An improved process for the preparation of n-acetylgalactosamine intermediates

Abstract

The present application relates to a kind of improved preparation method of N-acetylgalactosamine intermediate, specifically including the following steps: in the presence of NaIO4 and RuCl3, compound of formula II is subjected to oxidation reaction as shown below, to obtain compound of formula I, i.e..The preparation method has the advantages of simple operation and post-processing, high yield, high product purity, easy industrial production, etc., while effectively avoiding the generation of difficult to separate by-products.

Description

Technical Field

[0001] This invention relates to an improved method for preparing an N-acetylgalactosamine intermediate. Background Technology

[0002] GalNAc (N-acetylgalactosamine) conjugation is currently the most commonly used oligonucleotide drug delivery system. N-acetylgalactosamine (GalNAc) is covalently conjugated in a trivalent state to the 3′ end of the positive strand of different siRNA sequences, forming a polysaccharide-siRNA monoconjugate. This enables specific delivery to hepatocytes, and the drug enters the cell to exert its function through endocytosis. GalNAc is a targeting ligand for the sialic acid receptor (ASGPR), exhibiting high affinity and rapid internalization with liver surface cells. This allows the siRNA conjugate to specifically bind to membrane proteins and enter the cell. Such siRNA conjugates show great potential for the treatment of liver-related diseases involving gene overexpression.

[0003] Compound I is a key intermediate in the synthesis of GalNAc compounds. The traditional method for synthesizing N-acetylgalactosamine is as follows:

[0004]

[0005] The final core step, the oxidation of the double bond by NaIO4, is a stepwise process. First, a dihydroxylated intermediate compound 5 must be generated. Since the product and the intermediate have very weak UV absorption and similar polarities, it is difficult to accurately judge the reaction progress. In the subsequent separation and purification process, it is difficult to remove the dihydroxylated intermediate by column chromatography and reversed-phase HPLC. It is necessary to separate by reverse phase and then repeatedly heat-pulse and recrystallize with ethyl acetate to remove most of it. At the same time, the dihydroxylated intermediate will generate a key process byproduct in the subsequent condensation reaction. Summary of the Invention

[0006] To address the shortcomings of existing preparation methods, which easily generate difficult-to-separate dihydroxylated byproducts leading to low purity and complex post-processing steps, this invention provides an improved method for preparing N-acetylgalactosamine intermediates. This method offers advantages such as simple operation and post-processing, high yield, high product purity, and ease of industrial production, while effectively avoiding the formation of difficult-to-separate byproducts.

[0007] This invention provides an improved method for preparing an N-acetylgalactosamine intermediate, comprising the following steps: in a solvent, in the presence of NaIO4 and RuCl3, the compound of formula II is subjected to the following oxidation reaction to obtain the compound of formula I;

[0008]

[0009] In some embodiments, the solvent in the oxidation reaction is a conventional solvent in the art, preferably an organic solvent, or water and an organic solvent; the organic solvent is preferably an alkane solvent (e.g., dichloromethane) and / or a nitrile solvent (e.g., acetonitrile).

[0010] In some embodiments, NaIO4 and RuCl3 are applied to the oxidation reaction by forming a mixed solution. The mixed solution is preferably applied dropwise to the oxidation reaction. The solvent in the mixed solution is preferably a mixture of an alkane solvent (e.g., dichloromethane), a nitrile solvent (e.g., acetonitrile), and water; wherein the volume ratio of the alkane solvent, nitrile solvent, and water is preferably 1:(1-4):(3-10), more preferably 1:2:6. The molar volume ratio of NaIO4 to the solvent in the mixed solution is preferably (1-1.5):1 mol / L, more preferably 1.2:1 mol / L.

[0011] In some embodiments, the molar ratio of NaIO4 to RuCl3 in the oxidation reaction is a conventional molar ratio in the art, which may be (75-250):1, preferably 224.1:1.

[0012] In some embodiments, in the oxidation reaction, the molar ratio of the compound of formula II to RuCl3 is a conventional molar ratio in the art, which may be (10-75):1, preferably 50:1.

[0013] In some embodiments, in the oxidation reaction, the molar volume ratio of the compound of formula II to the solvent is a conventional molar volume ratio in the art, which may be (0.75-2.5):1 mol / L, preferably 1.2:1 mol / L.

