Method for preparing N-alpha-fluorenylmethoxycarbonyl-N-in-t-butyloxycarbonyl-L-tryptophan

Abstract

The invention relates to a method for preparing N-alpha-fluorenylmethoxycarbonyl-N-in-t-butyloxycarbonyl-L-tryptophan, which comprises the following steps: step 1, under the action of a first alkali, enabling L-tryptophan (L-Trp-OH) to react with 9-fluorenylmethyl-N-succinimido carbonate (FmocOSu), so as to obtain Fmoc-Trp-OH; step 2, enabling the Fmoc-Trp-OH to react with benzyl alcohol under the action of p-toluenesulfonic acid, so as to obtain Fmoc-Trp-OBzl; step 3, enabling the Fmoc-Trp-OBzl to react with Boc2O under the action of a second alkali, so as to obtain Fmoc-Trp (Boc)-OBzl; and step 4, carrying out hydrogenolysis reaction on the Fmoc-Trp (Boc)-OBzl under the catalysis of palladium carbon, so as to obtain the target compound Fmoc-Trp (Boc)-OH. All the raw materials in the method can be conveniently purchased on the market, and the method is simple in process route, mild in reaction condition, small in organic solvent dosage, less in separation operation, few in organic impurities, high in yield, high in purity and suitable for commercial production.

Description

Technical Field

[0001] The term amino acid synthesis technical field of the present invention specifically relates to a method for preparing N-alpha-fluorenylmethoxycarbonyl-N-tert-butyloxycarbonyl-L-tryptophan. Background Art

[0002] Tryptophan (Trp) is a unique residue in peptides and proteins. Since the development of insulin in 1923, more than 100 peptide drugs have been approved by the U.S. Food and Drug Administration (FDA) to enter the market, of which about 40 drugs for the treatment of a wide range of diseases such as cancer, cardiovascular disease and metabolic diseases contain at least one Trp residue (as shown below). Chemical modification of Trp residues embedded in peptide drugs can not only modulate drug-target interactions, but also provide opportunities to improve drug stability, bioavailability and pharmacokinetics.

[0003]

[0004] In the synthesis of peptide drugs, N-alpha-fluorenylmethoxycarbonyl-N-in-tert-butyloxycarbonyl-L-tryptophan (Fmoc-Trp(Boc)-OH, the structural formula is shown below) is a widely used synthon for introducing tryptophan based on the Fmoc strategy. Protecting the tryptophan indole ring with tert-butyloxycarbonyl (Boc) can reduce the activity of the carbon atom at the 2 position of the indole, thereby reducing the impurities caused by its reaction with nucleophilic reagents.

[0005]

[0006] At present, in the disclosed methods for preparing Fmoc-Trp(Boc)-OH, such as CN202211006819 and CN202110672717, L-tryptophan is usually used as the starting material, and after carboxylic acid protection (esterification reaction), amino protection (trifluoroacetyl, benzyloxycarbonyl or trityl), indole introduces tert-butyloxycarbonyl (Boc), and then removes the carboxylic acid and amino protection groups, and finally introduces fluorenylmethyloxycarbonyl (Fmoc) on the amino group to obtain the target compound. The reaction process can be shown as follows.

[0007]

[0008] However, commercially available Fmoc-Trp(Boc)-OH, after high pressure liquid chromatography (HPLC) detection, is usually found to contain impurity Fmoc-Trp-OH, i.e., impurity (hereinafter referred to as de-Boc impurity, structural formula is shown below) from which tert-butyloxycarbonyl (Boc) on the indole ring has fallen off. This is because the tert-butyloxycarbonyl (Boc) on the indole ring is extremely unstable, and it will be rapidly taken off in a strong acid and strong base environment, and can even be slowly taken off in weak acid, weak base and neutral protic solvents. Not only that, this impurity is difficult to remove by unit operations such as washing and crystallization during post-processing. This makes the two preparation methods of detrifluoroacetyl under alkaline conditions (such as sodium hydroxide and potassium carbonate aqueous solution) and detrityl under acidic conditions (such as formic acid, acetic acid, propionic acid) become very difficult in practical applications, especially in the production process, as the operation time is extended, the generation of impurity Fmoc-Trp-OH will be promoted, thereby sharply increasing the risk of unqualified product quality.

