Methods for preparing intermediates for the synthesis of sphingosine-1-phosphate receptor agonists

Abstract

This invention relates to a novel method for preparing compounds of chemical formula 2 as described in this specification, which can be effectively used to synthesize sphingosine-1-phosphate receptor agonists.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0048764, filed on April 14, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for preparing a key intermediate for the synthesis of sphingosine-1-phosphate receptor agonists. Background Technology

[0004] Sphingosine-1-phosphate (S1P) is produced via the intracellular ceramide pathway, the initiating substance of which is generated through two pathways: de novo biosynthesis and degradation of sphingomyelin, a cell membrane component. S1P levels in various tissues are controlled by two biosynthetic sphingosine kinases (SphK) and two biodegradable S1P phosphatases (S1P-lysozyme and lysophospholipid phosphatase). S1P, produced by sphingosine phosphorylation induced by sphingosine kinase, is known to mediate various cellular responses, such as cell proliferation, cytoskeleton organization and migration, adhesion and tight junction assembly, and morphogenesis. S1P exists in high concentrations (100–1000 nM) in plasma in combination with other plasma proteins (including albumin), but in low concentrations in tissues.

[0005] S1P binds to the G protein-coupled receptor S1P and exhibits different biological functions. To date, five S1P receptor subtypes have been identified, namely S1P1 to S1P5, which are named endothelial differentiation gene (EDG) receptors 1, 5, 3, 6, and 8. These S1P receptors are known to participate in a variety of biological functions, such as leukocyte recirculation, nerve cell proliferation, morphological changes, migration, endothelial function, vascular regulation, and cardiovascular development.

[0006] In recent years, numerous studies have revealed the crucial role of S1P signaling processes via these receptors in a range of responses associated with multiple sclerosis (MS), including inflammatory responses and repair processes. In fact, non-selective S1P1 agonists have recently been approved as therapeutic agents for MS. S1P receptors are widely expressed in many cells associated with MS. In particular, S1P1 receptors play a vital role in the immune system. S1P1 receptors are primarily expressed on the surface of lymphocytes such as T cells and B cells and respond to S1P, thereby participating in lymphocyte recirculation. Under normal conditions, the concentration of S1P in body fluids is higher than in lymphoid tissues; therefore, this concentration difference leads to lymphocytes leaving the lymphoid tissues and circulating along the efferent lymphatic system. However, if S1P1 receptors in lymphocytes are downregulated by S1P1 agonists, lymphocyte outflow from lymphoid tissues is prevented, thus reducing the infiltration of self-invasive lymphocytes that cause inflammation and tissue damage in the central nervous system (CNS). This leads to therapeutic effects against MS. Fingolimod, a nonselective S1P1 agonist, has been approved as an oral medication for the treatment of multiple sclerosis. When it binds to and is activated by the S1P1 receptor, the receptor is either degraded or internalized from the surface of lymphocytes. Thus, anomalously, fingolimod acts as a functional S1P1 antagonist.

[0007] Regarding S1P receptor agonists, Korean Patent Publication No. 10-2014-0104376 discloses a novel compound of Formula 1 as an effective S1P receptor agonist.

[0008] [Formula 1]

[0009]

[0010] In Equation 1,

[0011] X is C or N.

[0012] R1 is H or a substituted alkyl group.

[0013] R2 can be H, a substituted alkyl group, a halogen, CN, CF3, or COCF3.

[0014] W can be C, N, C-alkoxy, C-halogen, or C-CN.

[0015] Q is CH2O or ,

[0016] S is selected from the following residues:

[0017] , , ,

[0018] , ,

[0019] , ,

[0020] , , ,

[0021] , ,

[0022] , ,

[0023] , ,

[0024] and .

[0025] In the above structure,

[0026] m and n are 0, 1, 2, or 3.

[0027] R3 to R10 are each H, alkyl, halogen, haloalkyl, or alkoxyalkyl.

[0028] R11 is H, ,

[0029] R12 is OH or NH2. or .

[0030] In one specific embodiment of the document, the preparation of 1-[1-chloro-6-(3-chloro-1-isopropyl-1H-indazol-5-ylmethoxy)-3,4-dihydro-naphth-2-ylmethyl]-piperidine-4-carboxylic acid by the following reaction 1 (in reaction 1, "SG35" refers to "1-chloro-6-hydroxy-3,4-dihydro-naphth-2-carboxaldehyde").

[0031] [Reaction 1]

[0032]

[0033] In reaction 1, the steps for preparing 1-chloro-6-(3-chloro-1-isopropyl-1H-indazole-5-ylmethoxy)-3,4-dihydro-naphthalene-2-carboxaldehyde are now described in detail.

