step (3), a 20% (m / v) piperidine / DMF solution is used to remove the Fmoc protecting group of compound F to obtain compound G.
[0040] Preferably, in step (4), a mixture of TFA-TIS-H2O in a volume ratio of 95:2.5:2.5 is used to cleave the resin compound C to which compound H is connected.
[0041] Preferably, the post-treatment in step (4) comprises a step of purifying litensilate using an acetone-water mixture in a volume ratio of 5:3~5:2, wherein the volume-mass ratio of the acetone-water mixture to litensilate is 7:1~8:1, and the purification temperature is 40~50℃.
[0042] Further preferably, in step (4), the purification is performed using an acetone-water mixture in a volume ratio of 5:2 or 5:3.
[0043] Further preferably, in step (4), the volume-mass ratio of the acetone-water mixture to the crude litensilate is 7:1 or 8:1.
[0044] Further preferably, in step (4), the purification temperature is 40℃ or 50℃.
[0045] Advantages: Compared with the prior art, the present application has the following remarkable advantages:
[0046] The present application uses solid-phase synthesis to efficiently construct the amide bond in the structure of litensilate, with strong site directionality and without affecting the chiral configuration, effectively improving the chemical purity and optical purity of litensilate, facilitating product purification. At the same time, the reaction process is short and the operation is more convenient, avoiding the complex operations of hydrogenation deprotection and chiral resolution, reducing the occurrence of side reactions, improving the utilization rate of raw materials, and making the overall preparation more efficient and easy to implement, providing a new strategy for efficient preparation of litensilate. BRIEF DESCRIPTION OF DRAWINGS
[0047] Figure 1 Chemical purity detection spectrum of compound G prepared in Example 1;
[0048] Figure 2 Chemical purity detection spectrum of crude litensilate prepared in Example 1;
[0049] Figure 3 Chemical purity detection spectrum of finished litensilate prepared in Example 1;
[0050] Figure 4 Optical purity detection spectrum of finished litensilate prepared in Example 1. DETAILED DESCRIPTION
[0051] The technical solutions of the present application are further described below in combination with examples.
[0052] Example 1
[0053]
[0054] (1) Preparation of compound G
[0055]
[0056] 1) Preparation of compound A: SMA (11.2 g, 40 mmol), DIEA (10.4 g, 80 mmol), Fmoc-Cl (15.5 g, 60 mmol), DCM (50 mL) were added into a reaction bottle, and the reaction was carried out at room temperature for 2 h. The reaction solution was washed with saturated sodium bicarbonate solution to be neutral, and concentrated to dryness to obtain compound A, which was dissolved in DMF (200 mL) for use.
[0057]
[0058] 2) Preparation of compound B: SMB (12.4 g, 44 mmol), DIEA (11.4 g, 88 mmol), Fmoc-Cl (17.0 g, 66 mmol), DCM (50 mL) were added into a reaction bottle, and the reaction was carried out at room temperature for 2 h. The reaction solution was washed with saturated sodium bicarbonate solution to be neutral, and concentrated to dryness to obtain compound B for use.
[0059] 3) Preparation of compound E: The DMF solution of compound A was added into a reaction tube, and Wang resin pretreated with DMF (i.e. compound C, 22.4 g) was added, followed by addition of DIC (7.6 g, 60 mmol) and DMAP (0.49 g, 4 mmol), and the reaction was carried out by shaking for 2 h. 20% (m / v) piperidine / DMF solution (200 mL) was added into the system, and the shaking was continued for 30 min. Filtration was carried out, and the resin was washed with DMF (200 mL*4) to obtain compound E.
[0060] 4) Preparation of compound G: The obtained compound E was added into a reaction tube, followed by addition of DMF (200 mL), compound B, HOBT (8.1 g, 60 mmol) and DIC (7.6 g, 60 mmol), and the reaction was carried out by shaking for 1 h. 20% (m / v) piperidine / DMF solution (200 mL was added into the system, and the shaking was continued for 30 min. Filtration and washing of the resin with DMF (200 mL*4) were carried out, and the resin was vacuum dried at 40°C for 16 h to obtain compound G (39.4 g) with a purity of 98.00% (HPLC). Figure 1 Intermediate 1).