[0009] In addition, commercially available Fmoc-Trp(Boc)-OH usually contains hydrogenated impurities (structural formula shown below), i.e., a compound generated by reduction of a double bond on the indole ring. It is an impurity caused by excessive hydrogenation during the debenzyloxycarbonylation process. It is difficult to detect because its retention time is very close to that of the target compound in high pressure liquid chromatography (HPLC). This hydrogenated impurity is similar to the de-Boc impurity and is difficult to remove through unit operations such as washing and crystallization during post-treatment. Therefore, these two impurities are key impurities of the compound.

[0010]

[0011] Therefore, in view of the problems of existing preparation methods and product quality, there is still a need to improve the preparation method of Fmoc-Trp(Boc)-OH. Summary of the invention

[0012] In order to solve the above problems, the object of the present invention is to provide an economical, environmentally friendly and commercially available method for synthesizing high-quality Fmoc-Trp(Boc)-OH.

[0013] In a first aspect, the present invention provides a method for preparing N-alpha-fluorenylmethoxycarbonyl-N-in-tert-butyloxycarbonyl-L-tryptophan (Fmoc-Trp(Boc)-OH). The method can be carried out as shown in the following reaction path, comprising the following steps:

[0014]

[0015] Step 1, under the action of a first base, reacting L-tryptophan (L-Trp-OH) with 9-fluorenylmethyl-N-succinimidyl carbonate (FmocOSu) to obtain Fmoc-Trp-OH;

[0016] Step 2, reacting Fmoc-Trp-OH with benzyl alcohol under the action of p-toluenesulfonic acid or its hydrate to obtain Fmoc-Trp-OBzl;

[0017] Step 3, under the action of a second base, reacting Fmoc-Trp-OBzl with Boc2O to obtain Fmoc-Trp(Boc)-OBzl;

[0018] Step 4: Fmoc-Trp(Boc)-OBzl is subjected to hydrogenolysis reaction under the catalysis of palladium on carbon to obtain the target compound Fmoc-Trp(Boc)-OH.

[0019] In some embodiments, in step 1, the first base is selected from any one or a combination of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate. In a specific embodiment, the first base is sodium carbonate.

[0020] In some embodiments, in step 1, the molar ratio of L-Trp-OH:FmocOSu:first base is 1:(0.9-1):(1-3). In a specific embodiment, the molar ratio of L-Trp-OH:FmocOSu:first base is 1:0.95:1.5.

[0021] In one specific embodiment, step 1 uses water as solvent and reacts at room temperature (20° C. to 25° C.) for 2 to 3 hours.

[0022] In some embodiments, after step 1, the reaction system is acidified using, for example, hydrochloric acid, and then filtered to obtain a wet product Fmoc-Trp-OH.

[0023] In some embodiments, step 2 is performed at a temperature of 30°C to 70°C, preferably 40°C to 45°C.

[0024] In some embodiments, in step 2, the molar ratio of Fmoc-Trp-OH:benzyl alcohol:p-toluenesulfonic acid monohydrate is 1:(1.1-3):(0.02-0.2), preferably 1:1.5:0.05.

[0025] In a specific implementation, step 2 uses toluene as solvent and reacts for 8 to 24 hours under negative pressure reflux and water separation conditions.

[0026] In some specific embodiments, after the reaction in step 2 is completed, cooling and crystallization are performed, and then filtration and drying are performed to obtain Fmoc-Trp-OBzl.

[0027] In some embodiments, the second base is selected from p-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine, pyridine, preferably p-dimethylaminopyridine (DMAP).

