Bimatoprost crystalline form i   

This application is a Continuation of U.S. patent application Ser. No. 11/896,002, filed Aug. 29, 2007 which claims priority of Israeli Application Number 177762, filed Aug. 29, 2006, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to novel polymorphic form I of crystalline bimatoprost, method for preparation thereof and new crystalline intermediates in the preparation. This form I of crystalline bimatoprost is used in purification of crude bimatoprost, and in storage of bimatoprost as active pharmaceutical intermediate. Use of the physical form of bimatoprost in the manufacture of a medicament is also disclosed.

BACKGROUND OF THE INVENTION

Elevated intraocular pressure (TOP) is the major risk factor associated with the etiology of glaucoma, a progressive optic neuropathy that can ultimately cause blindness. Prostamide analogs represent potent therapeutic agents in clinical management of glaucoma and other conditions associated with elevated intraocular pressure. The synthetic prostamide analog used to reduce IOP includes (9S,11R,15S)-9,11,15-trihydroxy-17-phenyl-18,19,20-trinor-5Z,13E-prostadienoic acid ethylamide

known under international nonproprietary name bimatoprost, currently marketed by Allergan as Lumigan™—0.03% bimatoprost ophthalmic solution for the treatment of open-angle glaucoma and ocular hypertension (Drugs Aging, 2002, 19, 231).

US2005/209337 discloses crystalline physical form of bimatoprost, which we designate as form A. The form is characterized by powder x-ray diffractometry, IR DRIFTS (KBr) spectroscopy, DSC and TGA. The present invention includes new polymorphic form of bimatoprost which is the most thermodynamically stable polymorph of bimatoprost and method for preparation thereof.

SUMMARY

The present invention provides crystalline form I of bimatoprost and method for preparation thereof. The new crystalline form of bimatoprost is the most stable solid form of bimatoprost. Moreover, the new form of bimatoprost may be prepared so as to be substantially free of other physical forms.

The present invention also provides a method for purifying crude bimatoprost from related impurities, which comprises the steps of:

a) dissolving crude bimatoprost in an organic solvent or a mixture of organic solvent and anti-solvent at or near the boiling point; b) allowing the hot solution to cool; c) separating the precipitate from the supernatant solution; d) drying the resulting solid in vacuo at low temperature and then at 30 to 40° C. to give purified bimatoprost in crystalline form I.

The present invention also provides the use of bimatoprost crystalline form I in the manufacture of a medicament. The medicament is prepared by combining a therapeutically effective amount of bimatoprost crystalline form I, as an active ingredient, with conventional pharmaceutically-acceptable excipients, e.g. an ophthalmically-acceptable vehicle, and by preparation of unit dosage forms suitable for pharmaceutical use, e.g. topical ocular use.

The present invention also provides new crystalline intermediate in the synthesis of bimatoprost-crystalline (3aR,4R,5R,6aS)-4-[3R-(t-butyldimethylsiloxy)-5-phenyl-1E-pentenyl]-5-(4-phenylbenzoyloxy)-hexahydro-2H-cyclopenta[b]furan-2-one 5a.

The crystalline intermediate is useful for complete isolation of desired crystalline (3aR,4R,5R,6aS)-4-[3S-(t-butyldimethylsiloxy)-5-phenyl-1E-pentenyl]-5-(4-phenylbenzoyloxy)-hexahydro-2H-cyclopenta[b]furan-2-one 5 as MTBE solvate

from reaction mixture and for recovery of by-product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a characteristic x-ray powder diffraction pattern of bimatoprost crystalline form I, according to embodiments of the present invention. Vertical axis: intensity (counts per second); Horizontal axis: 20 (degrees).

FIG. 2 shows the differential scanning calorimetry (DSC) curve of bimatoprost crystalline form I, according to embodiments of the invention.

FIG. 3 shows the infrared spectrum (diffuse reflectance, DRIFTS) of bimatoprost crystalline form I in potassium bromide, according to embodiments of the invention.

FIG. 4 shows the infrared spectrum of bimatoprost crystalline form I in potassium bromide, according to embodiments of the invention.

FIG. 5 shows the infrared spectrum of bimatoprost crystalline form I in Nujol, according to embodiments of the invention.

FIG. 6 shows the 1H nuclear magnetic resonance (NMR) spectrum of compound 5 MTBE solvate in CDCl3, according to embodiments of the invention.

FIG. 7 shows a characteristic x-ray powder diffraction pattern of compound 5 MTBE solvate, according to embodiments of the present invention. Vertical axis: intensity (counts per second); Horizontal axis: 2θ (degrees).

FIG. 8 shows the infrared spectrum (diffuse reflectance, DRIFTS) of compound 5 MTBE solvate in potassium bromide, according to embodiments of the invention.

FIG. 9 shows the differential scanning calorimetry (DSC) curve of compound 5 MTBE solvate, according to embodiments of the invention.

FIG. 10 shows the thermograviometric (TGA) curve of compound 5 MTBE solvate, according to embodiments of the invention.

FIG. 11 shows the 1H nuclear magnetic resonance (NMR) spectrum of compound 5a in CDCl3, according to embodiments of the invention.

FIG. 12 shows a characteristic x-ray powder diffraction pattern of compound 5a, according to embodiments of the present invention. Vertical axis: intensity (counts per second); Horizontal axis: 2θ (degrees).

FIG. 13 shows the infrared spectrum (KBr) of compound 5a in potassium bromide, according to embodiments of the invention.

FIG. 14 shows the differential scanning calorimetry (DSC) curve of compound 5a, according to embodiments of the invention.

DETAILED DESCRIPTION

US2005/209337 discloses crystalline physical form of bimatoprost, which we designate as form A. The present invention discloses, according to its first aspect, a new crystalline form of bimatoprost, which we designate as form I. Moreover, the bimatoprost crystalline form I may be prepared so as to be substantially free of other physical forms.

The present invention provides a process for producing crystalline form I substantially free from other physical forms of bimatoprost by crystallization of bimatoprost in any physical form from an organic solvent or from a mixture of organic solvent and anti-solvent. Preferably, the crystallization comprises the steps of:

a) dissolving crude bimatoprost in an organic solvent or a mixture of organic solvent and anti-solvent at or near the boiling point; b) allowing the hot solution to cool; c) separating the precipitate from the supernatant solution; d) drying the resulting solid in vacuo at low temperature and then at 30 to 40° C. to yield bimatoprost crystalline form I substantially free from other physical forms.

The said organic solvent is selected from the group consisting of alcohols, esters, ketones, chloroorganic solvents, or mixture thereof. Preferably, said alcohols are selected from the group consisting of methanol, ethanol, isopropanol, butanol, isobutanol, t-butanol or mixture thereof. Preferably, said esters are selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate or mixture thereof. Preferably, said ketones are selected from the group consisting of acetone, methyl ethyl ketone, isopropylacetone or mixture thereof. Preferably, said chloroorganic solvents are selected from the group consisting of dichloromethane, chloroform, chlorobenzene or mixture thereof.

The said anti-solvent is selected from the group consisting of hydrocarbons, ethers or mixture thereof. Preferably, the anti-solvent is saturated hydrocarbon. Preferably, said saturated hydrocarbon is selected from the group consisting of pentane, heptane, hexane, cyclohexane or mixture thereof. Preferably, said ethers are selected from the group consisting of diethyl ether, diisopropyl ether, MTBE or mixture thereof.

A pure crystalline organic compound has, in general, a definite melting point range. The melting point is defined as the point at which the sample is entirely in the liquid phase. Bimatoprost crystalline form I has a characteristic melting point range determined by the capillary method from 62 to 64° C.

Differential scanning calorimetry (DSC), x-ray powder diffraction (XRPD) and infrared (IR) spectroscopy were used to characterize the new form.

The DSC curve of form I (FIG. 2) exhibits a melting endotherm at approximately 60-66° C.

Bimatoprost crystalline form I also exhibits distinctive x-ray powder diffraction pattern, as depicted in FIG. 1. The pattern has characteristic peaks expressed in degrees 20 at approximately 5.4±0.2, 10.9±0.2, 11.3±0.2, 13.7±0.2, 16.6±0.2, 17.5±0.2, 19.9±0.2, 20.7±0.2 and 22.7±0.2.

The crystalline form I was characterized by an infrared diffuse reflectance spectrum in potassium bromide as depicted in FIG. 3. The crystalline form I was further characterized by an infrared absorption spectrum carried out in potassium bromide and in Nujol as depicted in FIGS. 4 and 5.

Bimatoprost crystalline form I is the most stable crystalline modification of bimatoprost in a temperature range between −70 and +30° C. Stability data supports the retest period of not less than 6 months if bimatoprost crystalline form I is stored in an appropriate container at 2 to 8° C. and at 25° C.

The importance of bimatoprost crystalline form I rests primarily (but not exclusively) in its thermodynamic stability. Besides its greater stability, form I shows advantages with respect to form A because of the possibility of its preparation by crystallization employing different solvents in a wide temperature range. For example, the crystalline form I may be easily prepared by recrystallizing, triturating, or reslurring of crystalline form A.

Crude non-crystalline bimatoprost may be prepared by amidation of bimatoprost acid 3

with ethylamine optionally in the presence of carbodiimides. Preferably, the carbodiimides are selected from the group of N,N-dicyclohexylcarbodiimide (DCC) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC). Preferably, crude bimatoprost is prepared by reaction of bimatoprost acid methyl ester with ethylamine as described in US2004/171873, US2005/209337, US2005/154220 and U.S. Pat. No. 5,352,708.

Methyl ester of bimatoprost acid 2

may be prepared by reacting of bimatoprost acid 3 with methylation agent MeY wherein Y is a leaving group, in the presence of base.

Preferably, the methylation agent is methyl iodide, bromide, methanesulfonate, p-toluenesulfonate, 2,4-dinitrophenylsulfonate or triflate.

Optionally, the base is 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Preferably, the base is K2CO3. Most preferably, the base is cesium carbonate, hydrogencarbonate, hydroxide or fluoride or mixture thereof. If cesium alkali is used as base in the methylation reaction cesium salt of bimatoprost acid

is obtained as intermediate in the reaction.

Preferably, the methylation reaction of bimatoprost acid 3 is provided in the presence of solvent. Preferably, the solvent is aprotic organic solvent. More preferably, the solvent is polar organic solvent. For example, the polar organic solvent is N,N-dimethylformamide (DMF), N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone (NMP), dimethyl sulfoxide (DMSO), sulfolane or HMPA. Preferably the solvent is DMF.

The bimatoprost acid methyl ester 2 prepared by the reaction may be used in following amination reaction without purification; however ester 2 may be purified by flash chromatography. Preferably the purification is provided by preparative LC on silica gel or Phenomenex™ Luna CN silica gel.

According to embodiment of the invention, the bimatoprost acid 2 is prepared by Wittig reacting of lactol

with a metal salt of 5-(triphenylphosphoranylidene)pentanoic acid following by desilylation of intermediate protected bimatoprost acid.

Preferably, the Wittig reaction is provided in the presence of aprotic organic solvent. More preferably, the solvent is ether-type solvent. Most preferably the solvent is THF. Analytical HPLC showed that crude bimatoprost acid 3 prepared by the Wittig reaction contains up to 5% of 5-trans isomer 3b.

The lactol 4 may be prepared by reducing compound of formula

wherein with i-Bu2AlH at temperature range from −80 to −50° C. Preferably, the reaction temperature range is −50 to +20° C., more preferably −30 to 0° C. To increase the yield of lactol 4 it is desirable to add i-Bu2AlH to lactone 5 at −50 to +20° C. (preferably at −30 to 0° C.) to attain about 95-99% conversion of lactone group. Preferably, the reaction is provided in the presence of aprotic organic solvent. More preferably, the solvent is toluene, CH2Cl2, THF, ether or mixture thereof.

The process of the present invention for the synthesis of bimatoprost may be summarized by the Scheme 1. Analytical HPLC showed that crude bimatoprost 1 prepared according to Scheme 1 contains up to 5% of 5-trans isomer 1b (from the Wittig reaction).

In one embodiment of the invention, the lactone 5 is prepared by process comprising:

reduction of the carbonyl group of ketone 7

to yield a mixture of compounds of formulae 6 and 6a

which are subsequently converted into a mixture of compounds 5 and

followed by isolation of the compounds 5 and 5a from the mixture.

The process for the synthesis of compound 5 from enone 7 may be summarized by the following Scheme 2:

Basis of the synthesis is easy separation of lactone 5 as crystalline MTBE solvate from mixture of 5 and 5a isomers. The potential of the separation method may be illustrated by isolation of highly pure lactone 5 as MTBE solvate with 40% recovery and lactone 5a as solvent free crystalline compound with 33% recovery by serial of simple crystallizations of 1:1 mixture of 5 and 5a isomers from MTBE and hydrocarbon solvent.

The reduction of the compound 6 may be carried out with any reagent capable to reduce ketone function to alcohol. An example of the reagent is NaBH4 or (i-PrO)3Al. Preferably the reduction of the compound 6 is carried out with (−)-B-chlorodiisopinocampheylborane or with borane in the presence of 2-alkyl-CBS-oxazaborolydines. More preferably the reduction is carried out with (−)-B-chlorodiisopinocamphenylborane in organic solvent. Preferably the organic solvent is THF, ether, 1,2-dimethoxyethane, toluene, hexane, CH2Cl2 or mixtures of these solvents.

In another embodiment of the invention, the invention provides crystalline MTBE solvate of (3aR,4R,5R,6aS)-4-[3S-(t-butyldimethylsiloxy)-5-phenyl-1E-pentenyl]-5-(4-phenylbenzoyloxy)-hexahydro-2H-cyclopenta[b]furan-2-one 5

Crystalline MTBE solvate of lactone 5 has a characteristic melting point range determined by the capillary method from 60 to 64° C.

Differential scanning calorimetry (DSC), x-ray powder diffraction (XRPD) and infrared (IR) spectroscopy were used to characterize the new form.

Crystalline lactone 5 MTBE solvate (FIG. 9) exhibits a melting endotherm at approximately 60-66° C.

Crystalline lactone 5 MTBE solvate also exhibits distinctive x-ray powder diffraction pattern, as depicted in FIG. 7. The pattern has characteristic peaks expressed in degrees 20 at approximately 6.5±0.2, 7.1±0.2, 12.2±0.2, 12.5±0.2, 13.1±0.2, 13.6±0.2, 14.6±0.2, 15.0±0.2, 15.8±0.2, 16.2±0.2, 16.3±0.2, 17.0±0.2, 17.3±0.2, 18.0±0.2, 18.2±0.2, 18.8±0.2, 19.5±0.2, 19.7±0.2, 20.5±0.2, 20.8±0.2, 21.0±0.2, 21.8±0.2, 22.2±0.2, 23.0±0.2, 23.3±0.2, 24.2±0.2, 25.5±0.2, 26.5±0.2 and 26.7±0.2.

The crystalline lactone 5 MTBE solvate was characterized by an infrared diffuse reflectance spectrum in potassium bromide as depicted in FIG. 8. The crystalline lactone 5

MTBE solvate was further characterized by 1H NMR spectrum carried out in CDCl3 as depicted in FIG. 11.

In another embodiment of the invention, the invention further provides crystalline (3aR,4R,5R,6aS)-4-[3R-(t-butyldimethylsiloxy)-5-phenyl-1E-pentenyl]-5-(4-phenylbenzoyloxy)-hexahydro-2H-cyclopenta[b]furan-2-one 5a.

Crystalline lactone 5a has a characteristic melting point range determined by the capillary method from 93 to 94° C.

Crystalline lactone 5a (FIG. 14) exhibits a melting endotherm at approximately 83-97° C.

Crystalline lactone 5a also exhibits distinctive x-ray powder diffraction pattern, as depicted in FIG. 12. The pattern has characteristic peaks expressed in degrees 20 at approximately 5.7±0.2, 6.3±0.2, 14.0±0.2, 14.5±0.2, 14.8±0.2, 15.5±0.2, 16.3±0.2, 17.0±0.2, 17.5±0.2, 17.8±0.2, 18.1±0.2, 18.6±0.2, 18.9±0.2, 19.3±0.2, 21.5±0.2, 22.0±0.2, 22.4±0.2 and 23.8±0.2.

Lactone 5a was characterized by 1H NMR (CDCl3), powder x-ray diffractometry, DSC, and IR (KBr) spectroscopy as set forth above and illustrated in FIGS. 11-14.

Crystallinity of compounds 5 (as MTBE solvate) and 5a give very rare option to isolate the compounds in highly pure form with high yield from 5/5a 1:1 mixture by simple crystallization procedure.

In another embodiment of the invention, it is proposed process for utilization of undesired compound 5a to compound 7 which process comprises the steps of converting compound 5a into compound 6a and oxidizing the hydroxyl group of the compound 6a.

According to embodiment of the invention, the compound of the formula 7 may be prepared by Horner-Emmons-Wadsworth reaction of Corey aldehyde of formula 8

with a β-ketophosphonate BnCH2COCH2PO(OMe)2 in the presence of base. Preferably, the base is BuLi, NaH or Et3N/LiCl. More preferably, the base is alkali. For example the alkali is LiOH, NaOH, KOH, CsOH, Na2CO3, K2CO3 or Cs2CO3. Most preferably, the base is an aqueous alkali. Preferably, the Horner-Emmons-Wadsworth reaction is provided in the presence of organic solvents. For example, the solvent is CH2Cl2, CHCl3, toluene, THF, MTBE, ether or mixture thereof.

According to embodiment of the invention, Corey aldehyde 8 may be prepared by oxidation of (−)-Corey lactone 5-(4-phenylbenzoate) of formula 9

The oxidation of (−)-Corey lactone 5-(4-phenylbenzoate) 9 may be carried out with any oxidizing system capable to oxidize primary alcohol to aldehyde. An example of the oxidizing system is CrO3/C5H5N, Cl2/PhSMe, DMSO/DCC/ft, or Dess-Martin reagent. Preferably, the oxidizing system is aq NaClO/TEMPO, more preferably aq NaClO/TEMPO/NaBr, most preferably NaClO/TEMPO/NaBr/1-PrOH.

The process for the synthesis of enone 7 from (−)-Corey lactone 5-(4-phenylbenzoate) 9 may be summarized by the following Scheme 3:

The major related impurities in bimatoprost that can be formed during synthesis or storage of bimatoprost, included the following:

methyl ester of bimatoprost acid 2:

bimatoprost acid 3:

5-trans bimatoprost 1b:

15(R) bimatoprost 1a:

15-keto bimatoprost 1c:

As mentioned above, impurities 5-trans bimatoprost 1b, 15R-bimatoprost 1a, 15-keto bimatoprost 1c could be formed during synthesis or storage of bimatoprost. These compounds were synthesized as analytical markers for HPLC analysis and characterized. We prepared 15R-bimatoprost 1a from lactone 5a according to Scheme 4.

5-trans Bimatoprost 1b was prepared from methyl ester 2 according to Scheme 5.

The key step of the synthesis is isomerisation of methyl ester 10 to its 5-trans isomer 11 by irradiation in the presence of Ph2S.

15-keto Bimatoprost 1c was prepared by selective oxidation of 15-hydroxy group of bimatoprost.

It has been found that the 5-trans and 15R-isomers of bimatoprost are particularly difficult to remove because they have similar physical and chemical properties to bimatoprost. We found that it is possible to separate of bimatoprost from the impurities using an HPLC purification system. However the HPLC purification is expensive and is not practical for large scale separations.

These problems have been solved by the use of crystalline form I in purification of bimatoprost. The present invention provides a method for purifying crude bimatoprost from related impurities, which comprises the steps of:

a) dissolving crude bimatoprost in an organic solvent or a mixture of organic solvent and anti-solvent under reflux conditions; b) allowing the hot solution to cool; c) separating the precipitate from the supernatant solution; d) drying the resulting solid in vacuo at low temperature and then at 30 to 40° C. to give bimatoprost crystalline form I with desired LC purity.

By using the process of the present invention, it has been found possible to produce bimatoprost that is substantially free of 15R- and 5-trans isomers of bimatoprost. Using the process of the present invention, bimatoprost containing less than 0.2% each of 15R- and 5-trans isomers can be produced. In particular, bimatoprost containing less than 0.1% each of 15R- and 5-trans isomers can be produced. Preferably, bimatoprost containing less than 0.05% each of 15R- and 5-trans isomers can be produced.

The above processes thus enable bimatoprost having an extremely high degree of purity can be obtained, e.g. greater than 98% pure, greater than 99% pure, greater than 99.5% pure. Indeed, it has been found possible to achieve bimatoprost purities of greater than 99.8%.

The present invention also provides the use of bimatoprost crystalline form I in the manufacture of a medicament. The medicament is prepared in two steps, preparation of a composition containing bimatoprost and manufacture of unit dosage forms suitable for pharmaceutical use, e.g. topical ocular use. Preferably, the composition is prepared by combining a therapeutically effective amount of bimatoprost crystalline form I, as an active ingredient, with conventional pharmaceutically-acceptable excipients, e.g. an ophthalmically-acceptable vehicle. The therapeutically efficient amount typically is between about 0.0001 and about 5% (w/v), preferably about 0.001 to about 1.0% (w/v) in liquid formulations.

In addition to the above-described principal active ingredients, the compositions of the present invention may further comprise various formulatory ingredients, such as ophthalmically acceptable diluents, buffers, hydrochloric acid, sodium hydroxide, antimicrobial preservatives, stabilizers, tonicity adjustors, viscosity-enhancing agents, chelating agents, antioxidants, surfactants and/or solubilizers and combinations thereof.

Preferably, the diluent is purified water.

Preservatives are used in multi-use ophthalmic formulations to prevent microbial contamination of the composition after the packaging has been opened. A number of preservatives have been used including quaternary ammonium salts, mercury compounds, alcohols and stabilized chlorine dioxide. Preferred preservatives that may be used in the pharmaceutical compositions of the present invention include benzalkonium chloride, chlorobutanol, thimerosal, phenylmercuric acetate, methyl paraben, propyl paraben, phenylethyl alcohol, edetate disodium, sorbic acid, phenylmercuric nitrate, Polyquad™.

Viscosity-enhancing agents may be added as needed or convenient. They include, but are not limited to, sodium carboxymethylcellulose, hydroxypropylmethylcellulose, povidone, polyvinyl alcohol, polyethylene glycol, or combinations thereof.

Tonicity adjustors may be added as needed or convenient. They include, but are not limited to, salts, particularly sodium chloride, potassium chloride, mannitol, dextrose, propylene glycol and glycerin, or any other suitable ophthalmically acceptable tonicity adjustor.

Various buffers and means for adjusting pH may be used so long as the resulting preparation is ophthalmically acceptable. Accordingly, buffers include acetate buffers, citrate buffers, phosphate buffers and borate buffers. Hydrochloric acid or sodium hydroxide may be used to adjust the pH of these formulations as needed.