WO2017168442A1

WO2017168442A1 - Novel stable salts of pemetrexed

Info

Publication number: WO2017168442A1
Application number: PCT/IN2017/050110
Authority: WO
Inventors: Dharmesh Mahendrabhai Shah; Guruprasad Ramchandra Wader
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-03-26
Filing date: 2017-03-25
Publication date: 2017-10-05
Anticipated expiration: 2018-09-26

Abstract

The present invention relates to novel crystalline salts of anticancer drug Pemetrexed and its process thereof. More particularly, the present invention relates to stable and highly soluble crystalline Pemetrexed dilithium heptahydrate and process for preparation thereof.

Description

NOVEL STABLE SALTS OF PEMETREXED

Technical filed:

Background of the invention:

Pemetrexed is Non-proprietary common name for compound of Formula I.

Formula I

The Chemical name for Pemetrexed is (2S)-2-[[4-[2-(2-amino-4-oxo-l,7- dihydropyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]amino]pentanedioic acid.

The compound has been first disclosed in EP 432677.

Pemetrexed is a pharmaceutically active compound, which is used, in the treatment of malignant pleural mesothelioma and non-small cell lung cancer.

Pemetrexed of the above formula 1 is bivalent acid (a diacid) comprising two carboxylic groups. The product may form various types of salts with bases. On the other hand, Pemetrexed has basic nitrogens and, accordingly, it may form acid addition salts with various acids. The commercially available product, sold, e.g., under the brand name ALIMTA by Eli Lilly, comprises hydrated di sodium salt of Pemetrexed as the active substance and is supplied as a sterile lyophilized powder for intravenous infusion available in single-dose vials. The lyophilized product is available in strengths of lOOmg/vial and 500 mg/vial and is reconstituted with 0.9% sodium chloride at a concentration of 25mg/mL before its administration. The preparation of lyophilized Pemetrexed disodium composition is disclosed in US 7,138,521.

US 7,138,521 also describes a stable crystalline heptahydrate form of Pemetrexed disodium having a characteristic X-ray diffraction pattern. The patent reports that Pemetrexed disodium can exist in the form of a heptahydrate which is much more stable than the previously known 2.5 hydrate and also with respect to formation of related substances. It also shows that when the heptahydrate is subjected to elevated temperatures, low humidity, and/or vacuum, it converts into the 2.5 hydrate crystal form by loss of water.

Disodium salt of Pemetrexed is relatively more soluble in water than the Pemetrexed diacid of the formula (II).

Formula II

Formulating water soluble pemetrexed salts, however, has not proven to be an easy task, due to its stability issues. Moreover, the chemical instability of Pemetrexed is mainly attributed to their oxidative degradation and relatively rapid formation of degradants being the main factor.

According to WO 2012/015810, formation of five major degradants of Pemetrexed has been observed when subjected to different conditions. Under acidic conditions, decarboxylation of glutamic acid is observed; under alkaline conditions, degradation proceeds by side chain amide hydrolysis followed by deamination and two oxidative degradants result in the presence of oxygen.

Many prior arts tried to address the problem related to oxidative degradation of the drug by using an antioxidant or an amino acid or a chelating agent in their pharmaceutical composition. US6686365 discloses a stable ready-to-use (RTU) formulation of Pemetrexed which is developed by using antioxidants/amino acids like L-Cysteine, Monothioglycerol and Thioglycolic acid.

CN101081305 discloses a RTU formulation of Pemetrexed stabilized by using antioxidant like L-arginine, L-glutathione, L- methionine and L-tryptophan.

WO 2012/015810 claims a RTU solution formulation of Pemetrexed along with an antioxidant, a chelating agent and dissolved in a pharmaceutically acceptable fluid.

WO2013144814 discloses a stable ready-to-use pharmaceutical composition which comprises pemetrexed or pharmaceutically acceptable salts thereof, which is free from antioxidants, amino acids and chelating agents and wherein, the composition has a dissolved oxygen content of less than 7 mg/L, preferably less than 3 mg/L.