[0028] In some embodiments, in step 3, the molar ratio of Fmoc-Trp-OBzl:Boc2O:second base is 1:(1.0-1.1):(0.01-0.05), preferably 1:1.05:0.02.

[0029] In one specific embodiment, step 3 uses tetrahydrofuran as solvent and reacts at room temperature for 2 to 5 hours.

[0030] In some embodiments, in step 3, after the reaction is complete, the reaction solution is directly used in the next step without separation.

[0031] In some embodiments, in step 4, the mass ratio of Fmoc-Trp(Boc)-OBzl: palladium carbon (5% palladium carbon) is 1:(0.01-0.05), preferably 1:0.02.

[0032] In some embodiments, step 4 comprises adding a catalytic amount of palladium-carbon catalyst to the reaction solution obtained in step 3, and reacting at room temperature under a hydrogen environment for 6 to 30 hours.

[0033] In some embodiments, after the reaction in step 4 is completed, palladium carbon is removed by filtration and then washed with water. After tetrahydrofuran is concentrated at 20° C. to 25° C., n-heptane is added to obtain a suspension, which is finally filtered and dried to obtain the target compound.

[0034] The preparation method provided by the present invention adopts cheap and readily available L-Trp-OH, FmocOSu, benzyl alcohol and Boc2O as main raw materials, and uses a catalytic amount of p-toluenesulfonic acid monohydrate, p-dimethylaminopyridine and 5% palladium on carbon. Fmoc-Trp-OH, Fmoc-Trp-OBzl and Fmoc-Trp(Boc)-OBzl are synthesized in sequence according to the synthesis steps, and finally the target compound Fmoc-Trp(Boc)-OH is obtained by removing the benzyl ester.

[0035] From the perspective of sustainability, the atomic utilization of the method of the present invention is 60.5%, while the atomic utilization of the preparation methods based on trifluoroacetyl, benzyloxycarbonyl or trityl protecting groups is 45.4%, 46.9% and 41.5%, respectively. In addition, the reaction temperature involved in the method of the present invention is between 20°C and 45°C, which is very mild; and only toluene is used in step 2, tetrahydrofuran is used in step 3, and n-heptane is used in step 4, so the overall amount of organic solvent is small, and the single solvent in each step is easy to recycle.

[0036] From the production point of view, the wet cake Fmoc-Trp-OH in step 1 of the method of the present invention can be directly used in step 2 without drying; the Fmoc-Trp(Boc)-OBzl reaction solution in step 3 can be directly used in step 4 without post-treatment. The process operation is simple, the production time is shortened, and the production efficiency is improved.

[0037] From the perspective of product quality, this method uses low temperature (40°C to 45°C) negative pressure reflux water separation in step 2 to effectively control the impurities generated by the electrophilic substitution reaction at the 2-position of indole. In step 3, a very small amount of catalyst DMAP (0.02 equivalents) is used to inhibit the degradation of the Fmoc group. At the same time, in step 4, no strong acid, strong base system and protic solvent are used, tetrahydrofuran is concentrated at room temperature, solidified and dried at room temperature, and the de-Boc impurities are controlled to be below 0.2%, or even below 0.15%. In addition, no impurities caused by hydrogenation of the indole ring were found, which may be because the α-amino group is protected by the huge Fmoc, which increases the steric hindrance of the molecule, resulting in the indole ring being unable to be hydrogenated. The intermediates and products are separated and purified in steps 2 and 4, respectively, to further ensure the purity of the product.

[0038] In a second aspect, the present invention provides Fmoc-Trp(Boc)-OH obtained by the above preparation method, wherein the sum of the contents of de-Boc impurities and hydrogenated impurities is less than 0.15%.

[0039] In a third aspect, the present invention relates to the use of the above-mentioned preparation method in a route for synthesizing compounds (including drugs) containing Trp residues. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The reaction scheme of the present application is shown.

