A novel method for preparing baloxavir acid

Abstract

The invention discloses a novel preparation method of baloxavir acid, comprising: taking a substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazine-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate, an organic reaction solvent and a dealkylation agent for reaction, and adding one or more of sodium thiosulfate and a hydrate thereof during the reaction. The sulfur atoms in the molecules of sodium thiosulfate and its hydrate have a certain affinity with the sulfur atoms in the substrate molecules, and a temporary interaction or coordination is formed between them during the reaction, thereby regulating the reaction product to transform toward a dominant stereo configuration and generate a desired product, thereby improving the stereoselectivity of the reaction, and reducing side reactions such as configuration flipping or isomerization of the substrate, so that the generation of baloxavir acid in the reaction process is dominant, the generation of isomers is inhibited, and the purity and yield of baloxavir acid are improved through post-treatment solid-liquid separation and purification.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and in particular relates to a novel preparation method of baloxavir acid. Background Art

[0002] Baloxavir marboxil was first developed by Shionogi Pharmaceutical Co., Ltd. of Japan and was launched in Japan on February 23, 2018 for the treatment of influenza A and B under the trade name Xofluza®. It was approved for marketing in the United States on October 24, 2018. It is the first anti-influenza drug with a new mechanism of action approved in the United States in nearly 20 years.

[0003] Mabaloxavir is a prodrug, and its chemical name is: [[(12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,6,8,12,12a-hexahydro-6,8-dioxo-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazin-7-yl]oxy]methyl carbonate, and its structural formula is as follows:

[0004] .

[0005] After entering the human body, baloxavir is hydrolyzed by arylacetamide deacetylase (AADAC) to generate baloxavir acid, an active ingredient with anti-influenza virus effect. Baloxavir acid inhibits the activity of influenza virus RdRp by binding to PA protein with endonuclease activity (i.e., Cap-dependent endonuclease), blocks the synthesis of viral mRNA, and inhibits viral proliferation, thereby exerting an antiviral effect. It is one of the few new drugs on the market that can inhibit the proliferation of influenza virus, and therefore the drug has broad market prospects.

[0006] Baloxavir acid is a key intermediate in the preparation of mabaloxavir. The chemical name of baloxavir acid is: (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione. The structural formula is as follows:

[0007] .

[0008] The chemical name of the main stereoisomer produced in the preparation process of baloxavir acid is: (12aR)-12-[(11R)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione, and the structural formula is as follows:

[0009] .

[0010] The chemical name of the raw material for preparing baloxavir acid is: (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate, and the structural formula is as follows:

[0011] .

[0012] Patent EP3473629 discloses the synthesis route of Mabaloxavir, which is as follows:

[0013] ;

[0014] In the third step of this process, lithium chloride is used as the dehexylating agent and N-methylpyrrolidone (NMP) is used as the organic reaction solvent. However, when the process is repeated using lithium chloride, it is difficult to complete the dehexylating reaction.

[0015] Patents with application numbers 202011332799.6 and 202310377724.7 both disclose technical solutions using lithium bromide as a dealkylation agent. Although lithium bromide can significantly shorten the reaction time and reduce product decomposition, the new stereoisomer produced after the reaction will exceed 2%, and this stereoisomer is difficult to remove, which poses a potential risk to the quality control of drug intermediates and finished products.

[0016] In view of this, the present invention is proposed. Summary of the invention

[0017] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a novel method for preparing baloxavir acid, so as to achieve the purpose of obtaining high-purity baloxavir acid by a process method with simple operation, low cost and few side reactions.

[0018] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0019] A novel method for preparing baloxavir acid comprises the following steps:

[0020] The substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate, an organic reaction solvent and a dealkylation agent are reacted, and one or more of sodium thiosulfate and its hydrate are added during the reaction to obtain the product; the reaction equation is as follows:

[0021] ;

[0022] The sulfur atoms in the molecules of sodium thiosulfate and its hydrates have a certain affinity with the sulfur atoms in the substrate molecules, and they form a temporary interaction or coordination during the reaction, thereby regulating or stabilizing the spatial configuration of the substrate in the reaction, so that the reaction is transformed toward the dominant stereoisomer and the expected product is generated, thereby improving the stereoselectivity of the reaction, reducing side reactions such as configuration inversion or isomerization of the substrate, and thus reducing the generation of stereoisomers.

[0023] During the reaction, the generation of stereoisomers is often caused by the difference in spatial selectivity of the reaction, and sodium thiosulfate, through its affinity with the substrate molecule, causes the reaction to transform toward the dominant stereoisomer, which is beneficial to the generation of the target product, thereby improving the stereoselectivity of the reaction. In this way, during the reaction, the generation of baloxavir acid is dominant, and the generation of isomers is greatly reduced.

[0024] Wherein, the dealkylation agent is a lithium salt, preferably lithium bromide.

