FIELD OF THE INVENTION

The present invention relates to a process of preparation and purification of succinylcholine chloride of Formula I and its hydrates,

The present invention further relates to a process for the purification of succinylcholine chloride of Formula I and specifically of succinylcholine chloride dihydrate of Formula II.
.

BACKGROUND OF THE INVENTION
Succinylcholine Chloride is the chloride salt of succinylcholine, which is a quaternary ammonium compound and depolarizing agent with short-term muscle relaxant properties. The chemical name of succinylcholine chloride is 2,2'-[(1,4-dioxobutane-1,4-diyl)bis(oxy)]bis (N,N,N-trimethylethanaminium)chloride and is represented by Formula I,
.

U.S. Pat. No. 2,858,329 describes a process for the preparation of bis-dimethylaminoethylsuccinate by heating succinic anhydride and N,N-dimethyl amino ethanol at 135-145°C in benzene for 12-18 hr. The obtained succinylcholine is further purified by high vacuum distillation at very high temperature. The obtained succinylcholine is then purged with molar equivalent of methylchloride in isopropyl alcohol (IPA) and water at 40-50°C to obtain succinylcholine chloride.

GB706215 describes a process for the preparation of succinylcholine chloride hydrate in acetone and methylene dichloride followed by purification in absolute ethanol, which on heating at 163-165oC gives succinylcholine chloride.

U.S. Pat. No. 5,206,420 describes a process for the preparation of succinylcholine halide. According to this patent, dialkyl succinate is reacted with large excess of dimethyl amino ethanol, in presence of a base catalyst viz. alkali metal alcoholate or amide as catalyst. The bis(2-dimethylaminoethyl) succinate obtained is then reacted with methyl halide in benzene to yield succinylcholine halide. The prior art processes involve purification of bis(dimethyl amino ethyl) succinate using high vacuum distillation at very high temperature. Since the product is highly heat sensitive, substantial portion is decomposed during high vacuum distillation. Those processes need special heating facility, which is not feasible at industrial level. The high vacuum distillation further possess a safety risk. The prior art reaction is carried out in benzene which is carcinogenic, and thus, is not suitable at industrial level.

CN1062346A discloses a process for the preparation of succinylcholine chloride by reacting succinic acid or its anhydride with thionyl chloride by adding DMF in catalytic amount and heating to produce succinyl chloride, which was used directly in the esterification reaction, with a chlorinating choline in acetone to produce succinylcholine chloride of Formula I.

One of the major drawback of above said process is use of thionyl chloride that degrades into volatile side products, like SO2 which creates air and water pollution and also generate other impurities.

Based on aforesaid drawbacks of the prior known processes, there is always a need to develop a process that is substantially free from volatile side products and other impurities.

OBJECT OF THE INVENTION
The main object of the present invention is to provide an improved, cost effective and environment friendly process for the preparation of succinylcholine chloride of Formula I and its hydrates.

Another object of the present invention is to develop a purification process to obtain substantially pure succinylcholine chloride dihydrate of Formula II which is reproducible at large scale production.

SUMMARY OF THE INVENTION
The main aspect of the present invention provides a process for the preparation of succinylcholine chloride of Formula I and its hydrates,

wherein said process comprising the steps of:
a) refluxing succinic anhydride of Formula III with chlorine containing acid to obtain succinyl dichloride of Formula IV, wherein said succinyl dichloride of Formula IV is not isolated,
;
b) coupling the succinyl dichloride of Formula IV with choline chloride of Formula V in a suitable solvent, optionally in the presence of a base, to obtain succinylcholine chloride of Formula I,
;
c) purifying the succinylcholine chloride of Formula I in a suitable solvent; and
d) optionally, converting the succinylcholine chloride of Formula I to succinylcholine chloride dihydrate of Formula II.

Another aspect of the present invention provides a process for the purification of succinylcholine chloride dihydrate of Formula II;

wherein said process comprising the steps of:
a) dissolving the succinylcholine chloride of Formula I in one or more solvent(s) to get a solution;
b) heating the solution at 30-90oC;
c) optionally isolating a crude mass;
d) adding water either to the crude mass obtained in step c) or the solution of step b);
e) heating at 30-90oC and adding alcohol(s);
f) isolating to get succinylcholine chloride dihydrate of Formula II;
g) adding water to the succinylcholine chloride dihydrate of Formula II;
h) heating at 30-90oC and adding alcohol(s);
i) optionally repeating the steps f) to h) one or more time; and
j) isolating pure succinylcholine chloride dihydrate of Formula II.

