DESC:FIELD OF THE INVENTION
The present invention relates to a process for the preparation of L-alanine, N-[(S)-[[(1R)-2-(6-amino-9H-purin-9-yl)-1methylethoxy]methyl]phenoxyphosphinyl]-,1-methylethyl ester or Tenofovir Alafenamide of Formula (I).

(I)
BACKGROUND OF THE INVENTION
L-alanine, N-[(S)-[[(1R)-2-(6-amino-9H-purin-9-yl)-1methylethoxy]methyl]phenoxy phosphinyl]-,1-methylethyl ester, (2E)-2-butenedioate (2:1)or Tenofovir Alafenamide fumarate. Tenofovir Alafenamide fumarate is a phosphonoamidate prodrug of Tenofovir (2’deoxyadenosine monophosphate analog). Plasma exposure to Tenofovir Alafenamide fumarate allows for permeation into cells and then Tenofovir Alafenamide fumarate is intracellularly converted to Tenofovir through hydrolysis by cathepsin A. Tenofovir is subsequently phosphorylated by cellular kinases to the active metabolite Tenofovir diphosphate. Tenofovir diphosphate inhibits HIV replication through incorporation into viral DNA by the HIV reverse transcriptase, which results in DNA chain-termination.

Tenofovir specifically shows activity towards human immunodeficiency virus and hepatitis B virus. Cell culture studies have shown that both Emtricitabine and Tenofovir can be fully phosphorylated when combined in cells. Tenofovir diphosphate is a weak inhibitor of mammalian DNA polymerases that include mitochondrial DNA polymerase ? and there is no evidence of toxicity to mitochondria in cell culture.

Tenofovir Alafenamide fumarate was approved by USFDA in 2015 and is marketed under the brand name GENVOYA®, is a four-drug combination of Elvitegravir, an HIV-1 integrase strand transfer inhibitor (INSTI), Cobicistat, a CYP3A inhibitor, and Emtricitabine and Tenofovir Alafenamide (TAF), both HIV1 nucleoside analog reverse transcriptase inhibitors (NRTIs) and is indicated as a complete regimen for the treatment of HIV-1 infection in adults and pediatric patients 12 years of age and older who have no antiretroviral treatment history or to replace the current antiretroviral regimen in those who are virologically-suppressed (HIV-1 RNA less than 50 copies per mL) on a stable antiretroviral regimen for at least 6 months with no history of treatment failure and no known substitutions associated with resistance to the individual components of GENVOYA.

Tenofovir has activity that is specific to human immunodeficiency virus and hepatitis B virus. Cell culture studies have shown that both Emtricitabine and Tenofovir can be fully phosphorylated when combined in cells. Tenofovir diphosphate is a weak inhibitor of mammalian DNA polymerases that include mitochondrial DNA polymerase ? and there is no evidence of toxicity to mitochondria in cell culture.

Tenofovir Alafenamide fumarate is chemically known as L-alanine, N-[(S)-[[(1R)-2-(6-amino-9H-purin-9-yl)-1methylethoxy]methyl]phenoxy phosphinyl]-,1-methylethyl ester, (2E)-2-butenedioate). Tenofovir Alafenamide fumarate is a white to off-white or tan powder with a solubility of 4.7 mg per mL in water at 20 °C. It has a molecular formula of C23H31O7N6P and a molecular weight of 534.5.

Tenofovir Alafenamide fumarate is generically and specifically disclosed in US 7390791. US ‘791discloses a process for the preparation of Tenofovir Alafenamide fumarate starting from Tenofovir. The process is as demonstrated below:

US 8664386 discloses process for the preparation of Tenofovir Alafenamide comprises diastereomeric separation of 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl) ethyl]amino}phenoxyphosphinyl) methoxy]propyl}adenine.The process is as demonstrated below:

WO2014195724 discloses a process for preparing 9-[(R)-2-[[(R)-[[(S)-1- (isopropoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy]propyl]adenine or 9-[(R)-2- [[(S)-[[(S)-1-(isopropoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy]propyl] adenine reacting phenyl(R)-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methylphosphonochloridate with 2-amino propionic acid isopropyl ester in presence of chiral organic acid.

WO2015/040640 discloses a process for the preparation of Tenofovir Alafenamide comprises
(i) reacting PMPA with phenol in presence of a base and a condensing agent in a suitable organic solvent to obtain [(R)-2-(Phenylphosphonomethoxy) propyl] adenine
(ii) reacting the [(R)-2-(Phenylphosphonomethoxy) propyl]adenine or a reactive derivative with L-alanine isopropyl ester in presence of a base to obtain TenofovirAlafenamide.

