PRIORITY

This application claims the benefit under Indian Provisional Application No. 81 l/CHE/2012, filed on March 05, 2012 entitled "Tenofovir Phosphate, Processes for the preparation and Pharmaceutical composition thereof, the contents of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to a compound Tenofovir phosphate salt, processes for their preparation and pharmaceutical compositions containing the same.

BACKGROUND OF THE INVENTION

Tenofovir disoproxil, also known as 9-[(i?)-2-[[bis[[(isopropoxycarbonyl)oxy] methoxy]phosphinyl] methoxy]propyl]adenine (CipHsoNsOioP), is represented by the structure of Formula I:

Formula I

Tenofovir disoproxil is approved as its fumarate salt and is a potent antiviral agent, available in the market under the brand name VIREAD ^® in the form of 300mg of oral tablets and in combination with other antiviral agents.

U.S. Patent No. 5,922,695 ("the '695 patent") discloses phosphonomethoxy nucleotide analogs such as tenofovir disoproxil and the salts, hydrates, tautomers and solvates thereof. The '695 patent further discloses a process for preparation of tenofovir disoproxil as its fumarate salt form by reaction of tenofovir disoproxil with fumaric acid in isopropanol.

U.S. Patent No. 8,049,009 ("the Ό09 patent") discloses tenofovir disoproxil hemifumarate and process for preparation of the same. Patent publication No. WO 2009/074351 discloses crystalline solid forms of tenofovir disoproxil and an organic acid, wherein the organic acid is selected from the group consisting of succinic acid, tartaric acid, saccharic acid, citric acid, oxalic acid and salicylic acid; and processes for the preparation thereof.

CN Publication No. 101712692 ("the '692 publication") discloses salts of tenofovir disoproxil including hydrochloric acid, sulfuric acid, phosphoric acid, toluene sulfonic acid, salicylic acid, benzoic acid, formic acid, citric acid, fumaric acid, maleic acid, malic acid. The '692 publication however, does not describe the physical characteristics of the salts of tenofovir disoproxil so obtained. The entirety of the '692 publication is incorporated herein by reference.

Our co-pending Patent applications 1230/CHE/201 1 and 3876/CHE/201 1 discloses solid forms of tenofovir disoproxil and an acid, wherein the acid is selected from the group consisting of ferulic acid, caffeic acid, coumaric acid and sinapic acid; and processes for the preparation thereof.

The discovery of new forms of a pharmaceutically useful compound provides an opportunity to improve the performance characteristics of a pharmaceutical product. It enlarges the repertoire of materials that a formulation scientist has available for designing, for example, a pharmaceutical dosage form of a drug with a targeted release profile or other desired characteristics. There is a need in the art for pharmaceutically useful solid state forms of tenofovir disoproxil having good physiochemical properties, desirable bioavailability and advantageous pharmaceutical parameters.

SUMMARY OF THE INVENTION

The present invention encompasses tenofovir disoproxil phosphate, processes for the preparation and pharmaceutical composition containing the same.

In accordance with one embodiment, the present invention provides tenofovir disoproxil phosphate.

In accordance with a second embodiment, the present invention provides crystalline tenofovir disoproxil phosphate.

In accordance with a third embodiment, the present invention provides crystalline tenofovir disoproxil phosphate, characterized by an X-Ray diffraction (XRD) pattern substantially in accordance with Figure. 1.

In accordance with a fourth embodiment, the present invention provides crystalline tenofovir disoproxil phosphate, characterized by one or more X-Ray diffraction (XRD) peaks at about 5.5, 12.3, 13.5, 15.7, 16.3, 16.9, 22.3, 22.6, 24, 25, 25.3 and 32° ± 0.2° 2Θ.

In accordance with a fifth embodiment, the present invention provides crystalline tenofovir disoproxil phosphate, characterized by a predominant endotherm peak at about 147°C as measured by a differential scanning calorimetric (DSC) thermogram.

In accordance with a sixth embodiment, the present invention provides a process for preparation of crystalline tenofovir disoproxil phosphate, comprising:

a) providing a solution or a mixture of tenofovir disoproxil in one or more solvents,

b) combining orthophosphoric acid and the resultant solution or mixture of tenofovir disoproxil,

c) precipitating tenofovir disoproxil phosphate.

wherein one or more solvents is selected from the group consisting of water, alcohols, esters, ketones, amides, nitriles, ethers, halogenated hydrocarbons, aromatic hydrocarbons, cyclic hydrocarbons, nitroalkanes and the like and mixtures thereof.

In accordance with a seventh embodiment, the present invention provides a process for preparation of crystalline tenofovir disoproxil phosphate, comprising:

a) providing a solution or a mixture of tenofovir disoproxil in one or more solvents,

b) combining orthophosphoric acid and the resultant solution or mixture of tenofovir disoproxil,

c) precipitating and isolating the tenofovir disoproxil phosphate,

d) dissolving the tenofovir disoproxil phosphate in a C _1-4 alcohol at a temperature of about 30°C to about reflux temperature,

e) adding water to the resultant solution,

f) cooling the solution to less than 20°C, and

g) isolating the tenofovir disoproxil phosphate. wherein one or more solvents is selected from the group consisting of water, alcohols, esters, ketones, amides, nitriles, ethers, halogenated hydrocarbons, aromatic hydrocarbons, cyclic hydrocarbons, nitroalkanes and the like and mixtures thereof; wherein the C alcohol is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol or mixtures thereof.

