Method for purifying tafluprost

Abstract

[Problem] The present application aims to provide a simple and efficient method for purifying tafluprost, which can be scaled up. [Means for solving the problem] The present application relates to a method for purifying tafluprost, which includes purifying a crude product of tafluprost using a silica gel column chromatography and collecting a component containing tafluprost using HPLC analysis. In addition, the present application also relates to a method for producing tafluprost including the aforementioned method for purifying tafluprost.

Description

[0001] This application is a divisional application of an application with the application number 202110111991.0, the application date of January 27, 2021, and the invention title of “Purification method of tafluprost”. TECHNICAL FIELD

[0002] The present invention relates to a novel purification method of tafluprost. BACKGROUND

[0003] Tafluprost is represented by the following formula:

[0004]

[0005] Its chemical name is (5Z)-7-(1R,2R,3R,5S)-2-[(1E)-3,3-difluoro-4-phenoxy-1-butenyl]-3,5- dihydroxycyclopentyl]-5-heptenoic acid isopropyl ester, and has a viscosity of 2440 mPa·s at 25°C, and is a very highly viscous difluprost F 2α derivative. Tafluprost has an unstable chemical structure including 2 double bonds, an unsaturated fatty acid ester site, and 4 asymmetric centers, and has a structure in which the hydroxyl group and the hydrogen atom at the C15 position present in other prostaglandin derivatives are replaced with 2 fluorine atoms, and thus has a unique property of having a high liposolubility among prostaglandin derivatives, and although it is chemically stable, it also has a property of decomposing at high temperatures. In addition, tafluprost has a strong intraocular pressure lowering effect, and is used as eyedrops for the treatment of glaucoma and ocular hypertension (Patent Literature 1). Patent Literature 1 describes a difluprost F 2α derivative, and the same manufacturing method is also described in Non-Patent Literature 1.

[0006] The manufacturing method described in Patent Literature 1 includes a Wittig reaction process, and thus it is difficult to avoid the mixing of the α-chain trans isomer in the final product. In the manufacturing method described in Patent Literature 1, as a method for removing impurities including the α-chain trans isomer, a method of separating and purifying by using a fractionation HPLC (High Performance Liquid Chromatography) is reported (Patent Literature 2). However, tafluprost, and a carboxylic acid compound represented by the following formula (I) (hereinafter referred to as “tafluprost acid”) as a synthetic precursor thereof:

[0007]

[0008] All are liquid compounds having very high viscosity, and thus are difficult to purify. In addition, in the purification method of tafluprost described in Patent Literature 2, a large amount of organic solvent is used, and thus a very high cost is required, and it is also difficult to suppress the residual organic solvent concentration to a concentration limit value or less of the residual solvent guideline for pharmaceutical products (Non-Patent Literature 2). The column for fractionation is generally expensive, and is usually repeatedly used, and thus has problems of mixing of accumulated impurities, decomposition products, and reduction of the theoretical plate number due to deterioration of the column, and in order to reduce the risk caused by these problems, it is also often necessary to use a large amount of organic solvent for washing, and cumbersome effectiveness verification related to confirmation thereof, and confirmation of the separation performance of the column, and thus the manufacturing method for pharmaceutical products lacks practicality.

[0009] On the other hand, a method of reducing the mixing of impurities such as the α-chain trans isomer by forming an organic amine salt (Patent Literatures 3, 4) or a metal salt (Patent Literature 5) of tafluprost acid has also been reported, but with the addition of the salt formation step and the ionization step from the salt, there is also a possibility of an increase in by-products, dehydration products, other impurities, and the like based on condensation with organic amines, dimerization from condensation, and the like. In addition, there are also concerns about toxicity, mutagenicity, and the like of organic amines, metals, and the like, and in particular, there are problems in safety in the case of use as a purification method at a stage close to the final step of a pharmaceutical product.

[0010] Furthermore, a manufacturing method of tafluprost in which the mixing of the α-chain trans isomer is prevented by forming a macrolide ring and opening the macrolide ring (Patent Literature 6) has also been reported. However, the manufacturing method has a long manufacturing process and a low yield, and thus has low practicality.

[0011] Prior Art Documents

[0012] Patent Literature

[0013] Patent Literature 1: European Patent Application Publication No. 850926

[0014] Patent Literature 2: U.S. Patent Application Publication No. 2014 / 0051882

[0015] Patent Literature 3: International Publication No. 2013 / 118058

[0016] Patent Literature 4: International Publication No. 2016 / 090461

[0017] Patent Literature 5: Chinese Patent Application Publication No. 108299192

[0018] Patent Literature 6: Japanese Patent Application Publication No. 2015-36382

[0019] Non-Patent Literature

[0020] Non-patent literature 1: Tetrahedron Lett., 2004, 45, 1527-1529

[0021] Non-patent literature 2: Pharmaceutical Affairs No. 307, Director of the Pharmaceutical Safety Bureau, Pharmaceutical Affairs Division, Notification (March 30, 2004), Guidelines for Residual Solvents in Pharmaceuticals SUMMARY

[0022] Problem to be solved by the invention

[0023] An object of the present application is to provide a purification method of tafluprost which can easily and inexpensively purify tafluprost, which is a liquid compound having very high viscosity, to a degree of purity that can be directly provided as a pharmaceutical material, and which can also be scaled up.

[0024] Solution for solving the problem

[0025] The present inventors and others have conducted intensive research in order to solve the above problems and have found that, in a manufacturing method of tafluprost, a purification method including purifying a crude product of tafluprost obtained by an esterification process of tafluprost acid using a silica gel column chromatography and collecting a component containing tafluprost using HPLC analysis (hereinafter, sometimes referred to as "the purification method of the present application"), can obtain tafluprost having high purity. In addition, by conducting a purification method including a process of concentrating under reduced pressure a component containing tafluprost collected using HPLC analysis at 10 to 55°C, a process of dissolving the residue in a solvent and filtering, and a process of distilling off the solvent of the filtrate under reduced pressure at 10 to 55°C with a final ultimate vacuum degree of 5 torr or less (hereinafter, sometimes the purification method including all of the foregoing processes is referred to as "the purification method of the present application"), the residual organic solvent concentration can be suppressed to be below the concentration limit value of the residual solvent guidelines for pharmaceuticals, and tafluprost having a degree of purity that can be directly provided as a pharmaceutical material is obtained, thereby completing the present application.