Therefore, the infusion solution of Pemetrexed has to be prepared immediately before use, by dissolving the content of the single-dose vial in water followed by dilution of the obtained solution with an infusion liquid. Therefore, there remains a need in the art to provide stable crystalline Pemetrexed salts, with improved water solubility. In particular, it would be advantageous to provide alternate crystalline Pemetrexed salts, with improved water solubility and consequently bioavailability of the drug.

Therefore, the objective of the invention is to provide novel stable crystalline Pemetrexed salts with improved stability and solubility.

Summary of the invention:

In line with the above objective, the present invention provides novel stable salts of Pemetrexed, with improved water solubility over the existing di sodium salt.

In the first aspect, the invention provides stable and highly soluble dilithium salt of Pemetrexed, its hydrates and solvates thereof.

The stable and highly soluble di-lithium salt of Pemetrexed hydrate of formula III according to the invention has following structure.

Formula III

In a preferred aspect, the di-lithium salt of Pemetrexed is crystalline. In another preferred aspect, the di-lithium salt of Pemetrexed is a hydrate.

In a most preferred aspect, the novel salt of Pemetrexed is crystalline di-lithium salt of Pemetrexed heptahydrate of formula IV. In yet another aspect, the crystalline di-lithium salt of Pemetrexed heptahydrate is highly stable and highly water soluble than the known disodium salt of Pemetrexed heptahydrate.

In a further aspect, the invention provides a process for the preparation of stable crystalline Pemetrexed Dilithium Heptahydrate.

Description of drawings:

Figure 1 shows PXRD pattern of crystalline Pemetrexed Dilithium Heptahydrate Figure 2 shows DSC of crystalline Pemetrexed Dilithium Heptahydrate

Figure 3 shows Mass spectra of crystalline Pemetrexed Dilithium Heptahydrate Figure 4 depicts FTIR of crystalline Pemetrexed Dilithium Heptahydrate

Detailed description of the invention

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

Accordingly, the present invention provides novel stable salts of Pemetrexed, with improved water solubility over the existing disodium salt.

According to a preferred embodiment, the stable and highly soluble crystalline dilithium salt of Pemetrexed is crystalline in nature.

According to another preferred embodiment, the stable and highly soluble crystalline di-lithium salt of Pemetrexed is a hydrate of formula III.

Formula III

In a most preferred embodiment, the novel salt of Pemetrexed according to the invention is highly pure crystalline di-lithium salt of Pemetrexed heptahydrate of formula IV.

The term 'stable' as used herein, refers to the tendency to remain "substantially in the same physical form" for at least six months, more preferably at least a year, still more preferably at least two to three years, when stored under ambient conditions without external treatment. It should be noted that the amorphous forms of many compounds sometimes converted into the partly crystalline form in a relatively short time period and therefore not stable in many cases under normal storage conditions.

In one embodiment, the crystalline form of di-lithium salt of Pemetrexed heptahydrate of the present invention is substantially free from its amorphous form. The phrase "substantially in the same physical form" as referred herein above means that the di-lithium salt of Pemetrexed heptahydrate possess at least 70%, preferably at least 80% and more preferably at least 90% of the crystallinity even after the storage period. In a further embodiment, the invention provides a synthetic method for the preparation of di-lithium salt of Pemetrexed heptahydrate (Formula IV) from N-[4- [2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]-pyrimidin-5- yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt (4) by treating with appropriate quantities of lithium hydroxide in solvents like water, primary alcohols, acetone, THF or combinations thereof as shown in scheme 1.

Scheme 1

N-[4-[2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]-pyrimidin-5- yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt (4) can be prepared by known process, as shown in stages I and II of scheme 2 below.