[0014] In some embodiments, the oxidation reaction is carried out at a temperature that is conventional in the art, preferably from 0°C to room temperature (e.g., 25°C), and more preferably at 0°C first, followed by at room temperature.

[0015] In some embodiments, the NaIO4 and RuCl3 are added at 0°C during the oxidation reaction.

[0016] In some embodiments, the reaction time of the oxidation reaction is determined by the time it takes for the reaction to be completed by TLC, and can be 1.5-12 hours, preferably 2 hours.

[0017] In some embodiments, the oxidation reaction further includes the following post-processing steps: controlling the reaction solution to be alkaline (preferably pH 9-10, more preferably by adding a saturated aqueous solution of NaHCO3), filtration, washing (preferably washing with dichloromethane and water), extraction (preferably extraction with dichloromethane and water), controlling the aqueous phase to be acidic (preferably pH 2-3, more preferably by adding a semi-saturated aqueous solution of citric acid), extraction (preferably extraction with dichloromethane), drying (preferably drying with sodium sulfate), concentration, and purification (preferably purification using C18 reversed-phase HPLC).

[0018] In some embodiments, the method for preparing the improved N-acetylgalactosamine intermediate further includes the preparation method of the compound of formula II as follows: in a solvent, in the presence of a Lewis acid, compound 3 is subjected to a glycosylation reaction with 5-phenyl-1-butanol as shown below to obtain compound II;

[0019]

[0020] In some embodiments, the solvent used in the glycosylation reaction is a conventional solvent in the art, preferably a haloalkane solvent, such as dichloromethane.

[0021] In some embodiments, in the glycosylation reaction, the Lewis acid is a conventional Lewis acid in the art, such as one or more of scandium trifluoromethanesulfonate, bismuth trifluoromethanesulfonate, and trimethyl trifluoromethanesulfonate (TMSOTf), preferably trimethyl trifluoromethanesulfonate. The trimethyl trifluoromethanesulfonate is preferably added dropwise. The molar ratio of the Lewis acid to compound 3 is preferably 1:(1-3), for example, 1:2.

[0022] In some embodiments, the molar ratio of 5-phenyl-1-butanol to compound 3 in the glycosylation reaction is a conventional molar ratio in the art, which may be (0.8-1.5):1, preferably 1.1:1.

[0023] In some embodiments, during the glycosylation reaction, the molar volume ratio of compound 3 to the solvent is a conventional molar volume ratio in the art, which may be (0.45-1.5):1 mol / L, preferably 0.77:1 mol / L.

[0024] In some embodiments, the glycosylation reaction further includes the use of a dehydrating agent, such as a molecular sieve or anhydrous magnesium sulfate, preferably 4A molecular sieve. The mass ratio of the 4A molecular sieve to the compound 3 is preferably 1:(10-30), more preferably 1:20.

[0025] In some embodiments, the reaction temperature of the glycosylation reaction is a conventional reaction temperature in the art, preferably 0°C to room temperature (e.g., 25°C), more preferably the reaction is first carried out at room temperature, then at 0°C, and finally at room temperature.

[0026] In some embodiments, the Lewis acid is added at 0°C during the glycosylation reaction.

[0027] In some embodiments, the reaction time of the glycosylation reaction is based on the time it takes for the reaction to be completed as detected by TLC, and can be 4-18 hours, preferably 16.5 hours.

[0028] In some embodiments, the glycosylation reaction further includes the following post-processing steps: washing (e.g., washing with a saturated aqueous solution of NaHCO3 and dichloromethane), drying (e.g., drying with anhydrous sodium sulfate), concentration, purification (e.g., purification by column chromatography (preferably with silica gel 100-200 mesh, eluent polarity gradient: DCM / MeOH = 1 / 0 to 10 / 1)) and concentration.

[0029] In some embodiments, the method for preparing the improved N-acetylgalactosamine intermediate further includes the following method for preparing compound 3: in a solvent, in the presence of a Lewis acid, compound 2 is subjected to the following cyclization reaction to obtain compound 3;

[0030]

[0031] In some embodiments, the solvent in the cyclization reaction is a conventional solvent in the art, such as a haloalkane solvent (e.g., dichloromethane).