WO2015/079455 discloses a process for racemization of (R,R,S)-diastereomer or a mixture having (R,S,S) & (R,R,S)-diastereomer of Tenofovir Alafenamide, said method comprising treating the (R,R,S)-diastereomer or the mixture having (R,S,S) & (R,R,S)-diastereomer with a suitable base in a suitable organic solvent..

WO 2015/107451 discloses a process for the purification of Tenofovir Alafenamide, comprising the steps of
(i) reacting racemic Tenofovir Alafenamide with an acid to produce an acid salt; and
(ii) desaltification of the acid salt to get Tenofovir Alafenamide.
wherein acid is selected from chiral acid such as of (S)-(+)-mandelic acid, (R)-(-)-mandelic Acid, (lS)-(+)-10- camphor sulfonic acid, (lR)-(-)-10-camphor sulfonic acid, (D)-(-)-tartaric acid, (L)-(+)-Tartaric acid, (-)-di-p-toluoyl-L-tartaric acid, (+)-di-p-toluoyl-D-tartaric acid, (L)-(-)-malic acid, (D)-(+)-malic acid, (+)-dibenzoyl-D-tartaric acid, (-)- dibenzoyl-L-tartaric acid, (1R, 3S)-(+)-camphoric acid, (1S, 3R)-(-)-camphoric acid, L-pyroglutamic acid, and D-pyroglutamic acid; or an achiral acid such as orotic acid, fumaric acid, oxalic acid, maleic acid, benzoic acid, p-toluenesulphonic acid, succinic acid, orthophosphoric acid, and malonic acid.

The present inventors has repeated the above process and found the following disadvantages:
? In most of the patent literature, it appears that the chiral separation is not clear and yields in the formation of byproducts, which is tedious for the removal.
? Unwanted reactions are observed during the formation of Tenofovir Alafenamide, due to the involvement time lagging process.
? Incomplete reactions were observed with excessive impurity formation due to incomplete conversion.

In view of the above and to overcome the prior-art problems the present inventors had now developed an improved process for the preparation of Tenofovir Alafenamide, using industrially feasible and viable process, with the use of industrially friendly solvents, which does not include tedious work up and time lagging steps.

OBJECTIVE OF THE INVENTION
The main objective of the invention relates to aprocess for the preparation of L-alanine,N-[(S)-[[(1R)-2-(6-amino-9H-purin-9-yl)-methylethoxy]methyl]phenoxyphosphinyl]-1-methylethyl ester, (2E)-2-butenedioate or Tenofovir Alafenamide fumarate(I).

Yet another objective of the invention relates to a process for the preparation of highly pure Tenofovir Alafenamide, using chiral protected amino acids

SUMMARY OF THE INVENTION
The present invention relates to a process for the preparation of L-alanine, N-[(S)-[[(1R)-2-(6-amino-9H-purin-9-yl)-1methylethoxy]methyl]phenoxyphosphinyl]-,1-methylethyl ester, or Tenofovir Alafenamide(I)

(I)
comprising the steps of:
a) reacting 4-Dimethyl Amino pyridine of ((-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methylphosphonic acid Formula II with phenol to yield [(R)-2-(Phenylphosphonomethoxy) propyl] adenine of Formula III;

b) reacting [(R)-2-(Phenylphosphonomethoxy) propyl] adenine with halogenating agent to provide Phosphonochloridic acid, P-[[(1R)-2-(6-amino-9-H-purin-9-yl)-1-methylethoxy]methyl]-phenyl ester(IV);

c) reacting compound of Formula IV with L-Alanine Isopropyl Ester to provide9-[(R ) -2-[{(S )-[{(S )-1-(isopropoxycarbonyl) ethyl] amino] phenoxyphosphinyl] methoxy] propyl]adenine of Formula V;

d) reacting the compound of Formula V with protected amino acid of Formula VItoprovide Formula VII

e) reacting the Formula VII with base to yield Tenofovir Alafenamide

In another aspect of the invention relates to novel intermediate of Formula:

(VII)
Wherein R1 is hydrogen, -CH2COOH, methyl, ethyl, n-propyl, i-propyl, acetyl or a substituted or unsubstituted phenyl and hetero cyclic compounds. Where the substituent of the substituted phenyl is at least one of a CH3, OCH3, F, Cl, Br, I, nitro, cyano.; R2 or R3 selected from Hydrogen and the other group is selected from Fmoc, Boc, Cbz, acetyl, trifluoroacetamide, phthalimide, Benzyl, Triphenylmethylamine, Benzylideneamine, p-Toluene sulfonamide and Carbamate, Alkyl,Aryl,Hetero cyclic.

