PROCESS FOR PREPARING POLYMORPHIC FORMS OF (S)-ό-CHLORO- (CYCLOPROPYLETHYNYL)- i ,4-DIHYDRO-4-(TRIFLUOROMETHYL)-2H-3 , 1 -

BENZOXAZIN-2-ONE

Field of the Invention

This invjention, in general, relates to a process for preparing polymorphic forms of (S)-6 -chloro-(cyclopropylethynyl)- 1 ,4-dihydro-4-(trifluoromethyl)-2H-3 , 1 - benzoxazin-2-orie (Efavirenz). More particularly, the present invention provides a novel process for preparing polymorphic Forms of efavirenz referred as Mi, I, II, β, and ω.

Background of the Invention

Efavirenz is a non-nucleόside reverse transcriptase inhibitor (NNRTI) and is used as part of highly active antiretroviral therapy (HAART) for the treatment of a human immunodeficiency virus !(HIV) type 1. Efavirenz is also used in combination with other antiretroviral agents as part of an expanded postexposure prophylaxis regimen to prevent HIV transmission for those exposed to materials associated with a high risk for HIV transmission.

Efavirenz

Efavirenz product is first claimed in US 5,519,021. The process disclosed in this patent involves reaction of racemic Efavirenz with optically active acid derivative followed by repeated purifications to give diastereomer. It is further subjected to hydrolysis in the presence of acid in n-butanol to give crude Efavirenz which is then

recrystallized from hexane to give pure Efavirenz. However, this patent does not

I disclose any polymorphic forms of Efavirenz.

US patents 6,939,964 and 6,639,071 claimed _] crystalline efavirenz polymorphic Forms I, II and III. US 6,673,372 patent disclosed the crystalline efavirenz polymorphic Forms 1, 2, 3, 4 & 5. US 2006/0235008 claims different crystalline and amorphous forms of Efavirenz and process for, the preparation thereof.

WO 2006/040643 application further discloses Efavirenz polymorphic Forms α, β, γ, γl, γ2, ω, δ, N, O, P and processes for their preparation. The reproduction of examples for these polymorphs as disclosed in WO '643 is found to be very inconsistent. Also, it was found; that some of these forms were never reproduced in our laboratory.

In light of above disadvantages in prior art processes, there is a need to prepare the pure and stable Efavirenz polymorphic forms by an efficient, economic and reproducible process, particularly to large scale preparation. Further, it should be suitable for handling and should have excellent physical and chemical stability, mainly to different heat and humidity conditions.

Summary of the Invention

In accordance with prinicipal aspect of the present invention, there is provided a novel process for preparing polymorphic Forms of efavirenz, referred as Mi, I, II, β,

isolating the pure efavirenz polymorphic Form β.

water and water miscible organic solvent, removing the solvent and isolating the i , ! efavirenz polymorphic Form β, wherein the solvent is removed by employing freeze drying or distillation method.

! Brief Description of the Drawings:

Further objects of the present invention together with additional features contributing thereto and advantages accruing there from will be apparent from the following description of preferre ^' d embodiments of the invention which are shown in the accompanying drawing figures, wherein: Figure 1 : X-ray powder diffraction pattern of Efavirenz Form Mi Figure 2: DSC of Efavirenz Form Mj i Detailed Description of the Invention,

While this specification concludes with claims particularly pointing out and distinctly claiming that, which is regarded as the invention, jit is anticipated that the invention can be more readily | understood through reading the following detailed description of tlie invention and study of the included examples.

The disclosed embodiment of the present invention; deals with a novel and consistent process for preparing polymorphic forms of (S)-ό-chloro-

According to the present invention, the polymorphs disclosed herein are further characterized by X-ray powder diffraction pattern (XRD), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC),| and/or moisture content (MC). Powder X-rav Diffraction (PXRD)

The PXRD measurements were carried out using P[ANalytical, X'Pert PRO powder diffractometer equipped with goniometer of !θ/θ configuration and i !

X'Celerator detector. The Cu-anode X-ray tube was operated at 4OkV and 3OmA. The experiments were conducted over the 2θ range of 2.0°-50.0°, 0.030° step size and 50 seconds step time.

Differential Scanning Calorimetrv TDSO

The DSC measurements were carried out on Mettler Toledo 822 Star ^c instrument. The lexperiments were performed at a heating rate of 10.0°C/minute over a temperature range of 30°C-200°C purging with nitrogen at a flow rate of 50ml/minute. Standard aluminum crucibles covered by lids with three pin holes were

I I used. J '

According to the present invention the novel polymorphic form Mi of efavirenz is characterized by PXRD as shown in Figure 1 and DSC as shown in Figure 2.