[0025] Furthermore, one or both of sodium thiosulfate or sodium thiosulfate pentahydrate are added during the reaction.

[0026] Furthermore, sodium thiosulfate pentahydrate is added during the reaction.

[0027] Sodium thiosulfate pentahydrate has better solubility than anhydrous sodium thiosulfate, especially in polar solvents (such as N,N-dimethylacetamide). This means that sodium thiosulfate pentahydrate can be dispersed in the reaction system faster and more evenly, so that it can interact with the substrate or reaction intermediate more effectively to achieve better reaction results. Good solubility enables it to participate in the reaction more evenly, thereby improving reaction efficiency and reducing the generation of stereoisomers.

[0028] In addition, sodium thiosulfate pentahydrate increases the polarity of the reaction solvent due to the presence of hydrates in its molecular structure, which is beneficial to improving the reaction rate. Compared with the anhydrous form, the pentahydrate can reduce the reaction time and reduce the production of impurities and stereoisomers.

[0029] Furthermore, based on the amount of substance, the amount of sodium thiosulfate pentahydrate added is 0.05-0.25 times that of the substrate.

[0030] Further, the added amount of sodium thiosulfate pentahydrate is 0.107 times of the substrate.

[0031] When sodium thiosulfate pentahydrate is excessive, it will not only affect the reaction balance, but also inhibit the complete conversion of the reaction substrate, resulting in some substrates being unable to fully react and remaining during the reaction, which will in turn reduce the purity of the product, and these unreacted substrates are difficult to remove in the subsequent purification process, and the increase in impurity content makes the subsequent purification more difficult. An appropriate amount of sodium thiosulfate pentahydrate can maintain a balanced state in the reaction, which ensures that the reaction can proceed smoothly, reduces the generation of stereoisomers, and does not affect the complete conversion of the substrate.

[0032] Furthermore, the organic reaction solvent is selected from one or both of N,N-dimethylacetamide and N-methylpyrrolidone.

[0033] Furthermore, the organic reaction solvent is N,N-dimethylacetamide, and the amount of the organic reaction solvent used is 3 to 4 times, preferably 3.5 times, of the substrate by weight.

[0034] Adding too much organic reaction solvent will result in loss of product during crystallization; adding too little organic reaction solvent will affect the reaction process.

[0035] Furthermore, the reaction temperature during the reaction is 70-80°C; preferably 75°C.

[0036] Since the organic reaction solvent N,N-dimethylacetamide has a strong polarity and the dealkylation reagent lithium bromide has a strong reaction activity, if the reaction temperature is too high, it will cause the product to decompose. The decomposition reaction formula is as follows:

[0037] ;

[0038] Therefore, the reaction temperature is controlled to be 70-80°C, preferably 75°C. Once the reaction temperature is too high, such as higher than 90°C, the product decomposition is very obvious, and once the reaction temperature is too low, such as less than 70°C, the reaction will be slow and it will be difficult to reach the reaction endpoint.

[0039] Further, after the reaction is completed, the temperature is lowered to 35-40° C., acetonitrile and dimethyl sulfoxide are added with stirring, and then water is added dropwise with stirring to grow crystals. The amount of water added for crystallization is 4-11 times of the substrate by weight.

[0040] Furthermore, by weight, the amount of acetonitrile used is 1.1 to 1.5 times, preferably 1.33 times, of the substrate; the amount of dimethyl sulfoxide used is 0.3 to 0.7 times, preferably 0.5 times, of the substrate; and the amount of water added is 2 to 11 times, preferably 4.94 times, of the substrate.

[0041] Furthermore, the step of dripping water and stirring to grow the crystal includes: dripping a portion of water at 35-40° C., stirring to grow the crystal, and then dripping the remaining water at 25-30° C., stirring to grow the crystal.

[0042] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0043] The sulfur atoms in the molecules of sodium thiosulfate and its hydrates have a certain affinity with the sulfur atoms in the substrate molecules, and they form a temporary interaction or coordination during the reaction, thereby regulating or stabilizing the spatial configuration of the substrate in the reaction, so that the reaction is transformed toward the dominant stereoisomer and the expected product is generated, thereby improving the stereoselectivity of the reaction, reducing side reactions such as configuration inversion or isomerization of the substrate, and thus reducing the generation of stereoisomers.

[0044] In the present invention, one or more of sodium thiosulfate and its hydrates are added during the reaction process, which can reduce the incidence of side reactions and thus improve the selectivity of the reaction. In this way, during the reaction process, the generation of baloxavir acid is dominant, the generation of its stereoisomers is greatly reduced, and the purity and yield of baloxavir acid are improved.

