Preparation method and use of an abacavir impurity

Abstract

The application discloses a preparation method of an abacavir impurity, specifically, 2-azabicyclo[2,2,1]hept-5-en-3-one is used as raw material, and the abacavir impurity is prepared through ring opening, separation, separation, protection, reduction, deprotection, condensation, ring closure and condensation, and the application further discloses the use of the abacavir impurity prepared by the preparation method in detection and / or control of abacavir quality, and the application provides a new idea for synthesis of the abacavir impurity, the starting raw material of the synthesis method is easy to obtain, the synthesis route has mild reaction conditions, the reaction operation is safe, and the yield and purity are good, so that the preparation demand of the impurity can be met, and the application has important significance for research on the abacavir impurity.

Description

Technical Field

[0001] This invention relates to the field of chemical pharmaceuticals, specifically to a method for preparing an abacavir impurity and its uses. Background Technology

[0002] Abacavir is a novel anti-AIDS drug, originally produced by GlaxoVicor in the UK. It is a new carbocyclic 2'-deoxyguanosine nucleoside analogue used for retroviruses. It has high oral bioavailability, easily penetrates the central nervous system, and exhibits high therapeutic efficacy. It is said that patients only need to take one tablet twice a day to achieve the same effect as previous anti-AIDS drugs requiring dozens of tablets. Its tablets and oral solution (trade name Ziagen) were launched in the US in 1999, authorized in China in 2000, and launched in China in 2002. Abacavir exhibits good anti-HIV activity, low cross-resistance, and minimal kidney damage, making it particularly suitable for treating pediatric HIV / AIDS. Its combination with lamivudine, or the "triple-drug regimen" of abacavir, lamivudine, and zidovudine, is used to treat HIV-infected patients or those with progressive immunodeficiency, as well as HIV-infected adults and children over 3 months of age. Triumeq, a triple-drug HIV treatment combining abacavir, lamivudine, and dolutegravir, was approved by the FDA on June 27, 2014, for the treatment of HIV-1 infection. Triumeq combines the integrase strand transfer inhibitor dolutegravir with two nucleoside reverse transcriptase inhibitors, abacavir and lamivudine, providing a novel single-pill treatment option for many HIV-infected individuals.

[0003] The Chinese chemical name for abacavir is (1S,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purine-9-yl]-2-cyclopentene-1-methanol sulfuric acid, and its structural formula is:

[0004]

[0005] Impurity research is an important part of drug quality research and one of the key factors in drug quality assurance. As a pharmaceutical industry, it is essential to strictly control the impurity content in products. Research on material impurities helps optimize drug synthesis processes and control quality. In order to improve the safety of clinical drug use, it is necessary to conduct detailed research and control on drug process impurities and degradation impurities during storage.

[0006] Research has revealed an impurity, USP impurity b, present in the abacavir production process. This is a diastereomer of abacavir, with the scientific name (1R,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purine-9-yl]-2-cyclopenten-1-methanol. This impurity is likely caused by configurational inversion of the chiral center at position 1 due to the use of strong acids and bases during synthesis. This impurity is of significant importance for the quality control and impurity research of abacavir. Its structural formula is:

[0007]

[0008] The two chiral centers of this impurity originate from the following compound 2 (2-azabicyclo[2,2,1]hept-5-en-3-one):

[0009]

[0010] Heterocyclic compound 2 is a racemic mixture composed of the following two compounds:

[0011]

[0012] They are enantiomers of each other. Compound 2 retains its chiral center during ring opening, and abacavir and its enantiomers can be easily prepared by directed synthesis and resolution. However, the chiral inverted (1R,4R) configuration, i.e., abacavir USP impurity b, is difficult to obtain. Summary of the Invention

[0013] The purpose of this invention is to provide a method for preparing abacavir impurities and their uses, so as to solve the problems mentioned in the background art.

