Synthetic method of leuprorelin

Abstract

The invention discloses a synthetic method of leuprorelin, and relates to the technical field of pharmaceutical processes. The invention provides a method for synthesizing leuprorelin, which comprises the following steps of: performing solid-phase synthesis on a Pyr1-His2 (Trt)-Trp3 (Boc)-Ser4 (tBu)-Tyr5 (tBu)-D-Leu6-OH fragment, performing liquid-phase synthesis on an NH2-Leuu-Arg (pbf)-Pro-NHEt fragment, coupling the two obtained fragments to obtain a leuprorelin full-protection peptide, and performing splitting decomposition, precipitation and purification to obtain a pure leuprorelin product.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pharmaceutical process, in particular to a synthetic method of leuprorelin. BACKGROUND

[0002] Leuprorelin is a gonadotropin releasing enhancer, which can stimulate pituitary to secrete gonadotropin and induce the generation of sex steroids. It mainly acts on the anterior pituitary, and can cause transient increase of luteinizing hormone and follicle stimulating hormone release in the initial stage of large dose application, and then lead to the decrease of pituitary sensitivity, so as to reduce the secretion of LH, FSH and sex hormones. It is mainly used for treating sex hormone related diseases, including advanced prostate cancer, endometriosis and central precocious puberty, etc.

[0003] In the prior art, such as patents CN101538315A and CN1865280A, Fmoc method is used to synthesize a fully protected nonapeptide, and then ethylamine is coupled in liquid phase; but the diketopiperazine side reaction cannot be avoided, which can cause the peptide chain to fall off and reduce the yield; patent CN101195653B uses Fmoc-Arg(pbf)-OH as the C-terminal, and condenses amino acids one by one to obtain a fully protected octapeptide, and then couples with H-Pro-NHEt in liquid phase; although the problem of incomplete cutting of resin by using ethylamine is solved, Fmoc-Arg(pbf)-OH has a large protective group, and the space steric hindrance is large, so the connection efficiency with the resin is low, which further affects the overall yield; patent CN105330726A first synthesizes Fmoc-Leu-Arg(pbf)-OH dipeptide in liquid phase, and then condenses with H-Pro-CTC Resin; although the diketopiperazine side reaction can be avoided, the problem of low condensation efficiency of the difficult sequence Arg-Pro cannot be solved.

[0004] In summary, in order to solve the above problems, it is of great significance to develop a synthetic method of leuprorelin. SUMMARY

[0005] The present application aims to provide a synthetic method of leuprorelin to solve the problems in the background art.

[0006] In order to solve the above technical problems, the present application provides the following technical scheme: A synthetic method of leuprorelin, characterized in that it comprises the following steps: S1: modifying the solid-phase carrier resin with Fmoc-D-Leu-OH to obtain a modified resin; taking the modified resin as a starting material, first removing the Fmoc protecting group by a Fmoc removal reagent, then coupling Fmoc-Tyr(tBu)-OH, Fmoc-Ser(tBu)-OH, Fmoc-Trp(Boc)-OH, Fmoc-His(Trt)-OH, Pyr-OH in sequence by a coupling reagent, and fully protecting and cleaving to obtain Pyr 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -OH, denoted as a first fragment; S2: taking Fmoc-Leu-OH as a starting material for liquid-phase reaction, after activation, reacting with H-Arg(pbf)-OH, and then coupling with H-Pro-NHEt, removing the Fmoc protecting group by a Fmoc removal reagent to obtain NH2-Leu 7 -Arg 8 (pbf)-Pro 9 -NHEt, denoted as a second fragment; S3: coupling the first fragment with the second fragment and cleaving to obtain a crude leuprolide, and purifying the crude leuprolide by high-pressure preparative liquid chromatography to obtain pure leuprolide.

[0007] More preferably, the solid-phase carrier resin is 2-CTC Resin, and the substitution value ranges from 0.4 to 1.5 mmol / g, preferably from 0.6 to 1.3 mmol / g, and more preferably from 0.8 to 1.2 mmol / g; More preferably, in S2, the Fmoc removal reagent includes one or both of a piperidine-DMF mixed solution and a DBU-DMF mixed solution, and preferably the piperidine-DMF mixed solution; in S3, the Fmoc removal reagent includes one or both of a piperidine-DCM mixed solution and a diethylamine-DCM mixed solution, and preferably the diethylamine-DCM mixed solution.