[0034] (1-1) Synthesis of (3-chloro-1-isopropyl-1H-indazol-5-yl)-methanol

[0035] 1H-indazole-5-carboxylate was dissolved in dimethylformamide, and iodoisopropane and sodium hydride were slowly added dropwise at 0°C, followed by stirring at 50°C for 8 hours. A 1 N hydrochloric acid solution was added, and the mixture was extracted with ethyl acetate. The product was washed with brine, dried over anhydrous magnesium sulfate, and filtered. The filtrate was distilled under reduced pressure. The product was separated by column chromatography to obtain 1-isopropyl-1H-indazole-5-carboxylate.

[0036] The methyl 1-isopropyl-1H-indazole-5-carboxylate thus obtained was dissolved in dimethylformamide, and N-chlorosuccinimide (NCS) was added dropwise, followed by stirring at room temperature for 18 hours. Water was added, and the mixture was extracted with ethyl acetate. The product was washed with brine, dried over anhydrous magnesium sulfate, and filtered. The filtrate was distilled under reduced pressure. The residue was separated by column chromatography to give methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate.

[0037] The methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate thus obtained was dissolved in tetrahydrofuran, and lithium aluminum borohydride was added dropwise. After stirring at room temperature for 1 hour, water, 6 N sodium hydroxide aqueous solution, and water were added sequentially. Diatomaceous earth was added dropwise, and the mixture was filtered. The filtrate was distilled under reduced pressure. The residue was separated by column chromatography to give (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol.

[0038] (1-2) Synthesis of 1-chloro-6-hydroxy-3,4-dihydro-naphthalene-2-carboxaldehyde

[0039] First, N,N-dimethylformamide (DMF) and phosphorus oxychloride (POCl3) were added dropwise to a solution of 6-methoxy-3,4-dihydronaphth-1(2H)-one dissolved in toluene at 0 °C, followed by stirring at 70 °C for 6 hours. The reaction mixture was poured onto ice and then extracted with ethyl acetate. The organic layer was washed with brine, dried, and concentrated. The residue thus obtained was purified by silica gel column chromatography (hexane:ethyl acetate = 20:1 to 10:1) to give 1-chloro-6-methoxy-3,4-dihydro-2-naphthaldehyde.

[0040] Then, aluminum chloride (AlCl3) was added to a solution of 1-chloro-6-methoxy-3,4-dihydro-2-naphthaldehyde dissolved in dichloromethane at 0°C, and the mixture was stirred at 50°C for 6 hours. The reaction mixture was poured onto ice and extracted with ethyl acetate. The organic layer was dried and concentrated, and the residue thus obtained was purified by silica gel column chromatography (hexane:tetrahydrofuran = 5:1 to 3:1) to give 1-chloro-6-hydroxy-3,4-dihydro-2-naphthaldehyde.

[0041] (1-3) 1-Chloro-6-(3-chloro-1-isopropyl-1H-indazol-5-ylmethoxy)-3,4-dihydro-naphthalene-2-carboxaldehyde synthesis

[0042] The (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol and 1-chloro-6-hydroxy-3,4-dihydro-2-naphthaldehyde obtained above were dissolved in toluene, and then tributylphosphine (PBu3) and 1,1'-(azodicarbonyl)piperidine (ADD) were added dropwise. After stirring at room temperature for 18 hours, excess hexane was added. After filtration and vacuum distillation, the residue was purified by column chromatography to give 1-chloro-6-(3-chloro-1-isopropyl-1H-indazole-5-ylmethoxy)-3,4-dihydro-naphthaldehyde.

[0043] However, the above reactions may present the following problems when producing clinical APIs.

[0044] First, during the synthesis of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate, there may be issues with the production ratio of the N2 isomer. A drawback of using lithium aluminum hydride (LAH) for the synthesis of (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol is its very limited stability and susceptibility to water decomposition when used in large-scale synthesis.

[0045] Furthermore, the Vilsmeier-Haack reaction for obtaining 1-chloro-6-methoxy-3,4-dihydro-2-naphthaldehyde may present exothermic issues due to the high temperature of 70°C. Additionally, the reaction for obtaining 1-chloro-6-hydroxy-3,4-dihydro-2-naphthaldehyde may present reactor contamination issues due to the use of AlCl3 or stability issues due to the use of hazardous reagents. If AlCl3 is used, stability issues arise due to batch failures caused by reaction termination or side reaction progression, and the overall yield is 70%, thus requiring an increase in yield.

[0046] Furthermore, 1,1'-(azodicarbonyl)piperidine (ADD) for the coupling of (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol with 1-chloro-6-hydroxy-3,4-dihydro-naphthalene-2-carboxaldehyde is not preferred in terms of low yield and cost.

[0047] Therefore, the inventors of this invention have invented a new synthetic method, as shown in reaction 2 below, for the large-scale production of intermediate compounds such as 1-chloro-6-(3-chloro-1-isopropyl-1H-indazole-5-ylmethoxy)-3,4-dihydro-naphthalene-2-carboxaldehyde in high yields by a simpler method.

