Synthetic intermediate of entecavir, preparation method and application

Abstract

The invention discloses a synthetic intermediate of entecavir, a preparation method and application. The intermediate can be used for asymmetrically synthesizing optically pure (+)-entecavir. By utilizing the intermediate, asymmetric synthesis of entecavir can be efficiently and accurately realized, which is of great significance for improving the stereoselectivity of the product and improving the synthesis efficiency. The synthesis method of the entecavir and the intermediate thereof has the advantages of cheap and easily available reagents, simple synthesis steps, high reaction yield and the like, and is simple in reaction process, convenient to operate, green, environment-friendly and suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of drug synthesis, and more particularly to an intermediate for the synthesis of entecavir, a preparation method and an application thereof, and even more particularly to an intermediate for the synthesis of optically pure (+)-entecavir, a synthesis method and a use for the synthesis of optically pure entecavir. Background Art

[0002] Entecavir (ETV) is used for the treatment of chronic hepatitis B in adults. Its chemical name is 2-amino-9-[(1S,3S,4S)-4-hydroxy-3-(hydroxymethyl)-2-methylenepentyl]-1,9-dihydro-6H-purin-6-one monohydrate; its English chemical name is 2-amino-1,9-dihydro-9[(1S,3R,4S)-4-hydroxy-3-(hydroxymethyl)-2-methylenecyclopentyl]-6H-purin-6-one, monohydrate; the molecular formula is C 12 H 15 N5O3·H2O; this molecule has 3 chiral centers and a total of 8 isomers, and only the above-mentioned (1S,3R,4S) configuration is administered clinically. Entecavir forms a pharmacologically active triphosphate compound under the action of phosphokinase in vivo, and its action target is the reverse transcriptase of hepatitis B virus (HBV), thereby inhibiting the activity of HBV reverse transcriptase and ultimately producing anti-hepatitis B pharmacological activity.

[0003] The important physiological activity of entecavir has attracted many groups to devote themselves to the total synthesis research of entecavir. In 1997, the Bisacchi group first completed the synthesis of entecavir in 11 steps. This synthetic route introduced chiral centers through the asymmetric hydroboration-oxidation of cyclopentadiene, and it was difficult to control the optical impurities and the yield was low;

[0004] In 1997, the Li group completed the synthesis of entecavir in 16 steps. This synthesis used asymmetric Sharpless epoxidation and intramolecular nitrone cycloaddition to obtain entecavir. This synthetic step was relatively cumbersome and the yield was low;

[0005] In 2012, the Xie research group reported a method for preparing a five-membered carbon ring intermediate and synthesizing entecavir using propargyl alcohol and allyl bromide as raw materials. This route had a higher yield, was green and environmentally friendly, but used an expensive Grubbs second-generation catalyst to catalyze the diene metathesis to form a five-membered ring, resulting in a higher cost. Summary of the Invention

[0006] In view of this, the present invention has developed a new method to achieve the asymmetric synthesis of the key intermediate of formula 6, and finally achieve the synthesis of optically pure entecavir, providing a more superior technical solution in practical applications.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A synthesis intermediate of entecavir has the structure of the following formula 6:

[0009]

[0010] A preparation method of the above-mentioned synthesis intermediate of entecavir comprises the following steps:

[0011] (f) The compound of formula (S)-2 reacts with formaldehyde in a reaction solvent in the presence of a base to undergo a Morita-Baylis-Hillman reaction to generate an asymmetric compound of formula 5;

[0012] (j) The asymmetric compound of formula 5 reacts with a lithium reagent, a copper reagent and boron trifluoride diethyl ether in a reaction solvent to undergo a Michael addition reaction to generate an asymmetric compound of formula 6, which is the synthesis intermediate of entecavir;

[0013] The synthesis route is as follows:

[0014]

[0015] Preferably, in step (f), the reaction solvent is a mixed solvent of tetrahydrofuran and water with a volume ratio of tetrahydrofuran: water = 2:1, the base is 4-dimethylaminopyridine, the reaction temperature of the MBH reaction is room temperature, and the molar ratio of the compound of formula (S)-2, formaldehyde and the base is 1:1-2:0.01-0.1.

