Preparation method of high-efficiency selective antagonist BQ-788

Abstract

The invention provides a preparation method of an efficient selective antagonist BQ-788, and relates to the technical field of preparation of antagonists. A solid-liquid combination method is adopted for synthesis, due to the fact that dimethyl dialkanoate on a side chain of tryptophan (DTrp) is difficult, Fmoc-DTrp (CO2Me)-OH is obtained through liquid-phase synthesis, p-methoxybenzyl is selected for protecting carboxyl in the synthesis process, the carboxyl can be removed through trifluoroacetic acid subsequently, and the risk that an indole ring of tryptophan is reduced due to hydrogenation can be successfully avoided. According to the present invention, by using the solid phase synthesis method, the fragment can be rapidly and efficiently obtained, the racemization problem during the condensation process can be effectively avoided, the urea is formed on the solid phase, the operation is simple and convenient, the hydrogen and the diphosgene are not used during the preparation process, the production is safe, the obtained product has characteristics of high yield and high purity, and the preparation steps are less.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of antagonists, and particularly relates to a preparation method of a highly efficient and selective antagonist BQ-788. Background Art

[0002] BQ-788 is a very effective and selective ETB receptor antagonist;

[0003] English name: (2R)-2-[[(2R)-2-[[(2S)-2-[[(2R,6S)-2,6-dimethylpiperidine-1-carbonyl]amino]-4,4-dimethylpentanoyl]amino]-3-(1-methoxycarbonylindol-3-yl)propanoyl]amino]hexanoic acid;

[0004] Peptide sequence: cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle;

[0005] Structural formula: ;

[0006] Salt type: trifluoroacetic acid Molecular formula: C 34 H 51 N5O7 Molecular weight: 641.80 CAS No.: 173326-37-9 Properties: white powder,

[0007] Solubility: 100 mg can be dissolved in 1 mL DMSO (100 mg / mL) Storage conditions: 2-8 °C.

[0008] This antagonist is widely used to demonstrate the effects of endogenous or exogenous ET in vitro and in vivo. In vitro, BQ-788 effectively and competitively inhibits the binding of 125I-labeled ET-1 to the ETB receptor in human Girrardi heart cells (hGH) with an IC50 of 1.2 nM, but only weakly inhibits the binding of the ETA receptor in the human neuroblastoma cell line SK-N-MC cells (IC50 1300 nM). In isolated rabbit pulmonary arteries, BQ-788 does not show agonist activity up to 10 μM and competitively inhibits the vasoconstriction induced by an ETB selective agonist (pA2, 8.4). BQ-788 also inhibits several biological activities of ET-1, such as bronchoconstriction, cell proliferation, and the clearance of perfused ET-1, further confirming that BQ-788 is an effective and selective ETB receptor antagonist.

[0009] Currently, the synthesis of the antagonist BQ-788 involves a large number of steps, complex post-treatment, and low yield. Therefore, the development of a highly efficient and selective synthesis method for the antagonist BQ-788 is of great significance.

[0010] Due to the large steric hindrance of the raw material methyl leucine (tBuAla), it is difficult to form a urea with cis-2,6-dimethylpiperidine. In addition, due to the influence of the indole ring on the side chain of tryptophan (DTrp), it is also difficult to introduce dimethyl dicarboxylate. Moreover, during the multi-step hydrogenation debenzylation process, the indole ring of tryptophan may also be reduced and hydrogenated. As a result, the yield and purity of the product are relatively low, and there are many synthesis steps. The existing preparation process is not conducive to subsequent optimization and scale-up production. Summary of the Invention

[0011] To solve the problems of a large number of steps, low yield and purity in the preparation of the antagonist BQ-788 in the prior art, the present application provides a preparation method for a highly efficient and selective antagonist BQ-788.

[0012] In a first aspect, the present application provides a preparation method for a highly efficient and selective antagonist BQ-788:

[0013] A preparation method for a highly efficient and selective antagonist BQ-788, wherein the reactants include the following structural units: Structure (1), Structure (2),

[0014] wherein, A1 is an H group or a carboxyl protecting group;

[0015] Among them, the -NH2 group in Structure (1) and the -NH- structure in Structure (2) participate in the reaction and are connected through a carbonyl group to prepare the antagonist BQ-788.

[0016] Furthermore, the preparation method for a highly efficient and selective antagonist BQ-788 includes a liquid-phase reaction and a solid-phase reaction. Further, the carboxyl protecting group includes any one of 4-methoxybenzyl, WangResin-, and Bzl-.

[0017] Furthermore, the reactants of Structure (1) include the following structural units: Structure (3), Structure (4), Structure (5),

[0018] wherein, any one of A3 and A5 is an H group or a carboxyl protecting group, and any one of A2, A4, and A6 is an H group or an amino protecting group;

[0019] Among them, amidation reaction occurs between the amino group formed by connecting A2 or removing the A2 protection and the carboxyl group in structure (5), and amidation reaction occurs between the carboxyl group formed by connecting A3 or removing the A3 protection and the amino group formed by connecting A4 or removing the A4 protection to obtain structure (1).

[0020] Furthermore, the carboxyl protecting group includes 4-methoxybenzyl, WangResin-, Bzl-; the amino protecting group includes Fmoc-, Boc-.

[0021] Furthermore, -A2 in structure (3) is -Fmoc group and -A3 is -H group;

[0022] The preparation process of structure (3) is as follows:

[0023] 1): Liquid-phase synthesis of raw material Boc-DTrp-OPMB:

[0024] Dissolve 9 - 11 g of Boc-DTrp-OH in an organic solvent, add 4 - 6 g of sodium carbonate, slowly dropwise add 4 - 6 mL of 4-methoxybenzyl chloride. After dropping, stir at room temperature for 11 - 15 h for reaction, and then separate Boc-DTrp-OPMB after rotary evaporation under reduced pressure, extraction, washing, and purification. The reaction process is as follows: ;

[0025] 2): Liquid-phase synthesis of raw material Boc-DTrp(CO2Me)-OPMB:

[0026] Dissolve 9 - 11 g of Boc-DTrp-OPMB in 40 - 60 mL of acetonitrile, add 3 - 5 mL of dimethyl dicarbonate and 0.5 - 1 g of 4-dimethylaminopyridine, stir at 25 - 30 °C for 18 - 25 h, and then separate Boc-DTrp(CO2Me)-OPMB after rotary evaporation under reduced pressure, extraction, washing, and purification. The reaction process is as follows: ;

[0027] 3): Liquid-phase synthesis of raw material H-DTrp(CO2Me)-OH:

[0028] Dissolve 8 - 9.5 g of Boc-DTrp(CO2Me)-OPMB in 80 - 100 mL of cleavage solution, stir at room temperature for 1.5 - 3 h; after rotary evaporation to remove the cleavage solution, add water and acetonitrile and freeze-dry to obtain H-DTrp(CO2Me)-OH. The reaction process is as follows: ;