[0008] More preferably, in the piperidine-DMF mixed solution, the content of piperidine is 10-30%, and preferably 20%, of the total volume of the piperidine-DMF mixed solution; in the DBU-DMF mixed solution, the content of DBU is 2-10%, and preferably 5%, of the total volume of the DBU-DMF mixed solution; in the piperidine-DCM mixed solution, the content of piperidine is 10-20% of the piperidine-DCM mixed solution; and in the diethylamine-DCM mixed solution, the content of diethylamine is 40-60%, and preferably 50%, of the total volume of the diethylamine-DCM mixed solution.

[0009] More preferably, the coupling reagent is one or more of A, B, C, and D; wherein, A includes one of HOAt, HOBt, 6-Cl-HOBt, HOSU, HONB, and ethyl 2-oxime cyanoacetate, preferably HOBt; B includes one of DIC, DCC, and EDC·HCl, preferably DIC; C includes one of HATU, HBTU, TBTU, TSTU, PyBOP, and PyAOP, preferably HBTU; and D includes one of DIEA, NMM, TEA, and DMAP, preferably DIEA or DMAP.

[0010] Ideally, the coupling agent is one of the following: a combination of A+B, a combination of A+B+D, and a combination of C+D, with the combination of A+B being preferred.

[0011] In a more optimized manner, during the fully protected lysis process, the fully protected lysis reagent includes a TFE-DCM mixed solution and a TFA-DCM mixed solution; wherein the TFE content is 10-30% of the total volume of the TFE-DCM mixed solution, preferably 20%; and the TFA content is 0.5-2% of the total volume of the TFA-DCM mixed solution.

[0012] More preferably, during the activation process, the activating reagent is one or more of A, B, C, and D; wherein, A includes one of HOSU, HONB, HOBt, pentafluorophenol, and p-nitrophenol, preferably HOSU; B includes one of DIC, DCC, and EDC·HCl, preferably DCC; C includes one of TSTU, TNTU, HSTU, and HNTU, preferably TSTU; and D includes one of DIEA, TEA, and NMM, preferably DIEA.

[0013] Ideally, the activating agent is one of a combination A+B or a combination C+D, with a combination A+B being preferred.

[0014] In an optimized manner, during the pyrolysis process in S4, the pyrolysis reagent is a mixed solution of TFA-TIS-EDT-H2O, with a volume ratio of (85~95):(2~5):(0~2):(2~5); the pyrolysis time is 1.5~3h, preferably 2.0~2.5h; the pyrolysis temperature is 20~30℃, preferably 23~27℃; and the pyrolysis precipitant includes one or more of diethyl ether, isopropyl ether, and methyl tert-butyl ether, preferably methyl tert-butyl ether.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention provides a method for synthesizing leuprolide, which involves first synthesizing Pyr in a solid-state phase. 1 -His 2 (Trt)-Trp3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -OH fragment, and then liquid-phase synthesis of NH2-Leu 7 -Arg(pbf) 8 -Pro 9 -NHEt fragment, and then coupling of the two fragments to obtain the full-protected leuprolide, and then cleavage, precipitation and purification to obtain the pure leuprolide.

[0016] (1) The synthesis method provided by the application can effectively solve the problems of low solid-phase condensation efficiency of the difficult sequence Arg-Pro and easy generation of impurities with missing Arg; the liquid-phase synthesis of the NH2-Leu 7 -Arg 8 (pbf)-Pro 9 -NHEt, which avoids intramolecular cyclization of Pro as the C-terminal to generate piperazinedione side reactions, thereby falling off from the resin, resulting in a significant reduction in the synthesis yield; and can effectively avoid the problems of low connection efficiency of Fmoc-Arg(pbf)-OH with the resin due to large steric hindrance, and reduce the feeding equivalent and the material cost.

[0017] (2) The leuprolide prepared by the application has high purity, high yield and short cycle, the purity of the crude product reaches 88%, the total yield reaches 56%, and the cycle is shortened by 20%. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the HPLC spectrum of the first fragment (Pyr 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -OH.