[0014] To achieve the above objectives, the present invention provides the following technical solution:

[0015] A method for preparing an abacavir impurity, specifically: using 2-azabicyclo[2,2,1]hept-5-en-3-one as a starting material, the abacavir impurity is obtained through ring opening, resolution, further resolution, protection, reduction, deprotection, condensation, ring closing, and condensation. The synthetic route is as follows:

[0016]

[0017] As a further aspect of the present invention, the preparation method includes the following steps:

[0018] (1) Ring opening and resolution: 2-azabicyclo[2,2,1]hept-5-en-3-one was refluxed with sulfoxide and methanol, and the ring was opened and then resolved with D-tartaric acid. After filtration, compound 3 was obtained, and the filtrate was retained. The reaction temperature was 0℃~50℃.

[0019] (2) Resolution and protection: The above filtrate was further resolved with L-tartaric acid, and after filtration, compound 4 was obtained. The filtrate was retained. The filtrate was reacted with ditert-butyl dicarbonate to obtain compound 5.

[0020] (3) Reduction: Compound 5 was reduced with sodium borohydride to obtain compound 6;

[0021] (4) Deprotection: Add ethanol and concentrated hydrochloric acid to compound 6 and deprotect to obtain compound 7;

[0022] (5) Condensation: Compound 7 and 2-amino-4,6-dichloro-5-carbamoylpyrimidine were reacted in an organic solvent and under alkaline conditions to prepare compound 8;

[0023] (6) Cyclic closure: Compound 8 and triethyl orthoformate were cyclized in an organic solvent and under hydrochloric acid conditions to prepare compound 9;

[0024] (7) Condensation: Compound 9 and cyclopropylamine were reacted in an organic solvent and under alkaline conditions to prepare compound 1. Compound 1 was then separated by preparative liquid phase to obtain compounds 1a and 1b, wherein compound 1b is USP impurity b and compound 1a is an enantiomer of USP impurity b.

[0025] As a further aspect of the present invention: the reaction temperature in step (1) is 45°C.

[0026] As a further aspect of the present invention: the organic solvent in step (5) is any one of methanol, ethanol, and isopropanol, and the base is triethylamine, sodium bicarbonate, or sodium carbonate. The organic solvent in the present invention is preferably isopropanol, and the base is preferably sodium bicarbonate.

[0027] As a further aspect of the present invention: the organic solvent in step (6) is a mixed solvent formed by triethyl orthoformate and any one of methanol, ethanol, and isopropanol; the organic solvent of the present invention is preferably a mixed solvent of triethyl orthoformate and ethanol.

[0028] As a further aspect of the present invention: in step (7), the organic solvent is any one of methanol, ethanol, and isopropanol; the base is any one of triethylamine, sodium bicarbonate, and sodium carbonate; the organic solvent of the present invention is preferably isopropanol; the base is preferably sodium bicarbonate.

[0029] As a further aspect of the present invention, the present invention also discloses the use of abacavir impurities prepared using the preparation method of the present invention in the detection and / or control of abacavir quality.

[0030] Compared with the prior art, the beneficial effects of the present invention are: the present invention provides a new idea for the synthesis of abacavir impurities, the starting materials for the synthesis method are readily available, the reaction conditions of the synthesis route are mild and the reaction operation is safe, and the yield and purity are good enough to meet the preparation requirements of this impurity, which is of great significance to the study of abacavir impurities.

[0031] The chemical name of the compound described in this invention is:

[0032] Compound 2: 2-azabicyclo[2,2,1]hept-5-en-3-one

[0033] Compound 3: (1R,4S)-4-amino-2-cyclopentenyl carboxylate

[0034] Compound 4: (1S,4R)-4-amino-2-cyclopentenyl carboxylate

[0035] Compound 5: (1S,4S)-4-((tert-Butoxycarbonyl)amino)-2-cyclopentene-1-carboxylic acid methyl ester

[0036] Methyl (1R,4R)-4-((tert-butoxycarbonyl)amino)-2-cyclopenten-1-carboxylic acid

[0037] Compound 6: (1S,4S)-4-((tert-butoxycarbonyl)amino)-2-cyclopentene-1-methanol

