DESC:Technical field of the invention:
The present invention relates to a stable amorphous form of Tenofovir alafenamide phosphate and process for preparation thereof. Further the invention provide process for the preparation tenofovir alafenamide acid addition salts using amorphous form of tenofovir alafenamide phosphate.

Background of the invention:
9-[(R)-2-[[(S)-[[(S)-l-(isopropoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy]propyl] adenine, an isopropylalaninyl monoamidate phenyl monoester (tenofovir alafenamide), is a prodrug of (R)-9-(2-phosphonomethoxypropyl)adenine (tenofovir).

The process for preparation of the tenofovir alafenamide fumarate salt was first disclosed in the patent application WO2002008241.

The application WO2013025788 discloses Tenofovir alafenamide hemifumarate and process for preparation thereof.

The application WO2015040640 provides an improved process for the preparation of tenofovir alafenamide or pharmaceutically acceptable salts namely phosphate, succinate, citrate, tartarate, lactate, methanesulfonate.

WO2015176602 discloses Tenofovir alafenamide complex, preparation method and use thereof.

WO2016192692A1 provides solid forms of tenofovir alafenamide with inorganic and organic acids and methods for preparing the same namely hydrochloric, hydrobromic, sulfuric, phosphoric, maleic, citric, succinic, tartaric, gallic, benzenesulfonic, salicylic and 4-aminobenzoic acids. WO2016205141 discloses co-crystals, salts and crystalline forms of tenofovir alafenamide and methods for preparation, use and isolation of such compounds.
In view of the above discussed prior art references, it is evident that tenofovir alafenamide or salts exhibits different polymorphic forms under differential conditions that include solvent, moisture, temperature, time and drying conditions and thus the bioavailability of the same also varies with polymorphic modification.

A change in crystal structure of compound by means of change in polymorphism affects physicochemical properties like dissolution and solubility, chemical and physical stability, flowability and hygroscopicity of a compound. Therefore, there remains a need in the art for polymorphic forms of tenofovir alafenamide acid addition salts which are having greater stability, flowability, dissolution properties; thereby increasing the bioavailability of the drug.

Objectives of the invention:
An object of the present invention is to provide a stable amorphous form of tenofovir alafenamide phosphate.

Another object of the present invention is to provide a process for the preparation of amorphous form of tenofovir alafenamide phosphate.

Further object of the present invention is to provide process for the preparation tenofovir alafenamide acid addition salts using amorphous form of tenofovir alafenamide phosphate.

Brief description of drawings:
Figure 1 depicts powder X-ray diffraction (PXRD) of amorphous form of tenofovir alafenamide phosphate.

Detailed description of the invention:
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.
According to the first aspect of the invention, the present application provides a stable amorphous form of tenofovir alafenamide phosphate.

According to the second aspect of the invention, the present application provides an amorphous form of tenofovir alafenamide phosphate characterized by powder X-ray diffraction (PXRD) pattern substantially as illustrated by Figure 1.

According to the third aspect of the invention, the present invention provides a process for the preparation of an amorphous form of tenofovir alafenamide phosphate comprises steps of:
a) providing a solution of tenofovir alafenamide in a solvent,
b) treating the solution with phosphoric acid at 50°C or above,
c) stirring the solution at 50°C or above,
d) cooling the solution and optionally stirring,
e) isolating amorphous tenofovir alafenamide phosphate, and
f) drying the amorphous tenofovir alafenamide phosphate.

Providing a solution in step a) includes:
i) direct use of a reaction mixture containing tenofovir alafenamide that is obtained in the course of its synthesis; or
ii) dissolving tenofovir alafenamide in a solvent optionally by heating.

The tenofovir alafenamide may be obtained by the processes known in the art. The tenofovir alafenamide used in preparing the polymorph may be obtained by methods described in the prior art which are herein incorporated by reference in their entirety. The tenofovir alafenamide used as a starting material can be in any form, e.g. it can be in a reaction solution, suspension, crude or in anhydrous, hydrated or solvated form.

