FORM 2
PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention
"Process for preparation of Palonosetron"
2. Applicant(s)
Name Nationality Address
USV Limited Indian company incorporated Arvind Vitthal Gandhi Chowk, B.S.D. Marg, Govandi,
under Companies Act, 1956 Mumbai - 400 088, Maharashtra, India
3. Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention:
The present invention relates to a process for the preparation of Palonosetron or pharmaceutically acceptable salt thereof, in particular Palonosetron hydrochloride (I).

Background of invention:
Palonosetron, chemically known as (3aS)-2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2.3,3a,4,5,6-hexahydro-l-oxo-lH-benz[de]isoquinoline, is a serotonin subtype 3 (5-HT3) receptor antagonist with a strong binding affinity for this receptor and little or no affinity for other receptors. Palonosetron is commercially marketed as Palonosetron hydrochloride by Helsinn under the brand name of Aloxi®. Aloxi® injection is a sterile, clear, colorless, non-pyrogenic, isotonic, buffered solution for intravenous administration. Aloxi® is available as 5 ml single use vial or 1.5 ml single use vial. Each 5 ml vial contains 0.25 mg Palonosetron base as hydrochloride and each 1.5 ml vial contains 0.075 mg Palonosetron base as hydrochloride. It is indicated for prevention of acute and delayed nausea and vomiting associated with initial and repeat courses of moderately/highly emetogenic cancer chemotherapy as well as for prevention of post operative nausea and vomiting. The recommended dose of Aloxi is a single 0.25mg l.V. dose administered over 30 seconds and dosing should occur approximately 30 minutes before the start of chemotherapy or a single 0.075 mg I.V.dose administered over 10 seconds immediately before the induction of anaesthesia.
Palonosetron has two stereogenic centers and exists as four stereoisomers (3aS,2S), (3aR,2R), (3aS,2R) and (3aR,2S). Among the four stereoisomers, only (3aS,2S) possesses pharmacological activity. Palonosetron belongs to a class of drugs called

antiemetics. Nausea and vomiting may be caused by the release of serotonin with the use of some chemotherapy agents. Post operative nausea and vomiting is influenced by multiple patient, surgical and anaesthesia related factors and is triggered by release of 5-HT in a cascade of neuronal events involving both the central nervous system and the gastrointestinal tract. The 5-HT3 receptor has been demonstrated to selectively participate in the emetic response. This serotonin binds to cell receptors called 5-HT3 which stimulates the vomiting reflex. Palonosetron helps to prevent nausea and vomiting by blocking 5-HT3 receptors so that the serotonin is not able to bind to the receptor and initiate the vomiting reflex.
US5202333 discloses the process for the preparation of Palonosetron HC1 by reduction of (S)-2-(l-azabicyclo[2.2.2]oct-3-yl)-2,4,5,6-tetrahydrobenz[de]isoquinolin-l-one of formula II using 20% palladium hydroxide on carbon in presence of acetic acid and perchloric acid at 85°C and 50 psi for 24 hours to obtain a diastereomeric mixture of (S)-2-(]-azabicyc]o[2.2.2]oct-3-y])-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoqumolm-l-one.

The process disclosed in US5202333 suffers from the following drawbacks,
a) Purity of the diastereomeric mixture is not mentioned.
b) High temperature for hydrogenation is used.
c) Strong acid such as perchloric acid is used.
WO9601824 discloses a process for preparation of Palonosetron which involves hydrogenation of compound of formula II in the presence of THF and 10% Pd/C at ambient temperature. The reaction requires more than 5 days for completion. The

mixture is allowed to stand without stirring under hydrogen atmosphere for 2 hours. After hydrogenation, the catalyst is filtered and the filtrate is concentrated to reduce the volume. The concentrated solution is then treated with isopropyl alcohol and conc. HC1 to provide a diastereomeric mixture containing 97% of desired isomer. The hydrogenation requires more than 5 days for completion. In the process of the present invention, the hydrogenation reaction is completed in about 72 hours.
WO2009136405 discloses a process for preparation of highly pure Palonosetron base comprising the steps of,
a) dissolving (S)-2-(l -azabicyc]o[2.2.2]oct-3-yl)-2,4,5,6-tetrahydro-lH-benz[de] isoquinolin-1-one acid addition salt in lower aliphatic alcohol at room temperature;
b) hydrogenating this solution in the presence of palladium catalyst at 25-75°C for 24 hours;
c) filtering the catalyst and evaporating the solvent under reduced pressure to get the residue of racemic mixture of Palonosetron acid addition salt;
d) leaching the residue of racemic mixture of Palonosetron acid addition salt obtained from step c) with aqueous C1-C4 aliphatic alcohol at ambient temperature;
e) recrystallizing the Palonosetron acid addition salt from step d) in a suitable solvent or a solvent mixture;
f) isolating the pure Palonosetron acid addition salt by filtration;
g) treating the pure Palonosetron acid addition salt with a base and extracting the base into an organic solvent;
h) distilling of solvent under reduced pressure to get Palonosetron base; i) purifying Palonosetron base from a solvent to get chemically and enantiomerically pure Palonosetron base. The disadvantage of this process is that the yield of the desired product is low.
US7737280 discloses a process for preparation of Palonosetron salt, especially hydrochloride comprising reacting compound of formula-II in salt form in an alcohol

