WO2017168333A1

WO2017168333A1 - Amifampridine dihydrochloride

Info

Publication number: WO2017168333A1
Application number: PCT/IB2017/051781
Authority: WO
Inventors: Rafiuddin Dr; Akshay Kant CHATURVEDI
Original assignee: Shilpa Medicare Limited
Priority date: 2016-04-02
Filing date: 2017-03-29
Publication date: 2017-10-05

Abstract

The present invention relates to novel salt of 3,4-diaminopyridine as 3,4-diaminopyridine dihydrochloride (or Amifampridine dihydrochloride), useful in the preparation of pharmaceutical composition thereof. The present application also relates to an improved process for the preparation of substantially pure Amifampridine dihydrochloride (I) having purity of greater than 99.5% (by HPLC).

Description

AMIFAMPRIDINE DIHYDROCHLORIDE

FIELD OF THE INVENTION

The present invention relates to salts of Amifampridine, useful for the preparation of pharmaceutical composition thereof.

The present invention particularlyrelates to Amifampridinedihydrochloride, useful for the preparation of pharmaceutical composition thereof.

The present invention relates to a process for preparation Amifampridinedihydrochloride of Formula (I).

BACKGROUND OF THE INVENTION

Amifampridine is chemically known as 3, 4-diaminopyridine. The structural formula of Amifampridine is as described in Formula (II)

Amifampridine has an empirical formula C₅H₇N₃ and a molecular weight of 109.13.

Amifampridineis marketed in the form of Amifampridine phosphate. Amifampridine phosphate is a white crystalline powder with the empirical formula C₅H₇N₃ and a molecular weight of 109.13. It is practically soluble in water, slightly soluble in dimethylsulfoxide, glacial acetic acid and methanol and very slightly soluble in ethanol and dimethylformamide. No stereoisomerism is observed. The pure drug substance melts at 229 ± 2°C; pH of 1% solution in water at 25°C is 4.6 ± 0.2. Amifampridine is marketed under the brand name Zenas^® as an oral tablet.

Amifampridine well knows to block potassium channels in the nerve cells. This blockage causes depolarisation of the presynaptic membrane and slows down or inhibits repolarisation. Prolonged depolarisation induces the opening of slow voltage-gated calcium channels (VGCC) and the influx of calcium. The increased concentration of intracellular calcium induces exocytosis of the synaptic vesicles containing acetylcholine (Ach). It has been proposed that treatment with Amifampridine counteracts the pathologically-reduced ACh release in patients with Lambert-Eaton syndrome (LEMS) and hence provides symptomatic relief to the patient. These pharmacological actions support the proposed clinical indication. Amifampridine is also known to be used in treatments related to many of the congenital myasthenic syndromes, particularly those with defects in choline acetyl transferase, downstream kinase and those where any kind of defect causes "fast channel" behaviour of the acetylcholine receptor. EPO 156495 A 1 disclosed a process for the preparation of Amifampridine starting from 3- nitro-4-benzylaminopyridine. The process is as demonstrated below:

Scheme-I

This process involves deprotection of benzyl protected amino group at higher temperature, which is not feasible at large scale production and with lower yields resulting in the formation of byproducts/impurities

EP01591 12A1 disclosed different process for the preparation of Amifampridinemono hydrochloride starting from 3-nitro-4-chloropyridine. The processes disclosed are as demonstrated below in Scheme-II and III:

Scheme-II

cheme-Ill

diethyl ether

This patent discloses specifically mono hydrochloride of Amifampridine. However, the present inventors found that mono hydrochloride salt appears to be not stable or transiently stable.

Further, the process for this preparation involves ethyl carbazate and formation of hydrazine bonds in the intermediates, which are neitherindustrially feasible nor provides any ease in handling owing to hazardous, toxic and explosive nature.

Guyon, Francois et al in US20040106651A1 discloses tartrate and phosphate salts of

Amifampridine as only stable salts In our endevour to explore new stable salts with ease in handling for commercially viable processing, the present inventors first time prepared stable dihydrochloride salt of 3,4-diaminopyridine after extensive work of different salts preparations. Inventors compared the stabilityand solubility of newly invented dihydrochloirde salt with reported di phosphate salt. It was observed that stabilities are exceeding with similar or improved solubility with respect todiphosphate salt. Also, present inventors found that the formation of dihydrochloride salt appears to be more industrially feasible than reported diphosphate salt.