[0019] Figure 2 is the HPLC spectrum of the second fragment (NH2-Leu 7 -Arg 8 (pbf)-Pro 9 -NHEt.

[0020] Figure 3 is the HPLC spectrum of the crude leuprolide.

[0021] Figure 4 is the HPLC spectrum of the pure leuprolide. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0023] It should be noted that, by weight, all the raw materials involved in the present application have no special restrictions and exemplarily include the meanings of the abbreviations used in the specification and claims as follows: 1-hydroxy-7-azobenzotriazole (HOAt), 1-hydroxybenzotriazole (HOBt), 6-chloro-1-hydroxybenzotriazole (6-Cl-HOBt), N-hydroxy-5-norbornene-2,3-dicarboximide (HONB), diisopropyl carbodiimide (DIC), dicyclohexyl carbodiimide (DCC), 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride (EDC·HCl), O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU), O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HBTU), 4-dimethylaminopyridine (DMAP), 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU), N,N,N',N'-tetramethyl-O-(N-succinimidyl)uronium tetrafluoroborate (TSTU), (benzotriazol-1-yl-oxy)tripyrrolidinophosphonium hexafluorophosphate (PyBOP), benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyAOP), N,N-diisopropylethylamine (DIEA), N-methylmorpholine (NMM), triethanolamine (TEA), 9-fluorenylmethoxycarbonyl (Fmoc), dichloromethane (DCM), N,N-dimethylformamide (DMF), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), N-hydroxysuccinimide (HOSU), 2-(endo-5-norbornene-2,3-dicarboximide)-1,1,3,3-tetramethyluronium tetrafluoroborate (TNTU), N,N,N',N'-tetramethyluronium-O-(N-succinimidyl) hexafluorophosphate (HSTU), O-(endo-bicyclo[2,2,1]hept-5-ene-2,3-dicarboximide)-N,N,N',N' (HNTU), 2,2,2-trifluoroethanol (TFE), trifluoroacetic acid (TFA), triisopropylsilane (TIS), 1,2-ethanedithiol (EDT), 2,2,4,6,7-pentamethyl-dihydrobenzofuran-5-sulfonyl chloride (pbf), 2-chlorotrityl resin (2-CTC Resin).

[0024] Example 1: A synthetic method of leuprolide, comprising the following steps: I. Synthesis of the first segment (Pyr 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -OH): S1-1: 20 g of 2-CTC Resin with a degree of substitution of 1.0 mmol / g was weighed as a solid-phase reaction raw material, added to a solid-phase reaction column, swelled in 320 mL of DCM for 30 min, and the solution was removed to obtain pretreated resin; S1-2: 14.14 g of Fmoc-D-Leu-OH (40 mmol) was weighed, dissolved in 160 mL of DCM by stirring, 7.75 g of DIEA (60 mmol) was added, and after uniform stirring, the pretreated resin was added, nitrogen was blown for 3 h of reaction, the reaction solution was removed, 136 mL of DCM, 16 mL of methanol, and 8 mL of DIEA were added under a nitrogen atmosphere, and the reaction was performed for 30 min. The reaction solution was removed, 160 mL of DMF was added and washed for 3 min, and then removed, and the washing was repeated 3 times. Under a nitrogen atmosphere, 160 mL of a DMF solution containing 20% piperidine was added, and the reaction was performed for 5 min, and then removed to obtain Fmoc-D-Leu-CTC Resin modified resin; S1-3: 160 mL of a 20% piperidine-DMF mixed solution was added to the Fmoc-D-Leu-CTC Resin modified resin, and the reaction was performed for 25 min, and then removed. After washing with 160 mL of DMF for 3 min and then removing, the washing was repeated 6 times to obtain a once-deprotected Fmoc-protected group modified resin; S1-4: 18.38 g of Fmoc-Tyr(tBu)-OH (40 mmol), 5.41 g of HOBt (40 mmol), and 5.05 g of DIC (40 mmol) were dissolved in 160 mL of DMF by stirring, and activated for 10 min, and then added to the once-deprotected Fmoc-protected group modified resin. Nitrogen was blown for 1.5 h of reaction, and after the resin was detected to be colorless and transparent, 160 mL of DMF was added and washed for 3 min, and then removed. The washing was repeated 3 times to obtain Fmoc-Tyr(tBu)-D-Leu-CTC Resin; S1-5: Fmoc-Ser(tBu)-OH, Fmoc-Trp(Boc)-OH, Fmoc-His(Trt)-OH, and Pyr-OH were sequentially coupled according to the sequence. 160 mL of methanol was added, and the mixture was washed for 3 min, then dried under vacuum. This process was repeated once. The resin was removed, dried under vacuum, and 400 mL of a 20% TFE-DCM mixed solution was added for fully protected cleavage. The reaction was carried out at room temperature for 2 h, followed by filtration and concentration. 200 mL of n-heptane was added, and the mixture was slurried, washed three times, filtered, and the filter cake was collected and dried under vacuum to obtain the Pyr fragment. 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -OH.

