Title of Invention

METHOD FOR PREPARING SESQUITERPENE ENDOPEROXIDE DERIVATIVES

Abstract The present invention relates to an improved method for the preparation of sesquiterpene endoperoxide derivatives by reducing sesquiterpene lactone at a temperature in the range of -5° to 5°C, followed by reaction with an alcohol in the presence of acid catalyst and isolation using alkanol of from 1 - 4 carbon atoms, or mixture of water and alkanol of from 1 -4 carbon atoms.
Full Text FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
Method for preparing sesquiterpene endoperoxide derivatives
2. APPLICANT (S)
(a) NAME : Mr. SAXENA ALOK
(b) NATIONALITY : INDIAN
(c) ADDRESS : C/o. Elder Pharmaceuticals Ltd.,
Elder House. Plot No. C/9,
Dalia Indl. Estate, Off. New Link Road,
Andheri (W). Mumbai - 400 058, 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 cost effective and industrially advantageous process for the preparation of sesquiterpene endoperoxide derivatives.
Background of the invention
Malaria is one of the oldest and most prevalent parasitic disease, which affects mainly the countries of the tropical regions. Approximately. 4 billion people worldwide now suffered form malaria and about 3 million (mostly children) die every year from this disease. The malaria problem is further compounded with increasing emergence of malaria parasite's resistance to commonly used drugs such as chloroquine.
The effectiveness of dihydroartemisinin and its derivatives, such as artemether, arteether and like as antimalarial drugs for the treatment of chloroquine, mefloquine or multidrug resistant Plasmodium falciparum has received increasing attention in recent years. Artemether has undergone extensive preclinical, animal, toxicological and clinical studies and is effective against both chloroquine-sensitive and resistant malaria and because of its rapid action is well suited for treatment of the treatment of complicated, cerebral and multidrug resistant malaria. Artemether shows rapid shizonticidal action with quicker clearance rate, short fever clearance time with no side effect and low recrudence rate.
Brossi, et al; J. Med. Chem. 31, 646 - 649. 1988 reported the preparation of ethyl ether
derivative of dihydroartemisinin by reduction of artemisinin with sodium borohydride in methanol at 0 to -5°C in 3 hours to form dihydroartemisinin; and dissolving dihydroartemisinin in the mixture of benzene and ethanol solvent at 45°C, followed by addition of BF3 etherate and refluxing the reaction mixture at 70°C for 1 hour. The reaction mixture was worked up, dried over anhydrous sodium sulphate with removal of the solvent to yield arteether along with some impurities. The impure arteether was purified by column chromatography over silica gel in hexane-ethyl acetate (9:1) to yield pure alpha and beta arteether.