with not more than 20% by weight of a hydrogenation catalyst per gram of compound of formula-II in salt form to obtain Palonosetron hydrochloride. It further discloses that an anti-oxidizing agent in alcohol may be added to the reaction mixture before recovering Palonosetron salt, thus, preventing Palonosetron salt to convert back to compound of formula-II, from which it is difficult to separate. Preferably, the oxidizing agent is sulphur compound such as sulphur dioxide, bisulfites or thiosulfates. Use of sulphur dioxide on an industrial scale is not advisable since sulphur dioxide is hazardous, corrosive and difficult to handle.
US20080058367 discloses a reprocessing process for purification of Palonosetron or its salt having 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4.5,6-tetrahydro-lH-benz[de] isoquinolin-l-one hydrochloride content more than 1%, which process comprises reducing Palonosetron or its salt in the presence of a suitable reducing agent; and optionally, recrystallizing the obtained compound using alcohol.
There still exists a need to develop a simple, economical and commercially viable process for the preparation of Palonosetron or pharmaceutically acceptable salt thereof, in particular Palonosetron hydrochloride. The present invention provides a simple, cost-effective and industrially viable process for preparation of Palonosetron or pharmaceutically acceptable salt thereof substantially free of compound of formula II and/or undesired isomers.
Object of the invention:
An object of the present invention is to provide a simple, cost effective and industrially viable process for the preparation of Palonosetron or its pharmaceutically acceptable salt, in particular Palonosetron hydrochloride.
Another object of present invention is to provide Palonosetron or pharmaceutically acceptable salt thereof substantially free of compound of formula II and/or undesired isomers.

Summary of the invention:
According to one aspect of the present invention, there is provided a process for preparation of Palonosetron or pharmaceutically acceptable salt thereof, comprising the steps of,
a) subjecting 2-[(S)-l -Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-1 H-benz[de] isoquinolin-1-one or salt thereof to reduction to obtain a reaction mixture;
b) filtering the reaction mixture obtained in step a) under reducing conditions to obtain a diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one; and
c) converting the obtained diastereomeric mixture of 2-[(S)-l-azabicyclo [2,2.2]oct-3 -yl] -2,3,3a,4,5,6-hexahydro-1 H-benz[de] i soquinoline-1 -one to Palonosetron or pharmaceutically acceptable salt thereof.
Preferably, said 2-[(S)-l-AzabicycIo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-beriz [de] isoquinolin-1-one is in the form of acid addition salt and wherein said reduction is carried out in presence of catalyst selected from palladium/carbon, platinum/carbon or oxides thereof at a hydrogen pressure of about 8 to 12 Kg/cm2 and a temperature of 40 to 60°C.
Preferably, said filtration is carried out using in-line filtration set-up under hydrogen atmosphere and filtrate is collected in a flask containing a hydrogen transfer agent selected from ammonium formate, isopropanol or formic acid.
Preferably, said 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz [de] isoquinolin-1-one or salt thereof has chemical purity of more than 98%.
Another aspect of the present invention provides a process for conversion of diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl)-2,3,3a,4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one to Palonosetron or pharmaceutically acceptable salt thereof, comprising the steps of,
a) subjecting the diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one to salt formation so as

to enhance the content of 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one to more than 95%; and b) optionally, purifying the 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one salt by repeated crystallization,
Preferably, said salt formation is carried out by treating the diastereomeric mixture of 2-[(S)-1 -azabicyclo[2.2.2]oct-3-yl]-2,3,3a.4,5,6-hexahydro- 1H-benz[de]isoquinoline-1 -one with an acid forming agent selected from HC1, HBr, maleic acid, fumaric acid, succinic acid, methanesulfonic acid, ethanesulfonic acid or the like in presence of solvent selected from methanol, ethanol, isopropyl alcohol or mixture thereof.
Preferably, said salt is HC1 and diastereomeric mixture obtained in step a) has about 96.3% of 3aS, 2S isomer and about 3.6% of undesired 3aR, 2S isomer.
Another aspect of the present invention provides a process for preparation of 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de] isoquinolin-1-one or salt thereof comprising the steps of,
a) treating (S)-3-aminoquinuclidine or salt thereof with 5,6,7,8-tetrahydro-l-naphthalene carboxylic acid or derivative thereof to obtain (S)-N-(l-Azabicyclo[2.2.2]oct-3-yl)-5,6,7,8-tetrahydro-l-napthalenecarboxamide;
b) lithiation of (S)-N-(l-AzabicycIo [2.2.2] oct-3-yI)-5,6,7,8-tetrahydro-l-napthaienecarboxamide to obtain the lithiated product and subjecting the lithiated product to formylation, dehydration and optionally, salt formation to obtain 2-[(S)-1-Azabicyclo[2.2.2]oct-3-y]]-2,4,5,64etrahydro-lH-benz[de] isoquinolin-1-one or salt thereof; and
c) converting said 2-[(S)-I-AzabicycIo[2.2.2]oct-3-yI]-2,4,5,6-tetrahydro-lH-benz [de]isoquinolin-l-one or salt thereof to Palonosetron or pharmaceutical^ acceptable salt thereof.
Another aspect of the present invention provides a process for purification of Palonosetron hydrochloride comprising the steps of,
a) dissolving said Palonosetron hydrochloride in a solvent selected from