In yet another aspect of the invention relates to A process for the preparation of highly pure Tenofovir Alafenamide having an enantiomeric purity of greater than 99.5% comprises:
a) reacting the compound of Formula V with protected amino acid of Formula VI to provide Formula VII

b) reacting the Formula VII with base to yield Tenofovir Alafenamide
In yet another aspect of the present invention relates to substantially pure Tenofovir Alafenamide having enantiomeric purity of greater than 99.5% and total impurities A to J and diastereomeric impurity collectively less than 0.5% by HPLC.

Impurity-A Impurity-B

Impurity-C

Impurity-D
Impurity-E
Impurity-F

Impurity-G
Impurity-H
Impurity-I

Impurity-J
Diastereomeric Impurity

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an example of X-ray powder diffraction (“XRPD”) pattern of Tenofovir Alafenamide Fumarate obtained according to the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for the preparation of Tenofovir Alafenamide fumarate (I) comprising adding a suspension of ((-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methylphosphonic acid in toluene was subjected to azeotropic distillation to remove water. The obtained solid was dissolved in a solvent selected from alcohols, such as C2-C6 alcohols like ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, t-butyl alcohol; or nitriles, such as acetonitrile or propionitrile; amides such as ?,?-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone; sulfoxides such as dimethylsulfoxide; halogenated hydrocarbons such as dichloromethane; aromatic hydrocarbons such as toluene, xylene; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, isopropyl acetate, isobutyl acetate, t-butyl acetate; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 1 ,4-dioxane, 2-methoxyethanol, anisole; ketones such as acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; organic solvents such as dimethyl formamide, n-hexane, n-heptane, cyclohexane, cycloheptane; hetero aromatic solvents such as pyridine, dimethyl amino pyridine; water or mixtures thereof. To the reaction mass phenol was added. The reaction mass was heated to 60-90°C and then base was added, which was selected from organic base such as triethylamine, methylamine, pyridine, imidazole, benzimidazole; or inorganic base selected from carbonates such as sodium carbonate, potassium carbonate, calcium carbonate, ammonium carbonate; hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, barium hydroxide, magnesium hydroxide, lithium hydroxide, zinc hydroxide; bicarbonates such as sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, calcium bicarbonate, magnesium bicarbonate. The obtained reaction mass was heated to 80-120°C and maintained stirring for 4 hours to 8 hours. The reaction mass was cooled to 45°C, water was added and further cooled to room temperature. The reaction mass was filtered and washed with water. The obtained reaction mass was filtered through the Celite bed and washed with dichloromethane twice. The crude solid was isolated by filtration and washed with methanol. The wet cake was slurred and washed with methanol. The resulting solid was dried under reduced pressure to yield Phenyl hydrogen((R)-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methylphosphonate mono hydrate

Phenyl hydrogen((R)-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methylphosphonate mono hydrate obtained above under halogenations using a halogenating agent selected from Iodine, Bromine, Chlorine, thionyl chloride, oxalyl chloride, Phosphorous tri-chloride, Phosphorous penta-chloride, Phosphorous oxy chloride; at a temperature ranging from 75°C to 80°c for 3 hr. The solvent were removed at atmospheric pressure under nitrogen at 80°C, the reaction mixture were washed with toluene twice at atmospheric pressure under nitrogen at 80°C, cooled to 25°C, diluted with dichloromethane. The solution as such was used for next stage.

The present inventors found that the chloride intermediate was very unstable and unable to isolate. The diastereomeric purity of the chloride intermediate appears to be in the ratio of 70: 30. Further, it appears that the diastereomeric purity of chloride intermediate is less than 99 % and appears that that the formation of diastereomeric impurity greater than 1%.
The prior art process disclosed in prior art involves the stirring for long hours(92 hours) for chiral enhancement. The present inventors surprisingly found that the reaction will complete with in the 3 hours. However, the chiral purity is around 70-80%. Even after preparing the chloride intermediate with low diastereomeric purity. The present inventors are able to prepare the Tenofovir Alafenamide having a purity of greater than 99.5 % and free of diastereomeric impurities using the process as described in the present invention.

The prior art process involves the use of high volumes(5 volumes) of halogenating agent for completion of the reaction, which leads to the formation of highly chlorinated byproducts/impurities. The present inventors surprisingly found that the reaction will complete with the use of 2.5 equivalents of halogenating agent for completion of the reaction, which yields in a highly pure Tenofovir Alafenamide free of highly halogenated impurities.