[0025] Synthesize the second fragment (NH2-Leu) 7 -Arg 8 (pbf)-Pro 9 -NHEt): S2-1: Add 7.07g of Fmoc-Leu-OH (20mmol) and 2.53g of HOSU (22mmol) to 50mL of DCM, stir to dissolve, and slowly cool to 3℃ in an ice bath to obtain a mixed solution; S2-2: Add 4.54 g of DCC (22 mmol) to 20 mL of DCM, stir to dissolve, then add dropwise to the mixed solution, stir at room temperature, filter, wash the filter cake with 30 mL of DCM, combine the filtrates, wash twice with 55 mL of saturated saline, wash once with 55 mL of purified water, collect the organic phase, add 10.00 g of anhydrous sodium sulfate and dry for 30 min, filter, rotary evaporate, concentrate, dissolve in 30 mL of ethyl acetate, recrystallize in 150 mL of n-heptane for 2 h, filter, wash the filter cake three times with n-heptane, collect the filter cake, vacuum dry, add 50 mL of THF to obtain Fmoc-Leu-Osu solution; S2-3: Add 9.38 g of H-Arg(pbf)-OH (22 mmol) to 100 mL of aqueous solution containing 50% THF, stir to dissolve, add 3.87 g of DIEA (30 mmol) to adjust the pH, add dropwise to Fmoc-Leu-Osu solution, stir at room temperature, add 0.5 mol / L dilute hydrochloric acid to adjust the pH to 3, add 150 mL of ethyl acetate to extract twice, collect the organic phase, wash three times with saturated brine; collect the organic phase, dry with anhydrous sodium sulfate for 30 min, filter and concentrate to obtain Fmoc-Leu-Arg(pbf)-OH; S2-4: Add 3.75g of H-Pro-NHEt (21mmol) and 3.24g of HOBt (24mmol) to 100mL of THF and stir to dissolve. Add 2.02g of NMM and incubate at 3°C ​​on an ice bath to obtain the solution. S2-5: Add Fmoc-Leu-Arg(pbf)-OH to the solution, stir, slowly add 4.60 g of EDC·HCl, set the temperature to 3℃, react for 1 h, then stir the reaction at room temperature, concentrate the reaction solution to an oily state, add 100 mL of ethyl acetate to dissolve, wash successively with 0.01 mol / L hydrochloric acid, water, saturated saline, saturated sodium bicarbonate aqueous solution, and saturated saline, collect the organic phase, dry with anhydrous sodium sulfate for 30 min, filter and concentrate to a pale yellow solid, wash 3 times with n-hexane, filter and dry to obtain Fmoc-Leu-Arg(pbf)-Pro-NHEt; S2-6: Add Fmoc-Leu-Arg(pbf)-Pro-NHEt to 100 mL of 50% diethylamine-DCM solution, stir at room temperature to remove Fmoc, concentrate under reduced pressure, grind and slurry with 20% ethyl acetate-n-hexane, filter, and wash the filter cake three times with a small amount of 20% ethyl acetate-n-hexane and three times with n-hexane; filter and dry to obtain NH2-Leu 7 -Arg 8 (pbf)-Pro 9 -NHEt.

