N-[4-[2-(2-amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-d]-pyrimidin-5-yl)ethyl] benzoyl]-L-glutamic acid or N-[4-[2-(2-amino-4,7-dihydro-4-oxo-1 H-pyrrolo [2,3-d]-pyrimidin-5-yl)ethyl] benzoyl]-L-glutamic acid
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Pemetrexed is a chemotherapy drug used in the treatment of pleural mesothelioma as well as non-small cell lung cancer.Used in combination with cisplatin for the treatment of malignant pleural mesothelioma in adults whose disease is unresectable or who otherwise are not candidates for potentially curative surgery. Also used as a monotherapy for the treatment of locally advanced or metastatic non-small cell lung cancer (NSCLC) after prior chemotherapy.Click here to contact Logenex about this product.
Pemetrexed (brand name Alimta) is a chemotherapy drug manufactured and marketed by Eli Lilly and Company. Its indications are the treatment of pleural mesothelioma andnon-small cell lung cancer.
The molecular structure of pemetrexed was developed by Edward C. Taylor at Princeton University and clinically developed by Indianapolis based drug maker, Eli Lilly and Company in 2004.
Pemetrexed is chemically similar to folic acid and is in the class of chemotherapy drugs called folate antimetabolites. It works by inhibiting three enzymes used in purine andpyrimidine synthesis—thymidylate synthase (TS), dihydrofolate reductase (DHFR), andglycinamide ribonucleotide formyltransferase (GARFT). By inhibiting the formation of precursor purine and pyrimidine nucleotides, pemetrexed prevents the formation of DNAand RNA, which are required for the growth and survival of both normal cells and cancer cells.
Pemetrexed disodium is chemically described as L-Glutamic acid, N-[4-[2- (2-amino-4,7-dihydro-4-oxo-1 H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]- disodium salt heptahydrate, represented by the chemical structure of Formula (I).
Pemetrexed is an anti-folate anti-neoplastic agent that exerts its action by disrupting folate-dependent metabolic processes essential for cell replication. It is believed to work by inhibiting three enzymes that are required in purine and pyrimidine biosynthesis — thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyl transferase (GARFT). Pemetrexed is available in the market under the brand name ALIMTA®.
Taylor et al., in describe pemetrexed, its related compounds and pharmaceutically acceptable cation. Chelius et al., in WO 01/14379 A2 disclose pemetrexed disodium crystalline hydrate Form I and process for preparation thereof.
Chelius et al., in WO 01/62760 disclose pemetrexed disodium heptahydrate crystalline Form Il and process for the preparation thereof.
Journal of Organic Process Research & Development, Volume 3, 1999, page 184 describes a process for the preparation of pemetrexed diacid. Busolli et al., in WO200802141 1 disclose process for preparation of pharmaceutically acceptable salt of pemetrexed diacid.
Busolli et al., in WO2008021405A1 disclose seven crystalline forms of pemetrexed diacid designated as Form A, B, C, D, E, F, & G and processes for preparation thereof.
In February 2004, the Food and Drug Administration approved pemetrexed for treatment of malignant Pleural Mesothelioma, a type of tumor of the lining of the lung, in combination with cisplatin for patients whose disease is either unresectable or who are not otherwise candidates for curative surgery. In September 2008, the FDA granted approval as a first-line treatment, in combination with cisplatin, against locally-advanced and metastatic non-small cell lung cancer (NSCLC) in patients with non-squamous histology. A Phase III study showed benefits of maintenance use of pemetrexed for non-squamous NSCLC.Activity has been shown in malignant peritoneal mesothelioma.Trials are currently testing it against esophagus and other cancers.
Pemetrexed is also recommended in combination with carboplatin for the first-line treatment of advanced non-small cell lung cancer.However, the relative efficacy or toxicity of pemetrexed-cisplatin versus pemetrexed-carboplatin has not been established beyond what is generally thought about cisplatin or carboplatin doublet drug therapy
In addition to the brand name Alimta, this drug is also marketed in India by Abbott Healthcare as Pleumet and by Cadila Healthcare asPemecad.
Pemetrexed disodium is a multitargeted antifolate agent approved as a single agent for the treatment of non-small cell lung cancer, and in combination with cisplatin for the treatment of patient with malignant pleural mesothelioma, under the trade name Alimta®.
Pemetrexed disodium is available in a number of crystalline forms.
Barnett et al, Organic Process Research & Development, 1999, 3, 184-188 discloses synthesis and crystallization of pemetrexed disodium from water-ethanol. The product obtained by the process disclosed herein is the 2.5 hydrate of pemetrexed disodium.