In a second flask a mixture of L-alanine isopropyl ester hydrochloride was dissolved in a solvent selected from alcohols, such as C2-C6 alcohols like ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, t-butyl alcohol; or nitriles, such as acetonitrile or propionitrile; amides such as ?,?-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone; sulfoxides such as dimethylsulfoxide; halogenated hydrocarbons such as dichloromethane; aromatic hydrocarbons such as toluene, xylene; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, isopropyl acetate, isobutyl acetate, t-butyl acetate; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 1 ,4-dioxane, 2-methoxyethanol, anisole; ketones such as acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; organic solvents such as dimethyl formamide, n-hexane, n-heptane, cyclohexane, cycloheptane; water; or any mixtures. To the reaction mass base selected from organic base such as triethylamine, methylamine, pyridine, imidazole, benzimidazole; or inorganic base selected from carbonates such as sodium carbonate, potassium carbonate, calcium carbonate, ammonium carbonate; hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, barium hydroxide, magnesium hydroxide, lithium hydroxide, zinc hydroxide; bicarbonates such as sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, calcium bicarbonate, magnesium bicarbonate was added slowly at room temperature for 12h. The obtained reaction mass was cooled to -30°C to -50°C. To the reaction mass above obtained acid chloride solution was added slowly for a period of 10 to 15 min. The reaction mixture was stirred for 30 minutes to 1hour at same temperature (-30°c to -50°C),cooled to room temperature again stirred the reaction mass for 1hr at room temperature. The organic layer was washed with 10% sodium di hydrogen orthophosphate solution. Followed by treatment with 10% potassium bi carbonate solution The organic layer was concentrated and washed with acetonitrile under reduced pressure to obtain 9-[(R)-2-[{(S)-[{(S)-1-(isopropoxycarbonyl) ethyl] amino] phenoxyPhosphinyl] methoxy] propyl] adenine(Racemic R,S,S:R,R.S=70-80:30-20).

To a solution of 9-[(R)-2-[{(S)-[{(S)-1-(isopropoxycarbonyl)ethyl]amino] phenoxyphosphinyl] methoxy] propyl]adenine (Racemic Tenofovir Alafenamide) in acetonitrile,protected amino acid was added slowly. Stirred the reaction mass for 30 minutes to 1hour at 40-45°C. The reaction mixture was cooled to room temperature and maintained for 12 to 16 h. The reaction mixture was cooled to 0 to 5°C and maintained for 2 to 3 h at 0-5°C. The product was isolated and washed with chilled acetonitrile followed by n-Hexane and dried the solid under reduced pressure to yield protected amino acid salt of Tenofovir Alafenamide with 98.0% disatereomeric purity.

The above obtained Tenofovir Alafenamide protected amino acid salt was purified by dissolving the salt in amyl alcohol, heated to 60-65°C to get clear solution and the reaction mixture was maintained for 30 min at 60-65°C, cooled to room temperature, maintained for 2 hours after that again cooled to 0-5°C, stirred for 1hr.The product was isolated by filtration and washed with chilled amyl alcohol followed by chilled n-hexane and dried the solid under reduced pressure to yield protected amino acid salt of Tenofovir Alafenamide with 99.7% disatereomeric purity.
Tenofovir Alafenamide protected amino acid salt was dissolved in a solvent alcohols, such as C2-C6 alcohols like ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, t-butyl alcohol; or nitriles, such as acetonitrile or propionitrile; amides such as ?,?-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone; sulfoxides such as dimethylsulfoxide; halogenated hydrocarbons such as dichloromethane; aromatic hydrocarbons such as toluene, xylene; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, isopropyl acetate, isobutyl acetate, t-butyl acetate; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 1 ,4-dioxane, 2-methoxyethanol, anisole; ketones such as acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; organic solvents such as dimethyl formamide, n-hexane, n-heptane, cyclohexane, cycloheptane; water; or any mixtures at room temperature. The reaction mixture was cooled to 20°C to 25°C and pH was adjusted to 8 to 9 with 20% sodium carbonate solution. The reaction mixture was stirred and organic and aqueous layers were separated. The aqueous layer was extracted with Ethyl acetate twice, stirred, and layers were again separated. The organic layer was then dried with sodium sulphate and ethyl acetate layer was distilled out completely under vacuum to get pure Tenofovir Alafenamide free base.

The above obtained Tenofovir Alafenamide was dissolved in amyl alcohol, heated to 45-50°C and then Fumaric acid was added and stirred for 30 min. The reaction mixture was cooled to room temperature and maintained for 12 to 16 h after that cooled to 0-5°C then maintained for 30 min. The product was isolated by filtration, washed with chilled amylalcohol. The wet cake was dried under reduced pressure at 50-55°C to yield Tenofovir Alafenamide Fumaric acid salt.

Even after the diastereomeric purity of chloride intermediate is around 70%.The present inventors successfully removed the diastereomeric impurity by following the process as disclosed in the present invention to yield highly pure Tenofovir Alafenamide free of diastereomeric impurities. Tenofovir Alafenamide obtained by the present invention is having a enantiomerically purity of greater than 99.5% and substantially free of diastereomeric impurities.

