An amphiphilic polymer with a retinol derivative as the hydrophobic chain

Abstract

The present invention relates to an amphiphilic polymer with a retinol derivative as the hydrophobic chain. The amphiphilic polymer has the structure of formula I or formula II, with a water-soluble PEG as the hydrophilic segment, a retinol derivative as the hydrophobic segment, and an amino acid or oligopeptide containing a benzene ring side chain as the linker arm, forming an amphiphilic polymer with good biocompatibility. In an aqueous medium, it can self-assemble into a polymer micelle structure through strong π-π interactions and hydrophobic interactions between polymer chains. By adjusting the chain length of the hydrophilic segment or the hydrophobic end, amphiphilic polymers with different critical micelle concentrations can be obtained, and the product meets the requirements of biomedical materials.

Description

Technical Field

[0001] The present invention relates to the technical fields of biomedicine and medical polymer materials, and particularly relates to an amphiphilic polymer with a retinol derivative as a hydrophobic chain, and its preparation and application. Background Art

[0002] After amphiphilic molecules containing hydrophilic groups and hydrophobic groups reach and exceed a specific concentration in a solution, the molecules will self-assemble into micelle structures with a core-shell. This specific concentration is called the Critical Micelle Concentration (CMC). Polymer micelles self-assembled from amphiphilic polymers have a lower CMC than small molecule micelles and have a wide range of applications in the fields of biomedicine and medical polymer materials.

[0003] Polyethylene glycol (PEG) is a hydrophilic polymer material approved by the FDA and is commonly used as the hydrophilic chain of amphiphilic polymers. PEGs with different chain lengths can regulate the CMC value, solubilization ability, etc. of amphiphilic polymers. Amphiphilic molecules based on PEG as the hydrophilic segment, such as polyethylene glycol-15 hydroxystearate (Solutol HS 15), polysorbate 80, TPGS, etc., can be used as solubilizers for poorly soluble drugs to increase the solubility of poorly soluble drugs (CN101919819A, CN101701065A, CN112545988A). However, due to the relatively high CMC, poor drug loading stability and safety issues of such surfactants, their further application in the field of drug solubilization is limited.

[0004] mPEG-PDLLA is an amphiphilic polymer with mPEG as the hydrophilic segment and PDLLA as the hydrophobic segment. Samyang Company in South Korea developed a paclitaxel formulation based on mPEG-PDLLA micelles, which was launched in South Korea in 2006 and has since been launched in Asian countries such as India, the Philippines, Vietnam, and Indonesia. However, the room temperature stability of its aqueous dispersion is only 24 hours, and more than 30% of the drug leaks after 72 hours (US20030143184a). CN 102218027A disclosed an mPEG-PDLLA polymer micelle loaded with an anti-tumor drug paclitaxel, but the drug loading amount was less than 10%, and the room temperature stability was only 24 hours. The room temperature stability of the mPEG-PDLLA polymer micelle carrying docetaxel is only 30 minutes (CM01972480 A). Therefore, there is an urgent need to develop a polymer micelle system with a high drug loading amount, good safety and stability in clinical medication.

[0005] Retinoic acid is a molecule with in vivo pharmacological activity and can be used for the treatment of acute promyelocytic leukemia, psoriasis, ichthyosis, squamous cell carcinoma, melanoma and other diseases. WO2004 / 009528A1, WO2009 / 078804A1, PCT / SE02 / 00380, US10 / 098,873 and CN1668583A disclose a retinol derivative and its composition with paclitaxel or docetaxel. This composition uses N-(all-trans-retinoyl)-L-cysteic acid methyl estersodium salt and N-(13-cis-retinoyl)-L-cysteic acid methyl ester sodium salt as carrier materials, and utilizes the interaction between cis- and trans-retinoic acid (50:50) and the interaction between sulfonic acid groups and calcium ions to achieve the purpose of stabilizing paclitaxel or docetaxel. This retinol derivative also uses isotretinoin with higher toxicity as the hydrophobic part and sulfonate as the hydrophilic part, which is likely to introduce potentially mutagenic sulfonate esters impurities. CN 104399084 A discloses the application of PEGylated retinoic acid and its self-assembled micelles in drug delivery. This amphiphilic prodrug block has polyethylene glycol as the hydrophilic end and is combined with one molecule of hydrophobic retinoic acid through an ester bond to obtain an AB-type amphiphilic prodrug block. This PEGylated prodrug self-assembles into micelles in an aqueous medium and can serve as a reservoir for the poorly soluble drug retinoic acid, slowly releasing retinoic acid. This micelle has good safety and can be used for oral administration.