[0041] Figure 2 This is the HPLC spectrum of the wet product Fmoc-Trp-OH in step 1 of Example 2;

[0042] Figure 3 is the HPLC spectrum of Fmoc-Trp-OBzl after drying in step 2 of Example 2;

[0043] Figure 4 is the Fmoc-Trp-OBzl after drying in step 2 of Example 2 1 H NMR spectrum;

[0044] Figure 5 The reaction solution of Fmoc-Trp(Boc)-OBzl in step 3 of Example 2 1 H NMR spectrum;

[0045] Figure 6 This is the HPLC spectrum of the chemical purity of the product Fmoc-Trp(Boc)-OH in step 4 of Example 1;

[0046] Figure 7 This is the HPLC spectrum of the chemical purity of the product Fmoc-Trp(Boc)-OH in step 4 of Example 2;

[0047] Figure 8 This is the HPLC spectrum of the optical purity of the product Fmoc-Trp(Boc)-OH in step 4 of Example 2;

[0048] Fig. 9 The product Fmoc-Trp(Boc)-OH of step 4 of Example 2 1 H NMR spectrum. DETAILED DESCRIPTION

[0049] The present invention provides a method for preparing Fmoc-Trp(Boc)-OH (such as Figure 1 The method is simple, has mild reaction conditions, uses less organic solvent, has less separation operations, has less organic impurities, and has high product yield and purity. Therefore, it is an economical and environmentally friendly method for commercially synthesizing high-quality Fmoc-Trp(Boc)-OH, and has been verified in kilogram-level experiments.

[0050] It can be seen from the specific examples below that the method of the present invention has a stable yield and high product purity after kilogram-scale experiments.

[0051] Table 1. The abbreviations or English letters used in this invention have the following meanings:

[0052]

[0053]

[0054] The present invention will be further described below with a particularly preferred synthetic route. It should be understood by those skilled in the art that the present invention is not limited to the following specific examples. The reaction raw materials, catalysts, solvents, etc. used in the following preparation examples are all commercially available.

[0055] During the reaction, HPLC was used to detect the reaction and product purity. The specific method of HPLC is:

[0056] Analytical method 1, for step 1

[0057] Chromatographic column: Kromasil C18 250×4.6mm 5μm

[0058] Column temperature: 25°C

[0059] Flow rate: 1.0mL / min

[0060] Detector: UV (210nm)

[0061] Mobile phase: A: Chromatographic grade water containing 0.1% trifluoroacetic acid;

[0062] B Chromatographic Grade Acetonitrile

[0063] Gradient: 0 min 70% A and 30% B

[0064] 10 minutes 30% A and 70% B

[0065] 30% A and 70% B in 30 minutes

[0066] L-Trp-OH retention time 3.2 minutes

[0067] FmocOSu retention time 14.0 minutes

[0068] Fmoc-Trp-OH retention time 13.6 minutes

[0069] Analytical method 2, for steps 2 and 3

[0070] Compared with method 1, only the mobile phase gradient was changed.

[0071] Isocratic: 30% A and 70% B

[0072] Fmoc-Trp-OH retention time 3.0 min

[0073] Fmoc-Trp-OBzl retention time 4.5 minutes

[0074] Analysis method 3, used in step 4

[0075] Column: Nucleosil 100-5C18 250×4.6mm 5μm

[0076] Column temperature: 35°C

[0077] Flow rate: 1.0mL / min

[0078] Detector: UV (210nm)

[0079] Mobile phase: A: Chromatographic grade water containing 0.1% phosphoric acid and 0.1% triethylamine;

