Method for preparing ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate by chiral separation of a racemic mixture

Abstract

A method for chiral separation of ethyl 3-amino-1-[(3R, 4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (VI) from a racemic mixture (V) of ethyl 3-amino-1-[(3R, 4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate and ethyl 3-amino-1-[(3S, 4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate.

Description

Background Art

[0001] WO 2018 / 108969 discloses compounds of formula I as selective Janus kinase (JAK) inhibitors, and thus can be used to treat JAK-mediated diseases such as atopic dermatitis, arthritis and cancer. Specifically, 1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]-3-[(2-fluoro-6-methoxy-4-pyridinyl)amino]pyrazole-4-carboxamide (I) is disclosed.

[0002]

[0003] In the process of preparing compounds of formula (I), the racemic mixture (5) is subjected to chiral separation to isolate the key intermediate (6).

[0004]

[0005] Since racemic compound 5 has a low solubility in organic solvents commonly used as eluents for chiral chromatography, its separation must be performed by supercritical fluid chromatography using cellulose tris(3,5-dichlorophenylcarbamate) as the chiral stationary phase ( IC, 10 μM, 300×50 mm) and a mobile phase consisting of 45% 2-propanol and 55% CO2; under the following conditions (flow rate: 220 mL / min; column temperature: 38°C).

[0006] WO 2013 / 041042 discloses pyrazole carboxamide as a Janus kinase inhibitor, which can be used to treat rheumatoid arthritis, asthma, chronic obstructive pulmonary disease (COPD) and cancer. The disclosed compound has the following structure.

[0007]

[0008] EP18212188 and PCT / CN2018 / 120821 disclose a method for preparing 1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]-3-[(2-fluoro-6-methoxy-4-pyridinyl)amino]pyrazole-4-carboxamide. The process is summarized in Scheme 1 below.

[0009] Solution 1

[0010]

[0011] It is also disclosed that the separation of the racemic mixture of formula (V) and the enantiomers of formula (VI) is accomplished by HPLC, but the type of chromatographic column used is not disclosed. Summary of the invention

[0012] The inventors have developed a new and advantageous process for the chiral separation of ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (VI) from a racemic mixture of ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate and ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (V).

[0013] One embodiment of the present invention is a method for preparing a compound of formula VI, comprising

[0014]

[0015] The racemic mixture of formula V is separated from the mixture of enantiomers by chiral chromatography using an eluent and a chiral stationary phase selected from amylose tris(3-chloro-4-methylphenylcarbamate) or amylose tris(3-chloro-5-methylphenylcarbamate).

[0016]

[0017] The advantage of the method claimed in the present invention is the high productivity and high selectivity of effectively separating enantiomers. The method for preparing a single enantiomer generally involves the chiral separation of racemic compounds or the selective reaction of enantiomers. For methods requiring chiral separation, the earlier the chiral separation is completed in the preparation process, the better. Since the subsequent steps no longer bring in unwanted enantiomers for reaction, this will improve efficiency. In order to be truly effective, the method must be highly selective when separating two enantiomers. In addition, the method must also have a sufficiently high throughput or productivity, and can produce enough desired enantiomers within a reasonable time and at an affordable cost. In the method disclosed in WO2018 / / 108969 (see above), the chiral separation of similar intermediates can only achieve a productivity of less than 0.5KKD, which determines that the above-mentioned whole process of preparing the compound of formula (I) is not suitable for large-scale production.

[0018] 3-Amino-1-[(3R, 4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylic acid ethyl ester (VI) is a key intermediate for the synthesis of 1-[(3R, 4S)-4-cyanotetrahydropyran-3-yl]-3-[(2-fluoro-6-methoxy-4-pyridinyl)amino]pyrazole-4-carboxamide (I). As mentioned above, EP18212188 and PCT / CN2018 / 120821 disclose the separation of a racemic mixture of formula V into enantiomeric compounds of formula VI by using HPLC. Please refer to Scheme 2 below.