isopropanol, ethanol, methanol, water or mixture thereof to obtain a solution;
b) optionally, treating the obtained solution with charcoal; and
c) isolating pure Palonosetron hydrochloride.
Preferably, Palonosetron hydrochloride obtained by the process of the present invention has chemical purity of more than 99.5%.
Brief description of the Drawings:
Fig. 1; X-ray diffraction pattern of Palonosetron base obtained by the process of the present invention.
Fig. 2: X-ray diffraction pattern of Palonosetron hydrochloride obtained by the process of the present invention.
Detailed description of the invention:
The present invention relates to a simple, cost effective and industrially viable process for the preparation of Palonosetron or its pharmaceutically acceptable salt, in particular Palonosetron hydrochloride.
One embodiment of the present invention provides a process for preparation of Palonosetron or pharmaceutically acceptable salt thereof comprising the steps of,
a) subjecting 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz [de] isoquinolin-l-one or salt thereof to reduction to obtain a reaction mixture;
b) filtering the reaction mixture obtained in step a) under reducing conditions to obtain a diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3.3a,4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one; and
c) converting the obtained diastereomeric mixture of 2-[(S)-l-azabicyclo [2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-beriz[de]isoquinoline-l-one to Palonosetron or pharmaceutically acceptable salt thereof.
Pharmaceutically acceptable salt is selected from hydrochloride, hydrobromide, maleate, fumarate, succinate, mesylate, esylate or the like, preferably hydrochloride.
In a preferred embodiment, the process for preparation of Palonosetron hydrochloride

comprises the steps of,
Reducing 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de]iso
quinolin-1-one or salt thereof to obtain a diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a.4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one: A solution of 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de] isoquinolin-1-one acid addition salt is charged into a hydrogenation flask. If required, alcoholic HC1 is added to adjust the pH in the range of 3 to 5, preferably 3.5 to 4.5. A slurry of 10% Pd/C in acetic acid is added to the hydrogenation flask. The reaction is carried out under hydrogen pressure of about 8 to 12 Kg/cm2, preferably 10 Kg/cm2 at temperature of 40 to 60°C, preferably 50 to 55°C. The progress of the reaction is monitored by HPLC. When the concentration of 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,-tetrahydro-lH-benz[de]isoquinolin-l-one acid addition salt is not more than 0.2%, the mixture is filtered through hyflo bed using in-line filtration set-up under hydrogen atmosphere and the filtrate is collected in a flask containing a reducing agent such as hydrogen transfer agent and alcohol. The filtrate is concentrated under vacuum to obtain a residue. Water is added to the residue and the mixture is cooled to 5 to 20°C, preferably 10 to 15°C. The mixture is basified till pH 9 is achieved. The temperature of the mixture is raised to about 15 to 25°C, preferably 20°C and the mixture is stirred at the same temperature for about 2 to 5 hours, preferably for 3 hours. The reaction mixture is filtered. The residue is washed with water and dried to obtain a diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4.5.6-hexahydro-lH-benz[de]isoquinoline-l-one (Palonosetron base). This diastereomeric mixture contains about 61% of the desired isomer and 39% of undesired isomer.
Alcohol used is selected from C1-C4 alcohol such as methanol, isopropyl alcohol or ethanol, preferably methanol or isopropyl alcohol. Suitable catalyst used for the hydrogenation is selected from palladium/carbon, platinum/carbon or oxides thereof supported on various supports such as carbon, alumina and the like. Base is selected from ammonia, sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, calcium hydroxide, cesium hydroxide or mixture thereof. Hydrogen transfer agent is selected from ammonium

formate, isopropanol or formic acid, preferably ammonium formate.
It is reported in WO2009136405 that when the experimental procedure of US5202333 and WO9601824 are repeated, difficulties are encountered in getting desired product in reproducible yield and purity. The hydrogenation reaction is never complete and the unreacted starting material (compound of formula-II) is always present to the extent of 7 to 10%. Compound of formula-II is difficult to remove by crystallization process as the solubility properties of this compound and Palonosetron HC1 are very close.
Palonosetron or its salt has a tendency to dehydrogenate in presence of catalyst once the hydrogen atmosphere is removed. The catalyst acts as a dehydrogenation catalyst in absence of hydrogen atmosphere. Palonosetron or its salt has a tendency to convert back to compound of formula-II. The inventors of the present invention have surprisingly found that when the filtration of the hydrogenated mixture is carried out under hydrogen atmosphere, the conversion of Palonosetron or its salt to compound of formula-II is prevented. In the presence of Pd/C, ammonium formate decomposes to hydrogen, carbon dioxide and ammonia. This hydrogen gas is adsorbed on the surface of the palladium metal, thereby maintaining hydrogen atmosphere and thus preventing the dehydrogenation of Palonosetron.
It is surprisingly found that purity of compound of formula-II also plays an important role in controlling the reverse reaction .i.e., dehydrogenation of Palonosetron or salt thereof to compound of formula-II. Compound of formula-II obtained by the process of the present invention has a purity of more than 98%.
Palonosetron base obtained according to present invention is characterized by a X-ray diffraction pattern as represented in Fig. 1. It is further characterized by peaks expressed as 2-theta values at about 7.07, 10.80, 11.37, 12.93, 15.10, 15.50, 17.28, 17.80,20.55,21.64, 21.89,22.15,22.48, 23.77, 24.67, 30.44 and 33.80 degrees.
Conversion of diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4.5,6-hexahydro-lH-benz[de] isoquinoline-1-one to Palonosetron or