[0026] That is, the present application is as follows.

[0027] [1] A purification method of tafluprost, including purifying a crude product of tafluprost using a silica gel column chromatography and collecting a component containing tafluprost using HPLC analysis.

[0028] [2] The purification method of tafluprost according to the above [1], further comprising: a process of concentrating under reduced pressure the component containing tafluprost collected by HPLC analysis at 10 to 55°C; a process of dissolving the residue in a solvent and filtering; and a process of distilling off the solvent of the filtrate under reduced pressure at 10 to 55°C with a final ultimate vacuum of 5 torr or less.

[0029] [3] The purification method according to the above [1] or [2], wherein the particle diameter (d50) of the silica gel used in the silica gel column chromatography is 20 to 70 μm.

[0030] [4] The purification method according to any one of the above [1] to [3], wherein the silica gel used in the silica gel column chromatography is spherical.

[0031] [5] The purification method according to any one of the above [1] to [4], wherein the eluent of the silica gel column chromatography is a mixed solvent of n-hexane and a polar solvent, or a mixed solvent of n-heptane and a polar solvent.

[0032] [6] The purification method according to the above [5], wherein the eluent is a mixed solvent of n-hexane and a polar solvent.

[0033] [7] The purification method according to the above [5] or [6], wherein the polar solvent is ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol.

[0034] [8] The purification method according to any one of the above [1] to [7], wherein the HPLC analysis is a reverse phase HPLC analysis.

[0035] [9] The purification method according to any one of the above [1] to [8], wherein the component is a component containing 98% or more of tafluprost.

[0036]

[10] The purification method according to any one of the above [2] to [9], wherein the filtration is performed using a filter having a pore size of 0.5 μm or less.

[0037]

[11] The purification method according to any one of the above [2] to

[10] , wherein the solvent used for dissolving the residue is ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol, or a mixed solvent of ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol and a non-polar solvent.

[0038]

[12] The purification method according to the above

[11] , wherein the solvent used for dissolving the residue is ethyl acetate, or a mixed solvent of ethyl acetate and a non-polar solvent.

[0039]

[13] The purification method according to any one of the above

[11] or

[12] , wherein the non-polar solvent is n-hexane or n-heptane.

[0040]

[14] The purification method according to any one of the above [2] to

[13] , wherein the final limit vacuum degree is 1 torr or less.

[0041]

[15] The purification method according to any one of the above [2] to

[14] , wherein the residual solvent concentration of n-hexane after the process of distilling and removing the solvent of the filtrate is 290 ppm or less, and the residual solvent concentrations of n-heptane, ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol are 5000 ppm or less, respectively.

[0042]

[16] A production method of tafluprost, comprising subjecting a crude product of tafluprost to the process of the purification method according to any one of the above [1] to

[15] .

[0043]

[17] Tafluprost obtained by the production method according to the above

[16] .

[0044]

[18] A pharmaceutical product containing the tafluprost according to the above

[17] as an effective ingredient.

[0045]

[19] A pharmaceutical product containing the tafluprost according to the above

[17] as an effective ingredient, for the prevention or treatment of an ocular disease.

[0046]

[20] The pharmaceutical product according to the above

[19] , wherein the ocular disease is glaucoma or ocular hypertension.

[0047] Effects of the invention

[0048] By the purification method of the present application, in the final process of the production of tafluprost, when a crude product of tafluprost is separated and purified by silica gel column chromatography, by collecting a component containing tafluprost using HPLC analysis, the incorporation of impurities can be suppressed to a minimum. In addition, under the reduced pressure condition of low temperature and high vacuum degree, the solvent is distilled and removed for a long time, whereby the residual organic solvent concentration can be suppressed to be below the concentration limit value of the residual solvent guideline of pharmaceutical products, and the decomposition of tafluprost, which is unstable at high temperature, can also be suppressed. Furthermore, by incorporating a filter filtration process in the middle, fine powder of silica gel, airborne particles, and bacteria can be removed, and thus after the distillation and removal of the solvent, high-purity tafluprost that can be directly used as a pharmaceutical raw material can be simply and efficiently provided. The purification method of the present application can be widely applied to a crude product of tafluprost produced by a publicly known method, and can be scaled up in proportion. DETAILED DESCRIPTION

[0049] The following describes the details of the embodiments of the present application.

[0050] [Definitions of Terms]

[0051] The meanings of the terms in the present specification are as follows.

[0052] In the present specification, as the column for "silica gel column chromatography", either an ordinary pressure column or a flash column can be used.

[0053] The "silica gel column chromatography" in the present specification is a column chromatography of normal phase system.

[0054] In the present specification, the "crude product of tafluprost" means a product before purification after the work-up of the reaction in the final step of the known manufacturing method of tafluprost. Specifically, for example, as shown in the following examples, the product before purification in the final esterification reaction in the manufacturing method of tafluprost described in Patent Literature 1 can be mentioned.

[0055] In the present specification, the "impurities" include, in addition to the aforementioned similar substances such as residual reaction reagents, residual raw material compounds, by-products of the reaction, and decomposition products of tafluprost, which are contained in the crude product of tafluprost, all substances other than tafluprost such as residual organic solvents, residues derived from the packing material, and bacteria.

[0056] In the present specification, the "HPLC analysis" means that, when the crude product of tafluprost is separated and purified by the silica gel column chromatography, the presence or absence of tafluprost and the content ratio in each component are confirmed using an analytical high performance liquid chromatography (HPLC).

[0057] In the present specification, the "filtration" means filtration by a filter. The filtration is performed for the purpose of removing fine powder of the column packing material (silica gel), floating particles in the air, bacteria, and the like.