[0032] In some embodiments, in the cyclization reaction, the Lewis acid is a conventional Lewis acid in the art, such as one or more of scandium trifluoromethanesulfonate, bismuth trifluoromethanesulfonate, and trimethyl trifluoromethanesulfonate (TMSOTf), preferably trimethyl trifluoromethanesulfonate. The trimethyl trifluoromethanesulfonate is preferably added dropwise. The molar ratio of the Lewis acid to compound 2 is preferably (1-1.5):1, for example, 1.2:1.

[0033] In some embodiments, during the cyclization reaction, the molar volume ratio of compound 2 to the solvent is (0.37-1.3):1 mol / L, preferably 0.85:1 mol / L.

[0034] In some embodiments, the cyclization reaction is carried out at a temperature that is conventional in the art, preferably from 0°C to room temperature (e.g., 25°C), and more preferably at 0°C followed by a reaction at room temperature.

[0035] In some embodiments, the Lewis acid is added at 0°C during the cyclization reaction.

[0036] In some embodiments, the reaction time of the cyclization reaction is based on the time it takes for the reaction to be complete as detected by TLC, and can be 1-12 hours, preferably 2 hours.

[0037] In some embodiments, the cyclization reaction further includes the following post-processing steps: washing (e.g., washing with a saturated aqueous solution of NaHCO3), drying (e.g., drying with anhydrous sodium sulfate), and concentration.

[0038] In some embodiments, the method for preparing the improved N-acetylgalactosamine intermediate further includes the following method for preparing compound 2: in the presence of a base, compound 1 is subjected to an acetylation reaction with acetic anhydride as shown below to obtain compound 2;

[0039]

[0040] In some embodiments, the base is a conventional base in the art, such as one or more of acetate, pyridine, 4-dimethylaminopyridine, and triethylamine, preferably pyridine, 4-dimethylaminopyridine, and triethylamine. The pyridine can also be used as a solvent for the acetylation reaction. The molar volume ratio of compound 1 to pyridine can be (0.46-1.5):1 mol / L, preferably 0.93:1 mol / L. The molar ratio of 4-dimethylaminopyridine to compound 1 can be 1:(2-20), preferably 1:10. The molar ratio of triethylamine to compound 1 can be (0.8-3):1, preferably 1:1. The triethylamine is preferably added to the acetylation reaction by dropwise addition.

[0041] In some embodiments, the molar ratio of the acetic anhydride to the compound 1 is (5-8):1, preferably 6:1.

[0042] In some embodiments, the acetylation reaction is carried out at a conventional reaction temperature in the art, preferably from 0°C to room temperature (e.g., 25°C), more preferably by reacting first at room temperature, then at 0°C, and finally at room temperature.

[0043] In some embodiments, the reaction time of the acetylation reaction is determined by the time it takes for the reaction to be complete as detected by TLC, and can be 6-24 hours, preferably 16 hours.

[0044] In some embodiments, the acetylation reaction further includes the following post-processing steps: precipitation (e.g., adding ethyl acetate to precipitate the product), filtration, washing (e.g., washing with water), and drying (e.g., vacuum drying).

[0045] The present invention also provides a compound as shown in Formula 5:

[0046]

[0047] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0048] The reagents and raw materials used in this invention are all commercially available.

[0049] The positive and progressive effects of the present invention are as follows: the preparation method has the advantages of simple operation and post-processing, high yield, high product purity, and easy industrial production, while effectively avoiding the generation of difficult-to-separate by-products. Attached Figure Description

[0050] Figure 1 The hydrogen spectrum of compound 2 is shown below.

[0051] Figure 2 The hydrogen spectrum of compound 3 is shown below.

[0052] Figure 3 The hydrogen spectrum of compound II is shown below.

[0053] Figure 4 This is the proton NMR spectrum of the final product, compound I. Detailed Implementation

[0054] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0055] In the following examples, compound 1 was purchased from Jinan Shanmu Biomedical Technology Co., Ltd., product number SAM701.