[0080] B Chromatographic Grade Acetonitrile

[0081] Gradient: 40% A and 60% B at 0 min

[0082] 30 minutes 0% A and 100% B

[0083] 30% A and 70% B in 30 minutes

[0084] L-Trp(Boc)-OH retention time 3.5 minutes

[0085] Fmoc-beta-Ala-OH retention time 4.9 minutes

[0086] Fmoc-Trp-OH retention time 6.7 minutes

[0087] Fmoc-Trp(Boc)-OH retention time 9.1 minutes

[0088] Example 1

[0089] Step 1: Under nitrogen protection, add 515mL water, 31.5g L-tryptophan (0.154mol) and 24.5g sodium carbonate (0.231mol) to a 1L reaction bottle. Stir to clarify at 20-25°C, then add 49.4g FmocOSu (0.147mol), let the reaction system stir at 20-25°C for 2 hours, and the reaction system gradually clarifies. After the HPLC detection reaction is completed, add concentrated hydrochloric acid to adjust the pH value of the system to 2-3, at which time a large amount of white solid precipitates. Filter the reaction system, wash the filter cake with 100mL water, and obtain 130g white solid Fmoc-Trp-OH (wet product, theoretical 0.147mol), purity 99.6%, directly used in the next step.

[0090] Step 2: Under nitrogen protection, 130 grams of wet Fmoc-Trp-OH (theoretical 0.147 mol), 23.8 grams of benzyl alcohol (0.220 mol), 1.4 grams of p-toluenesulfonic acid monohydrate (7.3 mmol) and 525 mL of toluene were added to a 1L reaction bottle in sequence, and the reaction system was heated to 40-45°C, and the water was separated by reflux under reduced pressure. The reaction system gradually changed from a suspension to a clear solution, and then became turbid again. The reaction was reacted for 24 hours, and the reaction was complete when detected by HPLC. The obtained suspension was cooled to 0-5°C, stirred for 2 hours, filtered, and the filter cake was rinsed with 100 mL of toluene. The obtained filter cake was vacuum dried at 50-60°C for 4 hours to obtain 70.5 grams of white solid Fmoc-Trp-OBzl, with a purity of 99.6%, containing 0.2% Fmoc-Trp-OH, and other single impurities less than 0.1%. The total yield of the first two steps was 92%.

[0091] Step 3: Under nitrogen protection, add 40 g of Fmoc-Trp-OBzl (0.077 mol), 200 mL of tetrahydrofuran and 0.19 g of p-dimethylaminopyridine (1.5 mmol) to a 1 L reaction bottle in sequence. After stirring to clarify, add 17.7 g of Boc2O (0.081 mol) dropwise at 20-25°C. A small amount of gas is generated after addition, and almost no heat is released. Stir at 20-25°C for 4 hours. After the reaction is completed by HPLC detection, the reaction solution is directly used in the next step.

[0092] Step 4: Add 0.8 g of 5% palladium carbon (water content 50%) to the solution obtained in step 3, replace it with hydrogen three times, and then hydrogenate it at 20-25°C under normal pressure for 24 hours. After the reaction is completed by HPLC detection, filter and remove the palladium carbon catalyst, wash the filtrate twice with 100 mL of water, and then concentrate it under reduced pressure at 20-25°C to obtain an oily substance, add 400 mL of n-heptane, cool it to 0-5°C and stir it for 6 hours, and the product precipitates. Filter, rinse the obtained filter cake with 50 mL of n-heptane, and vacuum dry it at 20-25°C for 12 hours to obtain 36.6 g of white solid Fmoc-Trp(Boc)-OH, the yield of the latter two steps is 90%, and the total yield of the process is 82.8%. The chemical purity of the product is 99.86%, and the content of Fmoc-Trp-OH from the Boc impurity is 0.14% (the spectrum is shown in Figure 6 ). Optical purity 100%.

[0093] Example 2

[0094] Step 1: Under nitrogen protection, add 16.4L of water, 1kg of L-tryptophan (4.90mol) and 778.5g of sodium carbonate (7.34mol) to a 30L reaction bottle. Stir at 20-25°C to clarify, then add 1.57kg of FmocOSu (4.65mol), let the reaction system stir at 20-25°C for 2 hours, and the reaction system gradually becomes clear. After the reaction is completed by HPLC detection, add concentrated hydrochloric acid to adjust the pH value of the system to 2-3, at which time a large amount of white solid precipitates. Filter the reaction system, wash the filter cake with 3L of water, and obtain 4.5kg of white solid Fmoc-Trp-OH (wet product, theoretical 4.65mol), with a purity of 99.6% (the spectrum is shown in Figure 2 The wet product was directly used in the next step.