United States patent number 7,138,521 discloses a crystalline heptahydrate form of pemetrexed disodium, which has enhanced stability when compared to the known 2.5 hydrate.
To date workers have concentrated on producing stable crystalline forms of pemetrexed disodium and there has been no disclosure of any non-crystalline form of this active.
We have now found a new form of pemetrexed disodium, which is an amorphous form, as characterized by powder X-ray diffraction. Surprisingly, we have found that it is possible to prepare an amorphous form of pemetrexed disodium and that this form is stable. The amorphous form of the invention is stable contrary to expectations. The amorphous form of pemetrexed disodium of the present invention is stable as it retains it’s amorphous character under a variety of storage conditions. The amorphous form of the present invention is particularly advantageously characterized by a bulk density in the range of 0.15 to 0.35 gm/ml.
N-[4-[2-(2-amino-4,7-dihydro-4-oxo-3H-pyrrolo[2,3-d]-pyrimidin-5-yl)ethyl] benzoyl]-L-glutamic acid or N-[4-[2-(2-amino-4,7-dihydro-4-oxo-1 H-pyrrolo [2,3-d]-pyrimidin-5-yl)ethyl] benzoyl]-L-glutamic acid (also known as
R = H: Pemetrexed; I
R = Na: Pemetrexed Disodium; II is a known compound. Pemetrexed Disodium is an known anticancer agent. It is clinically active in several solid tumors and approved for treatment of malignant pleural mesothelioma (MPM) and metastatic non-small cell lung cancer (NSCLC). Pemetrexed Disodium is supplied as a sterile lyophilized powder for intravenous administration.
The compound of formula I including pharmaceutically salts thereof as well as a process for its preparation is at first and specifically disclosed in EP patent no. 0432677 B1. The preparation and isolation of Pemetrexed (compound of formula I) as its Disodium salt (compound of formula II) was described for the first time in WO patent no. 9916742 A1 and in Drugs of the future 1998, 23(5), 498-507 as well as by Charles J. Barnett et al. in Organic Process Research & Development, 1999, 3, 184-188 and by Peter Norman in Current Opinion in Investigational Drugs 2001 , 2(11 ), 1611-1622.
Detailed information about the crystalline form of Pemetrexed Disodium prepared according to the process as described above were not provided but it is reported by Charles J. Barnett et al. in Organic Process Research & Development, 1999, 3, 184-188 that the disodium salt II was obtained as a hygroscopic solid.
The first crystalline form of Pemetrexed Disodium has been described in WO patent no. 0114379 designated Disodium MTA Hydrate Form I (MTA = multi- targeted antifolate, disodium N-[4-[2-(2-amino-4,7-dihydro-4-oxo-3H- pyrrolo[2,3-d]-pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic acid salt). The Disodium MTA Hydrate Form I obtained according to the Examples 2, 3 and 4 contained different amounts of water (Example 2: water = 9.1%; Example 3: water = 17.7%; Example 4: water = 11.7%). The Disodium MTA Hydrate Form I has a typical XRD pattern as shown in Figure 4 (the corresponding 2theta values have been calculated from the provided d-spacing values).
An improved crystalline form of Pemetrexed Disodium has been disclosed in WO patent no. 0162760. It is teached that Pemetrexed Disodium can exist in the form of a heptahydrate (Form II; theoretical amount of water: approx 21%) which is much more stable than the previously known 2.5 hydrate (Form I; theoretical amount of water: 8.7%). The Pemetrexed Disodium Heptahydrate Form (Form II) has a typical XRD pattern as shown in Figure 5 (the corresponding 2theta values have been calculated from the provided d- spacing values).
The Chinese patent no. 1778802 describes a hydrate or trihydrate form of Pemetrexed Disodium. The preparation of Pemetrexed Disodium hydrate or trihydrate includes crystallization from water and water soluble solvent. An overview of the X ray powder diffraction data for Pemetrexed Disodium Hydrate provided in Chinese patent no. 1778802 is shown in Figure 6.
The WO patent no. 2008124485 disclose besides crystalline Forms of the diacid Pemetrexed also amorphous Pemetrexed Disodium as well as a crystalline Form III thereof including a composition containing a major amount of amorphous Form and a minor amount of crystalline Form III of Pemetrexed Disodium. An overview of the X ray powder diffraction data for Pemetrexed Disodium crystalline Form 3 is shown in Figure 7.
EP patent application no. 2072518 disclose a stable amorphous form of Pemetrexed Disodium.