[0056] Example 1

[0057]

[0058] Step 1:

[0059] Substrate compound 1 (3.50 kg, 16.2 mol) and acetic anhydride (9.94 kg, 97.4 mol) were added to pyridine (17.5 L) at room temperature (25 °C) to obtain a white suspension. Then, 4-dimethylaminopyridine (198.3 g, 1.62 mol) was added, and the reaction system was cooled to 0 °C. Triethylamine (1.64 kg, 16.2 mol) was then added dropwise, while controlling the temperature of the reaction system to not exceed 10 °C. After the addition was complete, the temperature was raised to room temperature (25 °C), and the reaction was stirred for 16 hours. After the reaction was complete as monitored by TLC (DCM / MeOH = 20 / 1), ethyl acetate (14 L) was added and stirred for 1 hour to precipitate the product. The resulting filter cake was then suspended in water (25 L) and stirred for 1 hour. After filtration again, the resulting filter cake was washed three times with water (4 L). The final solid was dried under vacuum at 45–50 °C for 48 hours to obtain 6.00 kg of dried white solid, which was compound 2 (yield 94.5%).

[0060] Structural characterization of compound 2:

[0061] 1 H-NMR (400MHz, DMSO-d6): δ7.90(d,J=9.2Hz,1H),5.63(d,J=8.0Hz,1H),5.26(s,1H),5.06(d,J=9.6Hz ,1H),4.22(s,1H),4.13-3.99(m,3H),2.12(s,3H),2.03(s,3H),1.99(s,3H),1.90(s,3H),1.78(s,3H).

[0062] The proton NMR spectrum of compound 2 is as follows: Figure 1 As shown.

[0063] Step 2:

[0064] Compound 2 (6.00 kg, 15.4 mol) was suspended in anhydrous DCM (18.0 L). Trimethylsilyl trifluoromethanesulfonate (4.11 kg, 18.5 mol) was added dropwise at 0 °C. The mixture was heated to room temperature (25 °C) and stirred for 2 hours until the starting material was completely dissolved. The reaction was monitored by TLC (DCM / MeOH = 20 / 1). After the reaction was complete, the reaction solution was added to a saturated NaHCO3 aqueous solution (15 L). The mixture was separated, and the organic phase was dried over anhydrous Na2SO4. The solution was filtered and concentrated to obtain 5.07 kg of a pale yellow oily substance, which is compound 3. No purification is required and it can be used directly in the next reaction.

[0065] Structural characterization of compound 3:

[0066] ESI-MS: m / z = 330.1 [M+H] +

[0067] 1 H-NMR (400MHz, DMSO-d6): δ6.04 (d, J=7.2Hz, 1H), 5.24 (t, J=3.6Hz, 1H), 4.88 (dd, J1=6.8Hz, J2=3.6Hz, 1H), 4.30-4.20 (m, 1H), 4.07 (dddd ,J1=30.0Hz,J2=11.6Hz,J3=7.2Hz,2H),3.95(td,J1=16.8Hz,J2=1.2Hz,1H),2.06(s,3H),2.01(s,3H),2.00(s,3H),1.95(d,J=1.2Hz,3H).

[0068] The proton NMR spectrum of compound 3 is as follows: Figure 2 As shown

[0069] Step 3:

[0070] Compound 3 (5.07 kg, 15.4 mol) and compound 4 (2.04 kg, 16.9 mol) were dissolved in DCM (20 L), and 250.0 g of 4A molecular sieve was added. The reaction system was stirred at room temperature (25 °C) for 0.5 h. After cooling the reaction system to 0 °C, trimethylsilyl trifluoromethanesulfonate (1.70 kg, 7.7 mol) was added dropwise, and the temperature was raised to room temperature (25 °C) and stirred at this temperature for 16 h. After the reaction was complete as monitored by TLC (DCM / MeOH = 20 / 1), the reaction solution was poured into a saturated NaHCO3 aqueous solution (10 L), stirred for 30 minutes, and the aqueous phase was extracted again with DCM (5 L) after separation. The organic phases were combined and dried with anhydrous Na2SO4. The crude product obtained by filtration and concentration was purified by column chromatography (silica gel 100-200 mesh, eluent polarity gradient: DCM / MeOH = 1 / 0 to 10 / 1). After concentration of the fraction, 3.50 kg of pale yellow oily substance was obtained, which is compound II (yield 53.0%).

