FIELD OF THE INVENTION

The present invention relates to a process for the preparation of Nitisinone of formula 1.

Formula (1)

BACKGROUND OF THE INVENTION

Nitisinone is a hydroxyphenyl-pyruvate dioxygenase inhibitor. It is indicated as an adjunct to dietary restriction of tyrosine and phenylalanine in the treatment of hereditary tyrosinemia type 1 (HT-1). Chemically, it is known as 2-(2-nitro-4- trifluoromethylbenzoyl) cyclohexane-1 ,3-dione.

Several processes have been reported for the preparation of Nitisinone for example, in U.S. Patent No. 4,695,673; 4,774,360; 5,006,158 5,550,165; 5,728,889; 9,783,485; 10,328,029; U.S. Patent Publication No. 2016/0324785; Indian Patent Application No. 201611023671; 201841016377, the contents of which are hereby incorporated as reference in their entirety. These processes require multiple steps or complicated purification processes such as chromatography and therefore inevitably lead to poorer yields or purity.

There is still a need for an improved and simplified process for the preparation of Nitisinone or salts thereof, which can reduce the burden of isolating, crystallizing, and purifying the intermediate compound(s), and thus minimize production time, provide high yield and is convenient to operate on a commercial scale and also, a need for a process that leads to formation of Nitisinone with an improved yield and purity, and in particular by avoiding use of toxic, hazardous and corrosive chemicals such as phosphorus oxychloride, thionyl chloride etc.

The present invention is associated with these advantages and enables practical and efficient manufacture of Nitisinone. Added advantages of the present invention are cost effectiveness, readily accessible raw materials, less hazardous reaction conditions, and simple work up procedures which all make the process more robust and cost-efficient.

The impurities associated to nitisinone can be either derived from the starting materials themselves (i.e., Formula (2) and Formula (3)) or obtained as side products during the process of synthesis and/or under storage conditions (i.e., Formula (4)) and are the following:

2-nitro-4-(trifluoromethyl)benzoic acid of formula (2), cyclohexane- 1, 3-dione of formula (3), and 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4).

Formula (2) Formula (3) Formula

(4) Impurities in nitisinone, or any active pharmaceutical ingredient (“API”), are undesirable and, in extreme cases, might even be harmful to a patient being treated with a dosage form containing the API.

The purity of an API produced in a manufacturing process is critical for commercialization. The product of a chemical reaction is rarely a single compound with sufficient purity to comply with pharmaceutical standards. Side products and byproducts of the reaction and adjunct reagents used in the reaction will, in most cases, also be present in the final product. At certain stages during processing of an API, it must be analyzed for purity, typically, by high performance liquid chromatography (“HPLC”) or thin-layer chromatography (“TLC”), to determine if it is suitable for continued processing and, ultimately, for use in a pharmaceutical product.

As known by those skilled in the art, the management of process impurities is greatly enhanced by understanding their chemical structures and synthetic pathways and by identifying the parameters that influence the amount of impurities in the final product. Extensive experimentation has been carried out by the present inventors. As a result, the present inventors found an improved method for the preparation of nitisinone which is substantially free of formula (2) and formula (4), by controlling critical process parameters. The nitisinone made by the process of the present invention is suitable for commercial scale production.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a process for the preparation of Nitisinone of formula (1). Formula (1)

The process comprises: reacting 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2) with cyclohexane- 1,3-dione of formula (3)

Formula (2) Formula (3) in the presence of a base, and a coupling agent to obtain Nitisinone of formula

(1).

In another general aspect, the present invention provides a process for the preparation of nitisinone substantially free of 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2), and 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4) in an amount of 0.001% or less as determined by HPLC method.

In yet another general aspect, the present invention provides a process for the preparation of nitisinone substantially free of 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2), and 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4) undetectable as determined by HPLC method.

BRIEF DESCRIPTION OF THE DRAWINGS

A SKILLED PERSON WILL UNDERSTAND THAT THE DRAWINGS, DESCRIBED BELOW, ARE FOR ILLUSTRATION PURPOSES ONLY. THE DRAWINGS ARE NOT INTENDED TO LIMIT THE SCOPE OF THE PRESENT INVENTION IN ANY WAY. FIG. 1 SHOWS AN X-RAY POWDER DIFFRACTION PATTERN (XRPD) OF NITISINONE AS OBTAINED BY THE PROCESS ACCORDING TO THE PRESENT INVENTION, AS DISCLOSED HEREIN IN EXAMPLE 1.