In accordance with an eighth embodiment, the present invention provides a process for preparation of crystalline tenofovir disoproxil phosphate, comprising: a) reacting tenofovir with chloro methyl isopropyl carbonate in presence of a base in an organic solvent to obtain tenofovir disoproxil,

b) combining orthophosphoric acid and the resultant tenofovir disoproxil in one or more solvents,

c) precipitating tenofovir disoproxil phosphate.

wherein one or more solvents is selected from the group consisting of water, alcohols, esters, ketones, amides, nitriles, ethers, halogenated hydrocarbons, aromatic hydrocarbons, cyclic hydrocarbons, nitroalkanes and the like and mixtures thereof.

In accordance with a ninth embodiment, the present invention provides a pharmaceutical composition comprising tenofovir disoproxil phosphate, prepared by the processes of the present invention, together with one or more pharmaceutically acceptable excipients.

BRIEF DESCRIPTION OF THE DRAWINGS:

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

Figure 1 is the characteristic powder X-ray diffraction (XRD) pattern of Tenofovir disoproxil phosphate.

Figure 2 is the characteristic differential scanning calorimetric (DSC) theremogram of tenofovir disoproxil phosphate.

DETAILED DESCRIPTION OF THE INVENTION

The solid state physical properties of an active pharmaceutical ingredient (API), such as tenofovir, affect the commercial usefulness of the API. Solid state physical properties include, for example, the flowability of the milled solid. Flowability affects the ease with which the material is handled during processing into a pharmaceutical product. When particles of the powdered compound do not flow past each other easily, a formulation specialist must take that fact into account in developing a tablet or capsule formulation, which may necessitate the use of glidants such as colloidal silicon dioxide.

Another important solid state property of a pharmaceutical compound is its rate of dissolution in aqueous fluid. The rate of dissolution of an active ingredient in a patient's stomach fluid may have therapeutic consequences since it imposes an upper limit on the rate at which an orally-administered active ingredient may reach the patient's bloodstream. The rate of dissolution is also a consideration in formulating syrups, elixirs and other liquid medicaments. The solid state form of a compound may also affect its behavior on compaction and its storage stability.

These practical physical characteristics are influenced by the conformation and orientation of molecules in the unit cell, which define a particular form of a substance. A particular form may also give rise to distinct spectroscopic properties that may be detectable by powder X-ray crystallography, solid state C-NMR spectrometry and infrared spectrometry. The present invention provides tenofovir disoproxil phosphate compound with increased solubility in water as compared to the tenofovir disoproxil fumarate. Increased solubility leads to improved bioavailability when the drug is administered to a patient, and, thus, allows reduced required dosages. One embodiment of the invention is crystalline Form of tenofovir disoproxil phosphate, which is more readily soluble than tenofovir disoproxil fumarate.

In one embodiment, the present invention provides a compound tenofovir disoproxil phosphate, particularly crystalline tenofovir disoproxil phosphate (herein after referred to as "Form Γ).

The tenofovir disoproxil phosphate of the present invention can be represented by the following molecular structure:

In one embodiment, the present invention provides crystalline tenofovir disoproxil phosphate as characterized by an X-Ray diffraction (XRD) pattern substantially in accordance with Figure. 1.

In another embodiment, the present invention further provides crystalline tenofovir disoproxil phosphate as characterized by one or more X-Ray diffraction (XRD) peaks at about 5.5, 12.3, 13.5, 15.7, 16.3, 16.9, 22.3, 22.6, 24, 25, 25.3 and 32° ± 0.2° 2Θ.

The crystalline tenofovir disoproxil phosphate of the present invention can be characterized by, for example, X-ray powder diffraction pattern and/or melting point. The powder XRPD spectrum for crystalline tenofovir disoproxil phosphate is presented in Figure 1. The X-Ray powder diffraction can be measured by an X-ray powder Diffractometer equipped with a Cu-anode ([λ] =1.54 Angstrom), X-ray source operated at 30kV, 15 mA and a Ni filter is used to strip K-beta radiation. Two-theta calibration is performed using an NIST SRM 640c Si standard. The sample was analyzed using the following instrument parameters: measuring range= 3 - 45°2Θ; step width=0.020° and scan speed=2 rninute. In one embodiment, the present invention provides crystalline tenofovir disoproxil phosphate as characterized by a differential scanning calorimetric (DSC) thermogram substantially in accordance with Figure. 2.

In another embodiment, the present invention provides crystalline tenofovir disoproxil phosphate as characterized by a predominant endotherm peak at about 147°C as measured by a differential scanning calorimetric (DSC) thermogram.

As shown in Figure 2, crystalline tenofovir disoproxil phosphate exhibits a predominant endotherm peak at about 147°C as measured by a Differential Scanning Calorimeter (DSC Q200, TA instrumentation, Waters) at a scan rate of 2°C per minute with an Indium standard. In this regard, it should be understood that the endotherm measured by a particular differential scanning calorimeter is dependent upon a number of factors, including the rate of heating (i.e., scan rate), the calibration standard utilized, instrument calibration, relative humidity, and upon the chemical purity of the sample being tested. Thus, an endotherm as measured by DSC on the instrument identified above may vary by as much as ± 1 °C or even ±2°C.

In another embodiment, the present invention provides a process for preparation of crystalline tenofovir disoproxil phosphate, comprising:

a) providing a solution or a mixture of tenofovir disoproxil in one or more solvents,

b) combining orthophosphoric acid and the resultant solution or mixture of tenofovir disoproxil,

c) precipitating tenofovir disoproxil phosphate.