[0071] Through the hydrogen at the 1-position of the sugar ring 1 The configuration is determined by chemical shifts on 1H NMR. In the target β configuration, the hydrogen at the 1-position is in an axial bond and located in the deshielded region of the six-membered sugar ring. It will shift to a higher field by 0.1 ppm compared to the 1-position hydrogen in the α configuration.

[0072] Structural characterization of compounds of formula II:

[0073] ESI-MS: m / z = 480.3 [M+H] +

[0074] 1H-NMR (400MHz, DMSO-d6): δ7.80(d,J=9.6Hz,1H),7.26(t,J=7.2Hz,2H),7.18-7.13(m ,3H),5.21(d,J=3.6Hz,1H), 4.96(dd,J1=11.2Hz,J2=2.8Hz,1H),4.49(d,J=8.4Hz,1H ),4.03(s,3H),3.87(q,J=11.2Hz,1H),3.78-3.68(m,1H),3.48-3.39(m,1H),2.55(t, J=7.2Hz,2H),2.09(s,3H),1.98(s,3H),1.88(s,3H),1.71(s,3H),1.65-1.48(m,4H).

[0075] The proton NMR spectrum of compound II is as follows: Figure 3 As shown.

[0076] Step 4:

[0077] NaIO4 (560 g, 2.6 mol) and RuCl3 (2.41 g, 11.6 mmol) were suspended in a mixed solvent of DCM (250 mL), acetonitrile (500 mL), and water (1.5 L). The mixture of compound II (206 g, 582.1 mmol), DCM (250 mL), and acetonitrile (250 mL) was added dropwise to the above reaction system at 0 °C. The temperature was then raised to room temperature (25 °C) and the reaction was stirred for 2 hours. After the reaction was complete, TLC (DCM / MeOH = 20 / 1 for monitoring the starting material, DCM / MeOH / AcOH = 5 / 1 / 0.01 for monitoring the product) was used to control the pH of the system to approximately 9–10 by adding an appropriate amount of saturated NaHCO3 aqueous solution. The filter cake was filtered and washed sequentially with DCM (2L) and H2O (2L). After separation, the aqueous phase was collected and adjusted to pH 2-3 with a semi-saturated citric acid aqueous solution. Then, it was extracted 10 times with DCM (1L). The organic phases were combined and dried over anhydrous Na2SO4. The crude product was filtered and concentrated. It was then purified by preparative HPLC (column: Phenomenex luna C18 (250x150mm x 15um); mobile phase: [water-acetonitrile]; acetonitrile gradient: 15%-45%, 20.0 min). After concentration, 138g of white solid was obtained, which was the compound of formula I (yield 71.8%).

[0078] Structural characterization of compounds of formula I:

[0079] ESI-MS: m / z = 448.1 [M+H] + .

[0080] 1 H-NMR (400MHz, DMSO-d6): δ12.0(brs,1H),7.82(d,J=9.2Hz,1H),5.21(d,J=3. 6Hz, 1H), 4.95 (dd, J1=11.2Hz, J2=3.2Hz, 1H), 4.47 (d, J=8.8Hz, 1H), 4.02 (s, 3H ),3.87(q,J=11.2Hz,1H),3.75-3.65(m,1H),3.45-3.35(m,1H),2.19(t,J=6.8 Hz,2H),2.10(s,3H),1.99(s,3H),1.88(s,3H),1.76(s,3H),1.55-1.40(m,4H).

[0081] The proton NMR spectrum of compound I is as follows: Figure 4 As shown.

Claims

1. A method for preparing an improved N-acetylgalactosamine intermediate, comprising the following steps: in a solvent, in the presence of NaIO4 and RuCl3, performing an oxidation reaction as shown below to obtain compound I; ； The solvents are water, dichloromethane, and acetonitrile; The molar ratio of NaIO4 to RuCl3 is (224.1-250):1; The molar ratio of the compound of formula II to RuCl3 is (50-75):1; The oxidation reaction is carried out first at 0 °C and then at 25 °C; The oxidation reaction also includes the following post-processing steps: controlling the pH of the reaction solution to 9-10, filtering, washing, extraction, controlling the pH of the aqueous phase to 2-3, extraction, drying, concentration and purification.