Scheme 2

According to the scheme 2, in the first stage, L-glutamic acid dimethyl ester hydrochloride^) is prepared by treating L-Glutamic acid (l)with methanol in presence of thionyl chloride at 0 to 5 °C to obtain residue, which is isolated by the removal of thionyl chloride followed by precipitating L-glutamic acid dimethyl ester hydrochloride^) from ethylacetate.

In the second stage, N-[4-[2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]- pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt (4) is prepared by the reaction of 4-[2-(2-amino-4,7-dihydro-4-oxo-lHpyrrolo[2,3- d]pyrimidin-5-yl)ethyl]benzoic acid (3) in dimethylformamide in presence of N- methylmorpholine with 2-Chloro-4,6-dimethoxy-l,3,5-triazine (CDMT) at 25-30 °C for a period of about 2.0 hrs at same temperature. After completion of the reaction, L-glutamic acid dimethyl ester hydrochloride ((2) of stage-1) is added into the reaction mass at room temperature and maintained at 25-30 °C for 1.0 hr. After completion of the reaction, added MDC and purified water into the reaction mass at RT. The organic layer is separated and washed with purified water. The organic layer is subjected to distillation to remove MDC to obtain residue, which is stripped with methanol to remove MDC traces from the residue. The residue is further treated with the solution of PTSA in Methanol at reflux temperature for about 3.0 hrs and cooled the reaction mass to room temperature to isolate N-[4-[2-(2-Amino- 4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]-pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt(4).

In stage III, pemetrexed dilithium heptahydrate(Formula IV) is prepared by reacting N-[4-[2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]-pyrimidin-5- yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt(4) with aqueous solution of Lithium hydroxide at 25 to 30°C under stirring. The pH of the reaction mass is adjusted to 8.0 to 8.5 with acetic acid followed by charcoalisation of the reaction mass. Filtered the reaction mass through Hyflo bed to obtain residue, which is slurried in acetone for 30 min at 25 to 30°C to obtain crude crystalline pemetrexed dilithiumheptahydrate. The chromatographic purity of the crude pemetrexeddilithum heptahydrate is 99.0 %. Accordingly, in yet another embodiment, the invention provides a process for the preparation of stable crystalline Pemetrexed Dilithium Heptahydrate directly from pemetrexed Diethyl Ester of PTSA salt which process comprises:

a) Reacting N-[4-[2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]- pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt(4) with a solution of Lithium hydroxide solution in water at 25 to 30°C; b) Adjusting the pH of the reaction mass to 8.0 to 8.5 with acetic acid followed by isolation of the crude pemetrexed dilithium heptahydrate and c) Optionally purifying the crude pemetrexed dilithium heptahydrate(Formula IV).

The chromatographic purity of the crude pemetrexed dilithum heptahydrate salt is 99.0 %.

In another embodiment, process for purification of pemetrexed dilithum heptahydrate which comprises;

a) Dissolving Pemetrexed dilithiumheptahydrate in purified water at 25-30 °C for sufficient time at room temperature; and

b) Adding ethanol as anti-solvent into the reaction mass at room temperature to isolate pure crystalline pemetrexed dilithium heptahydrate.

The pemetrexed dilithum heptahydrate salt thus isolated has a chromatographic purity of more than 99.78%.

In yet another embodiment, the invention provides process for preparation of highly pure crystalline pemetrexed dilithium heptahydrate which comprises;

a) Reacting Pemetrexed Diacid (Formula I) in Methanol under nitrogen at 40- 45°C with Lithium Hydroxide solution;

b) Subjecting filtered solution of step a) to distillation under vacuum to obtain a solid; and c) Drying the solid of step b) under the stream of nitrogen to isolate crystalline highly pure pemetrexed dilithium heptahydrate(Formula IV).

The process of the present invention enables to obtain crystalline pemetrexed dilithium heptahydrate with purity in the range of 99 to 99.9% purity. Further the process of the present invention provides pemetrexed dilithium heptahydrate with a yield in the range of of 70 to 80 %.

