DESC:FIELD OF THE INVENTION

The present invention relates to a novel process for preparation of 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I (remdesivir) and pharmaceutically acceptable salts thereof.

BACKGROUND OF THE INVENTION

Remdesivir is known to exhibit antiviral properties antiviral properties against Arenaviridae, Coronaviridae, Filoviridae, and Paramyxoviridae viruses as described in Warren, T. et al., Nature (2016) 531 :381-385.

Remdesivir is chemically known as 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate. Remdesivir is a white to off-white or yellow non-hygroscopic solid. It is practically insoluble in water and is represented by the following formula as:

Remdesivir is a prodrug that metabolizes into its active form GS-441524. GS- 441524 is an adenosine nucleotide analog that interferes with the action of viral RNA polymerase and evades proofreading by viral exoribonuclease, causing a decrease in viral RNA production.

US Patent Publication No. US20160122356A1 assigned to Gilead Sciences discloses remdesivir as compound. This patent discloses use of remdesivir in the treatment of treating Filoviridae virus infections, particularly methods and nucleosides for treating Ebola virus, Marburg virus and Cueva virus. This patent discloses preparation of remdesivir

The present invention is directed to provide novel process for the preparation of 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I which includes mild reaction conditions, simple operation, less expensive cost effective process.

The inventors have observed that during the condensation reaction of (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) in presences of Coupling agent base and solvent to obtain 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV) formation of an impurity of R-isomer at 0.98 RRT occurs about 1% to 30% in non-selective Coupling agent, base and solvent. The amount of impurity formation varies depending upon reaction conditions, amount of solvent, nature of solvent used. It is advantageous to remove impurity at condensation reaction of (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile compound of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) to obtain 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV), otherwise it hinders and remain in the final product of 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl] amino}propanoate compound of formula I. Further after the formation of impurity of R-isomer at 0.98 RRT, it is difficult form purify form the final product, hence difficult to remove. Further it is an isomeric impurity R-isomer of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy) phosphoryl)-L-alaninate, the inventors have further found that during condensation reaction of (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) in presences of Coupling agent, base and solvent impurity R-isomer at 0.98 RRT is generated. Once the impurity R-isomer at 0.98 RRT is generated in the reaction mixture it is difficult to remove as it is an isomeric impurity. An additional step for purification of impurity is required to obtain purified desired compound. To achieve a high efficiency of the reaction for industrial synthesis of 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I (remdesivir), it is necessary to minimize the formation of the impurities and improve the yields.

Thus, the present invention provides an efficient and industrially advantageous process for the preparation of highly pure 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I (remdesivir) in high yield and purity.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an improved process for the preparation of 2-ethylbutyl 2-Ethylbutyl(2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl] amino} propanoate of formula I (remdesivir) and pharmaceutically acceptable salts thereof.

An object of the present invention is to provide improved process for the preparation of 2-Ethylbutyl(2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I (remdesivir) comprising steps of:
a) reaction of (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) in presences of Coupling agent base and solvent to obtain 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV);

Wherein, L is leaving group selected from Pentafluorophenyl or 4-nitrophenyl.

b) treating of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV) to obtain 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I;

An object of the present invention is to provide improved process for the preparation of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV) wherein Coupling agent can be a lithium coupling agent, a sodium coupling agent, a magnesium coupling agent.

An object of the present invention is to provide improved process for the preparation of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f] [1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3] dioxol -4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate of formula I (remdesivir) wherein base is Piperidine or Triethylamine.

An object of the present invention is to provide improved process for the preparation of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV) wherein solvent is Acetonitrile or DMF or mixture of Acetonitrile and DMF.

An object of the present invention is to provide improved process for the preparation of (S)-2-ethylbutyl 2-(((S)-(((2R.3S.4R.5R)-5-(4-amino pyrrolor 2.1- firi,2,41triazin-7-yl)-5-cvano-3,4-ditivdroxytetratiydrofuran-2- yl)methoxy)( phenoxy)phosphoryl)amino)propanoate of formula I (remdesivir) wherein the purity is more than 90.00%.

An object of the present invention is to provide improved process for the preparation of (S)-2-ethylbutyl 2-(((S)-(((2R.3S.4R.5R)-5-(4-amino pyrrolor 2.1- firi,2,41triazin-7-yl)-5-cvano-3,4-ditivdroxytetratiydrofuran-2- yl)methoxy)( phenoxy)phosphoryl)amino)propanoate of formula I (remdesivir) wherein the impurity of Rp Isomer is less than 1.00%.

DETAILED DESCRIPTION OF DRAWINGS:
FIGURE 1: is a HPLC chromatograph of result of analysis of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate, Compound of Formula IV in presence of Solvent ACN and base DIPEA.

FIGURE 2: is a HPLC chromatograph of result of analysis of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate, Compound of Formula IV in presence of Solvent DMF and base DIPEA.