[0016] Preferably, in step (j), the reaction solvent is tetrahydrofuran, the lithium reagent is selected from n-butyllithium or sec-butyllithium, the copper reagent is selected from cuprous chloride, cuprous bromide, cuprous iodide or cuprous cyanide, the reaction temperature of the Michael addition reaction is -78 °C, and the molar ratio of the asymmetric compound of formula 5, the lithium reagent, the ketone reagent and boron trifluoride diethyl ether is 1:2-2.5:2-2.5:1-3.

[0017] Furthermore, the preparation method of the compound of formula (S)-2 comprises the following steps:

[0018] (a) The racemic compound of formula rac-1 undergoes a substitution reaction with tert-butyldimethylchlorosilane in a reaction solvent in the presence of a base to generate a racemic compound of formula rac-2;

[0019] (b) The racemic compound of formula rac-2 undergoes a reduction reaction with diisopropylaluminum hydride in a reaction solvent to form a cis-racemic compound of formula rac-3;

[0020] (c) The cis-racemic compound of formula rac-3 undergoes a stereoselective transesterification reaction with vinyl acetate under the catalysis of lipase in a reaction solvent to form a compound of formula 3 with (S,R) configuration and a compound of formula 4 with (R,S) configuration;

[0021] (d) The compound of formula 4 with (R,S) configuration undergoes a hydrolysis reaction under basic conditions in a reaction solvent to form a compound of formula 3 with (R,S) configuration;

[0022] (e) The compound of formula 3 with (S,R) configuration undergoes an oxidation reaction in the presence of manganese dioxide in a reaction solvent to form a compound of formula 2 with S configuration, i.e., the compound of formula (S)-2; The compound of formula 3 with (R,S) configuration undergoes an oxidation reaction in the presence of manganese dioxide in a reaction solvent to form a compound of formula 2 with R configuration;

[0023] The synthetic route is as follows:

[0024]

[0025] Preferably, in step (a), the reaction solvent is dichloromethane, the base is imidazole and 4-dimethylaminopyridine, the reaction temperature of the substitution reaction is room temperature, and the molar ratio of the racemic compound of formula rac-1, tert-butyldimethylchlorosilane, imidazole and 4-dimethylaminopyridine is 1:1-2:1-2:0.01-0.1;

[0026] In step (b), the reaction solvent is dichloromethane, the reaction temperature of the reduction reaction is -78 °C, and the molar ratio of the racemic compound of formula rac-2 and diisopropylaluminum hydride is 1:1-2;

[0027] In step (c), the reaction solvent is selected from benzene, methyl tert-butyl ether, methyl tert-butyl ether or water, the enzyme is selected from lipase (from Candida sp., porcine pancreas) or protease, the temperature of the transesterification reaction is 0-80 °C, the molar ratio of the cis-racemic compound of formula rac-3 and vinyl acetate is 1:1-2, and the enzyme amount ratio of the cis-racemic compound of formula rac-3 and the enzyme is 1 mmol / 150 mg enzyme / 1 mL solvent - 1 mmol / 300 mg enzyme / 1 mL solvent;

[0028] In step (d), the reaction solvent is methanol, the base is potassium carbonate, the reaction temperature of the hydrolysis reaction is room temperature, and the molar ratio of the compound of formula 4 with (R,S) configuration and potassium carbonate is 1:0.1-1;

[0029] In step (e), the reaction solvent is dichloromethane, the oxidation reaction temperature is room temperature, and the molar ratio of the compound of formula 3 in (S,R) configuration or the compound of formula 3 in (R,S) configuration to manganese dioxide is 1:1 to 10.