In yet another embodiment, the crystalline di-lithium salt of Pemetrexed heptahydrate is subjected to solubility tests in water at 32°C (shake flask method)and found that the crystalline di-lithium salt of Pemetrexed heptahydrate according to the invention is highly water soluble when compared to the known disodium salt of Pemetrexed heptahydrate. While the Pemetrexed Disodium Heptahydrate exhibits a solubility of 220 mg/ml; Pemetrexed Dilithium Heptahydrate according to the invention exhibits a solubility of 415 mg/ml.

Since the solubility of the Pemetrexed Dilithium Heptahydrate of the present invention is almost two times more than Pemetrexed Disodium Heptahydrate, a known compound; therefore, Pemetrexed Dilithium Heptahydrate of the present invention is expected to have more bioavailability than the Pemetrexed Disodium Heptahydrate, when administered.

Therefore, the stable crystalline Pemetrexed Dilithium Heptahydrate of the present invention is useful in the preparation of medicament for use in the treatment of malignant pleural mesothelioma and non-small lung cancer.

In yet another embodiment, crystalline Pemetrexed Dilithium Heptahydrate thus obtained is characterized by PXRD, DSC, FTIR, Mass spectroscopy using the following instruments. PXRD Instrument Details: XRD Diffractometer (powder) Philips Xpert MPD Range (2Θ): 3° to 136°; X-ray tube: Cu; JCPDF database; 2Θ vs intensity plots/X- ray diffractograms

DSC Instrument Details: Perkin Elmer, Pyris 1 DSC

FT-IR Instrument Details: Perkin Elmer FT IR instrument.

MASS Instrument details: LCQ Fleet and TSQ Quantum Access with Surveyor plus HPLC System.

Accordingly, crystalline Pemetrexed Dilithium Heptahydrate is characterized by PXRD pattern that shows at least one characteristic peak at about ± 0.25 18.903 degrees 2 theta angle(Fig. l). More particularly the PXRD pattern shows characteristic peaks at about 8.319, 9.094, 10.193, 14.812, 16.419, 17.431, 18.217, 18.903, 19.251, 19.824, 20.593, 21.058, 21.504, 22.350, 23.662, 23.927, 24.371, 25.175, 25.784, 26.238, 26.582, 28.163, 28.932, 29.745, 30.198, 31.586, 32.374, 33.180, 33.415, 33.812, 34.405, 35.416, 36.775, 37.465, 37.829, 38.272, 39.670, 40.129 and 40.840 ± 0.25 degrees 2 theta angles.

The crystalline Pemetrexed Dilithium Heptahydrate is further characterized by DSC Analysis, which shows onset point at 93.23°C with peak Point (Melting Point) at 127.14°C and with an end Point at 148.52°C. Thus the DSC of crystalline Pemetrexed Dilithium Heptahydrate shows a melting range of 93 °C to 149°C (Fig.2).

The analysis of mass spectra of the crystalline Pemetrexed Dilithium Heptahydrate that shows a peak at m/z 439 corresponding to Pemetrexed Dilithium Fragment and another peak at m/z 432 corresponding to Pemetrexed Monolithium Fragment (Fig. 3).

IR Analysis of the crystalline Pemetrexed Dilithium Heptahydrate shows characteristic stretching at 951.64 cm-1 (C-H stretching), 1156.17 cm-1 (C-N Stretching), 1631.61 cm-1 (N-H Stretching), 1676.90 cm-1 (C=0 Stretching) and 3356.50 cm-1 (COOH Stretching) (Fig.4).

The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it is being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

Example 1:

Stage- 1

L-glutamic acid dimethyl ester hydrochloride (2)

50.0 g L-Glutamic acid was taken in assembly containing 300 ml methanol, chilled the reaction mass up to 0 to 5 °C. Added dropwise 40.5 g Thionyl chloride into the reaction mass. The reaction mixture turned into a clear solution that was stirred for 40 hrs at room temperature. The solvent was evaporated to give crude L-glutamic acid dimethyl ester hydrochloride as residue. Added Methanol (150 ml) and distilled out to remove residual thionyl chloride. Added Ethyl Acetate (250 ml) to precipitate solid. Filter the product and washed with ethyl acetate (50 ml) to get 47.5 g L-glutamic acid dimethyl ester hydrochloride.