According to the more recent US 5,416,211 , which is incorporated herein by reference, pemetrexed can be synthesized from 4-[2-(2-amino-4,7-dihydro-4-oxo-1H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoic acid of formula 1, obtained from simple precursors, in accordance with the following Scheme 1:
This second method seems to be used also for the industrial preparation of the active ingredient. In fact, the same type of synthesis scheme is also described in C. J. Barnett, T. W. Wilson and M. E. Kobierski, Org. Proc. Res. & Develop., 1999, 3, 184-188, in which the experimental examples refer to a scale of the order of tens of kgs.
Example 1 Preparation of crude pemetrexed disodium
 N-[4-2-(2-Amino-4, 7-dihydro-4-oxo-
1 H-pyrrolo[2,3-d]pyrimidin-5-yl)ethyl]benzoyl]-L-glutamic Acid Diethyl Ester
4-Methylbenzenesulfonic Acid Salt and purified process water (PPW) (about 10 kg) are charged to a suitable vessel under nitrogen. The reactor is cooled to NMT 10Ό under nitrogen. Pre-cooled sodium hydroxide solution (about 1.5 kg )/PPW (about 11.4 kg) are added and the temperature is maintained at NMT 10Ό. The mixture is stirred at NMT 0 until the solid is dissolved. Pre-cooled isopropanol (about 62.8 kg) is added and the mixture temperature is maintained at NMT 5 . Pre-cooled 1 N hydrochloric acid in isopropanol is added to adjust the pH to 6.5 to 9.5, preferably between pH 7.5 to pH 8.5, at NMT 5 . The mixture is warmed to a room temperature (i.e., 15-30Ό, preferably 20-25″C) and stirred. The solids are filtered and washed with isopropanol/PPW. The wet cake is vacuum dried to provide crude pemetrexed disodium (about 2.30 kg).
Example 2 Purification of crude pemetrexed disodium to pemetrexed disodium
 Crude pemetrexed disodium (about 2.1 kg) and PPW (about 23.3 kg) are charged under nitrogen to a suitable vessel at 15 to 30 . Isopropanol (about 28.3 kg) is added slowly to cloud point and stirred. Isopropanol (up to about 55 kg) is charged and stirred. The solids are filtered arid washed with isopropanol/PPW. The wet cake is vacuum dried to provide pemetrexed disodium (about 1.9 kg) (90% Yiled). 1 H NMR (D20): δ 7.51 (2H, d, J=8.0 Hz), 6.98 (2H, d, J=8.0 Hz), 6.12 (1 H, s), 4.26-4.23 (H, m), 3.60-3.54 (4H, m), 2.27-2.23 (2H, m), 2.13-2.08 (1 H, m), 2.00-1.94 (1 H, m)
HPLC Analysis method
Reagent: Water :milliQ,
Sodium perchlorate :AR Grade
Perchloric acid :AR Grade
Acetonitrile :J.T.Baker gradient
Trifluroacetic acid :AR Grade
Buffer solution: 6.1 g of sodium perchlorate into a 1000ml water. Adjust the pH to 3.0 (± 0.1) with perchloric acid.
Mobile phase A:
mixture of buffer and acetonitrile in the proportion of (90:10).
Mobile phase B:
mixture of buffer and acetonitrile in the proportion of (10 : 90).
Diluent -1 : mixture of water and acetonitrile in the ratio of 50 : 50.
Diluent -2: mixture of water and acetonitrile in the ratio of 90 : 10.
Standard Stock Solution:
Transfer accurately weighed 1.5 mg impurity-E RS and into a 200 ml volumetric flask. Dissolve in and dilute upto mark with diluent-1.
Add 10 ml diluent-2 and 50µl of 3% trifluro acetic acid to a 50 ml volumetric flask, and dilute upto mark with diluent-2.
System suitability solution
Transfer about 25 mg accurately weighed pemetrexed disodium sample in to a 50 ml volumetric flask. First add 10ml of diluent-2 and sonicate to dissolve the contents.Then add 50µl of 3% trifluro acetic acid (prepared in water) and add 5 ml of standard stock solution and dilute up to mark with diluent-2.
Transfer about 25 mg accurately weighed pemetrexed disodium sample in to a 50 ml volumetric flask. First add 10ml of diluent-2 and sonicate to dissolve the contents.Then add 50µl of 3% trifluro acetic acid (prepared in water) and dilute up to mark with diluent-2 (500 µg/ml).
Chromatographic system :
Use a suitable high pressure liquid chromatography system equipped with Column: 250 mm x 4.6mm containing 5µ packing material (suggested column – Inertsil ODS 3V)
Detector: UV detector set to 240 nm
Cooler temp: 5°C.