[0030] The present invention also provides an application of the synthetic intermediate as described in the above technical solution or the synthetic intermediate prepared by the method in the synthesis of entecavir, including the following steps:

[0031] (k) The compound of formula 6 undergoes a reduction reaction in a reaction solvent in the presence of a reducing agent to form an asymmetric compound of formula 7;

[0032] (l) The asymmetric compound of formula 7 undergoes a Mitsunobu reaction in a reaction solvent in the presence of triphenylphosphine, diethyl azodicarboxylate and purine to form an asymmetric compound of formula 8;

[0033] (m) The asymmetric compound of formula 8 removes TBS, Boc, t-Bu protecting groups in the presence of an acid in a reaction solvent to form optically pure entecavir.

[0034] Preferably, in step (k), the reaction solvent is tetrahydrofuran, methanol or dichloromethane, the reducing agent is sodium borohydride, lithium borohydride, lithium tri-sec-butylborohydride, lithium diisobutylaluminum hydride or lithium diethylborohydride, the reaction temperature of the reduction reaction is -78 °C, and the molar ratio of the compound of formula 6 to the reducing agent is 1:1 to 3.

[0035] Preferably, in step (l), the reaction solvent is tetrahydrofuran or toluene, the purine is 2-amino-6-chloropurine, N-Boc-6-chloro-9H-purin-2-amine or 2-amino-6-benzyloxypurine, the reaction temperature of the Mitsunobu reaction is -20 °C to 10 °C, and the molar ratio of the asymmetric compound of formula 7, purine, triphenylphosphine, diethyl azodicarboxylate is 1:1 to 3:1 to 3:1 to 3.

[0036] Preferably, in step (m), the reaction solvent is tetrahydrofuran or dichloromethane, the acid is hydrochloric acid, the reaction temperature for removing the protecting group is 0 °C to 80 °C, and the molar ratio of the asymmetric compound of formula 8 to the acid is 1:1 to 3.

[0037] According to the above technical solution, compared with the prior art, the present invention discloses and provides a series of new asymmetric entecavir intermediates, and provides an optimized synthesis method for the intermediates. Using these intermediates as raw materials, optically pure entecavir can be prepared in high yield.

[0038] The synthetic method of entecavir and its intermediates of the present invention has the advantages of controllable chirality, high yield, and high product purity. The obtained intermediates and entecavir products all have high optical purity (>99% ee), and the raw materials are widely sourced, the reagents are cheap and easily available, the reactions are simple, the operations are convenient, it is environmentally friendly, and it is suitable for industrial scale-up production. Detailed Embodiments

[0039] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0040] Example 1

[0041] Preparation of compound rac-2:

[0042] S1. Add 150 ml of dichloromethane to a 500-ml round-bottom flask, add 10 g of 4-hydroxy-2-cyclopentenone, add 10.4 g of imidazole and 22.9 g of tert-butyldimethylchlorosilane at 0 °C, and react at room temperature for 6 hours. Monitor the reaction by thin layer chromatography until it ends (developing agent: ethyl acetate∶petroleum ether = 20∶1). After the reaction ends, add 200 ml of saturated brine, extract 3 times with 200 ml of dichloromethane, dry, concentrate, and separate by silica gel column chromatography to obtain 20 g of compound rac-2, with a yield of 95%.

[0043] The synthetic route is:

[0044]

[0045] NMR data: 1 HNMR(400MHz,CDCl3):δ7.43(dd,J=2.4,5.7Hz,1H),6.13(dd,J=1.3,5.7Hz,1H),4.95(tdd,J=1.4,2.4,6.0Hz,1H),2.68(dd,J=6.0,18.2Hz,1H),2.20(dd,J=2.4,18.2Hz,1H),0.88(s,9H),0.11(s,3H),and 0.09(s,3H).

[0046] 13 CNMR(101MHz,CDCl3):δ206.4,163.9,124.4,70.9,44.9,25.8,18.1,

[0047] -4.71,and -4.74.