[0095] Step 2: Under nitrogen protection, 4.5 kg of wet Fmoc-Trp-OH (theoretical 4.65 mol), 754 g of benzyl alcohol (6.98 mol), 44.2 g of p-toluenesulfonic acid monohydrate (0.233 mol) and 16.7 L of toluene were added to a 30 L reaction bottle in sequence, and the reaction system was heated to 40-45 ° C, and the water was separated by reflux under reduced pressure. The reaction system gradually changed from a suspension to a clear solution, and then became turbid again. The reaction was reacted for 30 hours, and the reaction was complete when detected by HPLC. The resulting suspension was cooled to 0-5 ° C, stirred for 2 hours, filtered, and the filter cake was rinsed with 3 L of toluene. The resulting filter cake was vacuum dried at 50-60 ° C for 4 hours to obtain 2165 g of white solid Fmoc-Trp-OBzl, with a purity of 99.5%, containing 0.3% Fmoc-Trp-OH, and other single impurities less than 0.1% (the spectrum is shown in Figure 3 ). The total yield of the first two steps is 89%.

[0096] The obtained product Fmoc-Trp-OBzl was subjected to NMR test, and the measured 1 H NMR spectrum is shown in Figure 4 , the test results are as follows:

[0097] 1 H NMR(DMSO-d6,300MHz): δ10.88(s,1H)7.87~7.95(dd,3H),7.64~7.68(t,2H),7.52~7,54(d,1H) ,6.99~7.54(m,14H),5.07~5.08(d,2H),4.36~4.3(m,1H),4.19~4.24(m,3H),3.06~3.23(m,2H).

[0098] Step 3: Under nitrogen protection, add 2 kg of Fmoc-Trp-OBzl (3.87 mol), 10 L of tetrahydrofuran and 9.4 g of p-dimethylaminopyridine (77.4 mmol) to a 30 L reaction bottle in sequence. After stirring to clarify, add 886 g of Boc2O (4.07 mol) dropwise at 20-25°C. A small amount of gas is generated after addition, and almost no heat is released. Stir at 20-25°C for 4 hours and detect by HPLC (the spectrum is shown in Figure 5 )After the reaction is completed, the reaction solution is directly used in the next step.

[0099] Step 4: Add 40 g of 5% palladium carbon (water content 50%) to the solution obtained in step 3, replace it with hydrogen three times, and then hydrogenate it at 20-25°C under normal pressure for 24 hours. After the reaction is completed by HPLC detection, filter and remove the palladium carbon catalyst, wash the filtrate twice with 5L of water, and then concentrate under reduced pressure at 20-25°C to obtain an oily substance, add 10L of n-heptane, cool to 0-5°C and stir for 6 hours, and the product precipitates. Filter, rinse the obtained filter cake with 2.5L of n-heptane, and vacuum dry it at 20-25°C for 12 hours to obtain 1790 g of white solid Fmoc-Trp(Boc)-OH, with a yield of 88% in the latter two steps and a total process yield of 78.3%. The chemical purity of the product is 99.91%, and the content of Fmoc-Trp-OH without Boc impurity is 0.09% (the spectrum is shown in Figure 7 ). Optical purity 99.9% (spectrum shown in Figure 8 ).

[0100] The obtained product Fmoc-Trp(Boc)-OH was subjected to NMR test, and the measured 1 H NMR spectrum is shown in Fig. 9 , the test results are as follows (the peaks with chemical shifts of 0.86 and 1.24 come from the residual solvent n-heptane):

[0101] 1 H NMR(DMSO-d6,300MHz): δ12.93(s,1H),8.02~8.04(d,1H),7.87~7.88(d,2H),7.80~7.82(d,1H),7.57~7.67(m,4H),7.1 0~7.50(m,7H),4.27~4.33(t,1H),4.19(s,2H),4.07~4.10(m,1H),3.17~3.22(dd,1H),2.00~3.06(dd,1H),1.57(s,9H).