Journal of Heterocyclic Chemistry (1999), 36(5), 1143-1145discloses a process in for the preparation of 3,4-Diaminopyridine starting from 3-nitropyridine. The process is as demonstrated below:

Scheme-IV:

After review of various literatures, and reproducing some of the processes, following were apparent disadvantages in different processes were noticed, which makes many such reported processes not amenable to scale up.

> In most of the patent literatures, hazardous chemical reagents are used, which are not feasible and cumbersome to handle on industrial scale. > Unwanted side /parallel reactions are observed during the formation of 3,4- diaminopyridine, due to the use of higher temperature reaction conditions. Further, the use of higher temperature is not industrially feasible.

Expensive Reducing agents like Pd/C is used during reduction of -N0₂ group to amino group in solvents is very difficult to handle at commercial level and makes the process commercially non-viable.

In view of the above and to overcome the prior-art disadvantages,the present inventors have now developed an improved process for the preparation of Amifampridine, using minimal steps, which is industrially feasible, with the use of industrial friendly solvents, which does not involve tedious work up and hazardous steps.

OBJECTIVE OF THE INVENTION

The main objective of the invention is to provide a stable & highly pure Amifampridine dihydrochloride salt.

Yet another objective of the invention is to provide an improved process for the preparation of Amifampridine dihydrochloride.

Yet another objective of the invention is to provide an improved process for the preparation of substantially pure Amifampridine dihydrochloride having purity of greater than 99.5%.

SUMMARY OF THE INVENTION

The present invention relates to a salt of 3,4-diaminopyridine is 3,4- diaminopyridinedihydrochloride or Amifampridine dihydrochloride having solubility exceeding 30 mg/ml.

In another aspect of the present invention relates to Amifampridinedihydrochloride having a purity of greater than 99.5 %

In another aspect of the present invention relates to Amifampridine dihydrochloride characterized by X-ray powder diffraction pattern comprising characteristic diffraction angle peaks selected from the XRPD peaks at 16.9, 23.7, 24.9, 25.4,25.8, 27.7, 28.8, 32.6, 36.3 and 36.8 ± 0.2 °2Θ and DSC isotherm comprising endofhermic peaks ranging between- :

a) Peak-1 between 158 and 168°C;

b) Peak-2 between 206 and 216°C; c) Peak-3 between 216 and 220°C;

In another aspect of the present invention relates to an improved process for the preparation of Amifampridine dihydrochloride of Formula (I)

comprising the steps of:

a) nitrating 4-amino pyridine (III) using a nitrating agent in presence/absence of a solvent to yield 4- Amino -3-Nitro Pyridine (IV);

(HI) (IV)

b) reacting 4- Amino -3-Nitro Pyridine (IV) with a reducing agent to provide Amifampridine (II); and

(IV) (II)

c) optionally, purifying Amifampridine(I) to obtain substantially pure Amifampridine(II) having a purity of greater than 99.5%.

d) reacting the Amifampridine (II) with hydrochloric acid to form Amifampridine dihydrochloride(I)

(II) (I)

e) optionally, purifying Amifampridine dihydrochloride (I) to obtain substantially pure Amifampridine dihydrochloride (I) having a purity of greater than 99.5%. In another aspect of the present invention relates to substantially pure Amifampridine dihydrochloride having a purity of greater than 99.5% and total impurities A to D collectively less than 0.5% by HP

Impurity-C Impurity-D

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.l: PXRD pattern of crystalline Amifampridine dihydrochloirde obtained as per the present invention.

Fig.2: Differential scanning calorimetry (DSC) pattern of crystalline Amifampridine dihydrochloirde obtained as per the present invention.

Fig.3: Thermo gravimetric analysis (TGA) of crystalline Amifampridine dihydrochloirde obtained as per the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Particular aspects of the present specification relate to the novel pharmaceutically acceptable di-hydrochloric acid addition salt of Amifampridine (I) and processes for its preparation thereof. Further, the invention of this application also relates to pharmaceutical compositions comprising of di-hydrochloric acid addition salt of Amifampridine(I), which may be useful in the treatment of various cancerous disorders.