[0058] In the present specification, the "polar solvent" means a solvent having a large dielectric constant. As specific examples of the polar solvent, esters such as ethyl acetate and propyl acetate, ethers such as diethyl ether, t-butyl methyl ether, and tetrahydrofuran, alcohols such as 2-propanol and ethanol, and the like can be mentioned. Among them, ethyl acetate, t-butyl methyl ether, 2-propanol, and ethanol are preferred.

[0059] In the present specification, the "non-polar solvent" means a solvent having a small dielectric constant. As specific examples of the non-polar solvent, chain hydrocarbons such as n-hexane and n-heptane can be mentioned. Among them, n-hexane is preferred.

[0060] In the present specification, the "external temperature" means the temperature of the outside of a reaction vessel or a concentration vessel, and is usually the temperature of the outside air or the temperature of a water bath or a hot water bath.

[0061] In the present specification, the "concentration limit value of the residual solvent guideline for pharmaceutical products" is a value defined for the allowable amount of residual solvent in pharmaceutical products as a result of research conducted as one of the subjects of the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) and for the safety of patients, and refers to a limit value that is toxicologically tolerable. As a specific example of the concentration limit value of the residual solvent for pharmaceutical products, as described in Non-Patent Literature 2, for example, n-hexane is 290 ppm, and n-heptane, ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol is 5000 ppm.

[0062] [Purification method of the present invention]

[0063] The purification method of the present invention is characterized by including a step (step 1) of purifying a crude product of tafluprost using silica gel column chromatography and collecting a component containing tafluprost using HPLC analysis. In addition, in order to suppress the residual organic solvent concentration to be below the concentration limit value of the residual solvent guideline for pharmaceutical products, the purification method of the present invention is characterized by, in addition to the aforementioned step 1, further including a concentration step (step 2) of performing concentration under reduced pressure at 10 to 55°C, a step (step 3) of dissolving the residue in a solvent and performing filtration, and a step (step 4) of distilling and removing the solvent of the filtrate under reduced pressure at 10 to 55°C with a final ultimate vacuum degree of 5 torr or less.

[0064] (Step 1)

[0065] This step is a step of purifying using silica gel column chromatography and collecting a component containing tafluprost using HPLC analysis.

[0066] As a packing material for silica gel column chromatography, there is no particular limitation as long as it is silica gel that can be used for a general normal phase column. As the shape of the silica gel, both a pulverized shape and a spherical shape are acceptable, and a spherical shape is more preferable. In addition, the particle diameter (d50) of the silica gel is not particularly limited, and is preferably 20 μm to 70 μm, more preferably 40 μm to 65 μm, and particularly preferably 45 μm to 60 μm. The particle diameter (d50) is the median particle diameter of the particle size distribution when the particle size distribution is made on a volume basis using a laser diffraction scattering type particle size distribution measuring device.

[0067] As the eluent for the silica gel column chromatography, there is no particular limitation as long as it is a solvent that can separate the crude product of tafluprost from impurities, and a mixed solvent of n-hexane and a polar solvent, or a mixed solvent of n-heptane and a polar solvent is preferred, and a mixed solvent of n-hexane and a polar solvent is more preferred. Here, the polar solvent is selected from ethyl acetate, t-butyl methyl ether, 2-propanol, and ethanol, of which 2-propanol or ethanol is preferred. The mixing ratio (volume ratio) of n-hexane and a polar solvent, or n-heptane and a polar solvent can be appropriately set according to the kind, shape, and / or particle diameter of the packing used. As a preferred specific example of the eluent, a mixed solvent of, for example, ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol and a non-polar solvent (preferably n-hexane or n-heptane) can be given, and a mixed solvent of 2-propanol or ethanol and a non-polar solvent (preferably n-hexane or n-heptane) is more preferred, and a mixed solvent of ethanol and n-hexane is particularly preferred. As the eluent, the mixing ratio (volume ratio) when a mixed solvent is used is not particularly limited, but from the viewpoint of controlling the residual solvent concentration to be below the reference value, in the case of a mixed solvent of ethanol and n-hexane, it is preferred to use a solvent in which ethanol and n-hexane are mixed at a ratio of 10:90 to 1:99, more preferably a solvent in which they are mixed at a ratio of 6:94 to 2:98, further preferably a solvent in which they are mixed at a ratio of 5:95 to 3:97, and particularly preferably a solvent in which they are mixed at a ratio of 4:96.

[0068] When purifying the crude product of tafluprost using silica gel column chromatography to confirm the presence or absence of tafluprost in the separated components, an HPLC for analysis is used. As this HPLC, either a normal phase HPLC or a reverse phase HPLC can be used, but a reverse phase HPLC is more preferred in terms of separation efficiency of impurities, detection sensitivity, and quantification, etc. As specific examples of the column and analysis conditions used in this HPLC analysis, the conditions described in the examples below can be given, but are not limited thereto.

[0069] Generally, when performing silica gel column chromatography purification, the presence or absence of the target substance in the separated components is confirmed using TLC (thin layer chromatography) (see Experimental Chemistry Lecture 1 Basic Operation I (4th edition), issued on November 5, 1990, Maruzen, 5 / 2 / 3 column chromatography, p. 293-296), but it was found that in the purification of the crude product of tafluprost, HPLC analysis was significantly superior to conventional TLC analysis in terms of detection sensitivity of components containing tafluprost and impurities.

[0070] For a plurality of batches of the crude product of tafluprost synthesized, silica gel column chromatography was performed, and the elution pattern of impurities was analyzed using HPLC analysis, and as a result, it was confirmed that the impurity elution pattern was consistently stable. By considering the impurity elution pattern, it is preferred to collect continuous components in which the HPLC area percentage of tafluprost of each component is 97% or more, and particularly preferably 98% or more.

[0071] (Step 2)

[0072] This step is a step of collecting the fraction containing tafluprost confirmed by HPLC analysis and concentrating under reduced pressure at 10 to 50°C.

