& ITS POLYMORPH

Field of the Invention:

The present invention pertains to process for preparing N-[(2,3,4,5,6- Pentafluorophenoxy)phenoxyphosphinyl]-L-alanine 1-methylethyl ester (formula 2) and resolving the formula 2 in the presence base to form N-[(S)-(2,3,4,5,6- Pentafluorophenoxy)phenoxyphosphinyl]-L-alanine 1-methylethyl ester (formula 2'). The present invention also relates to a novel crystalline form of N-[(S)-(2, 3, 4, 5, 6- Pentafluorophenoxy)phenoxyphosphinyl]-L-alanine 1-methylethyl ester.

Background of the Invention:

Sofosbuvir is chemically named as (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4- dioxo3,4- dihydropyrimidin-l(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrah ydrofuran- 2yl)methoxy)- (phenoxy)phosphorylamino)propanoate and is represented by the following chemical structure:

Formula 1

PCT publications WO2011123645 and WO2010135569 describes process for preparation of compound of formula 2' by reacting isopropyl (chloro(phenoxy)phosphoryl)-L-alaninate and pentaflurophenol in the presence of base.

Formula 2'

Description of drawings:

Figure 1 : illustrates Infra-red spectrograph of compound of formula 4.

Figure 2: illustrates X-ray powder diffraction pattern of crystalline form of formula 2'.

Figure 3: illustrates Nuclear magnetic resonance spectrograph of compound of formula 2'.

Summary of Invention:

In one aspect, the present invention relates to a process for preparation of compound of formula 2 in the absence of base.

Formula 2

The process for preparation of compound of formula 2 according to present invention is described by reaction scheme- 1

Scheme- 1

Wherein M is metal ion,

In another aspect, the present invention provides a resolution of compound of formula 2 in the presence of base.

In another aspect, the present invention relates to a novel crystalline form of compound of formula 2' and process for the preparation thereof.

Detail Description of the Invention:

There is always a need for alternative preparative routes, which for example, use reagents, solvents that are less expensive, and/or easier to handle, consume smaller amounts of reagents and solvents, provide a higher yield of product, involve fewer steps, have smaller and/or more eco-friendly waste products, and/or provide a product of higher purity.

According to one aspect the present invention, provides a process for preparation of formula 2:

Formula 2 comprising: i) reaction of compound of formula 3 or pharmaceutically acceptable salts thereof with compound of formula 4 or pharmaceutically acceptable salts thereof in the absence of base.

Wherein M ⁺ is a metal ion which can be selected from but not limited to sodium, Potassium, Magnesium.

Compound of formula 4 is prepared by treating pentaflurophenol with metal ion precursor such as sodium hydroxide, sodium methoxide, sodium hydride, potassium hydroxide.

The solvent for the above reaction can be selected from one or more of hydrocarbons like toluene, xylene; chlorinated hydrocarbons like methylene dichloride, ethylene dichloride and chlorobenzene; alcohols like methanol,ethanol; ethers like diethyl ether, diisopropyl ether, t- butyl methyl ether, 1 ,2-dimethoxy ether (DME), dibutyl ether, tetrahydrofuran, 1,4-dioxane; and acetonitrile or mixtures thereof. In particular, the solvent is methylene dichloride, 1, 2- dimethoxy ether (DME), 1,4-dioxane and tetrahydrofuran or mixtures thereof.

In another aspect, the invention provides process for preparation of specific stereo isomer of formula 2':

Formula 2' comprising treating of compound of formula 2 with a base to obtain a desired specific stereo isomer of formula 2'.

The base can be selected from organic bases selected from tertiary and secondary amines for example triethylamine; inorganic bases such as sodium hydroxide, Potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ C0 ₃ ), potassium hydroxide (KOH); potassium fluoride, tripotassium phosphate (K ₃ PO ₄ ).

Optionally the compound of formula 2 used in the above reaction obtaining an existing solution from a previous processing step.

According to another aspect, the present invention provides novel crystalline form of Formula 2' characterized by XRPD (X-ray powder diffractogram) which comprises of peaks expressed as 2Θ at 7.9, 8.3, 9.4,11.0, 14.9,16.5 and 31.72 ± 0.2 degrees.

In another aspect, the invention provides a process for preparation of novel crystalline forms of compound of formula 2' comprising the steps of:

(i) providing a solution of formula 2' in organic solvent;

(ii) optionally cooling the above solution; and

(iii) isolating crystalline form of compound of formula 2' .