In one embodiment, starting tenofovir disoproxil can be prepared either from the corresponding tenofovir disoproxil acid addition salts by neutralization or from the reaction by tenofovir with chloro methyl isopropyl carbonate in presence of a base. If, so the tenofovir disoproxil salt as mentioned above can be prepared by any method known in the art and thereafter adjusting the pH with a base to produce tenofovir disoproxil, which is immediately processed through the subsequent steps defined above. The pH adjustment can be made by the addition of about 1 molar equivalent of a suitable base. Examples of such base comprise but not limited to, all bases that neutralizes the acid, e.g. sodium hydroxide and the like.

In another embodiment, tenofovir disoproxil can be prepared by reaction of tenofovir with chloro methyl isopropyl carbonate in presence of a base in an organic solvent. Tenofovir can be prepared by any known method, for example tenofovir may be synthesized as disclosed in U.S. Patent No. 5,922,695 or our Indian pending Patent application No. 3791/CHE/2010. The organic solvent may be selected from amides such as dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, N-methyl pyrrolidinone and the like and mixtures thereof; hydrocarbons such as cyclohexane, toluene, xylene, and the like and mixtures thereof; and the base include, but is not limited to sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, triemylamine and the like and mixtures thereof. Preferably the organic solvent is N-methyl pyrrolidinone and the base is triethylamine.

In one embodiment, tenofovir can be purified before the reaction with chloro methyl isopropyl carbonate (CMIC). The purification may be carried out by mixing tenofovir crude compound in water and adjusting the pH to about 4 to about 7 with a suitable base. Examples of such suitable base include but are not limited to hydroxide base, carbonate base, bicarbonate base and the like; preferably sodium hydroxide, sodium carbonate, sodium bicarbonate; more preferably sodium hydroxide. Optionally, the resultant reaction mixture may be washed with a water immiscible organic solvent, wherein the water immiscible organic solvent is selected from the group consisting of ^■ methylene chloride, chloroform, toluene, methyl tertiary butyl ether and the like; preferably methylene chloride. Then, the product containing aqueous layer may be acidified to about 2 to about 4 with a suitable acid such as hydrochloric acid, hydrobromic acid and the like and isolating the pure tenofovir product.

The reaction of tenofovir with chloromethyl isopropyl carbonate may be carried out at a temperature of about 40°C to about 70°C. The reaction may take from about 2 hours to about 10 hours depending upon the solvent, base and temperature chosen. For instance, a reaction carried out with N-methyl pyrrolidinone, triemylamine base at temperature 50°C to 55°C, is completed about 3 hours. After completion of the reaction, the solid bi-product salts that are produced may be removed, such as by filtration and then the filtrate may be washed with water. The resultant product layer containing tenofovir disoproxil can be further processed directly in the same reaction vessel without isolating the tenofovir disoproxil base. Alternatively, the solvent from the product layer may be concentrated under vacuum to get tenofovir disoproxil base as residue by any method known in the art and then converted further to the tenofovir disoproxil phosphate of the invention.

The one or more solvents in a) of the foregoing process may be selected from the group consisting of alcohols, esters, ketones, amides, nitriles, ethers, halogenated hydrocarbons, aromatic hydrocarbons, cyclic hydrocarbons, nitroalkanes and mixtures thereof. The alcohols include, but are not limited to methanol, ethanol, isopropanol, n- propanol, n-butanol, isobutanol and the like; esters include, but are not limited to methyl acetate, ethyl acetate, isopropyl acetate and the like; ketones include, but are not limited to acetone, methyl isobutyl ketone, methyl ethyl ketone and the like; amides include, but are not limited to dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, N-methyl pyrrolidinone and the like; nitriles include, but are not limited to acetonitrile, propionitrile and the like; ethers include, but are not limited to tetrahydrofuran, dimethyl ether, diisopropyl ether, methyl tertiary butyl ether, 1 ,4- dioxane and the like; halogenated hydrocarbons include, but are not limited to methylene chloride, ethylene chloride, chloroform, carbon tetrachloride and the like; aromatic hydrocarbons include, but are not limited to toluene, xylene and the like; cyclic hydrocarbons include, but are not limited to n-hexane, n-heptane, cyclohexane and the like; nitroalkanes include, but are not limited to nitromethane, nitroethane and the like; water and mixtures thereof.

Preferably the one or more solvents selected from the group consisting of methanol, methylene chloride, cyclohexane, tetrahydrofuran, methyl tertiary butyl ether, dimethyl ether, dimethyl formamide, acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, methyl acetate, ethyl acetate, isopropyl acetate, acetonitrile, nitromethane, nitroethane, chloroform, water or mixture thereof. The reaction may be heated to dissolve or mixing the tenofovir disoproxil in the one or more solvents. The temperature suitable for dissolving or mixing the tenofovir disoproxil in the one or more solvents depends on the solvent used and the amount of tenofovir disoproxil in the solution. Typically, the solution is heated at a temperature of at least about 30°C to about reflux. Preferably, the solution is heated at about 30°C to about 80°C.

The orthophosphoric acid can range from about 0.5 to about 2 mole equivalents per mole of starting tenofovir disoproxil, preferably about 1.0 to about 1.5 moles. The orthophosphoric acid can be added either as a solution in one or more solvents defined above or it may be added directly to the solution of tenofovir disoproxil in one or more solvents. The sequence of addition of orthophosphoric acid is not particularly critical. Additionally, the phosphoric acid salt formation can be carried out in any known manner, for example, the orthophosphoric acid can be added into tenofovir disoproxil or tenofovir disoproxil may be added to the orthophosphoric acid.