[0073] The external temperature (temperature of a water bath or a hot water bath) at the time of collecting the fraction containing tafluprost confirmed by HPLC analysis and concentrating under reduced pressure is preferably 10 to 55°C, more preferably 15 to 50°C, and particularly preferably 20 to 45°C. As shown in the test example described later, it was confirmed that tafluprost is slowly decomposed at a temperature of 60°C or higher over time, and from this aspect, it is also desirable to perform concentration under reduced pressure or removal of the solvent by distillation at the above-mentioned temperature.

[0074] (Step 3)

[0075] This step is a step of dissolving the residue obtained in the aforementioned Step 2 in a solvent and performing filtration. Tafluprost has very high viscosity, and thus it is difficult to perform sterilization filtration after complete removal of the solvent by distillation. Therefore, the purification method of the present application is characterized in that a filtration step is incorporated after Step 2.

[0076] As the solvent used for dissolving the residue obtained in Step 2, the same solvent as that used for the eluent in the silica gel column chromatography in Step 1 can be mentioned, and a solvent in which tafluprost is sufficiently dissolved and which has a relatively low boiling point is preferred, and a mixed solvent with a non-polar solvent forming an azeotropic composition can also be used. Specifically, ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol, or a mixed solvent of ethyl acetate, t-butyl methyl ether, 2-propanol, or ethanol with a non-polar solvent (preferably n-hexane or n-heptane) is preferred, and ethyl acetate or a mixed solvent of ethyl acetate with a non-polar solvent (preferably n-hexane or n-heptane) is more preferred, and a mixed solvent of ethyl acetate with n-hexane is particularly preferred. The mixing ratio (volume ratio) when a mixed solvent is used is not particularly limited, and from the viewpoint of controlling the residual solvent concentration to be below a reference value, in the case of a mixed solvent of ethyl acetate with n-hexane, it is particularly preferred to use a solvent in which ethyl acetate and n-hexane are mixed at a ratio of 10: 1 to 1: 10, preferably 4: 1 to 1: 4, and more preferably 2: 1 to 1: 2.

[0077] As the filter used in the filtration of this step, there is no particular limitation as long as it does not swell or dissolve due to the solvent and can remove fine powder of the packing (silica gel), airborne particles, and the like, and glass fiber filters, polypropylene filters, nylon filters, fluororesin filters, and the like can be mentioned, and fluororesin filters such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferred, and polytetrafluoroethylene (PTFE) filters are particularly preferred.

[0078] The pore size of the filter is usually 0.5 μm or less, preferably 0.25 μm or less, and particularly preferably 0.22 μm or less, including the case where sterilization is intended.

[0079] (Step 4)

[0080] This step is a step of distillatively removing the solvent of the filtrate obtained in the aforementioned Step 3 under reduced pressure at 10 to 55°C and with a final limit vacuum degree of 5 torr or less.

[0081] Since the viscosity of tafluprost is very high, it is necessary to increase the surface area of the solvent evaporation as much as possible and to distillatively remove the solvent of the filtrate slowly while avoiding bumping. As a reduced-pressure concentration device for achieving the above purpose, for example, a rotary evaporator, a centrifugal evaporator, a high-vacuum thin-film evaporator, or the like can be mentioned.

[0082] In addition, as described above, from the aspect that tafluprost slowly decomposes over time at a temperature of 60°C or higher, the external temperature (the temperature of a water bath or a hot water bath) at the time of distillatively removing the solvent under reduced pressure is preferably 10 to 55°C, more preferably 15 to 50°C, and particularly preferably 20 to 45°C.

[0083] As for the degree of reduced pressure at the time of distillatively removing the solvent, it is necessary to increase the surface area of the solvent evaporation as much as possible and to slowly increase the degree of reduced pressure while avoiding bumping, and it is preferably controlled so that the final limit vacuum degree becomes 5 torr or less (preferably 3 torr or less, more preferably 1 torr or less, and particularly preferably 0.5 torr or less). In addition, at the time of releasing the reduced pressure, in order to prevent the intrusion of airborne particles and bacteria, it is preferable to use air that has passed through a filter to return to the normal pressure.

[0084] The time for distillatively removing the solvent is preferably 10 to 70 hours, more preferably 15 to 60 hours, and particularly preferably 20 to 60 hours.

[0085] By using the purification method of the present application, it is possible to suppress the residual organic solvent concentration to a value that is lower than the concentration limit value of the residual solvent guideline for pharmaceutical products (Non-Patent Document 2), and as described in the guideline, "Residual solvents are not helpful for treatment, and therefore all residual solvents should be reduced to a level that is lower than the product standard, GMP, or other quality standards," it is possible to stably produce tafluprost that further satisfies strict various quality standards and is of high quality.

[0086] As a solvent for dissolving the eluent and the residue used in the aforementioned silica gel column chromatography, it is desirable that the residual solvent concentration of the solvent exemplified as the preferable solvent, ethyl acetate, t-butyl methyl ether, 2-propanol, ethanol, or n-heptane, be more preferably controlled to 1000 ppm or less, and particularly preferably controlled to 100 ppm or less, respectively, and further, it is desirable that the residual solvent concentration of n-hexane be more preferably controlled to 200 ppm or less, and particularly preferably controlled to 20 ppm or less. The concentration of the residual solvent can be measured by gas chromatography (GC) or the like.

[0087] The present application also includes a method for producing tafluprost, which is a crude product of tafluprost produced by a publicly known method, by subjecting the crude product to the purification process (purification process including the above-mentioned processes 1 to 4) of the present application. As the publicly known production method of tafluprost, in addition to the above-mentioned Patent Literature 1 and Non-Patent Literature 1, there are several reports (for example, U.S. Patent Application Publication No. 2014 / 0046086 specification; J. Org. Chem. 2016, 81, 10832-844; Molecules, 2017, 22, 217, 1-16; Org. Lett. 2020, 22, 2991-2994, etc.), and these can also be included in the present application by being combined with the purification process of the present application.

[0088] As a specific example of the crude product of tafluprost used in the present application, there are, for example, a crude product of tafluprost obtained by a deprotection reaction using tafluprost protected by a hydroxyl group or the like, a crude product of tafluprost obtained by esterification using a salt of tafluprost acid, and a crude product of tafluprost obtained by esterification using tafluprost acid. Among them, the crude product of tafluprost obtained by esterification using tafluprost acid can be suitably used.

