Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D403/00—Heterocyclic compounds containing two or more hetero rings, having nitrogen atoms as the only ring hetero atoms, not provided for by group C07D401/00
  • C07D403/02—Heterocyclic compounds containing two or more hetero rings, having nitrogen atoms as the only ring hetero atoms, not provided for by group C07D401/00 containing two hetero rings
  • C07D403/06—Heterocyclic compounds containing two or more hetero rings, having nitrogen atoms as the only ring hetero atoms, not provided for by group C07D401/00 containing two hetero rings linked by a carbon chain containing only aliphatic carbon atoms
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P25/00—Drugs for disorders of the nervous system
  • A61P25/06—Antimigraine agents

Definitions

• the present invention refers to the synthesis of 3- ⁇ [ (2R)-l-methylpyrrolidin-2-yl]methyl ⁇ -5-[2- (phenylsulfonyl) ethyl ]-lH-indole f a drug known by the name Eletriptan, or of its salts.
• This reaction uses a palladium-based catalyst which is very sensitive to the impurities present in the reaction environment. It is thus essential that the 5-bromo-3- ⁇ [ (2R) -l-methylpyrrolidin-2-yl] methyl ⁇ - lH-indole intermediate be thoroughly purified before being reacted with phenyl vinyl sulfone.
• the problem addressed by the present invention is that of providing a process for the synthesis of Eletriptan through a 5-bromoindole intermediate with high purity.
• Figure 1 shows a synthesis diagram of Eletriptan according to the process of the prior art
• Figure 2 shows a synthesis diagram of Eletriptan according to a particular embodiment of the invention
• Figure 4 shows a DSC spectrum of Eletriptan hydrobromide obtained according to the inventive process (Mettler Toledo DSC820; 20°C/min.);
• Figure 5 shows a FT-IR spectrum of Eletriptan hydrobromide obtained according to the inventive process (Perkin-Elmer; nujol mulls) ;
• Figure 6 shows a FT-IR spectrum of Eletriptan hydrobromide obtained according to the inventive process, expanded in a narrower range of wavelengths;
• Figure 7 shows a FT-IR ATR spectrum of Eletriptan hydrobromide obtained according to the inventive process (Perkin-Elmer FT-IR ATR Spectrum 100) .
• the present invention concerns a process for the synthesis of Eletriptan comprising the following steps : a ⁇ Salifying the intermediate of formula 6
• step a) optionally, purifying said salt obtained according to step a) by solvent crystallization to obtain a purified salt of the intermediate of formula 6; c) Converting said salt of the intermediate of formula 6 according to step a) or said purified salt according to step b) into an intermediate of formula 10 d) Converting the intermediate of formula 10 into Eletriptan or its salt.
• steps a) and b ⁇ for salifying the intermediate 6 and crystallising the salt thus obtained are carried out in an organic solvent or in a mixture of water and organic solvent miscible in water.
• the organic solvent is an alcohol, more preferably an alcohol selected from among methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert-Butanol, pentanol.
• the alcohol is isopropanol.
• the amount of water in the mixture shall preferably be comprised between 10% and 20% in volume.
• the weight/volume percentage amount of crude intermediate 6 with respect to the solvent varies between 8% and 15% and shall be generally established through an experiment depending on the solvent used.
• the dicarboxylic acid is used in stoichiometric amount with respect to the crude intermediate 6 or with a molar excess up to 15%.
• HA is a dicarboxylic acid
• the preferred dicarboxylic acid is fumaric acid or oxalic acid, more preferably oxalic acid.
• a solution of intermediate 6 in isopropanol is dropped at room temperature into an isopropanol/water solution into which oxalic acid or fumaric acid is dissolved, in the amounts described previously.
• oxalic or fumaric acid is added in solid form to a solution of intermediate 6 in ethanol.
• the oxalate salt of the intermediate 6 is recrystallized with water by re-dissolving under heat and reprecipitation, obtaining - after washing and drying - the oxalate salt of the intermediate 6 with purity greater or equal to 99.5%, determined through the HPLC analysis.
• the water shall preferably be used in volume/weight amount of intermediate 6 of about 10:1.
• the step c) for converting the salt of intermediate 6 into intermediate 10 is obtained through acylation of indole nitrogen and subsequent Heck condensation of the intermediate thus obtained with phenyl vinyl sulfone.
• Such process requires, for reacting the two molecules, the presence of tri-o-tolylphosphine and a catalyst Pd(Ac) 2 .