In c) of the foregoing process, the precipitation of tenofovir disoproxil phosphate may be carried out by crystallization, solvent precipitation, concentrated by subjecting the solution to heating, spray drying, freeze drying, evaporation on rotary evaporator under vacuum, agitated thin film evaporator (ATFE) and the like. Preferably, the reaction may be cooled at a temperature from about 25°C or less such that the tenofovir disoproxil phosphate can be recovered by conventional techniques, for example filtration. The resultant product may optionally be further dried. Drying can be suitably carried out in a tray dryer, vacuum oven, air oven, fluidized bed drier, spin flash dryer, flash dryer and the like. The drying can be carried out at a temperature ranging from about 30°C to about 50°C. The drying can be carried out for any desired time until the required product purity is achieved, e.g., a time period ranging from about 1 hour to about 10 hours.

In another embodiment, the present invention provides tenofovir disoproxil phosphate thus obtained may be purified by dissolving the tenofovir disoproxil phosphate in a C^ alcohol such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol or mixtures thereof, with methanol being preferred. The solvent may be heated to obtain a solution at a temperature of from about ambient temperature to about reflux temperature. Then adding water to the resultant solution and the reaction solution may be cooled at a temperature from about 20°C or less such that the tenofovir disoproxil phosphate can be isolated by conventional techniques.

The tenofovir disoproxil phosphate recovered using the process of the present invention is substantially in crystalline Form. The crystalline tenofovir disoproxil phosphate can be characterized by one or more techniques such as an X-Ray diffraction (XRD) pattern substantially in accordance with Figure.1 or a DSC thermogram substantially in accordance with Figure. 2.

In another embodiment, the present invention provides crystalline tenofovir disoproxil phosphate having a chemical purity greater than or equal to about 97%, as measured by HPLC, preferably about 98% as measured by HPLC, and more preferably about 99.5%, as measured by HPLC.

The tenofovir disoproxil phosphate obtained by the process as described above may have an increased solubility as compared to the commercially available tenofovir disoproxil fumarate. Table I shows comparison study for solubility of tenofovir disoproxil phosphate of the invention and tenofovir disoproxil fumarate.

The present invention provides a tenofovir disoproxil phosphate, obtained by the above process, as analyzed using the high performance liquid chromatography ("HPLC") with the conditions described below:

Column : YMC pack ODS AQ, (250 x 4.6) mm, 5μπι

Column temperature : 35 °C

Diluent : Water and Methanol (1 : 1) v/v

Flow rate : 1.0 ml/min

Detection wavelength : 260nm

Injection volume : 20μΙ _^

Sample concentration : 0.5 mg/ml Run time 60 minutes

Elution Gradient

Buffer solution: disodiumhydrogen phosphate in water and pH at 5.5.

Mobile phase A: mixture of 700 ml of buffer, 275 ml of methanol and 25 ml tertiary butanol.

Mobile phase B: mixture of 300 ml of buffer, 675 ml of methanol and 25 ml tertiary butanol.

Gradient program

In one preferred embodiment, tenofovir disorpoxil phosphate is prepared according to Scheme I:

Scheme I

Tenofovir

Tenofovir disoproxil phosphate salt as obtained by the '692 publication has several limitations, which includes:

a) The particles obtained were too fine (less than 60μ); therefore the formulation of the active pharmaceutical ingredient requires wet granulation process. The six months stability data of the tablets, obtained by this process, revealed the product is unstable, and

b) The presence of closely related impurities are above the acceptable level recommended by the regulatory authorities; for instance a compound of Formula 2 was obtained at above 0.15% by HPLC and genotoxic impurity of compound of Formula 3 at above 5 ppm.

Formula 2 Formula 3

In contrast, the process herein described arrives at a tenofovir disoproxil phosphate, which includes optimized isolation techniques; for instance, tenofovir disoproxil phosphate obtained from a mixture of one or more of solvent or a mixture with water of the invention, not only reduced the contamination of the impurity of Formula 2, but also improved the particle size, with d(0.9) >120. The optimized isolation techniques include:

a) Isolation of tenofovir disoproxil phosphate from a mixture of One or more solvent and optional water improves the particle size and thus wet granulation process was avoided, thereby product stability significantly improved, and b) the contamination of the impurity of Formula 2 and diastereomeric impurities of Formula 4 was greatly controlled to below 0.03% levels with the help of purification process of the invention, and

Formula 4

c) Introduction of charcoal treatment to reduce the content of genotoxic impurity of Formula 3.

In one embodiment, tenofovir disoproxil phosphate disclosed herein for use in the pharmaceutical compositions of the present invention can independently have a D50 and D90 particle size less than about 200 microns, preferably less than about 150 microns, more preferably less than about 100 microns, still more preferably less than about 50 microns and most preferably less than about 25 microns. It is noted the notation Dx means that X% of the particles have a diameter less than a specified diameter D. Thus, a D50 of about 200 microns means that 50% of the micronized particles in a composition have a diameter less than about 200 microns. Any milling, grinding, micronizing or other particle size reduction method known in the art can be used to bring the tenofovir disoproxil phosphate into any desired particle size range set forth above. The tenofovir disoproxil phosphate of the present invention is useful as it is stable under conditions of high relative humidity and elevated temperatures. In another embodiment, the present invention provides a pharmaceutical composition comprising the tenofovir disoproxil phosphate described above and at least one pharmaceutically acceptable excipient.