The solvents which can be used in step a) include but are not limited to: alcoholic solvents such as methanol, ethanol, isopropyl alcohol, n-propanol, isoamyl alcohol and the like; halogenated hydrocarbons such as dichloromethane, 1 ,2-dichloroethane, chloroform, carbon tetrachloride and the like; ketones such as acetone, ethyl methyl ketone, methyl isobutyl ketone and the like; esters such as ethyl acetate, isopropyl acetate, n-propyl acetate, n-butyl acetate, t-butyl acetate and the like; ethers such as diethyl ether, dimethyl ether, di-isopropyl ether, 1 ,4-dioxane and the like; hydrocarbons such as toluene, xylene and the like; and any mixtures of two or more thereof. Most preferably the solvent is selected from ethyl acetate and isopropyl acetate.

In step b), the solution of tenofovir alafenamide obtained in step a) is treated with phosphoric acid at 50°C or above, preferably 80°C, most preferably 60°C

In step c) the reaction material obtained in step b) of the process is optionally further heated at least about 50°C to about reflux temperature for about 0.5 hour to about 6 hours.

In step d) prior to the isolation , the reaction material obtained in step c) of the process is optionally cooled to a temperature range of 15ºC to 45ºC and stirred for about 1 hour to about 10 hours, preferably for about 2 hours to about 8 hours, more preferably for about 3 hours to about 6 hours.

In step e) the material obtained in step d) is isolated optionally by removing the solvent. Suitable techniques which can be used for the removal of solvent include but not limited to evaporation, flash evaporation, simple evaporation, rotational drying, spray drying, agitated thin-film drying, agitated nutsche filter drying, pressure nutsche filter drying, freeze-drying or any other suitable technique known in the art. The solvent may be removed, optionally under reduced pressures, at temperatures less than about 100°C, less than about 75°C, less than about 60°C, less than about 50°C, or any other suitable temperatures.

The solid obtained from step e) may be optionally collected by using techniques such as by scraping, or by shaking the container, or other techniques specific to the equipment used.

In step f) the solid isolated from step e), may be optionally further dried to afford an amorphous form of tenofovir alafenamide phosphate.

Drying can be carried out in a tray dryer, vacuum oven, air oven, cone vacuum dryer, rotary vacuum dryer, fluidized bed dryer, spin flash dryer, flash dryer, or the like. The drying can be carried out at temperatures of less than about 60°C, less than about 50°C, less than about 40°C, less than about 30°C, less than about 20°C, or any other suitable temperatures; at atmospheric pressure or under a reduced pressure; as long as the product is not degraded in its quality. Suitable time for drying can vary from few minutes to several hours for example from about 30 minutes to about 24 hours or more.

According to forth aspect of the invention, the amorphous tenofovir alafenamide phosphate may be prepared using crystalline tenofovir alafenamide phosphate.

The novel polymorph of tenofovir alafenamide phosphate obtained according to the present invention is substantially free from other crystal forms of tenofovir alafenamide phosphate. “Substantially free” from other forms of tenofovir alafenamide phosphate shall be understood to mean that the polymorphs of tenofovir alafenamide phosphate contain less than 10%, preferably less than 5%, of any other forms of tenofovir alafenamide phosphate and less than 1% of other impurities, water or solvates. Thus, the tenofovir alafenamide phosphate prepared according to the present invention contains less than 11% total impurities, preferably less than 6% total impurities. In a particularly preferred embodiment, the amorphous form of tenofovir alafenamide phosphate prepared according to the present invention contains less than 1% total impurities.
The amorphous form of tenofovir alafenamide phosphate obtained according to the present invention was found to have dissolution and solubility comparable to tenofovir alafenamide hemifumarate.