• the purified salt of intermediate 6 is treated using a basic aqueous solution, for example a sodium or potassium hydroxide aqueous solution, in such a manner to free the base intermediate 6, which is then isolated, dissolved in a suitable solvent, preferably dirnethylformamide or analogous dipolar aprotic solvent, and treated with an organic base and an acylating agent.
• a suitable solvent preferably dirnethylformamide or analogous dipolar aprotic solvent
• acetic anhydride and triethylamine are used.
• indole nitrogen is acetylated.
• the reaction may be carried out at a temperature higher than 7O 0 C, preferably about 100 0 C, over a period of time sufficient to obtain the substantial complete conversion of the free base intermediate 6 to the acetylated product (molecule 8 of figure 2), which can be determined through the HPLC analysis.
• the obtained acetylated intermediate 6 is not isolated, but it is added into a solution in suitable solvent, preferably the same solvent used in the acylation process, containing Pd(Ac) 2 , tri-o-tolylphosphine, phenyl vinyl sulfone and triethylamine.
• the molar ratios between said reagents and intermediate 6 are determined by the conventional stoichiometry of the Heck reaction and may for example be about 1 : 1 phenyl vinyl sulfone/intermediate 6 ratio, about 1 : 10 tri-o- tolylphosphine/intermediate 6 ratio and 0.5-0.8 : 10 Pd(Ac) 2 /intermediate 6 ratio. It is obvious that such molar ratios may vary within given limits, under the supervision of a man skilled in the art, without jeopardising the development of the reaction.
• the condensation reaction is preferably carried out at a temperature comprised between 70 0 C and the boiling temperature of the solvent for a number of hours sufficient to complete the reaction.
• step dl) is performed by reaction with a base.
• a carbonate of an alkaline or alkaline earth metal or a trialkylamine in an alcohol is used.
• the reaction may be carried out in the presence of potassium carbonate or dimethylethylamine in methanol.
• step d2 is performed by catalytic hydrogenation, for example in the presence of a catalyst Pd/C .
• the deacylated intermediate 10 is salified with hydrobromic acid before being subjected to catalytic hydrogenation, directly obtaining, after such hydrogenation reaction, Eletriptan hydrobromide.
• step dl) and step d2) are carried out in one step, i.e. without isolating the respective intermediates.
• the intermediate of formula 6 may for example be prepared according to the synthesis diagram shown in figure 2, which provides for the condensation between R-benzyloxycarbonyl-proline and 5-bromoindole, after activation of the carboxylic group of proline, and the subsequent removal of the protective benzyloxy- carbonyl group, for example through reduction using lithium aluminium hydride. Still as an example, a detail of the process used is shown in examples 1, 2 and 3.
• the acetylated intermediate of formula 8 is purified by forming a salt, in particular a fumaric acid or oxalic acid salt, and subsequent crystallisation.
• a salt in particular a fumaric acid or oxalic acid salt
• the oxalate of the intermediate (8) may be possibly crystallised as described previously regarding the intermediate of formula 6.
• the process of the invention may skip step a) and b) of salifying and possibly purifying the salt of intermediate 6, replacing the salification of the intermediate 8 and possible purification of the salt thus obtained instead.
• HA is a dicarboxylic acid, preferably fumaric acid or oxalic acid.
• the process shall comprise the following steps: i)Salifying the intermediate of formula 8
• a dicarboxylic acid to obtain a derived salt, preferably a salt of fumaric acid or of oxalic acid; ii) optionally, purifying said salt obtained according to step i) by solvent crystallization to obtain a purified salt of the intermediate of formula 8; iii) Converting said salt of the intermediate of formula 8 according to step i) or said purified salt according to step ii) into an intermediate of formula 10; iv) Converting the intermediate of formula 10 into Eletriptan or its salt.
• the optical purity of Eletriptan can be enhanced up to substantially 100% optical purity by dissolving Eletriptan free base in ethanol and treating it with an amount of oxalic acid ranging from 2% to 6% in weight with respect of the weight of Eletriptan. This procedure allows the precipitation of Eletriptan oxalate (enriched in the S form) , while the predominating isomer (R isomer) remains in solution.
• the solution of the optically purified Eletriptan free base can then be converted into Eletriptan hydrobrornide salt by treating it with hydrobromic acid and crystallizing the resulting salt.