Flow rate: about 1.5 ml/min.
The system is also equipped to deliver the two phases in a programmed manner as shown in the following table :
Gradient programme :
0 92 8 15 85 15 30 65 35 35 65 35 36 92 8 40 92 8
Inject 20µl of blank and system suitability solution into the chromatograph set to above conditions and record the chromatograms up to 40 min.
Calculate the resolution between pemetrexed disodium and impurity-E. The resolution should not be less than 3.0. Calculate the Number of theoretical plate and tailing factor for pemetrexed peak. Number of theoretical plate is NLT 4000 and tailing factor is NMT 2.0.
Inject 20µl of test solution and calculate the chromatographic purity by area normalisation method.
Synthetic Route for the Preparation of Pemetrexed Disodium
Starting from commercially available materials a novel synthetic route for the synthesis of Pemetrexed-IM8 (the dimethyl ester of Pemetrexed) was developed which was then used for the preparation of Pemetrexed Disodium (Scheme 1).
The current synthetic route for the preparation of Pemetrexed IM8 starts with an aldol-condensation reaction of Methyl-4-formylbenzoate (SM1) with 1,1-Dimethoxyacetone (SM2) to give Pemetrexed IM1a. As Pemetrexed IM1a irreversibly converts to its aldol-addition product Pemetrexed IM1b under reaction conditions the reaction mixture is directly submitted to hydrogenation (i.e. without isolation of Pemetrexed IM1a) over Pd/C to give Pemetrexed IM2. As under the hydrogenation conditions not only the double-bond of IM1a is hydrogenated but also some amount of Pemetrexed IM2 is converted to Pemetrexed IM3 (hydrogenation of the carbonyl function to the corresponding secondary alcohol) a solution of NaBH4 is added to the reaction mixture to ensure complete conversion to Pemetrexed IM3. The Pd-catalyst is removed by filtration and the reaction mixture is extracted with toluene. The combined organic layers are evaporated to give crude Pemetrexed IM3 as oil. This oil is dissolved in THF and the alcohol functionality is converted to a mesylate using MsCl and NEt3. The salts are removed by filtration, glacial acetic acid is added and THF is removed by distillation. Upon addition of water Pemetrexed IM4 crystallizes and is isolated by filtration. The dried Pemetrexed IM4 is dissolved in glacial acetic acid and gaseous HCl is added to cleave the dimethoxy acetale and liberate the aldehyde functionality of Pemetrexed IM5. Upon complete deprotection a solution of 2,6-diamino-4-hydroxypyrimidine in aq. NaOH and acetonitrile is added. Upon complete conversion the crystallized Pemetrexed IM6 is isolated by filtration. The saponification of the methyl ester of Pemetrexed IM6 to Pemetrexed IM7 is done using aqueous NaOH. Upon addition of aq. HCl first the Na-salt of Pemetrexed IM7 crystallizes from the reaction mixture. The salt is isolated by filtration, purified by slurry in a mixture of MeOH and water and then converted to Pemetrexed IM7 by pH adjustment in water using aq. HCl. Dried Pemetrexed IM7 (water content not more than 6.0%) is dissolved in DMF, activated using 1,1-carbonyldiimidazolide (CDI) and then reacted with dimethyl-L-glutamate hydrochlorid to give, upon addition of water and filtration, crude Pemetrexed IM8. This intermediate is purified by tosylate salt formation, followed by recrystallization and liberation to give pure Pemetrexed IM8. Starting with the saponification of Pemetrexed IM8 the preparation of different solid forms of Pemetrexed Disodium can be achieved.
Methods For Preparing Pemetrexed Disodium Form IV and Investigation of its Stability
An overview on the possible transformations of Pemetrexed IM8 to Pemetrexed Disodium Form IV is shown in FIG. 20.
Description of Possible Routes for the Preparation of Pemetrexed Disodium Form IV Starting from Pemetrexed IM8
All routes start with saponification of Pemetrexed IM8 in water at IT=20° C. to 30° C. using 3.25 eq of NaOH. Upon complete conversion an aqueous solution of Pemetrexed Disodium with a pH of 13.0 to 13.5 is obtained. Starting from this mixture the desired route can be accessed by addition of HCl to adjust the pH to a certain value (depending on the route, FIG. 20).
