Process for preparing atazanavir sulphate

Abstract

The present invention relates to a process for the preparation of Compound (A): ##STR00001##
wherein the process comprises contacting atazanavir base (Compound (II)) ##STR00002##
with sulphuric acid in a combination of two or more solvents and isolating compound (A). The present invention also relates to substantially pure Compound (A), and to Compound (A) devoid of mesityl oxide impurity. Mesityl oxide has the following formula: ##STR00003##

Claims

1. A process for the preparation of Compound (A): ##STR00019## wherein the process comprises i) suspending atazanavir base (Compound (II)) ##STR00020## in a combination of two or more solvents, ii) contacting the suspension of Compound (II) and two or more solvents with sulphuric acid, and iii) isolating Compound (A) wherein the combination of two or more solvents comprises a first solvent which comprises a water immiscible, or moderately soluble in water, solvent that is selected from the group consisting of: ethyl acetate, isopropyl acetate, and isobutyl acetate, and a second solvent which comprises a water miscible solvent that is selected from the group consisting of: alcohol, dimethylsulfoxide, and dimethylformamide and wherein the ratio of first solvent to second solvent is in the range of 10:3 to 10:1.

2. The process according to claim 1, wherein to second solvent is 10:1.

3. The process according to claim 1, wherein the combination of two or more solvents comprises more than two solvents.

4. The process according to claim 1, wherein the combination of solvents is selected from the following group: a) ethyl acetate-methanol; b) ethyl acetate-dimethylsulfoxide; c) ethyl acetate-dimethylformamide; d) isopropyl acetate-methanol; e) isopropyl acetate-dimethylsulfoxide; and f) isopropyl acetate-dimethylformamide.

5. The process according to claim 4, wherein the combination of solvents is ethyl acetate-methanol.

6. The process according to claim 1, wherein the sulphuric acid is added at a temperature ranging from 35 C. to 60 C.

7. The process according to claim 1, wherein the sulphuric acid is added at a temperature of 432 C.

8. The process according to claim 1, wherein the Compound (A) is isolated by filtration.

9. The process according to claim 8, wherein prior to isolation by filtration, Compound (A) precipitates and the precipitated solid is mixed with a water immiscible solvent.

10. The process according to claim 9, wherein the solid is mixed with ethyl acetate.

11. The process according to claim 1, wherein Compound (A) isolated in step iii has 0.2% by weight of total impurities or less.

12. The process according to claim 11, wherein Compound (A) has 0.1% by weight of total impurities or less.

13. The process according to claim 11, wherein Compound (A) is devoid of mesityl oxide impurity: ##STR00021##

14. The process according to claim 11 further comprising combining Compound (A), together with one or more pharmaceutically acceptable excipients to produce a pharmaceutical composition.

15. The process according to claim 14, wherein the Compound (A) is present in the pharmaceutical composition in combination with another active pharmaceutical ingredient.

16. The process according to claim 9 wherein after filtration the solid is washed with ethyl acetate.

17. The process according to claim 16, wherein after washing the solid is dried under vacuum at 272 C. for 2 hours.

18. The process according to claim 17, wherein after drying the solid is powdered and dried again under vacuum at 532 C. for 4 hours.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present inventors have developed a process for preparing atazanavir sulphate, more specifically, Form A of atazanavir sulphate [hereinafter referred to as Compound (A)]. The process of the invention not only results in the formation of pure Compound (A), but also the product is devoid of mesityl oxide impurities. As used herein, the term substantially free refers to atazanavir sulphate Form A having about 0.3% by weight of total impurities or less, preferably about 0.2% by weight of total impurities or less, more preferably about 0.1% by weight of total impurities or less. The total impurity contents described herein relates to the impurities related to atazanavir sulphate as determined by high performance liquid chromatography (HPLC).

(2) According to an aspect of the present invention, there is provided a process for the preparation of Compound (A) that comprises preparing atazanavir sulphate by treating atazanavir base (Compound (II)) with sulphuric acid in a combination of solvents, and isolating Compound (A).

(3) Preferably, according to the present invention, a combination of solvents is used, in place of the aliphatic ketones used in the prior art, such as acetone, to obtain Compound (A). Compound (A) prepared by the process of the invention is, at least substantially, free of impurities.

(4) The process of the present invention may be particularly advantageous in that the need for repeated processing, such as washing and drying of Compound (A) to remove genotoxic impurity mesityl oxide, may be avoided.