In another embodiment, the present invention provides the use of tenofovir disoproxil phosphate, for the manufacture of a pharmaceutical composition, wherein the pharmaceutical composition can be useful for the treatment of viral infections.

The pharmaceutical composition of the present invention can be in a solid or a non- solid form. If the pharmaceutical composition is in a non-solid form, the tenofovir disoproxil phosphate in the composition can present as a solid in the non-solid pharmaceutical composition, e.g., as a suspension.

The pharmaceutical composition can be prepared by a process comprising combining the above-described tenofovir disoproxil phosphate with at least one pharmaceutically acceptable excipient. The tenofovir disoproxil phosphate can be obtained by any of the processes of the present invention as described above.

The pharmaceutical composition can be used to make appropriate dosage forms such as tablets, powders, capsules, suppositories, sachets, troches and lozenges.

Optionally, the pharmaceutical compositions of the invention may be combination products comprising one or more additional pharmaceutically active components in addition to tenofovir disoproxil phosphate.

Pharmaceutically acceptable excipients include, but are not limited to, diluents such as starch, pregelatinized starch, lactose, powdered cellulose, macrocrystalline cellulose, silicified macrocrystalline cellulose, dicalcium phosphate, tricalcium phosphate, magnesium oxide, magnesium carbonate, calcium carbonate, mannitol, sorbitol, xylitol and sugar; binders such as acacia, guar gum, tragacanth, gelatin, polyvinylpyrrolidone, hydroxypropyl celluloses, hydroxypropyl starch, hydroxypropylmethyl celluloses and pregelatinized starch; disintegrants such as starch, sodium starch glycolate, pregelatinized starch, crospovidone, polacrilin potassium, croscarmellose sodium and colloidal silicon dioxide; lubricants such as stearic acid, talc, magnesium stearate, calcium stearate and zinc stearate; glidants such as colloidal silicon dioxide; Other pharmaceutically acceptable excipients that are of use include but are not limited to film formers, film coating agents, plasticizers, colorants, flavoring agents, sweeteners, preservatives and antioxidants.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art, to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described. For purposes of the present invention, the following terms axe defined below.

The term "composition" includes, but is not limited to, a powder, a suspension, an emulsion and/or mixtures thereof. The term composition is intended to encompass a product containing the specified ingredients in the specified amounts, as well as any product, which results, directly or indirectly, from combination of the specified ingredients in the specified amounts. A "composition" may contain a single compound or a mixture of compounds.

The term 'pharmaceutical composition" is intended to encompass a product comprising the active ingredient(s), pharmaceutically acceptable excipients that make up the carrier, as well as any product which results, directly or indirectly, from combination, cornplexation or aggregation of any two or more of the ingredients, or from dissociation of one or more of the ingredients, or from other types of reactions or interactions of one or more of the ingredients. Accordingly, the pharmaceutical compositions of the present invention encompass any composition made by admixing the active ingredient, additional active ingredient(s), and pharmaceutically acceptable excipients.

The term "excipient" means a component of a pharmaceutical product that is not the active ingredient, such as filler, diluent, carrier, and so on. The excipients that are useful in preparing a pharmaceutical composition are preferably generally safe, nontoxic and neither biologically nor otherwise undesirable, and are acceptable for veterinary use as well as human pharmaceutical use. "A pharmaceutically acceptable excipient" as used in the specification and claims includes both one and more than one such excipient.

EXAMPLES

The following non limiting examples illustrate specific embodiments of the present invention. They are not intended to be limiting the scope of the present invention in any way.

EXAMPLE 1

Preparation of Tenofovir.

To a cooled slurry of 9-[2-(R)-(hydroxy)propyl] adenine (HPA, 100 gms) in dimethylformamide (400 ml), 0° to 5°C was added sodium amide (40.4 gms). The reaction mass was stirred for 30 minutes at same temperature and then allowed to warm to ambient temperature. After stirring for 2 hours, anhydrous magnesium chloride (49.2 gms) was charged and stirring continued for another hour. Toluene (300 ml) was charged. The temperature was raised to 50-55°C and stirred for 4 hours at same temperature. The temperature was further raised to 75-80°C and diethyl p- toluene sulfonyloxy methyl phosphonate (DESMP, 250 gms) was charged. After stirring at the same temperature for 4 hours HPLC analysis revealed a conversion of 70-78%. The reaction mass was allowed to cool to 70°C and solvent removed under vacuum to afford a thick residue. The residue was allowed to cool to ambient temperature and aqueous hydrobromic acid (650 ml) was charged. The temperature was raised to 90-95°C and stirred for 2 hours at same temperature. After completion of the de-alkylation reaction, the reaction mass was allowed to cool to ambient temperature and stirred for another 30 minutes at same temperature. The precipitate was filtered and the wet cake washed with methylene chloride (300 ml). The bottom organic layer was separated and the pH of the aqueous layer adjusted to 2.5 to 3.0 with 50% sodium hydroxide solution, at 20-25°C. The reaction mass stirred for 1 hour at 20- 25°C, cooled to 0-5°C and then stirred for 4 hours. The precipitated product was filtered and the wet cake was sequentially washed with chilled water (100 ml) and then with chilled acetone (100 ml) to provide crude Tenofovir.

EXAMPLE 2

Purification of Tenofovir.