[0089] As a specific feature of the purification process of the present application, the following can be exemplified.

[0090] (A) When the crude product of tafluprost is separated and purified by silica gel column chromatography, the collection of the component containing tafluprost by HPLC analysis (preferably, reverse phase HPLC analysis) can suppress the mixing of impurities to a minimum.

[0091] (B) The solvent is removed by distillation under a reduced pressure at a low temperature and a high vacuum degree for a long time, whereby the decomposition of tafluprost, which is unstable at a high temperature, can be suppressed, and further, the residual organic solvent concentration can be suppressed to a concentration limit value or less of the residual solvent guideline for pharmaceutical products.

[0092] (C) A filter filtration process is incorporated in the middle, whereby high-purity tafluprost that can be used directly as a drug substance for pharmaceutical products can be provided after the removal of the solvent by distillation.

[0093] (D) The purification method of the present application can also be applied to a crude product of tafluprost obtained by any of the publicly known methods for producing tafluprost, and in addition, can be easily scaled up, and thus a simple and efficient purification method can be provided.

[0094] The purification method of the present application, when performed with the aim of improving the purity of tafluprost, can include only the above-described process 1, or processes 2 to 4 can also be combined with process 1 as needed, as described in (A) above.

[0095] Examples

[0096] The present application is described in detail below by reference to Reference Examples, Examples and Test Examples, but the present application is not limited to these.

[0097] % mol% in the case of yield, and mass% in the case of other, unless otherwise specified. The ratio shown in the mixed solvent indicates a volume ratio, unless otherwise specified. In addition, room temperature indicates a temperature of 15 to 30°C, unless otherwise specified. The following 1 H-NMR values were measured using a nuclear magnetic resonance device, ECP400 (400 MHz) manufactured by JEOL Ltd. HPLC devices used were Shimadzu LC-10ADvp or LC-10A. GC devices used were Shimadzu GC-2014ATF.

[0098] Reference Example 1: Synthesis of tafluprost acid

[0099]

[0100] To (1S,5R,6R,7R)-6-[(1E)-3,3-difluoro-4-phenoxy-1-butenyl]-7-hydroxy-2-oxabicyclo[3.3.0]octan-3-one (280 g) was added tetrahydrofuran (1200 g) and dissolved under nitrogen atmosphere, diisobutylaluminum hydride (1 M toluene solution) (2160 mL) was added dropwise at -70°C. After completion of the dropwise addition, stirring was carried out for 30 minutes, 1 N hydrochloric acid was added, extraction was carried out with ethyl acetate. After the organic layers were combined and washed with water, the filtrate was concentrated under reduced pressure, whereby a reduction product (284 g) was obtained. To 4-carboxybutyltriphenylphosphonium bromide (1523 g) was added tetrahydrofuran (5030 g) under nitrogen atmosphere, sodium bis(trimethylsilyl)amide solution (1 M tetrahydrofuran solution) (6684 mL) was added dropwise, stirring was carried out for 1 hour or more. The above reduction product (286 g) dissolved in tetrahydrofuran (970 g) was added dropwise at 0°C and stirring was carried out for 3 hours. To the reaction solution was added water, extraction was carried out with ethyl acetate. After the aqueous layer was made acidic, extraction was carried out with ethyl acetate, after concentration under reduced pressure, insoluble matter was filtered off, purification was carried out by silica gel column chromatography (hexane / ethyl acetate = 1 / 1 to 1 / 3), whereby tafluposerp acid (222 g) was obtained.

[0101] 1 H NMR (CDCI3) δ 1.60 (m, 1H), 1.67 (m, 2H), 1.84 (m, 1H), 2.02-2.16 (m, 4H), 2.25-2.35 (m, 3H), 2.47 (m, 1H), 4.03 (m, 1H), 4.18 (m, 3H), 5.35-5.42 (m, 2H), 5.80 (m, 1H), 6.10 (m, 1H), 6.91 (m, 2H), 7.00 (m, 1H), 7.30 (m, 2H).

[0102] Reference Example 2: Synthesis of crude tafluposerp

[0103]

[0104] Under a nitrogen atmosphere, the terfluride acid (120 g) obtained in Reference Example 1 was charged in a 5 L flask, and dissolved in acetone (600 mL) while stirring. After cooling to 5°C, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (160 mL) was added dropwise while maintaining the temperature below 5°C, and then 2-iodopropane (146 mL) was added dropwise while maintaining the temperature below 5°C. After stirring at 30°C until the conversion of the reaction was 95% or more, ethyl acetate (1800 mL) and 5% aqueous citric acid solution (900 mL) were added to the reaction mixture and separated, and the organic layer was washed with 5% aqueous citric acid solution (900 mL, once), 5% aqueous sodium bicarbonate solution (900 mL, twice), and purified water (900 mL, once). The solvent was removed by distillation under reduced pressure at 40°C or lower, thereby obtaining a crude terfluride product (132 g, yield 100%, HPLC purity: 95.5%, α chain trans isomer content: 0.73%).

[0105] Example 1

[0106] (Step 1) A slurry prepared from silica gel (manufactured by AGC-SITECH CO., LTD., M.S. GEL D50-120A, particle size (d50): 50 μm, spherical, 50 g) and n-hexane / ethanol = 96 / 4 was packed in a column, and the crude terfluride product (1 g) obtained in Reference Example 2 was dissolved in n-hexane / ethyl acetate = 1 / 1, packed on the column, and eluted with n-hexane / ethanol = 96 / 4. Each fraction of the fractionation was analyzed by HPLC, and fractions containing terfluride were collected. As the fractions containing terfluride, fractions in which the area percentage of terfluride was 98% or more (calculated by subtracting the solvent peak) were collected.

[0107] (Step 2) The collected fractions containing terfluride were concentrated under reduced pressure at 35°C to 40°C.

[0108] (Step 3) The residue was dissolved in n-hexane / ethyl acetate = 3 / 2, filtered with a membrane filter (pore size: 0.2 μm), and washed with n-hexane / ethyl acetate = 3 / 2.