[0038] (1R,4R)-4-((tert-butoxycarbonyl)amino)-2-cyclopentene-1-methanol

[0039] Compound 7: (1S,4S)-(4-aminocyclopent-2-enyl)methanol hydrochloride

[0040] (1R,4R)-(4-aminocyclopentan-2-enyl)methanol hydrochloride

[0041] Compound 8: N-[2-amino-4-chloro-6-[[(1S,4S)-4-hydroxymethyl-2-cyclopenten-1-yl]amino]-5-pyrimidinyl]formamide Compound 9: (1S,4S)-4-[2-amino-6-chloro-9H-purine-9-yl]-2-cyclopenten-1-methanol

[0042] (1R,4R)-4-[2-amino-6-chloro-9H-purin-9-yl]-2-cyclopenten-1-methanol

[0043] Compound 1a: (1S,4S)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopenten-1-methanol

[0044] Compound 1b: (1R,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopenten-1-methanol Attached Figure Description

[0045] Figure 1 This is a synthetic route diagram of an abacavir impurity according to an embodiment of the present invention;

[0046] Figure 2 This is a liquid chromatography-mass spectrometry report chromatogram of an abacavir impurity as described in an embodiment of the present invention;

[0047] Figure 3 The 1H NMR spectrum of an abacavir impurity as described in an embodiment of the present invention;

[0048] Figure 4 This is a carbon NMR spectrum of an abacavir impurity as described in an embodiment of the present invention. Detailed Implementation

[0049] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] See Figure 1 This invention discloses a method for preparing abacavir impurities. Specifically, using 2-azabicyclo[2,2,1]hepten-5-en-3-one as a raw material, the abacavir impurities are prepared through ring-opening, resolution, further resolution, protection, reduction, deprotection, condensation, ring-closing, and condensation. Specific embodiments are as follows:

[0051] Example 1

[0052] (1) 2-azabicyclo[2,2,1]hepta-5-en-3-one (132 g, 1209.64 mmol) was dissolved in methanol (580 mL), and SOCl2 (100 mL, 1363.6 mmol) was added dropwise. The temperature was slowly raised to 45 °C, and the mixture was stirred at 45-50 °C for 48 h. The solvent was evaporated under reduced pressure to obtain 225 g of an oily substance. Methanol (137.2 mL), D-tartaric acid (107.36 g, 715.76 mmol), and water (65.12 mL) were added to the oily substance, and the mixture was stirred to dissolve. The pH value was measured (1.5-2). Triethylamine (78.48 g, 775.6 mmol) was added dropwise. After the addition was complete, the pH value was measured (around 4.5), and the temperature was lowered to around 20 °C to allow crystals to form. The mixture was filtered, and the filter cake was washed with methanol (100 mL) to obtain 150 g of compound 3 ((1R,4S) configuration). The mother liquor was retained for later use.

[0053] (2) Add L-tartaric acid (161.04 g, 1073.6 mmol) to the above mother liquor. After dissolving, the pH is measured to be approximately 3.5. Add triethylamine (108.64 g, 1073.6 mmol) dropwise. After the addition is complete, measure the pH value (approximately 4.5) and cool to approximately 20°C to allow crystallization. Filter the solution and wash the filter cake with methanol (84 g, 105 mL) to obtain 120 g of compound 4 ((1S,4R) configuration). Evaporate the mother liquor to dryness to obtain 106 g of an oily substance. Add EA (600 mL) to the oily substance, keeping the temperature <15°C, and add triethylamine (55.76 g, 550.8 mmol) dropwise. After the addition is complete, stir for 30 min, and add a Boc2O EA solution (98.88 g, 453.2 mmol of Boc2O and 118.8 mL of EA solution), keeping the temperature <10°C during the addition. After the addition was complete, the temperature was raised to approximately 20°C and the reaction was allowed to proceed for 16 hours. When clumping occurred and stirring became difficult, water (150 g) was added. The mixture was allowed to stand and separate into layers, retaining the EA layer. The EA layer was washed with 10% Na₂CO₃ solution (160 g) and saturated NaCl solution (165 mL), and dried over anhydrous sodium sulfate. The drying agent was removed by filtration, and the solvent was evaporated under reduced pressure (approximately 40°C) to obtain approximately 80 g of a viscous oily substance, namely compound 5 (a mixture of (1S,4S) and (1R,4R) configurations).