[0026] Synthetic Pyr 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -Leu 7 -Arg 8 (pbf)-Pro 9 -NHEt: 12.71g of Pyr 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -OH (10 mmol), 1.62 g of HOBt (12 mmol), were dissolved in 150 mL of 50% THF-DCM by stirring. The temperature was controlled at 3 °C. Then, 1.51 g of DIC was added, and the mixture was stirred for 30 min. Subsequently, 9.30 g of NH2-Leu was added. 7-Arg 8 (pbf)-Pro 9 -NHEt, stirred reaction, concentrated under reduced pressure, to obtain Pyr 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -Leu 7 -Arg 8 (pbf)-Pro 9 -NHEt.

[0027] Synthetic crude leuprolide: S4-1: Mix 180 mL of TFA, 10 mL of TIS, 5 mL of H2O and 5 mL of EDT evenly, and incubate in an ice bath at 3 °C to obtain the lysis solution; S4-2: Pyr 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -Leu 7 -Arg 8 (pbf)-Pro 9 -NHEt was slowly added to the lysis buffer and gradually restored to room temperature for 2 hours. After filtration, 1200 mL of methyl tert-butyl ether was added to the filtrate, the precipitate was collected, centrifuged, and washed three times with 200 mL of methyl tert-butyl ether. After centrifugation, the precipitate was collected and dried under vacuum to obtain crude leuprolide.

[0028] Crude purification of leuprorelin: 10.29 g of crude leuprolide was purified by preparative high-performance liquid chromatography (HPLC) using octadecylsilane-bonded silica gel as the packing material. The mobile phase consisted of: Phase A: 0.1%–0.3% aqueous phosphoric acid solution, adjusted to pH 2.0–3.0 with triethylamine; Phase B: acetonitrile-methanol mixture (4:1, v / v). The flow rate was 200–300 mL / min. The detection wavelength was 214 nm. The gradient was B%: 20–75% (34 min) to obtain pure leuprolide.

[0029] Example 2: Based on Example 1, the difference is that the degree of substitution of 2-CTC Resin is 0.6 mmol / g, and all other aspects are the same.

[0030] Example 3: Based on Example 1, the difference is that the degree of substitution of 2-CTC Resin is 1.5 mmol / g, and all other aspects are the same.

[0031] Performance testing: The purity of the first fragment obtained in Example 1 was determined by HPLC: Mobile phase: Phase A: 0.1%~0.2% trifluoroacetic acid / aqueous solution; Phase B: 0.1%~0.2% trifluoroacetic acid / acetonitrile. Flow rate: 1.0~1.5 mL / min. Detection wavelength: 214 nm. Gradient: B%: 20~75% (40 min); The second fraction was subjected to HPLC purity determination: Mobile phase: Phase A: 0.1%~0.2% trifluoroacetic acid / aqueous solution; Phase B: 0.1%~0.2% trifluoroacetic acid / acetonitrile. Flow rate: 1.0~1.5 mL / min. Detection wavelength: 214 nm, bandwidth 4 nm. Gradient: B%: 20~90% (40 min); HPLC purity determination of crude leuprolide: Mobile phase: 0.1%~0.3% triethylamine aqueous solution, pH adjusted to 2.0~3.0 with phosphoric acid; Phase B: acetonitrile. Flow rate: 1.0~1.5 mL / min. Detection wavelength: 214 nm. Gradient: B%: 20%~70% (34 min); HPLC purity determination of leuprorelin peptide: Mobile phase: 0.1%~0.3% triethylamine aqueous solution, pH adjusted to 2.0~3.0 with phosphoric acid; Phase B: acetonitrile. Flow rate: 1.0~1.5 mL / min. Detection wavelength: 214 nm. Gradient: B%: 20%~70% (34 min).

[0032] Conclusion: Figure 1 As shown: the first fragment had an HPLC purity of 98.98% and a yield of 86.71%. like Figure 2 As shown: the second fragment had an HPLC purity of 98.76% and a yield of 96.72%. like Figure 3 As shown: crude leuprorelin weighed 10.29 g; HPLC purity was 88.96%, and the overall yield was 85.11%. like Figure 4 As shown: Leuprorelin pure product weighs 6.85g; HPLC purity is 99.53% (purification yield 66.7%), total yield 56.8%.