Another method is reported by Lin. et. al; J. Med Chem., 38, 764 - 770, 1995, in which the new ether derivatives were prepared by dissolving dihydroartemisinin in anhydrous ether and adding appropriate alcohol followed by BF3 etherate. The reaction mixture was stirred at room temperature for 24 hours. Purification of the product was done with the use of silica gel chromatography.
In another method EL-Feraly et. al. reported the preparation of arteether by a process in which anhydrodihydroartemisinin was dissolved in absolute alcohol and the reaction was carried out in the presence of p-toluene sulphonic acid as a catalyst. On workup a mixture of beta arteether and C-l 1 epimer was obtained in the ratio of 3:1. Separation of C-l 1 epimer is difficult and preparation of anhydrodihydroartemisinin is a very tedious process and requires 22 hours to complete. Quantity of Lewis acid required is very high.
Bhakuni et. al., Ind. J. Chemistry, 34B, 529 - 30, 1995 reported the preparation of arteether, artemether and other ether derivatives from dihydroartemisinin in different alcohols and benzene, using chlorotrimethylsilane as a catalyst. After workup of the reaction mixture and removal of the solvent, the obtained residue was dissolved in n-hexane-ethyl acetate (96:4) and then chromatographic technique used, to obtain pure mixture of alpha, beta ethers.
Jain et. al reported the another method for preparation of ethers from artemisinin (reference US6346631) in which artemisinin is reduced to dihydroartemisinin, followed by isolation of dihydroartemisinin. and conversion of dihydroartemisinin by use of alcohol and trialkylorthoformate at 40 - 45°C in 10 hours to obtain required ethers.
Process for the preparation of artemether from Artemisinin using one pot reaction is reported by Bhakuni et. al. in US 2003/0181513. This involves reduction of artemisinin with sodium borohydride in methanol at 0 to -5°C into dihydroartemisinin, which without isolation is acylated (metherified) in the presence of solid/liquid acid catalyst at room temperature. After conventional workup, the impure artemether is purified by silica
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gel column chromatography (1:5 ratio) in hexane : ethyl acetate (96:4), yielded 80 - 82% (w/w) pure alpha/beta artemether.
WO2004/050662 describes single pot conversion of artemisinin to arteether in about 4
hours. The process comprises reduction of artemisinin into dihydroartemisinin by less quantity of sodium borohydride in ethanol at room temperature in the presence of a polyhydroxy catalyst, acylation of dihydroartemisinin in the presence of an acid catalyst followed by extraction of arteether from an aqueous reaction mixture using 1% ethyl acetate in n-hexane. Work up of the impure arteether followed by silica gel column chromatographic technique yielded 80 - 86% (w/w) pure alpha, beta arteether.
Single pot synthesis of artemether from artemisinin is described by Chandan Singh et. al. in Ind. J Chem, vol 4 IB, 2002, pp 2185 - 2186. The method describes the use of strongly acidic macroreticular cation exchanger Amberlyst-15 for converting dihydroartemisinin to Artemether. The crude product was purified using silica gel chromatographic technique using hexane - ethyl acetate as eluant.
The above-mentioned methods carry some disadvantages being less cost effective, time consuming and limited industrial application. Benzene is used as solvent in these processes, which on workup left a few non-volatile impurities. Also the use of benzene as a solvent is not acceptable according to the health standards due to its carcinogenic nature and is under Class-1 solvent as per the ICH guidelines. Further almost all the above methods require silica gel chromatographic method with use of hexane: ethyl acetate as eluant, and preparative TLC method for purification of the ethers, that results limited industrial use. Use of hexane: ethyl acetate in purification of the earlier processes is not economically viable and also the use of hexane is burdened with the risk of fire and explosion. Thus the present invention provides an industrially applicable and efficient method for conversion of artemisinin into sesquiterpene endoperoxide derivatives.
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Objects of the Invention