DETAILED DESCRIPTION OF THE INVENTION

The term “about”, as used herein, when used along with values assigned to certain measurements and parameters means a variation of up to 10% from such values, or in case of a range of values, means up to a 10% variation from both the lower and upper limits of such ranges.

Use of exemplary language, such as “for example”, “such as”, and the like, is merely intended to better illustrate the invention and does not indicate a limitation on the scope of the invention unless so claimed.

In one aspect, the present invention provides a process for the preparation of Nitisinone of formula (1)

Formula (1) which comprises: reacting 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2) with cyclohexane- 1,3-dione of formula (3)

Formula (2) Formula (3) in the presence of a base, and a coupling agent to obtain Nitisinone of formula

(1).

The 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2) may be obtained by any of the methods known in the art including those described in U.S. Patent No. 4,868,333.

In one embodiment of this aspect, the base includes, for example an amine, an inorganic base or ammonia.

Examples of amines include triethylamine, N-methyl morpholine, N,N- dimethyl benzyl amine, pyridine, picoline, and lutidine.

The inorganic base may be an alkali metal carbonate, bicarbonate or hydroxide. Examples of alkali metal carbonates include lithium carbonate, potassium carbonate and sodium carbonate. Examples of alkali metal bicarbonates include potassium bicarbonate and sodium bicarbonate. Examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide.

Preferably, the base is an amine. More preferably, the base is triethylamine.

In another embodiment of this aspect, the amount of base used with respect to 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2) is between 0.9 to 4 molar equivalents, more preferably between 1 to 2 molar equivalents, even more preferably between 1.1 to 1.3 molar equivalents, and most preferably about 1.2 molar equivalents.

In another embodiment of this aspect, the coupling agent includes, for example a carbodiimide, a 1,1 '-carbonyl compound, or a mixture thereof. Preferably, the coupling agent is selected from 1,3 -di cyclohexylcarbodiimide (DCC); 1,1'- carbonyldiimidazole (GDI); N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC . HC1); 1,3 -diisopropylcarbodiimide (DIC); or a mixture thereof. Preferably, the coupling agent is N-(3-Dimethylaminopropyl)-N'- ethylcarbodiimide hydrochloride (EDC . HC1)

In another embodiment of this aspect, the amount of coupling agent used with respect to 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2) is between 0.5 to 5 molar equivalents, more preferably between 0.9 to 2 molar equivalents, even more preferably between 0.95 to 1.25 molar equivalents, and most preferably about 1.05 molar equivalents.

In another embodiment of this aspect, the reaction may be carried out in the presence of a catalyst. In another embodiment, the reaction may be carried out in the presence of a catalytic amount of a source of cyanide. Preferably, the cyanide sources are cyanohydrins of methyl alkyl ketones having from C1-C4 carbon atoms in the alkyl groups, such as acetone or methyl isobutyl ketone cyanohydrins; cyanohydrins of benzaldehyde or of C2-C5 aliphatic aldehydes such as acetaldehyde, propionaldehyde; alkali metal cyanides such as sodium and potassium cyanide; zinc cyanide; trimethyl silyl cyanide. Among cyanohydrins, the preferred cyanide source is acetone cyanohydrin.

The cyanide source may be used in as little as about 0.1 mole equivalent to produce an acceptable rate of reaction on a small scale. Larger scale reactions give more reproducible results with slightly higher catalyst levels of about 0.12 to about 1 mole equivalent. Generally, about 0.001 to 1.5 mole % of the cyanide source is preferred.

In yet another embodiment of this aspect, the reaction may be carried out in the presence of a solvent. There are no specific limitations with respect to the organic solvent employed in the reaction, so far as the solvent does not participate in the reaction. The solvent includes, for example, water, alcohols, such as, methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol; aromatic hydrocarbon, such as, benzene, toluene, and xylene, substituted toluenes, substituted xylenes; halogenated hydrocarbons, such as, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, dichloropropane, chloroform, carbon tetrachloride; ethers, such as, diethyl ether, diisopropyl ether, tert-butyl methyl ether, dioxane, tetrahydrofuran; ketones, such as, acetone, methyl ethyl ketone, methyl isobutyl ketone; alkyl acetate, such as, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate; alkyl nitriles, such as, acetonitrile, propionitrile; amides, such as, N,N- dimethylformamide; dimethyl sulfoxide. The solvents may be employed singly or in combination.