The amorphous tenofovir alafenamide phosphate obtained by the processes disclosed in the present invention may be formulated as solid compositions together with a pharmaceutically acceptable carrier, glidant, diluent, or excipient, for oral administration in the form of capsules, tablets, pills, powders or granules.

According to fifth aspect of the invention, the present invention provides the preparation tenofovir alafenamide acid addition salts using amorphous form of tenofovir alafenamide phosphate obtained by the process of the present invention.

The process for preparation of tenofovir alafenamide acid addition salts from amorphous tenofovir alafenamide phosphate comprising the steps of:
i) providing solution of amorphous tenofovir alafenamide phosphate in a two-phase solvent system,
ii) treating solution from step i) with a base,
iii) treating the obtained tenofovir alafenamide from the organic layer with a suitable acid, other than the phosphoric acid and
iv) isolating tenofovir alafenamide acid addition salts.

Providing solution of amorphous tenofovir alafenamide phosphate in a two-phase solvent system wherein the two-phase solvent system comprises an aqueous and a non-miscible organic solvent. The non-miscible organic solvent is one in which the tenofovir alafenamide phosphate is substantially soluble. Examples of suitable non-miscible organic solvents are alkanes, cycloalkanes, alcohols, ketones, aldehydes, esters, aromatic hydrocarbons, chlorinated hydrocarbons and organic acids. Preferred solvents are chlorinated hydrocarbons, especially chlorinated alkanes such as methylene chloride.
Treating the solution of step i) with a base, wherein the base is selected from an organic base selected from the group comprising of dimethylamine, triethyl amine, 4-(Dimethylamino)pyridine, N-Ethyldiisopropylamine, Tetramethylammonium hydroxide and the like; or inorganic base selected from sodium hydroxide, ammonia, sodium carbonate, sodium bicarbonate, calcium hydroxide, and calcium carbonate and the like.

Treating the so obtained tenofovir alafenamide from the organic layer with a suitable acid other than the phosphoric acid in step iii) includes:
a) treating the tenofovir alafenamide in the organic layer with a suitable acid other than the phosphoric acid and
b) distilling the organic layer or
c) isolating the tenofovir alafenamide from the organic layer, dissolving in a suitable solvent & treating with suitable acid other than the phosphoric acid or
d) isolating & drying the tenofovir alafenamide from the organic layer & treating with suitable acid other than the phosphoric acid.

The suitable acids are selected from either organic acid or an inorganic acid excluding phosphoric acid. The organic acid may be selected from the group consisting of acetic acid, oxalic acid, fumaric acid, citric acid, succinic acid, tartaric acid, salicylic acid, benzoic acid, glycolic acid, methane sulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, lactic acid, maleic acid, malonic acid, malic acid, maleic acid, isethionic acid, lactobionic acid, mandelic acid, p-coumaric acid, ferulic acid, sinapic acid, caffeic acid, chlorogenic acid, caftaric acid, coutaric acid, p-hydroxy benzoic acid, vanillic acid, syringic acid, 4-(4- phenoxybenzoyl) benzoic acid, gentisic acid, protocatechuic acid, gallic acid, lipoic acid, aspartic acid and the like.

The inorganic acid may be selected from the group consisting of hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, sulfamic acid and the like.

The ratio of tenofovir alafenamide to the organic or inorganic acid compound may be stoichiometric or non-stoichiometric according to the present invention. For example, the ratio of tenofovir alafenamide to organic or inorganic acid compound may vary from 1:1, 1.5:1, 1 :1.5, 2:1 or 1 :2.

The reaction material obtained in step iii) of the process after treatment of suitable acid is optionally heated at least about 30°C to about reflux temperature for 0.5 hour to 6 hours.

The reaction material obtained in step iii), by following either the steps a and b or c or d; is optionally cooled to a temperature range of 10ºC to 45ºC.