[0048] Example 2

[0049] Preparation of compound rac-3:

[0050] S2. Add 200 mL of dichloromethane and 13 g of compound rac-2 to a 500 mL round-bottom flask. Add 73 mL of diisobutylaluminum hydride (1.0 M in hexane) at -78 °C and continue the reaction for 2 hours at -78 °C. Add 100 mL of saturated aqueous sodium potassium tartrate solution, stir at room temperature for 30 minutes, extract 3 times with 100 mL of dichloromethane, dry, concentrate, and separate by silica gel column chromatography to obtain 11.9 g of compound rac-3 with a yield of 90%.

[0051] The synthetic route is:

[0052]

[0053] NMR data: 1 HNMR(400 MHz, CDCl3): 5.95 (dt, J = 5.7, 1.4 Hz, 1H), 5.89 (dt, J = 5.7, 1.5 Hz, 1H), 4.66 - 4.63 (m, 1H), 4.59 - 4.56 (m, 1H), 2.68 (dt, J = 14.0, 7.1 Hz, 1H), 1.50 (dt, J = 13.8, 4.5 Hz, 1H), 0.89 (s, 9H), and 0.08 (s, 6H).

[0054] 13 CNMR(101 MHz, CDCl3): 137.0, 135.8, 75.3, 75.2, 44.7, 26.0, 18.3, -4.53, and -4.55.

[0055] Example 3

[0056] Preparation of compounds (S,R)-3 and (R,S)-4:

[0057] S3. Add 200 mL of methyl tert-butyl ether, 13.5 g of compound rac-3, 12 mL of vinyl acetate, and 18.9 g of lipase (20 u / mg, 300 mg / mmol) to a 500 mL round-bottom flask. React at 35 °C in a shaker at 150 rpm for 36 hours, filter, concentrate, and separate by silica gel column chromatography to obtain 5.8 g of compound (S,R)-3 with a yield of 43% and 7.3 g of compound (R,S)-4 with a yield of 45%.

[0058] The synthetic route is:

[0059]

[0060] NMR data:

[0061] (S,R)-3:[α] D 25 =-25.0°(c = 1.0, CHCl3).

[0062] (R,S)-4:[α] D 25 =+1.0°(c = 1.0, CHCl3).

[0063] (R,S)-4: 1 1H NMR (400 MHz, CDCl3): 5.97 (dt, J = 5.7, 1.4 Hz, 1H), 5.87 (dt, J = 5.7, 1.5 Hz, 1H), 5.45 (m, 1H), 4.71 (m, 1H), 2.80 (dt, J = 13.8, 7.3 Hz, 1H), 2.04 (s, 3H), 1.60 (dt, J = 13.8, 5.0 Hz, 1H), 0.89 (s, 9H), and 0.08 (s, 6H).

[0064] (R,S)-4: 13 13C NMR (101 MHz, CDCl3): 171.0, 139.0, 131.3, 77.1, 75.0, 41.3, 26.0, 21.3, 18.3, -4.5, and -4.6.

[0065] Example 4

[0066] Preparation of compound (R,S)-3:

[0067] S4. Add 100 mL of methanol to a 500 mL round-bottom flask, add 15 g of compound (R,S)-4 and 12 g of potassium carbonate, react at room temperature for 1 hour, add 200 mL of saturated brine, extract 3 times with 150 mL of dichloromethane, dry, concentrate, and separate by silica gel column chromatography to obtain 12.5 g of compound (R,S)-3, with a yield of 100%.

[0068] The synthetic route is:

[0069]

[0070] [α] D 25 =+25.2°(c = 1.0, CHCl3).

[0071] Example 5

[0072] Preparation of compound (S)-2:

[0073] S5. Add 200 mL of dichloromethane to a 500 mL round-bottom flask, add 12.2 g of compound (S,R)-3 and 49.4 g of manganese dioxide, react at room temperature for 24 hours, filter, concentrate, and separate by silica gel column chromatography to obtain 11.5 g of compound (S)-2 with a yield of 95%.