To a suspension of tenofovir crude (obtained from Example 1) in DM water (600 ml), at 25°C to 35°C was charged 50% aqueous sodium hydroxide (about 30 ml) and the pH adjusted to 5.0-6.0. The aqueous layer containing the product was washed with methylene chloride (300 ml) and the pH adjusted to 2.5-3.0 with CP HC1 (about 25 ml). The mass was stirred for 1 hour at 25-30°C; then cooled to 10-15°C and stirred for 2 hours at same temperature. The precipitated solid was filtered off and washed with chilled water (100 ml). The wet product was dried at 70-75 °C to provide the pure compound.

Yield: 90 gms

HPLC Purity: 98.7%

EXAMPLE 3

Preparation of Tenofovir disoproxil phosphate.

A mixture of tenofovir (100 gms), triethyl amine (68 gms) and cyclohexane (800 ml) were stirred at 80-85°C and water, completely, removed by azeotropic distillation. The reaction mixture was allowed to cool to 65 °C and concentrated under vacuum, while mamtaining temperature below 65 °C. Released the vacuum and in the presence of nitrogen atmosphere the residue was allowed to cool to ambient temperature. N- methylpyrrolidinone (300 ml), triethyl amine (64 gms) and tetrabutylammom ^' um bromide (53 gms) were charged to the residue at 25-30°C. The temperature was raised to 50-55°C and chloromethylisopropyl carbonate (250 gms) was added at same temperature and stirred for 2 hours. After completion of the reaction, the mass was cooled to 20-25°C. The reaction mixture was washed with cyclohexane (400 ml) and cooled to 10-15°C. Methylene chloride (500 ml) was charged and stirred for 1 hour. The precipitated material was filtered off and the filtrate washed with water (1000 ml). To the separated organic layer was added water (1000 ml) and the pH of the mass was adjusted to 6.5-7.5 with 10% ammonia solution. The layers were separated; the organic layer was treated with carbon (5g), filtered and concentrated, under vacuum, at below 35°C. To the residue obtained was charged Methanol (300 ml), at 25-3 °C, and then a solution of ort/zo-phosphoric acid (19.1 ml) in methanol (100 ml) was added. Reaction mass was cooled to 20°C and then stirred for 60 minutes at same temperature. Precipitated solid was filtered off and the wet cake washed with chilled methanol (100 ml). The wet product was dried at 35-40°C under vacuum to provide the title compound as crude.

Yield: 105 gms

The XRPD is set forth in Figure 1

EXAMPLE 4

Purification of Tenofovir disoproxil phosphate.

The crude product (105 gms, obtained from Example 3) in methanol (550 ml) was stirred, at 40-50°C, for 1 hour. The reaction mass was allowed to cool to 10°C and stirred for 60 minutes. The precipitated material was filtered off and the wet cake washed with chilled methanol (100 ml). The wet product was dried at 35-40°C for 6 hours under vacuum to provide the title compound.

Yield: 80 gms.

HPLC Purity: 99.50%

Phosphoric acid content: 1 .9 %w/w (by potentiometry method)

The XRPD is set forth in Figure 1

The DSC is set forth in Figure 2

Table 1 shows physicochemical properties of Tenofovir disoproxil phosphate and Tenofovir disoproxil fumarate.

TABLE 1

EXAMPLE 5 Preparation of Tenofovir disoproxil phosphate (without isolation of tenofovir disoproxil base).

A mixture of tenofovir (100 gms), triethyl amine (68 gms) and cyclohexane (800 ml) were stirred at 80-85°C Dean-Stark apparatus for 2 hours and water, completely, removed by azeotropic distillation. The reaction mixture was allowed to cool to 65 °C and concentrated under vacuum, while mamtaining temperature below 65°C. Released the vacuum and in the presence of nitrogen atmosphere the residue was allowed to cool to ambient temperature. N-methylpyrrolidinone (300 ml), triethyl amine (64 gms) and tetrabutylammonium bromide (53 gms) were charged to the residue at 25-30°C. The temperature was raised to 50-55°C and chloromethylisopropyl carbonate (250 gms) was added at same temperature and stirred for 2 hours. After completion of the reaction, the mass was cooled to 20-25°C. The reaction mixture was washed with cyclohexane (400 ml) and cooled to 10-15°C. Methylene chloride (500 ml) was charged and stirred for 1 hour. The precipitated material was filtered off and the filtrate washed with water (1000 ml). To the separated organic layer was added water (1000 ml) and the pH of the mass was adjusted to 6.5-7.5 with 10% ammonia solution. The layers were separated; the organic layer was treated with carbon (5g), filtered and concentrated up to 90% of the total volume, under vacuum, at below 35°C. To the oily residue obtained was charged Methanol (300 ml), at 25-35°C, and then a solution of ort io-phosphoric acid (19.1 ml) in methanol (100 ml) was added. Reaction mass was cooled to 20°C and then stirred for 60 minutes at same temperature. Precipitated solid was filtered off and the wet cake washed with chilled methanol (100 ml). The wet product was dried at 35-40°C under vacuum to provide the title compound as crude. Yield: 105 gms

EXAMPLE 6

Preparation of crystalline Tenofovir disoproxil phosphate (from methanol + water).