[0061] Take 100 mg sample at room temperature with TFA / TIS / H2O mixture (1 mL, v / v / v = 95:2.5:2.5) to treat the final resin 0.5 h, the filtrate is concentrated to obtain compound J.
[0062]
[0063] Compound J is consistent with the desired structure, and its structural confirmation information is as follows:
[0064] 1 HNMR (400Hz DMSO): 8.62 (1H, d), 7.84 (1H, s), 7.75 (1H, d), 7.65 (1H, d), 7.54 (1H, t), 7.21 (1H, s), 4.64 (1H, dd), 3.92 (2H, s), 3.26-3.29 (3H, m), 3.15 (3H, s), 3.06 (1H, m), 2.62 (2H, s).
[0065] (2) Preparation of crude letasturide
[0066] SMC (7.8 g, 48 mmol), HOBT (8.1 g, 60 mmol), DIC (7.6 g, 60 mmol), DMF (200 mL) were added to the reaction tube and shaken for 1 h. Compound G obtained in step (1) (39.4 g) was then added and shaken for 2 h. Filtration was performed and the resin was washed with DMF (200 mL*4). The final resin was treated with a mixture of TFA / TIS / H2O (200 mL, v / v / v = 95:2.5:2.5) at room temperature for 1.5 h, and the filtrate was concentrated to obtain 20 g of crude letasturide with a purity of 99.17% and a two-step yield of 81.2%.
[0067] (3) Preparation of finished letasturide
[0068] Acetone (100 mL), purified water (60 mL), and crude letasturide (20.0 g) were added to the reaction bottle, which was warmed to 40°C and stirred. The filter cake was added and stirred for 3 h at constant temperature, and then the temperature was lowered to 20°C and stirred for 2 h at constant temperature. Filtration was performed and vacuum drying was carried out to obtain 17.3 g of letasturide with a chemical purity of 99.96%, a yield of 86.5%, and an optical purity of 99.98%.
[0069] 1H H NMR (400 Hz DMSO): 12.95 (1H, br s), 9.08 (1H, d), 8.13 (1H, d), 7.91 (1H, s), 7.80 (1H, d), 7.75 (1H, d), 7.73 (1H, d), 7.70 (1H, d), 7.59 (1H, t), 7.46 (1H, s), 7.34 (1H, s), 7.05 (1H, d), 4.84 (1H, m), 4.80 (2H, m), 3.76 (2H, m), 3.34 (1H, dd), 3.07 (1H, dd), 3.18 (3H, s), 2.79 (2H, s).
[0070] Example 2
[0071] (1) Preparation of compound G
[0072] 1) Preparation of compound A: SMA (5.6 g, 20 mmol), DIEA (5.2 g, 40 mmol), Fmoc-Cl (7.8 g, 30 mmol), DCM (30 mL) were added into a reaction bottle, and reacted at room temperature for 2 h. The reaction solution was washed with saturated sodium bicarbonate solution to neutral, and concentrated to dryness to obtain compound A, which was dissolved in DMF (100 mL) for use.
[0073] 2) Preparation of compound B: SMB (8.5 g, 30 mmol), DIEA (7.8 g, 60 mmol), Fmoc-Cl (11.7 g, 45 mmol), DCM (50 mL) were added into a reaction bottle, and reacted at room temperature for 2 h. The reaction solution was washed with saturated sodium bicarbonate solution to neutral, and concentrated to dryness to obtain compound B for use.
[0074] 3) Preparation of compound E: The DMF solution of compound A was added into a reaction tube, and Wang resin (11.2 g) pretreated with DMF was added, followed by addition of DIC (3.8 g, 30 mmol) and DMAP (0.24 g, 2 mmol), and oscillation for 2 h. 20% (m / v) piperidine / DMF solution (100 mL) was added into the system, and oscillation was continued for 30 min. Filtration was performed, and the resin was washed with DMF (100 mL*4) to obtain compound E.