pharmaceutically acceptable salt thereof:
The obtained diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one is subjected to salt formation by treating the diastereomeric mixture with an acid in presence of alcohol under nitrogen atmosphere. Preferably, alcoholic solution of HC1 is used. The mixture is heated at reflux. If required, water is added till dissolution. The hot solution is filtered through hyfio bed. The filtrate is distilled to remove the solvent. The concentrated solution is cooled to 25 to 30°C and stirred for 40 to 80 min, preferably for 60 min. The mixture is further cooled to 10 to 20°C, preferably 15°C and stirred for 40 to 80 min, preferably 60 min and filtered. The solid obtained is washed with an alcohol and dried to obtain a diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl)-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinoline-l-one (Palonosetron hydrochloride). This diastereomeric mixture has about 96.3% of the desired isomer and about 3.6% of the undesired isomer. Thus the content of the desired isomer is enhanced to more than 95%.
Alcohol used is selected from C1-C4 alcohol such as isopropyl alcohol, methanol or ethanol, preferably isopropyl alcohol. Acid is selected from HC1, HBr, maleic acid, fumaric acid, succinic acid, methane sulfonic acid, ethane sulfonic acid or the like.
Purification of Palonosetron hydrochloride comprises the steps of:
a) dissolving Palonosetron hydrochloride in solvent such as alcohol selected from isopropyl alcohol, methanol, ethanol. water or mixture thereof to obtain a solution;
b) optionally, treating the obtained solution with charcoal; and
c) isolating pure Palonosetron hydrochloride having the desired isomeric purity.
Palonosetron hydrochloride and alcohol are charged under nitrogen atmosphere in a reaction vessel followed by addition of water. This mixture is heated till complete dissolution is achieved. The hot mixture is stirred for 10 to 20 min, preferably for 15 min. The mixture is concentrated and the concentrated mixture is cooled to 25 to 30°C and stirred for 40 to 80 min, preferably 60 min. The mixture is further cooled to 10 to

20°C, preferably 15°C and stirred for another 40 to 80 min, preferably for 60 min to obtain a solid. The solid is filtered, washed and dried to obtain Palonosetron hydrochloride having purity of more than 99%, Purity of the desired isomer is enhanced by repeated crystallization.
Pure Palonosetron hydrochloride obtained according to present invention is substantially free of undesired compounds and has chemical purity of more than 99.5% with all known impurities below 0.15% and unknown impurities below 0.1%.
Palonosetron hydrochloride obtained according to the present invention is characterized by X-ray powder diffraction pattern as shown in Fig. 2. Palonosetron hydrochloride is further characterized by peaks expressed as 2-theta values at about 10.43, 12.10, 14.45, 15.77,16.92,17,23,19.66,20.91, 23.72,24.07,24.77 and 25.36 degrees.
Another embodiment of the present invention provides Palonosetron or pharmaceutically acceptable salt thereof substantially free of compound of formula II and undesired isomers.
Another embodiment of the present invention provides a process for preparation of Palonosetron or pharmaceutically acceptable salt thereof comprising the steps of,
a) treating (S)-3-aminoquinuclidine or salt thereof, in particular its dihydrochloride with 5,6,7,8-tetrahydro-l-naphthalene carboxylic acid or derivative thereof to obtain (S)-N-(l-Azabicyclo[2.2.2]oct-3-yl)-5,6,7,8-tetrahydro-l-napthalene carboxamide;
b) Lithiation of (S)-N-(l-Azabicyclo[2.2.2]oct-3-yl)-556,7;8-tetrahydro-l-napthalene carboxamide to obtain the lithiated product and subjecting the lithiated product to formylation, dehydration and optionally, salt formation to obtain 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2!4,5,6-tetrahydro-lH-benz[de] isoquinolin-1-one or salt thereof; and
c) converting the obtained 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de]isoquinolin-l-one or salt thereof to Palonosetron or pharamceutically acceptable thereof.

Acid derivative is selected from acid halides such as acid chloride or acid bromide, ester, anhydride or the like, preferably acid chloride.
In a preferred embodiment, the process for preparation of Palonosetron hydrochloride comprises the steps of.
Step 1 involves treating (S)-3-aminoquinuclidine with 5,6,7,8-tetrahydro-l-naphthalene carboxylic acid chloride to obtain (S)-N-(l-Azabicyclo[2.2.2]oct-3-yi)-5,6,7,8-tetrahydro-1 -napthalene carboxamide,
To an alcoholic solution of a base, is added (S)-3-aminoquinuclidine salt, in particular its dihydrochloride to obtain a reaction mixture. The reaction mixture is refluxed for 1 to 3 hours, preferably for 2 hours. The solvent is removed completely to obtain a residue. Hydrocarbon solvent is added to the residue and the mixture is stirred for 2 to 8 minutes, preferably for 5 minutes at a temperature of 50 to 70°C, preferably for 60 to 65°C. The mixture is subjected to distillation followed by charging the residue with a hydrocarbon solvent. This mixture is stirred at the same temperature for 10 to 20 min, preferably for 15 min. This mixture is filtered through hyfjo bed and washed with hydrocarbon solvent. The filtrate is subjected to distillation to remove traces of water and cooled to a temperature of 30 to 50°C to obtain a solution containing (S)-3-aminoquinuclidine free base.
5,6,7,8-tetrahydro-l -napthalene carboxylic acid, hydrocarbon solvent and a polar aprotic solvent are taken in a flask followed by addition of chlorinating agent to the obtained mixture over a period of 20 to 40 min, preferably 25 to 30 minutes. The reaction mixture is heated at 35 to 55°C, preferably 40 to 45°C for 1 to 2 hours, preferably for 1.5 hours. The mixture is concentrated to obtain a residue. This residue is treated with a hydrocarbon solvent followed by removal of solvent. The residue is further treated with a hydrocarbon solvent to obtain a solution containing 5,6,7,8-tetrahydro-1-napthalene carboxylic acid chloride.
5,6,7,8-tetrahydro-l-naphthalene carboxylic acid chloride solution is added dropwise to the solution of (S)-3-aminoquinuclidine over a period of 20 to 60 min, preferably 35 to 45 min at a temperature of 20 to 70°C, preferably 40 to 60°C to obtain a reaction