Stage-II

N-[4-[2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]-pyrimidin-5- yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt(4).

50.0 g 4-[2-(2-amino-4,7-dihydro-4-oxo-lHpyrrolo[2,3-d]pyrimidin-5- yl)ethyl]benzoic acid (3) is taken in 300 ml Dimethylformamide, added 50 ml N- methylmorpholine and 35.73 g 2-Chloro-4,6-dimethoxy-l,3,5-triazine (CDMT) were taken in assembly under stirring at 25-30 °C. Maintained the reaction mass for 2.0 hrs at the same temperature. Check in process TLC for completion of Reaction. After completion of TLC added 40.79 g L-glutamic acid dimethyl ester hydrochloride ((2) of stage- 1) into the reaction mass at room temperature. Maintained the reaction mass for 1.0 hr at 25-30 °C. Check in process TLC for completion of Reaction. After completion of TLC, added 500 ml MDC and 250 ml purified water into the reaction mass at RT. Separated out organic and aqueous layers. The organic layer was extracted with 2X250 ml purified water. Distilled out MDC to get residue, which was given 50 ml methanol stripping to remove MDC traces from the residue. Added 1500 ml Methanol and solution of 80 g PTSA in 500 ml Methanol. Heated the reaction mass to get reflux temperature. Maintained the reaction mass for 3.0 hrs. Cooled the reaction mass to get room temperature. Filtered the product and washed with methanol (50 ml) to get 45.0 g N-[4-[2-(2- Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]-pyrimidin-5-yl)ethyl]benzoyl]-L- glutamic Acid Diethyl Ester PTSA salt.

Stage-Ill

Preparation of pemetrexed dilithium heptahydrate(Formula IV)

45.0 g N-[4-[2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]-pyrimidin-5- yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA salt was added to the solution of Lithium hydroxide solution (14 g LiOH dissolved in 3.5 Lit Purified water) at 25 to 30°C under stirring. The pH of the reaction mass was adjusted to 8.0 to 8.5 with acetic acid (IN, 5 ml) and then charcoalised the reaction mass. Filtered the reaction mass through Hyflo bed. Added 1250 ml acetone into the reaction mass and stirred for 30 min at 25 to 30°C. Filtered the product and washed with acetone (30 ml) to get 35 g crude pemetrexed dilithium heptahydrate. Chromatographic purity of pemetrexed dilithium: 99.0 %

Stage-IV

Purification of

pemetrexeddilithiumheptahydrate(Formula IV)

35 g Pemetrexed dilithium heptahydrate was stirred in 239 ml purified water at 25- 30 °C. The reaction mass was stirred for 20-30 min at room temperature. Added dropwise 1000 ml ethanol into the reaction mass at room temperature and stirred for 1.0 hr. Filtered the product and washed with ethanol (100 ml) to get pure crystalline pemetrexed dilithium heptahydrate.

The crystalline pemetrexed dilithium heptahydrate thus obtained is characterized by PXRD (Fig. l); DSC (Fig.2); Mass(Fig.3) and IR(Fig. 4).

Purity: 99.78 %

Yield: 80 %

Example 2:

Preparation of crystalline Di-lithium Pemetrexed heptahydrate from Pemetrexed Diacid:

Pemetrexed Diacid (500 mg) was taken in Methanol (10 ml) under nitrogen and warmed to 40-45°C. Lithium Hydroxide solution (10 %, 50 mg Lithium Hydroxide) was added to it to obtain clear solution. The solution was filtered and clear filtrate was subjected to distillation under vacuum to obtain a solid, which was dried under the stream of nitrogen and isolated the crystalline pemetrexed dilithium heptahydrate (530 gm).