[0075] 4) Preparation of compound G: The obtained compound E was added into a reaction tube, followed by addition of DMF (100 mL), compound B, HOBT (5.4 g, 40 mmol) and DIC (5.1 g, 40 mmol), and oscillation for 1 h. 20% (m / v) piperidine / DMF solution (100 mL) was added into the system, and oscillation was continued for 30 min. Filtration was performed, and the resin was washed with DMF (100 mL*4) and vacuum dried at 40°C for 16 h to obtain compound G (18.2 g).
[0076] Take 100 mg sample at room temperature with TFA / TIS / H2O mixture (1 mL, v / v / v = 95:2.5:2.5) to treat the final resin 0.5 h, the filtrate is concentrated to obtain compound J.
[0077] (2) Preparation of crude ritanserin
[0078] SMC (4.9 g, 30 mmol), HOBT (5.4 g, 40 mmol), DIC (5.1 g, 40 mmol), DMF (100 mL) were added into the reaction tube and shaken for 1 h. Compound G (18.2 g) obtained in step (1) was added and shaken for 2 h. Filtration was performed and the resin was washed with DMF (100 mL*4). The final resin was treated with TFA / TIS / H2O mixture (100 mL, v / v / v = 95:2.5:2.5) at room temperature for 1.5 h, and the filtrate was concentrated to obtain 9.6 g of crude ritanserin with a purity of 99.32% and a two-step yield of 77.8%.
[0079] (3) Preparation of finished ritanserin
[0080] Acetone (45 mL), purified water (18 mL), and crude ritanserin (9.0 g) were added into the reaction bottle, which was heated to 45°C and stirred. The filter cake was added and stirred for 3 h at 45°C, and then the temperature was lowered to 25°C and stirred for 2 h. Filtration was performed and the product was dried under vacuum to obtain 7.5 g of ritanserin with a chemical purity of 99.97%, a yield of 83.33%, and an optical purity of 99.98%.
[0081] Example 3
[0082] (1) Preparation of compound G
[0083] 1) Preparation of compound A: SMA (5.6 g, 20 mmol), DIEA (7.8 g, 60 mmol), Fmoc-Cl (10.4 g, 40 mmol), and DCM (30 mL) were added into the reaction bottle, which was reacted at room temperature for 2 h. The reaction solution was washed with saturated sodium bicarbonate solution until it became neutral, and then concentrated to dryness to obtain compound A, which was dissolved in DMF (100 mL) for later use.
[0084] 2) Preparation of compound B: SMB (6.2 g, 22 mmol), DIEA (8.6 g, 66 mmol), Fmoc-Cl (11.4 g, 44 mmol), and DCM (50 mL) were added into the reaction bottle, which was reacted at room temperature for 2 h.
[0085] 3) Preparation of compound E: DMF solution of compound A was added to the reaction tube, and then Wang resin pretreated with DMF (22.4 g) was added, followed by addition of DIC (5.1 g, 40 mmol) and DMAP (1.22 g, 10 mmol), and shaking for 2 h. A 20% (m / v) piperidine / DMF solution (100 mL) was added to the system, and shaking was continued for 30 min. Filtration was performed, and the resin was washed with DMF (100 mL*4), to obtain compound E.
[0086] 4) Preparation of compound G: the obtained compound E was added to the reaction tube, followed by addition of DMF (100 mL), compound B, HOBT (4.1 g, 30 mmol), and DIC (3.8 g, 30 mmol), and shaking for 1 h. A 20% (m / v) piperidine / DMF solution (100 mL) was added to the system, and shaking was continued for 30 min. Filtration was performed, and the resin was washed with DMF (100 mL*4) and vacuum dried at 40 °C for 16 h, to obtain compound G (17.4 g).