[0048] [Reaction 2]

[0049]

[0050] In reaction 2 above, the steps for preparing 1-chloro-6-(3-chloro-1-isopropyl-1H-indazole-6-ylmethoxy)-3,4-dihydro-naphth-2-carboxaldehyde are described in more detail below (in reaction 2, "SG26" refers to "6-hydroxy-3,4-dihydro-2H-naphth-1-one").

[0051] (2-1) Synthesis of 5-bromomethyl-3-chloro-1-isopropyl-1H-indazole

[0052] Dichloromethane (DCM), methyl tert-butyl ether (MTBE), and (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol were injected into the reactor, and the internal temperature was cooled to 0°C. PBr3 was slowly added dropwise to the reaction mixture over 70 minutes, and the reaction proceeded for 80 minutes. Ion-pair chromatography (IPC) was performed by HPLC. After the reaction was complete (3% > (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol), sodium hydroxide was slowly injected over 120 minutes to terminate the reaction. DCM was injected into the reaction mixture, and the mixture was stirred for 30 minutes. Layer separation was performed, and the aqueous layer was removed. The organic layer was washed with water and distilled under reduced pressure to obtain 5-bromomethyl-3-chloro-1-isopropyl-1H-indazole.

[0053] (2-2) Synthesis of 6-hydroxy-3,4-dihydro-2H-naphth-1-one

[0054] HBr dissolved in water and 6-methoxy-3,4-dihydro-2H-naphth-1-one were injected into the reactor, and the mixture was refluxed at an external temperature of 120 °C for 52 hours. The reaction was completed by IPC using HPLC (3% > 6-methoxy-3,4-dihydro-2H-naphth-1-one). The internal temperature was lowered to 10 °C, and the resulting solid was filtered. After washing with water and drying under nitrogen, 6-hydroxy-3,4-dihydro-2H-naphth-1-one (SG26) was obtained.

[0055] (2-3) Synthesis of 6-(3-chloro-1-isopropyl-1H-indazol-5-ylmethoxy)-3,4-dihydro-2H-naphth-1-one

[0056] 5-Bromomethyl-3-chloro-1-isopropyl-1H-indazole, 6-hydroxy-3,4-dihydro-2H-naphthyl-1-one, K₂CO₃, and DMF were injected into a reactor, and the reaction was carried out at an internal temperature of 25°C for 3 hours. IPC using HPLC revealed a residual 5% of 6-hydroxy-3,4-dihydro-2H-naphthyl-1-one. Therefore, an additional 5-bromomethyl-3-chloro-1-isopropyl-1H-indazole was injected to complete the reaction (1% > 6-hydroxy-3,4-dihydro-2H-naphthyl-1-one). Water was added to the reactor, and the internal temperature was lowered to 0°C. The resulting solid was then filtered off. The filtered solid was washed sequentially with water and MTBE, and then dried under nitrogen to give 6-(3-chloro-1-isopropyl-1H-indazole-5-ylmethoxy)-3,4-dihydro-2H-naphthyl-1-one.

[0057] (2-4) 1-Chloro-6-(3-chloro-1-isopropyl-1H-indazol-6-ylmethoxy)-3,4-dihydro-naphthalene-2-carboxaldehyde synthesis

[0058] Phosphoryl chloride (POCl3) was injected into the reactor, and the internal temperature was lowered to 0°C. DMF was slowly added dropwise, and the mixture was stirred at an internal temperature of 50°C for 2 hours. 6-(3-chloro-1-isopropyl-1H-indazole-5-ylmethoxy)-3,4-dihydro-2H-naphth-1-one was then injected, and the reaction was carried out at an internal temperature of 50°C for 3 hours. Excess HCl gas may be generated during the reaction; a vent line was installed so that excess HCl gas could be neutralized by a NaOH trap. IPC was performed using HPLC to complete the reaction. The internal temperature was lowered to 0°C, and then cold water, hexane (Hex), and MTBE were injected into another reactor. The above reaction mixture was slowly added dropwise to this reactor over 90 minutes to form crystals. The resulting solid was filtered off, washed sequentially with water and an MTBE / HEX mixed solvent, and dried to give 1-chloro-6-(3-chloro-1-isopropyl-1H-indazole-6-ylmethoxy)-3,4-dihydro-naphth-2-carboxaldehyde.

[0059] Based on the above reaction, the heat generation problem caused by the Wilsmayer-Hacker reaction can be solved, while the yield of N2 isomers can be increased. Furthermore, the coupling reaction can be carried out without the use of ADD. Therefore, it is expected to achieve mass production through a simpler process, while ensuring the stability of the compound and the stability of the preparation conditions for the key intermediate used in the synthesis of sphingosine-1-phosphate receptor agonists. Summary of the Invention

[0060] Technical issues

[0061] Therefore, an objective of the present invention is to provide a suitable method for producing the compound of formula 2, which is a key intermediate for a novel high-yield synthetic method for excellent sphingosine-1-phosphate receptor agonists.