mixture. The reaction is continued at the same temperature for 30 to 90 min, preferably for 60 min. Water is added to the reaction mixture at 30 to 60°C, preferably for 45 to 55°C followed by stirring for 5 to 15 min, preferably for 10 min to obtain a solution. The obtained solution is treated with a base followed by stirring the reaction mixture at the same temperature for 20 to 40 min, preferably 25 to 30 min. The layers are separated. The aqueous layer is extracted with a hydrocarbon solvent at the same temperature. The organic layers are combined and washed with water. The organic layer is then concentrated under vacuum at 40 to 60°C, preferably at 50 to 55°C to obtain a residue. The residue is further treated with a hydrocarbon solvent and the mixture is stirred for 5 to 15 min, preferably for 10 min at 30 to 60°C, preferably 40 to 50°C. The mixture is cooled to about 10 to 20°C, preferably 15°C and stirred for 30 to 90 min, preferably for 60 min to obtain a solid. The solid obtained is filtered, washed and dried to obtain (S)-N-(l-Azabicyclo[2,2.2]oct-3-yl)-5,6,7,8-tetrahydro-l-napthalene carboxamide.
Base used is selected from sodium hydroxide, potassium hydroxide or calcium hydroxide, preferably sodium hydroxide or potassium hydroxide. Hydrocarbon solvent is selected from aromatic or aliphatic hydrocarbon such as toluene, xylene, pentane, hexane or heptane, preferably toluene. Chlorinating agent is selected from thionyl chloride or phosphorus pentachloride, preferably thionyl chloride. Polar aprotic solvent is selected from dimethyl formamide, dimethylacetamide, dichloromethane, tetrahydrofuran or dimethyl sulfoxide preferably dimethyl formamide.
Step 2 involves conversion of (S)-N-(l-Azabicyclo [2.2.2]oct-3-yl)-5,6,7,8-tetrahydro-1-napthalene carboxamide to 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4.5,6-tetrahydro-lH-benz[de] isoquinolin-1-one or salt thereof.
(S)-N-(]-Azabicyclo[2.2.2]oct-3-yl) -5,6,7,8-tetrahydro -1-napthalene carboxamide and ether are charged in a round bottom flask under nitrogen atmosphere and cooled to -50 to -20°C, preferably -40 to -30°C to obtain a reaction mixture. A solution of n-butyl lithium in hexane is added to the reaction mixture at the same temperature and stirred for 1 to 3 hours, preferably for 2 hours at the same temperature. A formylating

agent such as N,N-dimethyIformamide is added to the mixture at a temperature of -40 to -20°C, preferably -35 to -25°C. The temperature of the mixture is allowed to reach 20 to 25°C and the mixture is stirred for 10 to 15 hours, preferably for 12 hours. The mixture is cooled to -5 to -15°C, preferably -10°C followed by treatment with an acid. The dehydration is carried out in the presence of an acid such as cone. HC1. The mixture is stirred for 40 to 80 min. preferably 60 min at 5 to 20°C, preferably 10 to 15°C followed by addition of water. The mixture is further stirred for 40 to 80 min, preferably 60 min and subjected to layer separation. The aqueous layer is washed with an ester solvent. The pH of the aqueous layer is adjusted to 9 by addition of 7N NaOH solution. The aqueous layer is extracted with an ester solvent. The organic layer is washed with brine, dried over sodium sulfate and concentrated to obtain an oily mass. The oily mass is dissolved in an alcohol at a temperature of 40 to 60°C, preferably at 50 to 55°C, and cooled to about 0 to 15CC, preferably 5 to 10°C. The solution is treated with acetyl chloride in a dropwise manner at a temperature below 30°C and stirred for 2 to 6 hours, preferably for 4 hours at a temperature of 5 to 20°C, preferably 10 to 15°C. The temperature of the mixture is raised to 20 to 30°C, preferably to 25°C and stirred for 1 to 3 hours, preferably for 2 hours at the same temperature. The product is filtered, washed and dried under vacuum. The obtained product can be used for the next step without further purification.
Ether is selected from tetrahydrofuran (THF), diethyl ether, diisopropyl ether, methyl tertiary butyl ether or 1,4-dioxane, preferably tetrahydrofuran (THF). Ester is selected from methyl acetate, ethyl acetate, propyl acetate or butyl acetate, preferably ethyl acetate. Alcohol used is selected from C1-C4 alcohol such as isopropyl alcohol, methanol or ethanol, preferably isopropyl alcohol (IPA). Other salt forming agent which can be used in place of acetyl chloride is selected from HC1, HBr, ammonium chloride, thionyl chloride or the like.
According to another embodiment of the present invention, there is provided a process for preparation of Palonosetron or its pharmaceutically acceptable salt comprising the steps of,