Structures of Pemetrexed (Compound I), Pemetrexed Disodium (Compound II) and Pemetrexed Monosodium (Compound IV)
Surprisingly we found that the crucial feature of all successful transformations to Pemetrexed Disodium Form IV is the presence of Pemetrexed Monosodium during the transformation. Routes starting from pure Pemetrexed Disodium Heptahydrate, Pemetrexed Disodium 2.5 hydrate or Pemetrexed Disodium Form A in the presence of seeding crystals of Pemetrexed Disodium Form IV were not successful and resulted in isolation of Pemetrexed Disodium Form A. The same transformations, if carried out in the presence of 0.15 eq of Pemetrexed Monosodium were successful and after addition of 0.15 eq NaOH allowed the isolation of pure Pemetrexed Disodium Form IV. The use of 0.15 eq HCl instead of 0.15 eq Pemetrexed Monosodium under the same conditions resulted in isolation of Pemetrexed Disodium Form A without any Pemetrexed Disodium Form IV. Transformations via isolated Pemetrexed Monosodium gave complete transformation to Pemetrexed Disodium Form IV if either 1.0 eq NaOH were added slowly (over a period of several hours) to Pemetrexed Monosodium or if initially only 0.85 eq of NaOH (based on Pemetrexed Monosodium) were added, followed by 0.15 eq once the transformation to Pemetrexed Disodium Form IV was complete. Very fast addition (<1 min) of 1.0 eq NaOH resulted in formation of Pemetrexed Disodium Form A containing traces of Pemetrexed Disodium Heptahydrate.
Starting from Pemetrexed (compound I) the transformation to Pemetrexed Disodium Form IV would be possible if initially 1.85 eq of NaOH were added followed by 0.15 eq once the transformation was complete. Alternatively, 2.0 eq of NaOH could be added over a long period of time (i.e several hours) to achieve formation of Pemetrexed Form IV. Fast addition (<1 min) of 2.0 eq of NaOH is assumed to result in formation of Pemetrexed Disodium Form A. All these experiments show the presence of Pemetrexed Monosodium to be crucial during the transformations. This presence can be achieved by either addition of catalytic amounts of Pemetrexed Monosodium to Pemetrexed Disodium, by slow addition over several hours of NaOH to Pemetrexed Monosodium or by portionwise addition of NaOH to Pemetrexed Monosodium. Addition of catalytic amounts of HCl to Pemetrexed Disodium (in situ preparation of Pemetrexed Monosodium) failed to give Pemetrexed Disodium Form IV.
Fast addition of NaOH to Pemetrexed Monosodium results in fast formation of Pemetrexed Disodium, thereby lacking the necessary catalytic amounts of Pemetrexed Monosodium to catalyze the transformation to Pemetrexed Disodium Form IV. EtOH as solvent and water content of EtOH were found to be crucial parameters for the transformation to Pemetrexed Disodium Form IV. So far the transformation has only been observed in EtOH containing 0-4% water (v/v). A water content>4% (v/v) results in formation of Pemetrexed Disodium Heptahydrate. Under the conditions used (EtOH containing 0-4% water (v/v)) both Pemetrexed Disodium Heptahydrate and Pemetrexed Disodium 2.5 hydrate are transformed to Pemetrexed Form A. Therefore the mechanism of the transformation to Pemetrexed Disodium Form IV is assumed to proceed via Pemetrexed Disodium Form A with Pemetrexed Monosodium acting as catalyst for the transformation.
Preparation of Pemetrexed Disodium Heptahydrate
a) Preparation of Pemetrexed Disodium Heptahydrate Starting from Pemetrexed IM8
Pemetrexed Disodium Heptahydrate was prepared by adjustment of the pH of the Pemetrexed Disodium solution after saponification from pH=13 to pH=8 using HCl followed by addition of EtOH (3 times the volume of water) to achieve crystallization. Precipitated Pemetrexed Disodium Heptahydrate was isolated by filtration, washed with a mixture of EtOH and water (4:1 v/v) followed by EtOH. The wet product was dried in vacuo at 200 mbar at 20° C. to 30° C. until water content of the dried product was 20.1% to 22.1%.
b) Conversion of Pemetrexed Disodium Form A to Pemetrexed Disodium Heptahydrate
To a suspension of Pemetrexed Disodium Form A in EtOH was added water until a mixture of EtOH containing 25% water (v/v) was obtained. The resulting suspension was stirred at 20° C. to 30° C. until conversion was complete according to PXRD. Pemetrexed Disodium Heptahydrate was isolated by filtration, washed with EtOH and dried in vacuo at 200 mbar at 20° C. to 30° C. until water content of the dried product was 20.1% to 22.1%.
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- National Cancer Institute: FDA Approval for Pemetrexed Disodium
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