[0074] The synthetic route is as follows:

[0075]

[0076] (S)-2: [α] D 25 = -50.0° (c = 1.0, CHCl3).

[0077] (R)-2: [α] D 25 = +55.3° (c = 0.5, CHCl3).

[0078] Example 6

[0079] Preparation of compound 5:

[0080] S6. Add 100 mL of tetrahydrofuran and 50 mL of water as a mixed solvent to a 500 mL round-bottom flask, add 20 g of (S)-2, 14.2 g of commercially available 30% aqueous formaldehyde solution, and 12.8 g of imidazole, keep the reaction at 25 °C, monitor the reaction by thin layer chromatography until it ends (developing solvent: ethyl acetate∶petroleum ether = 5∶1), after the reaction ends, add 200 mL of saturated brine, extract 3 times with 300 mL of dichloromethane, dry, concentrate, and purify by silica gel column chromatography to obtain 17 g of compound 5 with a yield of 75%.

[0081] The synthetic route is as follows:

[0082]

[0083] [α] D 25 = -40.0° (c = 1.0, CHCl3).

[0084] 1 1H NMR (400 MHz, CDCl3): 7.27 - 7.25 (m, 1H), 4.93 (m, 1H), 4.40 (m, 2H), 2.81 (dd, J = 5.9, 18.4 Hz, 1H), 2.35 (brs, 1H), 2.34 (dd, J = 2.2, 18.4 Hz, 1H), 0.90 (s, 9H), 0.12 (s, 3H), and 0.11 (s, 3H).

[0085] 13CNMR (101 MHz, CDCl3): 206.2, 157.7, 145.7, 69.2, 57.4, 46.0, 25.9, 18.2, -4.64, and -4.65.

[0086] Example 7

[0087] Preparation of Compound 6:

[0088] S7. Add 150 mL of methyl tert-butyl ether to a 1 L round-bottom flask, add 10 g of Compound 5, add 13.8 g of potassium tert-butoxide at -78 °C, 125 mL of sec-butyllithium solution (1.3 M THF solution), 500 mL of lithium 2-thienylcyanocuprate (0.25 M THF solution), and 22.5 mL of boron trifluoride diethyl etherate BF3·Et2O. Keep the reaction at -78 °C for 3 h. After the reaction is completed, add 100 mL of saturated brine, extract 3 times with 300 mL of dichloromethane, dry, concentrate, and purify by silica gel column chromatography to obtain 7.6 g of Compound 6 with a yield of 60%.

[0089] The synthetic route is:

[0090]

[0091] [α] D 25 = +24.5° (c = 1.0, CHCl3).

[0092] 1 HNMR (400 MHz, CDCl3): 6.10 (dd, J = 1.0, 2.6 Hz, 1H), 5.43 (dd, J = 1.0, 2.3 Hz, 1H), 4.32 (dt, J = 4.2, 6.2 Hz, 1H), 3.45 (dq, J = 5.7, 10.0 Hz, 2H), 2.85 (m, 1H), 2.65 (dd, J = 6.3, 18.0 Hz, 1H), 2.31 (ddd, J = 1.0, 4.5, 18.1 Hz, 1H), 1.16 (s, 9H), 0.87 (s, 9H), 0.08 (s, 3H), and 0.06 (s, 3H).

[0093] 13 CNMR (101 MHz, CDCl3): 205.1, 145.6, 119.1, 73.0, 69.7, 62.4, 52.1, 47.5, 27.5, 25.9, 18.2, -4.5, and -4.7.

[0094] Example 8

[0095] Preparation of Compound 7:

[0096] S8. Add 200 mL of tetrahydrofuran to a 500 mL round-bottom flask, add 15 g of Compound 6, and add 72 mL of lithium tri-sec-butylborohydride (1.0 mol / L THF solution) at -78 °C. The reaction is maintained at -78 °C for 2 hours. After the reaction is completed, add 200 mL of saturated sodium bicarbonate solution, extract 3 times with 300 mL of dichloromethane, dry, concentrate, and purify by silica gel column chromatography to obtain 12.8 g of Compound 7, with a yield of 85%.

