DESC:FIELD OF THE INVENTION
The present invention relates to novel compounds of Formula I. Further, the present invention relates to use of compound of Formula I for the preparation of Cisatracurium salt.

.
Particularly, the present invention relates to a novel process for the preparation of Cisatracurium salt by using novel compounds of Formula I.

BACKGROUND OF THE INVENTION
Cisatracurium Besylate is chemically defined as [1R-[1a,2a(1'R*,2'R*)]]-2,2'-[1,5-pentanediylbis[oxy(3-oxo-3,1-propanediyl)]]bis[1-[(3,4-dimethoxyphenyl) methyl]-1,2,3,4-tetrahydro-6,7-dimethoxy-2-methylisoquinolinium dibenzenesulfonate.

Cisatracurium Besylate is approved in US with brand name Nimbex and Nimbex Preservative Free as an adjunct to general anesthesia to facilitate tracheal intubation in adults and in paediatric patients 1 month to 12 years of age and to provide skeletal muscle relaxation in adults during surgical procedures or during mechanical ventilation in the ICU and it is represented by compound of Formula II below:

Formula II
US 4,179,507 discloses Atracurium and describes a series of bis veratryl isoquinolinium quaternary ammonium salts, preferably among them is atracurium Besylate. Atracurium Besylate synthesis given in US'507 involves coupling of (±)-tetrahydropapaverine with 1,5-pentamethylene diacrylate and treatment of the resulting base with oxalic acid to give N, N'-4,10-dioxa-3,11-dioxotridecylene-1,13-bis-tetrahydropapaverine dioxalate. The dioxalate salt is converted to the free base, which is further treated with methyl benzenesulfonate to give Atracurium Besylate. Above process is shown schematically in Scheme-1.

Scheme-1:

US'507 further describes stereoisomerism of Atracurium Besylate may be partly controlled by controlling stereochemical configuration of tetrahydropapaverine base. US '507 does not describe separating stereoisomers from the mixture.

US5,453,510 discloses Cisatracurium Besylate and its preparation. US'510 describes preparation of (R)-tetrahydropapaverine from racemic tetrahydro-papaverine which is converted into a mixture of R and S diastereoisomer salts with the chiral amino acid i.e. N-acetyl-L-leucine resulting in the formation of a mixture of 83% of the R and 17% of the S diastereoisomer. Crystallization of the mixture from acetone affords 97% (R)-tetrahydropapaverine-N-acetyl-L-leucinate and 3% (S)-tetrahydropapaverine-N-acetyl-L-leucinate which is converted into (R)-tetrahydropapaverine base. The (R)-tetrahydropapaverine is subsequently reacted with 1,5-pentamethylene diacrylate followed by oxalic acid to afford the dioxalate salt of (1R,1'R)-2,2'-(3,11-dioxo-4,10-dioxatridecamethylene)-bis-(1,2,3,4-tetrahydro-6,7-dimethoxy-1-veratrylisoquinoline). Conversion of the dioxalate salt into the free base, followed by treatment with methyl benzenesulfonate, affords an aqueous solution of (1R,1'R)-Atracurium Besylate. Lyophilization results in a pale yellow solid that includes a mixture of three isomers, namely, 1R-cis,1'R-cis; 1R-cis,1'R-trans; 1R-trans,1'R-trans (hereinafter referred to as the “Atracurium Besylate mixture”) in a ratio of about 58:34:6 respectively. The Atracurium Besylate mixture is subjected to preparative HPLC column chromatography on silica using a mixture of dichloromethane, methanol and benzenesulfonic acid in the ratio of 4000:500:0.25 as the eluent. The fractions containing the required isomer are collected and washed with water. The dichloromethane solution is evaporated to dryness, the residue dissolved in water and the pH of the solution adjusted to 3.5-4.0 with an aqueous solution of benzenesulfonic acid. The aqueous solution is lyophilized to afford Cisatracurium Besylate possessing an isomeric purity of about 99%. Above process is shown schematically in scheme 2:

Scheme-2:

Process disclosed in US’510 is not suitable for industrial scale synthesis of Cisatracurium Besylate as it involves to many reaction steps and tedious process of purification involving lyophilization and use of preparative HPLC.

