Methods and intermediates for preparation of carboprost and carboprost tranexamide, and carboprost tranexamide made therefrom

Abstract

The present application relates to methods and intermediates for the preparation of carboprost and carboprost tranexamic acid, and carboprost tranexamic acid prepared therefrom. The present invention relates to a process for the preparation of carboprost or carboprost tranexamide, to intermediates made by said process, and to carboprost or carboprost tranexamide free of 5, 6-trans isomers made therefrom. The present invention also relates to a novel crystalline form of carboprost tranexamide.

Description

[0001] This application is a divisional application of the invention patent application with application number 202211006177.3, filed on August 22, 2022, and entitled “Process and intermediates for the preparation of carboprost and carboprost tromethamine, and carboprost tromethamine made therefrom”. TECHNICAL FIELD

[0002] The present invention relates to novel processes and intermediates for the preparation of carboprost and carboprost tromethamine, and novel high melting point crystals of carboprost tromethamine made therefrom. BACKGROUND

[0003] Both carboprost and carboprost tromethamine (INN, trade name Hemabate, Tham) are synthetic prostaglandin analogs of PGF2α (specifically, 15-methyl-PGF2α) with oxytocic properties as shown in Scheme A below. Carboprost and carboprost tromethamine can induce uterine contractions and induce abortion in early pregnancy, and also can reduce postpartum hemorrhage.

[0004] Scheme A

[0005]

[0006] Despite the current regulations that increasingly restrict the content of impurities or impure substances in active pharmaceutical ingredients (APIs), almost all commercially available carboprost and carboprost tromethamine still contain about 3% of 5,6-trans isomer and about 2% of 15(R)-epimer. Scheme B below shows the chemical structures of carboprost and its isomers, i.e., 5,6-trans carboprost and 15-epimer carboprost. However, the methods used in the industry for mass production of carboprost or carboprost tromethamine have some problems to be solved, especially in terms of the spatial orientation of the cis-double bond at the C5-C6 position and the tertiary alcohol at the C15 position of carboprost or carboprost tromethamine. In addition, the purification methods currently used to remove impurities of carboprost or carboprost tromethamine are not effective and must be improved.

[0007] Scheme B

[0008]

[0009] C15-(R / S)-selectivity

[0010] Carboprost tromethamine is an original product of Upjohn. The first scale synthesis of carboprost tromethamine was disclosed by Upjohn chemists (Yankee et al., J. Am. Chem. Soc, 96(18), 5865-5876, 1974). As shown in Scheme C(1) below, the 15-methyl substituent is built from a benzoyl gamma-lactone-enone of formula a with trimethylaluminum or with methylmagnesium bromide. However, the selectivity for the 15(S)-product is only 50% in both cases, meaning that this method is not selective. WO 2008 / 081191 discloses that alkylation of a triethylsilyl gamma-lactone-enone of formula b with methylmagnesium chloride can give a 15(S)-product with a maximum selectivity of 70%, as shown in Scheme C(2) below. WO 2017 / 093770 discloses that alkylation of a p-phenylbenzoyl gamma-lactone-enone of formula c with methylmagnesium bromide can give a 15(S)-product with a selectivity of only 55%, and it also discloses the use of various chiral additives in order to increase the selectivity for the 15(S)-product, and it was found that the addition of (S)-Taddol can increase the selectivity to 70%, as shown in Scheme C(3) below. However, the maximum selectivity disclosed in WO 2017 / 093770 is at most the same as the selectivity disclosed in WO 2008 / 081191.

[0011] Scheme C

[0012]

[0013] C5,6-(trans / cis)-selectivity

[0014] WO 2008 / 081191 discloses that performing the Wittig reaction at ambient temperature and in dimethylsulfoxide (DMSO) solvent as disclosed by Yankee et al. will produce 6% to 8% of the undesired 5,6 trans-isomer, as shown in Scheme D(1) below. WO 2008 / 0181191 further discloses that a reaction at low temperature, i.e. between 5°C to +5°C, can reduce the content of the 5,6 trans-isomer to about 3%, as shown in Scheme D(2) below. In view of the above, since all commercially available carboprost and carboprost tromethamine contain about 3% of the 5,6-trans isomer, it seems that changing the reaction conditions of the Wittig reaction is not useful in terms of further reducing the content of the 5,6-trans isomer produced therefrom.

[0015] Scheme D

[0016]

[0017] Removal of 15(R)-epimer and trans-isomer by purification of carboprost methyl ester

[0018] As disclosed by Yankee et al. and in Eur. J. Pharm. Sci, 3, 27-38 (1995), the allylic tertiary alcohol at the C15 position of carboprost is extremely unstable; thus, only a small amount of acid or a small amount of heat will cause a large amount of 15(R)-epimer to be rapidly produced via epimerization. For this reason, the current industrial processes for the mass production of carboprost or carboprost tromethamine do not build the stereochemistry of the allylic tertiary alcohol in the intermediates formed in the early stage, because the stereochemistry of the allylic tertiary alcohol is difficult to maintain to the final stage. Therefore, almost all of the current industrial processes for the mass production of carboprost or carboprost tromethamine either build the stereochemistry of the allylic tertiary alcohol in the intermediates formed in the later stage or remove the undesired 15(R)-epimer and trans-isomer after the final product is formed.

[0019] Although the final product carboprost tromethamine is a crystalline solid at room temperature, it is still extremely difficult to purify by crystallization alone while effectively removing the 15(R)-epimer and trans-isomer. In addition, because the polarity of carboprost is extremely large, it is more difficult to remove the 15(R)-epimer and trans-isomer from carboprost by chromatography.

[0020] Therefore, the isomers produced during the preparation of carboprost or carboprost tromethamine cannot be effectively removed, and there is no suitable late-stage process intermediate for separating and removing the isomers in the prior art processes. In order to purify the final product, two additional steps are required to produce a late-stage process intermediate suitable for separating and removing the isomers. As disclosed in the known references, such as J, Am. Chem. Soc, 96(18), 5865-5876, 1974, WO 2008 / 081191, WO 2017 / 093770, CN 111777537, and CN 102816099, carboprost must be esterified to form carboprost methyl ester, then the 15(R)-epimer and trans-isomer of carboprost methyl ester are removed by chromatography, and carboprost methyl ester is hydrolyzed to carboprost with higher purity, but the yield and purity in this method are extremely unsatisfactory. CN 1136938 C discloses using expensive and specific simulated moving bed (SMB) chromatography to separate and remove the isomers of carboprost methyl ester, but the purity of the final product is still not good enough. CN 102816099 discloses using analytical grade HPLC column chromatography packing (5 μm) for separation, but the trans-isomer cannot still be completely removed. In addition, because the separation amount of the CN 102816099 disclosed method is small, this method is difficult to use for industrial mass production. SUMMARY

[0021] In view of the above, there is a need to develop a process for preparing high purity carboprost or carboprost tromethamine that can significantly reduce the formation of impurities or isomers including 15(R)-epimer and trans isomer and also can effectively remove the impurities or isomers produced.

[0022] It is an object of the present invention to provide an efficient process for forming carboprost or carboprost tromethamine. The process includes a macrolactonization step that can effectively remove the 5,6-trans isomer. The process also includes a methylation step of the macrolactone-enone for the directed construction of the tertiary alcohol at the C15 position of carboprost. In all previous cases, the 15(S)- selectivity of the methylation of the macrolactone-enone is much higher than the selectivity of the methylation of the γ-lactone-enone. The present invention also provides a novel purification process that can effectively remove all isomers and can more efficiently produce carboprost and carboprost tromethamine, thereby forming a final product with high purity, high melting point and good stability.

[0023] One aspect of the present invention provides a process for preparing high purity carboprost or carboprost tromethamine containing no more than about 1% total isomers from a compound of Formula la containing about 1% to 10% of the 5,6-trans isomer:

[0024]

[0025] wherein is or a carbonyl protecting group; and Pi and P2 are H or a hydroxyl protecting group.

[0026] The present invention also provides a process for preparing high purity carboprost or carboprost tromethamine containing no more than about 1% total isomers from a compound of Formula lb containing about 1% to 10% of the 5,6-trans isomer,

[0027]

[0028] wherein Pi and P2 are H or a hydroxyl protecting group.

[0029] The present invention also provides a process for purifying carboprost that effectively purifies low purity carboprost containing a significant amount of isomers, such as about 1% to 10% of the 5,6-trans isomer and about 1% to 50% of the 15(R)-epimer, to high purity carboprost containing no more than about 1% total isomers.