[0029] 4): Liquid-phase synthesis of raw material Fmoc-DTrp(CO2Me)-OH:

[0030] Dissolve 5 - 7.5 g of H-DTrp(CO2Me)-OH.TFA in 90 mL of water / tetrahydrofuran (1:2), add 2.5 - 4 g of sodium carbonate, and then add 5 - 7 g of Fmoc-OSu (9-fluorenylmethyl-N-succinimidyl carbonate). Stir at room temperature for 10 - 15 h; then separate and obtain Structure 2, namely Fmoc-DTrp(CO2Me)-OH, through rotary evaporation under reduced pressure, extraction, washing, and purification. The reaction process is as follows: 。

[0031] Furthermore, the preparation process of Structure (1) is as follows:

[0032] Solid-phase synthesis is adopted; among them, the -A4 group is -H, and the -A5 group is -Wang Resin;

[0033] The specific reaction is as follows:

[0034] 1): Swell the resin fully

[0035] Soak 16 - 18.5 g of Fmoc-DNle-Wang Resin in N,N-dimethylformamide for swelling. After vacuum filtering off N,N-dimethylformamide, add 200 - 300 mL of 20% piperidine / DMF solution, and deprotect by purging with nitrogen for 0.2 - 0.8 h to remove the Fmoc protecting group. Then wash with N,N-dimethylformamide to obtain Resin A;

[0036] 2): Couple Fmoc-DTrp(CO2Me)-OH

[0037] Based on the amount of Fmoc-DNle-Wang Resin, weigh 1.3 times the amount of Fmoc-DTrp(CO2Me)-OH and 1.3 times the amount of HOBt, dissolve them in 200 mL of N,N-dimethylformamide, cool down to -10 °C, add 1.3 times the amount of DIC, activate for 10 min, and then add to Resin A. Couple at room temperature for 1 - 2 h. After detecting that the amino group has been completely coupled, wash with N,N-dimethylformamide and then drain; then add 200 - 300 mL of 20% piperidine / DMF solution to remove Fmoc, deprotect by purging with nitrogen for 0.1 - 0.8 h, and then wash with N,N-dimethylformamide again to obtain Resin DTrp(CO2Me)DNle-Wang Resin;

[0038] 3): Couple Fmoc-tBuAla-OH:

[0039] Using DTrp(CO2Me)DNle-WangResin as the base quantity, weigh 1.2 - 1.8 times the amount of Fmoc-tBuAla-OH and 1.2 - 1.8 times the amount of HOBt, dissolve them in 200 mL of N,N-dimethylformamide, cool down to -10 °C, add 1.5 times the amount of DIC to activate for 10 min, then add it to the resin, couple at room temperature for 1 - 2 h. After Kaiser detection shows colorless, wash with N,N-dimethylformamide solution after the coupling is completed and filter to dryness;

[0040] 4): Removal of the Fmoc protecting group:

[0041] Filter off N,N-dimethylformamide by vacuum filtration, then wash with N,N-dimethylformamide solution and filter to dryness. Add 200 - 280 mL of 20% piperidine / DMF solution, purge with nitrogen for deprotection for 0.2 - 0.8 h, and then wash with N,N-dimethylformamide to obtain the resin tBuAla-DTrp(CO2Me)-DNle-WangResin;

[0042] The specific reaction is as follows: 。

[0043] Furthermore, the preparation method of the antagonist BQ-788 includes the following preparation process:

[0044] 1): Formation of urea from 2,6-dimethylpiperidine:

[0045] Using the resin tBuAla-DTrp(CO2Me)-DNle-WangResin as the base quantity, weigh 1.2 - 1.8 times the amount of 2,6-methylpiperidine and dissolve it in acetonitrile, add 2.8 - 3.5 times the amount of triethylamine, then add 2.5 - 3 times the amount of N,N'-succinimidyl carbonate DSC, stir at room temperature for reaction for 8 - 15 h, then concentrate, dissolve in dichloromethane, then add it to the resin, add 2.8 - 3.2 times the amount of N,N-diisopropylethylamine, react for 10 - 15 h. After Kaiser detection shows colorless, add N,N-dimethylformamide for washing and filter to dryness to obtain cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle-WangResin;

[0046] 2): Cleavage step

[0047] Disperse and suspend 20 - 23 g of cis - 2,6 - Dimethylpiperidine - CO - tBuAla - DTrp(CO2Me) - DNle - Wang Resin in 200 - 250 mL of Solution F, and shake on a shaker at room temperature for 2 - 3 h to obtain a resin suspension;

[0048] The specific ratio of Solution F is: 95 wt% TFA (trifluoroacetic acid), 2.5 wt% TIS (triisopropylsilane), and 2.5 wt% water.

[0049] After filtering the resin suspension, wash it with Solution F and methyl tert - butyl ether, and centrifuge and drain to obtain the crude product. After purification, obtain the resin cis - 2,6 - Dimethylpiperidine - CO - tBuAla - DTrp(CO2Me) - DNle. The reaction process is as follows; 。

[0050] Furthermore, the purity of the antagonist BQ - 788 obtained by the described preparation method is > 90%, and the total synthesis yield is > 20%.

[0051] Furthermore, the purification process is to first dissolve it in acetonitrile / water, and then filter it through a mixed cellulose ester membrane with a pore size of 0.35 - 0.55 μm; then purify it using a chromatographic column.

[0052] Beneficial effects: 1. This application uses a solid - liquid combination method for synthesis. Since it is difficult to obtain dimethyl diacid on the side chain of tryptophan (DTrp), liquid - phase synthesis is selected to obtain Fmoc - DTrp(CO2Me) - OH. During the synthesis process, p - methoxybenzyl is selected to protect the carboxyl group, which can be removed by trifluoroacetic acid later, successfully avoiding the risk of the indole ring of tryptophan being reduced by hydrogenation, improving the purity and yield; then, using the solid - phase synthesis method, the fragment can be obtained quickly and efficiently, effectively avoiding the problem of racemization during the condensation process, and forming urea on the solid phase, with simple and convenient operation. Hydrogen and diphosgene are not used during the preparation process, ensuring production safety. The obtained product has a high yield and purity, and fewer preparation steps. Description of the Drawings

[0053] Figure 1 The mass spectrum of Boc - DTrp(CO2Me) - OPMB prepared in Example 1 of this application;

[0054] Figure 2 The chromatogram of Fmoc - DTrp(CO2Me) - OH in Example 1 of this application;

[0055] Figure 3 The mass spectrum of the antagonist BQ - 788 prepared in Example 1 of this application;

[0056] Figure 4 Chromatogram of the antagonist BQ-788 prepared in Example 1 of this application. Detailed implementation mode

[0057] To make the technical solution of the present invention clearer, the following further describes the present invention in detail with specific examples.