In another embodiment of the present invention relates to substantially pure Tenofovir Alafenamide having enantiomeric purity of greater than 99.5% and total impurities A to J and diastereomeric impurity collectively less than 0.5% by HPLC.

Impurity-A Impurity-B

Impurity-C

Impurity-D
Impurity-E
Impurity-F

Impurity-G
Impurity-H
Impurity-I

Impurity-J
Diastereomeric Impurity

The word “Substantially pure” means Tenofovir Alafenamide having a purity of greater than 99.5 % by HPLC and less than 0.05 % of diastereomeric impurities or the impurity levels within the limits as per the ICH guidelines.

In one embodiment the substantially pure Tenofovir Alafenamide is having a purity of greater than 99.5 % and meeting the ICH guidelines.

In one embodiment the substantially pure Tenofovir Alafenamide is having a purity of greater than 99.6 % and meeting the ICH guidelines.

In one embodiment the substantially pure Tenofovir Alafenamide is having a purity of greater than 99.7 % and meeting the ICH guidelines.

In one embodiment the substantially pure Tenofovir Alafenamide is having a purity of greater than 99.8 % and meeting the ICH guidelines.

In one embodiment the substantially pure Tenofovir Alafenamide is having a purity of greater than 99.9 % and meeting the ICH guidelines.

The process related impurities that appear in the impurity profile of the Tenofovir Alafenamide may be substantially removed by the process of the present invention resulting in the formation of highly pure material. The process of the present invention is as summarized below:

In another embodiment, the Tenofovir Alafenamide obtained by the processes of the present application may be formulated as solid compositions for oral administration in the form of capsules, tablets, pills, powders or granules. In these compositions, the active product is mixed with one or more pharmaceutically acceptable excipients. The drug substance can be formulated as liquid compositions for oral administration including solutions, suspensions, syrups, elixirs and emulsions, containing solvents or vehicles such as water, sorbitol, glycerine, propylene glycol or liquid paraffin.

The compositions for parenteral administration can be suspensions, emulsions or aqueous or non-aqueous sterile solutions. As a solvent or vehicle, propylene glycol, polyethylene glycol, vegetable oils, especially olive oil, and injectable organic esters, e.g. ethyl oleate, may be employed. These compositions can contain adjuvants, especially wetting, emulsifying and dispersing agents. The sterilization may be carried out in several ways, e.g. using a bacteriological filter, by incorporating sterilizing agents in the composition, by irradiation or by heating. They may be prepared in the form of sterile compositions, which can be dissolved at the time of use in sterile water or any other sterile injectable medium.
Pharmaceutically acceptable excipients used in the compositions comprising Tenofovir Alafenamide obtained as per the present application process- include, but are but not limited to diluents such as starch, pregelatinized starch, lactose, powdered cellulose, microcrystalline cellulose, dicalcium phosphate, tricalcium phosphate, mannitol, sorbitol, sugar and the like; binders such as acacia, guar gum, tragacanth, gelatin, pre-gelatinized starch and the like; disintegrants such as starch, sodium starch glycolate, pregelatinized starch, Croscarmellose sodium, colloidal silicon dioxide and the like; lubricants such as stearic acid, magnesium stearate, zinc stearate and the like; glidants such as colloidal silicon dioxide and the like; solubility or wetting enhancers such as anionic or cationic or neutral surfactants, waxes and the like. Other pharmaceutically acceptable excipients that are of use include but not limited to film formers, plasticizers, colorants, flavoring agents, sweeteners, viscosity enhancers, preservatives, antioxidants and the like.

Pharmaceutically acceptable excipients used in the compositions derived from Tenofovir Alafenamide of the present application may also comprise to include the pharmaceutically acceptable carrier used for the preparation of solid dispersion, wherever utilized in the desired dosage form preparation.

The following examples illustrate the nature of the invention and are provided for illustrative purposes only and should not be construed to limit the scope of the invention.