• Eletriptan hydrobromide as a monotropic Beta form polymorph which is stable and not hygroscopic.
• the Beta stable form polymorph of Eletriptan hydrobromide of the invention comprises needle-shaped crystals.
• Beta form of Eletriptan hydrobromide is known and has been disclosed in US 6,110,940 in the name of Pfizer. However, in this patent it is reported that Form Beta of Eletriptan hydrobromide is not stable and converts into Form Alpha having a higher melting point. The conversion of Beta form to Alpha form is performed in aqueous acetone. In the later document EP1135381B1, Pfizer confirms the instability of Eletriptan hydrobromide Beta form. In WO2008/137134 Teva Pharmaceuticals USA describes the process of conversion of Beta form to Alpha form by slurrying in organic solvents such as isobutanol, methylacetate, mixtures of THF and water, cyclohexane.
• organic solvents such as isobutanol, methylacetate, mixtures of THF and water, cyclohexane.
• Beta form is prepared by simple heating of Beta form at 50 0 C, under vacuum for 24 hours.
• a process of conversion of Beta form to Amorphous is described by slurring the Beta form in THF/Water or Ethylacetate/Water or MIBK at 8O 0 C or Ethylene glycol at 25°C.
• the process of preparation of Eletriptan hydrobromide form Beta described by Pfizer and Teva differs from the process of the invention, for example, because the hydrogenation of molecule 11 is performed on the mesylate salt instead of the hydrobromide salt
• the process of the invention avoids the potential formation of genotoxic impurities related to Methansulphonate esters and the counter ion exchange.
• Figures 3-7 report the spectral data and the PXRD pattern, DSC curve and FT-IR spectrums of ⁇ letriptan hydrobromide Beta stable form obtained with the inventive process.
• Eletriptan hydrobromide Beta stable form as obtained in this invention is characterized by PXRD pattern having peaks at 5.4, 10.7, 12.6, 13.0, 15.4, 17.3, 17.9, 18.9, 19.9, 22.3, 23.3, 24.5, 27.5 degrees 2-Theta; DSC endotherm peak max. at 155 0 C (20°C/min.
• FT-IR absorption bands in nujol at 3240, 2673, 2528, 1449, 1409, 1302, 1293, 1237, 1152,1138, 1122, 1086, 973, 926, 870, 811, 791, 771, 747, 689, 631 cm-1; FT-IR ATR absorptions bands at 3237, 2941, 2656, 1479, 1447, 1432, 1409, 1302, 1293, 1237, 1152, 1122, 1087, 973, 926, 870, 790, 770, 745, 688 cm '1 .
• Example 18 below reports some tests that were performed on Eletriptan hydrobromide Beta stable form according to the invention, showing that the product remained stable in all the conditions tested, including also those described in the State of the Art for the conversion of Beta form to other forms.
• Example 19 below reports the hygroscopicity test of Eletriptan hydrobromide stable Beta form according to the invention, showing that the product in not hygroscopic .
• Example 1 (molecule 02 in figure 2)
• Example 2 (molecule 05 in figure 2)
• the upper aqueous phase was washed with 200 mL of 10% citric acid and 200 mL of water containing sodium chloride, then concentrated to residue under vacuum. After adding 800 mL of MTBE, the resulting suspension was heated at reflux for 60 minutes distilling the water off. The reaction mixture was cooled to 20-25 0 C and it was filtered after stirring for 2 hours. The product was washed with 200 mL of MTBE in portions and dried obtaining 109.6 g of the title compound with HPLC assay 99.4%, Karl Fischer 0.47%.
• Example 3 (molecule 06 in figure 2) 5-bromo-3- ⁇ [ (2R) -l-methyl ⁇ yrrolidin-2- yl]methyl ⁇ -lH-indole
• Example 8 (molecule 07 fumarate) 5-faromo-3- ⁇ I (2R) -l-meth ⁇ lp ⁇ rrolidin-2- yl]methyl ⁇ -lH-indole (2E) but-2-enedioat ⁇
• reaction mixture was added into a reactor containing 2550 mL of isopropyl acetate and 436 mL of water at 55°C. 44 g of activated charcoal were added and, after stirring for 1 hour, the reaction mixture was filtered on cartridge, washing with 939 mL of isopropyl acetate. Other 500 mL of isopropyl acetate were used to wash the cartridge and then distilled under vacuum to return to volume. 3489 mL of water were added - between 20 and 23 0 C - in 1 hour, leaving under stirring for about 16 hours. Then the reaction mixture was filtered, the crude product was washed with 1310 mL of water and dried at 35 0 C until the weight of 460.3 g (Karl Fischer 6.9%, HPLC purity 97.0%) was reached.