[0097] The synthetic route is as follows:

[0098]

[0099] [α] D 25 = -32.0° (c == 1.0, CHCl3).

[0100] 1 1H NMR (400 MHz, CDCl3): 5.38 (m, 1H), 5.14 (m, 1H), 4.36 (m, 1H), 4.35 - 4.32 (m, 1H), 3.30 (dd, J = 5.2, 9.2 Hz, 1H), 3.10 (d, J = 10.6 Hz, 1H), 2.85 (t, J = 9.4 Hz, 1H), 2.76 (m, 1H), 1.94 (dd, J = 5.0, 13.5 Hz, 1H), 1.83 (dt, J = 2.1, 13.6 Hz, 1H), 1.15 (s, 9H), 0.88 (s, 9H), 0.093 (s, 3H), and 0.091 (s, 3H).

[0101] 13 13C NMR (101 MHz, CDCl3): 154.8, 111.8, 76.4, 76.1, 72.8, 63.6, 53.3, 42.0, 27.6, 26.0, 18.1, -4.7, and -4.8.

[0102] Example 9

[0103] Preparation of Compound 8:

[0104] S9. Add 50 mL of tetrahydrofuran to a 250-mL round-bottom flask, then add 5 g of compound 7, 5.8 g of 2-amino-6-chloropurine, and 6.3 g of triphenylphosphine. Add 4.2 g of dimethyl azodicarboxylate at 0 °C, and keep the reaction at 0 °C. Monitor the reaction by thin-layer chromatography until it is completed (developing solvent: ethyl acetate∶petroleum ether = 3∶1). After the reaction is completed, add 100 mL of saturated brine, extract three times with 100 mL of dichloromethane, dry, concentrate, and purify by silica gel column chromatography to obtain 8.0 g of compound 8. The yield is 75%.

[0105] The synthetic route is as follows:

[0106]

[0107] [α] D 25 = +30.0° (c = 1.0, CHCl3).

[0108] 1 1H NMR (400 MHz, CDCl3): δ 8.44 (s, 1H), 5.65 (m, 1H), 5.26 (t, J = 2.3 Hz, 1H), 5.15 (t, J = 2.3 Hz, 1H), 4.38 (m, 1H), 3.61 (m, 2H), 2.67 (m, 1H), 2.29 (s, 1H), 2.18 (m, 1H), 1.41 (s, 18H), 1.22 (s, 9H), 0.87 (s, 9H), 0.05 (s, 3H), and 0.03 (s, 3H).

[0109] 13 13C NMR (101 MHz, CDCl3): δ 152.8, 151.7, 150.9, 150.6, 149.3, 146.2, 130.1, 112.4, 83.6, 73.2, 73.1, 62.3, 57.0, 53.0, 41.5, 28.0, 27.6, 25.9, 18.1, -4.6, and -4.7.

[0110] Example 10

[0111] Preparation of entecavir:

[0112] S10. Add 20 mL of tetrahydrofuran to a 100-mL round-bottom flask, then add 2 g of compound 8. Slowly add 5 mL of 3 M hydrochloric acid dropwise at 0 °C, and react at 60 °C for 6 hours. After the reaction is completed, add 50 mL of ethyl acetate and wash three times. Adjust the pH of the aqueous phase to 7 - 7.5 with NaOH solution (6 mol / L), rotary evaporate the solvent, and purify by silica gel column chromatography to obtain 660 mg of entecavir. The yield is 80%.

[0113] The synthetic route is as follows:

[0114]

[0115] [α] D 25 = +28.4° (c = 1.0, CHCl3).