[0109] (Step 4) The solvent of the filtrate was distilled off for one day and night under reduced pressure at 35°C to 40°C, with a final limit vacuum of 1 torr or less, thereby obtaining terfluride (colorless to pale yellow viscous liquid, yield: 82%, HPLC purity: 99.5%, α chain trans isomer content: 0.25%).

[0110] The residual solvent concentration of the obtained terfluride was analyzed by GC, and the results were 0 ppm for n-hexane, 0 ppm for ethyl acetate, and 0 ppm for ethanol.

[0111] 1 H NMR (CDC13) δ 1.22 (d, J = 6.2 Hz, 3 H), 1.22 (d, J = 6.2 Hz, 3 H), 1.58-1.63 (m, 1 H), 1.63-1.69 (m, 2 H), 1.84 (d, J = 14.7 Hz, 1 H), 2.02-2.08 (m, 1 H), 2.10-2.16 (m, 3 H), 2.25 (t, J = 7.3 Hz, 1 H), 2.26 (t, J = 7.1 Hz, 1 H), 2.30-2.35 (m, 1 H), 2.46-2.49 (m, 2 H), 2.61-2.63 (m, 1 H), 4.02-4.03 (m, 1 H), 4.18-4.21 (m, 3 H), 5.00 (heptet, J = 6.2 Hz, 1 H), 5.35-5.42 (m, 2 H), 5.80 (dt, J = 15.8, 11.2 Hz, 1 H), 6.10 (dd, J = 15.8, 8.8 Hz, 1 H), 6.91 (d, J = 8.8 Hz, 2 H), 7.00 (t, J = 7.3 Hz, 1 H), 7.30 (dd, J = 8.8, 7.3 Hz, 2 H);

[0112] 19 F NMR (CDC13) δ -102.8 (dq, J = 255.6, 21.7 Hz, 1 H), -103.6 (dq, J = 255.6, 21.7 Hz, 1 H). 2 J FF = 255.6 Hz), -103.6 (dq, J = 255.6 Hz). 2 J FF = 255.6 Hz).

[0113] <HPLC (reverse phase) analytical condition>

[0114] Column: YMC-Pack ODS-AM (5 μm, 6.0 x 150 mm)

[0115] Temperature: room temperature

[0116] Flow rate: 1 mL / min

[0117] Detection wavelength: 220 nm

[0118] Eluent: (A liquid) 1% triethylamine-phosphate buffer (pH 6.3), (B liquid) acetonitrile

[0119] Gradient condition: A / B = 50 / 50 (0-45 min), A / B = 25 / 75 (45-70 min)

[0120] <GC analytical condition>

[0121]

[0122] ​Column: G-column G300 (1.2 mm I.D., 40 m)

[0123] Column temperature: 50°C

[0124] Detection: hydrogen flame ionization detector

[0125] Carrier gas: helium

[0126] Injector temperature: 160°C

[0127] Detector temperature: 160°C

[0128] Examples 2 to 6

[0129] To investigate the influence of the kind of silica used in the silica gel column chromatography on the purity and yield of tafluprost, the following experiments were conducted in the same manner as in Example 1.

[0130] Using the crude tafluprost product (1 g; HPLC purity: 95.5%) and silica gel (50 g), the results of the silica gel column chromatography were shown in Table 1 below. The reverse phase HPLC analysis was conducted under the same conditions as described above.

[0131] [Table 1]

[0132]

[0133] Comparative Example 1

[0134] Using the crude tafluprost product (1 g; HPLC purity: 95.5%), the silica gel used in Example 2 (50 g), and the eluent, the silica gel column chromatography was conducted. Except that each fraction fractionated was analyzed by TLC instead of HPLC, the same as in Example 1, the fraction containing only tafluprost was collected visually, and as a result, the HPLC purity of the obtained tafluprost was 97.3%, which did not reach the quality level (limit value: 98%) required for a purified product as a pharmaceutical product.

[0135] When the particle size (d50) of the silica gel used was 65 μm or less, tafluprost having a purity of more than 98% was obtained in Examples 1 to 6, although the shapes were different. Among them, it was found that when spherical silica gel was used, tafluprost having a particularly high purity could be obtained at a high yield.

[0136] Example 7 (scaled-up study)

[0137] (Step 1)

[0138] The same way as in the procedure 1 of Example 1, the slurry prepared from silica gel (manufactured by AGC-SITECH CO., LTD., M.S. GEL D50-120A, particle size (d50): 50 μm, spherical, 6.0 kg) and n-hexane / ethanol = 96 / 4 was packed in a column, the crude tafluprost obtained in Reference Example 2 (120 g) was dissolved in n-hexane / ethyl acetate = 1 / 1, packed on the column, and eluted with n-hexane / ethanol = 96 / 4. Each fraction of the fractionation was analyzed by HPLC, and the fraction containing tafluprost was collected. As the fraction containing tafluprost, at least the fraction in which the area percentage of tafluprost was 98% or more (calculated by subtracting the solvent peak) was collected.

[0139] (Procedures 2 to 4)

[0140] The fraction containing tafluprost collected in the procedure 1 was concentrated under reduced pressure at 29°C to 35°C (procedure 2).

[0141] The residue was dissolved in n-hexane / ethyl acetate = 3 / 2, filtered with a membrane filter (pore size: 0.2 μm), and washed with n-hexane / ethyl acetate = 3 / 2 (procedure 3).

[0142] The solvent of the filtrate was distilled off under reduced pressure at 32°C to 36°C and a final ultimate vacuum degree of 0.30 torr for 26 hours (procedure 4), whereby tafluprost was obtained (colorless to pale yellow viscous liquid, yield: 86%, HPLC purity: 99.7%, α chain trans isomer content: 0.24%, microbial content: 10 cfu / 0.1 g or less).

[0143] The residual solvent concentration of the obtained tafluprost was analyzed by GC, and the results were 0 ppm for n-hexane, 0 ppm for ethyl acetate, and 0 ppm for ethanol.