In another aspect, the present invention provides a process for the preparation of succinylcholine chloride dihydrate of Formula II;

wherein said process comprising of:
a) refluxing succinic anhydride of Formula III with oxalyl chloride in the presence of catalytic amount of dimethyl formamide to obtain succinyl dichloride of Formula IV, wherein said succinyl dichloride of Formula IV is not isolated,
;
b) coupling the succinyl dichloride of Formula IV with choline chloride of Formula V in a suitable solvent, optionally in the presence of a base, to obtain succinylcholine chloride of Formula I;

,
c) dissolving the succinylcholine chloride of Formula I in one or more alcohol(s) to get a solution;
d) heating the solution at 30-90oC;
e) optionally isolating a crude mass;
f) adding water either to the crude mass obtained in step e) or the solution of step d);
g) heating at 30-90oC and adding alcohol(s);
h) isolating to get succinylcholine chloride dihydrate of Formula II;
i) adding water to the succinylcholine chloride dihydrate of Formula II;
j) heating at 30-90oC and adding alcohol(s);
k) optionally repeating the steps h) to j) one or more time; and
l) isolating pure succinylcholine chloride dihydrate of Formula II.

DETAILED DESCRIPTION
Brief Description of the drawings:
Fig. 1, represents the X-ray powder diffraction (XRPD) pattern of the crystalline form of succinylcholine chloride dihydrate.
Fig. 2, represents the differential scanning calorimetry (DSC) pattern of the crystalline form of succinylcholine chloride dihydrate.
Fig. 3, represents the thermo gravimetric analysis (TGA) pattern of the crystalline form of succinylcholine chloride dihydrate.

Definitions:
The term “suitable solvent” as used in the context of the present invention refers to solvents selected from the group comprising of, but not limited to, esters, alcohols, halogenated solvent, nitriles, ketones, hydrocarbons, ethers, sulfoxides, amides, carbonates, water and mixture thereof. Specifically, the suitable solvent is selected from, but not limited to, the group comprising of ethyl acetate, isopropyl acetate, butyl acetate, t-butyl acetate, propyl acetate, propylene acetate, acetonitrile, acetone, methyl tert-butyl ketone, methyl ethyl ketone, tetrahydrofuran, 1,4-dioxane, dichloromethane, methanol, ethanol, t-butanol, isopropyl alcohol, dimethyl formamide, dimethyl sulfoxide, toluene, cyclohexane, n-heptane, chloroform, carbon tetrachloride, and mixture thereof.

The preparation of succinylcholine chloride of Formula I and its hydrates may involve one or more embodiments. It is to be understood that the embodiments below are illustrative of the present invention and are not intended to limit the claims to the specific embodiments exemplified. It is also to be understood that the embodiments defined herein may be used independently or in conjunction with any definition, any other embodiment defined herein. Thus the invention contemplates all possible combinations and permutations of the various independently described embodiments.

In one embodiment, the present invention provides a process for the preparation of succinylcholine chloride of Formula I and its hydrates,

wherein said process comprising the steps of:
a) refluxing succinic anhydride of Formula III with oxalyl chloride in the presence of catalytic amount of dimethyl formamide to obtain succinyl dichloride of Formula IV, wherein said succinyl dichloride of Formula IV is not isolated;
;
b) coupling the succinyl dichloride of Formula IV with choline chloride of Formula V in a suitable solvent, optionally in the presence of a base, to obtain succinylcholine chloride of Formula I,
;
c) purifying the succinylcholine chloride of Formula I in a suitable solvent; and
d) optionally, converting the succinylcholine chloride of Formula I to succinylcholine chloride dihydrate of Formula II.

In another embodiment, the base used for preparation of succinylcholine chloride of Formula I is selected from, but not limited to, the group comprising of alkali and alkaline earth metal hydroxides, alkali and alkaline earth metal carbonates, alkali and alkaline earth metal bicarbonates, organic amines selected from primary, secondary and tertiary amines such as pyridine, triethylamine, diisopropyl ethyl amine, dicyclohexyl amine and the like.

In another embodiment, the present invention provides a process for the purification of succinylcholine chloride dihydrate of Formula II;

wherein said process comprising of:
a) dissolving the succinylcholine chloride of Formula I in one or more solvent(s) to get a solution;
b) heating the solution at 30-90oC;
c) optionally isolating a crude mass;
d) adding water either to the crude mass obtained in step c) or the solution of step b);
e) heating at 30-90oC and adding alcohol(s);
f) isolating to get succinylcholine chloride dihydrate of Formula II;
g) adding water to the succinylcholine chloride dihydrate of Formula II;
h) heating at 30-90oC and adding alcohol(s);
i) optionally repeating the steps f) to h) one or more time; and
j) isolating pure succinylcholine chloride dihydrate of Formula II.