(5) Preferred experimental conditions for the process for preparing Compound (A) are depicted in scheme I:

(6) ##STR00017##

(7) The present invention preferably provides a process for preparing Compound (A) comprising treating Compound (II) with sulphuric acid in the presence of a combination of solvents and isolating Compound (A).

(8) The purity (measured by HPLC) of the Compound (A) obtained according to the present invention is preferably above 99.6%, more preferably above 99.7%, more preferably above 99.8%, and still more preferably 99.9% or more.

(9) Compound (II) used as a starting material may be prepared by the processes known in the art, for example by using (1-[4-(pyridin-2-yl)phenyl]-5(S)-2,5-bis[tert-butoxycarbonyl)amino]-4(S)-hydroxy-6-phenyl-2-azahexane [Di-BOC compound] as the precursor.

(10) The sulphuric acid may be a concentrated sulphuric acid, and preferably a neat sulphuric acid is used. A neat sulphuric acid is defined herein as 98% pure sulphuric acid. Neat sulphuric acid is available commercially.

(11) The addition of sulphuric acid may be carried out at elevated temperature, and is preferably carried out at a temperature ranging from about 35 C. to about 60 C., more preferably ranging from about 40 C. to about 55 C., most preferably about 432 C.

(12) The combination of solvents used in the process of the present invention may comprise a combination of two or more water miscible solvents, a combination of two or more water immiscible, or moderately soluble in water, solvents, or a combination of one or more water miscible solvents and one or more water immiscible, or moderately soluble in water, solvents.

(13) The combination of solvents may comprise one or more water immiscible, or moderately soluble in water, solvents selected from the group consisting of esters, hydrocarbons, and ethers. Preferably the combination of solvents comprises an ester such as ethyl acetate, isopropyl acetate, or isobutyl acetate.

(14) The combination of solvents may comprise one or more water miscible solvents selected from the group consisting of polar protic solvents and polar aprotic solvents. Preferably the combination of solvents comprises one or more solvents selected from the group consisting of alcohol, dimethyl formamide (DMF), and dimethyl sulphoxide (DMSO).

(15) Preferably the combination of solvents comprises a water immiscible, or moderately soluble in water, solvent, and a water miscible solvent. Preferably the combination of solvents comprises a polar solvent and a non-polar, or weakly polar, or borderline polar aprotic, solvent. The polar solvent may be protic or aprotic. More preferably the combination of solvents comprises a first solvent that is water immiscible, or moderately soluble in water, and non-polar, or weakly polar, or borderline polar aprotic, and a second solvent that is water miscible and polar protic or polar aprotic.

(16) The combination of solvents may comprise a first solvent that is water immiscible and borderline polar aprotic and a second solvent that is water miscible and polar protic.

(17) The combination of solvents may comprise a first solvent that is water immiscible and borderline polar aprotic and a second solvent that is water miscible and polar aprotic.

(18) The combination of solvents may comprise a first solvent that is moderately soluble in water and non-polar to weakly polar and a second solvent that is water miscible and polar aprotic.

(19) Preferably the combination of solvents comprises two solvents. Alternatively, the combination of solvents may comprise more than two solvents.

(20) Preferably the combination of solvents is selected from the following group of solvent combinations: i) ethyl acetate-methanol, ii) ethyl acetate-dimethyl sulfoxide, iii) ethyl acetate-dimethylformamide, iv) isopropyl acetate-methanol, v) isopropyl acetate-dimethylsulfoxide or vi) isopropyl acetate-dimethylformamide. The most preferable combination of solvents is ethyl acetate-methanol.

(21) The combination of solvents may be prepared by mixing two solvents, preferably one water immiscible, or moderately soluble in water, solvent and one water miscible solvent, in a fixed proportion. The ratio of water immiscible, or moderately soluble in water, solvent to water miscible solvent used in the combination may be in the range of from 10:3 to 10:1. Preferably the ratio is 10:3, 10:2 or 10:1. Most preferably the ratio of solvents used in the combination is 10:1.

(22) According to the process of the present invention, a solid may be obtained when Compound (II) is treated with neat sulphuric acid and a combination of solvents, and the solid is then further isolated to obtain substantially pure Compound (A).