[0062] [Equation 2]

[0063]

[0064] In Equation 2,

[0065] R1 is hydrogen, or a substituted or unsubstituted alkyl group.

[0066] R2 is hydrogen, substituted or unsubstituted alkyl, halogen, CN, CF3, or COCF3.

[0067] X is C or N, and

[0068] L represents a leaving group.

[0069] Technical solution

[0070] In order to achieve the above goals,

[0071] According to one aspect of the present invention, a method for preparing an intermediate compound of formula 2 is provided, the method comprising the step of replacing an alcohol group of a compound of formula 3 with a leaving group in the presence of a single ether solvent.

[0072] [Equation 2]

[0073]

[0074] [Formula 3]

[0075]

[0076] In equations 2 and 3,

[0077] R1 is hydrogen, or a substituted or unsubstituted alkyl group.

[0078] R2 is hydrogen, substituted or unsubstituted alkyl, halogen, CN, CF3, or COCF3.

[0079] X is C or N, and

[0080] L represents a leaving group.

[0081] When the "alkyl" is substituted, the substituent in the alkyl group can be one or more, and the substituent can be selected independently from halogen, cyano, hydroxy, alkoxy, ketone, unsubstituted sulfonyl and alkyl-substituted sulfonyl.

[0082] According to one embodiment of the present invention, R1 in the above formula may be hydrogen or a C1-C6 substituted or unsubstituted alkyl group, and R2 may be hydrogen, a C1-C6 substituted or unsubstituted alkyl group, a halogen, CN, CF3 or COCF3.

[0083] According to another embodiment of the present invention, R1 may be a C1-C4 substituted or unsubstituted alkyl group, and R2 may be a halogen (F, Cl, Br or I).

[0084] According to one embodiment of the present invention, the leaving group (L) is a reactive group that provides a substitution position for the compound of formula 2 during the substitution reaction of the compound of formula 2 with an alcohol compound, and may be selected from, but not limited to, chlorine (Cl), bromine (Br), iodine (I), methanesulfonate (Oms), p-toluenesulfonate (OTs) and trifluoromethanesulfonate (OTf).

[0085] According to another embodiment of the present invention, L can be Br.

[0086] The present invention provides a compound of formula 2, which is a key intermediate in the synthesis of sphingosine-1-phosphate receptor agonists by replacing the terminal alcohol group of a compound of formula 3 with a leaving group. In particular, a technical feature is that the production ratio of N2 isomers is significantly reduced by performing the "leaving group substitution step" (hereinafter referred to as the "leaving group substitution step") in a single ether solvent.

[0087] In this invention, "single solvent" means that only one type of solvent is included in the reactor for the leaving group substitution reaction. In this case, it is not excluded that the single solvent includes a small amount of heterogeneous solvent that does not substantially affect the yield of the reaction product in the reactor for the leaving group substitution reaction. For example, the inclusion of heterogeneous solvent in amounts of 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, or 0% (i.e., not included at all) based on the total volume of the solvent used for the leaving group substitution reaction can be considered as the use of a single solvent.

[0088] Ether solvents may include, for example, but not limited to, dialkyl ether solvents such as diethyl ether, dipropyl ether, dibutyl ether, diisopentyl ether, ethyl methyl ether, methyl propyl ether, methyl butyl ether and ethyl propyl ether; arylalkyl ether solvents such as diphenyl ether and anisole; or cyclic ether solvents such as tetrahydrofuran and tetrahydropyran.

[0089] In one embodiment of the present invention, the ether-based single solvent may be methyl tert-butyl ether (MTBE).

[0090] In another embodiment of the invention, the compound of formula 2 can be obtained by mixing the compound of formula 3 with MTBE, cooling to 0°C, and then reacting with PBr3.

[0091] In another embodiment of the invention, after the reaction is completed by mixing the compound of formula 3 with MTBE, cooling to 0°C and reacting with PBr3, the mixture can be washed with water and filtered to obtain the compound of formula 2.

[0092] According to another aspect of the invention, the compound of formula 3 can be prepared by a method comprising the following steps:

[0093] 1) The step of introducing substituents R1 and R2 into the compound of formula 4 and crystallizing it in a crystallization solvent including an alcohol solvent to obtain the compound of formula 5; and

[0094] 2) The step of reacting the compound of formula 5 with a reducing agent to obtain the compound of formula 3:

[0095] [Formula 4]

[0096]

[0097] [Formula 5]

[0098]

[0099] In equations 4 and 5,

[0100] R1, R2, and X are the same as those defined in Equation 2 or Equation 3.

[0101] R3 is a C1-C6 substituted or unsubstituted alkyl group.

[0102] According to one embodiment of the present invention, R3 can be a C1-C4 substituted or unsubstituted alkyl group.