[0054] (3) Add NaBH4 (31.36 g, 828.78 mmol) and THF (500 mL) to the above oily substance (compound 5) into the reaction vessel, and add methanol (100 mL) dropwise while maintaining the temperature <25℃. After the addition is complete, keep the temperature at about 20℃ and stir for 16 h. After the reaction is complete, add methanol (50 mL) dropwise again, raise the temperature to 53-58℃, and maintain it for 1.5 h. When no more large amounts of bubbles are released, evaporate the solvent under reduced pressure, add EA (1500 mL) to the concentrate, and wash it successively with water (400 g) and saturated brine (2 × 440 g), retain the EA layer, and dry it with anhydrous sodium sulfate. Filter to remove the drying agent, evaporate the solvent under reduced pressure, and obtain 50 g of viscous oily liquid, namely compound 6 (a mixture of (1S,4S) configuration and (1R,4R) configuration).

[0055] (4) Add ethanol (300 mL) to the above oily substance (compound 6), and add concentrated hydrochloric acid (50 g, 42.0 mL) dropwise while maintaining the temperature at 55-60 °C. After the addition is complete, maintain the reaction temperature at 55-60 °C for 1.5 h. Evaporate the solvent under reduced pressure to obtain 25 g of oily substance, which is compound 7 (a mixture of (1S,4S) and (1R,4R) configurations).

[0056] (5) Add the oily substance (25g, 167.09mmol) from step (4), 2-amino-4,6-dichloro-5-carboxypyrimidine (27g, 130.43mmol), sodium bicarbonate (34g, 404.7mmol), and isopropanol (270ml) from step (4) to a 500ml three-necked flask, stir and heat to reflux for 6h. After the reaction is complete, cool to room temperature and filter. Evaporate the filtrate under reduced pressure to obtain an oily substance. Pass the oily substance through a silica gel column (eluent: dichloromethane:methanol = 30:1) to obtain a pale yellow solid (5.0g, 13.51%), namely compound 8 (a mixture of (1S,4S) and (1R,4R) configurations).

[0057] (6) Compound 8 (5.0 g, 17.62 mmol) obtained in step (5), triethyl orthoformate (50 ml, 10 V), and ethanol (35 ml, 7 V) were added to a 250 ml three-necked flask, stirred and cooled to 0-10 °C, and hydrochloric acid (5.3 ml, 62.75 mmol) was added dropwise. After the addition was completed, the temperature was raised to 25-30 °C and the mixture was stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain a white solid (3.0 g, 56.39%), namely compound 9 (a mixture of (1S,4S) and (1R,4R) configurations).

[0058] (7) Compound 9 (3.0 g, 9.93 mmol) obtained in step (6), IPA (18 ml), and NaHCO3 (2.49 g, 29.7 mmol) were stirred for 15 min. Cyclopropylamine (0.85 g, 14.9 mmol) was added dropwise at 15-20 °C. After the addition was complete, the temperature was raised to 77-82 °C and the reaction was maintained for 9 h. The reaction of the starting material was detected by HPLC. The temperature was lowered to 25-30 °C, and the mixture was filtered. The filtrate was evaporated under reduced pressure to obtain an oily substance (2.0 g, 70.42%), which is compound 1 (a mixture of compound 1a with (1S,4S) configuration and compound 1b with (1R,4R) configuration). Compound 1 was subjected to preparative liquid chromatography to obtain abacavir diastereomers 1a 0.5 g (1a is the enantiomer of USP impurity b) and 1b 0.8 g (1b is USP impurity b).

[0059] The prepared abacavir USP impurity b was subjected to NMR and LC-MS analysis, and the test results are as follows: Figure 2-4 The relevant data of its 1H NMR spectrum are as follows: 1H NMR(600MHz,)δ7.53(s,1H),7.25(s,1H),6.15(dd,J=3.7,1.8Hz,1H),5.89 (dd,J=3.4,2.2Hz,1H),5.83(s,2H),5.46–5.40(m,1H),4.70(t,J=5.2Hz,1H ),3.41(t,J=5.7Hz,2H),3.08(dd,J=24.0,18.6Hz,2H),2.16(ddd,J=13.5,8 .4,4.9Hz,1H),1.97–1.90(m,1H),0.68–0.62(m,2H),0.58(d,J=2.6Hz,2H).

[0060] LC-MS (m / z): 287 [M+H] +

[0061] Its liquid phase purity was calculated to be 95.68%.

[0062] Example 2

[0063] (1) 2-azabicyclo[2,2,1]hepta-5-en-3-one (132 g, 1209.64 mmol) was dissolved in methanol (580 mL), and SOCl2 (100 mL, 1363.6 mmol) was added dropwise. The temperature was slowly raised to 25 °C, and the mixture was stirred at 25-30 °C for 48 h. The solvent was evaporated under reduced pressure to obtain 220 g of an oily substance. Methanol (137.2 mL), D-tartaric acid (107.36 g, 715.76 mmol), and water (65.12 mL) were added to the oily substance and stirred to dissolve. The pH value was measured (1.5-2). Triethylamine (78.48 g, 775.6 mmol) was added dropwise. After the addition was complete, the pH value was measured (around 4.5), and the temperature was lowered to around 20 °C to crystallize. The mixture was filtered, and methanol (100 mL) was added to the filter cake for washing. After filtration, 155 g of compound 3 ((1R,4S) configuration) was obtained. The mother liquor was retained for later use.

[0064] (2) Add L-tartaric acid (161.04 g, 1073.6 mmol) to the above mother liquor. After dissolving, the pH is measured to be approximately 3.5. Add triethylamine (108.64 g, 1073.6 mmol) dropwise. After the addition is complete, measure the pH value (approximately 4.5) and cool to approximately 20°C to allow crystallization. Filter the mixture, add methanol (84 g, 105 mL) to the filter cake, and wash. After filtration, obtain 130 g of compound 4 ((1S,4R) configuration). Evaporate the mother liquor to dryness to obtain 100 g of oil. Add EA (616 mL) to the oil, maintain the temperature <15°C, and add triethylamine (13.94 g, 137.7 mmol) dropwise. After the addition was complete, the mixture was stirred for 30 min. Then, a solution of Boc₂O in EA (98.88 g, 453.2 mmol of Boc₂O, and 118.8 mL of EA solution) was added dropwise, with the temperature controlled below 10 °C. After the addition was complete, the temperature was raised to approximately 20 °C and the reaction was allowed to proceed for 16 h. When clumping occurred and stirring became difficult, water (160 g) was added. The mixture was allowed to stand and separate into layers, retaining the EA layer. The EA layer was washed with 10% Na₂CO₃ solution (160 g) and saturated NaCl solution (165 mL), and dried over anhydrous sodium sulfate. The drying agent was removed by filtration, and the solvent was evaporated under reduced pressure (approximately 40 °C) to obtain approximately 72 g of a viscous oily substance, namely compound 5 (a mixture of (1S,4S) and (1R,4R) configurations).

[0065] (3) Add NaBH4 (28.22 g, 745.99 mmol) and THF (500 mL) to the above oily substance (compound 5) into the reaction vessel, and add methanol (100 mL) dropwise while maintaining the temperature <25℃. After the addition is complete, keep the temperature at about 20℃ and stir for 16 h. After the reaction is complete, add methanol (50 mL) dropwise again, raise the temperature to 53-58℃, and maintain it for 1.5 h. When no more large amounts of bubbles are released, evaporate the solvent under reduced pressure, add EA (1892 mL) to the concentrate, and wash successively with water (400 g) and saturated brine (2 × 440 g), retain the EA layer, and dry with anhydrous sodium sulfate. Filter to remove the drying agent, evaporate the solvent under reduced pressure, and obtain 42 g of viscous oily liquid, namely compound 6 (a mixture of (1S,4S) configuration and (1R,4R) configuration).

[0066] (4) Add ethanol (300 mL) to the above oily substance (compound 6), and add concentrated hydrochloric acid (50 g, 42.0 mL) dropwise while maintaining the temperature at 55-60 °C. After the addition is complete, maintain the reaction temperature at 55-60 °C for 1.5 h. Evaporate the solvent under reduced pressure to obtain 20 g of oily substance, which is compound 7 (a mixture of (1S,4S) configuration and (1R,4R) configuration).

[0067] (5) Add the oily substance (20g, 133.67mmol) from step (4), 2-amino-4,6-dichloro-5-carboxypyrimidine (25g, 120.77mmol), sodium bicarbonate (30.4g, 362.31mmol), and ethanol (250ml) from step (4) to a 500ml three-necked flask, stir and heat to reflux for 6h. After the reaction is complete, cool to room temperature and filter. Evaporate the filtrate under reduced pressure to obtain an oily substance. Pass the oily substance through a silica gel column (eluent: dichloromethane:methanol = 30:1) to obtain 3.5g of a pale yellow solid, with a yield of 10.22%, which is compound 8 (a mixture of (1S,4S) and (1R,4R) configurations).

[0068] (6) Compound 8 (3.5 g, 12.34 mmol) obtained in step (5), triethyl orthoformate (35 ml, 10 V), and ethanol (24.5 ml, 7 V) were added to a 250 ml three-necked flask, stirred and cooled to 0-10 °C, and hydrochloric acid (3.7 ml, 43.19 mmol) was added dropwise. After the addition was complete, the temperature was raised to room temperature and the mixture was stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain 2.0 g of white solid, with a yield of 53.48%, which is compound 9 (a mixture of (1S,4S) and (1R,4R) configurations).

[0069] (7) Compound 9 (2.0 g, 6.62 mmol) obtained in step (6), IPA (12 ml), and triethylamine (2.0 g, 19.76 mmol) were stirred for 15 min. Cyclopropylamine (0.56 g, 9.8 mmol) was added dropwise at 15-20 °C. After the addition was complete, the temperature was raised to 77-82 °C and the reaction was maintained for 9 h. The reaction of the starting material was detected by HPLC. The temperature was lowered to 25-30 °C, and the mixture was filtered. The filtrate was evaporated under reduced pressure to obtain an oily substance (1.3 g, 68.42%), which is compound 1 (a mixture of compound 1a with (1S,4S) configuration and compound 1b with (1R,4R) configuration). The oily substance (compound 1) was separated by preparative liquid chromatography to obtain abacavir diastereomers 1a 0.3 g (1a is the enantiomer of USP impurity b) and 1b 0.5 g (1b is USP impurity b).

[0070] Example 3

[0071] (1) 2-azabicyclo[2,2,1]hepta-5-en-3-one (132 g, 1209.64 mmol) was dissolved in methanol (580 mL), and SOCl2 (100 mL, 1363.6 mmol) was added dropwise. The temperature was slowly raised to 10 °C, and the mixture was stirred at 10-15 °C for 48 h. The solvent was evaporated under reduced pressure to obtain 218 g of an oily substance. Methanol (137.2 mL), D-tartaric acid (107.36 g, 715.76 mmol), and water (65.12 mL) were added to the oily substance, and the mixture was stirred to dissolve. The pH value was measured (1.5-2). Triethylamine (78.48 g, 775.6 mmol) was added dropwise. After the addition was complete, the pH value was measured (around 4.5), and the mixture was cooled to around 20 °C to crystallize. The mixture was filtered, and methanol (100 mL) was added to the filter cake for washing. After filtration, 158 g of compound 3 ((1R,4S) configuration) was obtained. The mother liquor was retained for later use.

[0072] (2) Add L-tartaric acid (161.04 g, 1073.6 mmol) to the above mother liquor. After dissolving, the pH is measured to be approximately 3.5. Add triethylamine (108.64 g, 1073.6 mmol) dropwise. After the addition is complete, measure the pH value (approximately 4.5) and cool to approximately 20°C to allow crystallization. Filter the mixture, add methanol (84 g, 105 mL) to the filter cake, and wash. After filtration, obtain 132 g of compound 4 ((1S,4R) configuration). Evaporate the mother liquor to dryness to obtain 95 g of oil. Add EA (616 mL) to the oil, maintain the temperature <15°C, and add triethylamine (13.94 g, 137.7 mmol) dropwise. After the addition was complete, the mixture was stirred for 30 min. Then, a solution of Boc₂O in EA (98.88 g, 453.2 mmol of Boc₂O, and 118.8 mL of EA solution) was added dropwise, maintaining a temperature below 10 °C. After the addition was complete, the temperature was raised to approximately 20 °C, and the reaction proceeded for 16 h. When clumping occurred and stirring became difficult, water (160 g) was added. The mixture was allowed to stand and separate into layers, retaining the EA layer. The EA layer was washed with 10% Na₂CO₃ solution (160 g) and saturated NaCl solution (165 mL), and dried over anhydrous sodium sulfate. The drying agent was removed by filtration, and the solvent was evaporated under reduced pressure (approximately 40 °C) to obtain approximately 65 g of a viscous oily substance, namely compound 5 (a mixture of (1S,4S) and (1R,4R) configurations).

[0073] (3) Add NaBH4 (25.48 g, 673.46 mmol) and THF (500 mL) to the above oily substance (compound 5) into the reaction vessel, and add methanol (100 mL) dropwise while maintaining the temperature <25℃. After the addition is complete, keep the temperature at about 20℃ and stir for 16 h. After the reaction is complete, add methanol (50 mL) dropwise again, raise the temperature to 53-58℃, and maintain it for 1.5 h. When no more large amounts of bubbles are released, evaporate the solvent under reduced pressure, add EA (1892 mL) to the concentrate, and wash it successively with water (400 g) and saturated brine (2 × 440 g), retain the EA layer, and dry it with anhydrous sodium sulfate. Filter to remove the drying agent, evaporate the solvent under reduced pressure, and obtain 36 g of viscous oily liquid, namely compound 6 (a mixture of (1S,4S) configuration and (1R,4R) configuration).

[0074] (4) Add ethanol (300 mL) to the above oily substance (compound 6), and add concentrated hydrochloric acid (50 g, 42.0 mL) dropwise while maintaining the temperature at 55-60 °C. After the addition is complete, maintain the reaction temperature at 55-60 °C for 1.5 h. Evaporate the solvent under reduced pressure to obtain 14 g of oily substance, which is compound 7 (a mixture of (1S,4S) and (1R,4R) configurations).

[0075] (5) Add the oily substance (14 g, 93.57 mmol) from step (4), 2-amino-4,6-dichloro-5-carboxypyrimidine (23.0 g, 112.28 mmol), sodium bicarbonate (28.0 g, 333.33 mmol), and ethanol (230 ml) from step (4) to a 500 ml three-necked flask, stir and heat to reflux for 6 h. After the reaction is complete, cool to room temperature and filter. Evaporate the filtrate under reduced pressure to obtain an oily substance. Pass the oily substance through a silica gel column (eluent: dichloromethane: methanol = 30:1) to obtain a pale yellow solid (2.1 g, 7.9%), namely compound 8 (a mixture of (1S,4S) and (1R,4R) configurations).

[0076] (6) Compound 8 (2.1 g, 7.4 mmol) obtained in step (5), triethyl orthoformate (21 ml, 10 V), and ethanol (14.7 ml, 7 V) were added to a 250 ml three-necked flask, stirred and cooled to 0-10 °C, and hydrochloric acid (2.2 ml, 25.9 mmol) was added dropwise. After the addition was complete, the temperature was raised to room temperature and the mixture was stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain 1.2 g of white solid, with a yield of 53.67%, which is compound 9 (a mixture of (1S,4S) and (1R,4R) configurations).

[0077] (7) Compound 9 (1.2 g, 3.97 mmol) obtained in step (6), IPA (7.5 ml), sodium bicarbonate (1.0 g, 11.91 mmol), were stirred for 15 min. Cyclopropylamine (0.34 g, 9.5 mmol) was added dropwise at 15-20 °C. After the addition was complete, the temperature was raised to 77-82 °C and the reaction was maintained for 9 h. The reaction of the starting material was detected by HPLC. The temperature was lowered to 25-30 °C, and the mixture was filtered. The filtrate was evaporated under reduced pressure to obtain an oily substance (0.75 g, 65.79%), which is compound 1 (a mixture of compound 1a with (1S,4S) configuration and compound 1b with (1R,4R) configuration). The oily substance (compound 1) was separated by preparative liquid chromatography to obtain abacavir diastereomers 1a 0.15 g (1a is the enantiomer of USP impurity b) and 1b 0.35 g (1b is USP impurity b).

[0078] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0079] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing an abacavir impurity, characterized in that, Specifically, using 2-azabicyclo[2,2,1]hept-5-en-3-one as a starting material, the abacavir impurity was obtained through ring-opening, resolution, further resolution, protection, reduction, deprotection, condensation, ring-closing, and condensation. The abacavir impurity is compound 1. The synthetic route is as follows: .

2. The method for preparing an abacavir impurity according to claim 1, characterized in that, The preparation method includes the following steps: (1) Ring opening and resolution: 2-azabicyclo[2,2,1]hept-5-en-3-one was refluxed with sulfoxide and methanol, and after ring opening, it was resolved by D-tartaric acid. After filtration, compound 3 was obtained, and the filtrate was retained. The reaction temperature was 0℃~50℃. (2) Resolution and protection: The above filtrate was further separated with L-tartaric acid, and after filtration, compound 4 was obtained. The filtrate was retained. The filtrate was reacted with di-tert-butyl dicarbonate to obtain compound 5. (3) Reduction: Compound 5 was reduced with sodium borohydride to obtain compound 6; (4) Deprotection: Add ethanol and concentrated hydrochloric acid to compound 6 to obtain compound 7 after deprotection; (5) Condensation: Compound 7 and 2-amino-4,6-dichloro-5-carbamoylpyrimidine were reacted in an organic solvent and under alkaline conditions to prepare compound 8; (6) Cyclic closure: Compound 8 and triethyl orthoformate were cyclized in an organic solvent and under concentrated hydrochloric acid to prepare compound 9; (7) Condensation: Compound 9 and cyclopropylamine react under organic solvent and alkaline conditions to prepare compound 1. Compound 1 is then separated by preparative liquid phase to obtain compounds 1a and 1b, wherein compound 1b is USP impurity b and compound 1a is an enantiomer of USP impurity b.

3. The method for preparing an abacavir impurity according to claim 2, characterized in that, The reaction temperature in step (1) is 45°C.

4. The method for preparing an abacavir impurity according to claim 2, characterized in that, The organic solvent mentioned in step (5) is any one of methanol, ethanol, and isopropanol, and the base is triethylamine, sodium bicarbonate, or sodium carbonate.

5. The method for preparing an abacavir impurity according to claim 4, characterized in that, The organic solvent is isopropanol, and the base is sodium bicarbonate.

6. The method for preparing an abacavir impurity according to claim 2, characterized in that, The organic solvent mentioned in step (6) is any one of methanol, ethanol, and isopropanol.

7. The method for preparing an abacavir impurity according to claim 6, characterized in that, The organic solvent is ethanol.

8. The method for preparing an abacavir impurity according to claim 2, characterized in that, In step (7), the organic solvent is any one of methanol, ethanol, and isopropanol; the base is any one of triethylamine, sodium bicarbonate, and sodium carbonate.

9. The method for preparing an abacavir impurity according to claim 8, characterized in that, The organic solvent is isopropanol; the base is sodium bicarbonate.

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