(23) The Compound (A) may be isolated by filtering the solid, washing with a solvent and drying. Preferably the drying is done at a temperature in the range of from about 40 C. to about 65 C., more preferably in the range of from about 50 C. to about 60 C. Most preferably the Compound (A) is dried at about 532 C.

(24) The isolation may be, optionally, carried out by mixing the solid with a water immiscible solvent. Preferably, the solid is mixed with a water immiscible solvent selected from the group consisting of esters, hydrocarbons, and ethers. More preferably, the solvent used is ethyl acetate.

(25) An entire preferred process for synthesizing Atzanavir sulphate according to the present invention may be depicted by the following Scheme 2:

(26) ##STR00018##

(27) As depicted in Scheme 2, Compound (A) may be prepared using (1-[4-(pyridin-2-yl)phenyl]-5(S)-2,5-bis[tert-butoxycarbonyl)amino]-4(S)-hydroxy-6-phenyl-2-azahexane (Compound (V)) as a starting material. Compound (V) may deprotected using Cp grade HCl in methylene dichloride (MDC) to give (1-[4-(pyridine-2-yl)phenyl]-5(S)-2,5-Diamino]-4(S)-hydroxy-6-phenyl-2-azahexane (Compound (IV)). Compound (IV) may then be reacted with N-methoxy carbonyl-L-tert. leucine to give the atazanavir base (Compound (II)). Compound (II) is then contacted with a combination of solvents, such as EtAc-methanol, or EtAc-DMSO, or ETAc-DMF, or isopropyl acetate-DMSO, or isopropyl acetate-methanol, or isopropyl acetate-DMF, in sulphuric acid to provide atazanavir sulphate (Compound (A)).

(28) The process of the present invention described herein provides Compound (A), which is substantially free of impurities, and in particular, devoid of the gentotoxic impurity mesityl oxide. The level of mesityl impurity is controlled effectively by the process of the present invention as is indicated by non-detection by HPLC of the impurity in Compound (A).

(29) The present invention further provides a Compound (A) devoid of genotoxic impurities, substantially as described hereinbefore, for use in the manufacture of a medicament for the treatment of a viral disease such as HIV-AIDS and/or for the treatment of HIV-AIDS in its preliminary stages.

(30) The present invention further provides a pharmaceutical composition comprising substantially pure atazanavir sulphate Form A (Compound (A)), and a pharmaceutically acceptable carrier.

(31) According to another aspect of the invention there is provided a process of removing mesityl oxide impurity from Compound (A), wherein the process comprises (i) preparing atazanavir sulphate by methods described in the prior art which are herein incorporated by reference in their entirety and slurrying atazanavir sulphate in a combination of solvents and (ii) isolating Compound (A). Preferably the combination of solvents used in step (i) is as defined above according to the previous aspects of the invention. The Compound (A) that is isolated in step (ii) of this process may be substantially pure and may be devoid of mesityl oxide impurity.

(32) While the present invention has been described in terms of its specific embodiments, 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 invention.

EXAMPLES

Example 1: Preparation of Compound (A) Using Acetone as Per Example 1 of WO 99/36404/U.S. Pat. No. 6,087,383

(33) 644 ml of acetone and 92.0 gm of (3S,8S,9S,12S)-3,12-bis(1,1-dimethylethyl)-8-hydroxy-4,11-dioxo-9-(phenylmethyl)-6-[[4-(2-pyridinyl)phenyl]methyl]-2,5,6,10,13-pentaazatetradecanedioic acid dimethyl ester [Compound (II)] were mixed at 272 C. The reaction mass was heated to 502 C. 5 M Sulphuric acid (26 ml) was added at 502 C. and stirred for an hour. The contents were cooled to 282 C., chilled to 32 C. and maintained at 32 C. for 2 hours. The solid was filtered and washed with 1 volume of heptane. The solid was washed with 80 ml of acetone and dried under vacuum at 532 C. for 8 hours. The material was powdered and dried for further 4 hours under vacuum at 532 C. The drying process was continued till the LOD (loss on drying) was less than 0.5% w/w to obtain the title compound. Dry weight: 90-92 gms Yield: 85.8% to 87.8% HPLC Purity: 99.6%