[0103] According to another embodiment of the present invention, R3 may be a methyl group.

[0104] In step 1) above, substituents R1 and R2 are introduced into the compound of formula 4, and the compound of formula 5 is prepared by crystallization in a crystallization solvent containing an alcohol solvent.

[0105] The alcohol solvent used for crystallization can be, for example, but not limited to, one or more solvents selected from methanol, ethanol, isopropanol and butanol.

[0106] In one embodiment of the invention, the crystallization solvent may be a mixture of an alcohol solvent and water. By using a mixture of an alcohol solvent and water as the crystallization solvent, the yield of the N2 isomer can be reduced.

[0107] In another embodiment of the invention, given the yield of Formula 5, the mixed solvent for crystallization can be an alcohol solvent and water in a volume ratio of 5:1 to 1:5, 4:1 to 1:4, 3:1 to 1:3, 2:1 to 1:2, 2:1 to 1:1 or 1.5:1 to 1:1.

[0108] In one embodiment of the invention, the crystallization solvent may be a mixture of ethanol and water. In particular, ethanol and water with an ETOH:H2O volume ratio of 2:1 to 1:2, 2:1 to 1:1, 1.5:1 to 1:1, or 1:1 may be used.

[0109] In another embodiment of the invention, if the crystallization solvent is a mixture of alcohol and water, the alcohol and water can be injected sequentially or simultaneously to carry out crystallization.

[0110] In another embodiment of the invention, the compound of formula 5 can be obtained by injecting an alcohol solvent, such as EtOH, into the reaction product in which the substituent is introduced, cooling it to 0°C to 20°C, and then injecting water to crystallize it.

[0111] In another embodiment of the invention, crystallization can be carried out after purification of the reaction product containing the substituents. Purification of the reaction product removes unreacted residual compounds used in the reaction, thereby improving the crystallization yield.

[0112] Purification can be carried out using, for example, a polar solvent, such as a polar organic solvent, water, or a mixture thereof.

[0113] The polar organic solvent may be, for example, but not limited to, one or more solvents selected from ethyl acetate, hexane, and dichloromethane.

[0114] In another embodiment of the invention, the compound of formula 5 can be obtained by purifying the reaction product with the introduced substituent using a mixed solvent of ethyl acetate (EtOAc) and water, followed by crystallization.

[0115] In another embodiment of the invention, the reaction product with introduced substituents can be cooled to 25°C to 35°C, and the aqueous layer can be removed using ethyl acetate and water in a volume ratio of 2:1 to 1:2, along with a polar solvent other than water, and then crystallized.

[0116] In another embodiment of the invention, by purifying the reaction product containing the substituent and then crystallizing it using a mixture of a polar organic solvent and water, the precipitation of K2CO3 used in the substituent introduction reaction with the reaction product can be prevented, or the amount of precipitation can be reduced, thereby improving the purity of the crystal.

[0117] In this invention, the substitution of R1 and R2 substituents can be carried out by substituting R1 followed by R2, substituting R2 followed by R1, or substituting R1 and R2 simultaneously.

[0118] In another embodiment of the invention, R2 may be substituted onto the compound of formula 4 before R1. If the bulky R1 is substituted onto the compound of formula 4 first, for example, if the bulky R1 is substituted at the 3-position of the indazole (where X is N), the formation of the N2 isomer can be suppressed and the yield can be improved.

[0119] In step 2), the compound of formula 5 is reacted with a reducing agent to obtain the compound of formula 3.

[0120] The reducing agent used in step 2) can be a common reducing agent for reducing ester groups to alcohols, such as, but not limited to, one or more selected from sodium borohydride (NaBH4), lithium borohydride (LiBH4), borane (BH3), and diisobutylaluminum hydride (DIBAH).

[0121] In one embodiment of the invention, in the reduction reaction of the compound of formula 5, the reducing agent and solvent are injected together at the start of the reaction, and additional reducing agent may be injected as the reaction progresses. The additional injection of reducing agent can be carried out by adding it together with the solvent injected at the start of the reaction, or by adding only the reducing agent without adding the solvent.

[0122] In another embodiment of the invention, in the reduction reaction of the compound of formula 5, if a reducing agent and a solvent such as MeOH are injected together at the beginning of the reaction, and then, according to the progress of the reaction, additional reducing agent and methanol are injected to allow the remaining compound of formula 5 to react, the yield of the obtained compound of formula 3 can be further improved.

[0123] In one embodiment of the invention, after the reduction reaction of compound 5 is completed, the reaction product can be purified to obtain compound 3. In this case, to purify the reaction product of the reduction reaction, organic solvents such as dichloromethane (DCM), isopropyl acetate and ethyl acetate, water, or mixtures thereof can be used.

[0124] In another embodiment of the invention, after the reduction reaction of compound 5 is completed, the aqueous layer can be removed by injecting DCM and water, thereby showing an effect of further improving the yield of compound 3.