[0030] The present invention also provides a macrolactone-enone intermediate of Formula 2a' that is a novel intermediate for preparing carboprost or carboprost tromethamine,

[0031] The present invention also provides a macrolactone-enone intermediate of Formula 2a' that is a novel intermediate for preparing carboprost or carboprost tromethamine,

[0032] wherein P1 is H or a hydroxyl protecting group.

[0033] The present application further provides a method of preparing a macrolide tertiary alcohol of Formula 3 from a macrolide-enone of Formula 2a' with a methylating agent, which is an intermediate for preparing carboprost or carboprost tromethamine,

[0034]

[0035] wherein P1 is H or a hydroxyl protecting group.

[0036] The present application further provides a high melting point (106.4 ± 1 °C) crystal of carboprost tromethamine having an X-ray powder diffraction (XRPD) pattern exhibiting characteristic peaks at 2Θ reflection angles of 6.9 ± 0.2°, 10.3 ± 0.2°, 18.8 ± 0.2°, and 21.9 ± 0.2°.

[0037] The present application further provides a method for preparing a high melting point crystal of carboprost tromethamine comprising using a solvent of anhydrous acetonitrile.

[0038] Brief description of the drawings

[0039] Figure 1 X-ray powder diffraction (XRPD) pattern of the carboprost tromethamine crystal of the present application is shown.

[0040] Figure 2 Differential scanning calorimetry (DSC) thermogram of the carboprost tromethamine crystal of the present application is shown.

[0041] Figure 3 X-ray powder diffraction (XRPD) patterns of five different batches of carboprost tromethamine crystals according to the present application are shown.

[0042] Figure 4 Differential scanning calorimetry (DSC) thermograms of five different batches of carboprost tromethamine crystals according to the present application are shown.

[0043] Figure 5 Differential scanning calorimetry (DSC) thermogram of the carboprost tromethamine crystal prepared from Example 9 of the present application is shown.

[0044] Figure 6 Differential scanning calorimetry (DSC) thermogram of the carboprost tromethamine crystal prepared from Example 10 of the present application is shown. DETAILED DESCRIPTION

[0045] DEFINITIONS

[0046] The use of the term "a" or "an" when used in the context of the application patent scope and / or the specification is intended to mean "one," but also "a or more," "at least one," and "one or more." Although the application supports the definition of "only alternatives" and "and / or," the use of the term "or" in the application patent scope is used to mean "and / or" unless explicitly indicated to the contrary that alternatives are mutually exclusive. Throughout this application the term "about" is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study individuals.

[0047] As used in the specification and application patent scope, the words "comprising" (and any form of comprising, such as "comprise" and "comprises") "having" (and any form of having, such as "have" and "has") "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0048] In the depiction of compounds given in this specification, a wedge-shaped bold bond means a bond that protrudes above the plane of the paper; a wedge-shaped hashed bond means a bond that protrudes below the plane of the paper; and a wavy bond means a bond that protrudes about half above and half below the plane of the paper.

[0049] The term "high purity carboprost or carboprost tromethamine," "high purity carboprost," or "high purity carboprost tromethamine" as used herein means that the referenced carboprost and / or carboprost tromethamine contains no more than about 1% total isomers, preferably no more than about 0.8% total isomers or no more than about 0.5% total isomers, and more preferably no more than about 0.3% total isomers. The isomers or impurities or impurities indicated herein include the 5,6-trans isomer, the 15(R)-epimer, and any other stereoisomers.

[0050] As used herein, the term with respect to being substantially free of 5,6-trans isomers or the like means that the recited compound contains no more than about 0.5%, no more than about 0.3%, no more than about 0.2%, no more than about 0.1%, no more than about 0.05%, or no more than about 0.03% of impurities or isomers (such as 5,6-trans isomers), or contains no detectable amount of impurities or isomers (such as 5,6-trans isomers) as measured by HPLC, with a detection limit of no more than about 0.03%.

[0051] Unless otherwise specified, the term "hydroxyl protecting group" has its conventional meaning as defined in organic synthetic chemistry, i.e., a group capable of protecting a hydroxyl or moiety of a compound against chemical attack. Examples of hydroxyl protecting groups include, but are not limited to, methoxymethyl, methoxythiomethyl, 2-methoxyethoxymethyl, bis(2-chloroethoxy)methyl, tetrahydropyranyl, tetrahydrothiopyranyl, 4-methoxytetrahydropyranyl, 4-methoxytetrahydrothiopyranyl, tetrahydrofuranyl, tetrahydrothiofuranyl, 1-ethoxyethyl, 1-methyl-l-methoxyethyl, trityl, allyl, benzyl, substituted benzyl, acetyl, substituted acetyl, benzoyl, substituted benzoyl, and SiRaRbRc, where each of Ra, Rb, and Rc is independently unsubstituted or substituted alkyl or unsubstituted or substituted aryl, such as C 1-4 alkyl, phenyl, benzyl, substituted phenyl, and substituted benzyl.

[0052] Unless otherwise specified, the term "carbonyl protecting group" has its conventional meaning as defined in organic synthetic chemistry, i.e., a group capable of protecting a carbonyl or moiety of a compound against chemical attack. Examples of carbonyl protecting groups include, but are not limited to, dialkyl ketal, diaryl ketal, diacetyl ketal, dithio ketal, 1,3-dioxane, 1,3-dithiane, 1,3-dithiolane, and 1,3-oxathiolane. Preferred carbonyl protecting groups include dialkyl ketal, 1,3-dioxane, and 1,3-dithiolane. alkyl, phenyl, benzyl, substituted phenyl, and substituted benzyl. (1,3-dithiane), 1,3-dithiolane, and 1,3-oxathiolane. Preferred carbonyl protecting groups include dialkyl ketal, 1,3-dioxane, and 1,3-dithiolane. alkyl, phenyl, benzyl, substituted phenyl, and substituted benzyl.

[0053] Each of the above-mentioned groups, such as alkyl and aryl, can be optionally substituted with one or more substituents selected from the group consisting of halogen, alkyl, aryl, alkoxy, aryloxy, thioalkoxy, thioaryloxy, alkylamino, arylamino, cyano, alkoxycarbonyl, arylcarbonyl, arylaminocarbonyl, alkylaminocarbonyl, and carbonyl, or a heterocyclyl group selected from the group consisting of pyridyl, thienyl, furanyl, imidazolyl, morpholinyl, azolyl, piperidinyl, piperazinyl, tetrahydropyranyl, pyrrolidinyl, and the like. The term "alkyl" as used herein, unless otherwise indicated, refers to a straight or branched chain hydrocarbon group containing from 1 to 8, 1 to 6, or 1 to 4 carbon atoms, such as methyl, ethyl, isopropyl, tert-butyl, and the like; or a cyclic saturated hydrocarbon group having from 3 to 10 or 3 to 8 carbon atoms, such as cyclopropyl, cyclopentyl, cyclohexyl, and the like. The term "aryl" as used herein refers to a monocyclic or polycyclic aromatic hydrocarbon group and has from 6 to 20, 6 to 18, or 6 to 12 carbon atoms, such as phenyl, naphthyl, anthryl, phenanthryl, and the like.

[0054] Synthesis of high purity carboprost from known prostaglandin intermediates of Formula 1a or Formula 1b

[0055] According to the present application, high purity carboprost or carboprost tromethamine can be prepared according to the reactions shown in Scheme 1 and Scheme 2:

[0056] Scheme 1

[0057]

[0058] Scheme 2

[0059]

[0060] The compound of Formula 1a in Scheme 1, wherein is or a carbonyl protecting group; and P1and P2are hydroxyl protecting groups, is a well known prostaglandin F 2α intermediate. The compound of Formula 1b in Scheme 2, wherein P1and P2are hydroxyl protecting groups, is a well known 15-methyl prostaglandin F 2α intermediate. Both prostaglandin intermediates can be prepared from the well known Corey lactone via a Wittig reaction. Due to the different reaction conditions of the Wittig reaction, both prostaglandin intermediates contain almost entirely from about 1% to about 10% of the 5,6-trans isomer.