In one embodiment of the present application, the present invention provides hydrochloric acid addition salt of Amifam ridine represented by Formula (I)

In one embodiment of the present application, the present invention provides a salt of 3,4-diaminopyridine is 3,4-diaminopyridine dihydrochloride or Amifampridine dihydrochloride having solubility exceeding 30 mg/ml. The present inventors found that Amifampridine as such is slightly soluble in water at different pH conditions. However, the present inventors found that the formation of di hydrochloride salt of 3,4-diaminopyridineor Amifampridine improves the solubility and having a solubility exceeding 30 mg/ml.

In another embodiment of the present invention provides di hydrochloiric acid addition salt of Amifampridine contains Amifampridine base and hydrochloric acid in a ratio of about 1 :2. Ratio of about 1 :2 means that the hydrochloric acid addition salt of the present application has Amifampridine base and hydrochloric acid in stoichiometric ratio of 1 :2. This composition may vary up to range of ± 10% (mole ratios) i.e. stoichiometric ratio may range from 1 : 1.8 to 1 : 2.2, without deviating from the spirit of the invention. Said compositions of about 1 :2 stoichiometric ratio are found to retain the characteristic XRPD diffraction pattern along with other solid state parameters. Di-hydrochloric acid content in Di-hydrochloricacid addition salt of Amifampridine ranges from 36-40 % w/w as determined by titrimetry (on dried basis).

In a further embodiment of the present invention provides di-hydrochloric acid addition salt of Amifampridine represented by Formula (I) may be obtained as a crystalline solid or as an amorphous material.

In a preferred embodiment of the present invention di-hydrochloric acid addition salt of Amifampridine, prepared according to the process of this invention, is obtained in a crystalline form and is characterized by:

a) X-ray powder diffraction pattern substantially according to Fig- 1 ;

b) Differential Scanning Calorimetry ("DSC") curvesubstantially according to Fig-2.

c) Thermo gravimetric analysis (TGA) substantially according to Fig-3

In a still further embodiment of the present application, it provides stable crystalline di- hydrochloric acid addition salt of Amifampridine, characterized by X-ray powder diffraction pattern comprising 20° peaks selected from the XRPD peak set of 16.9, 23.7, 24.9, 25.4, 25.8, 27.7, 28.8, 32.6, 36.3 and 36.8 ± 0.2 °2Θ, and/or, DSC isotherm comprising of peaks ranging between- :

a) Peak-1 between 158 and 168°C;

b) Peak-2 between 206 and 216°C; c) Peak-3 between 216 and 220°C;

This crystalline form of Amifampridine dihydrochloride (I) is designated as Form-SDP. Crystalline Form-SDP of Amifampridine dihydrochloride is further characterized by X-ray powder diffraction pattern comprising of diffraction angle peaks at about 13.5, 13.9, 17.5, 17.7, 24.4, 24.7, 26.7, 27.5, 28.0, 31.4, 33.5, 38.0 ± 0.2 20°. In a preferred embodiment of the present invention, the diffraction angle peaks at about 16.9, 23.7, 24.9, 25.4, 25.8, 27.7, 28.8, 32.6, 36.3 and 36.8 ± 0.2 °2Θ are characterized by relative intensities of at least 10%. Diffraction angle peak at about 25.8 ± 0.2 20° is preferably a single maximum peak.

The characteristic peaks and the corresponding d-spacing values of the crystalline dihydrochloric acid addition salt of Amifampridine (Form-SDP) obtained by the process of the present invention are tabulated in the Table- 1.

S.No. Angle (2Θ°)±0.20 d-Spacing Value (A°)

1. 13.5 6.52

2. 13.9 6.32

3. 16.9 5.22

4. 17.5 5.04

5. 17.7 4.99

6. 23.7 3.74

7. 24.4 3.63

8. 24.7 3.60

9. 24.9 3.56

10. 25.4 3.50

11. 25.8 3.44

12. 26.7 3.32

13. 27.5 3.24

14. 27.7 3.21

15. 28.0 3.17

16. 28.8 3.09

17. 31.4 2.84

18. 32.6 2.73

19. 33.5 2.67

20. 36.3 2.47 S.No. Angle (2Θ°)±0.20 d-Spacing Value (A°)

21. 36.8 2.43

22. 38.0 2.36

Table- 1 : Characteristic XRPD Peaks of Crystalline Amifampridinedihydrochloride (Form- SDP)

The Crystalline Form- S DP of Amifampridinedihydrochloridedescribed herein may be characterized by X-ray powder diffraction pattern (XRPD) and Thermal techniques such as differential scanning calorimetric (DSC) Analysis. The samples of Amifampridine dihydrochloride Crystalline Form-SDP were analyzed by XRPD on a Bruker D8 Advance Diffractometer using X-ray source - Cu Ka radiation using the wavelength 1.5418 A, however, DSC analysis were carried out on a Perkin Elmer Jade instrument. Illustrative examples of analytical data for the crystalline solids Form-SDP obtained in the Examples are set forth in the Figs. 1-3.