[0045] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0047] Figure 1 , is the high performance liquid chromatogram of Example 1 of the present invention;

[0048] Figure 2 , is the high performance liquid chromatogram of Example 2 of the present invention;

[0049] Figure 3 , is the high performance liquid chromatogram of Example 3 of the present invention;

[0050] Figure 4 , is the high performance liquid chromatogram of Example 4 of the present invention;

[0051] Figure 5 , is the high performance liquid chromatogram of comparative example 1 of the present invention;

[0052] Figure 6 , is the high performance liquid chromatogram of comparative example 2 of the present invention;

[0053] Figure 7 , is the high performance liquid chromatogram of Comparative Example 3 of the present invention;

[0054] Figure 8 , is the high performance liquid chromatogram of Comparative Example 4 of the present invention;

[0055] Fig. 9 , is the high performance liquid chromatogram of comparative example 5 of the present invention.

[0056] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0058] Example 1

[0059] (1) Take a 500 ml three-necked flask and add the substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazin[3,4-c]pyrido[2,1-f][1,2,4]triazine-6 ,8-diketone methanesulfonate 80.0g (0.12mol) (substrate molecular weight is 663.76, the substrate is mixed with trace methanesulfonic acid, the content of methanesulfonic acid is negligible), lithium bromide 52.6g, sodium thiosulfate pentahydrate 3.2g, N,N-dimethylacetamide 280.0g (3.5 times the weight of the substrate); in terms of molar number, the amount of sodium thiosulfate pentahydrate is 0.107 times that of the substrate;

[0060] (2) Stir the reaction at 75±2℃ for 22.5h;

[0061] (3) After the reaction was completed, the temperature was lowered to 35-40°C, 40.0 g of dimethyl sulfoxide and 106.4 g of acetonitrile were added, and the mixture was stirred for 20 min. Then, 62.4 g of water was added dropwise at 35-40°C, and the mixture was stirred and crystallized at 35±2°C for 1 h. Then, 332.5 g of water was added dropwise at 25-30°C, and the mixture was stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process was 4.94 times the weight of the substrate). The filter cake was filtered, and 332.5 g of water was first added to wash the filter cake, and then 320.0 g of isopropanol was added to wash the filter cake. The filter cake was dried under reduced pressure to obtain 48.86 g of an off-white solid.

[0062] (4) HPLC test, such as Figure 1 As shown in Table 1 below, the product purity is 99.63%, the isomer content is 0.05%, the single impurity content is 0.05%, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 80.0*(483.49 / 663.76)=58.27 (g), wherein 483.49 is the molecular weight of the product, the content is 99.63%, and the actual yield is calculated to be (48.86 / 58.27)*99.63%=83.5%.

[0063] Table 1: Peak results

[0064] Retention time (RT) District City %area high 1 11.99 2209 0.03 283 2 13.018 3016 0.04 399 3 14.823 7632946 99.63 999608 4 15.901 3580 0.05 321 5 16.610 1131 0.01 157 6 19.033 2817 0.04 601 7 19.321 2589 0.03 463 8 21.091 778 0.01 170 9 21.234 1605 0.02 338 10 22.636 1170 0.02 151 11 22.775 4574 0.06 1073 12 22.866 5142 0.07 1088

[0065] Example 2

[0066] (1) Take a 250 ml three-necked flask and add 35.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of the substrate is 663.76, and the substrate contains a trace amount of methanesulfonic acid, the content of which is negligible), 23 g of lithium bromide, 1.4 g of sodium thiosulfate pentahydrate, and 122.5 g of N,N-dimethylacetamide at room temperature; in terms of molar number, the amount of sodium thiosulfate pentahydrate used is 0.107 times that of the substrate;

[0067] (2) Stir the reaction at 75±2℃ for 26h;

[0068] (3) After the reaction was completed, the temperature was lowered to 35-40°C, 17.5 g of dimethyl sulfoxide and 46.6 g of acetonitrile were added, and the mixture was stirred for 20 min. Then, 27.3 g of water was added dropwise at 35-40°C, and the mixture was stirred and crystallized at 35±2°C for 1 h. Then, 332.5 g of water was added dropwise at 25-30°C, and the mixture was stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process was 10.28 times the weight of the substrate). The filter cake was filtered, and 140.0 g of isopropanol was added to wash the filter cake. The filter cake was dried under reduced pressure to obtain 22.02 g of an off-white solid.

[0069] (4) HPLC test, such as Figure 2 As shown in Table 2 below, the product purity is 98.54%, the single impurity content is 0.95%, the isomer content is 0, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 35.0*(483.49 / 663.76)=25.49 (g), wherein 483.49 is the molecular weight of the product, the content is 98.54%, and the actual yield is calculated to be (22.02 / 25.49)*98.54%=85.1%.

[0070] Table 2: Peak results

[0071] Retention time (RT) District City %area high 1 13.247 6114 0.04 762 2 15.034 14908150 98.54 1792754 3 16.127 144010 0.95 13593 4 16.847 3364 0.02 444 5 19.125 15109 0.10 3336 6 19.449 30599 0.20 5434 7 21.319 3339 0.02 696 8 22.848 10610 0.07 2463 9 22.941 8133 0.05 1732

[0072] Example 3

[0073] (1) Take a 500 ml three-necked flask and, under nitrogen protection, add 20.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of the substrate is 663.76, and a trace amount of methanesulfonic acid is mixed in the substrate, and the content of methanesulfonic acid is negligible), 13.14 g of lithium bromide, 0.38 g of sodium thiosulfate pentahydrate, and 70.0 g of N-methylpyrrolidone at room temperature; in terms of molar number, the amount of sodium thiosulfate pentahydrate used is 0.05 times that of the substrate;

[0074] (2) Stir the reaction at 75±2℃ for 24h;

[0075] (3) After the reaction was completed, the temperature was lowered to 35-40°C, 10.0 g of dimethyl sulfoxide and 26.6 g of acetonitrile were added, and the mixture was stirred for 20 min. Then, 15.6 g of water was added dropwise at 35°C, and the mixture was stirred and crystallized at 35±2°C for 1 h. Then, 83.2 g of water was added dropwise at 25-30°C, and the mixture was stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process was 4.94 times the weight of the substrate). The filter cake was obtained by filtration, and 60.0 g of water was added to wash the filter cake, and then 80.0 g of isopropanol was added to wash the filter cake. The filter cake was dried under reduced pressure to obtain 12.12 g of an off-white solid.

[0076] (4) HPLC test, such as Figure 3 As shown in Table 3 below, the product purity is 99.74%, the single impurity content is 0.11%, the isomer content is 0, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 20.0*(483.49 / 663.76)=14.57 (g), wherein 483.49 is the molecular weight of the product, the content is 99.74%, and the actual yield is calculated to be (12.12 / 14.57)*99.74%=83.0%.

[0077] Table 3: Peak results

[0078] Retention time (RT) District City %area high 1 2.092 2775 0.03 380 2 14.912 8130273 99.74 565359 3 19.377 9346 0.11 938 4 22.862 8748 0.11 819

[0079] Example 4

[0080] (1) Take a 500 ml three-necked flask and, under nitrogen protection, add 20.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of the substrate is 663.76, and a trace amount of methanesulfonic acid is mixed in the substrate, and the content of methanesulfonic acid is negligible), 13.14 g of lithium bromide, 1.87 g of sodium thiosulfate pentahydrate, and 70.0 g of N-methylpyrrolidone at room temperature; in terms of molar number, the amount of sodium thiosulfate pentahydrate used is 0.25 times that of the substrate;

[0081] (2) Stir the reaction at 75±2℃ for 24h;

[0082] (3) After the reaction was completed, the temperature was lowered to 35-40°C, 10.0 g of dimethyl sulfoxide and 26.6 g of acetonitrile were added, and the mixture was stirred for 20 min. Then, 15.6 g of water was added dropwise at 35°C, and the mixture was stirred and crystallized at 35±2°C for 1 h. Then, 83.2 g of water was added dropwise at 25-30°C, and the mixture was stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process was 4.94 times the weight of the substrate). The filter cake was obtained by filtration, and 60.0 g of water was added to wash the filter cake, and then 80.0 g of isopropanol was added to wash the filter cake. The filter cake was dried under reduced pressure to obtain 12.51 g of an off-white solid.

[0083] (4) HPLC test, such as Figure 4 As shown in Table 4 below, the product purity is 99.53%, the single impurity content is 0.16%, the isomer content is 0, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 20.0*(483.49 / 663.76)=14.57 (g), wherein 483.49 is the molecular weight of the product, the content is 99.53%, and the actual yield is calculated to be (12.51 / 14.57)*99.53%=85.5%.

[0084] Table 4: Peak results

[0085] Retention time (RT) District City %area high 1 2.087 2425 0.03 348 2 14.905 8945091 99.53 621988 3 19.091 5580 0.06 809 4 19.372 9770 0.11 976 5 21.242 14575 0.16 1772 6 22.861 9692 0.11 914

[0086] Example 5

[0087] (1) Take a 500 ml three-necked flask and, under nitrogen protection, add 20.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of the substrate is 663.76, and a trace amount of methanesulfonic acid is mixed in the substrate, and the content of methanesulfonic acid is negligible), 13.14 g of lithium bromide, 0.38 g of sodium thiosulfate pentahydrate, and 60.0 g of N,N-dimethylacetamide at room temperature; in terms of molar number, the amount of sodium thiosulfate pentahydrate used is 0.05 times that of the substrate;

[0088] (2) Stir the reaction at 75±2℃ for 24h;

[0089] (3) After the reaction is completed, the temperature is lowered to 35-40°C, 10.0 g of dimethyl sulfoxide and 26.6 g of acetonitrile are added, and the mixture is stirred for 20 min. Then, 15 g of water is added dropwise at 35°C, and the mixture is stirred and crystallized at 35±2°C for 1 h. Then, 65 g of water is added dropwise at 25-30°C, and the mixture is stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process is 4 times the weight of the substrate). The filter cake is filtered, and 60.0 g of water is added to wash the filter cake, and then 80.0 g of isopropanol is added to wash the filter cake. The filter cake is dried under reduced pressure to obtain an off-white solid.

[0090] Example 6

[0091] (1) Take a 500 ml three-necked flask and, under nitrogen protection, add 20.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of the substrate is 663.76, and a trace amount of methanesulfonic acid is mixed in the substrate, and the content of methanesulfonic acid is negligible), 13.14 g of lithium bromide, 0.38 g of sodium thiosulfate pentahydrate, and 80.0 g of N,N-dimethylacetamide at room temperature; in terms of molar number, the amount of sodium thiosulfate pentahydrate used is 0.05 times that of the substrate;

[0092] (2) Stir the reaction at 75±2℃ for 24h;

[0093] (3) After the reaction is completed, the temperature is lowered to 35-40°C, 10.0 g of dimethyl sulfoxide and 26.6 g of acetonitrile are added, and the mixture is stirred for 20 min. Then, 20 g of water is added dropwise at 35°C, and the mixture is stirred at 35±2°C for 1 h to allow crystal growth. Then, 200 g of water is added dropwise at 25-30°C, and the mixture is stirred at 25±2°C for 1 h to allow crystal growth (the total amount of water added during the crystal growth process is 11 times the weight of the substrate). The filter cake is filtered to obtain a filter cake, and 60.0 g of water is added to wash the filter cake, followed by 80.0 g of isopropanol to wash the filter cake. The filter cake is dried under reduced pressure to obtain an off-white solid.

[0094] Comparative Example 1

[0095] This comparative example investigates the effect of not adding sodium thiosulfate pentahydrate on the product; the details are as follows:

[0096] (1) Take a 125 ml three-necked flask and add 20.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (the molecular weight of the substrate is 663.76, and there is a trace amount of methanesulfonic acid mixed in the substrate, and the content of methanesulfonic acid is negligible), 13.14 g of lithium bromide, and 70 g of N,N-dimethylacetyl at room temperature;

[0097] (2) Stir the reaction at 75±2°C for 23.6h;

[0098] (3) After the reaction was completed, the temperature was lowered to 35-40°C, 10 g of dimethyl sulfoxide and 26.6 g of acetonitrile were added, and the mixture was stirred for 20 min. Then, 15.6 g of water was added dropwise at 35-40°C, and the mixture was stirred at 35±2°C for 1 h to allow crystal growth. Then, 190 g of water was added dropwise at 25-30°C, and the mixture was stirred at 25±2°C for 1 h to allow crystal growth (the total amount of water added during the crystal growth process was 10.28 times the weight of the substrate). The filter cake was filtered, and 80 g of isopropanol was added to wash the filter cake. The filter cake was dried under reduced pressure to obtain 12.58 g of an off-white solid.

[0099] (4) HPLC test, such as Figure 5 As shown in Table 5 below, the product purity is 94.63%, the isomer content is 4.96%, the maximum single impurity content is 4.96%, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 20*(483.49 / 663.76)=14.57 (g), wherein 483.49 is the molecular weight of the product, the content is 94.63%, and the actual yield is calculated to be (12.58 / 14.57)*94.63%=81.7%.

[0100] Table 5: Peak results

[0101] Retention time (RT) District City %area high 1 14.736 8628050 94.63 604383 2 15.789 452580 4.96 27070 3 19.027 3648 0.04 644 4 19.128 4385 0.05 762 5 19.265 15311 0.17 1433 6 21.191 8031 0.09 919 7 22.831 5866 0.06 554

[0102] In Comparative Example 1, sodium thiosulfate pentahydrate was not added, resulting in a low purity of the reaction product of only 94.63%, and a significant increase in the isomer content, with the isomer content and the maximum single impurity content reaching 4.96%. In Example 1, after sodium thiosulfate pentahydrate was added, the product purity was significantly increased to 99.63%, and the isomer content was greatly reduced to 0.05%; and in Example 2, after sodium thiosulfate pentahydrate was added, the product purity was significantly increased to 98.54%, and the maximum single impurity content was reduced to 0.95%.

[0103] It can be seen that the addition of sodium thiosulfate pentahydrate in the present invention can effectively reduce the occurrence of isomers and side reactions, and improve the purity of baloxavir acid. The sulfur atoms in the molecules of sodium thiosulfate and its hydrate have a certain affinity with the sulfur atoms in the substrate molecules, and a temporary interaction or coordination is formed between them during the reaction process, so that the reaction is transformed toward the dominant stereoisomer and the expected product is generated, the stereoselectivity of the reaction is improved, and side reactions such as configuration inversion or isomerization of the substrate are reduced, thereby reducing the generation of stereoisomers.

[0104] Comparative Example 2

[0105] This comparative example does not add sodium thiosulfate pentahydrate, but adds anhydrous sodium thiosulfate, as follows:

[0106] (1) Take a 125 ml three-necked flask and add 10.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of substrate is 663.76, and there is a trace amount of methanesulfonic acid in the substrate, the content of methanesulfonic acid is negligible), 6.6 g of lithium bromide, 0.5 g of sodium thiosulfate, and 35 g of N,N-dimethylacetyl at room temperature;

[0107] (2) Stir the reaction at 75±2℃ for 21h;

[0108] (3) After the reaction was completed, the temperature was lowered to 35-40°C, 5 g of dimethyl sulfoxide and 13.3 g of acetonitrile were added, and the mixture was stirred for 20 min. Then, 7.8 g of water was added dropwise at 35-40°C, and the mixture was stirred and crystallized at 35±2°C for 1 h. Then, 95 g of water was added dropwise at 25-30°C, and the mixture was stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process was 10.28 times the weight of the substrate). The filter cake was filtered, and 40 g of isopropanol was added to wash the filter cake. The filter cake was dried under reduced pressure to obtain 4.94 g of an off-white solid.

[0109] (4) HPLC test, such as Figure 6As shown in Table 6 below, the product purity is 98.07%, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 10*(483.49 / 663.76)=7.28 (g), where 483.49 is the molecular weight of the product, the content is 98.07%, the maximum single impurity content is 1.66%, and the actual yield is calculated to be (4.94 / 7.28)*98.07%=67.0%.

[0110] Table 6: Peak results

[0111] Retention time (RT) District City %area high 1 14.641 6294299 98.07 301112 2 18.993 8126 0.13 904 3 19.203 9504 0.15 706 4 21.173 106539 1.66 10052

[0112] In Comparative Example 2, anhydrous sodium thiosulfate was added, and sodium thiosulfate pentahydrate was not added. The product purity was 98.07%, and the maximum single impurity content was 1.66%. Compared with Comparative Example 1 without adding sodium thiosulfate pentahydrate, the product purity increased and the maximum single impurity content decreased, indicating that anhydrous sodium thiosulfate improved the reaction selectivity to a certain extent.

[0113] In Example 1, after adding sodium thiosulfate pentahydrate, the product purity was significantly increased to 99.63%, and the isomer content was greatly reduced to 0.05%; and in Example 2, after adding sodium thiosulfate pentahydrate, the product purity was significantly increased to 98.54%, and the isomer content was reduced to 0.95%.

[0114] It can be seen that compared with adding anhydrous sodium thiosulfate, adding sodium thiosulfate pentahydrate has a better effect. On the one hand, sodium thiosulfate pentahydrate has better solubility than anhydrous sodium thiosulfate, especially in polar solvents such as N,N-dimethylacetamide (DMAc), which enables it to be more evenly dispersed in the reaction system, fully contact with the substrate, and play a more effective role. However, the solubility of anhydrous sodium thiosulfate in DMAc is significantly lower than that of sodium thiosulfate pentahydrate, resulting in uneven dispersion in the reaction system, affecting its effective contact with the substrate. In addition, due to the presence of hydrates in the molecular structure of sodium thiosulfate pentahydrate, the polarity of the reaction solvent is increased, which is beneficial to increase the reaction rate. Compared with the anhydrous form, the pentahydrate can reduce the reaction time and reduce the production of impurities and stereoisomers.

[0115] In summary, adding a small amount of sodium thiosulfate pentahydrate in the preparation process of baloxavir acid can effectively improve the purity of the product, reduce the isomer content, and maintain a high yield, which has obvious advantages. Although anhydrous sodium thiosulfate improves the product quality to a certain extent, there are more substrate residues and the isomer content is still slightly higher, and the overall effect is not as good as sodium thiosulfate pentahydrate.

[0116] Comparative Example 3

[0117] This comparative example adjusts the dosage of sodium thiosulfate pentahydrate, specifically as follows:

[0118] (1) Take a 125 ml three-necked flask and add 10.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of substrate is 663.76, and there is a trace amount of methanesulfonic acid in the substrate, the content of methanesulfonic acid is negligible), 6.6 g of lithium bromide, 0.8 g of sodium thiosulfate pentahydrate, and 35 g of N,N-dimethylacetyl at room temperature;

[0119] (2) Stir the reaction at 75±2℃ for 23.5h;

[0120] (3) After the reaction was completed, the temperature was lowered to 35-40°C, 5 g of dimethyl sulfoxide and 13.3 g of acetonitrile were added, and the mixture was stirred for 20 min. Then, 7.8 g of water was added dropwise at 35-40°C, and the mixture was stirred and crystallized at 35±2°C for 1 h. Then, 95 g of water was added dropwise at 25-30°C, and the mixture was stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process was 10.28 times the weight of the substrate). The filter cake was filtered, and 40 g of isopropanol was added to wash the filter cake. The filter cake was dried under reduced pressure to obtain 5.75 g of an off-white solid.

[0121] (4) HPLC test, such as Figure 7 As shown in Table 7 below, the product purity is 98.83%, the maximum single impurity content is 0.89%, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 10*(483.49 / 663.76)=7.28 (g), where 483.49 is the molecular weight of the product and the content is 98.83%. The actual yield is calculated to be (5.75 / 7.28)*98.83%=78.1%.

[0122] Table 7: Peak results

[0123] Retention time (RT) District City %area high 1 14.799 7474016 98.83 497020 2 19.135 8677 0.11 1335 3 19.292 12723 0.17 1219 4 21.227 67140 0.89 8390

[0124] The amount of sodium thiosulfate pentahydrate used in this comparative example is 0.21 times that of the substrate, and the amount of sodium thiosulfate pentahydrate used in Example 2 is 0.107 times that of the substrate, that is, the amount of sodium thiosulfate pentahydrate used in Comparative Example 3 is higher than that of sodium thiosulfate pentahydrate used in Example 2. In this comparative example, the amount of sodium thiosulfate pentahydrate used is relatively large. Although the isomers are not detected, the maximum single impurity content is 0.89%. It can be seen that excessive addition of sodium thiosulfate pentahydrate will inhibit the dealkylation reaction of lithium bromide, resulting in the inability to completely convert the substrate into the product; in addition, excessive addition of sodium thiosulfate pentahydrate and excessive additive concentration increase the viscosity of the reaction system and affect the reaction rate.

[0125] Therefore, selecting an appropriate amount of sodium thiosulfate pentahydrate can stabilize the reaction intermediates, reduce the generation of stereoisomers, and control the dosage within an appropriate range so that the sodium thiosulfate pentahydrate can play the role of an additive without affecting the normal progress of the reaction.

[0126] Comparative Example 4

[0127] This comparative example does not add sodium thiosulfate pentahydrate, but adds sodium bisulfite, as follows:

[0128] (1) Take a 125 ml three-necked flask and add 20.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (the substrate molecular weight is 663.76, and the substrate is mixed with a trace amount of methanesulfonic acid, the content of methanesulfonic acid is negligible), 13.1 g of lithium bromide, 0.2 g (0.0019 mol) of sodium bisulfite, and 70 g of N,N-dimethylacetyl at room temperature;

[0129] (2) Stir the reaction at 75±2℃ for 18h;

[0130] (3) After the reaction is completed, the temperature is lowered to 35-40°C, 10 g of dimethyl sulfoxide and 26.6 g of acetonitrile are added, and the mixture is stirred for 20 min. Then, 15.6 g of water is added dropwise at 35-40°C, and the mixture is stirred and crystallized at 35±2°C for 1 h. Then, 190 g of water is added dropwise at 25-30°C, and the mixture is stirred and crystallized at 25±2°C for 1 h (the total amount of water added during the crystallization process is 10.28 times the weight of the substrate). The filter cake is filtered, and 400.0 g of water is added to wash the filter cake, and then 40 g of isopropanol is added to wash the filter cake. The filter cake is dried under reduced pressure to obtain 11.27 g of an off-white solid.

[0131] (4) HPLC test, such as Figure 8 As shown in Table 8 below, the product purity is 99.57%, the isomer content is 0.07%, the maximum single impurity content is 0.14%, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyridino[2,1-f][1,2,4]triazine-6,8-dione is 20*(483.49 / 663.76)=14.57 (g), where 483.49 is the molecular weight of the product and the content is 99.57%. The actual yield calculated is (11.27 / 14.57)*99.57%=77.0%.

[0132] Table 8: Peak results

[0133] Retention time (RT) District City %area high 1 14.839 6422357 99.57 496592 2 15.876 4328 0.07 317 3 19.144 7207 0.11 895 4 19.346 9061 0.14 977 5 21.236 3804 0.06 600 6 22.817 3592 0.06 477

[0134] In Comparative Example 4, sodium bisulfite was added, the product purity was 99.57%, the isomer content was 0.07%, the single impurity was 0.14%, and the yield was 77.0%. Compared with Comparative Example 1 without adding sodium thiosulfate pentahydrate, the product purity increased, the isomer content decreased, but the yield was significantly reduced; This shows that sodium bisulfite improves the reaction selectivity to a certain extent, but has a negative impact on the yield.