[0061] As shown in step (1) of Scheme 1 and step (1) of Scheme 2, the macrolactonization reaction can involve activation of the carboxyl or / and hydroxyl functional groups. In this approach, the macrolactonization reaction includes initial formation of a thioester with a suitable reagent including, but not limited to, chloromethylthioate S-pyridin-2-yl ester, 2,2'-dipyridyl disulfide / triphenylphosphine, or 4-tert-butyl-2-(2-(4-tert-butyl-1-isopropyl-1H-imidazol-2-yl)disulfanyl)-1-isopropyl-1H- imidazole / triphenylphosphine.

[0062] The macrolactonization reaction can alternatively be used to initially form a mixed anhydride with a suitable reagent in the presence or absence of a base or Lewis acid. Suitable reagents for forming a mixed anhydride include, but are not limited to, 2,4,6-trichlorobenzoyl chloride, 2-nitro-6-nitrobenzoic anhydride, p-nitrofluoromethylbenzoic anhydride, p-nitrobenzoic anhydride, and the like. Examples of suitable bases include 4-(dimethylamino)pyridine, pyridine and pyridine, triethylamine, N,N-diisopropylethylamine, and isopropyl diethylamine. Examples of suitable Lewis acids include Sc(OTf)3, TiCl4, AgClO4, trimethylsilyl chloride (TMSCl), and TiCl2(OTf).

[0063] The macrolactonization reaction can also be achieved by using a condensing reagent and a base in a suitable solvent. Suitable condensing reagents include, but are not limited to, N,N'-dicyclohexylcarbodiimide, 2-chloro-l-methyl-pyridinium iodide, 2-chloro-4,5-dihydro-l,3-dimethyl-lH-imidazolium chloride, N,N- dibenzylethylammonium chloride, trichloroisonitrile, l,3-dimethyl-2-chloroimidazolium chloride, N,N,N,N-tetramethylchloroformamidinium chloride, and the like. Examples of suitable bases include pyridine, triethylamine, diisopropyl ethylamine, 4-dimethylaminopyridine (DMAP), and the like. Suitable solvents for the condensation reaction include dichloromethane, tetrahydrofuran, and 1,2-dichloroethane, and mixtures thereof.

[0064] Upon analysis of the resulting compound of Formula 2a, 2a', 2b, 3, or 4 by HPLC or UPLC, it was unexpectedly found that the resulting compound of Formula 2a, 2a', 2b, 3, or 4 contained no more than about 0.1% or less of the 5,6-trans isomer, which demonstrates that the macrolactonization reaction exhibits cis-selectivity; that is, the 5,6-cis compound of Formula la or lb predominates in the macrolactonization reaction, while the 5,6-trans compound of Formula la or lb undergoes little to no macrolactonization reaction.

[0065] Step (2) of Scheme 1 involves removal of P2 and / or PI at the omega-side chain of the compound of Formula 2a, wherein is Deprotection and oxidation of formula 2a. The conditions for carrying out the deprotection reaction are obvious to those skilled in the art. For example, a macrolide of formula 2a, wherein P1 and P2 are tetrahydropiperanyl protecting groups, is dissolved in a suitable solvent (such as methanol or a solvent mixture of acetone and water in a volume ratio of 5:1); treated with a deprotecting agent (such as hydrogen chloride, p-toluenesulfonic acid, or p-toluenesulfonic acid pyridinium); and stirred at room temperature for 10 minutes to 10 hours. The reaction is quenched with a base (such as ammonium hydroxide or the like) and the work-up procedure is carried out in a conventional manner. The deprotected product of formula 2a, wherein P1 and P2 are H, is oxidized with a suitable oxidizing agent (such as MnO2 or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)) to form a macrolide-enone of formula 2a', wherein P1 is H.

[0066] For example, a macrolide of formula 2a, wherein P1 is a tetrahydropiperanyl protecting group and P2 is a tributyldimethylsilyl protecting group, is dissolved in a suitable solvent (such as tetrahydrofuran (THF)); treated with a deprotecting agent (such as tetrabutylammonium fluoride (TBAF)); and stirred at room temperature for 10 minutes to 10 hours. The reaction is carried out in a conventional manner. The deprotected product of formula 2a, wherein P1 is a tetrahydropiperanyl protecting group and P2 is H, is then oxidized with a suitable oxidizing agent (such as Collins oxidant, Swern oxidant, PCC oxidant, PDC oxidant, and TEMPO oxidant, preferably TEMPO oxidant) to form a macrolide-enone of formula 2a', wherein P1 is a tetrahydropiperanyl protecting group.

[0067] Step (2) of process 1 also involves compound 2a (wherein) Deprotection of the carbonyl protecting group. The conditions for carrying out the deprotection reaction are obvious to those skilled in this art. For example, [the reaction involves...] For 1,3-two A macrolide of formula 2a, with an alkyl protecting group and P1 being H, is dissolved in a suitable solvent (such as THF or acetone); treated with a deprotecting agent (such as 1M HCl solution); and stirred at room temperature for 10 minutes to 10 hours. The reaction is quenched with a base (e.g., saturated NaHCO3 solution or similar) and the procedure is carried out in a conventional manner to form a macrolide-enone of formula 2a', where P1 is H.

[0068] Furthermore, step (2) of process 2 involves the deprotection of compound 2b (where P2 is a hydroxyl protecting group) by removing P2 and / or P1 from the ω-side chain. The conditions for carrying out the deprotection reaction are obvious to those skilled in the art.

[0069] Step (3) of Scheme 1 shows methylation of the macrolide-enone of Formula 2a’ wherein P1is a hydroxyl protecting group to form the macrolide tertiary alcohol of Formula 3a. According to the present application, the methylating reagent includes, but is not limited to, MeLi, MeMgCl, MeMgBr, MeMgI, Me3Al, or a mixture thereof. Preferably, the methylating reagent is MeMgCl, MeMgBr, MeMgI, MeLi, or a mixture thereof. Most preferably, the methylating reagent is MeLi. Non-limiting suitable solvents used in the reaction can be selected from tetrahydrofuran, diethyl ether, toluene, hexane, or a mixture thereof. The reaction is carried out at a temperature ranging from about -120 °C to room temperature, preferably from about -100 °C to about -40 °C. The methylating reagent is used in an amount to allow the reactants to be completely reacted as monitored by thin layer chromatography (TLC).

[0070] It was surprisingly found that the reaction of the macrolide-enone and the methyl Grignard reagent as the methylating reagent exhibited up to about 65% 15(S)- selectivity. However, as shown in Scheme A(1), the reaction of the γ-lactone-enone and the methyl Grignard reagent exhibited only 50% 15(S)-selectivity. It appears that the structure of the macrolide helps the 15(S)-selectivity than the γ-lactone. In addition, the present application surprisingly found that the methylation of the macrolide-enone can have about 75% or greater 15(S)-selectivity using the low cost and more suitable MeLi as the methylating reagent, which is extremely high and cannot be achieved even with the use of a chiral additive in the γ-lactone reaction (WO 2017 / 093770, using (S)-Taddol, the highest selectivity is only 70%).

[0071] Steps (4) of Scheme 1 and (3) of Scheme 2 involve purification of the macrolide tertiary alcohol of Formula 3 for removal of the 15(R)-epimer. Generally, separation of the isomers of treprostinil is the most expensive and time-consuming step in large scale production of treprostinil. However, the cost of separating the isomers of the present application is much lower than the prior art, for example, J, Am. Chem. Soc, 96(18), 5865-5876, 1974; WO 2008 / 081191; WO 2017 / 093770; CN 111777537; and CN102816099A. The reasons are listed as follows:

[0072] (a) In the prior art, treprostinil must be esterified to form the intermediate treprostinil methyl ester, which is suitable for removal of isomers, and then the isomers of treprostinil methyl ester can be removed by chromatographic purification. However, it was surprisingly found that the late-stage intermediate of Formula 3 is an intermediate suitable for removal of isomers; therefore, it is not necessary to use an additional esterification reaction in the present application.

[0073] (b) When using chromatographic purification to remove the 5,6-trans isomer and the 15(R)-epimer of carboprost intermediates, the 5,6-trans isomer (HPLC, 0.93) is generally more difficult to separate than the 15(R)-epimer (HPLC, RRT 0.88). CN 102816099 even uses analytical HPLC with a packing material (5 μιη) to remove the 5,6-trans isomer of carboprost methyl ester (RRT 0.93). In contrast, the intermediates of Formula 3 formed after macrolactonization and the compound of Formula 2a' are substantially free of the 5,6-trans isomer, and therefore, the 15(R)-epimer which is more easily removed, can be simply isolated using general silica gel column chromatography for industrial bulk production.