[0006] The applicant found through multiple experiments that an amphiphilic polymer synthesized with a retinol derivative as the hydrophobic segment, an amino acid or oligopeptide containing a benzene ring side chain as the linker arm, and methoxypolyethylene glycol or polyethylene glycol as the hydrophilic segment can self-assemble into a polymer micelle structure through strong π-π interactions and hydrophobic interactions between polymer chains in an aqueous medium. Moreover, this polymer micelle has a low CMC value and has potential drug solubilization effects. Summary of the Invention

[0007] The purpose of the present invention is to provide an amphiphilic polymer with a retinol derivative as the hydrophobic chain and its preparation method.

[0008] The described preparation method has mild reaction conditions, a simple process, and is easy to control.

[0009] The amphiphilic polymer with a retinol derivative as the hydrophobic chain (also known as: pegylated retinol derivative) has amphiphilicity and can self-assemble into a polymer micelle structure through strong π-π interactions and hydrophobic interactions between polymer chains in an aqueous medium. By adjusting the chain length of the hydrophilic segment or the length of the linker arm, amphiphilic polymers with different properties can be obtained, which can be used as drug delivery carriers.

[0010] To achieve the object of the present invention, the technical solution of the present invention is as follows:

[0011] An amphiphilic polymer with a retinol derivative as the hydrophobic chain, characterized in that it has the structure of formula I or formula II:

[0012]

[0013] Wherein:

[0014] R is a retinol derivative, selected from the following compounds:

[0015]

[0016] The carboxylic acid group therein and the amino part in formula I or formula II form an amide;

[0017] Wherein, the molecular weight of the methoxypolyethylene glycol or polyethylene glycol is 500-10000 Da; preferably 750-5000 Da.

[0018] Wherein, chiral carbon 1 is D-type, L-type or DL-type; m is 1-5; t is 0-5. Preferably, chiral carbon 1 is L-type; m is 1-3, n is 1 and 2. More preferably, m = 1, n = 1.

[0019] Wherein, R preferably has the following structure:

[0020]

[0021] The carboxylic acid group therein and the amino part in formula I or formula II form an amide.

[0022] The present invention further provides a method for preparing the polymer of the present invention. The method comprises the following steps:

[0023] (1) Methoxypolyethylene glycol or polyethylene glycol reacts with N-Boc protected phenylalanine to obtain an N-Boc protected intermediate.

[0024]

[0025] (2) The N-Boc protecting group is removed by using a reagent to obtain a de-N-Boc protected intermediate

[0026]

[0027]

[0028] (3) The de-N-Boc protected intermediate and the retinol derivative are subjected to amidation to obtain a cultivated retinol derivative.

[0029]

[0030] Among them,

[0031] In step (1), the esterification reaction is carried out in an anhydrous tetrahydrofuran system or anhydrous dichloromethane, the reaction temperature is 25-80 °C, and the reaction time is 24-72 hours.

[0032] In step (2), the de-Boc protecting agent is selected from: trifluoroacetic acid-dichloromethane solution, hydrogen chloride-ethyl acetate solution, hydrogen chloride-1,4-dioxane solution, zinc bromide-dichloromethane solution or trimethylsilyl trifluoromethanesulfonate / 2,6-dimethylpyridine-dichloromethane solution. Preferably, the de-Boc protecting agent is trifluoroacetic acid-dichloromethane solution, hydrogen chloride-ethyl acetate solution or hydrogen chloride-1,4-dioxane solution;

[0033] In step (3), the acid-binding agent used is triethylamine, N-ethyldiisopropylamine, anhydrous potassium carbonate or pyridine; the reaction temperature is 4-50 °C; the reaction time is 12-72 h. Preferably, the acid-binding agent used is triethylamine or N-ethyldiisopropylamine.