[0135] Comparative Example 5

[0136] This comparative example investigates the effect of the reaction solvent on the product; the details are as follows:

[0137] (1) Take a 125 ml three-necked flask and add 20.0 g of substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate (molecular weight of substrate is 663.76, and there is a trace amount of methanesulfonic acid in the substrate, the content of which is negligible), 13.1 g of lithium bromide, and 66 g of dimethyl sulfoxide at room temperature;

[0138] (2) Stir the reaction at 80±2℃ for 18h;

[0139] (3) After the reaction is completed, the temperature is lowered to 15-25°C, 200 g of water is added dropwise, and the mixture is stirred at 15-25°C for 1 hour to grow crystals; a filter cake is obtained by filtration, and 40 g of isopropanol is added to wash the filter cake. The filter cake is dried under reduced pressure to obtain 12.1 g of an off-white solid;

[0140] (4) HPLC test, such as Fig. 9 As shown in Table 9 below, the product purity is 24.15%, the maximum single impurity content is 59.13%, and the theoretical yield of the product (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-3,4,12,12a-tetrahydro-7-hydroxy-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is 20*(483.49 / 663.76)=14.57 (g), where 483.49 is the molecular weight of the product and the content is 24.15%. The actual yield is calculated to be (12.1 / 14.57)*24.15%=20%.

[0141] Table 9: Peak results

[0142] Retention time (RT) District City %area high 1 1.653 1075894 11.78 183437 2 12.527 22213 0.24 2201 3 14.884 2206063 24.15 258863 4 15.926 14340 0.16 1161 5 19.109 5402013 59.13 854023 6 21.245 90549 0.99 18067 7 21.480 5119 0.06 402 8 22.189 5680 0.06 887 9 22.631 311676 3.41 64399 10 23.076 2715 0.03 396

[0143] In Comparative Example 1, the reaction solvent used is N,N-dimethylacetamide, while in Comparative Example 5, dimethyl sulfoxide is used as the reaction solvent; when N,N-dimethylacetamide (Comparative Example 1) solvent is used for the reaction, it can provide a higher product purity and a lower isomer content. When dimethyl sulfoxide (DMSO) (Comparative Example 5) solvent is used, the purity of the product is significantly reduced to only 24.15%, and the maximum single impurity reaches 59.13%, indicating that dimethyl sulfoxide causes the decomposition of the product during the reaction. Therefore, DMSO is not suitable as a solvent for this reaction.

[0144] Although the use of DMSO as a reaction solvent leads to a serious decrease in product purity, it has a certain inhibitory effect on the formation of isomers, and the content of isomers is only 0.16%. That is, the sulfur atom in the DMSO molecule may form a certain affinity with the sulfur atom in the substrate molecule, thereby inhibiting the formation of stereoisomers and making the reaction tend to the dominant stereoisomer. Although this mechanism inhibits the formation of isomers, DMSO causes the decomposition of the reactants. Therefore, DMSO is not an ideal solvent for this reaction, but this experiment provides a new perspective: adding a small amount of sulfur-containing substances to the reaction system may help improve the stereoselectivity of the reaction.

[0145] Based on this, the inventors tested adding a small amount of sodium bisulfite (Comparative Example 4) and found that it had a significant effect on reducing isomers. Then, they tested adding a small amount of sodium thiosulfate pentahydrate or sodium thiosulfate, which had a better effect on reducing stereoisomers and a higher yield. Therefore, by adding sodium thiosulfate pentahydrate to the reaction system, the molar ratio of sodium thiosulfate pentahydrate to the substrate (raw material) was 0.107 times, which was the optimal solution (see Example 1), and a high-purity product with a high yield could be obtained.

[0146] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with the present invention can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for preparing baloxavir acid, characterized in that: include: A substrate (12aR)-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiazin-11-yl]-7-(hexyloxy)-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione methanesulfonate, an organic reaction solvent and a dealkylation agent are reacted, wherein the dealkylation agent is a lithium salt, and sodium thiosulfate pentahydrate is added during the reaction to obtain the product; wherein, based on the equivalent of the substance, the amount of sodium thiosulfate pentahydrate added is 0.05-0.25 times that of the substrate, and the reaction equation is as follows: 。 2. The method for preparing baloxavir acid according to claim 1, characterized in that: Calculated on the equivalent of the substance, the amount of sodium thiosulfate pentahydrate added is 0.05-0.107 times that of the substrate.

3. The method for preparing baloxavir acid according to claim 1 or 2, characterized in that: The organic reaction solvent is selected from one or two of N,N-dimethylacetamide and N-methylpyrrolidone.

4. The method for preparing baloxavir acid according to claim 3, characterized in that: The organic reaction solvent is N,N-dimethylacetamide, and the amount of the organic reaction solvent used is 3 to 4 times that of the substrate by weight.

5. The method for preparing baloxavir acid according to claim 1 or 2, characterized in that: The reaction temperature during the reaction is 70-80°C.

6. The method for preparing baloxavir acid according to claim 5, characterized in that: After the reaction is completed, the temperature is lowered to 35-40°C, acetonitrile and dimethyl sulfoxide are added with stirring, and water is then added dropwise with stirring to grow crystals. The amount of water added for crystallization is 4-11 times the amount of the substrate by weight.

7. The method for preparing baloxavir acid according to claim 6, characterized in that: The method of dripping water and stirring to grow crystals includes: first dripping part of water at 35-40° C., stirring to grow crystals, and then dripping the remaining water at 25-30° C., stirring to grow crystals.

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