EXAMPLES
Example 1
Process for the preparation of Phenylhydrogen((R)-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methylphosphonate mono hydrate:
Phenol (6.54 g, 0.069 mol), and 1-methyl 2-pyrrolidinone (NMP) (30.0 mL) was charged in to reaction flask containing anhydrous ((-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methyl phosphonic acid (10.0 g 0.034mol), The reaction mixture was heated to 85°C. and Triethylamine (TEA)(4.35 g, 0.043 mol) was added slowly. To the obtained reaction mass 1,3-dicyclohexylcarbodiamide (DCC) (11.69 g, 0.056 mol) in 1-methyl -2-pyrrolidinone (NMP) (1.1 mL) was added for a period of 6 hours at 100°C. The reaction mixture was stirred for 16 hours and then cooled to 45°C. To the obtained reaction mass, water (20.0 mL) was added slowly, and cooled to 25°C. pHof the reaction mass was adjusted not less than 10 with 25% sodium hydroxide in water. The reaction mass was filtered through the Celite bed and washed with water(3.0 mL). The filtrate was extracted with dichloromethane (20.0 mL) twice. The pH of the aqueous solution was adjusted to 2 to 3 with ConcHCl. The crude solid was isolated by filtration and washed with methanol (8.7 mL). The wet cake was slurred in methanol (40.0 mL). Solids were isolated by filtration and washed with methanol (6.0 mL). The resulting solid was dried under reduced pressure to yield title compound.
Yield: 5.0 g
Chromatographic Purity (By HPLC): 95.05 %

Example 2
Preparation of Racemic Tenofovir Alafenamide:
Thionylchloride(8.18 gm, 0.06873 mol ) was charged in to reaction flask containing [(R)-2-(Phenylphosphonomethoxy) propyl] adenine ( 5 gm, 0.01376 mol) in toluene (50 ml) solution. The obtained reaction mass was heated to 75°C to 80°c for 3 hr. The solvent were removed at atmospheric pressure under nitrogen at 80°C, the reaction mixture were washed with (5 ml ) of toluene twice at atmospheric pressure under nitrogen at 80°C, cooled to 25°C, diluted with dichloromethane (50 ml). In a second reaction flask a mixture of L-alanine isopropyl ester hydrochloride (8.09 g , 0.04815mol) and potassium bicarbonate (12.0 g , 0.12mol) in dichloromethane (70 ml) was stirred at room temperature for 12h. Salts formation was observed in reaction mass. Then filtered the inorganic solids and washed with dichloromethane (7 ml), and further cooled to -30°c to -50°c. The above obtained acid chloride reaction mass in dichloromethane was added slowly to L-alanineisopropyl ester reaction mass in dichloromethane over a period of 10 to 15 min. The reaction mixture were maintained for 1h at same temperature (-30°c to -50°C),cooled to room temperature again maintained for 1hr at room temperature. The organic layer was washed with water (25 ml ) then aqueous layer and organic layer were separated. The organic layer was washed with 10% sodium di hydrogen orthophosphate solution (3x 25 ml), followed by with 10% potassium bi carbonate solution and 10% sodium chloride solution. The organic solution was dried over anhydrous sodium sulphate, filtered and washed with dichloromethane. The organic layer was concentrated and washed with acetonitrile (5 ml) under reduced pressure to get yield titled compound (Racemic R,S,S:R,R.S=70-80:30-20)
Yield: 5 gm
Chromatographic Purity (By HPLC): 98.5%

Example 3
Protection of L-aspartic acid with Acetyl chloride:
A mixture of L-aspartic acid (5.0 g , 0.0375 mol) Triethylamine (5.69 g , 0.0563mol) and dichloromethane (50 ml) was stirred at 0-5°C for 30 min and Acetyl chloride (3.24 g , 0.0413 mol) were added to reaction mass at 0-5°C. Reaction mass temperature was raised to 25-30°C and maintained for 12h. The reaction mass was filtered and washed with dichloromethane and resulting solid was dried at 50°C.
Yield: 6.5 g

Example-4
Protection of L-aspartic acid with Boc anhydride
A mixture of L-aspartic acid (5.0 g, 0.0375 mol) Triethylamine (7.59 g, 0.0752 mol) and Boc-anhydride (12.3 g , 0.0563 mol) in dichloromethane (50 mL) was stirred at room temperature for 12 h. The reaction mass was concentrated under reduced pressure to get an oil residue.
Yield : 7.5 g (Oil Residue)

Example-5
Synthesis of N-pthalimido-L-aspartic acid acid
Into a 100 mL round bottomed flask with a stirring bar were placed (2.22 g, 0.015 mol) of pthalic anhydride, (1.995 g, 0.015 mol) of L-aspartic acid and 25 mL of acetic acid. The mixture was refluxed for overnight. The solvent was removed under reduced pressure and then 5.0 mL cold water was added to the residue. A white precipitate was formed then it washed with cold water and dried under reduced pressure to yield titled compound.
Yield: 3.74 g
Melting Point: 227-230°C