2. The preparation method according to claim 1, characterized in that, It meets one or more of the following conditions: (1) The NaIO4 and RuCl3 are applied to the above oxidation reaction by forming a mixed solution; (2) In the oxidation reaction, the molar volume ratio of the compound of formula II to the solvent is (0.75-2.5):1 mol / L; (3) The reaction time of the oxidation reaction is 1.5-12 hours.

3. The preparation method according to claim 2, characterized in that, It meets one or more of the following conditions: (1) The mixed solution is applied to the oxidation reaction by dropwise addition; (2) The solvent in the mixed solution is a mixed solvent formed by alkane solvent, nitrile solvent and water; (3) The molar volume ratio of NaIO4 to the solvent in the mixed solution is (1-1.5):1 mol / L; (4) In the oxidation reaction, the molar ratio of NaIO4 to RuCl3 is 224.1:1; (5) In the oxidation reaction, the molar ratio of the compound of formula II to RuCl3 is 50:1; (6) In the oxidation reaction, the molar volume ratio of the compound of formula II to the solvent is 1.2:1 mol / L; (7) In the oxidation reaction, NaIO4 and RuCl3 are added at 0 °C; (8) The reaction time of the oxidation reaction is 2 hours.

4. The preparation method according to claim 3, characterized in that, It meets one or more of the following conditions: (1) The solvent in the mixed solution is a mixed solvent formed by alkane solvent, nitrile solvent and water, wherein the alkane solvent is dichloromethane; (2) The solvent in the mixed solution is a mixed solvent formed by alkane solvent, nitrile solvent and water, wherein the nitrile solvent is acetonitrile; (3) The solvent in the mixed solution is a mixed solvent formed by alkane solvent, nitrile solvent and water, and the volume ratio of alkane solvent, nitrile solvent and water is 1:(1-4):(3-10); (4) The molar volume ratio of NaIO4 to the solvent in the mixed solution is 1.2:1 mol / L.

5. The preparation method according to claim 4, characterized in that, The solvent in the mixed solution is a mixture of alkane solvent, nitrile solvent and water, wherein the volume ratio of alkane solvent, nitrile solvent and water is 1:2:

6.

6. The preparation method according to claim 1, characterized in that, The method for preparing the improved N-acetylgalactosamine intermediate further includes the following method for preparing compound II: in a solvent, in the presence of a Lewis acid, compound 3 is subjected to a glycosylation reaction with 5-phenyl-1-butanol as shown below to obtain compound II; 。 7. The preparation method according to claim 6, characterized in that, It meets one or more of the following conditions: (1) In the glycosylation reaction, the solvent is a haloalkane solvent; (2) In the glycosylation reaction, the Lewis acid is selected from one or more of scandium trifluoromethanesulfonate, bismuth trifluoromethanesulfonate, and trimethyl trifluoromethanesulfonate; (3) The molar ratio of the Lewis acid to compound 3 is 1:(1-3); (4) In the glycosylation reaction, the molar ratio of 5-phenyl-1-butanol to compound 3 is (0.8-1.5):1; (5) In the glycosylation reaction, the molar volume ratio of compound 3 to the solvent is (0.45-1.5):1 mol / L; (6) The glycosylation reaction further includes the use of a dehydrating agent; (7) The reaction temperature of the glycosylation reaction is from 0 °C to room temperature; (8) The reaction time for the glycosylation reaction is 4-18 hours; (9) The glycosylation reaction also includes the following post-processing steps: washing, drying, concentration, purification and concentration.

8. The preparation method according to claim 7, characterized in that, It meets one or more of the following conditions: (1) In the glycosylation reaction, the solvent is dichloromethane; (2) In the glycosylation reaction, the Lewis acid is trimethylsilyl trifluoromethanesulfonate; (3) When the Lewis acid is trimethyl trifluoromethanesulfonate, the trimethyl trifluoromethanesulfonate is added by dripping. (4) The molar ratio of the Lewis acid to compound 3 is 1:2; (5) In the glycosylation reaction, the molar ratio of 5-phenyl-1-butanol to compound 3 is 1.1:1; (6) In the glycosylation reaction, the molar volume ratio of compound 3 to the solvent is 0.77:1 mol / L; (7) The dehydrating agent is a molecular sieve or anhydrous magnesium sulfate; (8) The reaction temperature of the glycosylation reaction is first at room temperature, then at 0 °C, and finally at room temperature; (9) In the glycosylation reaction, the Lewis acid is added at 0 °C; (10) The reaction time for the glycosylation reaction is 16.5 hours.