[0019] Scenario 2:

[0020]

[0021] An efficient method for chiral separation of ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (VI) from a racemic mixture of ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate and ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (V) is desired. This method allows the subsequent steps in Scheme 1 above to proceed using pure enantiomers, thereby resulting in higher step yields and overall yields. Initially, the reaction of compounds (IV) and (III) produces a mixture of four diastereomers. In addition to the (3R, 4S) and (3S, 4R) enantiomers present in the above enantiomeric mixture (V), two pairs of (3R, 4R) and (3S, 4S) enantiomers are also produced. However, the latter two enantiomers can be effectively separated from (V) by selective recrystallization.

[0022] IG is amylose tris(3-chloro-5-methylphenylcarbamate) immobilized on 3 μm silica gel.

[0023] AZ is amylose tris(3-chloro-4-methylphenylcarbamate) coated on 3 or 5 μm silica gel.

[0024] Chiral stationary phases (CSPs) are polysaccharide-derivatized silica-based materials modified with chiral selective agents designed to separate mixtures of enantiomeric compounds. CSPs are also known as chiral separation media.

[0025] The coated polysaccharide-derivatized chiral stationary phase has no covalent bonding of the polysaccharide to the underlying silica.

[0026] Immobilized polysaccharide derivatized chiral stationary phases have polysaccharides covalently linked to underlying silica.

[0027] The efficiency of a chiral separation process can be judged by the degree of separation achieved between the enantiomers of the racemate and by the productivity, which is measured as the mass of racemate processed per 24 hours / mass of chiral stationary phase used.

[0028] The productivity (KKD) is the amount of kilograms of racemate that can be separated per kilogram of chiral stationary phase (CSP) per day.

[0029] Selectivity (α) is the ratio of the retention factors of the two UV signals of the two enantiomers as shown in Formula 1. It can be considered as the distance between the vertices of the two UV signals.

[0030] Formula 1:

[0031]

[0032] Among them, T E2 is the retention time of the second eluting enantiomer, T E1 is the retention time of the first eluting isomer and T0 is the time taken for the mobile phase to pass through the column.

[0033] Baseline separation means that the process is selective enough so that in the UV chromatogram, the UV signal corresponding to the first component tails off to the baseline before the UV signal for the next component begins to show up.

[0034] The eluent is the mobile phase used to perform chromatography.

[0035] Chirality refers to the fact that a molecule is not superimposable on its mirror image.

[0036] An enantiomer is one of two non-superimposable mirror images. The Cahn-Ingold-Prelog system is used to define each enantiomer. The chiral center of a molecule is defined as either R or S, depending on the structure of the group attached to the chiral center. Each of the four groups on the asymmetric carbon atom (chiral center) is arranged according to a series of priority rules. When the molecule is fixed, the group with the lowest order is placed farthest from the observer, and the remaining groups are arranged in descending order of priority. If the order proceeds clockwise, the chiral center is designated as R. If the order proceeds counterclockwise, the chiral center is designated as S. (See March, Advanced Organic Chemistry, 3rd edition, 1985, page 97).

[0037] Enantiomeric excess (ee) or enantiomeric purity is an indication of the degree of enantiomeric purity in a composition, expressed as a percentage, as shown in Formula 2,

[0038] Formula 2:

[0039]

[0040] The term "ethyl 3-amino-1-[(3R,4S)-4-cyanotrihydropyran-3-yl]pyrazole-4-carboxylate (VI), substantially free of ethyl 3-amino-1-[(3S,4R)-4-cyanotrihydropyran-3-yl]pyrazole-4-carboxylate" refers to a composition comprising at least about 80% ee of compound (VI). Preferably, the composition comprises at least about 90% ee of compound (VI), more preferably, the composition comprises at least about 95% ee of compound (VI), and most preferably, the composition comprises greater than 98% ee of compound (VI).

[0041] SFC refers to supercritical fluid chromatography.

[0042] SMB refers to simulated moving bed chromatography.

[0043] A racemate or racemic mixture refers to a mixture having equal amounts of the enantiomers of the levorotatory and dextrorotatory (R and S) chiral molecules.

[0044] Another embodiment of the present invention is a method for isolating ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (VI) substantially free of ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate, the method comprising

[0045] a) adsorbing a racemic mixture (V) containing ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate and ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate onto a chiral separation medium;

[0046] b) passing the solvent system through a chiral separation medium in an amount sufficient to elute the enantiomer of ethyl 3-amino-1-[4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate from the separation medium;

[0047] c) isolating ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (VI) substantially free of ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate;

[0048] Wherein, the chiral separation medium is amylose tris(3-chloro-5-methylphenylcarbamate) fixed on silica gel or amylose tris(3-chloro-4-methylphenylcarbamate) coated on silica gel.

[0049] In another embodiment of the present invention, the chiral stationary phase is selected from amylose tris(3-chloro-4-methylphenylcarbamate), amylose tris(5-chloro-2-methylphenylcarbamate), amylose tris(3,5-dimethylphenylcarbamate) and amylose tris(3-chloro-5-methylphenylcarbamate).

[0050] In one embodiment, the chiral stationary phase is coated or immobilized on silica gel.

[0051] In another embodiment of the present invention, the chiral stationary phase is amylose tris(3-chloro-5-methylphenylcarbamate) immobilized on silica gel.

[0052] In another embodiment of the present invention, the chromatography column is amylose tris(3-chloro-4-methylphenylcarbamate) coated on silica gel.

[0053] In another embodiment of the present invention, the eluent is acetonitrile. In another embodiment of the present invention, the productivity of the method is greater than 2.0 KKD.

[0054] In another embodiment of the present invention, the productivity of the process is in the range of about 2.0 to about 6.0 KKD, preferably, in the range of about 3.0 to about 5.0 KKD.

[0055] In another embodiment of the present invention, the selectivity of the process is in the range of about 1.0 to about 4.0, preferably, in the range of about 1.5 to about 3.5.

[0056] In another embodiment of the present invention, the temperature is between about 20°C and about 40°C, preferably, between about 25°C and about 35°C.

[0057] In another embodiment of the present invention, the concentration of the racemate (V) is about 100 g / L to about 300 g / L, preferably, about 200 g / L. DETAILED DESCRIPTION

[0058] Example 1 Solubility of Compound (V) in Organic Solvents

[0059] The solubility of compound (V) in water and in a group of organic solvents was determined. The results are shown in Table 1.

[0060]

[0061] Surprisingly, it was found that compound (V) is highly soluble in acetonitrile, which is one of the solvents of choice for chromatographic separation.

[0062] Example 2: Chiral stationary phase screening

[0063] A set of chiral stationary phase separation effect tests were conducted, using acetonitrile as a solvent to dilute the sample and as an eluent (or mobile phase) for chromatographic separation, to test the effect of chiral separation of 3-amino-1-[(3R, 4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylic acid ethyl ester (VI) from a racemic mixture (V) of 3-amino-1-[(3S, 4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylic acid ethyl ester. The results are shown in Table 2 below.

[0064] The operating conditions for this test are shown in Table 2 below;

[0065] Table 2 Stationary Phase See Table 2 Column size (ID x Length) 4.6x250nm Mobile phase Acetonitrile Flow rate 1mL / min UV detection wavelength λ 220nm Column temperature 25℃ Sample temperature Room temperature Sample solvent Acetonitrile Sample concentration 2g / L

[0066] Table 3

[0067]

[0068]

[0069] The results shown in Table 3 show that only less than half of the chiral stationary phases tested can achieve a certain degree of separation of the racemic mixture (V). Among the chromatographic columns that can separate (V), only two chromatographic columns can achieve baseline separation of (V), namely, amylose tris (3-chloro-5-methylphenylcarbamate) column fixed on silica gel ( IG) and amylose tris(3-chloro-4-methylphenylcarbamate) column coated on silica gel ( AZ).

[0070] Example 3 - Productivity

[0071] 20 mg of the racemic mixture (V) was dissolved in acetonitrile at a concentration of 200 g / L. The solution was injected into a column of amylose tris(3-chloro-5-methylphenylcarbamate) immobilized on silica gel ( IG) (250 x 4.6 mm). The sample was eluted with acetonitrile at 25°C to give both enantiomers. The productivity (KKD) was estimated to be 3.0 to 3.5 kg racemate / kg chiral stationary phase / day.

[0072] 20 mg of the racemic mixture (V) was dissolved in acetonitrile at a concentration of 200 g / L. The solution was injected onto a column of amylose tris(3-chloro-4-methylphenylcarbamate) coated on silica gel ( AZ) (250 x 4.6 mm). After elution with acetonitrile at 25°C, two enantiomers were obtained. The productivity (KKD) was estimated to be 4.0 to 5.0 kg racemate / kg chiral stationary phase / day.

Claims

1. A process for preparing a compound of formula VI from a mixture of enantiomers, comprising separating the enantiomers of the racemic mixture of formula V by chiral chromatography using an eluent and a chiral stationary phase, The chiral stationary phase is selected from amylose tris(3-chloro-4-methylphenylcarbamate) or amylose tris(3-chloro-5-methylphenylcarbamate); The eluent is acetonitrile.

2. The method according to claim 1, wherein: The productivity of the method is greater than 2.0 KKD; KKD is the amount of kilograms of racemate that can be separated per kilogram of chiral stationary phase per day.

3. The method according to any one of claims 1 to 2, wherein: The chiral stationary phase is amylose tris(3-chloro-5-methylphenylcarbamate) fixed on silica gel.

4. The method according to any one of claims 1 to 2, wherein: The chiral stationary phase is amylose tris(3-chloro-4-methylphenylcarbamate) coated on silica gel.

5. The method according to any one of claims 1 to 2, wherein: The productivity of the process is in the range of 2.0 to 6.0 KKD; KKD is the amount of kilograms of racemate separable per kilogram of chiral stationary phase per day.

6. The method according to claim 5, wherein: The productivity of the process is in the range of 3.0 to 5.0 KKD; KKD is the amount of kilograms of racemate separable per kilogram of chiral stationary phase per day.

7. The method according to any one of claims 1 to 2, wherein: The selectivity of the process ranges from 1.0 to 4.

0.

8. The method according to claim 7, wherein: The selectivity of the process is in the range of 1.5 to 3.

5.

9. The method according to any one of claims 1 to 2, wherein: The process is carried out at a temperature of 20°C to 40°C.

10. The method according to claim 9, wherein: The process is carried out at a temperature of 25°C to 35°C.

11. The method according to any one of claims 1 to 2, wherein: The concentration of the racemic mixture (V) in the method is 100 g / L to 300 g / L.

12. The method according to claim 11, wherein: The concentration of the racemic mixture (V) in the method is 200 g / L.

13. A method for separating ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (VI) free of ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate, the method comprising: a) adsorbing a racemic mixture (V) containing ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate and ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate onto the chiral separation medium; b) passing the solvent system through the chiral separation medium in an amount sufficient to elute the enantiomer of ethyl 3-amino-1-[4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate from the separation medium; c) separating ethyl 3-amino-1-[(3R,4S)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate (VI) free of ethyl 3-amino-1-[(3S,4R)-4-cyanotetrahydropyran-3-yl]pyrazole-4-carboxylate; Wherein, the chiral separation medium is amylose tris(3-chloro-5-methylphenylcarbamate) fixed on silica gel or amylose tris(3-chloro-4-methylphenylcarbamate) coated on silica gel; The eluent is acetonitrile.

14. The method according to claim 13, wherein: The chiral separation medium is amylose tris(3-chloro-5-methylphenylcarbamate) fixed on silica gel.

15. The method according to claim 13, wherein: The chiral separation medium is amylose tris(3-chloro-4-methylphenylcarbamate) coated on silica gel.

16. The method according to any one of claims 13 to 15, wherein: The productivity of the process is in the range of 2.0 to 6.0 KKD; KKD is the amount of kilograms of racemate separable per kilogram of chiral stationary phase per day.

17. The method according to claim 16, wherein: The productivity of the process is in the range of 3.0 to 5.0 KKD; KKD is the amount of kilograms of racemate separable per kilogram of chiral stationary phase per day.

18. The method of any one of claims 13-15, wherein the selectivity of the method is in the range of 1.0 to 4.

0.

19. The method of claim 18, wherein the selectivity of the method is in the range of 1.5 to 3.

5.

20. The method according to any one of claims 13 to 15, wherein: The temperature is between 20°C and 40°C.

21. The method according to claim 20, wherein: The temperature is between 25°C and 35°C.

22. The method according to any one of claims 13 to 15, wherein: The concentration of the racemic mixture (V) is 100 g / L to 300 g / L.

23. The method according to claim 22, wherein: The concentration of the racemic mixture (V) was 200 g / L.

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