Example 6
Preparation of Tenofovir Alafenamide protected amino acid salt
Solution of 9-[(R)-2-[{(S)-[{(S)-1-(isopropoxycarbonyl)ethyl]amino] phenoxyphosphinyl] methoxy] propyl]adenine ( 2 g , 0.0042mol) in acetonitrile (10 ml ) was heated to 75-80°C then added n-Acetyl protected aspartic acid (0.66 g ,0.0037mol) was added under stirring for 1h at 75-80°C. The reaction mixture was cooled to room temperature and maintained for 12 to 16 h. The reaction mixture was further cooled to 0 to 5°C and seeded with pure Tenofovir Alafenamide free base. The reaction mixture was maintained for 2 to 3 h at 0-5°c. The product was isolated by filtration and washed with chilled acetonitrile (2 ml)followed by n-Hexane (2 ml) and dried the solid under reduced pressure to yield titled product.
Diastereomeric purity: 96.40%
Yield: 0.8 g

Example 7
Purification of protected amino acid Salt of Tenofovir Alafenamide
Tenofovir Alafenamide acetyl protected aspartic acid salt (0.8 g) was dissolved in amyl alcohol (1.6 ml), heated to 60-65°C to get clear solution and the reaction mixture was stirred for 30 min at 60-65°c, cooled to room temperature, maintained for 2 hr after that again cooled to 0-5°c, stirred for 1hr.The product was isolated by filtration and washed with chilled amyl alcohol (0.4 ml) followed by chilled n-hexane (1.6 ml) and dried the solid under reduced pressure to yield titled compound
Diastereomeric purity: 99.7.0%
Yield: 0.5 g

Example 8
Preparation of Tenofovir Alafenamide
Tenofovir Alafenamide protected aspartic acid salt (0.5 g), Ethyl acetate (2.5 ml), and purified water (2.5 ml) was combined in a flask at room temperature. The reaction mixture was cooled to 20°C to 25°c and pH was adjusted to 8 to 9 with 20% sodium carbonate solution. The reaction mixture was stirred and organic and aqueous layers were separated. The aqueous layer was extracted with Ethyl acetate twice, stirred, and layers were again separated. The organic layer was then dried with sodium sulphate and ethyl acetate layer was distilled out completely under vacuum to yield title compound.
Yield: 0.3 g
Chromatographic Purity (By HPLC): 99.8%

Example 9
Preparation of Tenofovir Alafenamide Fumarate
To a solution of 9-[(R)-2-[{(S)-[{(S)-1-(isopropoxycarbonyl)ethyl]amino] phenoxy phosphinyl] methoxy] propyl]adenine ( 5 g , 0.01 mol) in amyl alcohol (15 ml), heated to 45-50°C to dissolve the solids and Fumaric acid (1.1 g, 0.009 mol) was added and stirred for 30 min. The reaction mixture was cooled to room temperature and maintained for 12 to 16 h after that cooled to 0-5°C then maintained for 30 min. The product was isolated by filtration, washed with chilledamyl alcohol (5 ml). Wet cake washed with Chilled toluene (10 ml), and dried under reduced pressure at 50-55°C to yield title compound.
Yield: 5 g
Chromatographic Purity (By HPLC): 99.8 %

While the foregoing pages provide a detailed description of the preferred embodiments of the invention, it is to be understood that the description and examples are illustrative only of the principles of the invention and not limiting. Furthermore, as many changes can be made to the invention without departing from the scope of the invention, it is intended that all material contained herein be interpreted as illustrative of the invention and not in a limiting sense.
,CLAIMS:Claims:

1) A process for the preparation of Tenofovir Alafenamide(I)

(I)
comprising the steps of:
a) reacting 4-Dimethyl Amino pyridine of ((-1-(6-amino-9H-purin-9-yl)propan-2-yloxy)methylphosphonic acid Formula II with phenol to yield [(R)-2-(Phenylphosphonomethoxy) propyl] adenine of Formula III;

b) reacting [(R)-2-(Phenylphosphonomethoxy) propyl] adenine with halogenating agent to provide Phosphonochloridic acid, P-[[(1R)-2-(6-amino-9-H-purin-9-yl)-1-methyl ethoxy] methyl]-phenyl ester of Formula (IV);

c) reacting compound of Formula IV with L-Alanine Isopropyl Ester to provide 9-[(R ) -2-[{(S)-[{(S)-1-(isopropoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy] propyl]adenine of Formula V;

d) reacting the compound of Formula V with protected amino acid of Formula VI to provide Formula VII

e) reacting the Formula VII with base to yield Tenofovir Alafenamide

2) A process for the preparation of Tenofovir Alafenamide according to claim 1, wherein halogenating agent used in step b)is selected from is Iodine, Bromine, Chlorine, thionyl chloride, oxalyl chloride, Phosphorous tri-chloride, Phosphorous penta-chloride, Phosphorous oxy chloride;