To Tenofovir disoproxil (5 gms) in methanol (25 ml), at 50-55°C, was charged a solution of orthophosphoric acid (1.05 gms) in methanol (5 ml). The mass stirred for 15 minutes and water (20 ml) was added at same temperature. The reaction mass was stirred for another 15 minutes and then the temperature was allowed to cool to 25- 30°C. After stirring for another 60 minutes, at same temperature, the precipitated material was filtered off and the wet cake washed with chilled methanol (5 ml). The wet product was dried at 45-50°C, for 6 hours, under vacuum, to provide the title compound.

Yield: 3.7 gms

The XRPD is set forth in Figure 1

EXAMPLE 7 Preparation of crystalline Tenofovir disoproxil phosphate (from methylene chloride + cyclohexane)

To Tenofovir disoproxil (15 gms) in methylene chloride (135 ml), at 25-30°C, was charged a solution of ort zo-phosphoric acid (3.14 gms) in methylene chloride (15 ml). The mass stirred for 15 minutes and cyclohexane (75 ml) was added at same temperature. The reaction mass was stirred for another 15 minutes and then the precipitated material was filtered off. The wet product was dried at 45-50°C, for 6 hours, under vacuum, to provide the title compound.

Yield: 3.8 gms

The XRPD is set forth in Figure 1

EXAMPLE 8

Preparation of crystalline Tenofovir disoproxil phosphate (from acetone + water) To Tenofovir disoproxil (3 gms) in acetone (15 ml), at 25-30°C, was charged a solution of ort zo-phosphoric acid (0.63 gms) in DM water (3 ml). The mass stirred for 60 minutes and the precipitated material was filtered off. The wet product was dried at 45-50°C, for 6 hours, under vacuum, to provide the title compound.

Yield: 2.2 gms

The XRPD is set forth in Figure 1

EXAMPLE 9

Preparation of crystalline Tenofovir disoproxil phosphate (from tetrahydrofuran)

To Tenofovir disoproxil (3 gms) in tetrahydrofuran (15 ml), at 25-30°C, was charged a solution of ort zo-phosphoric acid (0.63 gms) in tetrahydrofuran (3 ml). The mass stirred for 60 minutes and the precipitated material was filtered off. The wet product was dried at 45-50°C, for 6 hours, under vacuum, to provide the title compound.

Yield: 2.8 gms

The XRPD is set forth in Figure 1

EXAMPLE 10-22

Preparation of crystalline Tenofovir disoproxil phosphate using a procedure analogous to that employed in Example 9 with using different solvents as described in the following table:

12 3 gms Methyl isobutyl 6 volumes 2.8 gms As set forth in Ex 4 ketone

13 3 gms Toluene 6 volumes 3.1 gms As set forth in Ex 4

14 3 gms Methyl tertiary 6 volumes 2.5 gms As set forth in Ex 4 butyl ether

15 3 gms Methyl ethyl ketone 6 volumes 2.6 gms As set forth in Ex 4

16 3 gms Methyl acetate 6 volumes 2.8 gms As set forth in Ex 4

3 gms Ethyl acetate 6 volumes 2.5 gms As set forth in Ex 4

17 3 gms Isopropyl acetate 6 volumes 2.8 gms As set forth in Ex 4

18 3 gms Acetonitrile 6 volumes 3.3 gms As set forth in Ex 4

19 3 gms Nitromethane 6 volumes 2.4 gms As set forth in Ex 4

20 3 gms Nitroethane 6 volumes 2.1 gms As set forth in Ex 4

21 3 gms Acetone 6 volumes 2.9 gms As set forth in Ex 4

22 3 gms DM Water 6 volumes 1.6 gms As set forth in Ex 4

EXAMPLE 23

Preparation of crystalline Tenofovir disoproxil phosphate (from methylene chloride) To Tenofovir disoproxil (5 gms) in methylene chloride (25 ml), at 25-30°C, was charged a solution of ort/zo-phosphoric acid (1.05 gms) in methylene chloride (5 ml). The mass stirred for 2 hours and the solvent was allowed to evaporate at atmospheric pressure to provide the title compound.

Yield: 4.6 gms

The XRPD is set forth in Figure 1

EXAMPLE 24

Preparation of crystalline Tenofovir disoproxil phosphate (from chloroform)

To Tenofovir disoproxil (3 gms) in chloroform (15 ml), at 25-30°C, was charged a solution of ort zo-phosphoric acid (0.63 gms) in chloroform (3 ml). The mass stirred for 60 minutes and the solvent was allowed to evaporate at atmospheric pressure to provide the title compound.

Yield: 3.1 gms

The XRPD is set forth in Figure 1

EXAMPLE 25

Preparation of Tenofovir disoproxil phosphate (Commercial scale, without carbon treatment).