[0058] Example 1, a preparation method of a highly efficient and selective antagonist BQ-788, includes the following preparation process:

[0059] Step S1: Preparation of structure (1) tBuAla-DTrp(CO2Me)-DNle-WangResin, including the following preparation process:

[0060] Preparation of structure (3) Fmoc-DTrp(CO2Me)-OH, the reaction process is as follows:

[0061] Formula 1: ;

[0062] Formula 2: ;

[0063] Formula 3: ;

[0064] Formula 4: .

[0065] Formula 1: The liquid-phase synthesis raw material Boc-DTrp-OPMB, using the raw materials as shown in Table 1, the preparation process is as follows:

[0066] Table 1. List of raw materials used to prepare Boc-DTrp-OPMB ;

[0067] (1) Dissolve 10.088 g of Boc-DTrp-OH in 50 mL of N,N-dimethylformamide (DMF), add 4.216 g of sodium carbonate, cure in the flask, slowly dropwise add 5 mL of 4-methoxybenzyl chloride (PMBCL), after dropping, stir at room temperature for 12 h.

[0068] (2) After the reaction, evaporate N,N-dimethylformamide (DMF) under reduced pressure, add 5% phosphoric acid aqueous solution, extract the aqueous phase with 100 mL of ethyl acetate, wash the organic phase with water and saturated brine in turn, evaporate ethyl acetate under reduced pressure, and then separate by silica gel column chromatography to obtain 10.3 g of Boc-DTrp-OPMB.

[0069] (3) Yield: 73.0%;

[0070] (4) Mass spectrum: 424.49 (425.31 (M+1), 369.19 (M-56+1), 447.19 (M+23)).

[0071] Formula 2: The raw material for liquid-phase synthesis is Boc-DTrp(CO2Me)-OPMB. The raw materials are shown in Table 2, and the preparation process is as follows:

[0072] Table 2. List of raw materials for the preparation of Boc-DTrp(CO2Me)-OPMB ;

[0073] (1) Dissolve 10.3 g of Boc-DTrp-OPMB in 50 mL of acetonitrile (CH3CN), add 3.6 mL of dimethyl dicarboxylate and 0.74 g of 4-dimethylaminopyridine (DMAP), and stir at 30 °C for 20 h.

[0074] (2) After the reaction, evaporate acetonitrile under reduced pressure, add 5% phosphoric acid aqueous solution, extract the aqueous phase with 100 mL of ethyl acetate, wash the organic phase successively with water and saturated brine, evaporate ethyl acetate under reduced pressure, and then separate by silica gel column chromatography to obtain 8.5 g of Boc-DTrp(CO2Me)-OPMB.

[0075] (3) Yield: 72.6%;

[0076] (4) Mass spectrum: 482.53 (483.32 (M+1), 383.3 (M-100+1), 427.19 (M-56+1)), and the mass spectrum is as shown in Figure 1 .

[0077] Formula 3: The raw material for liquid-phase synthesis is H-DTrp(CO2Me)-OH. The raw materials are shown in Table 3, and the preparation process is as follows:

[0078] Table 3. List of raw materials for the preparation of H-DTrp(CO2Me)-OH ;

[0079] (1) Dissolve 8.5 g of Boc-DTrp(CO2Me)-OPMB in 90 mL of Solution E and stir at room temperature for 2 h.

[0080] (2) Evaporate the cleavage solution, add water and acetonitrile, and freeze-dry to obtain 6.5 g of H-DTrp(CO2Me)-OH.

[0081] (3) Yield: 98.5%.

[0082] (4) Mass spectrometry: 262.26 (263.28 (M+1)) (MS604941YF-01-14).

[0083] Formula 4: The liquid-phase synthesis raw material Fmoc-DTrp(CO2Me)-OH, with the raw materials as shown in Table 4, and the preparation process is as follows:

[0084] Table 4. List of raw materials used in the preparation of Fmoc-DTrp(CO2Me)-OH ;

[0085] (1) Dissolve 6.5 g of H-DTrp(CO2Me)-OH.TFA in 90 mL of water / tetrahydrofuran (volume ratio 1:2), add 3.48 g of sodium carbonate, and then add 6.09 g of Fmoc-OSu (9-fluorenylmethyl-N-succinimidyl carbonate), and stir at room temperature for 12 h.

[0086] (2) After the reaction, rotary evaporate to remove tetrahydrofuran under reduced pressure, add 5% phosphoric acid aqueous solution, extract the aqueous phase with 100 mL of ethyl acetate, wash the organic phase successively with water and saturated brine, rotary evaporate to remove ethyl acetate under reduced pressure, and then separate by silica gel column chromatography to obtain 7.5 g of Fmoc-DTrp(CO2Me)-OH. The chromatogram is as Figure 2 .

[0087] (3) Yield: 94.4%, total liquid-phase synthesis yield: 49.3%

[0088] (4) Purity: 98.5%, the chromatogram is as Figure 3 .

[0089] (5) Mass spectrometry: 484.26 (485.31 (M+1), 969.55 (2M+1)) (MS604941YF-01-15).

[0090] Step S2: Structures (3), (4) and (5) react to form structure (1), and the reaction process is as follows:

[0091] Formula 5: ;

[0092] Formula 6-1: ;

[0093] Formula 6-2: ;

[0094] The preparation process of Formula 5 is as follows:

[0095] (1) Sufficient swelling of the resin and removal of Fmoc

[0096] Weigh 17.8 g of Fmoc-DNle-WangResin with a substitution degree of 0.563 mol / g, put it into a polypeptide solid-phase reactor, then add 250 mL of N,N-dimethylformamide (DMF) and soak and swell for 1 h. Filter off the N,N-dimethylformamide under vacuum, then wash three times with 250 mL of N,N-dimethylformamide solution, drain the N,N-dimethylformamide, add 250 mL of 20% piperidine / DMF solution (20% Pip / DMF), purge with nitrogen for deprotection for 0.5 h, wash 5 times with 250 mL of N,N-dimethylformamide to obtain resin DNle-WangResin;

[0097] Kaiser detection

[0098] Preparation of detection reagents: 1) Kaiser detection solution A: 20% ethanol + 80% phenol; 2) Kaiser detection solution B: redistilled pyridine; 3) Kaiser detection solution C: 5% ninhydrin ethanol solution. Detection operation: Take a small amount of resin in a test tube, wash twice with ethanol, add two drops each of Kaiser detection solution A, Kaiser detection solution B, and Kaiser detection solution C, heat to 110 °C for 2 minutes, observe the color of the resin. The color development result is transparent dark blue: When detecting the resin after removing the Fmoc protecting group in solid-phase synthesis, an opaque dark blue will be observed; if the amino acid in solid-phase synthesis is completely coupled and there is no free amino group, the detection at this time shows yellow or colorless.

[0099] (2) Linking structure (3) Fmoc-DTrp(CO2Me)-OH:

[0100] Based on resin DNle-WangResin, weigh 1.3 times the amount of Fmoc-DTrp(CO2Me)-OH and 1.3 times the amount of HOBt, dissolve them in 200 mL of N,N-dimethylformamide, cool down to -10 °C, add 1.3 times the amount of DIC for activation for 10 min, then add it to the resin, couple at room temperature for 1 - 2 h. After Kaiser detection shows colorless, add 300 mL of N,N-dimethylformamide and wash three times and drain; Filter off the N,N-dimethylformamide under vacuum, then wash three times with 300 mL of N,N-dimethylformamide solution; Drain the N,N-dimethylformamide, add 250 mL of 20% Pip / N,N-dimethylformamide, purge with nitrogen for deprotection for 0.5 h. After the departure of the Fmoc protecting group, wash 5 times with 300 mL of N,N-dimethylformamide to obtain DTrp(CO2Me)-DNle-WangResin.

[0101] The preparation process of Formula 6-1 is as follows:

[0102] (1)Connect Fmoc-tBuAla-OH

[0103] Based on DTrp(CO2Me)-DNle-WangResin, weigh 1.5 times the amount of Fmoc-tBuAla-OH and 1.5 times the amount of HOBt, dissolve them in 200 mL of N,N-dimethylformamide, cool down to -10 °C, add 1.5 times the amount of DIC for activation for 10 min, then add it to the resin, couple at room temperature for 1-2 h. After Kaiser test shows colorless, add 300 mL of N,N-dimethylformamide to wash three times. Vacuum filter to remove N,N-dimethylformamide, then wash with 300 mL of N,N-dimethylformamide solution three times, drain N,N-dimethylformamide, add 250 mL of 20% Pip / N,N-dimethylformamide, purge with nitrogen for deprotection for 0.5 h, and wash with 300 mL of N,N-dimethylformamide 5 times.

[0104] The preparation process of Formula 6-2 is as follows:

[0105] (1)2,6-Dimethylpiperidine forms urea

[0106] Based on the resin tBuAla-DTrp(CO2Me)-DNle-WangResin, weigh 1.5 times the amount of 2,6-dimethylpiperidine, dissolve it in acetonitrile, add 3 times the amount of triethylamine, then add 2.5 times the amount of DSC, stir at room temperature for reaction for 12 h, then concentrate, add 100 mL of dichloromethane to dissolve, add it to the resin tBuAla-DTrp(CO2Me)-DNle-WangResin, add 3 times the amount of N,N-diisopropylethylamine and react for 12 h. After Kaiser test shows colorless, add 300 mL of N,N-dimethylformamide to wash three times and drain.

[0107] (2)Resin washing

[0108] Add 300 mL of methanol to wash once, 300 mL of dichloromethane to wash twice, then add 300 mL of methanol to wash once again, and finally vacuum dry to obtain 21.912 g of cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle-WangResin.

[0109] (3)Cleavage step

[0110] 1) Disperse and suspend 21.9 g of the resin in 220 mL of Solution F, and shake on a shaker at room temperature for 2.5 h.

[0111] 2) Filter the resin suspension. Wash the resin twice with 20 mL of Solution F and once with 20 mL of methyl tert-butyl ether. Take a container and add 1200 mL of methyl tert-butyl ether. Then add the filtrate to the methyl tert-butyl ether. After stirring well, transfer it evenly to a centrifuge cup. Balance the centrifuge on a balance, let it stand for 10 min, and centrifuge at 3500 r / min for 2 min. Discard the supernatant.

[0112] 4) Wash the crude product. Add 500 mL of methyl tert-butyl ether and stir evenly. Balance the centrifuge on a balance and centrifuge at 3500 r / min for 2 min. Discard the supernatant. Wash it 3 more times in the same way and centrifuge. Transfer the precipitate to a drying oven and dry it by suction to obtain 6.4 g of the crude product of cis-2,6-Dimethyl-piperidine-CO-tBuAla-DTrp(CO2Me)-DNle. The purity is 79.4% (HPLC604941C). Mass spectrum: 641.8 (642.52(M+1))(MS604941C). The mass spectrum is as shown in Figure 4 .

[0113] 5) Preparation and purification of the crude product

[0114] 1) Sample pretreatment: Dissolve the sample in 50% acetonitrile / water and filter it through a 0.45 μm mixed cellulose ester membrane.

[0115] 2) Purification preparation method:

[0116] Chromatographic column: Hypersil C18 10 μm 100A 50*450 mm (P06);

[0117] Mobile phase A: 0.1% aqueous TFA solution

[0118] Mobile phase B: Acetonitrile

[0119] Sample loading flow rate: 60 mL / min Elution flow rate: 60 mL / min Detection wavelength: 220 nm

[0120] Elution gradient: 60 - 90% for 60 minutes

[0121] For the purification preparation chromatogram, see the purification record 6049412311142123111422

[0122] After preparation and purification, collect the product, freeze-dry it, and obtain 3.0 g of 604941

[0123] Purity: 98.1% (HPLC: 60494123100031Final)

[0124] Mass spectrum: 641.8(642.65(M+1)) (MS: 604941)

[0125] Solid-phase synthesis yield: 46.9%, total synthesis yield: 23.1%.

[0126] Example 2, a preparation method of a highly efficient selective antagonist BQ-788, which is different from Example 1 in that the preparation process of structure (3) Fmoc-DTrp(CO2Me)-OH is different, including Reaction A1, Reaction A2, Reaction A3 and Reaction A4. The specific preparation process is as follows:

[0127] Formula 7: ;

[0128] Reaction A1:

[0129] Dissolve 1.0 equivalent of Boc-DTrp-OH (as the reference substrate) in anhydrous dichloromethane / N,N-dimethylformamide to form a solution with a concentration of 8 mL / mmol. Cool it to 0 °C in an ice bath, and successively add 1.5 equivalents of HOBt and 1.5 equivalents of EDC·HCl. Stir at 0 °C for 30 minutes (activate to form the active ester), slowly add 1.8 equivalents of benzyl alcohol, maintain 0 °C, and add 1.2 equivalents of triethylamine (TEA) to neutralize the hydrochloric acid generated in the reaction; remove the ice bath, raise the temperature to room temperature and stir for 20 hours, add dilute hydrochloric acid (1 M) to quench, and adjust the pH to neutral; extract with ethyl acetate (3 × 20 mL), combine the organic phases; wash successively with saturated sodium bicarbonate (neutralize the acid) and brine, dry over anhydrous sodium sulfate, and then separate by silica gel column chromatography to obtain Boc-DTrp-OBzl with a yield of 80%.

[0130] Reaction A2:

[0131] Dissolve 1.0 equivalent of Boc-DTrp-OBzl (the substrate) in 15 mL of anhydrous tetrahydrofuran, cool it to 0 °C in an ice bath, add 0.2 equivalent of 4-dimethylaminopyridine, stir for 5 minutes to disperse it evenly, and slowly add 3 equivalents of dimethyl carbonate DMDC (dissolved in a small amount of anhydrous solvent) through a constant pressure dropping funnel, maintain 0 °C, remove the ice bath, raise the temperature to room temperature and continue to stir for 6 - 12 hours (confirm the reaction end point by TLC). Add 10 mL of saturated sodium bicarbonate solution to quench the unreacted dimethyl carbonate. Then wash successively with 0.1 M dilute hydrochloric acid and saturated brine to remove 4-dimethylaminopyridine and residual reagents. Dry the organic phase over anhydrous sodium sulfate, and then separate by silica gel column chromatography to obtain Boc-DTrp(CO2Me)-OBzl. The yield is 70%.

[0132] Reaction A3:

[0133] Boc-DTrp(CO2Me)-OBzl was added into a round-bottom flask, and 10 mL of 4M HCl / dioxane solution was added. It was cooled to 0 °C in an ice bath and stirred for 10 minutes to disperse the substrate evenly. The ice bath was removed, and the mixture was stirred at room temperature (25 °C) for another 4 hours. The reaction solution was slowly poured into an ice-water mixture (20 mL) for rapid quenching. Saturated sodium bicarbonate solution was slowly added dropwise until the pH reached 7. The aqueous phase was extracted with ethyl acetate (3 × 20 mL). The organic phase was washed with saturated brine and dried over anhydrous sodium sulfate. Then the solvent was removed by rotary evaporation, and H-DTrp(CO2Me)-OBzl was obtained by silica gel column chromatography with a yield of 78%.

[0134] Reaction A4: The reaction process is as follows: ;

[0135] 1) Protection of the amino group with Fmoc: 1.0 equivalent of H-DTrp(CO2Me)-OBzl (the reference substrate) was dissolved in 12 mL of anhydrous dichloromethane, cooled to 0 °C in an ice bath, 3.0 equivalents of NMM were added dropwise, and the mixture was stirred for 5 minutes. 1.5 equivalents of Fmoc-Cl solution (1.5 equivalents of Fmoc-Cl dissolved in 2 mL of dichloromethane) was slowly added dropwise while maintaining 0 °C. The ice bath was removed, and the mixture was stirred at room temperature for 4 h (TLC showed that the raw material disappeared). 1M HCl was added to adjust the pH to acidic pH = 3. The mixture was extracted with dichloromethane (3 × 20 mL), and the organic phases were combined. The organic phase was washed successively with saturated sodium bicarbonate and brine, dried over anhydrous sodium sulfate, concentrated, and the crude product was obtained by rotary evaporation, and then Fmoc-DTrp(CO2Me)-OBzl was obtained by silica gel column chromatography.

[0136] 2) Hydrolysis of the benzyl ester: 1.0 equivalent of Fmoc-DTrp(CO2Me)-OBzl was dissolved in 20 mL of tetrahydrofuran, and 0.2 g of Pd-C catalyst was added. After evacuation, H2 was charged (repeated 3 times), and the H2 gas pressure was maintained (low pressure 2 atm). The mixture was stirred at 25 °C for 5 h (TLC showed that the benzyl ester was completely hydrolyzed). The Pd-C was filtered off through diatomaceous earth, and the catalyst was washed with tetrahydrofuran. Tetrahydrofuran was removed by rotary evaporation to obtain the crude product. 0.1M HCl (10 mL) was added to acidify to pH = 2. The mixture was extracted with ethyl acetate (3 × 20 mL), and the organic phases were combined. It was dried over anhydrous sodium sulfate, and then Fmoc-DTrp(CO2Me)-OH was obtained by silica gel column chromatography.

[0137] Comparative Example 1, a preparation method of a highly efficient and selective antagonist BQ-788, which adopts a liquid-phase preparation method, includes the following preparation steps:

[0138] Step S1: Preparation of H-DTrp(CO2Me)-OBzl. The reaction process is as shown in Formula 7 and the preparation process is the same as that of H-DTrp(CO2Me)-OBzl in Example 2:

[0139] Formula 7: ;

[0140] Step S2: Preparation of cis-2,6-Dimethylpiperidine-CO-tBuAla-OH. The reaction process is as shown in Formula 8.

[0141] Formula 8: ;

[0142] The preparation process is as follows:

[0143] Reaction B1:

[0144] 1) Benzyl esterification reaction (Boc-tBuAla-OH → Boc-tBuAla-OBzl)

[0145] Add Boc-tBuAla-OH (1 mmol) and cesium carbonate (1.5 mmol) into a flask, inject anhydrous N,N-dimethylformamide (5 mL), start stirring until the solid is completely dissolved (about 10 minutes); heat in an oil bath at 50 °C (cooled by a reflux condenser); slowly dropwise add benzyl bromide (1.2 mmol), maintain a nitrogen atmosphere, stir and react for 6 hours, monitor by TLC (developing agent: ethyl acetate / petroleum ether = 1:2, UV or iodine color development). Cool to room temperature, pour the reaction solution into 50 mL of ice water, and stir for 10 minutes. Extract with ethyl acetate (3 × 20 mL), combine the organic phases; then wash successively with saturated sodium bicarbonate (10 mL), water (10 mL), and saturated brine (10 mL), then dry over anhydrous sodium sulfate and concentrate under reduced pressure to obtain a white solid crude product.

[0146] 2) Boc deprotection (Boc-tBuAla-OBzl → H-tBuAla-OBzl):

[0147] Dissolve Boc-tBuAla-OBzl (1 mmol) in 4M HCl / dioxane (5 mL), cool to 0 °C in an ice bath, slowly warm to room temperature, stir and react for 1 - 2 hours, monitor by TLC (developing agent: dichloromethane / MeOH = 10:1, confirm the exposure of the amino group by ninhydrin color development).

[0148] Most of the solvent was removed by reduced-pressure concentration. The residue was dissolved in 10 mL of dichloromethane, and saturated sodium bicarbonate solution was slowly added dropwise until pH = 8 (to neutralize the excess HCl); the layers were separated, and the aqueous phase was back-extracted with dichloromethane (2×10 mL), and the organic phases were combined; then it was dried over anhydrous sodium sulfate and concentrated to obtain the crude product as a white solid. It can be further purified by recrystallization (such as ether / n-hexane).

[0149] Reaction B2:

[0150] 1) Generation of isocyanate (H-tBuAla-OBzl → R-NCO)

[0151] Dissolve H-tBuAla-OBzl (1 mmol) in anhydrous dichloromethane (5 mL), cool it to 0 °C in an ice bath, and slowly add dropwise phosgene (0.6 mmol, dissolved in 5 mL of dichloromethane). After the addition was complete, the ice bath was removed, and the temperature was raised to room temperature (25 °C), and the reaction was stirred for 2 hours. TLC monitoring (developing solvent: dichloromethane / MeOH = 10:1, confirmed by ninhydrin color development that the amino group disappeared).

[0152] Quench the reaction solution with ice water (10 mL), separate the layers, and retain the organic phase; back-extract the aqueous phase with dichloromethane (2×10 mL), combine the organic phases; dry over anhydrous sodium sulfate and concentrate under reduced pressure to obtain the isocyanate intermediate.

[0153] 2) Formation of urea bond (R-NCO + cis-2,6-dimethylpiperidine → target product)

[0154] Dissolve the isocyanate intermediate in anhydrous dichloromethane (5 mL), then add cis-2,6-dimethylpiperidine (1.2 mmol) and triethylamine (2 mmol), and stir the reaction at room temperature (25 °C) for 20 hours. TLC monitoring (developing solvent: EtOAc / Hexane = 1:1, UV or iodine color development); then wash the reaction solution with 1M HCl (10 mL) to remove the unreacted amine; wash the organic phase successively with saturated sodium bicarbonate (10 mL) and saturated brine (10 mL), then dry over anhydrous sodium sulfate and concentrate under reduced pressure to obtain the crude product.

[0155] Reaction B3:

[0156] Dissolve cis-2,6-Dimethylpiperidine-CO-tBuAla-OBzl (1 mmol) in 20 mL of anhydrous methanol, add it to a pressure-resistant three-necked flask, add Pd / C catalyst (50 mg, 10% loading), and stir to suspend evenly; displace the gas in the reactor with hydrogen 3 times, and maintain a hydrogen pressure of 1 atm; stir the reaction at room temperature (25 °C) for 12 hours. TLC monitoring (developing solvent: dichloromethane / MeOH = 5:1, UV or iodine color development, observe the disappearance of benzyl ester).

[0157] After the reaction is completed, turn off the hydrogen and displace the gas in the reactor with nitrogen. Filter through a diatomaceous earth pad to remove the Pd / C catalyst, and wash the filter cake with methanol (3 × 10 mL). Combine the filtrates and concentrate them to dryness under reduced pressure to obtain a crude white solid product;

[0158] Dissolve the crude product in 10 mL of water, add 1 M HCl dropwise until pH = 2 - 3, and stir for 30 minutes; extract with ethyl acetate (3 × 15 mL) to remove hydrophobic impurities, adjust the aqueous phase to pH = 7 with NaOH, and extract again with ethyl acetate, then dry and concentrate.

[0159] Step S3: Preparation of cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle, and the reaction process is as shown in Formula 9.

[0160] Formula 9: ;

[0161] The preparation process is as follows:

[0162] Reaction C1:

[0163] Amide bond coupling (mediated by EDC·HCl / HOBt)

[0164] Dissolve cis-2,6-Dimethylpiperidine-CO-tBuAla-OH (1 mmol) in anhydrous N,N-dimethylformamide (10 mL), add it to a round-bottom flask equipped with a magnetic stir bar, and then successively add EDC·HCl (1.5 mmol), HOBt (1.5 mmol), and N,N-diisopropylethylamine (3 mmol) to form a mixed solution. Stir at room temperature for 30 minutes; then dissolve H-DTrp(CO2Me)-OBzl (1.2 mmol) in anhydrous N,N-dimethylformamide (10 mL) and slowly add it dropwise to the mixed solution; stir and react at room temperature (25 °C) for 24 hours, monitored by TLC (developing solvent: dichloromethane / MeOH = 5:1, visualized by UV or ninhydrin); then adjust the reaction solution to pH = 3 with 1 M HCl, extract with ethyl acetate (3 × 30 mL), and combine the organic phases; then wash successively with saturated sodium bicarbonate, water, and saturated brine; dry over anhydrous sodium sulfate and concentrate under reduced pressure to obtain a crude product, and obtain an intermediate.

[0165] 2) Benzyl ester hydrogenolysis (catalyzed by Pd / C / H2)

[0166] Hydrogenolysis reaction:

[0167] Dissolve the intermediate from step 1) (1 mmol) in deoxygenated methanol (20 mL), and add Pd / C (50 mg); charge with H2 (1 atm), stir at room temperature for 12 hours, monitor by TLC (eluent: dichloromethane / MeOH = 5:1, disappearance of the benzyl ester spot); filter to remove Pd / C (diatomaceous earth pad), wash the cake with methanol (3 × 10 mL); combine the filtrates and concentrate to dryness under reduced pressure. Dissolve the crude product in water (10 mL), add 1 M HCl dropwise until pH = 2 - 3, stir for 30 minutes; extract with ethyl acetate to remove hydrophobic impurities, adjust the aqueous phase to pH = 7, extract again, dry and concentrate to obtain a white solid product.

[0168] Reaction C2:

[0169] 1) Dissolution and activation:

[0170] Dissolve the carboxylic acid cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-OH (1 mmol) in anhydrous N,N-dimethylformamide (10 mL), add it to a round-bottom flask equipped with a magnetic stir bar, then add HBTU (1.2 mmol) and N,N-diisopropylethylamine (DIPEA) (3 mmol), stir at room temperature (25 °C) for 30 minutes to form an activated ester intermediate.

[0171] Dissolve H-DNle-OBzl·HCl (1.2 mmol) in anhydrous N,N-dimethylformamide (10 mL), add N,N-diisopropylethylamine (1.5 mmol) and stir for 5 minutes to free the amino group (-NH2).

[0172] 2) Coupling reaction:

[0173] Slowly add the free amine solution dropwise to the activated ester solution, stir at room temperature for 12 - 24 hours; monitor by TLC (eluent: dichloromethane / MeOH = 5:1, visualize with UV or ninhydrin, observe the disappearance of the carboxylic acid starting material).

[0174] 3) Work-up

[0175] Pour the reaction mixture into 50 mL of ice water, stir for 10 minutes, precipitate a solid or emulsion; extract with ethyl acetate (3 × 30 mL), combine the organic phases, wash successively with 1 M HCl (10 mL, to remove excess N,N-diisopropylethylamine), saturated sodium bicarbonate (10 mL, to neutralize the acid), and saturated brine (10 mL); dry the organic phase over anhydrous sodium sulfate and concentrate under reduced pressure to obtain a yellow oily or solid crude product, and concentrate to obtain a white solid product, yield: 73%.

[0176] Reaction C3:

[0177] 1) Dissolve the substrate cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle-OBzl (1 mmol) in 20 mL of anhydrous methanol and add it to a pressure-resistant three-necked flask. Then add Pd / C catalyst (50 mg, 10% loading), stir to form a homogeneous suspension, displace the gas in the reactor with hydrogen 3 times, maintain a hydrogen pressure of 1 atm, and stir the reaction at room temperature (25 °C) for 12 hours. Monitor by TLC (developing agent: dichloromethane / MeOH = 5:1, visualized by UV or iodine, observe the disappearance of the benzyl ester spot).

[0178] 2) After the reaction is completed, turn off the hydrogen, displace the gas in the reactor with nitrogen, filter through a diatomaceous earth pad to remove the Pd / C catalyst, wash the filter cake with methanol (3 × 10 mL), combine the filtrates, and concentrate to dryness under reduced pressure to obtain a crude white solid product.

[0179] 3) Wash the crude product, add 500 mL of methyl tert-butyl ether and stir evenly, balance with a balance, centrifuge at 3500 r / min for 2 min, discard the supernatant, and wash and centrifuge 3 more times in the same way. Transfer the precipitate to a drying oven and dry it to obtain the crude product of cis-2,6-Dimethyl-piperidine-CO-tBuAla-DTrp(CO2Me)-DNle.

[0180] 4) Preparation and purification of the crude product

[0181] 1) Sample pretreatment: Dissolve the sample in 50% acetonitrile / water and filter through a 0.45 μm mixed fiber membrane.

[0182] 2) Purification preparation method:

[0183] Chromatographic column: Huapu C18 10 μm 100A 50*450 mm (P06)

[0184] Mobile phase A: 0.1% aqueous TFA solution

[0185] Mobile phase B: Acetonitrile

[0186] Sample loading flow rate: 60 mL / min Elution flow rate: 60 mL / min Detection wavelength: 220 nm

[0187] Elution gradient: 60 - 90% for 60 minutes.

[0188] Comparative Example 2, a preparation method of an efficient selective antagonist BQ-788, is different from Example 1 in that Fmoc-tBuAla-OH in Formula 6-1 is replaced with an equimolar amount of tBuAla-OBzl; Formula 6-1 is cancelled, tBuAla-OBzl and cis-2,6-Dimethylpiperidine are added simultaneously, and after reacting for 12 h, the -Bzl group is removed (the process is the same as Reaction C3), then dichloromethane is added for dissolution, and the reaction is carried out in resin tBuAla-DTrp(CO2Me)-DNle-WangResin. The specific reaction equation is as follows:

[0189] Formula 10-1: ;

[0190] The purity and yield of each step of the examples and comparative examples are shown in Tables 5 and 6:

[0191] Single-step yield = theory / actual × 100%;

[0192] Total yield (%) = (yield 1 × yield 2 ×... × yield n) × 100%.

[0193] Table 5, purity, yield and total reaction steps of Example 1, Example 2 and Comparative Example 2 .

[0194] Table 6, purity, yield and total reaction steps of Comparative Example 1 .

[0195] In Example 1 of this application, Boc-DTrp-OH is used at the beginning of liquid-phase synthesis to connect the carboxyl group to p-methoxybenzyl, and the Trp side chain reacts with dimethyl dialkanoate under the action of 4-dimethylaminopyridine to obtain Boc-DTrp(CO2Me)-OPMB. Boc on the amino group and PMB on the carboxyl group are simultaneously removed with trifluoroacetic acid, and Fmoc-DTrp(CO2Me)-OH is obtained under alkaline conditions using Fmoc-OSu (9-fluorenylmethyl-N-succinimidyl carbonate). This is used as the raw material for solid-phase synthesis. The total yield of liquid-phase synthesis is 49.3%. Solid-phase synthesis uses Fmoc-DNle-WangResin as the starting material, and the protected amino acids are sequentially coupled from the carbon end to the nitrogen end using the solid-phase synthesis method to obtain fragments. Then, after removing Fmoc, the product formed by N,N'-succinimidyl carbonate and cis-2,6-dimethylpiperidine to form urea is obtained. Finally, the final product is obtained after cleavage and purification. 3.0 g of the final product is obtained after preparation and purification, the yield of solid-phase synthesis is 46.9%, and the total yield of this method is 23.11%.

[0196] Compared with Example 1, the overall liquid-phase yield and purity of Example 2 are lower because the indole ring of tryptophan is also reduced and hydrogenated during the debenzylation process in step A4 of the reaction, resulting in more by-products and a decrease in yield.

[0197] Compared with Example 1, the steric hindrance of methyl leucine (tBuAla) in reaction B2 of Comparative Example 1 is relatively large, making it difficult to form a urea with cis-2,6-dimethylpiperidine. Also, during the debenzylation process in reactions C1 and C3, the indole ring of tryptophan is reduced and hydrogenated, further resulting in lower purity and yield of the product.

[0198] Compared with Example 1, the steric hindrance in reaction D1 of Comparative Example 2 is relatively large, making it difficult to form a urea with cis-2,6-dimethylpiperidine, resulting in lower yield and purity. It also shows that connecting methyl leucine (tBuAla) to the DTrp(CO2Me)-DNle-WangResin group is beneficial for forming a urea with cis-2,6-dimethylpiperidine. This may be because the side products of the carboxyl amidation reaction of methyl leucine (tBuAla) are fewer. Additionally, after the reaction of methyl leucine (tBuAla) with DTrp(CO2Me)-DNle-WangResin, the DTrp(CO2Me)-DNle-WangResin group is beneficial for the amine on methyl leucine (tBuAla) to remove the H group, making it easier to form a urea with cis-2,6-dimethylpiperidine.

[0199] The equipment used in this application is shown in Table 7 in detail, and the budget for Example 1 of this application is shown in Tables 8 and 9 in detail.

[0200] Table 7. Equipment List 。

[0201] Table 8. Budget List for Example 1 of this Application 。

[0202] Table 9. Budget List for Example 1 of this Application 。

[0203] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A preparation method of the highly effective selective antagonist BQ-788, characterized in that, The reactants include the following structural units: Structure (1), Structure (2), wherein, A1 is an H group or a carboxyl protecting group; wherein, the -NH2 group in structure (1) and the -NH- structure in structure (2) participate in the reaction and are connected through a carbonyl group, and the antagonist BQ-788 is obtained through the reaction preparation.

2. The preparation method of an efficient selective antagonist BQ-788 according to claim 1, characterized in that, It includes liquid-phase reaction and solid-phase reaction.

3. A preparation method of an efficient selective antagonist BQ-788 according to claim 1, characterized in that, The carboxyl protecting group includes any one of 4-methoxybenzyl, WangResin-, Bzl-.

4. A preparation method of an efficient selective antagonist BQ-788 according to claim 1, characterized in that, The reactant of structure (1) includes the following structural units: Structure (3), Structure (4), Structure (5), wherein, any one of A3 and A5 is an H group or a carboxyl protecting group, and any one of A2, A4, and A6 is an H group or an amino protecting group; wherein, the amino group formed by connecting A2 or deprotecting A2 reacts with the carboxyl group in structure (5) to undergo an amidation reaction, and the carboxyl group formed by connecting A3 or deprotecting A3 reacts with the amino group formed by connecting A4 or deprotecting A4 to undergo an amidation reaction to obtain structure (1).