[0034] Preferably, for the polymer described in the present invention, the hydrophilic part is methoxypolyethylene glycol with molecular weights of 750, 1000 or 1500 Da respectively. When chiral carbon 1 is of the L type and m is 1 and t is 1, when the structure of the polymer is the following structure, the polymers are respectively labeled as mPR 750 、mPR 1000 or mPR 1500 ,

[0035]

[0036] Beneficial effects: By using polyethylene glycol or methoxypolyethylene glycol as the hydrophilic segment and retinol derivatives as the hydrophobic segment, and using aromatic amino acids or oligopeptides as the linker in the middle, the prepared retinoid derivatives can be used as amphiphilic drug-loading polymer materials. The synthetic route of the carrier material of the present invention is simple and the production cost is low. In an aqueous medium, it can self-assemble into a polymer micelle structure through strong π-π interactions and hydrophobic interactions between polymer chains. By adjusting the chain length of the hydrophilic segment or the hydrophobic end, amphiphilic polymers with different CM Cs can be obtained, and the product meets the requirements of biomedical materials. Description of the Drawings

[0037] Figure 1 1H NMR spectrum of retinoid derivative mPR 1000 1HNMR spectrum.

[0038] Figure 2 Infrared spectrum of retinoid derivative mPR 1000 Infrared spectrum.

[0039] Figure 3 mPR1000 Transmission electron microscopy image of aqueous solution Detailed implementation manners

[0040] The above content of the present invention will be further described in detail below in the form of embodiments. However, it should not be understood that the scope of the above main body of the present invention is limited to the following cases. All technologies implemented based on the above content of the present invention belong to the scope of the present invention.

[0041] Example 1 mPR 750 Preparation of polymer

[0042] (1) Weigh 74.87 g of methoxypolyethylene glycol (molecular weight: 750 Da) and 53.07 g of Boc-L-phenylalanine, add 3.69 g of DMAP and 57.56 g of EDCI. Dissolve the reaction mixture in 400 ml of anhydrous tetrahydrofuran, then evacuate, replace with nitrogen for 3 - 5 times, maintain the reaction temperature at 75°C, condense and reflux, react for 40 h. After the reaction is completed, a light yellow to milky white clear viscous liquid is obtained. Concentrate by rotary evaporation. Add an appropriate amount of dichloromethane to dissolve the concentrated mixture, wash it 3 - 5 times with 0.1 M hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution respectively, concentrate by rotary evaporation, add ice ether to precipitate, and then filter and dry to obtain N-Boc protected phenylalanine. Take an appropriate amount of N-Boc protected phenylalanine, add an appropriate amount of hydrogen chloride - 1,4-dioxane solution, with a dosage of 5 ml per gram of polymer, react at room temperature for 45 min. After the reaction is completed, concentrate by rotary evaporation and then dry under vacuum to obtain peptidyl phenylalanine.

[0043] (2) Weigh 9.01 g of all-trans retinoic acid, dissolve it in 150 ml of anhydrous dichloromethane, add 7.66 g of EDCI, 5.44 g of HOBT, add 21 ml of DIPEA, and react under ice-salt bath conditions for 1 h. Remove the ice-salt bath and continue to react at room temperature for 1 h. After the reaction is completed, an all-trans retinoic acid active ester solution is obtained; continue to add 20.68 g of the above-mentioned peptidyl phenylalanine to the solution, evacuate, replace with nitrogen for 3 - 5 times, maintain the reaction temperature at 40°C, condense and reflux, react for 48 h. After the reaction is completed, a brown viscous liquid is obtained. Add an appropriate amount of dichloromethane to dilute it, wash it 3 - 5 times with 0.1 M hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution respectively, concentrate by rotary evaporation. Add 20 ml of tetrahydrofuran to dissolve the liquid after rotary evaporation, continue to add 400 ml of anhydrous ether, and let it stand at -20°C to -15°C for 8 - 20 h. Filter quickly and then dry to obtain mPR 750 。 11H NMR (500 MHz, Deuterium Oxide) δ 8.01 (d, 1H, NH), 7.47–7.09 (m, 5H, -C6H5), 6.81 (s, 1H, -CO-CH=), 6.14 (s, 1H, =CH-C(CHCO)-CH3), 5.84 (s, 1H, =CH-CH=C(CH3)), 4.35 (d, J=4.5 Hz, 1H, CH3-CH=CH-), 4.30 (m, 2H, -CH=CH-CH=CH-), 3.82 (s, 1H, -CH(CHCO)-NH), 3.77–3.64 (m, 64H, -(O-CH2-CH2)n-), 3.43 (d, J=6.5 Hz, 3H, -O-CH3), 3.10–3.30 (m, 2H, -CH2-C6H5), 2.20 (s, 3H, =C(CHCO)-CH3), 2.01 (d, J=1.3 Hz, 2H, -CH2-CH2-C(CH3)=), 1.88 (s, 3H, =C(CH)-CH3), 1.67 (s, 3H, -CH2-CH2-C(CH3)=), 1.45 (s, 2H, -CH2-CH2-C(CH3)=), 1.23–1.10 (m, 2H, -CH2-C(CH3)2), 1.01 (s, 6H, -CH2-C(CH3)2).