[0144] Example 8

[0145] The fraction containing tafluprost purified and collected in the same way as in the procedure 1 of Example 7 was concentrated under reduced pressure under the same conditions as in the procedure 2 of Example 7.

[0146] The obtained residue was dissolved in ethyl acetate, filtered with a membrane filter (pore size: 0.2 μm), and washed with ethyl acetate (procedure 3).

[0147] The solvent of the filtrate was distilled off under reduced pressure at 23°C to 37°C and a final ultimate vacuum degree of 0.26 torr for 27 hours (procedure 4), whereby tafluprost was obtained (colorless to pale yellow viscous liquid, yield: 85%, HPLC purity: 99.7%, α chain trans isomer content: 0.27%, microbial content: 10 cfu / 0.1 g or less).

[0148] The residual solvent concentration of tafluprost obtained by GC analysis was 0 ppm for n-hexane, 0 ppm for ethyl acetate, and 0 ppm for ethanol.

[0149] Example 9

[0150] The component containing tafluprost purified and collected in the same manner as in Step 1 of Example 7 was concentrated under reduced pressure under the same conditions as in Step 2 of Example 7, the residue was dissolved in n-hexane / ethyl acetate = 3 / 2, filtered with a membrane filter (pore size: 0.2 μm), and washed with n-hexane / ethyl acetate = 3 / 2 (Step 3).

[0151] The solvent of the filtrate was distilled off for 3 hours under reduced pressure at 20°C to 36°C with a final limit vacuum of 2.6 torr (Step 4), whereby tafluprost was obtained (colorless to pale yellow viscous liquid, yield: 75%, HPLC purity: 99.4%, α chain trans isomer content: 0.30%, microbial content: 10 cfu / 0.1 g or less).

[0152] The residual solvent concentration of tafluprost obtained by GC analysis was 36 ppm for n-hexane, 4803 ppm for ethyl acetate, and 66 ppm for ethanol.

[0153] Example 10

[0154] The component containing tafluprost purified and collected in the same manner as in Step 1 of Example 7 was concentrated under reduced pressure under the same conditions as in Step 2 of Example 7, the residue was dissolved in n-hexane / ethyl acetate = 3 / 2, filtered with a membrane filter (pore size: 0.2 μm), and washed with n-hexane / ethyl acetate = 3 / 2 (Step 3).

[0155] The solvent of the filtrate was distilled off for 5 hours under reduced pressure at 34°C to 37°C with a final limit vacuum of 2.1 torr (Step 4), whereby tafluprost was obtained (colorless to pale yellow viscous liquid, yield: 78%, HPLC purity: 99.5%, α chain trans isomer content: 0.32%, microbial content: 10 cfu / 0.1 g or less).

[0156] The residual solvent concentration of tafluprost obtained by GC analysis was 2 ppm for n-hexane, 785 ppm for ethyl acetate, and 0 ppm for ethanol.

[0157] Example 11

[0158] The component containing tafluposcope purified and collected in the same manner as in Step 1 of Example 7 was subjected to concentration under reduced pressure under the same conditions as in Step 2 of Example 7, the residue was dissolved in n-hexane / ethyl acetate = 3 / 2, filtered with a membrane filter (pore size: 0.2 μm), and washed with n-hexane / ethyl acetate = 3 / 2 (Step 3).

[0159] The solvent of the filtrate was distilled off under reduced pressure at 32°C to 36°C and a final ultimate vacuum degree of 0.92 torr for 8 hours (Step 4), whereby tafluposcope was obtained (colorless to pale yellow viscous liquid, yield: 82%, HPLC purity: 99.6%, α chain trans isomer content: 0.26%, microbial content: 10 cfu / 0.1 g or less).

[0160] The residual solvent concentration of tafluposcope obtained by GC analysis was n-hexane: 0 ppm, ethyl acetate: 86 ppm, and ethanol: 0 ppm.

[0161] Example 12

[0162] The component containing tafluposcope purified and collected in the same manner as in Step 1 of Example 7 was subjected to concentration under reduced pressure under the same conditions as in Step 2 of Example 7, the residue was dissolved in n-hexane / ethyl acetate = 3 / 2, filtered with a membrane filter (pore size: 0.2 μm), and washed with n-hexane / ethyl acetate = 3 / 2 (Step 3).

[0163] The solvent of the filtrate was distilled off under reduced pressure at 35°C to 39°C and a final ultimate vacuum degree of 0.09 torr for 50 hours (Step 4), whereby tafluposcope was obtained (colorless to pale yellow viscous liquid, yield: 80%, HPLC purity: 99.5%, α chain trans isomer content: 0.26%, microbial content: 10 cfu / 0.1 g or less).

[0164] The residual solvent concentration of tafluposcope obtained by GC analysis was n-hexane: 0 ppm, ethyl acetate: 0 ppm, and ethanol: 0 ppm.

[0165] Example 13

[0166] The component containing tafluposcope purified and collected in the same manner as in Step 1 of Example 7 was subjected to concentration under reduced pressure under the same conditions as in Step 2 of Example 7, the residue was dissolved in n-hexane / ethyl acetate = 3 / 2, filtered with a membrane filter (pore size: 0.2 μm), and washed with n-hexane / ethyl acetate = 3 / 2 (Step 3).

[0167] The solvent of the filtrate was distilled off under reduced pressure at 36°C to 45°C and a final limit vacuum of 0.24 torr for 60 hours (step 4), whereby tafluprost was obtained (colorless to yellowish viscous liquid, yield: 79%, HPLC purity: 99.5%, α-chain trans isomer content: 0.26%, microbial content: 10 cfu / 0.1 g or less).

[0168] The residual solvent concentration of tafluprost obtained by GC analysis was 0 ppm for n-hexane, 0 ppm for ethyl acetate, and 0 ppm for ethanol.

[0169] The results of the conditions for distilling off the solvent, the yield, purity, and α-chain trans isomer content of tafluprost, and the residual solvent concentration in Examples 7 to 13 described above are shown in Table 2 below.