The solvents which can be used include but are not limited to: alcoholic solvents such as methanol, ethanol, isopropyl alcohol, n-propanol, isoamyl alcohol and the like; halogenated hydrocarbons such as dichloromethane, 1 ,2-dichloroethane, chloroform, carbon tetrachloride and the like; ketones such as acetone, ethyl methyl ketone, methyl isobutyl ketone and the like; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, t-butyl acetate and the like; ethers such as diethyl ether, dimethyl ether, di-isopropyl ether, 1 ,4-dioxane and the like; hydrocarbons such as toluene, xylene and the like; and any mixtures of two or more thereof.

The material obtained in step iii) of the process is optionally isolated by removal of solvent.

Suitable techniques which can be used for the removal of solvent include but not limited to evaporation, flash evaporation, simple evaporation, rotational drying, spray drying, agitated thin-film drying, agitated nutsche filter drying, pressure nutsche filter drying, freeze-drying or any other suitable technique known in the art. The solvent may be removed, optionally under reduced pressures, at temperatures less than about 100°C, less than about 75°C, less than about 60°C, less than about 50°C, or any other suitable temperatures.

The solid obtained from step iv) may be collected by using techniques such as by scraping, or by shaking the container, or other techniques specific to the equipment used. The isolated solid may be optionally further dried to afford tenofovir alafenamide acid addition salt.

Drying can be carried out in a tray dryer, vacuum oven, air oven, cone vacuum dryer, rotary vacuum dryer, fluidized bed dryer, spin flash dryer, flash dryer, or the like. The drying can be carried out at temperatures of less than about 60°C, less than about 50°C, less than about 40°C, less than about 30°C, less than about 20°C, or any other suitable temperatures; at atmospheric pressure or under a reduced pressure; as long as the product is not degraded in its quality. Suitable time for drying can vary from few minutes to several hours for example from about 30 minutes to about 24 or more hours.

The tenofovir alafenamide acid addition salts obtained by the processes disclosed in the present invention were found to have improved yield and of improved purity.
In a preferred embodiment, tenofovir alafenamide acid addition salt is tenofovir alafenamide fumarate salt.

Tenofovir alafenamide fumarate salt obtained by the process above may be formulated into appropriate pharmaceutical composition.

The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

Preparation of amorphous tenofovir alafenamide phosphate

Example 1
To a reaction flask charged tenofovir alafenamide (100gm), Isopropyl acetate (2000ml) and heated the reaction material at 85°C to 90°C. The reaction material obtained was cooled to 60°C and Phosphoric acid (20.54 gm) was added. The resulting reaction material was stirred for 4hrs at room temperature. The solid obtained was filtered, washed with isopropyl acetate and dried under vacuum at 50-55°C for 8-12 hours. The obtained solid was identified as amorphous tenofovir alafenamide phosphate by PXRD Figure 1.

Dry weight-92gm

Example 2
To a reaction flask charged tenofovir alafenamide (10gm), ethyl acetate (176ml) and heated to reflux. The reaction material obtained was cooled, Phosphoric acid (2gm) was added at 70°C. The resulting reaction material was then stirred for 3hrs at room temperature. The solid obtained was filtered, washed with ethyl acetate and dried under vacuum at 50-55°C for 8-12 hours.
Dry weight-8.4gm

Preparation of tenofovir alafenamide fumarate

Example 3
To a reaction flask charged 100gm amorphous tenofovir alafenamide phosphate and 500ml methylene chloride and 500ml water. 50 ml aq. Ammonia was added. The reaction mass was stirred and the organic layer and aqueous layer were separated. The aqueous layer was discarded and the organic layer was distilled out under vacuum. The oily mass obtained was dissolved in 450ml acetone. The reaction mass was filtered and 9.2gm fumaric acid was added. The reaction mass was heated, stirred and cooled. The obtained tenofovir alafenamide fumarate was filtered and washed with Acetone. Wet solid was dried under vacuum at 75-80°C for 5 hrs.
Dry weight -80 gm.