In specific embodiment, the alcohol(s) used for purification of succinylcholine chloride dihydrate is selected from methanol, ethanol, isopropanol, t-butanol, n-butanol and mixture thereof.

In another embodiment, the present invention provides a process for the preparation of succinylcholine chloride dihydrate of Formula II;

wherein said process comprising of:
a) refluxing succinic anhydride of Formula III with oxalyl chloride in the presence of catalytic amount of dimethyl formamide to obtain succinyl dichloride of Formula IV, wherein said succinyl dichloride of Formula IV is not isolated,
;
b) coupling the succinyl dichloride of Formula IV with choline chloride of Formula V in suitable solvent, optionally in the presence of a base, to obtain succinylcholine chloride of Formula I;

;
c) dissolving the succinylcholine chloride of Formula I in one or more alcohol(s) to get a solution;
d) heating the solution at 30-90oC;
e) optionally isolating a crude mass;
f) adding water either to the crude mass obtained in step e) or the solution of step d);
g) heating at 30-90oC and adding alcohol(s);
h) isolating to get succinylcholine chloride dihydrate of Formula II;
i) adding water to the succinylcholine chloride dihydrate of Formula II;
j) heating at 30-90oC and adding alcohol(s);
k) optionally repeating the steps h) to j) one or more time; and
l) isolating pure succinylcholine chloride dihydrate of Formula II.

In one another embodiment the succinylcholine chloride dihydrate of Formula II is purified by one or more repetitive purification steps wherein said succinylcholine chloride dihydrate of Formula II is purified by adding water followed by heating at 30-90oC which is then followed by addition of alcohol such as isopropyl alcohol at ambient temperature. The precipitates so obtained are filtered and purified repetitively in water and isopropyl alcohol as mentioned above. The repetition is optional and is performed to achieve desired purity of succinylcholine chloride dihydrate of Formula II with purity of 99.5% and above.

In a preferred embodiment, the succinylcholine chloride dihydrate of Formula II may be isolated by techniques such as purification, centrifugation, crystallization, filtration, extraction or evaporation, freeze drying, spray drying, lyophilization and other conventional techniques.

In another embodiment, the succinylcholine chloride used for preparation of succinylcholine chloride dihydrate is prepared as per the process of the present invention or by any conventional method.

In one another preferred embodiment, succinylcholine chloride dihydrate of Formula II obtained as per the process of the present invention is crystalline in nature. The succinylcholine chloride dihydrate of Formula II as obtained herein is substantially crystalline in nature with less than about 10% w/w of amorphous form, preferably less than 5%w/w of amorphous form and most preferably less than 1% w/w of amorphous form.

In one another embodiment, succinylcholine chloride dihydrate of Formula II obtained herein is amorphous in nature. The amorphous succinylcholine chloride dihydrate of Formula II obtained as per the process of the present invention is substantially free from crystallinity.

In one another embodiment, the succinylcholine chloride dihydrate of Formula II is characterized by X-Ray powder diffraction pattern (XRPD) having peaks at diffraction angles 2-theta of about 15.65, 19.89, 20.01, 21.89, 23.52, 27.49 and 27.68 ±0.2

In another embodiment, the succinylcholine chloride dihydrate of Formula II is characterized by X-Ray powder diffraction pattern (XRPD) having peaks at diffraction angles 2-theta of about 10.69, 11.65, 13.68, 14.50, 15.65, 17.18, 18.18, 18.87, 19.21, 19.89, 21.57, 21.86, 23.31, 23.52, 24.93, 26.02, 26.25, 26.51, 26.84, 27.48, 27.67, 27.99, 28.19, 28.44, 29.12, 30.16, 30.76, 31.05, 31.35, 31.80, 32.72, 33.05, 33.58, 34.12, 34.71, 35.25, 35.61, 36.10, 36.42, 36.83, 37.68, 38.07, 38.25, 38.26, 38.72, 39.16 and 39.29 ±0.2.

In yet another embodiment succinylcholine chloride dihydrate of Formula II is characterized by X-Ray powder diffraction pattern (XRPD) as depicted in Fig. 1.

In one another embodiment, succinylcholine chloride dihydrate of Formula II is characterized by Differential scanning calorimetry (DSC) curve having endothermic peaks at 159.24oC.

In one another embodiment, succinylcholine chloride dihydrate of Formula II is characterized by Differential scanning calorimetry (DSC) curve as depicted in Fig. 2.

In one another embodiment succinylcholine chloride dihydrate of Formula II is characterized by thermal gravimetric analysis (TGA) curve corresponding to a weight loss as depicted in Fig. 3.

In one embodiment succinylcholine chloride dihydrate of Formula II obtained herein has water content of about 7.9% w/w.

In other embodiment, the present invention provides succinylcholine chloride of Formula I, wherein succinylcholine chloride of Formula I is crystalline or amorphous in nature or may be the mixture of amorphous and crystalline form.

In furthermore embodiment, there is provided a substantially pure succinylcholine chloride dihydrate, wherein said succinylcholine chloride dihydrate is substantially free of impurities of Formula A, B, C, D, E, F and G and wherein each impurity is less than about 0.3% w/w or total impurity is less than about 1% w/w, more specifically less than about 0.15% w/w of any impurity;
.

In further embodiment, the present invention provides succinylcholine chloride dihydrate of Formula II characterized by particle size distribution wherein, d90 is between 0.1µm to 200µm, specifically between 2.0 µm to 150µm.

In one another embodiment, the succinylcholine chloride dihydrate of Formula II prepared as per the process of the present invention is characterized with purity above 99%, preferably above 99.5%, and more preferably above 99.9%.

In one another embodiment, the present invention further provides a composition comprising succinylcholine chloride dihydrate of Formula II as prepared by the process of the present invention along with one or more pharmaceutical acceptable excipients.

In another embodiment, the crystalline form of succinylcholine chloride dihydrate of present application is stable on storage as shown in Table-1 as measured by Karl Fischer method, wherein the crystalline form of succinylcholine chloride dihydrate does not convert to any other solid form when stored at a temperature of up to about 40oC and at a relative humidity of about 25% to about 75% for about six months and more.
Table 1:

25°C±2°C, 60%±5% (RH) Parameters Initial 3rd month 6th month Spec. Limit
Crystallinity A white crystalline powder A white crystalline powder A white crystalline powder --
Succinic acid ND ND ND NMT 0.10
Choline ND ND ND NMT 0.10
Unspecified Impurity 0.01 0.01 0.01 NMT 0.10
Chromatographic purity 99.3% 99.2% 99.1% Above 98.0%
40°C±2°C, 75%±5% (RH) Organic impurities A white crystalline powder A white crystalline powder A white crystalline powder --
Succinic acid ND ND ND NMT 0.5
Choline ND ND ND NMT 0.5
Unspecified Impurity 0.01 0.04 0.05 NMT 0.10
Chromatographic purity 99.3% 99.4% 99.5% Above 99.0%

The present invention can be illustrated by the following examples, which are not to limit the scope of invention.

EXAMPLES:

Example-1 Synthesis of Succinylcholine chloride of Formula I:
Charged succinic anhydride (100g) and oxalyl chloride (380.7g) into a round bottom flask at 20-25oC. Added DMF (1.6g) slowly to the reaction mass in 10-15 min at 20-25oC. Reaction mass was stirred for 40-45 hours at 20-25°C.
Charged choline chloride (280.16 g) of Formula V in separate round bottom flask and added dichloromethane (1000ml). Reaction mass was stirred at 40-45oC. Dichloromethane was distilled out and reaction mass was cooled to 20-25oC. Charged acetonitrile (300ml) in reaction mass having succinyl chloride of Formula IV and charged this reaction mass in choline chloride at 20-25oC. Reaction mass was stirred for 4-5 hours at 20-25oC. After the completion, reaction mass was cooled to 10-15oC. Charged methanol (200ml) in the reaction mixture followed by acetone (900ml) at 10-15oC for 10-15 mins. Added liquid ammonia (100ml) slowly within 30-35 mins at 10-15oC and stirred for 1-2 hours. Filtered the reaction mass at 10-15oC and washed with acetone (50ml) to get crude succinylcholine chloride (390g) of Formula I.

Example-3 Purification of Succinylcholine chloride of Formula I:
Charged methanol (400ml) and isopropyl alcohol (800ml) to the round bottom flask of 5 litre at 25-30°C. Charged crude succinylcholine chloride (390g) of Formula I to the above solvent mixture at 25-30°C. Stirred the reaction mass for 2-3 hours at 50-55oC. Filtered the reaction mass to get pure succinylcholine chloride of Formula I as wet cake.

Example-4 Preparation and purification of Succinylcholine chloride dihydrate of Formula II:
Charged succinylcholine chloride of Formula I wet cake obtained from example 3 in the round bottom flask at 25-30°C. Added DM water (250.0ml) to the above wet cake at 25-30°C. Reaction mass was heated at 50-55ºC till clear solution. Added isopropyl alcohol (1500ml) in the reaction mass within 2-3 hours at 50-55ºC and stirred the reaction mass for 2-3 hrs. Filtered the reaction mass at 50-55ºC to get crude succinylcholine chloride dihydrate of Formula II as wet cake. Added DM water (250ml) to the above cake at 25-30°C and heated at 50-55ºC. After getting clear reaction mass, charged isopropyl alcohol (1500ml) within 2-3 hours at 50-55ºC. Reaction mass was stirred for 1-2 hrs at 75-80ºC. Cooled the reaction mass gradually to 50-55ºC and filtered. Added DM water (175ml) to the wet cake so obtained at 25-30°C and heated at 50-55ºC. After getting clear reaction mass, charged activated carbon to the above reaction mass at 50-55ºC and stirred the reaction mass for 30 minute. Filtered the reaction mass through hyflo bed at 50-55ºC and washed the hyflo bed with hot DM water (75ml) 50-55ºC. Suck dried the solid material properly. Charged filtrate mother liquor to the round bottom flask of 3 litre at 50-55°C and added isopropyl alcohol (2000ml) within 2-3 hours at 50-55°C. After complete addition of isopropyl alcohol, heated the reaction mass at 75-80ºC and stirred the reaction mass for 1-2. Reaction mass was cooled to 50-55°C and stirred for 1 hour at 50-55°C. Filtered the reaction mass at 50-55ºC. Added DM water (200ml) to the above cake at 25-30°C and heated at 50-55ºC. After getting the clear reaction mass, charged isopropyl alcohol (2000ml) within the within 2-3 hours at 50-55ºC. Stirred the reaction mass for 1-2 hrs at 75-80ºC.Cooled the reaction mass gradually to 50-55ºC and filtered the reaction mass at 50-55ºC to get pure succinylcholine chloride dihydrate of Formula II.

WE CLAIM

1. An improved process for the preparation of succinylcholine chloride of Formula I and its hydrates,

wherein said process comprising the steps of:
a) refluxing succinic anhydride of Formula III with chlorine containing acid to obtain succinyl dichloride of Formula IV,
;
b) coupling the succinyl dichloride of Formula IV with choline chloride of Formula V in a suitable solvent, optionally in the presence of a base, to obtain succinylcholine chloride of Formula I, wherein said succinyl dichloride of Formula IV is not isolated,
;
c) purifying the succinylcholine chloride of Formula I in a suitable solvent; and
d) optionally, converting the succinylcholine chloride of Formula I to succinylcholine chloride dihydrate of Formula II.

2. A process for the purification of succinylcholine chloride dihydrate of Formula II,

wherein said process comprising the steps of:
a) dissolving succinylcholine chloride of Formula I in one or more solvent(s) to get a solution;
b) heating the solution at 30-90oC;
c) optionally isolating a crude mass;
d) adding water either to the crude mass obtained in step c) or the solution of step b);
e) heating at 30-90oC and adding alcohol(s);
f) isolating to get succinylcholine chloride dihydrate of Formula II;
g) adding water to the succinylcholine chloride dihydrate of Formula II;
h) heating at 30-90oC and adding alcohol(s);
i) optionally repeating the steps f) to h) one or more time; and
j) isolating pure succinylcholine chloride dihydrate of Formula II.

3. The process as claimed in claim 2, wherein the purification steps from f) to h) are repetitive.

4. The process as claimed in claim 1, wherein said base is selected from pyridine, triethylamine, diisopropyl ethyl amine, dicyclohexyl amine.

5. The process as claimed in claim 2, wherein succinyl choline chloride dihydrate of Formula II is crystalline in nature and characterized by at least one of:
a) X-ray powder diffraction (XRD) pattern having peaks at 15.68, 19.89, 20.01, 21.89, 23.54 and 27.51 ±0.2 degrees two-theta,
b) weight loss of about 8.35% w/w, as measured by a Thermo gravimetric analysis (TGA), or
c) melting endotherms of 161.52oC as measured by differential scanning calorimetry.
6. Substantially pure succinylcholine chloride dihydrate of Formula II having purity of 99.0% and more, wherein said succinylcholine chloride dihydrate is free of impurities of Formula A, B, C, D and E, wherein each impurity is less than about 0.15% w/w,

.

7. The process as claimed in claim 2, wherein said succinylcholine chloride dihydrate of Formula II obtained in step (j), is stable when stored at a temperature of up to about 40oC and at a relative humidity of about 25% to about 75%.