The object of the present invention is the development of an economically effective and industrially advantageous process for the preparation of sesquiterpene endoperoxide derivatives, without using silica gel chromatographic separation technique.
Summary of the Invention
The present invention provides a method for the preparation of sesquiterpene endoperoxide derivatives which comprises of: reducing artemisinin into dihydroartemisinin by sodium borohydride at a temperature in the range of -5 to 5°C, reacting dihydroartemisinin with an alcohol in the presence of an acid catalyst, followed by isolation in alkanol of from 1 - 4 carbon atoms, or mixture of alkanol of from 1 - 4 carbon atoms and water, avoiding the silica gel chromatographic separation technique to obtain pure sesquiterpene endoperoxide derivatives.
Detailed description of the invention
Accordingly, the present invention provides a process for the preparation of sesquiterpene endoperoxide derivatives comprising the steps of:
a) charging artemisinin in methyl alcohol at room temperature to obtain a thin slurry;
b) cooling the slurry at a temperature in the range of -5° to 5°C, and adding a small quantity of reducing agent to the slurry;
c) stirring the reaction mixture at a temperature in the range of-5° to 5°C for about 1 - 2 hours;
d) neutralizing the reaction mixture;
e) adding the reaction mixture of step d) in chilled water, stirring the reaction mixture for about 1 - 2 hours at a temperature in the range of 0° to 5°C and filtering to obtain dihydroartemisinin;
f) adding dihydroartemisinin obtained in step e) in an alcohol and a solvent in an inert atmosphere, followed by addition of an acid catalyst;
g) stirring the reaction mixture of step f) at a temperature in the range of 30 - 70°C for 10 hours;
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h) adding the reaction mixture of step g) to sodium acetate solution and stirring at room
temperature for 25 to 30 minutes, followed by separating the organic layer;
i) distilling the solvent from the organic layer to obtain a residue;
j) dissolving the residue in alkanol of from 1 - 4 carbon atoms, or mixture of alkanol of
from 1 - 4 carbon atoms and water, and stirring the solution for about 15-20 minutes at
a temperature in the range of 40° to 80°C. preferably 40 - 60°C, more preferably 40 -
45°C;
k) cooling the solution of step j) at a temperature in the range of-5° to 35°C, preferably at
-5 to 0°C for 1 - 2 hour, and filter to obtain pure sesquiterpene endoperoxide derivatives.
The alcohol used in the process is selected from the group consisting of methyl alcohol or ethyl alcohol. The reducing agent is selected from the group consisting of sodium borohydride, lithium aluminium hydride, lithium tritert-butoxy aluminium hydride, lithium trimethoxy aluminium hydride, sodium trimethoxy borohydride, sodium bis-2-methoxy, ethoxy aluminium hydride or a mixture of lithium or sodium in alcohol or liquid ammonia. The preferred reducing agent is sodium borohydride. The ratio of artemisinin and reducing agent is 1:0.25 w/w. The ratio of water : alkanol of from 1 - 4 carbon atoms in a mixture of water : alkanol of from 1 - 4 carbon atoms is 1:1 - 1:3, preferably 1:2.
In step b) and step c) the temperature is in the range of-5 to 5°C. The reaction mixture is neutralize using acetic acid. The solvent is preferably toluene. The acid catalyst is chlorotrimethylsilane, boron trifluoride etherate, trifluoroacetic acid or p-toluene sulphonic acid, preferably chlorotrimethylsilane.
The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.
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Example - 1
Conversion of Artemisinin to Dihydroartemisinin
Artemisinin (100 g) was charged in methyl alcohol (1.0 ltr) at room temperature and then chilled to -5 to 5°C. Sodium borohydride (25 g) was added slowly over a period of 1 -1.5 hours, and the reaction mixture was stirred for 1 - 2 hours at the same temperature. The reaction was monitored on TLC to check completion of the reduction step. The pH of the reaction mixture was adjusted to 6.5 - 7.0 using acetic acid. The reaction mixture was then quenched in chilled water and further stirred at a temperature in the range of 0° to 5°C for about 2 hours to obtain dihydroartemisinin (yield 93% w/w).
Example - 2
Preparation of Crude Artemether