[0087] A 100 mg sample was used to treat the final resin with a mixture of TFA / TIS / H2O (1 mL, v / v / v = 95:2.5:2.5) at room temperature for 0.5 h, and the filtrate was concentrated to obtain compound J.
[0088] (2) Preparation of crude letastignt
[0089] The reaction tube was added with SMC (3.9 g, 24 mmol), HOBT (5.4 g, 40 mmol), DIC (5.1 g, 40 mmol), and DMF (100 mL), and shaking was performed for 1 h. Then, the obtained compound G in step (1) (17.4 g) was added, and shaking was performed for 2 h. Filtration was performed, and the resin was washed with DMF (100 mL* 4). The final resin was treated with a mixture of TFA / TIS / H2O (100 mL, v / v / v = 95:2.5:2.5) at room
[0090] (3) Preparation of finished letastignt
[0091] The reaction bottle was added with acetone (45 mL), purified water (27 mL), and crude letastignt (9.0 g), and the temperature was raised to 40 °C, followed by stirring, addition of the filter cake, and stirring at constant temperature for 3 h, and then the temperature was lowered to 20 °C, and stirring was performed at constant temperature for 2 h. Filtration was performed, and vacuum drying was performed to obtain 7.1 g of letastignt, with a chemical purity of 99.96%, a yield of 78.9%, and an optical purity of 99.98%.
[0092] Example 4
[0093] (1) Preparation of compound G
[0094] 1) Preparation of compound A: SMA (5.6 g, 20 mmol), DIEA (7.8 g, 60 mmol), Fmoc-Cl (10.4 g, 40 mmol), DCM (30 mL) were added into a reaction flask and reacted at room temperature for 2 h. The reaction solution was washed with saturated sodium bicarbonate solution until neutral, and concentrated to dryness to obtain compound A, which was dissolved in DMF (100 mL) for use.
[0095] 2) Preparation of compound B: SMB (6.2 g, 22 mmol), DIEA (8.6 g, 66 mmol), Fmoc-Cl (11.4 g, 44 mmol), DCM (50 mL) were added into a reaction flask and reacted at room temperature for 2 h. The reaction solution was washed with saturated sodium bicarbonate solution until neutral, and concentrated to dryness to obtain compound B for use.
[0096] 3) Preparation of compound E: The DMF solution of compound A was added into a reaction tube, and Wang resin (22.4 g) pretreated with DMF was added, followed by addition of DIC (5.1 g, 40 mmol) and DMAP (0.24 g, 2 mmol), and oscillation for 2 h. A 20% (m / v) piperidine / DMF solution (100 mL) was added into the system, and oscillation was continued for 30 min. Filtration was performed, and the resin was washed with DMF (100 mL*4) to obtain compound E.
[0097] 4) Preparation of compound G: The obtained compound E was added into a reaction tube, followed by addition of DMF (100 mL), compound B, HOBT (4.1 g, 30 mmol), and DIC (3.8 g, 30 mmol), and oscillation for 1 h. A 20% (m / v) piperidine / DMF solution (100mL) was added into the system, and oscillation was continued for 30 min. Filtratio was performed, and the resin was washed with DMF (100 mL*4) and vacuum dried at 40 °C for 16 h to obtain compound G (18.4 g).
[0098] A 100 mg sample was taken to treat the final resin with a mixture of TFA / TIS / H2O (1 mL, v / v / v = 95:2.5:2.5) at room temperature for 0.5 h, and the filtrate was concentrated to obtain compound J.
[0099] (2) Preparation of crude litaoxeride
[0100] The reaction tube was added with SMC (4.2 g, 26 mmol), HOBT (5.4 g, 40 mmol), DIC (5.1 g, 40 mmol), DMF (100 mL), and shaken for 1 h. Then the compound G obtained in step (1) (18.4 g) was added, and shaken for 2 h. The resin was filtered and washed with DMF (100 mL*4). The final resin was treated with a mixture of TFA / TIS / H2O (100 mL, v / v / v = 95:2.5:2.5) at room temperature for 1.5 h, and the filtrate was concentrated to obtain 10.3 g of the crude letasturide with a purity of 99.23%, and a two-step yield of 83.4%.