9. The preparation method according to claim 8, characterized in that, The dehydrating agent is 4A molecular sieve.

10. The preparation method according to claim 9, characterized in that, The mass ratio of the 4A molecular sieve to the compound 3 is 1:(10-30).

11. The preparation method according to claim 10, characterized in that, The mass ratio of the 4A molecular sieve to the compound 3 is 1:

20.

12. The preparation method according to claim 6, characterized in that, The method for preparing the improved N-acetylgalactosamine intermediate further includes the following method for preparing compound 3: in a solvent, in the presence of a Lewis acid, compound 2 is subjected to the following cyclization reaction to obtain compound 3; 。 13. The preparation method according to claim 12, characterized in that, It meets one or more of the following conditions: (1) In the cyclization reaction, the Lewis acid is selected from one or more of scandium trifluoromethanesulfonate, bismuth trifluoromethanesulfonate, and trimethyl trifluoromethanesulfonate; (2) When the Lewis acid is trimethyltrifluoromethanesulfonate, the Lewis acid is added by dropwise addition; (3) The molar ratio of the Lewis acid to compound 2 is (1-1.5):1; (4) In the cyclization reaction, the molar volume ratio of compound 2 to the solvent is (0.37-1.3):1 mol / L; (5) The reaction temperature for the cyclization reaction is from 0 °C to room temperature; (6) In the cyclization reaction, the Lewis acid is added at 0 °C; (7) The reaction time for the cyclization reaction is 1-12 hours; (8) The cyclization reaction also includes the following post-processing steps: washing, drying and concentration.

14. The preparation method according to claim 13, characterized in that, It meets one or more of the following conditions: (1) In the cyclization reaction, the Lewis acid is trimethyltrifluoromethanesulfonate; (2) The molar ratio of the Lewis acid to compound 2 is 1.2:1; (3) In the cyclization reaction, the molar volume ratio of compound 2 to the solvent is 0.85:1 mol / L; (4) The cyclization reaction is first carried out at 0 °C and then at room temperature; (5) The reaction time for the cyclization reaction is 2 hours.

15. The preparation method according to claim 12, characterized in that, The method for preparing the improved N-acetylgalactosamine intermediate further includes the following method for preparing compound 2: in the presence of a base, compound 1 is subjected to an acetylation reaction with acetic anhydride as shown below to obtain compound 2; 。 16. The preparation method according to claim 15, characterized in that, It meets one or more of the following conditions: (1) The base is selected from one or more of acetate, pyridine, 4-dimethylaminopyridine and triethylamine; (2) The molar ratio of the acetic anhydride to compound 1 is (5-8):1; (3) The reaction temperature of the acetylation reaction is from 0 °C to room temperature; (4) The reaction time for the acetylation reaction is 6-24 hours; (5) The acetylation reaction further includes the following post-processing steps: precipitation, filtration, washing and drying.

17. The preparation method according to claim 16, characterized in that, It meets one or more of the following conditions: (1) The base is pyridine, 4-dimethylaminopyridine and triethylamine; (2) The molar ratio of the acetic anhydride to compound 1 is 6:1; (3) The acetylation reaction is first carried out at room temperature, then at 0 °C, and finally at room temperature; (4) The reaction time for the acetylation reaction is 16 hours.

18. The preparation method according to claim 16, characterized in that, It meets one or more of the following conditions: (1) The pyridine also serves as a solvent for the acetylation reaction; (2) The molar volume ratio of compound 1 to pyridine is (0.46-1.5):1 mol / L; (3) The molar ratio of 4-dimethylaminopyridine to compound 1 is 1:(2-20); (4) The molar ratio of the triethylamine to compound 1 is (0.8-3):1; (5) The triethylamine is applied to the acetylation reaction by dropwise addition.

19. The preparation method according to claim 18, characterized in that, It meets one or more of the following conditions: (1) The molar volume ratio of compound 1 to pyridine is 0.93:1 mol / L; (2) The molar ratio of 4-dimethylaminopyridine to compound 1 is 1:10; (3) The molar ratio of the triethylamine to the compound 1 is 1:

1.

20. A compound as shown in Formula 5: 。

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