Dihydroartemisinin (40 g) obtained according to the method described in example-1 was taken in toluene (360 ml), and then methyl alcohol (120 ml) was added under inert atmosphere. Chlorotrimethylsilane (0.24 ml) was added to the reaction mixture, and maintained the reaction mixture at a temperature in the range of 30 - 70°C for 10 hours. In a separate flask, sodium acetate (40 gm) was dissolved in water (400 ml) to which the reaction mixture was added. This was stirred for 0.5 hours, and the layers were allowed to separate. The organic layer was separated and toluene was distilled off completely to obtain a crude artemether.
Example -3
Preparation of Artemether
The crude artemether was dissolved in isopropyl alcohol (80 ml), and the solution was stirred for 15 minutes at 40 - 45°C. Water (40 ml) was then added dropwise in the solution. The solution was then cooled at a temperature in the range of 0° to -5°C and stirred for 1 hour and filter. Wash the residue with 1:2 water: Isopropyl alcohol to obtain crystals of p-artemether (HPLC purity above 99%).
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Example- 4
Preparation of Artemether
The crude Artemether (9 gm) was dissolved in isopropyl alcohol (9 ml), and the solution was stirred for 15 minutes at 40 - 45°C. Water (9 ml) was then added dropwise in the solution. The solution was then cooled, chilled slowly at a temperature in the range of 0° to -5°C and stirred for 1 hour and filter. Wash the residue with (1:1) water : Isopropyl alcohol to obtain crystals of (3-artemether (HPLC purity: above 99.5%).
Example-5
Preparation of Artemether
The crude Artemether (40g) was dissolved in isopropyl alcohol (120 ml), and the solution was stirred for 15 minutes at 40 - 45°C. Water (40 ml) was then added dropwise in the solution. The solution was then cooled at a temperature in the range of 0° to -5°C and stirred for 1 hour and filter. Then the residue was washed with 1:3 water : Isopropyl alcohol to obtain crystals of p-artemether (HPLC purity: above 99.5%).
Example - 6
Preparation of Artemether
The crude artemether (40 gm) was dissolved in isopropyl alcohol (40 ml), and the
solution was stirred for 15 minutes at 40 - 45°C. The solution was then cooled at a
temperature in the range of 0° to -5°C. stirred for 1 hour and filter. Wash the obtained residue with Isopropyl alcohol (20 ml) to form crystals of P-artemether (HPLC purity: above 99%).
Example - 7
Preparation of Artemether
The crude Artemether (20 gm) was dissolved in isopropyl alcohol (50 ml), and the solution was stirred for 15 minutes at 40 - 45°C. Water (20 ml) was added dropwise in the solution. The solution was then cooled, chilled at a temperature in the range of 0° to -5°C and stirred for 1 hour and filter. Wash the residue with 1:2.5 water : Isopropyl alcohol to obtain crystals of β-artemether (HPLC purity: above 99%).
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Example - 8
Preparation of Artemether
The crude artemether (20 gm) was dissolved in isopropyl alcohol (60 ml), and the solution was stirred for 15 minutes at 40 - 45°C. Water (30 ml) was then added dropwise in the solution. The solution was then cooled at a temperature in the range of 0° to -5°C and stirred for 1 hour and filter. Wash the residue with 1.5:3 water : Isopropyl alcohol to obtain crystals of β-artemether (HPLC purity: above 99%).
Example-9
Preparation of Artemether
The crude artemether (16 gm) was dissolved in isopropyl alcohol (40 ml), and the solution was stirred for 15 minutes at 40 - 45°C. Water (16 ml) was then added dropwise in the solution. The solution was then cooled at a temperature in the range of 0° to -5°C and stirred for 1 hour and filter. Wash the residue with 0.8:2 water : Isopropyl alcohol to
obtain crystals of β-artemether (HPLC purity: above 99%).
Example- 10 Preparation of Artemether
The crude artemether (14 gm) was dissolved in isopropyl alcohol (40 ml), and the solution was stirred for 15 minutes at 40 - 45°C. Water (14 ml) was then added dropwise in the solution. The solution was then cooled at a temperature in the range of 0° to -5°C and stirred for 1 hour and filter. Wash the residue with 0.7:2 water : Isopropyl alcohol to obtain crystals of β-artemether (HPLC purity: above 99%).
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We Claim:
1) A process for the preparation of sesquiterpene endoperoxide derivatives comprising
the following steps:
i) reducing artemisinin into dihydroartemisinin by less quantity of sodium
borohydride at a temperature in the range of-5 to 5°C; ii) reacting dihydroartemisinin with an alcohol in the presence of acid catalyst;
and iii) isolating the crude sesquiterpene endoperoxide derivatives in alkanol of from
1 - 4 carbon atoms, or mixture of water and alkanol of from 1 - 4 carbon
atoms.
2) A process according to claim 1, wherein the sesquiterpene endoperoxide derivative is
prepared according to the following steps:
a) charging artemisinin in methyl alcohol at 25 - 35°C to obtain a thin slurry;
b) cooling the slurry at a temperature in the range of -5° to 5°C, and adding a reducing agent to the slurry;
c) stirring the reaction mixture of step b) at a temperature in the range of -5° to 5°C for about 1 - 2 hours:
d) neutralizing the reaction mixture;
e) adding the reaction mixture of step d) in chilled water, stirring the reaction mixture for about 1 - 2 hours at a temperature in the range of 0° to 5°C and filtering to obtain dihydroartemisinin;
f) adding dihydroartemisinin obtained in step e) in an alcohol and a solvent in an inert atmosphere, followed by addition of an acid catalyst;
g) stirring the reaction mixture of step f) at a temperature in the range of 30 - 70°C for 10 hours;
h) adding the reaction mixture of step g) in sodium acetate solution and stirring at room
temperature for 25 to 30 minutes, followed by separating the organic layer;
i) distilling the solvent from the organic layer to obtain crude sesquiterpene endoperoxide
derivative;
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j) purifying the crude sesquiterpene endoperoxide derivatives of stage (i) by alkanol of from 1 - 4 carbon atoms, or mixture of water : alkanol of from 1 - 4 carbon atoms to obtain pure sesquiterpene endoperoxide derivative.
3) A process according to claim 2. wherein the alcohol used in step (f) is selected from the group consisting of methyl alcohol or ethyl alcohol.
4) A process according to claim 2, wherein the reducing agent used in step (b) is selected from the group consisting of sodium borohydride, lithium aluminium hydride, lithium tritert-butoxy aluminium hydride, lithium trimethoxy aluminium hydride, sodium trimethoxy borohydride, sodium bis-2-methoxy, ethoxy aluminium hydride or a mixture of lithium or sodium in alcohol or liquid ammonia.
5) A process according to claim 4, wherein the reducing agent is sodium borohydride.
6) A process according to claim 2, wherein the ratio of artemisinin and reducing agent is 1:0.25 w/w.
7) A process according to claim 2, wherein the solvent is toluene.
8) A process according to claim 2, wherein the acid catalyst is chlorotrimethylsilane, boron trifluoride etherate, trifluoroacetic acid, or p-toluene sulphonic acid, preferably chlorotrimethylsilane.
9) A process according to claim 2. wherein the step (j) further comprises the step of dissolving the crude sesquiterpene endoperoxide derivative in alkanol of from 1 - 4 carbon atoms, or mixture of water and alkanol of from 1 - 4 carbon atoms to obtain a solution.
10) A process according to claim 9. wherein the solution is stirred at a temperature in the
range of40°-80°C.
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11) A process according to claim 10. wherein the solution is stirred at a temperature in the range of 40° - 65°C.
12) A process according to claim 11. wherein the solution is stirred at a temperature in the range of 40° - 45°C.
13) A process according to claim 12. further comprises cooling the solution at a temperature in the range of-5 to 35°C for 1 hour; filter and further purified in alkanol of from 1 - 4 carbon atoms, or mixture of water and alkanol of from 1 - 4 carbon atoms.
14) A process according to claim 13. wherein the solution is cooled at a temperature in the range of -5° to 0°C;
15) A process according to claim 9. wherein in the mixture, the ratio of water : alkanol of from 1 - 4 carbon atoms : water is 1:1 — 1:3
16) A process according to claim 15, wherein in the mixture, the ratio of water : alkanol of from 1 - 4 carbon atoms is 1:2.
17) A process of preparing sesquiterpene endoperoxide derivatives such as herein
described with reference to forgoing examples.


