A synthetic intermediate of entecavir, a preparation method of entecavir

Abstract

The application provides a synthetic intermediate of entecavir and a preparation method of entecavir. The preparation method of the synthetic intermediate of entecavir comprises the following steps: S1. 4-[(tert-butyldimethylsilyloxymethylsilyl)oxy]-2-cyclopentenone is used as raw material, and a compound III is obtained by reaction under the condition of imidazole and formaldehyde. S2. Michael addition reaction is carried out between the compound III and a lithium reagent in-situ generated from potassium tert-butoxide, sec-butyllithium and methyl tert-butyl ether to obtain a compound IV, i.e. the synthetic intermediate of entecavir. The synthetic intermediate of entecavir is prepared through two steps, and the entecavir is prepared through five steps. The process steps are simple, the raw materials used in each step are cheap and easy to obtain, the process is simple, the product is easy to purify, the total yield is high, and the industrial production is easy to realize.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical synthesis technology, specifically to a method for preparing a synthetic intermediate of entecavir and a method for preparing entecavir. Background Technology

[0002] Hepatitis B (HBV) is one of the most threatening infectious diseases in the world. The hepatitis B virus (HBV) is a major cause of chronic hepatitis, cirrhosis, and hepatocellular carcinoma (primary liver cancer). Currently, there are two main types of antiviral drugs used clinically in my country: alpha-interferon and nucleoside or nucleotide analogues.

[0003] Entecavir, chemically named 2-amino-1,9-dihydro-9-[(1S,3R,4S)-4-hydroxy-3-(hydroxymethyl)-2-methylenecyclopentyl]-6H-purine-6-one, is a guanine nucleoside analog developed by Bristol-Myers Squibb in 1997. It was approved by the U.S. Food and Drug Administration (FDA) in March 2005 for the treatment of hepatitis B. Entecavir phosphorylates in the body to become an active nucleoside analog, competitively incorporating into the HBV DNA chain, terminating the elongation and synthesis of the HBV DNA chain, and inhibiting the activity of viral DNA polymerase and reverse transcriptase, thereby inhibiting viral replication. Compared to other anti-HBV drugs, entecavir has a strong antiviral effect, few side effects, and a low incidence of clinical drug resistance, making it one of the best drugs currently available for the treatment of chronic hepatitis B.

[0004]

[0005] As shown in the formula above, entecavir contains a chiral five-membered carbon ring and a guanine core. The chiral five-membered carbon ring has three chiral centers and an exocyclic methylene group, making its structure relatively complex. Many synthetic methods have been reported.

[0006] US Patent No. 5206244, published in 1993, describes the preparation of entecavir and its use as an HBV inhibitor. The disclosed method uses cyclopentadiene as a starting material and synthesizes entecavir through multiple steps. This route is difficult to control due to the gradual introduction of chiral centers, resulting in low yields. The synthetic route is shown below:

[0007]

[0008] Patent WO2004 / 052310 (Bristol-Myers squibb) discloses a route using (+)-Coreyl-actone diol as a starting material. The advantage of using (+)-Coreylactone diol as a starting material is that it already contains all the chiral centers required for the product. The starting material itself has excellent optical purity and extremely low optical isomerism. Subsequent synthesis of entecavir only requires transformation of some functional groups. The final product exhibits excellent chiral purity. The synthetic route is shown below:

[0009]

[0010] However, this route has a problem: the coupling reaction of 2-amino-6-chloropurine with the five-membered ring core has a very low yield and the purity of the coupling product is poor, which affects the economics of the entire route.

[0011] Patent WO2010 / 074534 discloses another route for preparing entecavir, but the reaction conditions are harsh and the reagents used are expensive, making it difficult to apply to industrial production. The synthetic route is shown below:

[0012]

[0013] Chinese patent CN 103304375 discloses a route for preparing a five-membered carbon ring intermediate using propargyl alcohol and allyl bromide as raw materials, and further synthesizing entecavir. This route has a high yield and low environmental pollution. However, it uses an expensive Grubbs second-generation catalyst to catalyze the diolefin metathesis to generate a five-membered ring, resulting in high cost. The synthetic route is shown below:

[0014] Summary of the Invention

[0015] Therefore, it is necessary to address the problems of existing entecavir synthesis methods, such as harsh reaction conditions, safety hazards, high equipment requirements, cumbersome processes, low yields, and high costs, which are not conducive to industrial production, and to provide a synthetic intermediate for entecavir and a method for preparing entecavir.