[0044] Example 2 mPR 1000 Preparation of the polymer.

[0045] (1) Weigh 50.10 g of polyethylene glycol monomethyl ether (molecular weight: 1000 Da) and 26.53 g of Boc-L-phenylalanine, add 1.83 g of DMAP and 26.95 g of EDCI, dissolve the reaction mixture in 300 ml of anhydrous tetrahydrofuran, evacuate, displace with nitrogen 3 - 5 times, maintain the reaction temperature at 75 °C, condense and reflux, react for 40 h. After the reaction is completed, a light yellow to milky white clear viscous liquid is obtained. Concentrate by rotary evaporation, add an appropriate amount of dichloromethane to dissolve the concentrated mixture, wash it 3 - 5 times with 0.1 M hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution respectively, concentrate by rotary evaporation, precipitate with ice ether, and then filter and dry to obtain N-Boc protected phenylalanine. Take an appropriate amount of N-Boc protected phenylalanine, add an appropriate amount of hydrogen chloride-1,4-dioxane solution, with a dosage of 5 ml per gram of polymer, react at room temperature for 45 min. After the reaction is completed, concentrate by rotary evaporation and then dry under vacuum to obtain peptidyl phenylalanine.

[0046] (2) Weigh 9.02 g of all-trans retinoic acid, dissolve it in 150 ml of anhydrous dichloromethane, add 7.66 g of EDCI, 5.43 g of HOBT, add 21 ml of DIPEA, react for 1 h under ice-salt bath conditions, remove the ice-salt bath, and continue to react for 1 h at room temperature. After the reaction is completed, obtain an all-trans retinoic acid active ester solution; continue to add 25.05 g of the above-mentioned phenylalanine to the solution, then evacuate and replace with nitrogen 3 - 5 times, maintain the reaction temperature at 40 °C, carry out condensation reflux, and react for 48 h. After the reaction is completed, obtain a brown viscous liquid, add an appropriate amount of dichloromethane for dilution, wash it 3 - 5 times with 0.1 M hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution respectively, rotate and evaporate to concentrate, add 20 ml of tetrahydrofuran to the liquid after rotary evaporation for dissolution, continue to add 400 ml of anhydrous ether, stand still for 8 - 20 h under the condition of -20 °C to -15 °C, quickly filter by suction and then freeze-dry to obtain mPR 1000 。 1 H NMR(500MHz,DMSO-d6)δ8.36(d,J=7.7Hz,1H,NH),7.31–7.16(m,5H,-C 6 H 5 ),6.26(d,J=10.7Hz,1H,-CO-CH=),6.15(d,J=16.0Hz,1H,=CH-C(CHCO)-CH 3 ),5.87(s,1H,=CH-CH=C(CH 3 )),4.55–4.48(m,1H,CH 3 -CH=CH-),4.14(ddd,J=9.1,5.8,3.7Hz,2H,2H,-CH=CH-CH=CH-),3.65(s,1H,-CH(CHCO)-NH),3.53–3.47(m,88H,-(O-CH 2 -CH 2 )n-),3.24(s,3H,-O-CH 3 ),3.07–2.90(m,2H,-CH 2 -C 6 H 5 ),2.21(s,3H,=C(CHCO)-CH 3 ),2.01(t,J=6.5Hz,2H,-CH2-CH 2 -C(CH 3 )=),1.96(s,3H,=C(CH)-CH 3 ),1.68(s,3H,-CH 2 -CH 2-C(CH3)=), 1.57 (td, J=7.7, 6.8, 4.1 Hz, 2H, -CH 2 -CH 2 -C(CH 3 )=), 1.48–1.40 (m, 2H, -CH 2 -C(CH 3 ) 2 ), 1.01 (s, 6H, -CH 2 -C(CH 3 ) 2 )

[0047] Example 3 mPR 1500 Polymer preparation.