[0074] (c) The methylation of the macrolactone-enone of the present application exhibits higher selectivity, and therefore, the amount of 15(R)-epimer produced is less and can be more easily removed.

[0075] In step (4) of Scheme 1 and step (3) of Scheme 2, the chromatographic purification can be performed using ester, ether, ketone or halogenated solvents or the like or mixtures thereof. For using a mixture of dichloromethane and acetone, good separation can also be achieved with ethyl acetate, isopropyl acetate, methyl tertiary butyl ether, acetone, methyl ethyl ketone or mixtures thereof. By chromatography, the amount of the unwanted 15(R)-epimer can be reduced to a specified limit, i.e. < about 0.5%, < about 0.3%, < about 0.2%, < about 0.1% or less.

[0076] As shown in step (5) of Scheme 1 and step (4) of Scheme 2, the macrolactone tertiary alcohol of Formula 3 is hydrolyzed to a methanolic solution containing carboprost by treatment with lithium hydroxide solution. Acidification to obtain carboprost must be performed rapidly to avoid epimerization reactions in the acidic medium.

[0077] Accordingly, the present application provides a process for preparing carboprost containing no more than 1% total isomers, said process comprising the steps of:

[0078] (1) macrolactonizing a compound of Formula la containing 1% to 10% of the 5,6-trans isomer

[0079]

[0080] wherein is or a carbonyl protecting group; and P1and P2are H or a hydroxyl protecting group, to form

[0081] the compound of Formula 2a:

[0082] the compound of Formula 2a:

[0083] wherein P1and P2are as defined above for Formula 1a;

[0084] (2) when is a carbonyl protecting group, removing the carbonyl protecting group of the compound of Formula 2a; or when is P2and / or oxidizing the compound of Formula 2a; to form a compound of Formula 2a':

[0085]

[0086] wherein P1is H or a hydroxyl protecting group;

[0087] (3) methylating the compound of Formula 2a' with a methylating reagent to form a compound of Formula 3:

[0088]

[0089] wherein P1is H or a hydroxyl protecting group;

[0090] (4) chromatographically separating the compound of Formula 3 to remove isomers;

[0091] (5) hydrolyzing the compound of Formula 3 to form a compound of Formula 4:

[0092]

[0093] wherein P1is H or a hydroxyl protecting group; and

[0094] (6) when P1is a hydroxyl protecting group, performing a deprotection reaction of the compound of Formula 2a, 2a', 3, or 4, as appropriate, to form a compound of Formula 2a, 2a', 3, or 4, wherein P1is H.

[0095] The present application also provides a method for preparing high purity carboprost with no more than 1% total isomers, the method comprising the steps of:

[0096] (1) macrocyclic lactonizing a compound of Formula 1b containing 1% to 10% 5,6-trans isomer and 1% to 50% 15(R)-epimer,

[0097]

[0098] wherein P1and P2are H or a hydroxyl protecting group, to form a compound of Formula 3a:

[0099]

[0100] wherein P1and P2are as defined above;

[0101] (2) when P1 is H or a hydroxyl protecting group and P2 is a hydroxyl protecting group, performing a deprotection reaction of the compound of Formula 3a to form a compound of Formula 3a, wherein P1 is H or a hydroxyl protecting group and P2 is H;

[0102] (3) chromatographically separating the compound of Formula 3a, wherein P1 is H or a hydroxyl protecting group and P2 is H, to remove isomers;

[0103] (4) hydrolyzing the compound of Formula 3a to form a compound of Formula 4:

[0104]

[0105] wherein P1 is H or a hydroxyl protecting group; and

[0106] (5) when P1 is a hydroxyl protecting group, optionally performing a deprotection reaction of the compound of Formula 3a or 4 to form a compound of Formula 3a or 4, wherein P1 is H.

[0107] Purification of low purity carboprost from a reaction mixture

[0108] Crude carboprost obtained from a reaction mixture or from an overreaction of a retro-aldol reaction often contains a significant amount or excess of isomers. The present inventors have discovered that carboprost containing an excess of isomers can be further purified using the methods of the present invention. The methods of the present invention comprise providing a low purity carboprost containing at least about 1% to 10% of the 5,6-trans isomer and about 1% to 50% of the 15(R)-epi isomer; lactonizing the low purity carboprost to form a macrocyclic lactone tertiary alcohol; chromatographically separating the excess isomer of the macrocyclic lactone tertiary alcohol; and hydrolyzing the macrocyclic lactone tertiary alcohol to form a high purity carboprost containing no more than about 1% total isomers.

[0109] Accordingly, the present invention provides a method for purifying carboprost comprising the steps of:

[0110] (1) lactonizing a low purity carboprost containing 1% to 10% of the 5,6-trans isomer and 1% to 50% of the 15(R)-epi isomer to form a compound of Formula 3b:

[0111]

[0112] (2) chromatographically separating the isomers of the compound of Formula 3b; and

[0113] (3) hydrolyzing the compound of Formula 3b to form a high purity carboprost containing no more than 1% total isomers.

[0114] Forming a carboprost salt with trisodium citrate

[0115] To form carboprost tromethamine from carboprost, the inventive process further comprises salt formation with tromethamine, and crystallization of carboprost tromethamine. The salt formation and crystallization steps can follow the methods disclosed in CN 102336693 or WO 2017 / 093770. Generally, carboprost can first be dissolved in a suitable solvent, such as acetone, acetonitrile, methanol, ethanol, isopropanol, and combinations thereof; a suitable solvent containing tromethamine, such as water, methanol, ethanol, isopropanol, and combinations thereof, can then be added to the solution; and the mixture can be heated to about 85 °C for about 1 hour to form a homogeneous solution. Subsequently, the homogeneous solution can be allowed to cool to about 60 °C, and white solids begin to precipitate slowly. The reaction mixture can be further cooled to room temperature, and then filtered to obtain white crystals of carboprost tromethamine. The white crystals thus obtained generally have a melting point of about 95 °C to 105 °C, as originally disclosed by Pfizer (e.g., from the prescribing information provided by Pfizer).

[0116] In the case of Example 1 of CN 102336693, about 1.20 g of carboprost tromethamine was precipitated from a mixture of 100 ml of acetonitrile and 0.5 ml of water during a temperature reduction, and the melting point of the white crystals was measured to be 103.97 °C (see Figure 2 ). The present inventors repeated Example 1 of CN 102336693 and found that the melting point of the obtained carboprost tromethamine crystals was measured to be 103.41 °C.

[0117] In the case of Example Ig of WO 2017 / 093770, about 593 g of carboprost tromethamine was precipitated from a mixture of isopropanol and acetone. WO 2017 / 093770 does not disclose the melting point of the carboprost tromethamine crystals obtained from Example Ig. The present inventors repeated Example Ig of WO 2017 / 093770 and found that the melting point of the obtained carboprost tromethamine crystals was measured to be 97.49 °C.

[0118] The melting point of the known carboprost tromethamine crystals described above ranges from about 97 °C to about 104 °C, which is actually within the range (95 °C to 105 °C) as originally provided by Pfizer.

[0119] Recrystallization of carboprost tromethamine

[0120] ​Recrystallization of carboprost tromethamine can have an impact on reducing the content of 15(R)-isomer. The recrystallization method of carboprost tromethamine has been disclosed in CN 102336693 and WO 2017 / 093770. The present inventors repeated the method disclosed in CN 102336693 using water and acetone, and found that the recrystallized carboprost tromethamine had a melting point of 103.85 °C as measured. The present inventors also repeated the method disclosed in WO 2017 / 093770 using isopropanol and acetone, and found that the recrystallized carboprost tromethamine had a melting point of 99.46 °C as measured.

[0121] It was unexpectedly found that a particular high melting point carboprost tromethamine crystal can be obtained by a recrystallization method of carboprost tromethamine using a particular solvent of anhydrous acetonitrile. The high melting point carboprost tromethamine crystal thus formed has a differential scanning calorimetry (DSC) thermogram comprising an endothermic peak with a peak maximum of 106.4 ± 1.0 °C, which is significantly higher than the melting point range originally provided by Pfizer and the upper limit of the melting point range of the above-mentioned carboprost tromethamine crystal disclosed in the prior art.

[0122] Preparation of high melting point carboprost tromethamine crystal

[0123] The present invention provides a method for preparing a high melting point crystalline form of carboprost tromethamine, comprising the steps of:

[0124] a. adding carboprost tromethamine to anhydrous acetonitrile to form a mixture, wherein the amount of the anhydrous acetonitrile is about 80 ml to 250 ml per 1 g of carboprost tromethamine;

[0125] b. heating the mixture to a temperature ranging from about 70 °C to 90 °C to obtain a homogeneous solution;

[0126] c. allowing the homogeneous solution to cool to form the crystalline form of carboprost tromethamine; and

[0127] d. optionally isolating the crystalline product.

[0128] In some embodiments, the mixture can be heated to about 80 °C to completely dissolve the carboprost tromethamine; the homogeneous solution can then be slowly cooled, and white solids slowly begin to precipitate; and the mixture can be further cooled to room temperature, and then filtered and dried to obtain the crystalline form of carboprost tromethamine.

[0129] In some embodiments, the amount of anhydrous acetonitrile used in step a ranges from about 80 ml to 250 ml, about 100 mL to 220 ml, or about 150 ml to 200 ml per 1 g of treprostinil tromethamine; the water content (w / w) of the anhydrous acetonitrile is less than about 0.05%, less than about 0.01%, less than about 0.005%, or less than about 0.001%; and the process is preferably carried out without the addition of water. The crystalline form of treprostinil tromethamine produced by the process has a differential scanning calorimetry (DSC) thermogram comprising an endothermic peak with a peak maximum at 106.4 ± 1.0 °C, which is higher than that of another known crystalline form of treprostinil tromethamine. Since the treprostinil tromethamine crystal obtained by the present application has the highest melting point compared to all other known treprostinil tromethamine crystals, it is the most stable crystalline form of treprostinil tromethamine.

[0130] Furthermore, the high melting point treprostinil tromethamine crystal of the present application has an X-ray powder diffraction (XRPD) pattern exhibiting characteristic peaks at 2Θ reflection angles of 6.9 ± 0.2°, 10.3 ± 0.2°, 18.8 ± 0.2°, and 21.9 ± 0.2°, which are clearly different from the 2Θ reflection angles of the crystal disclosed in CN 102336693: 6.6 ± 0.2°, 9.9 ± 0.2°, 18.5 ± 0.2, and 21.6 ± 0.2°. The high melting point treprostinil tromethamine crystal represents a novel crystalline form of treprostinil tromethamine.

[0131] In one embodiment of the present application, the treprostinil tromethamine crystal has an XRPD pattern exhibiting characteristic peaks at 2Θ reflection angles of 6.9 ± 0.2°, 10.3 ± 0.2°, 18.8 ± 0.2°, and 21.9 ± 0.2°. In a preferred embodiment, the XRPD pattern further comprises characteristic peaks at 2Θ reflection angles of 9.1 ± 0.2°, 9.5 ± 0.2°, 11.0 ± 0.2°, and 20.5 ± 0.2°. More preferably, the XRPD pattern of the treprostinil tromethamine crystal is in accordance with Figure 1 Specific data of the treprostinil tromethamine crystal are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] In one embodiment, the present application provides a crystalline form of treprostinil tromethamine having an XRPD pattern substantially as shown in Figure 1 FIG. 1.

[0136] In one embodiment, the present application provides XRPD patterns of carboprost tromethamine crystals of five different batches (a) to (e), as shown in Figure 3 Table 1. The specific data of the four main isolated characteristic peaks are clearly labeled and shown in Table 2. The average positions of the characteristic peaks are at about 6.9°, 10.3°, 18.8° and 21.9°, respectively.

[0137] Table 2

[0138]

[0139]

[0140] The XRPD characteristic peak positions of the carboprost tromethamine crystals of the present application are at higher 2-theta angles (6.9±0.2°, 10.3±0.2°, 18.8±0.2° and 21.9±0.2°) compared to 6.6±0.2°, 9.9±0.2°, 18.5±0.2° and 21.6±0.2° disclosed by CN 102336693. The characteristic peak at 6.621° of carboprost tromethamine disclosed by CN 102336693 represents a d-spacing of 13.3397 On the other hand, the characteristic peak at 6.92° of carboprost tromethamine of the present application represents a d-spacing of 12.76 A d-spacing difference of more than 0.5 is a very clear evidence of different molecular packing in the crystal structure. This result shows that the carboprost tromethamine crystals are a novel crystalline form with a more stable and more tightly packed structure compared to the prior art.

[0141] In one embodiment, the present application provides carboprost tromethamine crystals having a DSC thermogram comprising an endothermic peak with a peak onset temperature of about 103.9°C and a peak maximum of about 106.4±1.0°C. In a preferred embodiment, the present application provides a crystalline form of carboprost tromethamine having a DSC thermogram substantially as shown in Figure 2 Table 3.

[0142] In one embodiment, the present application provides DSC thermograms of carboprost tromethamine crystals of five different batches (a) to (e), as shown in Figure 4 Table 3. The specific data of the single endothermic peak's peak maximum are clearly labeled and shown in Table 3. The average peak maximum of this endothermic peak is about 106.4°C.

[0143] Table 3

[0144] Sample Peak maximum (°C) (a) 106.27 (b) 106.63 (c) 106.44 (d) 106.34 (e) 106.40 Average 106.42

[0145] The DSC peak maximum temperature of about 106.4 °C of the treprostinil tromethamine crystals of the present invention is far beyond the disclosed melting point of treprostinil tromethamine of 95 °C to 105 °C (as originally provided by Pfizer) and the peak maximum temperature of 103.97 °C disclosed in CN 102336693, indicating that the treprostinil tromethamine crystals of the present invention are novel crystals with higher thermal stability compared to the prior art. It is well known to those skilled in the art that the crystal comprising the highest melting point is the most stable crystalline form in thermodynamics; therefore, the novel treprostinil tromethamine crystals of the present invention are the most stable one compared to the prior art.

[0146] The United States Pharmacopeia (USP) recommends that treprostinil tromethamine should be stored in a refrigerator (-20 °C). In contrast, the present invention demonstrates that the high melting point crystalline form of treprostinil tromethamine is extremely stable even after 6 months at 20 °C, 18 months at 5 °C, and 3 days at 80 °C. Therefore, the stability of the treprostinil tromethamine crystals of the present invention is significantly improved.

[0147] Although the word "about" is used in front of the minimum and maximum values of the ranges, the use of numerical values in the specification of the present application is stated as approximations unless explicitly indicated otherwise. In this manner, slight variations of the stated values can be employed as long as the variations result in substantially the same results. In addition, the ranges of the present disclosure are intended to cover all ranges encompassed by such values, including every value between the minimum and maximum values, and any range created by the inclusion of such values. Also disclosed herein are any and all ratios that can be formed by dividing any stated value by any other stated value (and ranges of any such ratios). Accordingly, those skilled in the art will appreciate that many of the ratios, ranges and ranges of ratios disclosed herein can be derived from the values presented herein, and that such ratios, ranges and ranges of ratios represent embodiments of the present invention.

[0148] All compounds and / or methods disclosed and taught herein can be made and executed without undue experimentation in light of the present disclosure. While compounds and methods of the present invention have been described in terms of preferred embodiments, it will be apparent to those with ordinary skill in the art that variations can be applied to the compositions and / or methods described and steps or order of steps in methods described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications

[0149] Examples

[0150] X-ray powder diffraction (XRPD) analysis: XRPD patterns were collected on a Bruker D2 PHASER diffractometer with fixed divergence slits and 1D LYNXEYE detector. The sample (approximately 100 mg) was placed flat on the sample holder. Cu Ka radiation (1.5418 A) was used with a power of 10 mA and 30 kV. α The prepared samples were analyzed over a range of 5 to 40° 2-theta with a step size of 0.02 degrees and a step time of 1 second. Cu Ka radiation was removed by a divergent beam nickel filter. β

[0151] Differential scanning calorimetry (DSC) analysis: DSC thermograms were collected on a TA DISCOVERY DSC 25 instrument. The sample was weighed into an aluminum pan with crimped lid closure. The prepared sample was analyzed from 25 °C to 150 °C at a scan rate of 10 °C / min under a nitrogen flow (approximately 50 ml / min). The melting temperature and heat of fusion were calibrated prior to measurement by indium (In). The melting point of all samples was determined by the peak maximum of the endothermic peak during DSC measurement.

[0152] Example 1

[0153] (8aR,9R,10R,11aS,Z)-10-((tert-butyldimethylsilyl)oxy)-9-((S,E)-3-((tert- butyldimethyl-silyl)oxy)oct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin- 2(3H)-one

[0154]

[0155] ​At ambient temperature under nitrogen, 1.4 kg of 7-((1R,2R,3R,5S)-3-((tert- butyldimethylsilyl)oxy)-2-((S,E)-3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)-5- hydroxycyclopentyl)hept-5(Z)-enoic acid, which includes about 6.5% of 5,6-trans isomer as determined by detecting its deprotected product in HPLC analysis, and 475 g of pyridine were dissolved in 6.5 L of dichloromethane. Then, 843 g of benzoyl chloride was added to the mixture and stirred for one hour. The reaction mixture was checked by TLC to confirm the completion of the reaction. The mixture was quenched with 6 L of saturated aqueous sodium bicarbonate solution and stirred for 10 minutes. The solution was allowed to separate into two phases, and the organic layer was collected. The organic layer was further evaporated. The concentrated residue was diluted with 6 L of toluene, and washed with 0.1 N aqueous hydrochloric acid and brine, respectively. The organic layer was collected and evaporated to obtain the crude silyl-protected 1,9-lactone compound. The crude compound was further purified by silica gel chromatography using a mixture of hexane and ethyl acetate as a gradient eluent. The yield of the obtained silyl-protected 1,9-lactone was 1.0 kg (74%).

[0156] The 0.1 g of the product was further treated with a hydrolysis reaction and a deprotection reaction to obtain a crude product. HPLC analysis showed that no 5,6-trans isomer was detected for the crude compound.

[0157] 1 H-NMR (CDCI3): δ 5.156-5.595 (m, 5H), 4.067 (q, 1H), 3.809 (q, 1H), 1.247-2.532 (m, 20H), 0.852-0.898 (m, 21H), -0.005-0.034 (m, 12H); 13 C-NMR (CDCI3): δ 173.620, 136.520, 131.169, 129.135, 127.890, 72.809, 72.088, 55.345, 44.567, 41.599, 38.669, 36.134, 31.831, 26.730, 26.571, 25.895, 25.835, 25.349, 25.136, 22.624, 18.222, 18.063, 14.047, -4.252, -4.556, -4.579, -4.768; MS (m / z, EI): C 32 H 60 O4Si2Na(M + ) of 587.4 and an experimental value of 587.5.

[0158] Example 2

[0159] (8aR,9R,10R,11aS,Z)-9-((S,E)-3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)-10- ((tetra-hydro-2H-pyran-2-yl)oxy)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin- 2(3H)-one

[0160]

[0161] (8aR,9R,10R,11aS,Z)-9-((S,E)-3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)-10- ((tetra-hydro-2H-pyran-2-yl)oxy)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin- 2(3H)-one

[0162] The 0.1 g product was further treated with a hydrolysis reaction and a deprotection reaction to obtain a crude product. HPLC analysis showed that no 5,6-trans isomer was detected for the crude compound.

[0163] 1 H-NMR (CDCI3): δ 5.172-5.630 (m, 5H), 4.813-4.944 (m, 1H), 3.428-4.091 (m, 4H), 1.230-2.619 (m, 26H), 0.845-0.879 (m, 12H), 0.012-0.038 (m, 6H); 13C-NMR (CDCI3): δ 173.635 (173.559), 136.778 (136.619), 131.260, 129.666, (129.507), 127.640, 95.390 (94.623), 81.933 (77.910), 73.159, 62.457 (61.106), 53.971 (53.106), 44.962 (44.855), 39.618, 38.662 (38.578), 37.417, 31.816 (31.778), 30.639 (30.601), 26.730, 25.417, 25.319, 24.962, 22.601, 19.732 (19.573), 18.237 (18.222), 14.009, -4.252, -4.267, -4.806, -4.844; MS (m / z, EI): C 31 H 54 O5SiNa(M + ) of 557.4 and an experimental value of 557.4.

[0164] Example 3

[0165] (8aR,9R,10R,11aS,Z)-9-((E)-3-oxooct-1-en-1-yl)-10-((tetrahydro-2H-pyran-2- yl)oxy)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one

[0166]

[0167] Example 3 (cont.) (8aR,9R,10R,11aS,Z)-9-((E)-3-oxooct-1-en-1-yl)-10-((tetrahydro-2H-pyran-2- yl)oxy)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one

[0168] 1H-NMR (CDC13): δ 6.688 (ddd, 1H), 6.235 (dd, 1H), 5.326 (dt, 1H), 5.197 (br s, 2H), 4.592 (t, 0.5H), 4.550 (t, 0.5H), 4.060 (dd, 0.5H), 3.952 (dd, 0.5H), 3.692-3.800 (m, 1H), 3.388-3.447 (m, 1H), 1.236-2.684 (m, 26H), 0.887 (t, 3H); 13 C-NMR (CDC13): δ 200.466 (200.299), 173.499 (173.408), 146.569 (146.417), 131.951, 131.784, 126.873, 96.321 (96.612), 81.386 (78.790), 72.445 (72.111), 62.646 (61.736), 54.130 (53.546), 45.030 (44.939), 40.582 (40.309), 39.808 (38.024), 35.998, 31.451 (31.421), 30.677 (30.601), 26.715, 25.364 (25.303), 23.952, 22.442, 19.550, 18.988, 13.895; MS (m / z, EI): C 25 H 38 O5Na (M+Na + ) calculated 441.3 and found 441.3.

[0169] Example 4

[0170] (8aR,9R,10R,11aS,Z)-10-Hydroxy-9-((S,E)-3-hydroxyoct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one

[0171]

[0172] At ambient temperature, 480 g of (8aR,9R,10R,11aS,Z)-10-((tert-butyldimethylsilyl)oxy)-9-((S,E)-3-((tert-butyldimethyl-silyl)oxy)oct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one (from Example 1) was dissolved in 4.5 L of tetrahydrofuran. Then, 775 g of tetrabutylammonium fluoride trihydrate was added to the solution. The homogeneous solution was heated at 45 °C and stirred for 6 hours. The reaction mixture was checked by TLC to confirm the completion of the reaction. The mixture was cooled at ambient temperature and then quenched with 8 L of saturated aqueous sodium bicarbonate solution. The solution was allowed to settle into two phases and the organic layer was collected. The organic layer was evaporated to obtain the crude 1,9-lactol diol compound. The crude compound was purified by silica gel chromatography using a mixture of hexane and ethyl acetate as the gradient eluent. Then, the diol compound was further crystallized in a mixed solvent of ethyl acetate and hexane. The yield of the obtained crystal of the diol compound was 259 g (91%).

[0173] 1 H-NMR (CDC13): δ 5.203-5.642 (m, 5H), 4.409 (q, 1H), 3.800 (q, 1H), 3.304 (br s, 1H), 1.281-2.608 (m, 21H), 0.868 (t, 3H); 13 C-NMR (CDC13): δ 173.437, 136.785, 131.973, 131.411, 127.464, 76.065, 73.158, 71.936, 56.201, 45.074, 40.285, 37.196, 36.050, 31.655, 26.722, 26.532, 25.272, 25.158, 22.562, 13.971; MS (m / z, EI): C 20 H 30 O4(M + ) of 336.2 and an experimental value of 336.2.

[0174] Example 5

[0175] (8aR,9R,10R,11aS,Z)-10-Hydroxy-9-((E)-3-hydroxyoct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one

[0176]

[0177] At ambient temperature, 300 g of (8aR,9R,10R,11aS,Z)-10-hydroxy-9-((S,E)-3- hydroxyoct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one (from Example 4) was dissolved in 3 L of tetrahydrofuran, and 2,3-dichloro-5,6-dicyano-1,4- benzoquinone was added. The reaction mixture was heated at 55 °C and stirred for 2 hours. After the reaction was completed, the mixture was cooled at ambient temperature and evaporated. Then, the dark brown residue was diluted with dichloromethane, and yellow solid was precipitated. The mixture was filtered, and the filtrate was further concentrated to obtain the crude ketone compound. The crude compound was purified by silica gel chromatography using a mixture of hexane and ethyl acetate as a gradient eluent. The yield of the obtained 15-keto 1,9-lactone was 276 g (93%).

[0178] 1 H-NMR (CDC13): δ 5.183-6.686 (m, 5H), 3.991-4.062 (m, 1H), 1.251-2.642 (m, 21H), 0.887 (t, 3H); 13 C-NMR (CDC13): δ 200.101, 173.316, 145.536, 132.064, 131.737, 126.865, 76.383, 72.406, 56.239, 45.591, 40.983, 40.839, 36.027, 31.435, 26.729, 25.302, 23.754, 22.433, 13.895; MS (m / z, EI): C 20 H 30 O4(M + ) of 334.2144 and an experimental value of 334.2130.

[0179] Example 6

[0180] (8aR,9R,10R,11aS,Z)-10-hydroxy-9-((S,E)-3-hydroxy-3-methyloct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one

[0181]

[0182] Method A: 275 g of (8aR,9R,10R,11aS,Z)-10-hydroxy-9-((E)-3-oximinioxy- oct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one (from Example 5) was dissolved in 4.5 L of tetrahydrofuran at ambient temperature under nitrogen and cooled at -70 °C. 1.0 L of methyllithium (2 M in ether) was slowly added to the reaction mixture at -70 °C and the reaction was checked by TLC. After the reaction was complete, the mixture was quenched with saturated aqueous ammonium chloride solution and stirred for 10 minutes. Then, 1 L of ethyl acetate was added to the reaction mixture and allowed to warm at ambient temperature. The mixture was allowed to separate into two phases and the organic layer was collected and dried over anhydrous sodium sulfate. Subsequently, the solid was filtered off and the filtrate was evaporated. A crude 15-methyl mixture compound was obtained and tested by HPLC. The ratio of 15-R / 15-S of the crude compound was about 25 / 75. The crude compound was further purified by silica gel chromatography using a mixture of dichloromethane and acetone as the gradient eluent. The yield of the obtained pure 15-methyl compound was 163 g (57%).

[0183] Method B: 2 g of (8aR,9R,10R,11aS,Z)-10-hydroxy-9-((E)-3-oximinioxy- oct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one (from Example 5) was dissolved in 20 ml of tetrahydrofuran at ambient temperature under nitrogen and cooled at -70 °C. Then, 21 ml of methylmagnesium bromide (1 M in THF) was slowly added to the reaction mixture at -70 °C and warmed at 0 °C. The mixture was checked by TLC to confirm the completion of the reaction. The reaction mixture was sampled to check the ratio of 15-R / 15-S of the product was about 35 / 65.

[0184] 1 H-NMR (CDCI3): δ 5.203-5.713 (m, 5H), 3.787 (q, 1H), 1.167-2.535 (m, 25H), 0.859 (t, 3H); 13 C-NMR (CDCI3): δ 173.399, 140.709, 131.336, 127.556, 127.526, 76.331, 72.840, 72.187, 56.233, 45.281, 42.875, 40.317, 36.029, 32.173, 27.520, 26.693, 26.579, 25.274, 23.801, 22.541, 13.950; MS (m / z, EI): C 21 H 32 O3(M+ The calculated value of (M-H2O) is 332.2351 and the experimental value is 332.2349.

[0185] Example 7

[0186] (8aR,9R,10R,11aS,Z)-10-((tert-butyldimethylsilyl)oxy)-9-((S,E)-3-hydroxy-3- methyloct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopenta[b]oxecin-2(3H)-one

[0187]

[0188] Example 7 (continued) At ambient temperature, 2.0 g of (8aR,9R,10R,11aS,Z)-10-((tert-butyldimethylsilyl)oxy)-9-((E)-3-hydroxyoct-1-en-1-yl)-4,5,8,8a,9,10,11,11a- octahydrocyclopenta[b]oxecin-2(3H)-one was taken in 20 ml of tetrahydrofuran and cooled at -70 °C. 3.5 ml of methyllithium (2 M in ether) was slowly added to the reaction mixture at -70 °C and the reaction was checked by TLC. After completion of the reaction, the mixture was quenched with saturated aqueous ammonium chloride solution and stirred for 10 minutes. Then, 1 ml of ethyl acetate was added to the reaction mixture and allowed to warm up at ambient temperature. The mixture was allowed to separate and the organic layer was dried over anhydrous sodium sulfate. Subsequently, the solid was filtered off and the filtrate was evaporated to obtain the crude 15-methyl mixture compound. The crude compound was purified by silica gel chromatography using a mixture of dichloromethane and acetone as the gradient eluent. The yield of the pure 15-methyl compound obtained was 1.05 g (51%).

[0189] 1 H-NMR (CDCI3): δ 5.168-5.689 (m, 5H), 3.807 (q, 1H), 1.258-2.551 (m, 24H), 0.857-0.944 (m, 12H), 0.011 (s, 6H); 13 C-NMR (CDCI3): δ 173.582, 140.368, 131.275, 127.746, 127.678, 76.954, 72.938, 72.005, 55.610, 44.483, 42.844, 41.569, 36.127, 32.279, 28.081, 26.738, 26.487, 25.789, 23.839, 22.579, 18.070, 14.040, -3.592, -4.518, -4.624.

[0190] MS(m / z,EI): C 27 H 48 O4SiNa(M+Na + The calculated value is 487.3 and the experimental value is also 487.3.

[0191] Example 8

[0192] (Z)-7-((1R,2R,3R,5S)-3,5-dihydroxy-2-((S,E)-3-hydroxy-3-methyloct-1-en-1-yl)cyclopentyl)hept-5-enoic acid, carboprost

[0193]

[0194] 143 g of (8aR,9R,10R,11aS,Z)-10-hydroxy-9-((S,E)-3-hydroxy-3-methyloct-1-en-1-yl)-4,5,8,8a,9,10,11,11a-octahydrocyclopentan[b]oxocine-2(3H)-one (from Example 6) was dissolved in 750 mL of methanol, and 1.5 L of 1N aqueous lithium hydroxide solution was added. The reaction mixture was heated at 60 °C for 2 hours. After the reaction was complete, the mixture was cooled to room temperature, and the pH of the solution was adjusted to approximately 8.5. The mixture was concentrated to remove methanol, and the residue was further purified by acid-base extraction. The yield of carboprost was 129 g.

[0195] 1 H-NMR (CDCl3): δ5.278~5.610(m,7H), 4.112~4.133(m,1H), 3.866~3.911(m,1H), 1.252~2.298(m,23H), 0.843(t,3H);

[0196] 13 C-NMR(CDCl3): δ177.316,138.903,129.431,129.226,128.839,77.599,73.333,72.339,55.292,5 0.427,42.731,42.488,33.031,32.257,26.966,26.245,25.099,24.507,23.809,22.610,14.063;

[0197] MS(m / z,EI): C 21 H 34 O4(M + The calculated value of -H2O) is 350.2 and the experimental value is 350.3.

[0198] Example 9

[0199] Formation of carboprost tromethamine salt

[0200] 2-amino-2-(hydroxymethyl)propane-1,3-diol; (Z)-7-((1R,2R,3R,5S)-3,5-dihydroxy-2-((S,E)-3-hydroxy-3-methyloct-1-en-1-yl)cyclopentyl)hept-5-enoate, carboprost tromethamine

[0201]

[0202] Method A:

[0203] Dissolve 114 g of carboprost in 1.2 L of acetonitrile at 60 °C and heat the solution to 65 °C. Slowly add 120 ml of water containing 37.4 g of tromethamine to the solution. Further heat the reaction mixture to 85 °C to reflux for 10 minutes. Allow the homogeneous solution to cool to 60 °C and white solids begin to precipitate slowly. Further cool the mixture to room temperature and stir for over 16 hours. Filter the reaction mixture to obtain white crystalline form of carboprost tromethamine (118 g). Measure the melting point of the crystals by DSC to be 103.41 °C as shown in (a) in Figure 5

[0204] 1 H-NMR (D20): δ 5.336-5.594 (m, 4H), 4.109 (br s, 1H), 3.819 (br s, 1H), 3.632 (s, 6H), 1.193-2.427 (m, 23H), 0.764 (t, 3H);

[0205] 13 C-NMR (CDC13): δ 183.433, 138.523, 130.584, 129.203, 128.854, 75.928, 73.576, 71.109, 71.109, 61.257, 59.451, 54.327, 41.971, 41.902, 37.136, 31.565, 26.601, 25.850, 25.743, 24.779, 23.277, 21.888, 13.288;

[0206] MS (m / z, ESI): C 25 H 48 NO8 (MH + ) calculated 490.3374 and found 490.3384.

[0207] Method B:

[0208] ​Crystalline carboprost tromethamine was prepared from an acetone / water solution by the method disclosed in Example 3 of CN 102336693. The inventors measured the melting point of the crystals to be 103.22 °C, as shown in Figure 5 (b) below.

[0209] Method C:

[0210] Crystalline carboprost tromethamine was prepared from an ethyl ether / water solution by the method disclosed in Example 7 of CN 102336693. The inventors measured the melting point of the crystals to be 103.43 °C, as shown in Figure 5 (c) below.

[0211] Method D:

[0212] Crystalline carboprost tromethamine was prepared from an isopropanol / acetone solution by the method disclosed in Example Ig of WO 2017 / 093770. The inventors measured the melting point of the crystals to be 97.49 °C, as shown in Figure 5 (d) below.

[0213] Example 10

[0214] Re-crystallization of carboprost tromethamine

[0215] Method A:

[0216] At 85 °C, 10.0 g of carboprost tromethamine was dissolved in 1 L of acetonitrile containing 0.02% water to obtain a homogeneous solution, and then the homogeneous solution was cooled to 60 °C, and white solid began to precipitate slowly. The mixture was further cooled to room temperature. The resulting precipitated crystals were filtered and dried. After re-crystallization, the yield of the obtained high purity carboprost tromethamine crystals was 9.0 g. The melting point of the crystals was measured by DSC to be 106.40 °C, as shown in Figure 6 (a) below. After HPLC analysis, the amount of 15(R)-epimer was 0.05%, and no 5,6-trans isomer was detected.

[0217] Method B:

[0218] Crystalline carboprost tromethamine was prepared from an acetone / water solution by the method disclosed in Example 2, 4, 6, or 8 of CN 102336693. The inventors measured the melting point of the crystals to be 103.85 °C, as shown in Figure 6 (b) below. Method C:

[0219] Crystalline carboprost tromethamine was prepared from an isopropanol / acetone solution by the method disclosed in Example 1h of WO2017093770. The inventors measured the melting point of the crystals to be 99.46 °C, as shown inFigure 6 (c) as shown.

[0220] Example 11

[0221] Purification of low purity carboprost tromethamine

[0222] Three grams of commercially available carboprost tromethamine, which includes 2.5% of 5,6-trans isomer and 1.5% of 15(R)-epimer, was dissolved in acidic water at pH 3 and extracted with ethyl acetate to obtain 2 g of carboprost. A solution of carboprost in 8 ml of anhydrous and oxygen-free xylene was treated with 1.73 g of 2,2'-dipyridyl disulfide and 2.06 g of triphenylphosphine. After stirring at 25 °C for 18 hours, the mixture was diluted with 500 ml of xylene and heated under reflux for 4 hours. The reaction mixture was further evaporated to remove the solvent, and the residue was partitioned between a cold aqueous sodium bicarbonate solution and ethyl acetate. The organic layer was collected and washed with brine, and dried over anhydrous sodium sulfate. The mixture was filtered and concentrated to obtain the crude 1,9-lactone compound. The crude compound was purified by silica gel chromatography using a mixture of dichloromethane and acetone as a gradient eluent. The yield of the obtained 15-methyl 1,9-lactone was 1.67 g.

[0223] The 1,9-lactone product was further treated by a hydrolysis reaction to obtain carboprost including 2.5% of 15(R)-epimer but no detectable 5,6-trans isomer in HPLC analysis. Carboprost tromethamine was formed from carboprost and tromethamine according to the method of Example 9, and crystallized and recrystallized according to the methods of Example 10 (Method A) and Example 11 to obtain high purity carboprost tromethamine. After HPLC analysis, the amount of 15(R)-epimer was 0.15%, and no 5,6-trans isomer was detected.

[0224] Example 12

[0225] Stability of carboprost tromethamine crystals

[0226] The stability data shown in Tables 4 and 5 show that the high melting point carboprost tromethamine crystals are stable even after 6 months of treatment at 20 °C, 18 months of treatment at 5 °C, and 3 days of treatment at 80 °C. The high melting point carboprost tromethamine crystals are extremely stable at room temperature, and even at higher temperatures, so that the formation of degradation impurities can be effectively avoided.

[0227] Table 4

[0228]

[0229]

[0230] Table 5

[0231]

[0232] In another aspect, the hygroscopicity of the high-melting carboprost tromethamine crystals prepared from Example 10 (Method A) and the low-melting carboprost tromethamine crystals prepared from Example 10 (Method B) was measured. The samples were placed in glass bottles with 99% RH at 25 °C for 3 hours, and the water content of the samples was measured by Karl Fischer titration, as shown in Table 6. The high-melting carboprost tromethamine crystals exhibited a relatively low rate of water uptake compared to the low-melting carboprost tromethamine crystals, indicating that the high-melting carboprost tromethamine crystals are more stable and can be stored for a longer time under high humidity conditions, thus the high-melting carboprost tromethamine crystals are more advantageous for product handling, storage, and shipping.

[0233] Table 6

[0234]

[0235] While the present application has been described with reference to illustrative examples, it is understood that the present application can be carried out in many ways, and that modifications or substitutions can be made without departing from the scope and spirit of the application as disclosed in the specification and the appended claims.

Claims

1. A method for preparing carboprost containing no more than 1% total isomers, the method comprising the following steps: (1) Macrocyclic lactone formation of a compound of formula 1b containing 1% to 10% of the 5,6-trans isomer and 1% to 50% of the 15(R)-epomer. Where P1 and P2 are H or hydroxyl protecting groups, to form a compound of formula 3a: P1 and P2 are as defined above; (2) When P1 is an H or hydroxyl protecting group and P2 is a hydroxyl protecting group, perform the deprotection reaction of the compound of formula 3a to form the compound of formula 3a, wherein P1 is an H or hydroxyl protecting group and P2 is H; (3) The compound of formula 3a is separated by chromatography, wherein P1 is an H or hydroxyl protecting group and P2 is H, to remove the isomer; (4) Hydrolyze the compound of formula 3a to form the compound of formula 4: Where P1 is an H or hydroxyl protecting group; and (5) When P1 is a hydroxyl protecting group, perform the deprotection reaction of the compound of formula 3a or 4 as appropriate to form the compound of formula 3a or 4, wherein P1 is H.

2. The method of claim 1, used to prepare carboprost thrombin, the method further comprising forming a salt with thrombin and purifying carboprost thrombin by crystallization.

3. A method for purifying carboprost, comprising the following steps: (1) Macrolide carboprost containing 1% to 10% of the 5,6-trans isomer and 1% to 50% of the 15(R)-epomer to form a compound of formula 3b: (2) Chromatographic separation of the isomers of the compound of formula 3b; and (3) Hydrolyze the compound of formula 3b to form carboprost containing no more than 1% of total isomers.

4. A method for preparing compounds of formula 3, Where P1 is an H or hydroxyl protecting group, the method comprises making a compound of formula 2a' It reacts with a methylating agent, where P1 is an H or hydroxyl protecting group.

5. The method of claim 4, wherein the methylating agent is selected from the group consisting of: MeLi, MeMgBr, MeMgCl, MeMgI, Me3Al and mixtures thereof.

6. The method of claim 5, wherein the methylating agent is MeLi.

7. A crystalline form of carboprost thromboxane, having a differential scanning calorimetry (DSC) thermogram containing an endothermic peak with a maximum value of 106.4 ± 1.0 °C, and an X-ray powder diffraction (XRPD) pattern containing characteristic peaks at the following 2θ reflection angles: 6.9 ± 0.2°, 10.3 ± 0.2°, 18.8 ± 0.2°, and 21.9 ± 0.2°.

8. The crystalline form of carboprost thromboxane as claimed in claim 7, wherein the XRPD plot further includes characteristic peaks at the following 2θ reflection angles: 9.1±0.2°, 9.5±0.2°, 11.0±0.2°, and 20.5±0.2°.

9. The crystalline form of carboprost thromboxane as described in claim 7, wherein it contains less than 0.1% of the 5,6-trans isomer.

10. The crystalline form of carboprost thromboxane as described in claim 9, wherein it contains less than 0.03% of the 5,6-trans isomer.

11. A method for preparing the crystalline form of carboprost thromboxane as described in claim 7, comprising the following steps: (a) Add carboprost thromboxane to anhydrous acetonitrile to form a mixture, wherein the amount of anhydrous acetonitrile is 80 ml to 250 ml per 1 g carboprost thromboxane; (b) heating the mixture to a temperature between 70°C and 90°C to obtain a homogeneous solution; and (c) Cool the homogeneous solution to form the crystalline form of carboprost thromboxane.

12. The method of claim 11, wherein the anhydrous acetonitrile has a water content of less than 0.05%.

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