[0102] Comparative Examples 1 to 4

[0103] Four types of Fmoc-Trp(Boc)-OH purchased from the market were analyzed by HPLC. The results are shown in the following table.

[0104] Table 2

[0105] Sample source Chemical purity Removal of Boc impurities Hydrogenated impurities Commercial sample 1 99.6％ 0.29％ 0 Commercial sample 2 99.5％ 0.25％ 0.2％ Commercial sample 3 99.5％ 0.39％ 0 Commercially available sample 4 99.5％ 0.35％ 0 Example 1 99.86％ 0.14％ 0 Example 2 99.91％ 0.09％ 0

[0106] It can be seen that the method of the present invention has a simple process route, mild reaction conditions, small amount of organic solvent, few separation operations, few organic impurities, high yield and high purity.

Claims

1. A method for preparing N-alpha-fluorenylmethoxycarbonyl-N-in-tert-butyloxycarbonyl-L-tryptophan (Fmoc-Trp(Boc)-OH), wherein: The method comprises the following steps: Step 1, under the action of a first base, reacting L-tryptophan (L-Trp-OH) with 9-fluorenylmethyl-N-succinimidyl carbonate (FmocOSu) to obtain Fmoc-Trp-OH; Step 2, reacting Fmoc-Trp-OH with benzyl alcohol under the action of p-toluenesulfonic acid or its hydrate to obtain Fmoc-Trp-OBzl; Step 3, under the action of a second base, reacting Fmoc-Trp-OBzl with Boc2O to obtain Fmoc-Trp(Boc)-OBzl; Step 4: Fmoc-Trp(Boc)-OBzl is subjected to hydrogenolysis reaction under the catalysis of palladium on carbon to obtain the target compound Fmoc-Trp(Boc)-OH.

2. The method according to claim 1, wherein: The first alkali is selected from any one or a combination of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate; preferably, it is selected from sodium carbonate.

3. The method according to claim 1 or 2, wherein: In step 1, the molar ratio of L-Trp-OH:FmocOSu:first base is 1:(0.9-1):(1-3), preferably 1:0.95:1.

5.

4. The method according to any one of claims 1 to 3, wherein: Step 2 is carried out at a temperature of 30°C to 70°C, preferably 40°C to 45°C.

5. The method according to any one of claims 1 to 4, wherein: In step 2, the molar ratio of Fmoc-Trp-OH:benzyl alcohol:p-toluenesulfonic acid monohydrate is 1:(1.1-3):(0.02-0.2), preferably 1:1.5:0.

05.

6. The method according to any one of claims 1 to 5, wherein: The second base is selected from p-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine, pyridine, and preferably p-dimethylaminopyridine (DMAP).

7. The method according to any one of claims 1 to 6, wherein: In step 3, the molar ratio of Fmoc-Trp-OBzl:Boc2O:DMAP is 1:(1.0-1.1):(0.01-0.05), preferably 1:1.05:0.

02.

8. The method according to any one of claims 1 to 7, wherein: In step 4, the mass ratio of Fmoc-Trp(Boc)-OBzl: palladium carbon is 1:(0.01-0.05), preferably 1:0.

02.

9. The method according to any one of claims 1 to 8, wherein: Step 1, step 3 and step 4 are all carried out at room temperature.

10. N-alpha-fluorenylmethoxycarbonyl-N-in-tert-butyloxycarbonyl-L-tryptophan (Fmoc-Trp(Boc)-OH) obtained according to the process of any one of claims 1 to 9, wherein the sum of the de-Boc impurity and the hydrogenated impurity content is less than 0.15%.

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