US 8,357,807 discloses stereoselective process for the preparation Cisatracurium salt by first preparing stereospecific tetrahydropapaverine salt which is used as starting material and reacting stereospecific tetrahydropapaverine salt with 1,5-pentanediol to produce Cisatracurium salt. Above process is shown schematically in scheme 3 below:

Process disclosed in US’807 does not provide pure cisatracurium besylate as product obtained in US’807 has only 80% HPLC purity,

Scheme-3:

wherein X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, and tartrate and Y is OR1 or NR2R3, wherein R1, R2 and R3 are the same or different and each is independently selected from hydrogen, alkyl, aryl, and heteroaryl.

US5,556,978 discloses a process for the preparation of Cisatracurium Besylate, using high performance liquid chromatography with a silica stationary phase and a non-aqueous mobile phase in the presence of a strong acid. The resulting product may contain less than 2% w/w of other geometrical and optical isomers based on the total weight of the relevant mixture. The above procedures suffer from several disadvantages. A major problem in the procedures is attributable to the HPLC purification step. The need for HPLC purification is undesirable in a large-scale operation because only relatively small amounts of product can be purified at a time, it is expensive, time-consuming and generates large quantities of waste, e.g., waste solvents.
In light of processes disclosed in prior art there is always a scope to develop new process which is commercially viable and having better purity of final API. Present invention discloses a process for preparation of Cisatracurium Besylate which is commercially viable and can be used for large-scale synthesis of Cisatracurium besylate and does not require HPLC purification/separation.

OBJECT OF THE INVENTION
The main object of the present invention is to prepare novel compounds of Formula I,
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate , camphor sulphonate and tartrate.

Another object of the present invention is to provide process for preparation of Cisatracurium or its salt of Formula IIa by using compound of Formula I.

Yet another object of the present invention is to provide process of purification of Cisatracurium or its salt of Formula IIa.
SUMMARY OF THE INVENTION
The main aspect of the present invention involves novel compounds of Formula I and its preparation,
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate , camphor sulphonate and tartrate.

In another aspect, present invention provides a process for Cisatracurium or its salt of Formula IIa using compound of Formula I.

In yet another aspect, the present invention provides a process for preparation of Cisatracurium or its salt comprising the steps of:
a) converting racemic tetrahydropapaverine of Formula III to R-tetrahydropapaverine hydrochloride of Formula IV;
,
b) treating R-tetrahydropapaverine hydrochloride of Formula IV obtained in step a) with a suitable base to give R-tetrahydropapaverine of Formula V;
,
c) reacting R-tetrahydropapaverine compound of Formula V with acrylonitrile in presence of suitable solvent, optionally in presence of acid catalyst, to give compound of Formula VI;
,
d) methylating the compound of Formula VI with suitable methylating agent to give compound of Formula I;
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate , camphor sulphonate and tartrate.
e) reacting compound of Formula I with 1,5-pentane diol in presence of suitable solvent and acid to give Cisatracurium or its salt;
; and optionally purifying Cisatracurium or its salt obtained in step e).

In one another aspect, the present invention provides a process for preparation of novel compound of Formula I comprising the steps of:
a) reacting R-tetrahydropapaverine of Formula V with acrylonitrile in presence of suitable solvent optionally in presence of acid catalyst to compound of Formula VI;
,
b) reacting compound of Formula VI obtained in step a) with suitable methylating agent to give compound of formula I;
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate , camphor sulphonate and tartrate.

In another aspect, the present invention provides a process for preparation of novel compound of Formula I comprising the steps of:
a) reacting compound of formula VI with suitable methylating agent to give compound of formula I;
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate, camphor sulphonate and tartrate.