In one embodiment, the organic solvent used in step-(i) is selected from but not limited to water, methanol, ethanol, isopropyl alcohol, n-butanol, tert-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl tert-butyl ketone, n-heptane, cyclohexane, toluene, methylene chloride, Di-isopropyl ether and mixtures thereof. Instrument settings for XRPD

The X-ray powder diffraction spectrum (XRPD) was recorded at room temperature using PANalytical X'pert PRO diffractogram with Cu K radiation ( = 1.54060 A°), running at 45 kv and 40ma. Example-1:

Preparation of sodium 2,3,4,5,6-pentaflurophenolate using sodium hydride

10.2g of sodium hydride was dissolved in 100 ml anhydrous THF. This solution was slowly added to a solution of pentafluorophenol (50g) in THF (100ml), Reaction mass was stirred for 60-120 min at 25-30°C. Reaction mass was distilled under reduced pressure, obtained solid was dried under vacuum at 45-50°C (yield=55g, confirmed by IR)

Example-2:

Preparation of sodium 2,3,4,5,6-pentaflurophenolate using sodium methoxide

2,3,4,5, 6-pentafluorophenol (lOg) was dissolved in methanol (100ml), solution was cooled to 5-10°C. To this was added a solution of sodium methoxide in methanol. The reaction mass was stirred for 60-120 min at 25-30°C. Reaction mass was distilled under reduced pressure, obtained residue was striped with toluene. Obtained solid was dried under vacuum at 45- 50°C (yield=l lg)

Example 3:

Preparation of sodium 2,3,4,5,6-pentaflurophenolate using sodium hydroxide 2,3,4,5, 6-pentafluorophenol (lOOg) dissolved in methanol (—ml), solution was cooled to 5- 10°C. To this was added a solution of sodium hydroxide (— g) in methanol. The reaction mass was stirred for 60-120 min at 25-30°C. Reaction mass was distilled under reduced pressure, obtained residue was striped with dichloromethane. Obtained solid was dried under vacuum at 45-50°C (yield=— g) Example 4:

Preparation of (2S)-isopropyl-2-((chloro(phenoxy)posphoryl)amino)propanoate : phenyl phosphodichloridate (30.6g) was dissolved in dichloromethane , to this was added a solution of 1-alanine isopropyl ester free base (19.16g) in dichloromethane at-60°C under nitrogen. Solution of triethylamine (20.7ml) was added to above reaction mass. Reaction mass was stirredat -60°C for 30 min and then temperature was raised to 25 °C. Reaction mass was stirred at 20-25 °C for 60 min & filtered and washed with dichloromethane. Clear filtrate was distilled under reduced pressure obtained residue was stirred with diisopropyl ether & filtered. Clear filtrate was distilled under reduced pressure to get (2S)-isopropyl-2- ((chloro(phenoxy)posphoryl)amino)propanoate compound.

Example 5:

Preparation of isopropyl ((perfluorophenoxy)(phenoxy)phosphoryl)-L-alaninate (formula 2):

(Formula 2)

Obtained (2S)-isopropyl-2-((chloro(phenoxy)phosphoryl)amino)propanoat e (1.2 mol eq.) was dissolved in dichloromethane and cooled to 0-5°C under nitrogen atmosphere. To this was added solution of sodium 2,3,4,5,6-pentaflurophemolate (1 mol eq.) in tetrahydrofuran . Temperature of reaction mass was raised to 25°C and reaction mass was stirred for 3 hrs. After completion of reaction, reaction mass was distilled under reduced pressure & obtained residue was dissolved I ethyl acetate. Ethyl acetate layer was washed with water, dried over sodium sulfate & distilled off under reduced pressure. Diisopropyl ether was added to obtained residue and stirred for 60 min at 25 °C, obtained mass was filtered & washed with diisopropyl ether. Solid product was dried under vacuum at 40-45 °C .(yield=20g, enantiomer purity=93.45%)

Example 6:

Preparation of (S)-isopropyl 2-(((S)-

(perfluorophenoxy)phenoxy)phosphoyl)amino)propanoate (Formula 2'):

Formula 2'

(2S)-isopropyl-2-((chloro(phenoxy)phosphoryl)amino)propan oate (1.2 mol eq.) was dissolved in tetrahydrofuran (3.5 volumes). The reaction mass was cooled to -10°C. Solution of sodium salt of pentafluorophenol (1 mol eq.) in tetrahydrofuran (3.5 volumes) was added dropwise to the reaction mass at -10°C. After completion of the reaction solvent was distilled off. Ethyl acetate and water were added to the reaction mass. Reaction mass was stirred, ethyl acetate layer was separated and washed with sodium bicarbonate solution and brine. Ethyl acetate layer was concentrated under reduced pressure. Reaction mass was stripped with n- hepatane to get crude product. Crude product was dissolved in Methyl tert-butyl ether and n- heptane (1 : 1 ratio). The pH of reaction mass was adjusted to pH 8 by using triethylamine. Reaction mass was stirred overnight. Solid mass was filtered and washed with a mixture of methyl tertiary-butyl ether: n-heptane (1 : 1). The obtained product was dissolved in ethyl- acetate and washed with water and 20% brine solution. Ethyl acetate layer was separated; solvent was distilled off under reduced pressure. Reaction mass was stripped with diisopropyl ether. Di-isopropyl ether was added to the reaction mass. Reaction mass was stirred at 45- 50°C. Reaction mass was cooled to 5-10°C and stirred. The titled compound was isolated by filtration and washed with di-isopropyl ether. The titled compound was dried under reduced pressure at 40°C. Yield 66.81%.