[0033] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing leuprorelin, characterized in that: Includes the following steps: S1: The solid-phase support resin was modified with Fmoc-D-Leu-OH to obtain the modified resin. Using the modified resin as the starting material, the Fmoc protecting group was first removed with a de-Fmoc reagent, and then Fmoc-Tyr(tBu)-OH, Fmoc-Ser(tBu)-OH, Fmoc-Trp(Boc)-OH, Fmoc-His(Trt)-OH, and Pyr-OH were sequentially coupled using coupling agents. After full-protection cleavage, Pyr was obtained. 1 -His 2 (Trt)-Trp 3 (Boc)-Ser 4 (tBu)-Tyr 5 (tBu)-D-Leu 6 -OH, denoted as the first segment; S2: Using Fmoc-Leu-OH as the starting material for the liquid-phase reaction, after activation, it reacts with H-Arg(pbf)-OH, then couples with H-Pro-NHEt, and after removing the Fmoc protecting group with a de-Fmoc reagent, NH2-Leu is obtained. 7 -Arg 8 (pbf)-Pro 9 -NHEt, denoted as the second segment; S3: The first and second fragments were coupled and cleaved to obtain crude leuprorelin, which was then purified by high-pressure preparative liquid chromatography to obtain pure leuprorelin.

2. The method for synthesizing leuprolide according to claim 1, characterized in that: The solid support resin is 2-CTC Resin with a substitution value ranging from 0.4 to 1.5 mmol / g.

3. The method for synthesizing leuprolide according to claim 1, characterized in that: In S2, the deFmoc removal reagent includes one or both of piperidine-DMF mixed solution and DBU-DMF mixed solution; in S3, the deFmoc removal reagent includes one or both of piperidine-DCM mixed solution and diethylamine-DCM mixed solution.

4. The method for synthesizing leuprolide according to claim 3, characterized in that: In the piperidine-DMF mixed solution, the piperidine content is 10-30% of the total volume of the piperidine-DMF mixed solution; in the DBU-DMF mixed solution, the DBU content is 2-10% of the total volume of the DBU-DMF mixed solution; in the piperidine-DCM mixed solution, the piperidine content is 10-20% of the piperidine-DCM mixed solution; and in the diethylamine-DCM mixed solution, the diethylamine content is 40-60% of the diethylamine-DCM mixed solution.

5. The method for synthesizing leuprolide according to claim 1, characterized in that: The coupling reagent is one or more of A, B, C, and D; wherein, A includes one of HOAt, HOBt, 6-Cl-HOBt, HOSU, HONB, and ethyl 2-oxime cyanoacetate; B includes one of DIC, DCC, and EDC·HCl; C includes one of HATU, HBTU, TBTU, TSTU, PyBOP, and PyAOP; and D includes one of DIEA, NMM, TEA, and DMAP.

6. The method for synthesizing leuprolide according to claim 5, characterized in that: The coupling agent is one of the following: A+B composition, A+B+D composition, and C+D composition.

7. The method for synthesizing leuprolide according to claim 1, characterized in that: In the fully protected lysis process, the fully protected lysis reagents include a TFE-DCM mixed solution and a TFA-DCM mixed solution; wherein the TFE content is 10-30% of the total volume of the TFE-DCM mixed solution, and the TFA content is 0.5-2% of the total volume of the TFA-DCM mixed solution.

8. The method for synthesizing leuprolide according to claim 1, characterized in that: During the activation process, the activating reagent is one or more of A, B, C, and D; wherein, A includes one of HOSU, HONB, HOBt, pentafluorophenol, and p-nitrophenol; B includes one of DIC, DCC, and EDC·HCl; C includes one of TSTU, TNTU, HSTU, and HNTU; and D includes one of DIEA, TEA, and NMM.

9. The method for synthesizing leuprolide according to claim 8, characterized in that: The activating agent is one of the A+B composition and the C+D composition.

10. The method for synthesizing leuprolide according to claim 1, characterized in that: In S4, during the pyrolysis process, the pyrolysis reagent is a mixed solution of TFA-TIS-EDT-H2O, with a volume ratio of (85~95):(2~5):(0~2):(2~5); the pyrolysis time is 1.5~3h; the pyrolysis temperature is 20~30℃; and the pyrolysis precipitating reagent includes one or more of diethyl ether, isopropyl ether, and methyl tert-butyl ether.

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