Minor variations in the observed 2 θ° angles values may be expected based on the analyst person, the specific XRPD diffractometer employed and the sample preparation technique. Further possible variations may also be expected for the relative peak intensities, which may be largely affected by the non-uniformity of the particle size of the sample. Hence, identification of the exact crystalline form of a compound should be based primarily on observed 2 theta angles with lesser importance attributed to relative peak intensities. The 2 theta diffraction angles and corresponding d-spacing values account for positions of various peaks in the X-ray powder diffraction pattern. D-spacing values are calculated with observed 2 theta angles and copper K a wavelength using the Bragg equation well known to those of having skill in the art of XRPD diffractometry science. In view of possibility of marginal error in the assigning 2 theta angles and d-spacing, the preferred method of comparing X-ray powder diffraction patterns in order to identify a particular crystalline form is to overlay the X-ray powder diffraction pattern of the unknown form over the X-ray powder diffraction pattern of a known form.

Di-hydrochloric acid addition salt of Amifampridine can be converted into its amorphous form or its solid dispersion with suitable pharmaceutically acceptable excipients which are preferably selected from polyvinylpyrrolidones (povidones for e.g. Plasdone-K), copolymers of N-vinylpyrrolidone, gums, cellulose derivatives (for e.g. hydroxypropylmethylcelluloses-HPMC), mannitol, cyclodextrins, gelatins, sugars, polyhydroxy alcohols, polyethylene glycols, polyethylene oxides, polyoxyethylene derivatives, polyvinylalcohols, propylene glycol derivatives, or a mixture thereof. Amorphous form of Amifampridine dihydrochloirde may be prepared by techniques known to the person skilled in art, such techniques comprising but not limited to dissolving in an organic solvent and suitably utilizing spray drying or film drying methods. In one of the embodiments amorphous form of Amifampridine dihydrochloridewas prepared by using rotavapor technique in presence or absence of reduced pressure conditions.

The novelsalt form of Amifampridine i.e. Amifampridine dihydrochlorideas described by the present applicationhas been found to be quite stable and easy to handle and store for longer time without any measurable changes in its morphology and physicochemical characteristics, while retaining itsproperties within the defined limits. This may offer advantages for large scale manufacturing in terms of handling, storage, shelf life and favorable impurity profile. Besides the physical/chemical properties, the novel salt form of the current application further provides advantage in terms of solubility of the drug and hence providespossibility of better bioavailability and pharmacological profile.

In an another embodiment, the present invention relates to an improved process for the preparation of Amifampridine dihydrochlorideof Formula (I) comprising the steps of nitrating 4-amino pyridine (III) using a nitrating agent in presence/absence of a solvent acids such as sulfuric acid, acetic acid; nitriles such acetonitrile; nitro methane; alcohols such as CI -5 alcohols; Glycol ethers such as 2-Butoxyethanol, Diglyme, Dimethoxyethane, 2-Ethoxy ethanol, 2-(2-Ethoxyethoxy)ethanol, 2-Methoxyethanol, 2-(2-Methoxyethoxy) cthanol, Octaethylene glycol monododecyl ether, Pentaethylene glycol monododecyl ether, Phenoxyethanol, Propylene glycol methyl ether acetate, Tetraethylene glycol dimethyl ether, Triethylene glycol, Triethylene glycol dimethyl ether; water or mixtures thereof; in presence of nitrating agent selected from nitric acid, nitric acid + sulfuric acid, sodium nitrate, potassium nitrate, silver nitrate, Methyl nitrate, nitric acid + sulfuric acid+ urea; at a temperature ranging from 50 to 90°C. The reaction mixture was stirred for a period of 4 hours to 8 hours to yield 4- Amino -3 -Nitro Pyridine (IV)

The present inventors found that the use of potassium nitrate as a nitrating agent completes the reaction at a temperature ranging from 60-65°C, which is industrially feasible, cost effective and avoids unwanted reactions, which minimized the formation of impurity. After completion of the reaction, the removal of potassium nitrate is modest and does not require any cumbersome workup.

The above obtained 4- Amino -3-Nitro Pyridine (IV) was reduced in presence of a reducing agent selected from hydrogen sulfide, sodium sulfide, potassium sulfide, sodium hydrogen sulfide, Zn/Magnesium in presence of Hydrazine hydrate or a mixture thereof; at a temperature ranging from 30-75°Cin presence of a solvent-2 selected from acids such as sulfuric acid, acetic acid; nitriles such acetonitrile; nitro methane; alcohols such as CI -5 alcohols; Glycol ethers such as 2-Butoxyethanol, Diglyme, Dimethoxyethane, 2-Ethoxy ethanol, 2-(2- Ethoxyethoxy)ethanol, 2-Methoxyethanol, 2-(2-Methoxyethoxy) ethanol, Octaethylene glycol monododecyl ether, Pentaethylene glycol monododecyl ether, Phenoxyethanol, Propylene glycol methyl ether acetate, Tetraethylene glycol dimethyl ether, Triethylene glycol, Triethylene glycol dimethyl ether; water or mixtures thereof. The obtained reaction mixture was stirred at a temperature ranging from 35-75°C for 30 minutes -1 hour. To the obtained reaction mass water was cooled and stirred for 30 min to 3 hour. Filtered the solid and washed the wet cake with to provide Amifampridine

The present inventors surprisingly found that the use of sulfide reducing agents in the reduction step leads to the formation of pure Amifampridine, which is devoid of other process related impurities. Further, the prior-art process utilizes palladium carbon in reduction step. However, the Amifampridineobtained is not much pure and the reaction is incomplete leads to the formation of lower yields as well unwanted by-products.

The obtained Amifampridine was purified by treating the residue with a suitable solvent selected from, but are not limited to: alcohols, such as C2-C6 alcohols like ethanol. 1 -propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, t-butyl alcohol; or nitriles, such as acetonitrile or propionitrile; amides such as Ν,Ν-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone; sulfoxides such as dimethylsulfoxide; halogenated hydrocarbons such as dichloromethane; aromatic hydrocarbons such as toluene, xylene; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, isopropyl acetate, isobutyl acetate, t-butyl acetate; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 1 ,4- dioxane, 2-methoxyethanol, anisole; ketones such as acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; organic solvents such as dimethyl formamide, n-hexane, n- heptane, cyclohexane, cycloheptane; water; or any mixtures of one or more of these solvents; at a temperature ranging from 25-60°C for about 30 minutes to 2 hours to yield pure Amifampridine. The purification is repeated using different solvents to obtain the desired purity. If required the Amifampridine was purified by using column chromatography to give pure Amifampridine.

Purification of Amifampridine further comprises of providing a solution of Amifampridine using a solvent selected from alcohol (CI -4) or Ketones (C3-6) or organic solvents (CI -8 alkanes, dimethyl formamide) or halogenated organic solvents (Methylene dichloride, Ethylene dichloride) or Ethers (Methyl tertiary butyl ether, tetrahydrofuran, Di-isopropyl ether ) or sulphoxides (dimethyl sulphoxide), water or mixtures thereof; acidifying the solution using an acid selected from organic/inorganic acid not limited to formic acid, citric acid, acetic acid, sulfuric acid, phosphoric acid; followed by basification using an organic /inorganic base and isolating the substantially pure Amifampridine having a purity of greater than 99.5%.

The obtained Amifampridine(III) reacts with hydrochloric acid in absence/presenceofsolvent selected from acids such as sulfuric acid, acetic acid; nitriles such acetonitrile; nitro methane; alcohols such as CI -5 alcohols; Glycol ethers such as 2- Butoxyethanol, Diglyme, Dimethoxyethane, 2-Ethoxy ethanol, 2-(2-Ethoxyethoxy)ethanol, 2- Methoxyethanol, 2-(2-Methoxyethoxy) ethanol, Octaethylene glycol monododecyl ether, Pentaethylene glycol monododecyl ether, Phenoxyethanol, Propylene glycol methyl ether acetate, Tetraethylene glycol dimethyl ether, Triethylene glycol, Triethylene glycol dimethyl ether; water or mixtures thereof; at a temperature ranging from 30 C °to 70°Cfor 1 hour-4 hours. Filtered the wet cake and washed with a solvent as described above to provide Amifampridinedihydrochloirde (I).

In view of this, the present inventors developed an improved process for the preparation of Ami ampridinedihydrochloride, by using industrial friendly solvents and reagents, which leads in the formation of good yield with high purity. Purification of Amifampridine dihydrochloride further comprises of providing a solution of

Amifampridine dihydrochlorideusing a solvent selected from alcohol such as ethanol, 1- propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, t-butyl alcohol;organic solvents such as dimethyl formamide, n-hexane, n-heptane, cyclohexane, cycloheptane; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone; halogenated hydrocarbons such as dichloromethane; aromatic hydrocarbons such as toluene, xylene; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, isopropyl acetate, isobutyl acetate, t-butyl acetate; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 1 ,4-dioxane, 2- methoxyethanol, anisole; sulfoxides such as dimethyl sulfoxide; water or mixtures thereof;The obtained reaction mixture was stirred for 30 minutes to 3 hours at a temperature ranging from 25-30°C. Filtered the material and washed with corresponding solvent or water. The obtained solid material was dried to yield substantially pure Amifampridinedihydrochloridehaving a purity of greater than 99.5%.

The Amifampridine dihydrochlorideobtained as per the present invention is highly pure and having a purity of greater than 99.5%. This purity is achieved due to the formation of pure intermediates, which are devoid of process related impurities.

In view of this, the present inventors developed an improved process for the preparation of Amifampridinedihydrochloride, by using industrial friendly solvents and reagents, which leads in the formation of good yield with high purity.

The present inventors developed a process for the preparation of Amifampridinedihydrochloride, wherein the reaction course is extremely smooth and achievable at ordinary feasible temperature conditions of 30-60°C, which is not only industrially feasible but also cost effective and provide pure materials/intermediates.

To overcome these serious industrially non-viable process concerns as cited above, the present inventors aimed for a process, which is not only industrially upscale process but also cost effective and least time consuming. The inventors in the present invention found that the use of base in the condensation step makes the reaction to move smoothly at ordinary lower temperatures i.e. at about 30-70°C, which was found to help in avoiding the formation of large number impurities due to unwanted parallel reactions and resulting in recovering purer material.

Drying may be also be performed by any conventional process not limited to spray drying or distillation to remove the solvent. Drying may be performed under reduced pressure conditions also. Reduced pressure conditions may be suitably utilized by person skilled in the art in order to obtain the dried material. The drying may be performed at a temperature ranging from 50-60°C for time ranging from 12 to 16 hrs depending upon the physical attributes of the end product obtained i.e. Pure Amifampridine dihydrochloirde.

The process related impurities that appear in the impurity profile of the Amifampridine dihydrochloride may be substantially removed by the process of the present invention resulting in the formation of highly pure material. The process of the present invention is as summarized in the Scheme-I as represented below:

(III) (IV) (II) Scheme-V: Process for preparation of Amifampridinedihydrochloirdeof the present invention:

In another embodiment the present invention provides substantially pure Amifampridinedihydrochloride having a purity of greater than 99.5% and total impurities A to D collectively less tha

Impurity-C Impurity-D

In further embodiment of the present invention provides substantially pure Amifampridine dihydrochloride having a purity of greater than 99.6% by HPLC.

In further embodiment of the present invention provides substantially pure Amifampridine dihydrochloride having a purity of greater than 99.7% by HPLC.

In further embodiment of the present invention provides substantially pure

Amifampridine dihydrochloride having a purity of greater than 99.8% by HPLC.

In further embodiment of the present invention provides substantially pure Amifampridine dihydrochloride having a purity of greater than 99.9% by HPLC.

In further embodiment of the present invention provides substantially pure Amifampridine dihydrochloride having a purity of greater than 99.95% by HPLC. In another embodiment, the Amifampridine dihydrochloride obtained by the processes of the present application may be formulated as solid compositions for oral administration in the form of capsules, tablets, pills, powders or granules. In these compositions, the active product is mixed with one or more pharmaceutically acceptable excipients. The drug substance can be formulated as liquid compositions for oral administration including solutions, suspensions, syrups, elixirs and emulsions, containing solvents or vehicles such as water, sorbitol, glycerine, propylene glycol or liquid paraffin.