The present invention provides a novel process fori preparing polymorphic Form Mi of efavirenz, wherein said process comprises of dissolving efavirenz in a suitable solvent at a temperature range between 20-30 ⁰ C, preferably at 25-30 ⁰ C, cooling the resultant to 0-10°C,i preferably 0-5 °C followed by the addition of water and isolating the efavirenz Form Mi. The solvent used herein for dissolution is selected from a group consisting of formic acid, pyridine or mixtures thereof with water.

In another embodiment, the present invention provides a process for preparing polymorphic Form I of efavirenz, wherein the process comprises of heating crystalline efavirenz Form] Mi at 70-80 ⁰ C under vaccum for several hours to obtain Form I of efavirenz. j ' '

In another embodiment of the present invention, there is provided a process for preparing polymorphic Form I of efavirenz, wherein said process comprises of dissolving efavirenz in a solvent selected from the group consisting of lower aliphatic carboxylic acids, chlorinated solvents, hetero-aromatics, esters, or mixtures thereof, preferably selected from acetic acid, dichloromethane (DCM), pyridine, ethyl acetate

J ' j or mixtures thereof with water followed by addition of n-heptane, water or mixtures thereof and recovering the crystalline efavirenz Form I using different crystallization methods like anti-solvent or slow or fast crystallization or by idistillation method.

The present invention also provides a process for preparing Form II of efavirenz, wherein said process comprises of dissolving efavirenz in n-butanol,

cooling the resultant to 0-5 ⁰ C followed by addition of water to obtain efavirenz Form II.

Further embodiment of the present invention provides a novel process for preparing polymorphic Form β of efavirenz, wherein the process comprises of dissolving efavirenz in a solvent at room temperature, cooling the resultant solution followed by seeding the resultant solution, adding anti-solvent and isolating the pure efavirenz polymorphic Form β. The temperature used herein for dissolving the efavirenz is in the range of 20-30 ⁰ C, preferably 25-3O ⁰ C. The clear solution is then cooled to 0-10°C, preferably to 0-5 ⁰ C and then seeded (~4°/o) with efavirenz Form β in lots, preferably in 1 -3 lots. The antisolvent is then added to the above solution over a period of 1-3 hours. The precipitated solid is filtered and dried to obtain polymorphic Form β of efavirenz. i

According to the present invention, the solvent used herein for the preparation of β form of efavirenz is selected from the group comprising (lower aliphatic alcohols, lower aliphatic! carboxylic acids, hetero aromatics, polar laprotic solvents, esters, aliphatic hydrocarbons, or mixtures thereof with water, preferably methanol (MeOH), ethanol (EtOH), isopropyl alcohol (IPA), formic acid, acetic acid, ethyl acetate (EtOAc), isopropyl acetate, dimethylformamide (DMF), l-methyl-2-pyrrolidinone (NMP). According to the present invention, the anti solvent is selected from n- heptane, water or mixtures thereof.

In an alternative embodiment of the present invention, the β form of efavirenz is prepared by a process comprising of dissolving efayirenz in a mixture of acetone/water or methanol/water followed by lyophilization or freeze-drying.

The β form of efavirenz, according to the present invention, can also be prepared by slurring Form M ₁ in heptane, Isopropyl ether] (IPE), water or mixture thereof at ambient temperature for several hours.

The β form of efavirenz ¹ can also be prepared by exposing Form Mj to relative humidity (RH> ¹ 90%) at ambient temperature for several hours at ambient temperature.

According to the present invention the β form of efavirenz is prepared consistently by above said processes having higher purity and stability under different heat and humid conditions.

In another embodiment, the present invention provides a process for preparing

I i polymorphic Form ω of efavirenz, wherein the process comprises of dissolving efavirenz in a mixture of methanol and water followed by lyophilization or freeze- drying.

In the foregoing, embodiments are described by way of below examples to illustrate the process of invention. However, these are not intended in any way to limit the scope of the present invention and several variants of these examples would be evident to person ordinarily skilled in the art.

Example 1

Preparation of polymorphic Form Mx of efavirenz i I

Efavirenz (3 g) was dissolved in formic acid (30 mli) and the resulting clear solution was cooled to about 0-5 ⁰ C, stirred for 30 min. Then added 400 ml of DM Water slowly and maintained at 0-5 ⁰ C, then filtered and dried at ambient temperature. The resulting crystalline solid was identified as Efavirenz Form M]. XRD of the dried sample showed it to be Form Mi

, Example 2

Preparation of polymorphic Form M^ of efavirenz

Efavirenz (3 g) was dissolved in pyridine (20 ml)ι and the resulting clear solution was cooled to about 0-5 ⁰ C, stirred for 30 min. Then 400 ml of DM Water was added slowly and maintained for 1 hr at 0-5°C, then filtered and dried at ambient temperature. The resulting crystalline solid was identified as Efavirenz Form Mj XRD of the dried sample showed it to be Form Mi.