[0125] The compounds prepared according to the present invention can be used as key intermediates in the synthesis of sphingosine-1-phosphate receptor agonists. The compounds prepared according to the present invention can be used as key intermediates in known synthetic methods of sphingosine-1-phosphate receptor agonists, and can also be used as key intermediates in novel synthetic methods to be developed after this application. The uses of the present invention are not limited to specific synthetic methods of sphingosine-1-phosphate receptor agonists.

[0126] Furthermore, the compounds prepared according to the present invention can be used for purposes other than synthesizing sphingosine-1-phosphate receptor agonists, and the uses of the present invention are not limited to synthesizing sphingosine-1-phosphate receptor agonists.

[0127] Beneficial effects

[0128] By using the preparation method of the present invention, it is possible to achieve the effect of producing compound 2 in large quantities with high yield. Detailed Implementation

[0129] The embodiments described below in more detail with reference to examples are provided to aid in understanding the invention. However, embodiments of the invention may be implemented in different forms and should not be considered as limiting oneself to the embodiments described herein. These embodiments of the invention are provided to provide a more complete explanation of the invention to those skilled in the art.

[0130] Example 1-1. Synthesis of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate

[0131]

[0132] Methyl 1H-indazole-5-carboxylate (6.2 kg, 35.19 mol), N-chlorosuccinimide (NCS, 5.64 kg, 42.2 mol), and dimethylformamide (DMF, 31.0 ml, 5 times) were injected into the reactor to raise the internal temperature of the reaction mixture to 75°C, and then the reaction was allowed to proceed for 1.5 hours.

[0133] The reaction was performed by ion-pair chromatography (IPC) by HPLC. After the reaction (methyl 1H-indazole-5-carboxylate: N / D) was completed, the reactor was cooled to 0°C for 60 minutes. While maintaining the internal temperature of the reactor at 50°C, K₂CO₃ (10.7 kg, 77.4 mol) and 2-iodopropane (8.98 kg, 52.8 mol) were added, and alkylation was carried out at 60°C for 120 minutes.

[0134] As a result of the IPC reaction performed by HPLC, the remaining 19.3% of methyl 3-chloro-1H-indazole-5-carboxylate was further injected twice with K₂CO₃ (2.14 kg, 15.5 mol) and 2-iodopropane (1.80 kg, 10.6 mol). The remaining 2.4% of methyl 3-chloro-1H-indazole-5-carboxylate was further injected with K₂CO₃ (1.08 kg, 7.75 mol) and 2-iodopropane (0.9 kg, 5.3 mol), terminating the reaction (1% > methyl 3-chloro-1H-indazole-5-carboxylate).

[0135] The reaction mixture was cooled to 30°C, and water (43.4 L) and EtOAc (43.4 L) were added, followed by stirring for 30 minutes. Layer separation was performed, and the aqueous layer was removed. Water (31.0 L) was added, and the organic layer was washed separately. EtOAc was removed by vacuum distillation, and EtOH (24.8 L) was added, raising the temperature to 40°C. The product was heated until a clear solution was obtained. The reactor was cooled, and the internal temperature was maintained at 20°C. Water (24.8 L) was then slowly added dropwise to produce crystals. The solid thus formed was aged for 30 minutes, then filtered, washed twice with water (31.0 L), and dried under nitrogen to give the title compound (6.56 kg, net yield 64.9%).

[0136] 1 H NMR (400MHz, CDCl3): 1.58 (d, 6H), 3.96 (s, 3H), 4.81 (m, 1H), 7.42 (d, 1H), 8.06 (dd, 1H), 8.44 (s, 1H).

[0137] Examples 1-2. Synthesis of (3-chloro-1-isopropyl-1H-indazol-5-yl)-methanol

[0138]

[0139] THF (34.2 L, 6-fold) and methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate (Example 1-1, 5.7 kg, 22.6 mol) were injected into the reactor to raise the internal temperature to 60 °C. NaBH4 (1.68 kg, 44.4 mol) and MeOH (5.7 L, 1-fold) were slowly added dropwise to the reaction mixture over 80 minutes, and the reaction was allowed to proceed for 30 minutes. At 90-minute intervals, NaBH4 (0.44 kg, 11.6 mol) was added, followed by two injections of MeOH (1.69 L, 0.3-fold), and the reaction was allowed to proceed for 30 minutes. IPC was performed using HPLC.

[0140] The remaining 14.3% of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was added with an additional 0.22 kg (5.8 mol) of NaBH4, and the reaction was carried out for 120 minutes. The remaining 2.5% of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was added, the reaction was terminated, the product was cooled, and the internal temperature was set to 10 °C.

[0141] To remove the B-complex (generated by the complex of NaBH4 and boron conjugated with alcohol (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol) and the remaining NaBH4, 3 N HCl (39.3 kg) was slowly injected over 60 minutes to maintain the pH of the reaction solution at 3.0, and the solvent was removed by vacuum distillation.