Example 2: Preparation of Compound (A) Using Ethyl Acetate:Methanol

(34) A solvent mixture of 500 ml of ethyl acetate and 50 ml of methanol was added to 100 gms of (3S,8S,9S,12S)-3,12-bis(1,1-dimethylethyl)-8-hydroxy-4,11-dioxo-9-(phenylmethyl)-6-[[4-(2-pyridinyl)phenyl]methyl]-2,5,6,10,13-pentaazatetradecanedioic acid dimethyl ester [Compound (II)]. The reaction mixture was stirred at a temperature of 272 C. to get a suspension. The temperature of the suspension was then raised to 432 C. and 7.5 ml (13.9 gms) of sulphuric acid was added slowly. The solution was maintained for an hour at a temperature of 432 C. whereby a solid was obtained. The material was cooled down to a temperature of 272 C. To this 200 ml of ethyl acetate was added, followed by chilling the reaction mixture at a temperature of 32 C. The solid obtained was filtered and washed with 1 volume of ethyl acetate. The solid was then exposed to drying process under vacuum at 272 C. for 2 hours. The material was powdered and again exposed to drying process under vacuum (63020 mm of Hg) at 532 C. for 4 hours. The drying process was continued till the LOD (loss on drying) was less than 0.5% w/w to obtain the title compound.

(35) Dry weight: 100 gms

(36) Yield: 87.8%

(37) HPLC Purity: 99.9%

Example 3: Preparation of Compound (A)

(38) 1) 644 ml of acetone and 92.0 gm of (3S,8S,9S,12S)-3,12-bis(1,1-dimethylethyl)-8-hydroxy-4,11-dioxo-9-(phenylmethyl)-6-[[4-(2-pyridinyl)phenyl]methyl]-2,5,6,10,13-pentaazatetradecanedioic acid dimethyl ester [Compound (II)] were mixed at 272 C. The reaction mass was heated to 502 C. Sulphuric acid (26 ml) was added at 502 C. and stirred for an hour. The contents were cooled to 282 C., chilled to 32 C. and maintained at 32 C. for 2 hours, filtered and suck dried.

(39) 2) To the solid obtained in step 1), 200 ml of a mixture of ethyl acetate:methanol (10:1) was added, followed by chilling the reaction mixture at a temperature of 32 C. The compound obtained was filtered and washed with 1 volume of ethyl acetate. The solid was then exposed to drying process under vacuum at 272 C. for 2 hours. The material was powdered and again exposed to drying process under vacuum (63020 mm of Hg) at 532 C. for 4 hours. The drying process was continued till the LOD (loss on drying) was less than 0.5% w/w to obtain the title compound.

(40) Dry weight: 92 gms

(41) Yield: 80.7%

(42) Determination of the Content of Mesityl Oxide Impurity

(43) Method of Analysis

(44) The title compound obtained from the three examples as above was analyzed by HPLC for the content of mesityl oxide.

(45) HPLC Specifications Column: Purosphere star RP-18e, 10 cm4.6 mm, 3 m Eluent: Gradient of Trifluoro acetic acid buffer and Acetonitrile Flow: 1.0 ml per minute Detector: UV Sample volume: 20 l Diluent A: Mix 25 ml ammonia solution (25%) in 475 ml of methanol Diluent B: Diluent A:water (80:20) Mobile phase composition and flow rate may be varied in order to achieve required system suitability.

(46) Sample Preparation:

(47) About 500 mg of atazanavir sulphate is weighed in a 10 ml volumetric flask. The sample is dissolved and diluted to volume with diluent B. Sonicated and filtered through 0.45 m filter.

(48) Standard Preparation:

(49) About 100 mg of mesityl oxide is weighed in a 100 ml volumetric flask. The sample is dissolved and diluted to volume with diluent A. Diluted 10 ml of the solution to 100 ml with diluent A. 5 ml of the above solution transferred to 100 ml volumetric flask and diluted to volume with diluent B.

(50) Method

(51) The freshly prepared sample solutions are injected into the chromatograph and the chromatogram of the sample is continued up to the end of the gradient. The areas for each peak in each solution is determined using a suitable integrator.

(52) Results

(53) The title compound obtained from the three examples as above was analyzed by HPLC for the content of mesityl oxide as shown in Table 1 in accordance with the above method. The results indicate the absence of mesityl oxide impurity by the process of the present invention.

(54) TABLE-US-00001 TABLE 1 Mesityl oxide content value Example 1 13 ppm Example 2 Not detected Example 3 Not detected

(55) The present invention has been described above purely by way of example. It should be noted that modifications in detail may be made within the scope of the appended claims.