In another aspect, the present invention provides a process for preparation of Cisatracurium or its salt, comprising the steps of:
a) reacting compound of Formula VI with suitable methylating agent to give compound of formula I;
,
b) where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate , camphor sulphonate and tartrate;
c) reacting compound of Formula I with 1,5-pentanediol in presence of acid to give Cisatracurium or its salt.

In another aspect, the present invention provides a process for preparation of Cisatracurium Besylate of Formula II, comprising the steps of:
a) reacting compound of formula VI with suitable methylating agent to give compound of formula I;
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate , camphor sulphonate and tartrate;
b) converting compound of Formula I to Cisatracurium Besylate.
In another aspect, the present invention provides a novel compound of Formula VI,
.
In another aspect, the present invention provides a process of preparing Cisatracurium Besylate by using compound of Formula VI.

Yet another aspect of the present invention, provides process for purification of Cisatracurium or its salt of Formula IIa.

DETAILED DESCRIPTION
Definitions:
The terms “salt” as used in the context of the present invention includes organic and inorganic acid addition salts. Inorganic acids are selected from, but are not limited to, hydrochloric acid, hydrobromic acid, sulphuric acid, phosphoric acid, carbonate; organic acids are selected from, but are not limited to, succinic acid, formic acid, acetic acid, diphenyl acetic acid, palmoic acid, triphenylacetic acid, caprylic acid, dichloroacetic acid, trifluoro acetic acid, propionic acid, butyric acid, lactic acid, citric acid, gluconic acid, mandelic acid, tartaric acid, malic acid, adipic acid, aspartic acid, fumaric acid, glutamic acid, maleic acid, malonic acid, benzoic acid, p-chlorobenzoic acid, dibenzoyl tartaric acid, oxalic acid, nicotinic acid, o-hydroxybenzoic acid, p-hydroxybenzoic acid, 1-hydroxy-naphthalene-2-carboxylic acid, hydroxynaphthalene-2-carboxylic acid, ethanesulfonic acid, ethane-1,2-disulfonic acid, 2-hydroxyethane sulfonic acid, methanesulfonic acid, (+)-camphor-10-sulfonic acid, benzenesulfonic acid, naphthalene-2-sulfonic acid, p-toluenesulfonic acid and the like. The inorganic salts may further includes alkali metal and alkaline earth metal salts such as sodium, potassium, barium, lithium, calcium, magnesium, rhodium, zinc, cesium, selenium, and the like or, benethamine, benzathine, diethanolamine, ethanolamine, 4-(2-hydroxyethyl)morpholine, 1-(2-hydroxyethyl)pyrrolidine, N-methyl glucamine, piperazine, triethanol amine or tromethamine and the like.

The term “suitable solvent” as used in the context of the present invention i.e. during reaction or purification process comprises of polar and non-polar solvent selected from, but not limited to, the group comprising of alcohols such as methanol, ethanol, 2-nitroethanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, hexafluoroisopropyl alcohol, ethylene glycol, 1-propanol, 2-propanol (isopropyl alcohol), 2-methoxyethanol, 1-butanol, 2-butanol, t-butyl alcohol, 2-ethoxyethanol, diethylene glycol, polyethylene glycol, 1-, 2-, or 3-pentanol, neo-pentyl alcohol, t-pentyl alcohol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, cyclohexanol, phenol, glycerol; halogenated hydrocarbons such as dichloromethane, 1,2-dichloroethane, trichloroethylene, perchloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, chloroform, carbon tetrachloride; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, glyme, diglyme, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, dibutyl ether, dimethylfuran, 2-methoxyethanol, 2-ethoxyethanol, anisole; ketone solvents such as acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; esters solvents such as ethyl acetate, n-propyl acetate, n-butyl acetate, iso propyl acetate, isobutyl acetate, t-butyl acetate, ethyl formate, methyl acetate, methyl propanoate, ethyl propanoate, methyl butanoate, ethyl butanoate; hydrocarbon such as toluene, xylene, hexane, n-heptane, n-pentane, anisole, ethyl benzene, cyclohexane and the like; nitriles such as acetonitrile, propionitrile, butanenitrile; sulfoxides such as dimethyl sulfoxide; formamides such as N-methyl formamamide; carbonates; water; and mixtures thereof.