3) A process for the preparation of Tenofovir Alafenamide according to claim 1, wherein solvent used in step d) is selected from alcohols, such as C2-C6 alcohols like ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, t-butyl alcohol; or nitriles, such as acetonitrile or propionitrile; amides such as ?,?-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone; sulfoxides such as dimethylsulfoxide; halogenated hydrocarbons such as dichloromethane; aromatic hydrocarbons such as toluene, xylene; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, isopropyl acetate, isobutyl acetate, t-butyl acetate; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 1 ,4-dioxane, 2-methoxyethanol, anisole; ketones such as acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; organic solvents such as dimethyl formamide, n-hexane, n-heptane, cyclohexane, cycloheptane; water; or any mixtures

4) A process for the preparation of Tenofovir Alafenamide according to claim 8, wherein base used in step e) is selected from organic base such as triethylamine, methylamine, pyridine, imidazole, benzimidazole; or inorganic base selected from carbonates such as sodium carbonate, potassium carbonate, calcium carbonate, ammonium carbonate; hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, barium hydroxide, magnesium hydroxide, lithium hydroxide, zinc hydroxide; bicarbonates such as sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, calcium bicarbonate, magnesium bicarbonate;

5) A process for the preparation of Tenofovir Alafenamide according to claim 1, wherein protected amino acid of Formula VI

(VI)
Wherein R1 is hydrogen, CH2COOH, methyl, ethyl, n-propyl, i-propyl, acetyl or a substituted or unsubstituted phenyland hetero cyclic compounds. Where the substituent of the substituted phenyl is at least one of a CH3, OCH3, F, Cl, Br, I, nitro, cyano.; R2 or R3 selected from Hydrogen and the other group is selected from Fmoc, Boc, Cbz, acetyl, trifluoroacetamide, phthalimide, Benzyl, Triphenylmethylamine, Benzylideneamine, p-Toluene sulfonamide and Carbamate.

6) A compound of Formula:

(VI)
Wherein R1 is hydrogen, -CH2COOH, methyl, ethyl, n-propyl, i-propyl, acetyl or a substituted or unsubstituted phenyl and hetero cyclic compounds. Where the substituent of the substituted phenyl is at least one of a CH3, OCH3, F, Cl, Br, I, nitro, cyano.; R2 or R3 selected from Hydrogen and the other group is selected from Fmoc, Boc, Cbz, acetyl, trifluoroacetamide, phthalimide, Benzyl, Triphenylmethylamine, Benzylideneamine, p-Toluene sulfonamide and Carbamate.

7) A process for the preparation of highly pure Tenofovir Alafenamide having an enantiomeric purity of greater than 99.5% comprises:
a) reacting the compound of Formula V with protected amino acid of Formula VI to provide Formula VII

wherein R1, R2, R3 are as summarized above
b) reacting the Formula VII with base to yield Tenofovir Alafenamide
c) optionally converting Tenofovir Alafenamide to its corresponding Pharmaceutically acceptable salts

8) A process for the preparation of Tenofovir Alafenamide according to claim 7, wherein solvent used in step a) is selected from alcohols, such as C2-C6 alcohols like ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, t-butyl alcohol; or nitriles, such as acetonitrile or propionitrile; amides such as ?,?-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone; sulfoxides such as dimethylsulfoxide; halogenated hydrocarbons such as dichloromethane; aromatic hydrocarbons such as toluene, xylene; esters such as ethyl acetate, n-propyl acetate, n-butyl acetate, isopropyl acetate, isobutyl acetate, t-butyl acetate; ethers such as diethyl ether, diisopropyl ether, methyl t-butyl ether, tetrahydrofuran, 1 ,4-dioxane, 2-methoxyethanol, anisole; ketones such as acetone, ethyl methyl ketone, diethyl ketone, methyl isobutyl ketone; organic solvents such as dimethyl formamide, n-hexane, n-heptane, cyclohexane, cycloheptane; water; or any mixtures

9) A process for the preparation of Tenofovir Alafenamide according to claim 7, wherein base selected from organic base such as triethylamine, methylamine, pyridine, imidazole, benzimidazole; or inorganic base selected from carbonates such as sodium carbonate, potassium carbonate, calcium carbonate, ammonium carbonate; hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, barium hydroxide, magnesium hydroxide, lithium hydroxide, zinc hydroxide; bicarbonates such as sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, calcium bicarbonate, magnesium bicarbonate;

10) Substantially pure Tenofovir Alafenamide having enantiomeric purity of greater than 99.5% and total impurities A to J an diastereomeric impurity collectively less than 0.5% by HPLC.

Impurity-A Impurity-B

Impurity-C

Impurity-D
Impurity-E
Impurity-F

Impurity-G
Impurity-H
Impurity-I

Impurity-J
Diastereomeric Impurity