[0170] [Table 2]

[0171]

[0172] As shown in Table 2, tafluprost was obtained in good purity and at a high yield in Examples 7 to 13, and the residual organic solvent concentration was suppressed to be below the concentration limit value of the residual solvent guideline for pharmaceutical products, and the purification method of the present application is a general-purpose purification method that can be scaled up. On the other hand, it was confirmed that in the comparative example in which the final limit vacuum was 8 torr, the residual organic solvent concentration exceeded the concentration limit value of the residual solvent guideline for pharmaceutical products.

[0173] Test Example

[0174] Study on the thermal stability of tafluprost

[0175] About 120 mg of tafluprost obtained in Example 1 was measured in a glass container, and stored in a constant temperature bath at 40°C, and the change in the content of tafluprost over time was quantitatively studied by reverse phase HPLC analysis. Similarly, about 20 mg of tafluprost was measured in a glass container, and stored in a constant temperature bath at 60°C or 80°C, and the change in the content of tafluprost over time was studied.

[0176] <HPLC (reverse phase) analysis conditions>

[0177] Column: YMC-Pack Pro C18 AS-303 (5 μm, 4.6 x 250 mm)

[0178] Temperature: 50°C

[0179] Flow rate: 1 mL / min

[0180] Detection wavelength: 220 nm

[0181] Eluent: (A liquid) 10 mmol / L phosphoric acid (sodium) buffer (pH 6.9),

[0182] (B liquid) acetonitrile

[0183] Gradient condition: A / B = 50 / 50 (0-45 minutes), A / B = 25 / 75 (45-70 minutes)

[0184] The results of the study of the temporal change in the amount of tafluprost at each temperature are shown in Tables 3 to 5 below.

[0185] [Table 3]

[0186] Stability of tafluprost at 40°C

[0187] Time (month) 0 3 6 Talprost content (%) 101.3 99.8 99.4

[0188] [Table 4]

[0189] Stability of tafluprost at 60°C

[0190] Time (day) 0 3 7 14 Talprost content (%) 99.0 98.9 98.5 95.4

[0191] [Table 5]

[0192] Stability of tafluprost at 80°C

[0193] Time (day) 0 1 3 7 Talprost content (%) 99.5 99.1 94.4 86.7

[0194] From the results of Tables 3 to 5, it can be confirmed that tafluprost is slowly decomposed with the passage of time even at a temperature of 60°C or higher, i.e., for a storage period of several days to about 2 weeks, and is significantly decomposed at 80°C, but is stably present even at 40°C for 6 months.

[0195] From the above results, it can be seen that, in the purification method of the present application, the decomposed impurities (analogous substances) derived from tafluprost are inhibited from being mixed by performing the concentration under reduced pressure and the removal of the solvent by distillation at a temperature of 55°C or lower (particularly preferably 45°C or lower).

[0196] Industrial applicability

[0197] By the purification method of the present application, in the final step in the manufacture of tafluprost, when the crude product of tafluprost is separated and purified by silica gel column chromatography, the collection of the fraction containing tafluprost by HPLC analysis thereby makes the mixing of impurities to be minimized. Further, under the reduced pressure condition of low temperature and high vacuum degree, the solvent is distilled off with time, thereby the residual organic solvent concentration can be inhibited to be below the concentration limit value of the residual solvent guideline of pharmaceuticals, and the decomposition of tafluprost which is unstable at high temperature can be inhibited. Furthermore, the filter filtration process is incorporated in the middle, thereby the fine powder of silica gel, the floating particles in the air, and the bacteria can be removed, thus having the advantage that after the distillation removal of the solvent, the high purity tafluprost which can be directly used as the drug substance of pharmaceuticals can be simply and efficiently provided. In addition, the purification method of the present application can be widely applied to the crude product of tafluprost manufactured by the known method, and is a highly versatile method which can also be scaled up.

Claims

1. A method for purifying tafluprost, comprising: The process of purifying the crude tafluprost product using spherical silica gel column chromatography and collecting the fraction containing tafluprost by HPLC analysis was described. The HPLC analysis was reversed-phase HPLC analysis. The purification method further includes: a step of concentrating the tafluprost-containing fraction collected by HPLC analysis under reduced pressure at 10–55°C; a step of dissolving the residue in a solvent and filtering it; and a step of removing the solvent from the filtrate by distillation at 10–55°C and a final ultimate vacuum of less than 5 torr. The silica gel used in silica gel column chromatography has a particle size d50 of 20–70 μm. The eluent for silica gel column chromatography is a mixture of n-hexane and a polar solvent, or a mixture of n-heptane and a polar solvent. The polar solvents are ethyl acetate, tert-butyl methyl ether, 2-propanol, or ethanol.

2. The purification method according to claim 1, wherein, The eluent is a mixture of n-hexane and a polar solvent.

3. The purification method according to claim 1 or 2, wherein, The components contain more than 98% tafluprost.

4. The purification method according to claim 1 or 2, wherein, Filtration is performed using a filter with a pore size of less than 0.5 μm.

5. The purification method according to claim 1 or 2, wherein, The solvent used to dissolve the residue is ethyl acetate, tert-butyl methyl ether, 2-propanol or ethanol, or a mixture of ethyl acetate, tert-butyl methyl ether, 2-propanol or ethanol and a nonpolar solvent.

6. The purification method according to claim 5, wherein, The solvent used to dissolve the residue is ethyl acetate, or a mixture of ethyl acetate and a nonpolar solvent.

7. The purification method according to claim 5, wherein, The nonpolar solvent is n-hexane or n-heptane.

8. The purification method according to claim 6, wherein, The nonpolar solvent is n-hexane or n-heptane.

9. The purification method according to claim 1 or 2, wherein, The ultimate vacuum level is below 1 torr.

10. The purification method according to claim 1 or 2, wherein, After the solvent removal process by distillation, the residual solvent concentration of n-hexane in the filtrate is below 290 ppm, and the residual solvent concentrations of n-heptane, ethyl acetate, tert-butyl methyl ether, 2-propanol, or ethanol are below 5000 ppm.

11. A method for manufacturing tafluprost, comprising the step of feeding crude tafluprost into the purification method according to any one of claims 1 to 10.

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