CLIAMS:We Claim:

1. A process for the preparation of isolated indane isomer of Atovaquone of formula II:

Formula II

comprising the steps of:

a) reacting atovaquone with aqueous solution of base at reflux temperature;

b) treating the reaction mixture with an acid followed by extraction with ester solvent;

c) precipitating the solid from the mixture of step b) using an organic solvent.

2. The process of claim 1, wherein said base of step a) is selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

3. The process of claim 1, wherein said base of step a) is sodium hydroxide.

4. The process of claim 1, wherein said acid of step b) is hydrochloric acid.

5. The process of claim 1, wherein said ester of step b) is selected from ethyl acetate, isopropyl acetate and 2-methoxyethyl acetate.

6. The process of claim 1, wherein said precipitation of step c) is performed by suing recrystallization technique.

7. The process of claim 1, wherein said organic solvent of step c) is acetonitrile.

8. The process of claim 1, wherein said isolated indane isomer is having purity greater than 98% by HPLC.

Dated this 26 day of March 2013 For Wockhardt Limited

(Dr Mandar Kodgule)
Authorized Signatory
,TagSPECI:DESCRIPTION

The present invention provides a chemical process for preparing isolated impurity of Atovaquone, for example, Indene isomer of Atovaquone of Formula II, which is useful as reference marker.

Formula II

Atovaquone, chemically known as trans-2-[4-(4-chlorophenyl)cyclohexyl]-3-hydroxy-1,4-naphthalenedione of Formula I:

Formula I

Atovaquone is a widely used antiprotozoal and is potently active (in animals and in vitro) against Pneumocystis carinii, Plasmodia, and tachyzoite and cyst forms of Toxoplasma gondii. It is a highly lipophilic compound resembling ubiquinone and has a low aqueous solubility. This is the reason for the poor bioavailability of atovaquone after oral administration.

U.S. Patent No. 4,981,874 discloses the use of atovaquone against Pneumocystis carinii infection in a mammal. EP Patent No. 0 123 238 and U.S. Patent No. 5,053,432 disclose the use of atovaquone against Plasmodium falciparum and also against Eimeria species such as E. tenella and E. acervulina which are causative organisms of coccidiosis. Further, use of atovaquone against Toxoplasmosis and Cryptosporidiosis is disclosed in EP Patent No. 0 445 141 and 0 496 729 respectively.

Currently, atovaquone suspension marketed under trade name MEPRON is a formulation of micro-fine particles of atovaquone.

The skilled in the art of drug manufacturing research and development understand that a compound in a relatively pure state can be used as a "reference standard." A reference standard is similar to a reference marker, which is used for qualitative analysis only, but is used to quantify the amount of the compound of the reference standard in an unknown mixture, as well. A reference standard is an "external standard," when a solution of a known concentration of the reference standard and an unknown mixture are analyzed using the same technique. (Strobel p. 924, Snyder p. 549, Snyder, L. R.; Kirkland, J. J. Introduction to Modern Liquid Chromatography, 2nd ed. (John Wiley & Sons: New York 1979)). The amount of the compound in the mixture can be determined by comparing the magnitude of the detector response.

The reference standard can also be used to quantify the amount of another compound in the mixture if a "response factor," which compensates for differences in the sensitivity of the detector to the two compounds, has been predetermined. (Strobel p. 894). For this purpose, the reference standard is added directly to the mixture, and is known as an "internal standard." (Strobel p. 925, Snyder p. 552).

Use of a compound as a reference marker requires recourse to a sample of substantially pure compound. Therefore, there is a need to develop an efficient process to provide isolated indane isomer of Formula II, which can be used as reference marker to establish the level of the purity of Atovaquone.

The inventors of the present invention developed a conventional and industrially feasible process to provide isolated compound of Indane isomer of atovaquone of Formula II.

As used herein, the term "isolated" refers to a compound that is at least 95 % purity determined by HPLC.

In an aspect of the present invention, there is provided a process for the preparation of isolated indane isomer of Atovaquone of formula II comprising the steps of:

a) reacting atovaquone with aqueous solution of base at reflux temperature;

b) treating the reaction mixture with an acid followed by extraction with ester solvent;

c) precipitating the solid from the mixture of step b) using an organic solvent.

The step a) involves reacting atovaquone with aqueous solution of base at reflux temperature.

The starting material, Atovaquone, is prepared by the known process of the prior art, for example, WO 2009/001367, US 2008/0241254 or as per the process of pending application No. IN 17/MUM/2012.

The base used as aqueous solution of base for step a) includes but are not limited to sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and the like.

The reflux temperature and reaction maintenance for a period of 3 to 4 days or more affects the rearrangement of atovaqone to provide indane isomer of formula II.

After completion of the reaction, the reaction mixture is cooled to room temperature and subjected for extraction with ether, for example, diethyl ether, diisopropyl ether, ethyl tert-butyl ether, 1,4-dioxane and THF to remove color impurity.

The step b) involves treating the reaction mixture with an acid followed by extraction with ester solvent.

The reaction mixture of step a) obtained after removal of color impurities, i.e. aqueous layer is treated with acid, for example, hydrochloric acid, hydrobromic acid, and the like.

The reaction mixture is extracted from resultant aqueous layer into organic layer by using ester solvent and then concentrated completely. The ester solvent for extraction includes but are not limited to ester such as ethyl acetate, isopropyl acetate and 2-methoxyethyl acetate.

The step c) involves precipitating the solid from the mixture of step b) using an organic solvent to provide isolated indane isomer of formula II.

The crude of reaction mixture obtained from the step b) is subjected to precipitation of solid in presence of nitrile solvent using recrystallization technique.

The nitrile solvent used for recrystallization of solid from crude includes but are not limited to acetonitrile, propionitrile, and the like.

The isolated indane isomer of formula II is having the purity greater than or equal to 95%, or greater than 98% determined by HPLC method.

The present invention is further illustrated by the following example, which does not limit the scope of the invention. Certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present application.

EXAMPLE:

Example-1: Synthesis of Indene isomer of Atovaquone

Atovaquone (50 g, 0.13 mol) was treated with 8 % Sodium hydroxide solution (2.5 L) at reflux temperature for 4 days. Sample analyzed in HPLC to ensure absence of Atovaquone. The reaction mixture cooled to room temperature and extracted with diisopropyl ether (250 mL) to remove color impurity. Aqueous layer was acidified with Conc. HCl (400 mL), and extracted with ethyl acetate (1.0 L). The organic layer was washed with water and recovered ethyl acetate under vacuum. The resultant crude product was recrystallised from acetonitrile (200 mL) to get 32.7 g pure Indene isomer of Atovaquone.
Melting point, 287.5 – 289.2 oC
Purity: 98.59 % determined by HPLC

1H NMR, dppm (DMSO-d6): 1.42 – 1.96 (8H, m, 4 x CH2), 2.56 (1H, m, CH), 3.06 (1H, m, CH), 7.25 – 7.32 (5H, m, 5 x ArH), 7.40 – 7.48 (3H, m, 3 x ArH), 13.9 (1H, br s, COOH, D2O exchangeable).

13C NMR, dppm (DMSO-d6): 30.37, 33.96, 35.37, 42.84, 122.74, 123.32, 128.60, 129.06, 129.13, 129.63, 130.83, 135.06, 143.07, 143.93, 144.83, 146.50, 166.04, 197.60.

Mass Spectrometry: The protonated molecular ion at m/z 365.2 (M+) confirms the mass, which corresponds to molecular formula of C22H19ClO3