[0016] To achieve the above objectives, the present invention adopts the following technical solution:

[0017] A method for preparing a synthetic intermediate of entecavir includes the following steps:

[0018] S1. Using 4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone as a starting material, the reaction was carried out under imidazole and formaldehyde conditions to obtain compound III;

[0019] S2. Compound III is subjected to a Michael addition reaction with potassium tert-butoxide, sec-butyllithium, and lithium reagent generated in situ from methyl tert-butyl ether to obtain compound IV, which is the synthetic intermediate of entecavir.

[0020] The reaction pathway is shown below:

[0021]

[0022] Furthermore, in step S2, the Michael addition reaction is carried out at a temperature of -78°C; the reaction reagents also include boron trifluoride diethyl ether and copper reagent; wherein the molar ratio of compound III, lithium reagent, copper reagent and boron trifluoride diethyl ether is 1:2~5:2~5:1~3, preferably 1:4:2:2; the reaction temperature is -78°C; the copper reagent includes any one of cuprous chloride, cuprous bromide, cuprous iodide, cuprous cyanide and lithium 2-thiophenecocyanoacetate, preferably cuprous bromide.

[0023] Furthermore, in step S1, a solvent obtained by mixing tetrahydrofuran and water is used as the base solvent, and 4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone, imidazole, and formaldehyde are reacted in the base solvent; wherein, the molar ratio of 4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone, formaldehyde, and imidazole is 1:1 to 5:1 to 3, preferably 1:1.5:2; the reaction temperature is 0℃ to 30℃, preferably 25℃.

[0024] This invention also relates to a method for preparing entecavir, comprising the following steps:

[0025] S100. The synthetic intermediate of entecavir is reduced by a reducing agent to obtain compound V;

[0026] S200. Compound V is reacted with a purine compound via a Mitsunobu reaction to obtain compound VI;

[0027] S300. Compound VI is deprotected under acidic conditions and hydrolyzed to obtain entecavir;

[0028] The synthetic intermediates of entecavir are prepared using the method described above for preparing synthetic intermediates of entecavir.

[0029] The reaction route for the preparation of entecavir is as follows:

[0030]

[0031] Further, in step S100, methanol, dichloromethane, or tetrahydrofuran is used as the base solvent, and the entecavir synthesis intermediate and reducing agent react in the base solvent; wherein, the molar ratio of the entecavir synthesis intermediate to the reducing agent is 1:1 to 3, preferably 1:1 to 1.5; the reaction temperature is -78℃ to 30℃, preferably -78℃; the reducing agent includes any one of sodium borohydride, lithium borohydride, trisec-butyllithium borohydride, lithium diisobutylaluminum hydride, and diethyllithium borohydride, preferably trisec-butyllithium borohydride.

[0032] Further, in step S200, tetrahydrofuran or toluene is used as the base solvent, and compound V and the purine compound react in the base solvent; the purine compound includes any one of 2-amino-6-chloropurine, N-BOC-6-chloro-9H-purine-2-amine, and 2-amino-6-benzyloxypurine, preferably N-BOC-6-chloro-9H-purine-2-amine; the reaction reagents also include an azo reagent and triphenylphosphine; wherein, the molar ratio of compound V, purine compound, triphenylphosphine and azo reagent is 1:1 to 3:1 to 3:1 to 3, preferably 1:1:1.5:1.5; the azo reagent includes diethyl azodicarbonate or diisopropyl azodicarbonate, preferably diethyl azodicarbonate.

[0033] Furthermore, in step S300, tetrahydrofuran or dichloromethane is used as the base solvent, preferably tetrahydrofuran; the reaction temperature is 25°C to 70°C, preferably 60°C; compound VI and the acid react in the base solvent; the acid used is hydrochloric acid, sulfuric acid, phosphoric acid or trifluoroacetic acid, preferably hydrochloric acid; wherein, the molar ratio of compound VI to the acid is 1:1 to 3, preferably 1:5.

[0034] Compared with the prior art, the beneficial effects of the present invention include:

[0035] This invention obtains the synthetic intermediate of entecavir through two steps, and the entire process of obtaining entecavir involves five steps. The process is simple, and the raw materials used in each step are inexpensive and readily available. The process is simple, the product is easy to purify, the overall yield is high, and it is easy to realize industrial production. Attached Figure Description

[0036] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Wherein:

[0037] Figure 1 This invention introduces a synthetic intermediate for entecavir. 1 H-NMR spectrum. Detailed Implementation

[0038] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0039] Please see Figure 1 This embodiment describes a method for preparing a synthetic intermediate of entecavir, the specific steps of which are as follows:

[0040] S1. Compound II was reacted with formaldehyde under imidazole conditions to prepare compound III; wherein, compound II was 4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone, and compound III was 4-tert-butyldimethoxy-2-hydroxymethyl-2-cyclopenten-1-one.

[0041] In the above steps, the reaction uses a mixture of tetrahydrofuran (THF) and water as the base solvent, with a volume ratio of 1 to 4:1, preferably 2:1, and the reaction temperature is 0°C to 30°C, preferably 25°C. The molar ratio of compound II, formaldehyde, and imidazole is 1:1 to 5:1 to 3, preferably 1:1.5:2.

[0042] S2. Compound III undergoes a Michael addition reaction with potassium tert-butoxide, tert-butyllithium, and lithium reagent generated in situ from methyl tert-butyl ether to give compound IV; compound IV is the synthetic intermediate of entecavir, and its Chinese name is 3-tert-butyloxymethyl-4-tert-butyldimethoxy-2-methylene-cyclopenten-1-one.

[0043] In the above steps, a mixture of tetrahydrofuran and methyl tert-butyl ether is used as the base solvent in a volume ratio of 1:1 to 3, preferably 1:1, and the reaction temperature is -78°C. Other reagents reacting with compound III include copper reagent and boron trifluoride diethyl ether (BF3Et2O). The molar ratio of compound III, lithium reagent, copper reagent, and BF3Et2O is 1:2 to 5:2 to 5:1 to 3, preferably 1:4:2:2.

[0044] tert-butyllithium can be replaced with sec-butyllithium. Copper reagents include, but are not limited to, the following: cuprous chloride, cuprous bromide, cuprous iodide, cuprous cyanide, and lithium 2-thienylcopper cyanate, with cuprous bromide being preferred.

[0045] The synthetic intermediate for entecavir prepared above is compound IV. The specific steps for preparing entecavir using compound IV as a starting material are as follows:

[0046] S100. Compound IV was reduced to compound V via a lithium trisec-butylborohydride reaction.

[0047] In the above steps, lithium trisec-butylborohydride, used as a reducing agent, can be replaced by any one of sodium borohydride, lithium borohydride, lithium diisobutylaluminum hydride, and lithium diethylborohydride. The solvent used in the reaction is methanol, tetrahydrofuran, or dichloromethane, preferably tetrahydrofuran. The reaction temperature is -78°C to 30°C, preferably -78°C. The molar ratio of compound IV to the reducing agent is 1:1 to 3, preferably 1:1 to 1.5.

[0048] S200. Compound V was reacted with a purine compound via a Mitsunobu reaction to prepare compound VI.

[0049] In the above steps, tetrahydrofuran or toluene is used as the base solvent, preferably tetrahydrofuran, and the reaction temperature is controlled at -15℃ to 0℃, preferably 0℃. The purine compound is 2-amino-6-chloropurine, N-BOC-6-chloro-9H-purine-2-amine, or 2-amino-6-benzyloxypurine, preferably N-BOC-6-chloro-9H-purine-2-amine. The reaction reagents also include an azo reagent and triphenylphosphine; wherein the molar ratio of compound V, purine compound, triphenylphosphine, and azo reagent is 1:1 to 3:1 to 3:1 to 3, preferably 1:1:1.5:1.5. The azo reagent is diethyl azodicarbonate or diisopropyl azodicarbonate, preferably diethyl azodicarbonate.

[0050] Compound VI of S300 undergoes deprotection under hydrochloric acid conditions and hydrolysis to yield entecavir.

[0051] In the above steps, tetrahydrofuran or dichloromethane is used as the base solvent, preferably tetrahydrofuran, and the reaction temperature is 25℃~70℃, preferably 60℃. The acid used is hydrochloric acid, sulfuric acid, phosphoric acid, or trifluoroacetic acid, preferably hydrochloric acid. The molar ratio of compound VI to the acid is 1:1~10, preferably 1:5.

[0052] The reaction route for the preparation of entecavir is as follows:

[0053]

[0054] In this context, HCHO represents formaldehyde, imidazole represents imidazole, t-BuOK represents potassium tert-butoxide, s-BuLi represents lithium tert-butyl, MTBE represents methyl tert-butyl ether, CuBr represents cuprous bromide, L-selectride represents lithium trisec-butylborohydride, purine represents purine, PPH3 represents triphenylphosphine, DEAD represents diethyl azodicarbonate, and HCl represents hydrochloric acid.

[0055] The specific preparation examples of each compound are described below.

[0056] Example 1

[0057] Preparation of compound III:

[0058]

[0059] In a 500 mL round-bottom flask, 100 mL of tetrahydrofuran and 50 mL of water were added as a mixed solvent. 20 g of 4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone, 14.2 g of commercially available 30% formaldehyde aqueous solution, and 12.8 g of imidazole were added. The reaction was maintained at 25 °C. Thin-layer chromatography was performed to monitor the reaction until completion (eluent: ethyl acetate: petroleum ether = 5:1). After the reaction was complete, 200 mL of saturated brine was added, and the mixture was extracted three times with 300 mL of dichloromethane. The extract was dried, concentrated, and purified by silica gel column chromatography to obtain 17 g of compound III, with a yield of 75%.

[0060] The NMR data for compound III are as follows: 1 HNMR (CDCl3, 400MHz): 7.27-7.25 (m, 1H), 4.93 (dtt, 1H), 4.40 (dtt, 2H), 2.81 (dd, J = 5.9, 18.4Hz, 1H), 2.35 (br s, 1H), 2.34 (dd, J = 2.2, 18.4Hz, 1H), 0.90 (s, 9H), 0.12 (s, 3H), and 0.11 (s, 3H).

[0061] Example 2

[0062] Preparation of compound IV:

[0063]

[0064] In a 500 mL round-bottom flask, 160 mL of methyl tert-butyl ether was added, followed by 10 g of compound III. At -78 °C, 18.5 g of potassium tert-butoxide, 165 mL of sec-butyllithium solution (1.0 mol / L THF solution), 11.8 g of cuprous bromide, and 21 mL of boron trifluoride diethyl ether (BF3·Et2O) were added. The reaction was continued at -78 °C for 3 hours. After the reaction was complete, 100 mL of saturated brine was added, and the mixture was extracted three times with 300 mL of dichloromethane. The extract was dried, concentrated, and purified by silica gel column chromatography to obtain 7.8 g of compound IV, with a yield of 61%.

[0065] like Figure 1 As shown, the NMR data for compound IV are as follows: 1HNMR (CDCl3, 400MHz): 6.10 (dd, J=1.0, 2.6Hz, 1H), 5.43 (dd, J=1.0, 2.3Hz, 1H), 4.32 (dt, J=4.2, 6.2Hz, 1H), 3.45 (dq, J=5.7, 10.0 Hz,2H),2.85(m,1H),2.65(dd,J=6.3,18.0Hz,1H),2.31(ddd,J=1.0,4.5,18.1Hz,1H),1.16(s,9H),0.87(s,9H),0.08(s,3H),and 0.06(s,3H).

[0066] Example 3

[0067] Preparation of compound V:

[0068]

[0069] In a 500 mL round-bottom flask, 200 mL of tetrahydrofuran was added, followed by 15 g of compound IV. Then, 72 mL of tri-sec-butylborohydride (1.0 mol / L THF solution) was added at -78 °C. The reaction was maintained at -78 °C for 2 hours. After the reaction was complete, 200 mL of saturated sodium bicarbonate solution was added, and the mixture was extracted three times with 300 mL of dichloromethane. The extract was dried, concentrated, and purified by silica gel column chromatography to obtain 12.8 g of compound V, with a yield of 85%.

[0070] The NMR data for compound V are as follows: 1 HNMR (CDCl3, 400MHz): 5.38 (m, 1H), 5.14 (nofd, 1H), 4.36 (m, 1H), 4.35-4.32 (m, 1H), 3.30 (dd, J = 5.2, 9.2Hz, 1H), 3.10 (d, J = 10.6Hz, 1H), 2 .85(t,J=9.4Hz,1H),2.76(m,1H),1.94(dd,J=5.0,13.5Hz,1H),1.83(dt,J=2.1,13.6Hz,1H),1.15(s,9H),0.88(s,9H),0.093(s,3H),and 0.091(s,3H).

[0071] Example 4

[0072] Preparation of compound VI:

[0073]

[0074] In a 250 mL round-bottom flask, 50 mL of tetrahydrofuran, 5 g of compound V, 5.8 g of a purine compound, and 6.3 g of triphenylphosphine were added. 4.2 g of dimethyl azodicarbonate was added at 0 °C. The reaction was maintained at 0 °C, and the reaction was monitored by thin-layer chromatography (eluent: ethyl acetate: petroleum ether = 3:1). After the reaction was complete, 100 mL of saturated brine was added, and the mixture was extracted three times with 100 mL of dichloromethane. The extract was dried, concentrated, and purified by silica gel column chromatography to obtain 8.0 g of compound VI. Yield: 75%.

[0075] The NMR data for compound VI are as follows: 1 HNMR (CDCl3, 400MHz): 8.44 (s, 1H), 5.65 (m, 1H), 5.26 (t, J = 2.3Hz, 1H), 5.15 (t, J = 2.3Hz, 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).