The compositions for parenteral administration can be suspensions, emulsions or aqueous or non-aqueous sterile solutions. As a solvent or vehicle, propylene glycol, polyethylene glycol, vegetable oils, especially olive oil, and injectable organic esters, e.g. ethyl oleate, may be employed. These compositions can contain adjuvants, especially wetting, emulsifying and dispersing agents. The sterilization may be carried out in several ways, e.g. using a bacteriological filter, by incorporating sterilizing agents in the composition, by irradiation or by heating. They may be prepared in the form of sterile compositions, which can be dissolved at the time of use in sterile water or any other sterile injectable medium.

Pharmaceutically acceptable excipients used in the compositions comprising Amifampridine dihydrochloride obtained as per the present application process- include, but are but not limited to diluents such as starch, pregelatinized starch, lactose, powdered cellulose, microcrystalline cellulose, dicalcium phosphate, tricalcium phosphate, mannitol, sorbitol, sugar and the like; binders such as acacia, guar gum, tragacanth, gelatin, pre-gelatinized starch and the like; disintegrants such as starch, sodium starch glycolate, pregelatinized starch. Croscarmellose sodium, colloidal silicon dioxide and the like; lubricants such as stearic acid, magnesium stearate, zinc stearate and the like; glidants such as colloidal silicon dioxide and the like; solubility or wetting enhancers such as anionic or cationic or neutral surfactants, waxes and the like. Other pharmaceutically acceptable excipients that are of use include but not limited to film formers, plasticizers, colorants, flavoring agents, sweeteners, viscosity enhancers, preservatives, antioxidants and the like. Pharmaceutically acceptable excipients used in the compositions derived from

Amifampridinedihydrochlorideof the present application may also comprise to include the pharmaceutically acceptable carrier used for the preparation of solid dispersion, wherever utilized in the desired dosage form preparation. The following examples illustrate the nature of the invention and are provided for illustrative purposes only and should not be construed to limit the scope of the invention.

EXAMPLES

Example 1

Preparation of 3-nitro 4-amino pyridine (III)

4- amino pyridine (50gm,0.5319mol) was added in to reaction flask containing Sulfuric acid(350 mL) slowly at a temperature of 10 to 20 °C. To the reaction mixture Potassium nitrate (57.5 gram)) was added for a period of 30 minutesatl5-20°C under stirring. Raised temperature to room temperature then heated up to 60-65°C under stirring. Maintain the temperature for 6 hours under stirring. Cooled the reaction mixture to room temperature and then quenched to another reaction containing water (700 ml) was added. Cool to 0-5°Cand adjust pH of the reaction mass to 7.3-7.5 using aqueous ammonia solution. Filtered the material and washed with water (200ml). Dried the material under vacuum at 50°C for 10 to 12 hours till constant weight appears to yield the tilted compound.

Yield: 90.0gm

Chromatographic purity (By HPLC): 90.65%

Example 2

Preparation of 3, 4-diamino pyridine (Amifampridine)

Methanol (66.7ml) and Water (70.0ml) was charged in to reaction flask containing 4-amino-3- nitro pyridine (46.0g,0.33mol. The reaction mixture was heated to 60-65°C under stirring. Sodium sulfide solution (Na₂S103.04gm in 114mlD.M. water) was slowly added in to reaction mass at 50-55°C for 30 min. Cooled the reaction mass to 0-5°C and then stirred the reaction mass for 1 -2 hours. Filtered the material and washed with water (46 ml). Suck dry the material to yield the tilted compound.

Yield: 31.0gm (Wet)

Chromatographic Purity (By HPLC): 94.73%

Example 3

Purification of Amifampridine(II)

Water was charged in to reaction flask containing Crude Amifampridine (31.0 gm). The reaction mass was heated to 75-80°C to get clear solution. Activated carbon was added and stirred the contents for 10 to 15 minutes at 75-80°C. Filtered through celite bed and washed with water. Dried the material at 55-60°C for 15 minutes to 1 hour to yield pure

Amifampridine

Yield: 18.0gm (Wet)

Chromatographic Purity (By HPLC): 99.87 %

Example 4

Preparation of Amifampridinedihydrochloride(I)

Methanol (67.5 ml) was charged in to reaction flask containing Amifampridine (4.5 gm). The reaction mass was heated to 45-50°C to get clear solution. Concentrated hydrochloric acid (13.5 ml) was added under stirring at 45-50°C and continue stirring for 10-15 minutes. Cooled the reaction mass to 25-30°C and then further colled to 0-5°C. Filtered the material and washed with methanol (4.5 ml). Dried the material under vacuum at 55-60°C for 5hours to 10 hours to yield highly pure Amifampridinedihydrochloride.