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ABSTRACT
The present invention relates to an improved method for the preparation of sesquiterpene endoperoxide derivatives by reducing sesquiterpene lactone at a temperature in the range of -5° to 5°C, followed by reaction with an alcohol in the presence of acid catalyst and isolation using alkanol of from 1 - 4 carbon atoms, or mixture of water and alkanol of from 1 - 4 carbon atoms.

Documents:

432-MUM-2007-ABSTRACT(25-6-2009).pdf

432-mum-2007-abstract(granted)-(13-9-2010).pdf

432-mum-2007-abstract.doc

432-mum-2007-abstract.pdf

432-mum-2007-cancelled pages(11-1-2010).pdf

432-MUM-2007-CLAIMS(25-6-2009).pdf

432-MUM-2007-CLAIMS(AMENDED)-(11-1-2010).pdf

432-MUM-2007-CLAIMS(AMENDED)-(25-6-2009).pdf

432-mum-2007-claims(granted)-(13-9-2010).pdf

432-mum-2007-claims.doc

432-mum-2007-claims.pdf

432-mum-2007-correspondence 1(11-1-2010).pdf

432-mum-2007-correspondence(23-2-2007).pdf

432-MUM-2007-CORRESPONDENCE(25-6-2009).pdf

432-MUM-2007-CORRESPONDENCE(29-7-2010).pdf

432-mum-2007-correspondence(ipo)-(21-9-2010).pdf

432-MUM-2007-CORRESPONDENCE(IPO)-(25-6-2009).pdf

432-mum-2007-correspondence-received.pdf

432-mum-2007-description (complete).pdf

432-MUM-2007-DESCRIPTION(COMPLETE)-(25-6-2009).pdf

432-mum-2007-description(granted)-(13-9-2010).pdf

432-MUM-2007-FORM 1(25-6-2009).pdf

432-MUM-2007-FORM 18(25-6-2009).pdf

432-mum-2007-form 2(25-6-2009).pdf

432-mum-2007-form 2(granted)-(13-9-2010).pdf

432-MUM-2007-FORM 2(TITLE PAGE)-(25-6-2009).pdf

432-mum-2007-form 2(title page)-(granted)-(13-9-2010).pdf

432-MUM-2007-FORM 26(11-1-2010).pdf

432-MUM-2007-FORM 26(29-7-2010).pdf

432-MUM-2007-FORM 3(25-6-2009).pdf

432-mum-2007-form 3(7-3-2007).pdf

432-MUM-2007-FORM 5(25-6-2009).pdf

432-mum-2007-form 5(7-3-2007).pdf

432-mum-2007-form-1.pdf

432-mum-2007-form-18.pdf

432-mum-2007-form-2.doc

432-mum-2007-form-2.pdf

432-mum-2007-form-3.pdf

432-mum-2007-form-5.pdf

432-mum-2007-form-9.pdf

432-mum-2007-marked copy(11-1-2010).pdf

432-MUM-2007-REPLY TO EXAMINATION REPORT(11-1-2010).pdf


Patent Number 242800
Indian Patent Application Number 432/MUM/2007
PG Journal Number 38/2010
Publication Date 17-Sep-2010
Grant Date 13-Sep-2010
Date of Filing 07-Mar-2007
Name of Patentee SAXENA ALOK
Applicant Address C/o. ELDER PHARMACEUTICALS LTD, Elder House, Plot No. C/9, Dalia Indl. Estate, Off. New Link Road, Andheri (W), Mumbai
Inventors:
# Inventor's Name Inventor's Address
1 FIRAKE PANDHARINATH NILKANTH ELDER PHARMACEUTICALS LTD D-220,TTC Industrial Area, Thane Belpur Road, Navi Mumbai-400 706,
2 PANCHAL RAJESH VASANT ELDER PHARMACEUTICALS LTD D-220,TTC Industrial Area, Thane Belpur Road, Navi Mumbai-400 706,
3 BABREKAR CHANDAN NAGESH ELDER PHARMACEUTICALS LTD D-220,TTC Industrial Area, Thane Belpur Road, Navi Mumbai-400 706,
4 MOHITE DHANAJI MADHUKAR ELDER PHARMACEUTICALS LTD D-220,TTC Industrial Area, Thane Belpur Road, Navi Mumbai-400 706,
5 SAKHARDANDE RAJIV RAWALNATH ELDER PHARMACEUTICALS LTD, D-220,TTC Industrial Area, Thane Belpur Road, Navi Mumbai-400706
6 KHATRI NAVIN KANJI ELDER PHARMACEUTICALS LTD D-220,TTC Industrial Area, Thane Belpur Road, Navi Mumbai-400 706,
PCT International Classification Number A61K31/357
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA