Preparation method and application of abacavir impurity

Abstract

The invention discloses a preparation method of abacavir impurities, and particularly, the abacavir impurities are prepared by taking 2-azabicyclo [2, 2, 1] hept-5-ene-3-ketone as a raw material through ring opening, resolution, resolution, upper protection, reduction, deprotection, condensation, ring closing and condensation. The invention also discloses application of the abacavir impurity prepared by the preparation method in detection and / or control of abacavir quality, a new thought is provided for synthesis of the abacavir impurity, the initial raw materials of the synthesis method are easy to obtain, the reaction conditions of the synthesis route are mild, the reaction operation is safe, and the method is suitable for industrial production. And the yield and the purity are good, so that the preparation requirements of the impurity can be met, and the abacavir impurity is of great significance to research of abacavir impurities.

Description

Technical Field

[0001] The present invention relates to the field of chemical pharmacy, and in particular to a preparation method and application of an abacavir impurity. Background Art

[0002] Abacavir is a new anti-AIDS drug, first produced by Glaxo Wellcome in the UK. It is a new carbon ring 2'-deoxyguanosine nucleoside drug used for retroviruses. It has high oral bioavailability, easily penetrates the central nervous system, and has a high therapeutic effect. It is said that patients only need to take one tablet in the morning and evening to achieve the same therapeutic effect as dozens of tablets of previous anti-AIDS drugs. Its tablets and oral solution (trade name Ziagen) were launched in the United States in 1999, authorized in China in 2000, and launched in 2002. Abacavir has good anti-HIV activity, low cross-resistance, and little damage to renal function, making it particularly suitable for the treatment of pediatric AIDS. Its compound preparation with lamivudine and the "Sanxiewei" drug composed of lamivudine and zidovudine are used to treat patients with HIV infection or progressive immunodeficiency, as well as HIV-infected adult patients and children over 3 months old. Triumeq, a three-in-one HIV drug composed of deglutegravir and lamivudine, 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 new single-tablet treatment option for many HIV-infected people.

[0003] The Chinese chemical name of abacavir is (1S, 4R)-4-[2-amino-6-(cyclopropylamino)-9H-purine-9-yl]-2-cyclopentene-1-methanol sulfate, and the 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 very necessary to strictly control the impurity content in products. Research on material impurities helps optimize the synthesis process and quality control of drugs. 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] The study found that there is an impurity in the production process of Abacavir, which is USP impurity b. It is a diastereoisomer of Abacavir. Its chemical name is (1R, 4R)-4-[2-amino-6-(cyclopropylamino)-9H-purine-9-yl]-2-cyclopentene-1-methanol. This impurity may be caused by the use of strong acid and strong base in the synthesis process, which leads to the configuration flip of the chiral center at position 1. This impurity is of great significance to the quality control and impurity research of Abacavir. Its structural formula is:

[0007]

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

[0009]

[0010] Heterocyclic compound 2 is a racemate, consisting of the following two compounds:

[0011]

[0012] They are enantiomers of each other. Compound 2 keeps the chiral center unchanged during the ring-opening process, and abacavir and its enantiomers can be easily prepared through directional synthesis and resolution, but the chiral inverted (1R, 4R) configuration, i.e. abacavir USP impurity b, is difficult to prepare. Summary of the invention

[0013] The object of the present invention is to provide a method for preparing abacavir impurities and uses thereof, so as to solve the problems raised in the above-mentioned background technology.

[0014] To achieve the above object, the present invention provides the following technical solutions:

[0015] A method for preparing an abacavir impurity, specifically comprising: using 2-azabicyclo[2,2,1]hept-5-en-3-one as a raw material, and preparing the abacavir impurity through ring opening, splitting, splitting, protecting, reducing, deprotecting, condensing, ring closing, and condensing. The synthetic route is as follows:

[0016]

[0017] As a further solution of the present invention: the preparation method comprises the following steps:

[0018] (1) Ring opening and resolution: 2-azabicyclo[2,2,1]hept-5-en-3-one is refluxed with thionyl chloride and methanol, the ring is opened and then resolved with D-tartaric acid, and the compound 3 is obtained by filtration. The filtrate is retained. The reaction temperature is 0°C to 50°C;

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

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

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

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

[0023] (6) Ring closure: Compound 8 and triethyl orthoformate are cyclized in an organic solvent and hydrochloric acid to obtain compound 9;

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

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

[0026] As a further embodiment 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 of the present invention is preferably isopropanol, and the base is preferably sodium bicarbonate.

[0027] As a further embodiment 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 in the present invention is preferably a mixed solvent of triethyl orthoformate and ethanol.

[0028] As a further embodiment 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 embodiment of the present invention, the present invention also discloses the use of the impurities of abacavir prepared by the preparation method of the present invention in detecting and / or controlling the quality of abacavir.

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

[0031] The chemical name of the compound of the present invention is:

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

[0033] Compound 3: (1R,4S)-4-amino-2-cyclopentenecarboxylic acid methyl ester

[0034] Compound 4: (1S,4R)-4-amino-2-cyclopentenecarboxylic acid methyl ester

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

[0036] (1R,4R)-4-((tert-Butyloxycarbonyl)amino)-2-cyclopentene-1-carboxylic acid methyl ester

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

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

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

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

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

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

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

[0044] Compound 1b: (1R, 4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene-1-methanol BRIEF DESCRIPTION OF THE DRAWINGS

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

[0046] Figure 2 This is a LC-MS report spectrum of an abacavir impurity described in an embodiment of the present invention;

[0047] Figure 3 This is a hydrogen nuclear magnetic spectrum of an abacavir impurity described in an embodiment of the present invention;

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

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] See also Figure 1 The present invention discloses a method for preparing an abacavir impurity. Specifically, 2-azabicyclo[2,2,1]hept-5-en-3-one is used as a raw material, and the abacavir impurity is prepared by ring opening, splitting, splitting, protecting, reducing, deprotecting, condensing, ring closing, and condensing. The specific embodiments are as follows:

[0051] Example 1

[0052] (1) 2-Azabicyclo[2,2,1]hept-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 temperature was kept at 45-50°C and stirred 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 stirred to dissolve. The pH value was measured (1.5-2). Triethylamine (78.48 g, 775.6 mmol) was added dropwise, and the pH value was measured (about 4.5) after the addition was completed, and the temperature was lowered to about 20°C for crystallization. The mixture was filtered and the filter cake was washed with methanol (100 mL) to obtain 150 g of compound 3 ((1R, 4S) configuration) and 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, and after dissolution, measure the pH to about 3.5. Add triethylamine (108.64 g, 1073.6 mmol) dropwise, measure the pH value (about 4.5), and cool to about 20°C for crystallization. Filter by suction, wash the filter cake with methanol (84 g, 105 mL), and obtain 120 g of compound 4 ((1S, 4R) configuration). Evaporate the mother liquor to dryness to obtain 106 g of oil. Add EA (600 mL) to the oil, control the temperature to <15°C, and add triethylamine (55.76 g, 550.8 mmol) dropwise. Stir for 30 min after the addition, and add Boc2O EA solution (98.88 g, 453.2 mmol of Boc2O and 118.8 mL of EA solution) dropwise, and control the temperature to <10°C during the addition. After the addition is complete, the temperature rises to about 20°C and the reaction is continued for 16 hours. When lumps appear and it is difficult to stir, add water (150 g). Let stand to separate the layers and retain the EA layer. The EA layer is washed with 10% Na2CO3 solution (160 g) and saturated NaCl solution (165 mL) respectively, and dried over anhydrous sodium sulfate. Filter to remove the desiccant, evaporate the solvent under reduced pressure (about 40°C), and obtain about 80 g of viscous oil, i.e., compound 5 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[0054] (3) NaBH4 (31.36 g, 828.78 mmol) and THF (500 mL) were added to the above oil (Compound 5) in a reactor, and methanol (100 mL) was added dropwise while the temperature was controlled at <25°C. After the addition, the mixture was kept at about 20°C and stirred for 16 h. After the reaction was completed, methanol (50 mL) was added dropwise again, and the temperature was raised to 53-58°C and maintained for 1.5 h. When no more bubbles were released, the solvent was evaporated under reduced pressure, and EA (1500 mL) was added to the concentrate, which was washed with water (400 g) and saturated brine (2×440 g) in turn. The EA layer was retained and dried over anhydrous sodium sulfate. The desiccant was filtered out, and the solvent was evaporated under reduced pressure to obtain 50 g of a viscous oily liquid, i.e., Compound 6 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

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

[0056] (5) Add the oily substance (25 g, 167.09 mmol) of step (4), 2-amino-4,6-dichloro-5-formylaminopyrimidine (27 g, 130.43 mmol), sodium bicarbonate (34 g, 404.7 mmol), and isopropanol (270 ml) into a 500 ml three-necked flask, and stir and heat to reflux for 6 h. After the reaction is completed, cool to room temperature, filter, and evaporate the filtrate to dryness under reduced pressure to obtain an oily substance. The oily substance is passed through a silica gel column (eluting with dichloromethane: methanol = 30:1) to obtain a light yellow solid (5.0 g, 13.51%), i.e., compound 8 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[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 placed in 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, the temperature was raised to 25-30°C and stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain a white solid (3.0 g, 56.39%), i.e., compound 9 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[0058] (7) Compound 9 (3.0 g, 9.93 mmol) obtained in step (6), IPA (18 ml), NaHCO3 (2.49 g, 29.7 mmol) were stirred for 15 min, and cyclopropylamine (0.85 g, 14.9 mmol) was added dropwise at 15-20°C. After the addition was completed, the temperature was raised to 77-82°C and kept for 9 h. The reaction of the raw materials was complete after HPLC detection. The temperature was lowered to 25-30°C, filtered, and the filtrate was decompressed and dried to obtain an oil (2.0 g, 70.42%), i.e., compound 1 (a mixture of compound 1a with (1S, 4S) configuration and compound 1b with (1R, 4R) configuration). Compound 1 was separated by preparative liquid phase 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 nuclear magnetic resonance and liquid chromatography-mass spectrometry testing. The test results are as follows: Figure 2-4 , its nuclear magnetic hydrogen spectrum related data 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] The calculated liquid purity is 95.68%

[0062] Example 2

[0063] (1) 2-Azabicyclo[2,2,1]hept-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 temperature was kept at 25-30°C and stirred 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, and the pH value was measured (about 4.5) after the addition was completed, and the temperature was lowered to about 20°C for crystallization. The mixture was filtered and methanol (100 mL) was added to the filter cake for slurry washing. After filtration, 155 g of compound 3 ((1R, 4S) configuration) was obtained and 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, and after dissolution, measure the pH to about 3.5. Add triethylamine (108.64 g, 1073.6 mmol) dropwise, measure the pH value (about 4.5), and cool to about 20°C for crystallization. Filter by suction, add methanol (84 g, 105 mL) to the filter cake for pulping and washing, and filter to obtain 130 g of compound 4 ((1S, 4R) configuration), and evaporate the mother liquor to dryness to obtain 100 g of oil. Add EA (616 mL) to the oil, control the temperature to <15°C, and add triethylamine (13.94 g, 137.7 mmol) dropwise. After the addition, stir for 30 minutes, add Boc2O EA solution (98.88g, 453.2mmol Boc2O and 118.8mL EA solution), and control the temperature to <10℃ during the addition. After the addition, the temperature rises to about 20℃ and reacts for 16h. When lumps appear and it is difficult to stir, add water (160g). Let it stand and separate, and keep the EA layer. Wash the EA layer with 10% Na2CO3 solution (160g) and saturated NaCl solution (165mL), respectively, and dry it with anhydrous sodium sulfate. Filter to remove the desiccant, evaporate the solvent under reduced pressure (about 40℃), and obtain about 72g of viscous oil, i.e., compound 5 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[0065] (3) NaBH4 (28.22 g, 745.99 mmol) and THF (500 mL) were added to the above oil (Compound 5) in a reactor, and methanol (100 mL) was added dropwise while the temperature was controlled at <25°C. After the addition, the mixture was kept at about 20°C and stirred for 16 h. After the reaction was completed, methanol (50 mL) was added dropwise again, and the temperature was raised to 53-58°C and maintained for 1.5 h. When no more bubbles were released, the solvent was evaporated under reduced pressure, and EA (1892 mL) was added to the concentrate, which was washed with water (400 g) and saturated brine (2×440 g) in turn. The EA layer was retained and dried over anhydrous sodium sulfate. The desiccant was filtered out, and the solvent was evaporated under reduced pressure to obtain 42 g of a viscous oily liquid, i.e., Compound 6 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[0066] (4) Add ethanol (300 mL) to the above oil (Compound 6), and add concentrated hydrochloric acid (50 g, 42.0 mL) dropwise at 55-60°C. After the addition, maintain 55-60°C for 1.5 h. Evaporate the solvent under reduced pressure to obtain 20 g of an oil, namely Compound 7 (a mixture of (1S, 4S) and (1R, 4R) configurations).

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

[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 placed in 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, the temperature was raised to room temperature and stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain 2.0 g of a white solid with a yield of 53.48%, i.e., compound 9 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[0069] (7) Compound 9 (2.0 g, 6.62 mmol) obtained in step (6), IPA (12 ml), triethylamine (2.0 g, 19.76 mmol) were stirred for 15 min, and cyclopropylamine (0.56 g, 9.8 mmol) was added dropwise at 15-20°C. After the addition was completed, the temperature was raised to 77-82°C and kept for 9 h. The reaction of the raw materials was complete by HPLC. The temperature was lowered to 25-30°C, filtered, and the filtrate was decompressed and dried to obtain an oil (1.3 g, 68.42%), i.e., compound 1 (a mixture of compound 1a with (1S, 4S) configuration and compound 1b with (1R, 4R) configuration). The oil (compound 1) was separated by preparative liquid phase 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]hept-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 temperature was kept at 10-15°C and stirred 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 stirred to dissolve. The pH value was measured (1.5-2). Triethylamine (78.48 g, 775.6 mmol) was added dropwise, and the pH value was measured (about 4.5) after the addition was completed, and the temperature was lowered to about 20°C for crystallization. The mixture was filtered and methanol (100 mL) was added to the filter cake for slurry washing. After filtration, 158 g of compound 3 ((1R, 4S) configuration) was obtained and 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, and after dissolution, measure the pH to about 3.5. Add triethylamine (108.64 g, 1073.6 mmol) dropwise, measure the pH value (about 4.5), and cool to about 20°C for crystallization. Filter by suction, add methanol (84 g, 105 mL) to the filter cake for pulping and washing, and filter to obtain 132 g of compound 4 ((1S, 4R) configuration), and evaporate the mother liquor to dryness to obtain 95 g of oil. Add EA (616 mL) to the oil, control the temperature to <15°C, and add triethylamine (13.94 g, 137.7 mmol) dropwise. After the addition, stir for 30 minutes, add Boc2O EA solution (98.88g, 453.2mmol Boc2O and 118.8mL EA solution), and control the temperature to <10℃ during the addition. After the addition, the temperature rises to about 20℃ and reacts for 16h. When lumps appear and it is difficult to stir, add water (160g). Let it stand and separate, and keep the EA layer. Wash the EA layer with 10% Na2CO3 solution (160g) and saturated NaCl solution (165mL), respectively, and dry it with anhydrous sodium sulfate. Filter to remove the desiccant, evaporate the solvent under reduced pressure (about 40℃), and obtain about 65g of viscous oil, i.e., compound 5 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[0073] (3) NaBH4 (25.48 g, 673.46 mmol) and THF (500 mL) were added to the above oil (Compound 5) in a reactor, and methanol (100 mL) was added dropwise while the temperature was controlled at <25°C. After the addition, the mixture was kept at about 20°C and stirred for 16 h. After the reaction was completed, methanol (50 mL) was added dropwise again, and the temperature was raised to 53-58°C and maintained for 1.5 h. When no more bubbles were released, the solvent was evaporated under reduced pressure, and EA (1892 mL) was added to the concentrate, which was washed with water (400 g) and saturated brine (2×440 g) in turn. The EA layer was retained and dried over anhydrous sodium sulfate. The desiccant was filtered out, and the solvent was evaporated under reduced pressure to obtain 36 g of a viscous oily liquid, i.e., Compound 6 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