[0142] DCM (28.5 L) and water (57.0 L) were injected into the residue for layer separation. The aqueous layer was removed, and the residue was washed with water (42.8 L) and subjected to vacuum distillation to give the title compound (4.32 kg, net yield 85%).

[0143] 1 H NMR (400MHz, CDCl3): 1.5-1.7 (m, 6H), 1.82 (m, 1H), 3.72 (m, 1H), 4.70-5.10 (m, 2H), 7.30-7.50 (m, 2H), 7.62 (s, 1H).

[0144] Examples 1-3. Synthesis of 5-bromomethyl-3-chloro-1-isopropyl-1H-indazole

[0145]

[0146] MTBE (43.3 L, 8-fold) and (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol (Examples 1-2, 4.32 kg, 19.3 mol) were injected into the reactor, and the internal temperature was cooled to 0°C. PBr3 (3.64 kg, 13.5 mol) was slowly injected into the reaction mixture over 90 minutes, and the reaction proceeded for 180 minutes.

[0147] The reaction was completed using IPC by HPLC (Examples 1-2: N / D). 1.5 N NaOH (34.7 L) was slowly injected over 60 minutes, followed by stirring for 30 minutes to terminate the reaction. Water (21.7 L) was added to the reaction mixture, followed by stirring and layer separation over 10 minutes. The aqueous layer was removed, and the mixture was washed with an additional 17.3 L of water. The organic layer was then distilled under reduced pressure to synthesize the title compound (4.97 g, net yield 90.0%).

[0148] 1 H NMR (400MHz, CDCl3): 1.53 (d, 6H), 4.7 (s, 2H), 4.88 (m, 1H), 7.51-7.6 (m, 2H), 7.68 (s, 1H).

[0149] Experimental Example 1. Evaluation of the reaction solvent in the reaction of alcohols in which leaving groups are substituted for (3-chloro-1-isopropyl-1H-indazol-5-yl)-ethanol.

[0150] Reference Synthesis Example 1

[0151] 5-Bromomethyl-3-chloro-1-isopropyl-1H-indazole was obtained using the same method as in Examples 1-3, but a 4:1 mixed solvent of DCM / MTBE was used in the substitution reaction, and DCM was used instead of water in the extraction of the reaction product.

[0152] In the preparation of Reference Synthesis Example 1, if the leaving group substitution reaction is carried out under DCM and MTBE, the phenomenon of viscous oil coating the reactor wall can be continuously observed, and it can be confirmed that when the reaction is terminated with NaOH, the viscous oil disappears by dissolution.

[0153] To examine the viscous oil component generated during the reaction, HPLC analysis was performed, confirming an N2:N1 isomer ratio of 1.5:1 and a very high N2 isomer ratio. Furthermore, it was confirmed that the (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol form was not substituted by the leaving group.

[0154] Based on the results, it was confirmed that the use of a single solvent, MTBE, effectively removed the N2 isomer and improved the yield in the reaction process in which the leaving group replaced the alcohol group of (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol.

[0155] In the reaction process in which the alcohol group of (3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol is replaced by a leaving group, the measured yields of the N2 isomer and the target compound ((3-chloro-1-isopropyl-1H-indazole-5-yl)-methanol) are shown in Table 1 below, depending on the reaction solvent and extraction conditions.

[0156] In Table 1 below, "SG15" represents "(3-chloro-1-isopropyl-1H-indazol-5-yl)-methanol", and "SG20" represents " 5- bromomethyl-3-chloro-1-isopropyl-1H-indazole ".

[0157] [Table 1]

[0158]

[0159] As shown in Table 1 above, it has been demonstrated that when the alcohol is substituted with a leaving group in a single solvent of MTBE and extracted with MTBE, the N2 isomer can be reduced to less than 2%.

[0160] Example 2. Evaluation of the crystallization solvent in the synthesis of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate 1

[0161] Reference Synthesis Example 2

[0162] Methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was obtained by the same method as in Examples 1-1, but crystallization was carried out by injecting water without purification after the alkylation reaction was completed.

[0163] Refer to Example 3 of Synthesis

[0164] Methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was obtained by the same method as in Example 1-1, but after purifying the reaction mixture and removing EtOAc, crystallization was carried out by injecting the same amount of n-hexane instead of EtOH.

[0165] Refer to Example 4 of Synthesis

[0166] Methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was obtained by the same method as in Examples 1-1, but after purifying the reaction mixture and removing EtOAc, crystallization was carried out by injecting the same amount of isopropanol (IPA) instead of EtOH.

[0167] As a result of the comparative evaluation of the amount of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate and the amount of N2 isomer obtained according to Examples 1-1 and Reference Synthesis Examples 2 to 4, it was confirmed that, given the removal rate of N2 isomer, Examples 1-2, Reference Synthesis Examples 3 and 4 were all excellent, except for Reference Synthesis Example 2, which did not use an organic solvent.