[0101] (3) Preparation of the finished letasturide
[0102] The reaction bottle was added with acetone (50 mL), purified water (30 mL), and the crude letasturide (10.0 g), and warmed to 40 °C, stirred, and the filter cake was added, and warmed and stirred for 3 h, and cooled to 20 °C, and stirred for 2 h. Filtration and vacuum drying gave 8.2 g of letasturide with a chemical purity of 99.98%, a yield of 82.0%, and an optical purity of 99.98%.
Claims
1. A method for preparing ristatin, characterized in that, Includes the following steps: ， (1) SMA and SMB were protected with Fmoc-Cl and then post-treated to obtain the protected product compounds A and B, respectively; (2) The compound A obtained in step (1) is fixed onto resin compound C to obtain compound D, and then the Fmoc protection is removed to obtain compound E; (3) React compound E obtained in step (2) with compound B to obtain compound F, and then remove Fmoc protection to obtain compound G; (4) React the compound G obtained in step (3) with SMC, then remove the resin compound C, and then perform post-treatment to obtain ristat.
2. The method for preparing ristatin according to claim 1, characterized in that, In step (1), under the catalysis of DIEA, SMA is protected by Fmoc-Cl to obtain compound A, wherein the molar ratio of Fmoc-Cl to SMA is 1.5:1~2:1, and the molar ratio of DIEA to SMA is 2:1~3:
1.
3. The method for preparing ristatin according to claim 1, characterized in that, In step (1), under the catalysis of DIEA, SMB is protected by Fmoc-Cl to obtain compound B, wherein the molar ratio of Fmoc-Cl to SMB is 1.5:1~2:1, and the molar ratio of DIEA to SMB is 2:1~3:
1.
4. The method for preparing ristatin according to claim 1, characterized in that, The resin compound C used in step (2) is selected from Wang resin or Rinkamide resin.
5. The method for preparing ristatin according to claim 1, characterized in that, In step (2), the mass ratio of resin compound C to compound A is 2:1 to 4:
1.
6. The method for preparing ristatin according to claim 1, characterized in that, In step (2), compound A is fixed onto resin compound C by coupling agent and organic base catalysis.
7. The method for preparing ristatin according to claim 6, characterized in that, The coupling agent is selected from DIC, DCC, and CDI, and the molar ratio of the coupling agent to SMA is 1.5:1 to 2:
1.
8. The method for preparing ristatin according to claim 6, characterized in that, The organic base is selected from DMAP, TEA, DIEA, and NMM, and the molar ratio of the organic base to SMA is 0.1:1 to 0.5:
1.
9. The method for preparing ristatin according to claim 1, characterized in that, In step (3), compound E and compound B undergo a condensation reaction catalyzed by the DIC / HOBT or HATU / DIEA system. In step (4), compound G and SMC undergo a condensation reaction catalyzed by the DIC / HOBT or HATU / DIEA system.
10. The method for preparing ristatin according to claim 9, characterized in that, In steps (3) and (4), the DIC / HOBT system is used for condensation reaction, wherein the molar ratio of DIC to HOBT is 1:
1.
11. The method for preparing ristatin according to claim 1, characterized in that, The molar ratio of SMA to SMB is 1:1.1 to 1:1.
5.
12. The method for preparing ristatin according to claim 1, characterized in that, The molar ratio of SMA to SMC is 1:1.2 to 1:1.
5.
13. The method for preparing ristatin according to claim 1, characterized in that, The post-processing in step (4) includes purifying ristatin with an acetone-water mixture in a volume ratio of 5:3 to 5:2, wherein the volume-to-mass ratio of the acetone-water mixture to ristatin is 7:1 to 8:1.