Example 3 Preparation of β form of efavirenz:

2 g Efavirenz was dissolved in indicated solvents at ithe indicated volumes at 50-60 ⁰ C. The resulting solution is then filtered through hy-flow bed to remove undissolved particulate. The resulting clear solution was then subjected to freeze drying (Model: Virtis Genesis i SQ Freeze Dryer) at -104 ⁰ C and below 200 Torr

_I I vacuum. The results are shown in following Table 1.

Table 1

Input Solvents Volume ratio (v/v) Result i Water : Acetone 1 :1.25

Efavirenz _Water . _Methanol 1 :1.5 Form β

Methanol 1 :5

Example 4

Preparation of β form of efavirenz:

3g of Efavirenz was dissolved in indicated solvents at the indicated volumes at 25-30°C and stirred for 30 min; The resulting solution was cooled to 0-5 °C and an indicated anti solvent at the indicated volumes are added slowly. The resulting reaction mass was stirred at 0-5°C. The solid is filtered and washed with 5 ml of

; . i indicated solvents. The wet solid was dried at 25-30°C. The results are shown in following Table 2.

Tabled

Process Input i Solvents Volume ratio (v/v) PXRD Result

Acetic acid : water 1 :20

Antisolvent Efavirenz DMF : water 1:14 Form β

NMP : water 1:114

, Example 5

Preparation of β form of efavirenz:

Efavirenz (3 g) is suspended in Ethyl acetate (30 ml) at room temperature. Stir for 15 min to get clear solution. ¹ Filtered through cotton and cooled the solution to 0-

5°C. Seeds added to the clear solution at 0-5 ⁰ C. To this solution n-heptane (400 ml) added in two lo 'ts, with addition ^'1 of second lot of the seeds an id stirred for 30 min at 0-

5°C. Distilled to half of the volume, then cooled to 0-5 ⁰ C arid maintained for 1 hour. Solid material formed was filtered and air-dried. The solid obtained was identified as

Efavirenz Form β. i

XRD of the dried sample showed it to be Form β

Example 6

Preparation of β form of efavirenz:

Efavirenz (5 g) is suspended in methanol (50 ml) at room temperature. Stir for 15 min to get clear solution. Filtered through cotton and cooled the solution to 0-5 ⁰ C Seeds of form-β (approx. 4%) in two lots added to the clear solution and stirred for 30

XRD showed it' to be Form β

' Example 7

Preparation of Form I of Efavirenz:

1 g of Efavirenz Form Mj obtained as described above was kept in a static dryer and heated at 80 ⁰ C under vacuum for 15 hr. The resulting solid was identified as Efavirenz Form I. '

XRD showed it to be Form I

Example 8 Preparation of Form I of Efavirenz:

Taken 3 g of Efavirenz in formic acid (30 ml) and heated to 8O ⁰ C to obtain a clear solution. Cooled to room temperature and added water (100 ml) slowly for 15-

30 min and maintained for 36 'hrs at Room Temperature (RT) with agitation. The resulting white free flowing solid was filtered and identified J as. ^' Efavirenz Form I.

XRD showed it to be Form I '

I ! Example 9

Preparation of Form I of efavirenz:

Taken Efavirenz (1 g) in pyridine (2 ml) and filtered to remove undissolved particulate. The resulting solution was kept in Petri dish for aerial drying. The solid obtained was identified as Efavirenz Form I. XRD showed it to be Form I

Example 10

Preparation of Form I of efavirenz:

Taken Efavirenz (1 g) in dichloromethane (25 ml) at room temperature and the resulting clear solution was distilled completely under vacuum. The solid obtained was identified as Efavirenz Form I. XRD showed it to be Form I

Example 11 Preparation of Form I of efavirenz:

Taken Efavirenz (3 g) in ethyl acetate (30 ml) and stirred for 15-30 min at room temperature. To the resulting solution added n-heptaneι(300 ml) and stirred for 1 hr at room temperature. The resulting clear solution was distilled half of the volume of reaction mass and cooled to room temperature and filtered. The obtained solid was identified as Efavirenz Form I.

XRD showed it to be Form I

Example 12 Preparation of Form II of efavirenz:

Taken 3 g of Efavirenz in n-butanol (30 ml) and the resulting clear solution was filtered though hy-flow bed to remove undissolved particulate. The solution was cooled to 0-5 ⁰ C, added water (400 ml) maintained for 1 hr and filtered. The obtained solid was identified as Efavirenz Form II. XRD showed it to be Form II

While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present invention is not limited to those precise embodiments rather, in view of the present disclosure, which describes the current best mode for practicing the invention, many modifications and variations, would present themselves to those skilled in the art without departing from the scope and spirit of this invention. This invention is susceptible to considerable variation in its practice within the spirit and scope of the appended claims.