Yield: 85 %

Purity: 99.82 %

Claims

We claim,

1. A stable and highly soluble crystalline hydrate of di-lithium salt of Pemetrexed of formula III.

Formula III

2. The stable and highly soluble crystalline hydrate of di-lithium salt of Pemetrexed according to claim 1, wherein, the said hydrate is crystalline di- lithium salt of Pemetrexed heptahydrate of formula IV.

The stable and highly soluble crystalline hydrate of di-lithium salt of Pemetrexed according to claim 2, wherein, the said hydrate is characterized by PXRD pattern that shows at least one characteristic peak at about 18.903 ± 0.25 degrees 2 theta angle.

The stable and highly soluble crystalline hydrate of di-lithium salt of Pemetrexed according to claim 2, wherein, the said hydrate is characterized by PXRD pattern that shows characteristic peaks at about 8.319, 9.094,

10.193, 14.812, 16.419, 17.431, 18.217, 18.903, 19.251, 19.824, 20.593, 21.058, 21.504, 22.350, 23.662, 23.927, 24.371, 25.175, 25.784, 26.238, 26.582, 28.163, 28.932, 29.745, 30.198, 31.586, 32.374, 33.180, 33.415, 33.812, 34.405, 35.416, 36.775, 37.465, 37.829, 38.272, 39.670, 40.129 and 40.840 ± 0.25 degrees 2 theta angles.

5. The stable and highly soluble crystalline hydrate of di-lithium salt of Pemetrexed according to claim 2, wherein, the said hydrate is characterized by DSC Analysis which shows a melting range of 93°C to 149°C.

6. The stable and highly soluble crystalline hydrate of di-lithium salt of Pemetrexed according to claim 2, wherein, the said hydrate is characterized by mass spectra that shows a peak at m/z 439 corresponding to Pemetrexed Dilithium Fragment and another peak at m/z 432 corresponding to Pemetrexed Monolithium Fragment.

7. The stable and highly soluble crystalline hydrate of di-lithium salt of Pemetrexed according to claim 2, wherein, the said hydrate is characterized by FTIR having characteristic stretching at 951.64 cm^"1 (C-H stretching), 1156.17 cm^"1 (C-N Stretching), 1631.61 cm^"1 (N-H Stretching), 1676.90 cm

¹ (C=0 Stretching) and 3356.50 cm^"1 (COOH Stretching).

8. A process for the preparation of stable and highly soluble crystalline Pemetrexed Dilithium Heptahydrate directly from pemetrexed Diethyl Ester of PTSA salt which process comprises:

a) Reacting N-[4-[2-(2-Amino-4, 7-dihydro-4-oxo-lH-pyrrolo[2,3-d]- pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester PTSA with a solution of Lithium hydroxide solution in water at 25 to 30°C; b) Adjusting the pH of the reaction mass to 8.0 to 8.5 with acetic acid followed by isolation of the crude pemetrexed dilithium heptahydrate and

c) Optionally purifying the crude pemetrexed dilithium heptahydrate.

9. The process according to claim 8, wherein the purification step comprises;

a) Dissolving Pemetrexed dilithium heptahydrate in purified water at 25-30 °C for sufficient time at room temperature; and b) Adding anti-solvent such as ethanol into the reaction mass at room temperature to isolate pure crystalline pemetrexed dilithium heptahydrate.

10. A process for preparation of stable and highly soluble crystalline pemetrexed dilithium heptahydrate which comprises;

a) Reacting Pemetrexed Diacid in Methanol under nitrogen at 40-45°C with Lithium Hydroxide solution;

b) Subjecting filtered solution of step a) to distillation under vacuum to obtain a solid; and

c) Drying the solid of step b) under the stream of nitrogen to isolate crystalline highly pure pemetrexed dilithium heptahydrate.