Yield: 6.3gm

Chromatographic Purity (By HPLC):99.97 %

Chloride content: 37.99 %

Water Content (By KF): 0.11%

Total impurities (By HPLC): 0.03 % While the foregoing pages provide a detailed description of the preferred embodiments of the invention, it is to be understood that the description and examples are illustrative only of the principles of the invention and not limiting. Furthermore, as many changes can be made to the invention without departing from the scope of the invention, it is intended that all material

Claims

We Claim:

1) A salt of 3,4-diaminopyridine is 3,4-diaminopyridine dihydrochloride or Amifampridine dihydrochloride having solubility exceeding 30 mg/ml.

2) Amifampridine dihydrochloride according to claim- 1 , characterized by chloride content ranging from 36-40 % w/w.

3) Amifampridine dihydrochloride according to claim- 1 , having a purity of greater than

99.5 %.

4) Amifampridine dihydrochloride according to claim- 1 , characterized by X-ray powder diffraction pattern comprising characteristic diffraction angle peaks selected from the XRPD peaks at 16.9, 23.7, 24.9, 25.4,25.8, 27.7, 28.8, 32.6, 36.3 and 36.8 ± 0.2 °20 and DSC isotherm comprising endothermic peaks ranging between-:

a) Peak-1 between 158 and 168°C;

b) Peak-2 between 206 and 216°C

c) Peak-3 between 216 and 220°C

5) A process for the preparation of Amifampridinedihydrochlorideof Formula (I)

comprising the steps of:

a) nitrating 4-amino pyridine (III) using a nitrating agent in presence/absence of a solvent to yield 4-Amino -3-nitro Pyridine (IV);

(ΠΙ) (IV)

b) reacting 4-Amino-3-nitro Pyridine (IV) with a sulfide reducing agent to provide Amifampridine(II); and

• ^ Sulf de reagent

(IV) (II)

c) optionally, purifying Amifampridine to obtain substantially pure Amifampridine(II) having a purity of greater than 99.5%.

(II) (I)

e) optionally, purifying Amifampridine dihydrochloride (I) to obtain substantially pure Amifampridine dihydrochloride(I) having a purity of greater than 99.5% (by HPLC). 6) A process for the preparation of Amifampridine dihydrochloride according to claim 6, wherein nitrating agent is selected from nitric acid, nitric acid + sulfuric acid, sodium nitrate, potassium nitrate, silver nitrate, Methyl nitrate, nitric acid + sulfuric acid+ urea

7) A process for the preparation of Amifampridine dihydrochloride according to claim 6, wherein solvent used in step a) or step b) or step d) is selected from acids such as sulfuric acid, acetic acid; nitriles such acetonitrile; nitro methane; alcohols such as CI -5 alcohols;Glycol ethers such as 2-Butoxyethanol, Diglyme, Dimethoxyethane, 2-Ethoxy ethanol, 2-(2-Ethoxyethoxy)ethanol, 2-Methoxyethanol, 2-(2-Methoxyethoxy) ethanol, Octaethylene glycol monododecyl ether, Pentaethylene glycol monododecyl ether, Phenoxyethanol, Propylene glycol methyl ether acetate, Tetraethylene glycol dimethyl ether, Triethylene glycol, Triethylene glycol dimethyl ether; water or mixtures thereof.

8) A process for the preparation of Amifampridin dihydrochloride according to claim 6, wherein sulfide reducing agent is selected from hydrogen sulfide, sodium sulfide, potassium sulfide, sodium hydrogen sulfide, Zn/Magnesium in presence of Hydrazine hydrate or a mixture thereof. ) Substantially pure Amifampridine dihydrochloride obtained according to claim-5, having a purity of greater than 99.5% and total impurities A to D collectively less than 0.5% by HPLC.

Impurity-C Impurity-D