A mixture of tenofovir (6.0 Kg), triethylamine (4.08 Kg) and cyclohexane (48 Lit) were stirred at 80-85°C, with azeotropic removal of water. The reaction mixture was allowed to cool to 65°C and concentrated under vacuum, while maintaining temperature below 65 °C. The vacuum released and in the presence of nitrogen atmosphere the residue was allowed to cool to ambient temperature. N- Methylpyrrolidone (18 Lit), triethyl-unine (3.84 Kg) and tetrabutylammonium bromide (3.18 Kg) were charged to the residue at 25-30°C. The temperature was raised to 50- 55°C and chloromethylisopropyl carbonate (15 Kg) was added at same temperature and stirred for 2 hours. After completion of the reaction, the mass was cooled to 20- 25°C. The reaction mixture was washed with cyclohexane (24 Lit) and cooled to 10- 15°C. Methylene chloride (30 Lit) was charged and stirred for 1 hour. The precipitated material was filtered off and the filtrate washed with water (60 Lit). To the separated organic layer was added water (60 Lit) and the pH of the mass was adjusted to 6.5-7.5 with 10% ammonia solution. The layers were separated and the organic layer was concentrated up to 90% of the original volume, under vacuum, at below 35°C. To the oily residue obtained was charged Methanol (18 Lit), at 25-35°C, and then a solution of ortfto-phosphoric acid (1.15 Lit) in methanol (6 Lit) was added. Reaction mass was cooled to 20°C and then stirred for 60 minutes at same temperature. Precipitated solid was filtered off and the wet cake washed with chilled methanol (6 Lit). The wet product was dried at 35-40°C under vacuum to provide the title compound as crude (6.5 Kg). The crude product was dissolved in methanol (35.75 Lit), at 40-50°C. Water (13 Lit) was charged over a period of 30 min and then the reaction mass was allowed to cool to 5°C and stirred for 60 minutes. The precipitated material was filtered off and the wet cake washed with chilled methanol (6 Lit). The wet product was dried at 35- 40°C for 6 hours under vacuum to provide the title compound.

Yield: 4.2 Kg.

Phosphoric acid content: 15.9%

HPLC Purity: 99.7%, Formula 2: 0.01%, Formula 4: 0.02%, Formula 3: 9.1 ppm. Particle size distribution: d (0.9): 148.5μιη.

EXAMPLE 26

Preparation of Tenofovir disoproxil phosphate (Commercial scale, with carbon treatment).

A mixture of tenofovir (80.0 Kg), triethylarnine (54.4 Kg) and cyclohexane (640 Lit) were stirred at 80-85°C, with azeotropic removal of water. The reaction mixture was allowed to cool to 65°C and concentrated under vacuum, while maintaining temperature below 65°C. The vacuum released and in the presence of nitrogen atmosphere the residue was allowed to cool to ambient temperature. N- Methylpyrrolidone (240 Lit), triemylarnine (51.2 Kg) and tetrabutylammonium bromide (42.4 Kg) were charged to the residue at 25-30°C. The temperature was raised to 50-55°C and chloromethylisopropyl carbonate (200 Kg) was added at same temperature and stirred for 2 hours. After completion of the reaction, the mass was cooled to 20-25°C. The reaction mixture was washed with cyclohexane (320 Lit) and cooled to 10-15°C. Methylene chloride (400 Lit) was charged and stirred for 1 hour. The precipitated material was filtered off and the filtrate washed with water (800 Lit). To the separated organic layer was added water (800 Lit) and the pH of the mass was adjusted to 6.5-7.5 with 10% ammonia solution. The layers were separated; the organic layer was treated with carbon (4 Kg), filtered and concentrated up to 90% of the original volume, under vacuum, at below 35°C. To the oily residue obtained was charged Methanol (240 Lit), at 25-35°C, and then a solution of ortho-phosphoric acid (15.3 Lit) in methanol (80 Lit) was added. Reaction mass was cooled to 20°C and then stirred for 60 minutes at same temperature. Precipitated solid was filtered off and the wet cake washed with chilled methanol (80 Lit). The wet product was dried at 35- 40°C under vacuum to provide the title compound as crude (80 Kg). The crude product was dissolved in methanol (440 Lit), at 40-50°C. Water (160 Lit) was charged over a period of 30 min and then the reaction mass was allowed to cool to 5°C and stirred for 60 minutes. The precipitated material was filtered off and the wet cake washed with chilled methanol (80 Lit). The wet product was dried at 35-40°C for 6 hours under vacuum to provide the title compound.

Yield: 53.8 Kg.

Phosphoric acid content: 16.1%

HPLC Purity: 99.5%, Formula 2: 0.02%, Formula 4: 0.04, Formula 3: 0.35 ppm.

Particle size distribution: d(0.9): 144.2μιη.

EXAMPLE 27

Composition for the preparation of tenofovir disoproxil phosphate tablets with tenofovir disoprbxil phosphate obtained from Example 4.

EXAMPLE 28

Composition for the preparation of tenofovir disoproxil phosphate tablets with tenofovir disoproxil phosphate obtained from Example 4. S. No Ingredient Qty (mg)

01 Tenofovir disoproxil phosphate 291

02 Microcrystlline Cellulose 168

03 Lactose Monohydrate 167.5

04 Pregelatinised Starch 42

05 Croscarmellose Sodium 24.5

06 Magnesium Stearate 7

Total 700

Opadry 14

Grand Total 714

EXAMPLE 29

Dissolution of Tenofovir disoproxil phosphate Formulations according to the invention in the USP dissolution medium.

The dissolution of tenofovir disoproxil phosphate Formulations according to the invention were assessed in the USP dissolution medium (900 ml of 0.1 N HC1) over a period of 30 minutes. The results are summarized in Table 2: TABLE 2

EXAMPLE 30 Stability of Tenofovir disoproxil phosphate Formulations according to the invention

Tenofovir disoproxil phosphate Tablets (Example 28) were packed in HDPE bottles with adsorbent cotton and silica gel bag and loaded to the stability chambers at 30°C/65%RH stability testing condition. The results of stability studies are as shown in Table 3:

TABLE 3

ND: Not detected

It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. For example, the functions described above and implemented as the best mode for operating the present invention are for illustration purposes only. Other arrangements and methods may be implemented by those skilled in the art without departing from the scope and spirit of this invention. Moreover, those skilled in the art will envision other modifications within the scope and spirit of the specification appended hereto.