[0116] 1 1H NMR (DMSO-d6, 400 MHz): 10.84 (s, 1H), 7.65 (s, 1H), 6.40 (s, 2H), 5.36 (dd, J = 10.3, 8.0 Hz, 1H), 5.10 (s, 1H), 4.85 (d, J = 3.1 Hz, 1H), 4.81 (t, J = 5.3 Hz, 1H), 4.56 (s, 1H), 4.23 (s, 1H), 3.54 (t, J = 6.1 Hz, 2H), 2.55 - 2.50 (m, 1H), 2.26 - 2.17 (m, 1H), and 2.04 (dd, J = 12.5, 7.8 Hz, 1H).

[0117] 13 13C NMR (101 MHz, DMSO-d6): 156.9, 153.8, 151.5, 151.4, 136.0, 116.2, 109.3, 70.4, 63.0, 55.2, 54.1, and 39.2.

[0118] Through the lipase resolution strategy, the present invention uses racemic 4-hydroxycyclopentene-2-one as the starting material and obtains optically pure 4-hydroxycyclopentene-2-one through 4-step transformation. Subsequently, the highly efficient asymmetric synthesis of entecavir is achieved through 5-step reactions. This synthetic route is the simplest and most efficient asymmetric synthesis strategy of entecavir reported so far. The process steps are simple, the raw materials used in each process are cheap and easily available, the product is easy to purify, the total yield is high, the optical purity of the obtained entecavir is as high as 99.5%, and it has good prospects for industrial application.

[0119] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A synthetic intermediate of entecavir, characterized in that, It has the structure of formula 6 as follows:

2. A method for preparing the synthetic intermediate of entecavir according to claim 1, characterized in that, It includes the following steps: (f) The compound of formula (S)-2 undergoes a Morita-Baylis-Hillman reaction with formaldehyde in a reaction solvent in the presence of a base to form an asymmetric compound of formula 5; (j) The asymmetric compound of formula 5 undergoes a Michael addition reaction with a lithium reagent, a copper reagent, and boron trifluoride diethyl ether in a reaction solvent to form an asymmetric compound of formula 6, which is an intermediate for the synthesis of entecavir; The synthetic route is as follows:

3. The preparation method of a synthetic intermediate of entecavir according to claim 2, characterized in that, In step (f), the reaction solvent is a mixed solvent of tetrahydrofuran and water with a volume ratio of tetrahydrofuran:water = 2:1, the base is 4-dimethylaminopyridine, the reaction temperature of the MBH reaction is room temperature, and the molar ratio of the compound of formula (S)-2, formaldehyde, and the base is 1:1-2:0.01-0.

1.

4. The preparation method of a synthetic intermediate of entecavir according to claim 2, characterized in that, In step (j), the reaction solvent is tetrahydrofuran, the lithium reagent is selected from n-butyllithium or sec-butyllithium, the copper reagent is selected from cuprous chloride, cuprous bromide, cuprous iodide, or cuprous cyanide, the reaction temperature of the Michael addition reaction is -78 °C, and the molar ratio of the asymmetric compound of formula 5, the lithium reagent, the ketone reagent, and boron trifluoride diethyl ether is 1:2-2.5:2-2.5:1-3.

5. The preparation method of a synthetic intermediate of entecavir according to claim 2, characterized in that, The preparation method of the compound of formula (S)-2 includes the following steps: (a) The racemic compound of formula rac-1 undergoes a substitution reaction with tert-butyldimethylchlorosilane in a reaction solvent in the presence of a base to form a racemic compound of formula rac-2; (b) The racemic compound of formula rac-2 undergoes a reduction reaction with diisopropylaluminum hydride in a reaction solvent to form a cis-racemic compound of formula rac-3; (c) The cis-racemic compound of formula rac-3 undergoes a stereoselective transesterification reaction with vinyl acetate under the catalysis of lipase in a reaction solvent to form a compound of formula 3 with (S,R) configuration and a compound of formula 4 with (R,S) configuration; (d) The compound of formula 4 with (R,S) configuration undergoes a hydrolysis reaction under basic conditions in a reaction solvent to form a compound of formula 3 with (R,S) configuration; (e) The compound of formula 3 with (S,R) configuration undergoes an oxidation reaction in a reaction solvent in the presence of manganese dioxide to form a compound of formula 2 with S configuration, that is, the compound of formula (S)-2; the compound of formula 3 with (R,S) configuration undergoes an oxidation reaction in a reaction solvent in the presence of manganese dioxide to form a compound of formula 2 with R configuration; The synthetic route is as follows:

6. The preparation method of a synthetic intermediate of entecavir according to claim 5, wherein, In step (a), the reaction solvent is dichloromethane, the base is imidazole and 4-dimethylaminopyridine, the reaction temperature of the substitution reaction is room temperature, and the molar ratio of the racemic compound of formula rac-1, tert-butyldimethylchlorosilane, imidazole, and 4-dimethylaminopyridine is 1:1-2:1-2:0.01-0.1; In step (b), the reaction solvent is dichloromethane, the reaction temperature of the reduction reaction is -78 °C, and the molar ratio of the racemic compound of formula rac-2 and diisopropylaluminum hydride is 1:1-2; In step (c), the reaction solvent is selected from benzene, methyl tert-butyl ether, methyl tert-butyl ether or water, the enzyme is selected from lipase or protease, the temperature of the transesterification reaction is 0-80°C, the molar ratio of the cis-racemic compound of formula rac-3 to vinyl acetate is 1:1-2, and the enzyme amount ratio of the cis-racemic compound of formula rac-3 to the enzyme is 1 mmol / 150 mg enzyme / 1 mL solvent to 1 mmol / 300 mg enzyme / 1 mL solvent; In step (d), the reaction solvent is methanol, the base is potassium carbonate, the temperature of the hydrolysis reaction is room temperature, and the molar ratio of the compound of formula 4 in (R,S) configuration to potassium carbonate is 1:0.1-1; In step (e), the reaction solvent is dichloromethane, the temperature of the oxidation reaction is room temperature, and the molar ratio of the compound of formula 3 in (S,R) configuration or the compound of formula 3 in (R,S) configuration to manganese dioxide is 1:1-10.

7. Use of the synthetic intermediate according to claim 1 or the synthetic intermediate prepared by the method according to any one of claims 2 to 6 in the synthesis of entecavir, characterized in that, Comprising the following steps: (k) The compound of formula 6 undergoes a reduction reaction in a reaction solvent in the presence of a reducing agent to form an asymmetric compound of formula 7; (l) The asymmetric compound of formula 7 undergoes a Mitsunobu reaction in a reaction solvent in the presence of triphenylphosphine, diethyl azodicarboxylate and purine to form an asymmetric compound of formula 8; (m) The asymmetric compound of formula 8 removes the TBS, Boc, t-Bu protecting groups in the presence of an acid in a reaction solvent to form optically pure entecavir.

8. The application according to claim 7, characterized in that In step (k), the reaction solvent is tetrahydrofuran, methanol or dichloromethane, the reducing agent is sodium borohydride, lithium borohydride, lithium tri-sec-butylborohydride, lithium diisobutylaluminum hydride or lithium diethylborohydride, the reaction temperature of the reduction reaction is -78°C, and the molar ratio of the compound of formula 6 to the reducing agent is 1:1-3.

9. The application according to claim 7, wherein In step (l), the reaction solvent is tetrahydrofuran or toluene, the purine is 2-amino-6-chloropurine, N-Boc-6-chloro-9H-purin-2-amine or 2-amino-6-benzyloxypurine, the reaction temperature of the Mitsunobu reaction is -20°C to 10°C, and the molar ratio of the asymmetric compound of formula 7, purine, triphenylphosphine, diethyl azodicarboxylate is 1:1-3:1-3:1-3.

10. The application according to claim 7, wherein, In step (m), the reaction solvent is tetrahydrofuran or dichloromethane, the acid is hydrochloric acid, the reaction temperature of the deprotection reaction is 0°C to 80°C, and the molar ratio of the asymmetric compound of formula 8 to the acid is 1:1-3.

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