a) treating (S)-3-ammoquinuclidine or salt thereof, in particular its dihydrochloride with 5,6,7,8-tetrahydro-l-naphthalene carboxylic acid or derivative thereof to obtain (S)-N-(l-Azabicyclo[2.2.2]oct-3-yl)-5,6,7.8-tetrahydro-l-napthalene carboxamide;
b) Lithiation of (S)-N-(l-Azabicyclo[2.2.2]oct-3-yl) -5,6,7,8-tetrahydro -1-napthalene carboxamide to obtain the lithiated product and subjecting the lithiated product to formylation, dehydration and optionally, salt formation to obtain 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz [de] isoquinolin-1-one or salt thereof;
c) subjecting 2-[(S)-l-Azabicyclo[2,2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de] isoquinolin-1-one or salt thereof obtained in step b) to reduction to obtain a reaction mixture followed by filtration of the obtained reaction mixture under reducing conditions to yield a diastereomeric mixture of 2[(S)-1-azabicyclo[2.2.2]oct-3-yl)-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one;
d) separating the desired isomer (3aS, 2S) from the diastereomeric mixture obtained in step c) by salt formation to obtain (3aS, 2S) isomer in more than 95% purity; and
e) optionally, enhancing the purity of 3aS, 2S isomer (Palonosetron) by repeated purification.
The process for preparation of Palonosetron or pharmaceutically acceptable salt thereof as described above is represented in the below Scheme I,


Another embodiment of the present invention provides pharmaceutical composition comprising Palonosetron hydrochloride, prepared by the process of the present invention. Palonosetron hydrochloride obtained by the process of the present invention may be combined with pharmaceutically acceptable excipients to obtain suitable pharmaceutical compositions, used in the prevention of chemotherapy-induced nausea and vomiting and post operative nausea and vomiting.
Unless otherwise indicated, the following definitions are set forth to illustrate and define the meaning and scope of the various terms used to describe the invention herein.
The term "substantially free" means Palonosetron or pharmaceutic ally acceptable salt thereof, in particular Palonosetron hydrochloride having less than about 1%, preferably less than about 0.5%, more preferably less than about 0.3%. most preferably less than about 0.15% of undesired compounds including other polymorphic forms.
The term "pharmaceutically acceptable" means that which is useful in preparing a

pharmaceutical composition that is generally non-toxic and is not biologically undesirable and includes that which is acceptable for human pharmaceutical use.
X-ray powder diffraction pattern was obtained on Xpert'PRO, PANalytical, diffractometer equipped with accelerator detector using Copper Ka (n = 1.5406 A0) radiation with scanning range between 2-theta 4-50° at a scanning speed of 2°/min.
The following examples are for illustrative purposes only and are not intended to limit the scope of the invention in any way.
Examples:
Example 1
Preparation of (S)-N-(l-Azabicyclo[2.2.2]ocr-3-yl)-5,6,7,8-tetrahydro-l-
napthalcne carboxamide
To methanol (442 ml) was charged potassium hydroxide pellets (65.58 gm) in one lot followed by addition of (S)-3-aminoquinuclidine dihydrochloride (100 gm) to obtain a reaction mixture. The reaction mixture was refluxed for 2 hours. The solvent was completely'removed followed by addition of toluene (147 ml) to the obtained residue. This mixture was stirred for 5 min at 60-65°C. The solvent was completely distilled at 60-65°C under vacuum followed by addition of toluene (590 ml) to the obtained residue. This mixture was stirred at the same temperature for 15 min and was filtered through hyflo bed. The residue was washed with toluene. The filtrate was distilled to remove traces of water and cooled to 40-45°C to obtain a solution containing (S)-3-aminoquinuclidine free base.
In another flask, 5,6,7,8-tetrahydro-l-naphthalenecarboxylic acid (73.7 gm) was charged with toluene (370 ml) and DMF (0.5 ml) followed by addition of thionyl chloride (36.8 ml) over 25-30 min to obtain a reaction mixture. The reaction mixture was heated at 40-45°C for 1.5 hours. The solvent was distilled out at 60°C under vacuum to obtain a residue. Toluene (147 ml) was added to the residue. The solvent was distilled out under vacuum at 60-65°C. Toluene (370 ml) was again added to the residue to obtain a solution. This solution containing 5,6,7,8-tetrahydro-l-naphthalene

carboxylic acid chloride was used for the farther reaction.
The above solution of 5,6,7,8-tetrahydro-l-naphthalenecarboxylic acid chloride was added drop wise to the above solution of (S)-aminoquinuclidine at 40-60°C over 30-45 min. The reaction was continued at 55-60°C for 1 hour. Water (221 ml) was added at 45-55°C and stirred for 10 min to obtain a solution followed by addition of solution of sodium hydroxide (36.8 gm in 370 ml water) over 5 min. The reaction mixture was stirred at the same temperature for 25-30 min. The organic layer was separated. The aqueous layer was extracted with toluene (221 ml) at the same temperature. Toluene layers were combined and washed with water (221 ml). The toluene layer was concentrated under vacuum at 50-55°C to obtain a residue. Toluene (442 ml) was charged to the obtained residue and stirred for 10 min at 40-50°C. The reaction mixture was cooled to 15°C and stirred for 1 hour to obtain a solid. The solid was filtered, washed with toluene and dried at 65-70°C to obtain the title compound. Yield: lOOgm (84%); Purity: more than 98%
Example 2
Preparation of 2-[(S)-l-AzabicycIo[2.2.2Joct-3-yl]-2,4,5,6-tetrahydro-lH-benz
[dejisoquinolin-l-one hydrochloride
(S)-N-(l-azabicyclo[2.2.2]oct-3-yl)-5J6J7,8-tetrahydro-l-naphthalene carboxamide (100 gm) and THF (1.2 lit) were charged into a RB flask under nitrogen atmosphere and cooled to -40 to -30°C to obtain a reaction mixture, n-buty] lithium solution in hexane (1.6M, 0.776 lit) was added to the obtained reaction mixture at the same temperature. The reaction mixture was stirred for 2 hours at the same temperature. N,N-dimethylformamide (110 ml) was added to the mixture at a temperature of -35 to -25°C. The temperature of the mixture was allowed to reach 20-25°C and stirred for 12 hours at the same temperature. The reaction mixture was cooled to -10°C and cone. HC1 (0.25 lit) was added in a dropwise manner. The reaction mixture was stirred for 1 hour at 10-15°C followed by addition of water (0.5 lit). The mixture was further stirred for 1 hour and subjected to layer separation. The aqueous layer was washed with ethyl acetate. The pH of aqueous layer was adjusted to 9 by addition of 7N NaOH solution,