[0048] (1) Weigh 60.11 g of methoxypolyethylene glycol (molecular weight: 1500 Da) and 21.24 g of Boc-L-phenylalanine, add 1.47 g of DMAP and 23.23 g of EDCI. Dissolve the reaction mixture in 350 ml of anhydrous tetrahydrofuran, then evacuate, displace with nitrogen 3 - 5 times, maintain the reaction temperature at 75 °C, condense and reflux, and react for 40 h. After the reaction is completed, a light yellow to milky white clear viscous liquid is obtained. Concentrate by rotary evaporation, add an appropriate amount of dichloromethane to dissolve the concentrated mixture, wash it 3 - 5 times with 0.1 M hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution respectively, concentrate by rotary evaporation, add ice-cold diethyl ether to precipitate, and then filter and dry to obtain N-Boc-protected phenylalanine. Take an appropriate amount of N-Boc-protected phenylalanine, add an appropriate amount of hydrogen chloride-1,4-dioxane solution, with a dosage of 5 ml per gram of polymer, and react at room temperature for 45 min. After the reaction is completed, concentrate by rotary evaporation and then dry under vacuum to obtain peptidyl phenylalanine.

[0049] (2) Weigh 9.02 g of all-trans retinoic acid, dissolve it in 150 ml of anhydrous dichloromethane, add 7.66 g of EDCI, 5.43 g of HOBT, add 21 ml of DIPEA, and react under ice-salt bath conditions for 1 h. Remove the ice-salt bath and continue to react at room temperature for 1 h. After the reaction is completed, an all-trans retinoic acid active ester solution is obtained; continue to add 35.21 g of the above-mentioned peptidyl phenylalanine to the solution, evacuate, displace with nitrogen 3 - 5 times, maintain the reaction temperature at 40 °C and react for 48 h. After the reaction is completed, a brown viscous liquid is obtained. Add an appropriate amount of dichloromethane to dilute it, wash it 3 - 5 times with 0.1 M hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution respectively, concentrate by rotary evaporation, add 20 ml of tetrahydrofuran to dissolve the liquid after rotary evaporation, continue to add 400 ml of anhydrous diethyl ether, and let it stand at -20 °C to -15 °C for 8 - 20 h. Filter quickly and dry to obtain mPR 1500 . 11H NMR (500 MHz, Deuterium Oxide) δ 8.01 (d, 1H, NH), 7.56–7.25 (m, 5H, -C6H5), 6.84 (s, 1H, -CO-CH=), 6.16 (s, 1H, =CH-C(CHCO)-CH3), 5.87 (s, 1H, =CH-CH=C(CH3)), 4.35 (t, J=4.6 Hz, 1H, CH3-CH=CH-), 3.89 ((m, 2H, -CH=CH-CH=CH-), 3.82 (s, 1H, -CH(CHCO)-NH), 3.75–3.67 (m, 132H, -(O-CH2-CH2)n-), 3.43 (s, 3H, -O-CH3), 3.09–3.29 (m, 2H, -CH2-C6H5), 2.17 (s, 3H, =C(CHCO)-CH3), 2.01 (s, 2H, -CH2-CH2-C(CH3)=), 1.88 (s, 3H, =C(CH)-CH3), 1.68 (s, 3H, -CH2-CH2-C(CH3)=), 1.23 (t, J=7.1 Hz, 2H, -CH2-CH2-C(CH3)=), 1.17 (m, 2H, -CH2-C(CH3)2), 1.03 (s, 6H, -CH2-C(CH3)2).

[0050] Preparation of the blank nano-polymer micelle preparation in Example 4.

[0051] (1) Take the mPR prepared in Example 1 750 6 g of the polymer, 60 ml of ethanol, and 60 ml of ultrapure water, and set aside.