Example 4
To a reaction flask charged 10gm amorphous tenofovir alafenamide phosphate and 50ml methylene chloride and 50ml water. 5ml aq. Ammonia was added. The reaction mass was stirred and the organic layer and aqueous layer were separated. The aqueous layer was discarded and the organic layer was distilled out under vacuum. The oily mass obtained was dissolved in 40ml acetone. The reaction mass was filtered and distilled out completely under vacuum. The solid obtained was charged with acetone and 0.9gm fumaric acid was added. The reaction mass was heated, stirred and cooled. The obtained tenofovir alafenamide fumarate was filtered and washed with Acetone. Wet solid was dried under vacuum.
Dry weight -7.0gm.

,CLAIMS:We Claims,

1. A stable amorphous form of Tenofovir alafenamide phosphate.

2. The amorphous form of Tenofovir alafenamide phosphate of claim 1, characterized by a PXRD pattern substantially as depicted in FIG. I

3. A process for preparing amorphous form of Tenofovir alafenamide phosphate of claim 1, comprising steps of:
a) providing a solution of tenofovir alafenamide in a solvent,
b) treating the solution with phosphoric acid at 50°C or above,
c) stirring the solution at 50°C or above,
d) cooling the solution, and optionally stirring,
e) isolating amorphous tenofovir alafenamide phosphate, and
f) drying the amorphous tenofovir alafenamide phosphate.

4. The process of claim 3, wherein the solvent comprises alcoholic solvents such as methanol, ethanol, isopropyl alcohol, n-propanol, isoamyl alcohol and the like; halogenated hydrocarbons such as dichloromethane, 1 ,2-dichloroethane, chloroform, carbon tetrachloride ketones such as acetone, ethyl methyl ketone, methyl isobutyl ketone and the like; esters such as ethyl acetate, isopropyl acetate, n-propyl acetate, n-butyl acetate, t-butyl acetate and the like; ethers such as diethyl ether, dimethyl ether, di-isopropyl ether, 1 ,4-dioxane and the like; hydrocarbons such as toluene, xylene and the like; and any combination thereof.

5. The process of claim 4 wherein the solvent is selected from ethyl acetate and isopropyl acetate.

6. The process of claim 3, further comprises, treating solution of tenofovir alafenamide obtained in step a) with phosphoric acid at 50°C or above, preferably 80°C, most preferably 60°C.

7. The process of claim 6, further comprises one or more steps, stirring the reaction material obtained in step b) for about 0.5 hour to about 6 hours.

8. The process of claim 7, further comprises cooling the reaction material obtained in step c) to a temperature range of 15ºC to 45ºC and stirring for about 1 hour to about 10 hours, preferably for about 2 hours to about 8 hours, more preferably for about 3 hours to about 6 hours.

9. The process of claim 8, further comprises isolating the reaction material obtained in step d), wherein isolation includes removal of solvent.

10. The process of claim 9, wherein solvent is removed by techniques such as evaporation, flash evaporation, simple evaporation, rotational drying, spray drying, agitated thin-film drying, agitated nutsche filter drying, pressure nutsche filter drying, or freeze-drying.

11. The process of claim 10, further comprises drying of amorphous tenofovir alafenamide phosphate in a tray dryer, vacuum oven, air oven, cone vacuum dryer, rotary vacuum dryer, fluidized bed dryer, spin flash dryer, flash dryer, or the like.

12. The process of claim 11, wherein the drying is carried at a temperature of less than about 60°C, less than about 50°C, less than about 40°C, less than about 30°C or less than about 20°C, for about 30 minutes to about 24 hours.

13. A pharmaceutical composition comprising a therapeutically effective amount of the amorphous tenofovir alafenamide phosphate of claim 1, and a pharmaceutically acceptable carrier, glidant, diluent, or excipient.

14. A pharmaceutical composition of claim 13, in the form of capsules, tablets, pills, powders or granules.

15. The process for obtaining amorphous tenofovir alafenamide phosphate as hereinbefore described with reference the examples.