The aqueous layer was extracted with ethyl acetate (2 x 0.5 lit). The ethyl acetate layer was washed with brine and dried over sodium sulfate. This organic layer was concentrated to yield an oily mass. The oily mass was dissolved in isopropanol (650 ml) at 50 to 55°C and cooled to 5-10°C. To this mass was further added acetyl chloride (105 gm) in a drop wise manner below 30°C. The mass was stirred for 4 hours at 10-15°C and the temperature was raised to 25°C and stirred for 2 hours at the same temperature. The mass was filtered, washed with isopropanol and dried under vacuum at 55-60°C. Yield: 80%: Purity: more than 98%
Example 3
Preparation of 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-
benzfde]isoquinolin-1-one hydrochloride
2-[(S)-1 -Azabicydo[2.2.2]oct-3-yI]-2,4,5,6-tetrahydro-1 H-benz[de]isoquinolin-1 -one hydrochloride (110 gm) was dissolved in methanol (2.2 lit) and charged into a hydrogenation flask. The slurry of 10% Pd/C (44 gm) in acetic acid (1.1 lit) was added to the above mixture and this mixture was hydrogenated at 10 Kg/cm2 pressure at 50-55°C. The progress of the reaction was monitored by HPLC. Once the concentration of 2 -[(S)-1 -Azabi cyclo[2.2.2]oct-3 -yl] -2,4,5.6-tetrahydro- .1 H-benz[de] isoquinol in-1 -one hydrochloride reached below 0.15%, the reaction mixture was filtered through hyflo bed using in-line filtration set-up under hydrogen atmosphere in a flask containing ammonium formate and methanol. The filtrate was concentrated under vacuum to obtain a residue. The residue was treated with water (1.65 lit) and this mixture was cooled to 10-15°C followed by basification by adding ammonia solution till pH 9.0 was achieved. The temperature of the mixture was raised to 20°C. The reaction mixture was stirred at 20-25°C for 3 hours and filtered. The residue was washed with water and air dried to yield a diastereomeric mixture (Palonosetron base) (85 gm, desired isomer, 3aS, 2S = 61%; undesired isomer, 3aR: 2S = 39%, Starting Material = 0.12%). The obtained diasteroisomeric mixture of Palonosetron base was charged with isopropanol (700 ml) and HC1 (30 ml) under nitrogen atmosphere to obtain a reaction mixture. The obtained reaction mixture was heated at reflux and the hot solution was filtered through

hyflo bed. The filtrate was distilled to remove the solvent (350 ml). The concentrated solution was cooled to 25-30°C and stirred for 1 hour. This mixture was filtered and the residue obtained was washed with isopropanol and dried under vacuum to yield a diastereomeric mixture containing 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one hydrochloride (Palonosetron hydrochloride).
Yield: 47 gm; desired isomer 3aS, 2S = 96.3%; undesired isomer 3aR, 2S = 3.6%; Content of 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de]iso quinolin-1-one hydrochloride (starting material) = 0.10%
Example 4
First Purification of 3aS-l2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-
hexahydro-lH-benz[de]isoquinolin-l-one hydrochloride
The diastereomeric mixture containing 3aS-[2-(S)-l-Azabicyc!o[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoqumolin-l-one hydrochloride (47 gm) was charged with isopropanol (700 ml) under nitrogen atmosphere followed by addition of water (47 ml) to obtain a reaction mixture. The obtained reaction mixture was heated to dissolve the mixture completely. The mixture was stirred for 15 min followed by removal of the solvent (350 ml). The concentrated mixture was allowed to cool to 25-30°C and stirred for 1 hour. The mixture was further cooled to 15°C and stirred for 1 hour at the same temperature to obtain a solid. The obtained solid was filtered, washed with isopropanol and dried under vacuum to yield the desired isomer (Pure Palonosetron hydrochloride).
Yield: 38.7 gm; desired isomer 3aS, 2S = 99.1%; undesired isomer 3aR, 2S = 0.8. Content of 2-[(S)-I-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de] isoquinolin-1-one hydrochloride (starting material) = 0,07%
Example 5
Second Purification of 3aS-[2-(S)-l-Azabicyclo[2.2.2]ocr-3-yl]-2,3,3a,4,5,6-
hexahydro-lH-benz[de]isoquinolin-l-one hydrochloride
The diastereomeric mixture containing 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-