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

[0075] (5) Add the oily substance (14 g, 93.57 mmol) of step (4), 2-amino-4,6-dichloro-5-formylaminopyrimidine (23.0 g, 112.28 mmol), sodium bicarbonate (28.0 g, 333.33 mmol), and ethanol (230 ml) into a 500 ml three-necked flask, stir and heat to reflux for 6 h. After the reaction is complete, cool to room temperature, filter, and evaporate the filtrate to dryness under reduced pressure to obtain an oily substance. The oily substance is passed through a silica gel column (eluting with dichloromethane: methanol = 30:1) to obtain a light yellow solid (2.1 g, 7.9%), i.e., compound 8 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[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 placed in 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, the temperature was raised to room temperature and stirred for 5 h. After the reaction was completed, the mixture was filtered to obtain 1.2 g of a white solid with a yield of 53.67%, i.e., compound 9 (a mixture of (1S, 4S) configuration and (1R, 4R) configuration).

[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), stirred for 15 min, cyclopropylamine (0.34 g, 9.5 mmol) was added dropwise at 15-20°C, and the temperature was raised to 77-82°C, and the reaction was kept at this temperature for 9 h. The reaction of the raw materials was complete when detected by HPLC. The temperature was lowered to 25-30°C, filtered, and the filtrate was decompressed and dried to obtain an oil (0.75 g, 65.79%), i.e., compound 1 (a mixture of compound 1a with (1S, 4S) configuration and compound 1b with (1R, 4R) configuration). The oil (compound 1) was separated by preparative liquid phase 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 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 the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0079] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing abacavir impurities, characterized in that: Specifically, 2-azabicyclo[2,2,1]hept-5-en-3-one is used as a raw material, and abacavir impurities are prepared by ring opening, splitting, splitting, protection, reduction, deprotection, condensation, ring closing, and condensation. The synthetic route is as follows:

2. The method for preparing an abacavir impurity according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Ring opening and resolution: 2-azabicyclo[2,2,1]hept-5-en-3-one is refluxed with thionyl chloride and methanol, the ring is opened and then resolved with D-tartaric acid, and the compound 3 is obtained by filtration. The filtrate is retained. The reaction temperature is 0°C to 50°C; (2) Resolution and protection: The filtrate is further resolved with L-tartaric acid, and compound 4 is obtained after filtration. The filtrate is retained; the filtrate is reacted with di-tert-butyl dicarbonate to obtain compound 5; (3) Reduction: Compound 5 is reduced with sodium borohydride to obtain compound 6; (4) Deprotection: Add ethanol and concentrated hydrochloric acid to compound 6 to obtain compound 7 through deprotection; (5) Condensation: Compound 7 and 2-amino-4,6-dichloro-5-formylaminopyrimidine are reacted in an organic solvent under alkaline conditions to obtain compound 8; (6) Ring closure: Compound 8 and triethyl orthoformate are cyclized in an organic solvent and hydrochloric acid to obtain compound 9; (7) Condensation: Compound 9 and cyclopropylamine are reacted in an organic solvent under alkaline conditions to obtain compound 1, and compound 1 is separated by preparative liquid phase to obtain compounds 1a and 1b, wherein compound 1b is USP impurity b, and compound 1a is the 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: In step (5), the organic solvent 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 described in step (6) is a mixed solvent formed by triethyl orthoformate and 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 a mixed solvent of triethyl orthoformate and 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; and 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; and the alkali is sodium bicarbonate.

10. Use of the abacavir impurities prepared by the preparation method according to claims 1 to 9 in detecting and / or controlling the quality of abacavir.

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