The term “acid” or “acid catalyst” as used in the context of the present invention includes, but not limited to, organic acid such as oxalic acid, fumaric acid, acetic acid, formic acid, sulfonic acid and inorganic acid such as sulphuric acid, hydrochloric acid, hydrobromic acid, HI, methane sulfonic acid, benzene sulfonic acid, TMSCl, TBDMSCl, BF3 etherate, Boric acid and the like.

The terms “base” as used in the context of the present invention includes organic or inorganic base. Inorganic base is selected from but not limited to sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, potassium tert. butoxide, potassium acetate, sodium acetate, cesium carbonate, potassium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, lithium hydroxide, ammonium hydroxide, sodium methoxide, potassium methoxide, and the like. Organic base is selected from but not limited to pyridine, liquid ammonia, dimethyl amine, triethyl amine, ?,?-diisopropylethyl amine, l,8-Diazabicyclo[5.4.0]undec-7-ene, N-methyl morpholine, ?,?-dimethyl piperazine, N-methyl piperidine and the like.

In one embodiment, the present invention provides a process for preparation of Cisatracurium or its salt comprising the steps of:
a) converting racemic tetrahydropapaverine of Formula III to R-tetrahydropapaverine hydrochloride of Formula IV;

,
b) treating R-tetrahydropapaverine hydrochloride of Formula IV obtained in step a) with suitable base to give R-tetrahydropapaverine of Formula V;
,
c) reacting R-tetrahydropapaverine compound of Formula V with acrylonitrile in presence of suitable solvent, optionally in presence of acid catalyst, to give compound of Formula VI;
,
d) methylating compound of Formula VI with a suitable methylating agent to give compound of Formula I;
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, and tartrate,
e) reacting compound of Formula I with 1,5-pentane diol in presence of suitable solvent and acid to give Cisatracurim or its salt of Formula IIa;
; and
f) optionally purifying Cisatracurium or its salt obtained in step e).

In another embodiment when Cisatracurium or its salt is other than besylate then converting Cisatracurium or its salt to Cisatracurium besylate.

In another embodiment, present invention involves process for Cisatracurium or its salt with or without isolation and purification of intermediate compounds.

Resolution of tetrahydropapaverine is carried out by process known in prior art such as those disclosed in US5453510 and WO2007/091753 and other known similar process.

Compound of Formula VI is prepared by reacting R-tetrahydropapaverine with acrylonitrile optionally in presence of acid catalyst.

Methylation of compound of Formula VI is done using methylating agent in presence of suitable solvent.

Suitable methylating agent used for the synthesis of compound of Formula I can be selected from but not limited to dimethylcarbonate, dimethylsulfate, iodomethane, bromomethane, methyl triflate, methyl benzenesulfonate, trimethyloxonium tetrafluoroborate or methyl fluorosulfonate. Preferred methylating agents are iodomethane and methyl benzenesulfonate.

In another embodiment, the present invention provides a process for the purification of Cisatracurium or its salt, comprising the steps of:
a) providing a solution or dispersion of Cisatracurium salt in suitable solvent; and
b) isolating the pure Cisatracurium or its salt.

In yet another embodiment, the present invention provides a process for the purification of Cisatracurium or its salt, comprising the steps of:
a) providing a solution or dispersion of Cisatracurium or its salt in suitable solvent; and
b) adding suitable anti-solvent to solution of step a) and isolating pure Cisatracurium or its salt.

In another embodiment, the present invention provides a process for the purification of Cisatracurium or its salt, comprising the steps of:
a) providing a solution or dispersion of Cisatracurium or its salt in a ternary solvent; and
b) isolating the pure Cisatracurium or its salt.

In another embodiment ternary solvent used in the purification of Cisatracurium or its salt is selected from ether and halogenated solvent.

Solvents according to one embodiment of the invention are preferably selected from solvents having a solubility of Cisatracurium or its salt of about 50 mg/mL at room temperature and anti-solvent used must promote the precipitation of Cisatracurium or its salt once added to solution containing Cisatracurium salt. Preferably anti-solvent having a temperature of -200C to 500C, preferable 00C to 25°C, is added to the solution of Cisatracurium salt that is preferably kept at a temperature between -200C to reflux temperature, preferable between 00C to reflux temperature. The anti-solvent is preferably added slowly, i.e. over a period of 0.01 hour to 24 hours, more preferably over a period of 0.05 hour to 10 hours, even more preferably over a period of 0.1 hour to 5 hours. During the addition of the anti-solvent the mixture is preferably stirred.

Optionally, the solution may be concentrated by evaporation of solvent under reduced pressure.

In another embodiment, the present invention provides a process for the purification of Cisatracurium or its salt, by acid base treatment method.

In another embodiment, the present invention provides a process for the preparation of a stable amorphous form of Cisatracurium or its salt, comprising the steps of;
a) providing a solution of Cisatracurium or its salt; in one or more suitable solvent;
b) removing the solvent from the solution obtained in step a); and
c) isolating stable amorphous form of Cisatracurium or its salt.

In another embodiment, removal of solvent at any stage of preparation of amorphous form of Cisatracurium or its salt may include, but not limited to, solvent evaporation under atmospheric pressure or reduced pressure / vacuum such as a rotational distillation using Büchi® Rotavapor®, flash evaporation, rotational dying, agitated nutsche filter drying, spray drying, freeze drying, thin film drying, agitated thin film drying, rotary vacuum paddle dryer (RVPD), lyophilization, and the like. In preferred embodiment, the solvent may be removed under reduced pressures and at a temperature of less than about 100°C, less than about 60°C, less than about 40°C, less than about 20°C, less than about 0°C, less than about -20°C, less than about -40°C, less than about -60°C, less than about -80°C, or any other suitable temperatures.

In another embodiment, the present invention provides a solid form of Formulae VI and Formula I. More preferably present invention provides a crystalline and amorphous form of Formulae VI and Formula I.

In another embodiment, the present invention provides a compounds of Formulae VI and Formula I having a purity of greater than 99.5%.

In another embodiment, the amorphous form of Cisatracurium or its salt is characterized by particle size distribution wherein d90 is less than about 500 µm, preferably less than about 100 µm, and most preferably less than about 10 µm.

In another embodiment, the present invention provides Cisatracurium or its salt, having isomeric purity more than 99.5% as measured by HPLC. Preferred embodiment involves Cisatracurium or its salt, having isomeric purity of 99.9% or more as measured by HPLC.

In another embodiment, Cisatracurium or its salt synthesised using process of the present invention have impurity less than about 0.2% by area percentage of HPLC. In particular, less than about 0.1% by area percentage of HPLC. More particular, not in detectable amount by area percentage of HPLC.

In another embodiment, present invention provides a solid pharmaceutical composition of Cisatracurium or its salt and one or more pharmaceutically acceptable carrier.

The pharmaceutical composition according to present invention can be formulation in any dosage form i.e. solid oral such as tablet, capsules, granules, beads, pellets, powder or the like; liquid dosage form such as solution/suspension for oral administration; ophthalmic solution or dispersion; injectable solution or dispersion; lyophilised powder for injection; spray dried powder and the like.

In another embodiment, present invention provides a pharmaceutical composition of Cisatracurium salt, wherein Cisatracurium or its salt is having particle size distribution d90 less than about 100 µm, preferably less than about 50 µm and most preferably less than about 10 µm.

According to yet another embodiment, the present invention provides a stable injectable composition which is in the form of solution, emulsion or suspension.

Certain specific aspects and embodiments of the present application will be explained in details with reference of the following examples, which are provided only for purposes of illustration and should not able constructed as limited the scope of the application in any manner.

EXAMPLES
Example 1: Preparation of Cisatracurium Besylate
a) Preparation of (R)-tetrahydropapaverine
Racemic tetrahydropapaverine free base (50gm) and Isopropanol (75 mL) was charged into a RBF at 25-30?. Leucine (0.5 to 1 M. eq) was added and L-Leucine salt of R-tetrahydropapaverine was isolated. Obtained salt was dissolved in water (50 mL) and treated with aqueous ammonia to obtain of R-tetrahydropapaverine. To R-tetrahydropapaverine was added absolute EtOH (6 volumes) and aqueous 37% HCl (1.05 eq) was added at room temperature. The solution was kept under stirring and after 10 minutes the precipitation of the compound started. After 1 hour at room temperature, the precipitate was filtered, washed with EtOH (1 volume) and dried in oven under vacuum at 70oC to get hydrochloride salt of R- tetrahydropapaverine.

b) Preparation of compound of Formula VI
(R)-tetrahydropapaverine hydrochloride (50gm) obtained in step a) was treated with equivalent amount of Aq. NaOH to obtain free base of (R)-tetrahydropapaverine. To (R)-tetrahydropapaverine was added acrylonitrile (60 ml) and acetic acid (2.5 g). Resulting mass was heated at 40- 50oC, stirred for 10 hours and distilled at 70oC. diisopropyl ether (2 x 50mL) was added and further distilled under vacuum. diisopropyl ether (500 mL) was added and refluxed for 1-2 hours and gradually cooled the reaction mass to room temperature. Stirred the reaction mass for 6 hours, filtered, washed with diisopropyl ether and dried to get the desired compound. wt 48.5 gm.

c) Preparation of compound of Formula I (X-= Besylate)
Compound of Formula VI (50 gm) and methyl benzenesulfonate (250 ml) was charged in to RBF. Reaction mass was heated to 75oC and stirred for 24 hours at 70-75oC. Reaction mass was gradually cooled to room temperature. Added water (500 ml), methyl tert-butyl ether (400 ml) and separated the aqueous layer. Aqueous layer was taken and washed with methyl tert-butyl ether (150 ml). Extracted aqueous layer with dichloromethane (250ml x 2) and distilled under vacuum at 40oC to obtain quaternary besylate compound of Formula I. wt. 60gm.

d) Preparation of Cisatracurium Besylate:
Compound of Formula I (60gm) and dichloromethane (650 ml) was taken in round bottom flask. Cooled to 5-15oC. HCl gas was passed along with addition of 1,5-pentane diol (10.5gm) slowly. Stirred the reaction mass for 4hours at 5-15oC. Water (250ml) was added and separated organic layer. Organic layer was distilled and dried to obtain Cisatracurium Besylate. wt 55g.

e) Purification of Cisatracurium Besylate
Cisatracurium Besylate (55g) was dissolved in water and added ethyl acetate and stirred to separate the layer. Aqueous layer thus obtained was extracted with dichloromethane and then distilled organic layer under vacuum and recrystallized using isopropyl ether to obtained the pure product having isomeric purity of 99.5%.

Example 2: Preparation of Cisatracurium Besylate
a) Preparation of R-THP nitrile (Compound VI)
R-Tetrahydropaverine (THP) hydrochloride (Compound IV; 1 Kg) and water (2L) was charged into a round bottom flask and stirred. Ammonia solution (2 L) was added to the reaction mass and stirred. Dichloromethane (2 x 3L) was added to the reaction mixture and stirred. Dichloromethane layer extracted from reaction mixture was distilled out completely. The obtained material (viscous material) dissolved in acrylonitrile (1.25 L) and added acetic acid (50mL) and stirred. The mixture was heated at 55-65°C and stirred for 12-16 hours. The reaction mixture is distilled completely and degassed to obtain reaction mass. Isopropyl ether (10 L) was added to the obtained reaction mass and refluxed for 2-3 hours. The reaction mass is cooled to 25-30ºC and stirred for 3-4 hours. Reaction mass was filtered, washed the wet cake with isopropyl ether (2x0.5L), suck dried and dried the material under vacuum for 6-8 hours at 45-50°C.
Yield: >95%; Purity: 99%.

b) Preparation of R-THP quaternary nitrile (Compound I)
R-THP nitrile compound of Formula VI (493g) and methyl benzene sulphonate ester (1.5 L) was charged in to a round bottom flask. The reaction mass was heated to 45-50°C under stirring and stirred at 45-50°C for 18-24 hours. Reaction mass was extracted with toluene (2x2.5L) and water (5L). Aqueous layer containing R-THP quaternary nitrile was extracted with dichloromethane (2x2.5L). Organic layer obtained was distilled out completely and degassed to obtain compound of formula I. Compound of Formula I obtained was charged in to a round bottom flask containing 2-methoxy ethanol (10L) and isopropyl alcohol (25L). The reaction mixture was heated to 50-55ºC, cooled to 20-30ºC and filtered to obtain 200g of cis-R-THP quaternary nitrile (Compound I) in >99.5% purity (by HPLC).
c) Preparation of Cisatracurium Besylate
Pentane 1,5-diol (5g) was dissolved in dichloromethane (500 mL) under continuous purging of HCl gas and cooled to 0-5°C. Solution of R-THP quaternary nitrile compound of formula I (50g) dissolved in dichloromethane (500mL) was added to above mixture in 2-4 hours. The reaction mas obtained after completion of reaction was quenched using water (200 mL). Organic layer was separated, washed with water (10x250 mL) and distilled completely to obtain white solid.

The obtained solid above was stirred in mixture of dichloromethane (100 mL), MTBE (750 mL) and methyl THF (250 mL) at 20-30ºC and filtered. The obtained material was dissolved in aqueous solution of benzene sulphonic acid of pH 3-5 (preferably pH 3.5-3.8) and lyophilized to give 22g while solid of purity >99% (by HPLC).

Example 3: Preparation of amorphous form of Cisatracurium Besylate
Cisatracurium Besylate (1.0g) was dissolved in isopopanol (50 mL) at 25°C and stirred at 60oC to get the reaction mixture for 4-6h. Lyophilized the solution to get title compound.

Example 4: Purification of Cisatracurium Besylate
Cisatracurium Besylate (55g) was dissolved in water and added n-pentane and stirred to separate the layer. Aqueous layer thus obtained was extracted with dichloromethane and then distilled organic layer under vacuum and recrystallized using ethanol to obtained the pure product having isomeric purity of 99.5%.

Example 5: Purification of Cisatracurium Besylate
Cisatracurium Besylate (55g) was dissolved in water and added n-heptane and stirred to separate the layer. Aqueous layer thus obtained was extracted with dichloromethane and then distilled organic layer under vacuum and recrystallized using isopropyl ether to obtained the pure product having isomeric purity of 99.5%.

Example 6: Purification of Cisatracurium Besylate
Cisatracurium Besylate (55g) was dissolved in water and added cyclohexane and stirred to separate the layer. Aqueous layer thus obtained was extracted with dichloromethane and then distilled organic layer under vacuum and recrystallized using isopropanol to obtained the pure product having isomeric purity of 99.5%.
,CLAIMS:WE CLAIM:
1. A process for preparation of Cisatracurium or its salt comprising the steps of:
a) methylating compound of Formula VI with a suitable methylating agent to give compound of Formula I;
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, tartrate, and
b) converting compound of Formula I to Cisatracurium or its salt.

2. The process as claimed in claim 1, wherein said process further comprising the steps of:
a) reacting compound of Formula I with 1,5-pentane diol in presence of suitable solvent and acid to give Cisatracurim or its salt of Formula IIa;

wherein X- is as defined above; and
b) optionally purifying Cisatracurium or its salt obtained in step a).

3. A process for preparation of Cisatracurium or its salt comprising the steps of:
a) converting racemic tetrahydropapaverine of Formula III to R-tetrahydropapaverine hydrochloride of Formula IV;

,
b) treating R-tetrahydropapaverine hydrochloride of Formula IV obtained in step a) with suitable base to give R-tetrahydropapaverine of Formula V;
,
c) reacting R-tetrahydropapaverine compound of Formula V with acrylonitrile in presence of suitable solvent, optionally in presence of acid catalyst, to give compound of Formula VI;
,
d) methylating compound of Formula VI with a suitable methylating agent to give compound of Formula I;
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, and tartrate,
e) reacting compound of Formula I with 1,5-pentane diol in presence of suitable solvent and acid to give Cisatracurim or its salt of Formula IIa;
; and
f) optionally purifying Cisatracurium or its salt obtained in step e).

4. The process as claimed in claims 1 and 3, wherein said methylating agent is selected from dimethylcarbonate, dimethylsulfate, iodomethane, bromomethane, methyl triflate, methyl benzenesulfonate, trimethyloxonium tetrafluoroborate or methyl fluorosulfonate.

5. The process as claimed in claims 2 and 3, wherein said solvent is selected from the group comprising of methanol, ethanol, ethylene glycol, 1-propanol, 2-propanol (isopropyl alcohol), 2-methoxyethanol, 1-butanol, 2-butanol, t-butyl alcohol, 2-ethoxyethanol, diethylene glycol, polyethylene glycol, cyclohexanol, glycerol; dichloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, chloroform, carbon tetrachloride; diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, dibutyl ether, dimethylfuran, 2-methoxyethanol, 2-ethoxyethanol, anisole; acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; ethyl acetate, n-propyl acetate, n-butyl acetate, iso propyl acetate, isobutyl acetate, t-butyl acetate, ethyl formate, methyl acetate, methyl propanoate, ethyl propanoate, methyl butanoate, ethyl butanoate; toluene, xylene, hexane, n-heptane, n-pentane, anisole, ethyl benzene, cyclohexane; acetonitrile, propionitrile, butanenitrile; dimethyl sulfoxide; N-methyl formamamide; water; and mixtures thereof.

6. The process as claimed in claims 2 and 3, wherein said acid or acid catalyst is selected from oxalic acid, fumaric acid, acetic acid, formic acid, sulfonic acid, sulphuric acid, hydrochloric acid, hydrobromic acid, hydrogen iodide, methane sulfonic acid, benzene sulfonic acid, or boric acid.

7. A process of purification of Cisatracurium or its salt prepared as per the process claimed in claims 1 to 3, comprising the steps of:
a) providing a solution of Cisatracurium or its salt in a solvent selected from alcohol, hydrocarbon, halogenated, ether, water or mixture thereof; and
b) isolating the pure Cisatracurium or its salt.

8. The process as claimed in any of the preceding claims, wherein said Cisatracurium or its salt is isolated in stable amorphous form having a purity of greater than 99.5%.

9. Compound of Formula I,
,
where X- is an anion selected from chloride, bromide, iodide, tetrafluoroborate, sulfate, hydrogensulfate, methanesulfonate, benzenesulfonate, p-toluenesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, oxalate, phthalate, mandelate formate, camphor sulphonate and tartrate.

10. Compound of Formula VI,
.

Dated this, 6th Day of May, 2022 For Mankind Pharma Ltd.

Dr. Anil Kumar
Chief Scientific Officer