[0168] In particular, in Examples 1-2, where a mixed solvent of EtOH and water was used, excellent results were demonstrated in both the removal of N2 isomers and the recovery of the target compound.

[0169] The yields of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate after alkylation and purification, based on the crystallization solvent, are shown in Tables 2 and 3 below.

[0170] In Tables 2 and 3 below, “SG10” means “methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate”.

[0171] [Table 2]

[0172]

[0173] [Table 3]

[0174]

[0175] In the experiments shown in Table 2, aggregation was observed during crystallization when t-BuOH or DCM was used as the crystallization solvent. When IPA was used, an increase in the loss of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was observed, given the net yield. Furthermore, as confirmed in Table 3, it can be demonstrated that approximately 10% of the N2 isomer was removed by using methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate containing approximately 17% of the N2 isomer and crystallizing it using EtOH, IPA, and n-hexane as crystallization solvents, respectively.

[0176] Tables 2 and 3 confirm that the removal and recovery rates of N2 isomers are excellent when EtOH is used as the crystallization solvent. Furthermore, it is shown that increasing the amount of H2O used as the antisolvent reduces the removal efficiency of N2 isomers as the aging temperature decreases.

[0177] Example 3. Evaluation of the crystallization solvent in the synthesis of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate 2

[0178] Refer to Example 5 of Synthesis

[0179] Methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was obtained by the same method as in Example 1-1, but EtOH:H2O was used in a volume ratio of 3:7 during crystallization.

[0180] Reference Synthesis Example 6

[0181] Methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was obtained by the same method as in Examples 1-1, but EtOH:H2O was used in a volume ratio of 1:1 during crystallization.

[0182] Refer to Example 7 of Synthesis

[0183] Methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate was obtained by the same method as in Example 1-1, but EtOH:H2O was used in a volume ratio of 7:3 during crystallization.

[0184] The comparative evaluation results of the amounts of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate and the N2 isomer obtained according to Reference Synthesis Examples 5 to 7 confirmed that if the amount of EtOH is increased and the amount of H2O is decreased, the amount of the remaining N2 isomer decreases.

[0185] In particular, a yield loss was observed when the amount of EtOH was increased, confirming that using EtOH and H2O in a 1:1 ratio, which is four times the amount of the reaction product, is effective given the reduction in N2 isomers and the recovery of the target compound.

[0186] The yield measurements based on the volume ratio of EtOH to H2O used in the crystallization of methyl 3-chloro-1-isopropyl-1H-indazole-5-carboxylate are shown in Table 4 below.

[0187] [Table 4]

[0188]

Claims

1. A method for preparing an intermediate compound of formula 2, the method comprising: 1) The step of introducing substituents R1 and R2 into the compound of Formula 4 and crystallizing it in a crystallization solvent including an alcohol solvent to obtain the compound of Formula 5, wherein the crystallization solvent is a mixed solvent of EtOH:H2O in a volume ratio of 2:1 to 1:

1. 2) The step of reacting the compound of formula 5 with a reducing agent to obtain the compound of formula 3; as well as 3) The step of replacing the alcohol group of the compound of formula 3 with a leaving group in a single ether solvent to obtain the compound of formula 2, wherein the single ether solvent is methyl tert-butyl ether (MTBE): [Equation 2] [Formula 3] [Formula 4] [Formula 5] In equations 2 to 5, R1 is an unsubstituted C1-C4 alkyl group. R2 is a halogen. R3 is a C1-C6 substituted or unsubstituted alkyl group. X is N, and L is a leaving group selected from chlorine, bromine, iodine, methanesulfonate, p-toluenesulfonate and trifluoromethanesulfonate.

2. The method according to claim 1, wherein the mixed solvent of EtOH and H2O is a solvent in which EtOH and H2O are mixed in a 1:1 volume ratio.

3. The method according to claim 1, wherein L is a leaving group selected from chlorine, bromine and iodine.

4. The method according to claim 1, wherein the compound of formula 3 is obtained by purification using a mixed solvent of a polar organic solvent and water after the reduction reaction of the compound of formula 5 in step 2).

5. The method according to claim 4, wherein the polar organic solvent is one or more solvents selected from ethyl acetate, hexane and dichloromethane.

6. The method according to claim 5, wherein the polar organic solvent is dichloromethane.

7. The method according to claim 1, wherein R1 is a C1-C4 unsubstituted alkyl group. R2 is chlorine, and L is a leaving group selected from bromine.

8. The method according to claim 7, wherein the step of replacing the alcohol group with the leaving group is carried out by mixing the compound of formula 3 with methyl tert-butyl ether (MTBE), cooling to 0°C, and then reacting with phosphorus tribromide (PBr3).