5. A method for preparing an efficient selective antagonist BQ-788 according to claim 4, characterized in that, The carboxyl protecting group includes 4-methoxybenzyl, WangResin-, Bzl-; the amino protecting group includes Fmoc-, Boc-.

6. The preparation method of a highly efficient and selective antagonist BQ-788 according to claim 4, characterized in that -A2 in structure (3) is an -Fmoc group and -A3 is an -H group; The preparation process of structure (3) is as follows: 1): Liquid-phase synthesis of the raw material Boc-DTrp-OPMB: Dissolve 9-11 g of Boc-DTrp-OH in an organic solvent, add 4-6 g of sodium carbonate, slowly dropwise add 4-6 mL of 4-methoxybenzyl chloride, after dropping, stir at room temperature for 11-15 h for the reaction, and then separate Boc-DTrp-OPMB through reduced-pressure rotary evaporation, extraction, washing, and purification. The reaction process is as follows: ； 2): Liquid-phase synthesis of the raw material Boc-DTrp(CO2Me)-OPMB: Dissolve 9-11 g parts by mass of Boc-DTrp-OPMB in 40-60 mL of acetonitrile, add 3-5 mL of dimethyl diallylmalonate and 0.5-1 g of 4-dimethylaminopyridine, stir at 25-30 °C for 18-25 h, and then separate Boc-DTrp(CO2Me)-OPMB through reduced-pressure rotary evaporation, extraction, washing, and purification. The reaction process is as follows: ； 3): Liquid-phase synthesis of the raw material H-DTrp(CO2Me)-OH: Dissolve 8-9.5 g of Boc-DTrp(CO2Me)-OPMB in 80-100 mL of cleavage solution, stir at room temperature for 1.5-3 h; after rotary evaporation to remove the cleavage solution, add water and acetonitrile and freeze-dry to obtain H-DTrp(CO2Me)-OH. The reaction process is as follows: ； 4): Liquid-phase synthesis of the raw material Fmoc-DTrp(CO2Me)-OH: Dissolve 5 - 7.5 g of H-DTrp(CO2Me)-OH obtained in step 3) in a mixture of 90 mL of water and tetrahydrofuran, add 2.5 - 4 g of sodium carbonate, then add 5 - 7 g of 9-fluorenylmethyl-N-succinimidyl carbonate, and stir at room temperature for 10 - 15 h; then obtain structure (2) by rotary evaporation under reduced pressure, extraction, washing, and purification, which is Fmoc-DTrp(CO2Me)-OH. The reaction process is as follows: 。 7. A method for preparing an efficient selective antagonist BQ-788 according to claim 6, characterized in that, The preparation process of the said structure (1) is as follows: Solid-phase synthesis is adopted; among them, the -A4 group is -H, and the -A5 group is -WangResin; The specific reaction is as follows: 1): The resin is fully swollen Soak 16 - 18.5 g of Fmoc-DNle-WangResin in N,N-dimethylformamide for swelling, vacuum filter off N,N-dimethylformamide, add 200 - 300 mL of 20% piperidine / DMF solution, purge with nitrogen for deprotection for 0.2 - 0.8 h to remove the Fmoc protecting group, and then wash with N,N-dimethylformamide to obtain resin A; 2): Connect Fmoc-DTrp(CO2Me)-OH Based on the amount of Fmoc-DNle-WangResin resin, weigh 1.3 times the amount of Fmoc-DTrp(CO2Me)-OH and 1.3 times the amount of HOBt and dissolve them in 200 mL of N,N-dimethylformamide. Cool down to -10 °C, add 1.3 times the amount of DIC, activate for 10 min, and then add it to resin A. Couple at room temperature for 1 - 2 h. After detection, the amino group has been completely coupled. After the coupling is completed, wash with N,N-dimethylformamide and then filter to dryness; then add 200 - 300 mL of 20% piperidine / DMF solution to remove Fmoc, purge with nitrogen for deprotection for 0.1 - 0.8 h, and then wash with N,N-dimethylformamide again to obtain resin DTrp(CO2Me)DNle-WangResin; 3): Connect Fmoc-tBuAla-OH: Based on the amount of DTrp(CO2Me)DNle-WangResin, weigh 1.2 - 1.8 times the amount of Fmoc-tBuAla-OH and 1.2 - 1.8 times the amount of HOBt and dissolve them in 200 mL of N,N-dimethylformamide. Cool down to -10 °C, add 1.5 times the amount of DIC to activate for 10 min, and then add it to the resin. Couple at room temperature for 1 - 2 h. After the Kaiser test shows colorless, after the coupling is completed, wash with N,N-dimethylformamide solution and filter to dryness; 4): The departure of the Fmoc protecting group: Vacuum filter off N,N-dimethylformamide, wash with N,N-dimethylformamide solution and filter to dryness, add 200 - 280 mL of 20% piperidine / DMF solution, purge with nitrogen for deprotection for 0.2 - 0.8 h, and then wash with N,N-dimethylformamide to obtain resin tBuAla-DTrp(CO2Me)-DNle-WangResin; The specific reaction is as follows: 。 8. The preparation method of an efficient selective antagonist BQ-788 according to claim 7, characterized in that the preparation method of the antagonist BQ-788 comprises the following preparation process: 1): Formation of urea from 2,6-dimethylpiperidine: Based on the resin tBuAla-DTrp(CO2Me)-DNle-WangResin, weigh 1.2 - 1.8 times the amount of 2,6-methylpiperidine and dissolve it in acetonitrile. Add 2.8 - 3.5 times the amount of triethylamine, then add 2.5 - 3 times the amount of N,N'-succinimidyl carbonate DSC. Stir the reaction at room temperature for 8 - 15 h, then concentrate, add dichloromethane to dissolve, then add it to the resin, add 2.8 - 3.2 times the amount of N,N-diisopropylethylamine, react for 10 - 15 h. After Kaiser detection is colorless, after the coupling ends, add N,N-dimethylformamide for washing and suction drying to obtain cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle-WangResin; 2): Cleavage step Disperse and suspend 20 - 23 g of cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle-WangResin in 200 - 250 mL of solution F, shake it on a shaker at room temperature for 2 - 3 h to obtain a resin suspension; After filtering the resin suspension, wash it with solution F and methyl tert-butyl ether, centrifuge and suction dry to obtain the crude product, and obtain the resin cis-2,6-Dimethylpiperidine-CO-tBuAla-DTrp(CO2Me)-DNle after purification. The reaction process is as follows: 。 9. The preparation method of an efficient selective antagonist BQ-788 according to claim 1, characterized in that, The purity of the antagonist BQ-788 obtained by the described preparation method is >90%, and the total synthesis yield is >20%.

10. A method for preparing an efficient selective antagonist BQ-788 according to claim 1, characterized in that, The purification process is to first dissolve it with acetonitrile / water, filter it with a mixed fiber membrane of 0.35 - 0.55 μm, and then purify it with a chromatographic column.

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