[0052] (2) Add 60 ml of ethanol to the mPR 750 polymer to dissolve it, and shake to dissolve; under the conditions of 37 °C and a rotation speed of 110 rpm / min, rotary evaporate for 1 - 3 h to remove ethanol to obtain a blank polymer film, add 60 ml of ultrapure water to hydrate at room temperature to obtain a blank micelle solution, then filter and sterilize, and freeze-dry.

[0053] Determination of the CMC of the peylated retinol derivative in Example 5.

[0054] Prepare a pyrene stock solution with a concentration of 0.012 mg / ml: Weigh 3 mg of pyrene into a 250-ml volumetric flask and make up the volume to the mark with acetone. Take 100 μl of each solution and transfer it to a brown bottle. Use a nitrogen evaporator to blow for 10 min until the acetone has completely evaporated. Weigh 25 mg of the sample into a 50-ml volumetric flask and make up the volume to the mark with UP water to obtain a 0.5 mg / ml mother liquor. Gradient dilute it to obtain working sample solutions with concentrations of 0.1, 0.05, 0.02, 0.01, 0.005, 0.002, 0.001, and 0.0005 mg / ml. Add the working sample solutions to the above-mentioned brown bottles respectively and place them in the dark for 24 h to obtain the sample solutions to be measured. Measure the fluorescence intensities of the sample solutions to be measured at 373 nm and 384 nm.

[0055] Table 1 CMC values of retinyl palmitate derivatives

[0056] Polymer CMC (μg / mL) <![CDATA[mPR 750 > 6.42 <![CDATA[mPR 1000 > 6.85 <![CDATA[mPR 1500 > 16.91

Claims

1. An amphiphilic polymer with a retinol derivative as the hydrophobic chain, the polymer having the structure of formula I or formula II: Wherein: R is a retinol derivative, selected from the following compounds: The carboxylic acid group therein and the amine group in formula I or formula II form an amide; The molecular weight of the monomethyl ether of polyethylene glycol or polyethylene glycol is 500 - 10000 Da; Chiral carbon 1 is of D-type, L-type or DL-type; m is 1 - 5; t is 0 - 5.

2. The polymer according to claim 1, characterized in that, The molecular weight of the monomethyl ether of polyethylene glycol or polyethylene glycol is 750 - 5000 Da.

3. The polymer according to claim 1, characterized in that: R has the following structure: The carboxylic acid group therein and the amine group in formula I or formula II form an amide.

4. The polymer according to claim 1, characterized in that: Chiral carbon 1 is of L-type; m is 1 - 3, n is 1 and 2.

5. The polymer according to claim 1, characterized in that: The structure is as follows:

6. The preparation method of the polymer according to claim 1, characterized in that: The method comprises the following steps: (1) The monomethyl ether of polyethylene glycol or polyethylene glycol undergoes an esterification reaction with N-Boc protected phenylalanine to obtain an N-Boc protected intermediate, (2) The N-Boc protecting group is removed using a reagent to obtain a de-N-Boc protected intermediate, (3) The de-N-Boc protected intermediate and the retinol derivative are subjected to amidation to obtain a cultivated retinol derivative, 7. The preparation method according to claim 6, characterized in that, In step (1), the esterification reaction is carried out in an anhydrous tetrahydrofuran system or anhydrous dichloromethane, the reaction temperature is 25 - 80 °C, and the reaction time is 24 - 72 hours.

8. The preparation method according to claim 6, characterized in that, The reagent in step (2) is selected from: trifluoroacetic acid - dichloromethane solution, hydrogen chloride - ethyl acetate solution, hydrogen chloride - 1,4-dioxane solution, zinc bromide - dichloromethane solution or trimethylsilyl trifluoromethanesulfonate / 2,6-dimethylpyridine - dichloromethane solution.

9. The preparation method according to claim 6, characterized in that, The de-N-Boc protecting agent used in step (3) is triethylamine, N-ethyldiisopropylamine, anhydrous potassium carbonate or pyridine; the reaction temperature is 4 - 50 °C; the reaction time is 12 - 72 h.

10. The preparation method according to claim 6, characterized in that, The reagent in step (2) is trifluoroacetic acid - dichloromethane solution, hydrogen chloride - ethyl acetate solution or hydrogen chloride - 1,4-dioxane solution; the de-N-Boc protecting agent used in step (3) is triethylamine or N-ethyldiisopropylamine.

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