[0076] Example 5

[0077] Preparation of entecavir (compound I):

[0078]

[0079] 20 mL of tetrahydrofuran and 2 g of compound VI were added to a 100 mL round-bottom flask. 5 mL of 3M hydrochloric acid was slowly added dropwise at 0 °C. The reaction was carried out at 60 °C for 6 hours. After the reaction was completed, 50 mL of ethyl acetate was added and the mixture was washed three times. The pH of the aqueous phase was adjusted to 7-7.5 with NaOH solution (6 mol / L). The solvent was evaporated and the mixture was purified by silica gel column chromatography to obtain 660 mg of the compound, with a yield of 80%.

[0080] The NMR data for compound I are as follows: 1 HNMR (DMSO-D6, 400MHz): 10.84(s,1H),7.65(s,1H),6.40(s,2H),5.36(dd,J=10.3,8.0Hz,1H),5.10(s,1H),4.85(d,J=3.1Hz,1H),4.8 1(t,J=5.3Hz,1H),4.56(s,1H),4.23(s,1H),3.54(t,J=6.1Hz,2H),2.55-2.50(m,1H),2.26-2.17(m,1H),2.04(dd,J=12.5,7.8Hz,1H).

[0081] This invention provides a two-step synthesis intermediate for entecavir, and a total five-step synthesis process for entecavir. The process is simple, using readily available and inexpensive raw materials, resulting in easy product purification, high overall yield, and ease of industrial production. It should be noted that the applicant has previously proposed a low-cost process for preparing 4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone, used as a raw material in this embodiment, significantly reducing raw material costs.

[0082] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for preparing a synthetic intermediate of entecavir, characterized in that, It includes the following steps: S1. Using (S)-4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone as a starting material, the reaction was carried out under imidazole and formaldehyde conditions to obtain compound III; S2. Compound III is subjected to a Michael addition reaction with potassium tert-butoxide, sec-butyllithium, lithium reagent generated in situ from methyl tert-butyl ether, cuprous bromide, and boron trifluoride diethyl ether to obtain compound IV, which is the synthetic intermediate of entecavir. The reaction pathway is shown below: 。 2. The method for preparing the entecavir synthetic intermediate according to claim 1, characterized in that, In step S2, at -78 o The Michael addition reaction was carried out at temperature C; wherein the molar ratio of compound III, lithium reagent, cuprous bromide and boron trifluoride diethyl ether was 1:2~5:2~5:1~3.

3. The method for preparing the synthetic intermediate of entecavir according to claim 1, characterized in that, In step S1, a solvent obtained by mixing tetrahydrofuran and water is used as the base solvent, and (S)-4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone, imidazole, and formaldehyde are reacted in the base solvent; wherein, the molar ratio of (S)-4-[(tert-butyldimethoxysilyl)oxo]-2-cyclopentenone, formaldehyde, and imidazole is 1:1 to 5:1 to 3.

4. A method for preparing entecavir, characterized in that, It includes the following steps: S100. The synthetic intermediate of entecavir was reduced by L-selectride to obtain compound V; S200. Compound V was reacted with N-BOC-6-chloro-9H-purine-2-amine, diethyl azodicarbonate, and triphenylphosphine via the Mitsunobu reaction to obtain compound VI; S300. Compound VI was hydrolyzed under hydrochloric acid conditions to give entecavir; The synthetic intermediate of entecavir is prepared by the method for preparing the synthetic intermediate of entecavir as described in any one of claims 1-3. The reaction route for the preparation of entecavir is as follows: 。 5. The method for preparing entecavir according to claim 4, characterized in that, In step S100, methanol, dichloromethane, or tetrahydrofuran is used as the base solvent, and the synthetic intermediate of entecavir and L-selectride react in the base solvent; wherein the molar ratio of the synthetic intermediate of entecavir to L-selectride is 1:1 to 3.

6. The method for preparing entecavir according to claim 4, characterized in that, In step S200, tetrahydrofuran or toluene is used as the base solvent, and compound V and N-BOC-6-chloro-9H-purine-2-amine react in the base solvent.

7. The method for preparing entecavir according to claim 4, characterized in that, In step S200, the molar ratio of compound V, N-BOC-6-chloro-9H-purine-2-amine, triphenylphosphine, and diethyl azodicarbonate is 1:1 to 3:1 to 3:1 to 3.

8. The method for preparing entecavir according to claim 4, characterized in that, In step S300, tetrahydrofuran or dichloromethane is used as the base solvent, and compound VI and hydrochloric acid react in the base solvent; wherein the molar ratio of compound VI to hydrochloric acid is 1:1 to 3.

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