• Example 10 (molecule 08 oxalate) 1- (5-bromo-3- ⁇ [ (2R) -l-meth ⁇ lpyrrolidin-2- yl]methyl ⁇ -lH-indole-1-yl) ethanone ethanedioate
• the phases were separated and the aqueous phase was extracted with 75 ml of methyltetrahydrofuran .
• the organic phases were collected and washed with water.
• the resulting organic phase was concentrated under vacuum at 50°C f obtaining 46.8 g of molecule 11 as an oil.
• This oil was dissolved in 450 ml of methanol and treated dropwise with 9 ml of 62% aqueous HBr until pH 1.5 was reached,, obtaining molecule 12.
• 1625 g of 5% Pd/C ⁇ 50% wet were added to the suspension, and the reaction mixture was hydrogenated in autoclave at 5 atm of hydrogen and 20-25 0 C.
• the reaction was monitored by HPLC until the starting product was present in amount less than 0.5%, then the catalyst was filtered off and the mixture was concentrated under vacuum to an oil.
• the residue was dissolved in 135 ml of isopropanol and again concentrated under vacuum to an oil.
• the residue was diluted with 450 ml of isopropanol and heated at reflux for 30 minutes. Further 200 ml of isopropanol were added, the mixture was filtered on activated carbon and concentrated to the initial volume.
• Raw molecule 13 (70 g) was diluted with 168 ml of acetone and 672 ml of isopropanol- The resulting mixture was heated at reflux until dissolution, treated with decolorizing charcoal and the solvent was removed. The residue was diluted with 154 ml of acetone and 616 ml of isopropanol, then it was cooled in 1 hour to 1O 0 C and stirred for at least 2 hr at 10 0 C. The solid was filtered and washed with 140 ml of isopropanol, then dried to give 61.6 g of Eletriptan hydrobromide, crystallization yield 88%, HPLC purity 99.7%.
• Eletriptan hydrobromide having an enantiomeric purity of 91% R form and 9% S form
• 355 mL of CH 2 Cl 2 and approx. 190 mL of NaOH 2% in water The pH is adjusted to 12, then the aqueous phase is separated and extracted with 106 mL of CH 2 Cl 2 .
• the two organic phases are combined and washed with 106 mL of H 2 O.
• the solvent is removed by rotary evaporation and 56,3 g of eletriptan free base as an oil are obtained.
• Eletriptan free base having an enantiomeric purity of 91% R form and 9% S form, were dissolved in 530 ml of ethanol and a solution of 2.5 g of anhydrous oxalic acid in 265 ml of ethanol was added dropwise. The reaction mixture was kept at room temperature overnight, then it was filtered and the solid ⁇ Eletriptan oxalate enriched in S-enantiomer) ) was discharged. The filtrate was treated with 2 g of carbon, filtered and concentrated to dryness giving 31.3 g of Eletriptan free base, 100% R form.
• the product so obtained is dissolved in 300 ml of methylene chloride and 100 ml of water and the pH is brought to pH 12 by adding 10% aqueous KOH.
• the aqueous phase is separated, while the organic phase is concentrated to give a residue of 29.6 g.
• This residue is dissolved in 592 ml of isopropanol and treated with 5.8 ml of 62% aqueous hydrobromic acid to reach a final pH 2.5.
• the hydrobromide salt crystallizes. After 2 hr under stirring, it is filtered and washed with 60 ml of isopropanol. After drying, 29.8 g of Eletriptan hydrobromide, 100% R form, are obtained.
• Eletriptan hydrobromide Beta form obtained according to the inventive process has been subject to a series of experiments to assess its stability against the conversion into Form Alpha of higher melting point or in amorphous.
• Eletriptan hydrobromide Form Beta did not convert into Form A 1 amorphous or other crystalline forms or in any hydrated form.
• the DSC trace is the same for all the product prepared according to Example 18 and is the same of that of Beta polymorph.
• Eletriptan hydrobromide Beta stable form obtained according to the inventive process has been subject to the hygroscopicity test as described in the European Pharmacopoeia 5.0 ⁇ 25°C, 80% rel. umidity, 24h) . Eletriptan hydrobromide results not hygroscopic (0,1%).

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