2,3,3a.4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one hydrochloride (38 gm) was charged with isopropano] (700 ml) under nitrogen atmosphere followed by addition of water (38 ml) to obtain a reaction mixture. The obtained reaction mixture was heated to dissolve the mixture completely. The mixture was treated with charcoal and filtered through hyflo bed. The filtrate obtained was distilled to remove the solvent (310 ml), cooled to 25°C and stirred for 1 hour. The mixture was further cooled to 15°C and stirred for 1 hour at the same temperature to obtain a solid. The obtained solid was filtered, washed with isopropano! and dried under vacuum to yield the desired isomer (Pure Palonosetron hydrochloride).
Yield: 33.3 gm; desired isomer 3aS, 2S = 99.8%; undesired isomer 3aR, 2S =0.2%; Content of 2-[(S)-1 -Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-1 H-benz[de] isoquinolin-1-one hydrochloride (starting material) = 0.05%
Example 6
Third Purification of 3aS-[2-(S)-l-Azabicyc!o[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexa
hydro-lH-benz[de]isoquinolin-l-one hydrochloride
The diastereomeric mixture containing 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yi]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one hydrochloride (33. gm) was charged with isopropanol (600 ml) under nitrogen atmosphere followed by addition of water (33 ml) to obtain a reaction mixture. The obtained reaction mixture was heated to dissolve the mixture completely. The mixture was distilled to remove the solvent (270 ml) followed by cooling the concentrated mixture to 25°C and stirring for 1 hour. The mixture was further cooled to 15°C and stirred for another 1 hour at the same temperature to obtain a solid. The obtained solid was filtered, washed with isopropanol and dried to yield the desired isomer (Pure Palonosetron hydrochloride). Yield: 28.3gm; desired isomer 3aS, 2S = 99.96%; undesired isomer 3aR,2S =0.04%; Content of 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yI]-2,4,5,6-tetrahydro-lH-benz[de]iso quinolin-1-one hydrochloride (starting materiaf)= 0.04%

We claim:
1. A process for preparation of Palonosetron or pharmaceutically acceptable salt
thereof comprising the steps of,
a) subjecting 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz [de]isoquinolin-l-one or salt thereof to reduction to obtain a reaction mixture;
b) filtering the reaction mixture obtained in step a) under reducing conditions to obtain a diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one; and
c) converting the obtained diastereomeric mixture of 2-[(S)-l-azabicyclo [2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro- lH-benz[de]isoquinoline-l -one to Palonosetron or pharmaceutically acceptable salt thereof.

2. The process as claimed in claim 1, wherein said 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de]isoquinolin-l-one is in the form of acid addition salt and wherein said reduction is carried out in presence of catalyst selected from palladium/carbon, platinum/carbon or oxides thereof at a hydrogen pressure of about 8 to 12 Kg/cm2 and a temperature of 40 to 60°C.
3. The process as claimed in claim 1, wherein said filtration is carried out using in-line filtration set-up under hydrogen atmosphere and filtrate is collected in a flask containing a hydrogen transfer agent selected from ammonium formate, isopropanol or formic acid.
4. The process as claimed in claim 1, wherein said 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5.6-tetrahydro-lH-benz[de]isoquinoIin-l-one or salt thereof has chemical purity of more than 98%.
5. The process as claimed in claim 1, wherein said conversion of diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de] isoquinoline-1-one to Palonosetron or pharmaceutically acceptable salt thereof comprises the steps of,

a) subjecting said diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinoline-l-one to salt formation so as to enhance the content of 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one to more than 95%; and
b) optionally purifying said 3aS-[2-(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2f3,3a,4,5,6-hexahydro-lH-benz[de]isoquinolin-l-one salt by repeated crystallization.

6. The process as claimed in claim 5. wherein said salt formation is carried out by treating said diastereomeric mixture of 2-[(S)-l-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro-lH-benz[de]isoquinoline-l-one with an acid forming agent selected from HC1, HBr, maleic acid, fumaric acid, succinic acid, methanesulfonic acid, ethanesulfonic acid or the like, in the presence of solvent selected from methanol, ethanol. isopropyl alcohol or mixture thereof.
7. The process as claimed in claim 5, wherein said salt is HC1 and diastereomeric mixture obtained in step a) has about 96.3% of 3aS, 2S isomer and about 3.6% of undesired 3aR, 2S isomer.
8. The process as claimed in claim 1, wherein said 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de]isoquinolin-l-one or salt thereof is prepared by a process comprising the steps of,

a) treating (S)-3-aminoquinuclidine or salt thereof with 5,6,7,8-tetrahydro-l-naphthalene carboxylic acid or derivative thereof to obtain (S)-N-(l-Azabicyc]o[2.2.2]oct-3-yl)-5,6.7,8-tetrahydro-l-napthalene carboxamide;
b) lithiation of (S)-N-(l-Azabicyclo [2.2.2] oct-3-yl)-5,6,7,8-tetrahydro-l-napthalenecarboxamide to obtain the lithiated product and subjecting the lithiated product to formylation, dehydration and optionally, salt formation to obtain 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4,5,6-tetrahydro-lH-benz[de] isoquinolin-1-one or salt thereof; and

c) converting said 2-[(S)-l-Azabicyclo[2.2.2]oct-3-yl]-2,4.5,6-tetrahydro-lH-benz[de]isoquinolin-l-one or salt thereof to Palonosetron or pharmaceutically acceptable salt thereof.
9. The process as claimed in claim 7, wherein said purification in step b)
comprises the steps of,
a) dissolving said Palonosetron hydrochloride in a solvent selected from isopropanol, ethanol, methanol, water or mixture thereof to obtain a solution;
b) optionally treating the obtained solution with charcoal; and
c) isolating pure Palonosetron hydrochloride.
10. The process as claimed in claim 9, wherein said Palonosetron hydrochloride has
chemical purity of more than 99.5%.