Preferably, the solvent is halogenated hydrocarbon. More preferably, the solvent is dichloromethane.

In yet another embodiment of this aspect, 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2) and cyclohexane- 1,3-dione of formula (3) can be taken in the mole ratio of about 1:0.9 to about 1: 1.5, preferably, about 1: 1 to about 1:1.2, more preferably, about 1 :1.05.

In yet another embodiment of this aspect, the reaction can be carried out in one-pot.

In yet another embodiment of this aspect, the temperature at which the reaction of 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2) with cyclohexane- 1, 3-dione of formula (3) may be carried out may range from about -20°C to about 120°C, for example from about 0°C to about 40°C or from about 20°C to about 35°C. In particular, it may be carried out at a temperature from about 25 °C to about 30°C.

In yet another embodiment of this aspect, the process involves addition of 2- nitro-4-(trifluoromethyl)benzoic acid of formula (2), cyclohexane- 1,3-dione of formula (3), triethylamine (base), in dichloromethane (solvent) in optional order of succession at a temperature of about 25°C to 30°C, optionally under stirring, and maintaining at a temperature of about 25 to 30°C for about 0.5 hours, followed by the addition of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride [EDC . HC1] (coupling agent), and acetone cyanohydrin (catalyst), in optional order of succession at a temperature of about 25°C to 30°C, optionally under stirring, and maintaining at a temperature of about 25 to 30°C for about 2 to 3 hours, to obtain nitisinone, and the isolation of the nitisinone involves common isolation techniques such as one or more of washing, crystallization, precipitation, cooling, filtration, filtration under vacuum, decantation and centrifugation, or a combination thereof.

In yet another embodiment of this aspect, the Nitisinone obtained may be further or additionally dried to achieve the desired moisture values. For example, the product may be further or additionally dried in a tray drier, dried under vacuum, dried at 50-55°C in hot air oven and/or in a Fluid Bed Drier.

In another embodiment, the Nitisinone of formula (1) obtained may have X- Ray powder diffraction (XRPD) pattern as shown in FIG. 1 and the 2 theta values

In another general aspect, the present invention provides a process for the preparation of nitisinone substantially free of 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2), and 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4) in an amount of 0.001% or less as determined by HPLC method.

In yet another general aspect, the present invention provides a process for the preparation of nitisinone substantially free of 2-nitro-4-(trifluoromethyl)benzoic acid of formula (2), and 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4) as determined by HPLC method.

While the present invention has been described in terms of its specific aspect, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention. In the following section, the aspect is described by way of examples to illustrate the processes of the invention. However, these do not limit the scope of the present invention. Several variants of these examples would be evident to persons ordinarily skilled in the art.

EXAMPLES

EXAMPLE 1 : PROCESS FOR THE PRERPATIN OF NITISINONE

2-Nitro-4-(trifhroromethyl)benzoic acid (5.0 g), Triethylamine (2.57 g) and then, Cyclohexane- 1, 3-dione (2.50 g) were added into Dichloromethane (50 ml) at 25-30°C and maintained at 25-30°C for 30 minutes. N-(3-Dimethylaminopropyl)-N'- ethylcarbodiimide hydrochloride [EDC. HC1] (3.46 g) was added to the mixture at 25-30°C in one lot. Acetone cyanohydrin (0.18 g) was added at 25-30°C, and the mixture was maintained at 25-30°C for 2-3 hours. Purified water (50 ml) was charged at 25-30°C. The mixture was stirred and settled for 15 minutes. The aqueous layer was separated, and washed with methylene dichloride (25 ml). The aqueous layer was cooled to 15-20°C and concentrated hydrochloric acid (5 ml) was charged slowly over 15-20 minutes. The mixture was maintained at 25-30°C for 30 minutes and distilled below 40°C under vacuum to completely remove methylene dichloride. Acetonitrile (25 ml) was added with the residue at 25-30°C and heated at 45-50°C for 30 minutes. Purified water (30 ml) was added at 45-50°C, slowly over 30 minutes. The mixture was maintained at 45-50°C for 30 minutes and then cooled to 25-30°C for 2 hours. The solid obtained was filtered, washed with purified water (5 ml), suck dried under vacuum and dried at 50-55°C in hot air oven.

Yield (%): 48.6%

Purity (%): 99.98% (by HPLC)

2-nitro-4-(trifluoromethyl)benzoic acid of formula (2): ND (by HPLC) 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4): ND (by HPLC) (ND = Not Detected)

EXAMPLE 2: PROCESS FOR THE PRERPAHON OF NITISINONE

2-Nitro-4-(trifluoromethyl)benzoic acid (5.0 g), Triethylamine (2.57 g) and then, Cyclohexane- 1, 3-dione (2.50 g) were added into Dichloromethane (50 ml) at 25-30°C and maintained at 25-30°C for 30 minutes. N,N'-Dicyclohexylcarbodiimide- [DCC] (4.6 g) was added to the mixture at 25-30°C in one lot. Acetone cyanohydrin (0.18 g) was added at 25-30°C, and the mixture was maintained at 25-30°C for 2-3 hours. Purified water (50 ml) was charged at 25-30°C. The mixture was stirred and settled for 15 minutes. The aqueous layer was separated, and washed with methylene dichloride (25 ml). The aqueous layer was cooled to 15-20°C and concentrated hydrochloric acid (5 ml) was charged slowly over 15-20 minutes. The mixture was maintained at 25-30°C for 30 minutes and distilled below 40°C under vacuum to completely remove methylene dichloride. Acetonitrile (25 ml) was added with the residue at 25-30°C and heated at 45-50°C for 30 minutes. Purified water (30 ml) was added at 45-50°C, slowly over 30 minutes. The mixture was maintained at 45-50°C for 30 minutes and then cooled to 25-30°C for 2 hours. The solid obtained was filtered, washed with purified water (5 ml), suck dried under vacuum and dried at SO- 55 °C in hot air oven.

Yield (%): 46.4%

Purity (%): 99.97% (by HPLC)

2-nitro-4-(trifluoromethyl)benzoic acid of formula (2): ND (by HPLC) 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4): ND (by HPLC)

(ND = Not Detected)

EXAMPLE 3: PROCESS FOR THE PRERPATIN OF NITISINONE

2-Nitro-4-(trifhroromethyl)benzoic acid (5.0 g), Triethylamine (2.57 g) and then, Cyclohexane- 1, 3-dione (2.50 g) were added into Dichloromethane (50 ml) at 25-30°C and maintained at 25-30°C for 30 minutes. N,N'-carbonyldiimidazole-[CDI] (3.61 g) was added to the mixture at 25-30°C in one lot. Acetone cyanohydrin (0.18 g) was added at 25-30°C, and the mixture was maintained at 25-30°C for 2-3 hours. Purified water (50 ml) was charged at 25-30°C. The mixture was stirred and settled for 15 minutes. The aqueous layer was separated, and washed with methylene dichloride (25 ml). The aqueous layer was cooled to 15-20°C and concentrated hydrochloric acid (5 ml) was charged slowly over 15-20 minutes. The mixture was maintained at 25-30°C for 30 minutes and distilled below 40°C under vacuum to completely remove methylene dichloride. Acetonitrile (25 ml) was added with the residue at 25-30°C and heated at 45-50°C for 30 minutes. Purified water (30 ml) was added at 45-50°C, slowly over 30 minutes. The mixture was maintained at 45-50°C for 30 minutes and then cooled to 25-30°C for 2 hours. The solid obtained was filtered, washed with purified water (5 ml), suck dried under vacuum and dried at SO- 55 °C in hot air oven.

Yield (%): 47.1%

Purity (%): 99.96% (by HPLC)

2-nitro-4-(trifluoromethyl)benzoic acid of formula (2): ND (by HPLC) 6-(trifluoromethyl)-3,4-dihydro-lH-xanthene-l,9(2H)-dione of formula (4): ND (by HPLC)

(ND = Not Detected)