FORM 2
THE PATENT ACT, 1970
(39 OF 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
1. (See section 10 and rule 13)

TITLE OF THE INVENTION:
PROCESS FOR PREPARATION OF SUCCINYLCHOLINE CHLORIDE
DIHYDRATE
2. APPLICANT:
a. NAME: INDOCO REMEDIES LIMITED
b. • NATIONALITY: INDIAN
c. ADDRESS: Indoco House, 166 C.S.T. Road,
Santacruz East, Mumbai - 400 098,
3. Maharashtra, India

PREAMBLE TO THE DESCRIPTION:
Th 5 following specification particularly describes the invention and the manner in
which it is to be performed.

BACKGROUND OF THE INVENTION:
Succinylcholine chloride also known as suxamethonium chloride and chemically known
as 2,2,-((l,4-dioxo-l,4-butanediyl)bis(oxy))bis(N,N,N-trimethylethanaminium)
dichloride. Succinylcholine chloride dihydrate of formula I is approved by the United States Food and Drug Administration (FDA) as a provision to other sedatives or hypnotics and is marketed as under the trade names Anectine, Quelicin, Scoline and Sucostrin.

Succinylcholine chloride is a quaternary ammonium compound and depolarizing agent which is a paralytic drug used to induce muscle relaxation and short-term paralysis, usually to facilitate tracheal intubation. It blocks the action of acetylcholine (ACh); hence, it disrupts all cholinergic receptors of the parasympathetic and sympathetic nervous systems. Its use can expedite rapid endotracheal intubation, facilitate surgical procedures, and aid in mechanical ventilation by relaxation of skeletal muscles. Succinylcholine is often used as an adjunct therapy in patients undergoing electroconvulsive shock therapy (ETC) to control muscle contractions induced due to the electrical impulses delivered during the procedure.
Article published in Gazzetta Chimica Italiana, 79, 129-141 (1949) discloses the preparation of succinylcholine chloride via four different methods. In the first method

reaction of succinyl dichloride with choline chloride in toluene under reflux condition to give succinylcholine chloride. In the second method, succinylcholine chloride is prepared by the reaction of bis(2-chloroethyl) succinate with trimethylamine in benzene at 80°C in an autoclave. In the third method succinic dichloride is reacted with 2-dimethylaminoethanol in diethyl ether under reflux condition to get bis(2-dimethylaminoethyl) succinate which is methylated with methyl chloride in acetone under reflux condition to obtain succinylcholine chloride. In the fourth method, esterification of sodium succinate with 2-dimethylaminoethanol in acetone under reflux condition or trahsesterification of diethyl succinate with 2-dimethylaminoethanol in presence of sodium in ethanol to get bis(2-dimethylaminoethyl) succinate which is methylated with methyl chloride in acetone under reflux condition to obtain succinylcholine chloride. The disadvantage of the process is the use of benzene, which is well known carcinogen.
US Patent No. US2858239 discloses a process for the preparation of succinylcholine chloride by heating succinic anhydride with 2-dimethylaminoethanol in benzene to get bis(2-dimethylaminoethyl) succinate; which is then methylated with methyl chloride in isopropanol and water to obtain succinylcholine chloride.
The article published in Acad. Rep. Populare Rotnine Inst. Biochimie, studii ceetari biochimie, 1, 167-170 (1958) discloses the preparation of succinylcholine chloride by esterification of succinic acid with 2-chloroethanol in solvent benzene in presence of sulphuric acid to get bis(2-chloroethyl) succinate; which is further reacted with trimethylamine in benzene at 125-130°C in a sealed tube to provide succinylcholine chloride. In this process, trimethylamine is used as gas and the reaction is earned out by bubbling of trimethylamine through the reaction mixture and hence difficult to handle. Therefore, the method is not feasible on plant level. Another disadvantage of the process is the use of benzene, which is a carcinogen.
Chinese patent application CN1062346 discloses a process for preparation of succinylcholine chloride from succinic acid or succinic anhydride. In this process, succinic acid or succinic anhydride is reacted with thionyl chloride in the presence of dimethylformamide at 60-100°C to get succinyl dichloride, which is then reacted with choline chloride in solvent acetone under reflux condition to obtain succinylcholine

chloride. In this method, the synthesis of intermediate succinyl chloride requires thionyl chloride chlorination, which produces a large amount of sulfur dioxide gas, which causes serious environmental pollution and not suitable in plant level.
Chinese patent application CN110776435 discloses the preparation of succinylcholine chloride from succinic acid. In this process, succinic acid is reacted with phosphorus pentachioride (PCI5) under neat condition to get succinyl dichloride, which is then reacted with choline chloride in solvent chloroform at 60°C to form succinylcholine chloride. The use of PCI5 produces phosphorus oxyehloride as by-product, which is corrosive and hazardous and is dangerous to human health.
The Indian patent application IN201911012419 discloses the preparation of succinylcholine chloride and its hydrate wherein the preparation involves refluxing succinic anhydride with chlorine containing acid to obtain succinyl dichloride. Coupling of succinyl dichloride with choline chloride in a suitable solvent optionally in the presence of a base to obtain succinylcholine chloride, purifying succinylcholine chloride and then converted into succinylcholine chloride dihydrate. In this process, by-products such as dimethyl succinate, succinic acid monomethyl ester, succinyl monocholine chloride, succinic acid, choline chloride, 2-dimethylaminoethanol and maleic acid monocholine chloride are present each in less than about 0.15% w/w along with succinylcholine chloride.
Therefore, there remains a need in the art to develop a process for the preparation of succinylcholine chloride dihydrate, which ameliorate the above drawbacks of the prior arts and makes the process industrially viable,
OBJECTIVES OF THE INVENTION:
An objective of the present invention is to ameliorate the drawbacks of the prior arts and provide useful alternative process.
Another objective of the present invention is to provide a process for the preparation of pure succinylcholine chloride dihydrate substantially free from impurities.

SUMMARY OF THE INVENTION:
Accordingly, the present invention relates to a process for preparation of succinylcholine chloride dihydrate of formula I illustrated by a reaction sequence in Scheme 1.

In another aspect, the present invention provides a process for preparation of succinylcholine chloride dihydrate of formula I, wherein said process comprising the steps of


a) reacting succinic acid of formula II with a chlorinating agent in a suitable solvent
to obtain succinyl chloride of formula III;

b) treating the reaction mass with an organic solvent and extracting the succinyl
dichloride-organic solvent solution;
c) reacting the succinyl dichloride-organic solvent solution with choline chloride of
formula IV in an organic solvent to give a mixture of succinylcholine chloride
dihydrate of formula (I) and maleic acid choline chloride ester of formula V;

d) isolating the mixture of succinylcholine chloride dihydrate of formula (J) and
maleic acid choline chloride ester of formula V in a solvent;
e) hydrogenation of the mixture of succinylcholine chloride dihydrate of for inula (I)
and maleic acid choline chloride ester of formula V in presence of a catalyst in a
solvent; and

f) isolating the succinylcholine chloride dihydrate of formula I.

DETAILED DESCRIPTION OF THE INVENTION:
The present invention describes a cost-effective process for preparing succinylcholine chloride dihydrate of formula I, which is substantially devoid of known and unknown impurities.
The main aspect of the present invention is to provide a process for preparing succinyicholme chloride dihydrate of formula I.
In an embodiment of the present invention, a process for preparation of succinylcholine chloride dihydrate of formula I, wherein said process comprising the steps of

a) reacting succinic acid of formula II with a chlorinating agent in a suitable solvent
to obtain succinyl chloride of formula III;

b) treating the reaction mass with an organic solvent and extracting the succinyl dichloride-organic solvent solution;
c) reacting the succinyl dichloride-organic solvent solution with choline chloride of formula IV in an organic solvent to give a mixture of succinylcholine chloride dihydrate of formula (I) and maleic acid choline chloride ester of formula V;


d) isolating the mixture of succinylcholine chloride dihydrate of formula (I) and
nialeic acid choline chloride ester of formula V in a solvent;
e) hydrogenation of the mixture of succinylcholine chloride dihydrate of formula (I)
and maleic acid choline chloride ester of formula V in presence of a catalyst in a
solvent; and

f) isolating the succinylcholine chloride dihydrate of formula L
In an embodiment of the present invention, the solvent used in the chlorination reaction in step a) is selected from the group consisting of dichloromethane, 1,2-dichloroethane, toluene, xylene or a mixture thereof.
In an embodiment of the present invention, the chlorinating agent used in the chlorination reaction in step a) is selected from the group consisting of oxalyl chloride, thionyl chloride or phosphorus oxychloride.
In another embodiment of the present invention, the organic solvent used for extraction in step b) is selected from the group consisting of cyclohexane, toluene, xylene or a mixture thereof The preferred solvent is cyclohexane.
In another embodiment of the present invention, the organic solvent used for coupling reaction in step c) is selected from the group consisting of cyclohexane, toluene, xylene or a mixture thereof. The preferred solvent is cyclohexane. The reaction is carried out a temperature of 70°C to 90°C, preferably at SOX.

The reaction of succinyl dichloride with choline chloride produces succinylcholine chloride dihydrate along with unwanted maleic acid choline chloride as product related impurity. Removal of the maleic acid choline chloride ester impurity of formula V from the required product is very difficult by normal chemical purification as it has the same properties of succinylcholine chloride*
In another embodiment of the present invention, the solvent used for isolation in step d) is selected from the group consisting of isopropanol, n-propanol, n-butanol, ethanol, methanol, water or a mixture thereof.
In another embodiment of the present invention, the catalyst used for hydrogenation in step e) is selected from the group consisting of palladium on carbon or Raney nickel.
In another embodiment of the present invention, the solvent used for hydrogenation in step e) is selected from the group consisting of water, methanol, ethanol, isopropanol or a-mixture thereof.
Some of the key advantages of the present invention are:
1. Succinic acid and oxalyl chloride are used as raw materials, which are simple,
cheap and easily available.
2. In the chlorination reaction, succinic anhydride is formed as by-product, which reacts with choline chloride to form mono impurity makes the reaction mass became sticky and not stirrable. In cyclohexane solvent, the succinyl dichloride •formed is dissolved and succinic acid and succinic anhydride are not dissolved; and hence succinic acid and succinic anhydride are easily separated by simple technique.
3. The choline chloride is moisture sensitive and not stable at higher temperature; therefore, removal of water is required. The use of cyclohexane as a solvent at 80°C temperature to remove water and cyclohexane is also better solvent for the condensation reaction of succinyl chloride with choline chloride.
4. The reaction of succinyl dichloride with choline chloride produces succinylcholine chloride along with unwanted maleic acid choline chloride as product related impurity. Removal of the maleic acid choline chloride impurity from the required product is very difficult by normal chemical purification as it

has the same properties of succinylcholine chloride. Therefore, the maleic acid choline chloride ester formed is converted to succinylcholine chloride by hydrogenation using palladium carbon and water as solvent. 5. Instead of removing the maleic acid choline chloride ester impurity of formula V, it is converted into succinylcholine chloride gives better yield of the product.
The following examples, which fully illustrate the practice of the preferred embodiments of the present invention, are intended to be for illustrative purpose only, and should not be considered to be limiting to the scope of the present invention.
EXAMPLES:
Example 1: Preparation of succinylcholine chloride from succinic acid.
A flask was charged succinic acid (100 gm, 0.846 mole), dichloromethane (1000 ml) and dimethylformamide (1 ml) at room temperature. Added slowly bxalyl chloride (257.3 gm, 2.0271 mole) into the reaction mass and stirred at room temperature for 18 hours. The completion of the reaction was monitored on HPLC. After completion of the reaction, the reaction mass was distilled out under vacuum at 25°C to 30°C. Charged cyclohexane and the reaction mass was stirred for 15 minutes and stripped out dichloromethane under vacuum at room temperature. Charged cyclohexane (500 ml) and stirred the reaction mass for 15 minutes, allowed to settle and the layers were separated. The upper cyclohexane layer was kept side and the lower layer was again extracted with cyclohexane (200 ml). Combined both the cyclohexane layers and kept aside to use in the next step.
In a flask charged choline chloride (126 gm, 0.904 mole) and cyclohexane (420 ml) and heated the reaction mass to reflux temperature (80°C), separated out water by Dean-Stark assembly, and maintained the reflux temperature until complete removal of water from choline chloride. Added the above cyclohexane layer containing succinyl chloride into the reaction mass and heated to 80°C (reflux temperature) for 12-14 hours. Then cyclohexane was distilled out under vacuum at 55°C to 60°C. After complete distillation, added isopropanol (350 ml) into the reaction mass and heated the reaction mass to 65°C

to 70°C. Then added purified water (7ml) and maintained the reaction mass at 65°C to 70°C for one hour. Stopped heating and cooled the reaction mass to 25°C to 30°C, and maintained the reaction mass for one hour at 25 to 30°C. Filtered the solid to get a wet solid of a mixture of succinylcholine chloride dihydrate and maleic acid choline chloride ester (186.1 gm).
HPLC purity = 89.71%; maleic acid choline chloride ester = 1.23%.
An autoclave was charged the wet solid (120 gm)., purified water (140 ml), 10% PH/C (6.0 gm) stirred at room temperature and applied hydrogen pressure (5 kg). Maintained reaction mass at 25°C to 30°C with (5 kg) H2 pressure. The reaction completion was monitored on HPLC. After completion of the reaction, the reaction mass was filtered through Hyflow bed and washed with water (60 ml). The filtrate was heated to 70°C and charged isopropanol (1970 ml). Stirred the reaction mass at 70°C for one hour. Cooled the reaction mass at 0°C to 5°C and filtered the solid mass to obtain 101.6 gm of wet cake of the product, which was dried at 50°C to 55°C to get 97.5 gm succinylcholine chloride dihydrate.
HPLC purity = 98.47%; Maleic acid choline chloride ester = 0.05%.
Example 2: Purification of succinylcholine chloride
In a flask charged the crude succinylcholine chloride obtained from example 1 (97gm. 0.268 mole) and purified water (145ml) and the reaction mass was stirred and heated at 50°C to 55°C. Charged charcoal (6 gm) and stirred for 30 minutes, filtered charcoal through Hyflow bed. The filtrate was heated at 50°C to 55°C and isopropanol (970 ml) was added up to precipitation of solid. Maintained at 50°C to 55°C for one hour, then the reaction mass was cooled gradually at room temperature. Filtered the solid to obtain the v/et product (78.1 .gm), which was dried at 50°C to 55°C to get succinylcholine chloride dihydrate (110.6 gm).
Yield-80.5%.
HPLC purity = 99.70%; Maleic acid choline chloride ester impurity = 0.03%.

Example 3:
An autoclave was charged 30 gm of the mixture of succinylcholine chloride dihydrate (purity: 95.40%) and maleic acid choline chloride ester (2.56%), methanol (300 ml), 10% Pd/C (3.0 gm). The mixture was stirred at room temperature and applied hydrogen at pressure of 5 kg. Maintained the reaction mass at 25°C to 30°C with hydrogen pressure of 5 kg. The reaction completion was monitored on HPLC, After the reaction completion., the reaction mass was filtered through Hyflow bed. Distilled out the filtrate to get 30 gm degassed mass. Charged purified water (30 ml), isopropanol (60 ml), heated at 70°C to 75 °C, and then added isopropanol (200 ml) up to solid precipitation observed. Maintained at 65°C to 70°C for one hour. The reaction mass was gradually cooled at 0°C to 10°C, filtered the solid and dried at 50°C to -55°C to obtain 26.6 m of succinylcholine chloride. Yield = 88.6%. HPLC purity = 98.49%; Maleic acid choline chloride ester impurity: Not detected.
Example 4: One-pot preparation of succinylcholine chloride from succinic acid.
In a flask charged succinic acid (50 gm, 0.423 mole), dichloromethane (500 ml) and DMF (0.5 ml) at room temperature, Added slowly oxalyl chloride (107.48 gm, 0.846 mole) at room temperature, stirred reaction mass at 25°C to 30°C fori 8 hours. The reaction completion was monitored on HPLC. Simultaneously, in another flask was charged choline chloride (118.23 gm, 0.846 mole) and cyclohexane (300ml). The reaction mass was heated to reflux (80°C). Separated out water by din and stark assembly. Reflux temperature was maintained up to complete removal of water of choline chloride. Cooled the reaction mass 25°C to 30°C .Then added above reaction mass of succinyl chloride. Reaction mass was heated slowly at 45°C to 50°C and distilled out dichloromethane completely, then again heated to 85°C for 12-14 hours. Then cyclohexane was distilled out at 55°C to 60°C under vacuum pressure. After complete distillation, isopropanol was added (500 ml) into the reaction mass and heated to 70°C. Added purified water (10 ml) to the reaction mass, and the reaction mass was maintained at 70°C for one hour. Then the reaction mass was cooled to 20°C to 25°C and the reaction mass was maintained at 20°C to 25°C for two hour. Then solid was filtered and the wet cake washed with

isopropanol to get 155 gm of wet cake of the mixture of succinylcholine chloride
dihydrate and maleic acid choline chloride ester.
HPLC purity = 81.28%; Maleic acid choline chloride ester impurity = 2.10%.
In autoclave charged the above wet cake of the mixture of succinylcholine chloride dihydrate and maleic acid choline chloride ester (155 gm), purified water (155 ml), 10% Pd/C (3.1gm). The reaction mixture was stirred at room temperature, applied hydrogen pressure of 5 kg, and maintained the reaction mass at 25°C to 30°C with hydrogen pressure of 5 kg. The reaction completion was monitored on HPLC. After the reaction completion, filtered the reaction mass through Hyflow bed and the Hyflow bed was washed with purified water (77.5 ml). The filtrate was heated at 65°C to 70°C and isopropanol (1550 ml) was added up to solid precipitation observed and maintained at 65°C to 70°C for one hour.-The reaction mass was cooled gradually at 25°C to 30°C, filtered the solid mass to obtain 132 gm of wet cake of the product, which was dried at 50°C to 55°C to get 95.6 gm of succinylcholine chloride dihydrate free from maleic acid choline chloride ester impurity. HPLC purity = 98.86%; Maleic acid choline chloride ester impurity = 0.02%.
Example 5: Purification of succinylcholine chloride
In a flask charged the crude succinylcholine chloride obtained in example 4 (90 gm, 0.249 mole) and purified water (135 ml) and the reaction mass was stirred and heated at 50°C to 55°C. Charged charcoal (5.4 gm) and stirred for 30 minutes, filtered charcoal through Hyflow bed. The filtrate was heated at 50°C to 55°C and isopropanol (900 ml) was added up to precipitation of the solid. Maintained the reaction mass at 50°C to 55°C for one hour, then the reaction mass was gradually cooled at 25°C to 30°C. Filtered the solid to obtain the wet product (92 gm), which was dried at 50°C to 55°C to get succinylcholine chloride dihydrate. (74,4 gm). Yield-82.6%. HPLC purity'= 99.49%; Maleic acid choline chloride ester impurity = 0.01%.

We claim,
1. A process for preparation of succinylcholine chloride dihydrate of formula I, wherein said process comprising the steps of

a) reacting succinic acid of formula II with a chlorinating agent in a suitable solvent
to obtain succinyl chloride of formula III;

b) treating the reaction mass with an organic solvent and extracting the succinyl
dichloride-organic solvent solution;
c) reacting the succinyl dichloride-organic solvent solution with choline chloride of
formula IV in an organic solvent to give a mixture of succinylcholine chloride
dihydrate of formula (I) and-maleic acid choline chloride ester of formula V;

d) isolating the mixture of succinylcholine chloride dihydrate of formula (I) and
maleic acid choline chloride ester of formula V in a solvent;
e) hydrogenation of the mixture of succinylcholine chloride dihydrate of formula (I)
and maleic acid choline chloride ester of formula V in presence of a catalyst in a
solvent; and


f) isolating the succinylcholine chloride dihydrate of formula I.
2. The process as claimed in claim 1, wherein the solvent used in the chlorination
reaction in step a) is selected from the group consisting of dichloromethane, 1,2-
dichloroethane, toluene, xylene or a mixture thereof.
3. The process as claimed in claim 1, wherein the chlorinating agent used in the
chlorination reaction in step a) is selected from the group consisting of oxalyl
chloride, thionyl chloride or phosphorus oxychloride.
4. The process as claimed in claim 1, wherein the organic solvent used for extraction
in step b) is selected from the group consisting of cyclohexane, toluene, xylene or
a mixture thereof, preferably cyclohexane.
5. The process as claimed in claim 1, wherein the organic solvent used for coupling
reaction in step c) is selected from the group consisting of cyclohexane, toluene,
xylene or a mixture thereof, preferably cyclohexane.
6. The process as claimed in claim 1, the coupling reaction is carried out at a
temperature of 70°C to 90°C, preferably at 80°C.
7. The process as claimed in claim 1, wherein the solvent used for isolation in step
d) is selected from the group consisting of isopropanol, n-propanol, n-butanol,
ethanol, methanol, water or a mixture thereof.
8. The process as claimed in claim 1, wherein the catalyst used for hydrogenation in
step e) is selected from the group consisting of palladium on carbon or Raney
nickel.
9. The process as claimed in claim 1, wherein the solvent used for hydrogenation in
step e) is selected from the group consisting of water, methanol, ethanol,
isopropanol or a mixture thereof.