FIGURE 3: is a HPLC chromatograph of result of analysis of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate, Compound of Formula IV in presence of Solvent DMF and base TEA.

FIGURE 4: is a HPLC chromatograph of result of analysis of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate, Compound of Formula IV in presence of Solvent ACN and base Piperidine.

FIGURE 5: is a HPLC chromatograph of result of analysis of (S)-2-ethylbutyl 2-(((S)-(((2R.3S.4R.5R)-5-(4-amino pyrrolor 2.1- firi,2,41triazin-7-yl)-5-cvano-3,4-ditivdroxytetratiydrofuran-2- yl)methoxy)( phenoxy)phosphoryl)amino)propanoate of formula I (Remdesivir) in presence of Solvent ACN and base Piperidine.

DETAILED DESCRIPTION OF THE INVENTION

The following terms and phrases as used herein are intended to have the following meanings:

When trade names are used herein, applicants intend to independently include the trade name product and the active pharmaceutical ingredient(s) of the trade name product.

The singular forms "a," "an," and "the" may refer to plural articles unless specifically stated otherwise.

The term "about," as used herein, is intended to qualify the numerical values which it modifies, denoting such a value as variable within a margin of error. When no particular margin of error, such as a standard deviation to a mean value given in a chart or table of data, is recited, the term "about" should be understood to mean that range which would encompass the recited value and the range which would be included by rounding up or down to that figure as well, taking into account significant figures.

The use of “e.g.,” “etc,” “for instance,” “in example,” “for example,” and “or” and grammatically related terms indicates non-exclusive alternatives without limitation, unless otherwise noted. The use of “including” and grammatically related terms means “including, but not limited to,” unless otherwise noted. The use of the articles “a,” “an” and “the” are meant to be interpreted as referring to the singular as well as the plural, unless the context clearly dictates otherwise. The use of “optionally,” “alternatively,” and grammatically related terms means that the subsequently described element, event or circumstance may or may not be present/occur, and that the description includes instances where said element, event or circumstance occurs and instances where it does not. The use of “preferred,” “preferably,” and grammatically related terms means that a specified element or technique is more acceptable than another, but not that such specified element or technique is a necessity, unless the context clearly dictates otherwise.

For the purpose of clarity and as an aid in the understanding of the invention, as disclosed and claimed herein, the following terms and abbreviations are defined below:
ACN: acetonitrile
DIPEA: N,N-Diisopropylethylamine
DMF: N,N-Dimethylformamide
TBTU: 2-[lH-benzotriazole- 1 -yl)- 1 , 1 ,3,3-tetramethyluronium
tetrafluoroborate
HOBt: N-hydroxybenzotriazole
TFA: trifluoroacetic acid
t-Bu: tert-butyl
TIS: Triisopropylsilane
EDT: Ethanedithiol
Trt: trityl
MDC: Methylene dichloride
DIPE: Diisopropyl ether
MgCl2: magnesium chloride
CuI: copper iodide
n-BuLi: n-butyl lithium
NaH: sodium hydride
LAH or LiAIH4: lithium aluminum hydride
iPrMgCl: isopropylmagnesium chloride
iPrMgCl—LiCl: isopropylmagnesium chloride-lithium chloride
tBuMgCl: tert-butylmagnesium chloride
PhMgCl: phenylmagnesium chloride
ZnCl2 : Zinc chloride
CuCl2 : Cupric chloride
Cu(OAc)2 : Copper(II) acetate,
CuI : copper iodide
Cu2O : cuprous oxide
Ni(OAc)2 : Nickel(II) acetate
LiCl : lithium chloride

The present invention relates to an novel process for the preparation of present invention is to provide improved process for the preparation of (S)-2-ethylbutyl 2-(((S)-(((2R.3S.4R.5R)-5-(4-aminopyrrolor2.1- firi,2,41 triazin-7-yl) -5-cvano-3,4-ditivdroxytetratiydrofuran-2- yl)methoxy)( phenoxy)phosphoryl)amino)propanoate of formula I (remdesivir).

In one embodiment the present invention provides a novel process for the preparation of (S)-2-ethylbutyl 2-(((S)-(((2R.3S.4R.5R)-5-(4-aminopyrrolor2.1- firi,2,41 triazin-7-yl) -5-cvano-3,4-ditivdroxytetratiydrofuran-2- yl)methoxy)( phenoxy)phosphoryl)amino)propanoate of formula I (remdesivir) comprising steps of:
a) reaction (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with . 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) in presences of Coupling agent, base and solvent to obtain 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV);

L is leaving group; Pentafluorophenyl or 4-nitrophenyl

b) treating 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV) to obtain 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I;

In a preferred process according to the invention, coupling (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) wherein with a suitable coupling reagents. The suitable coupling reagents are selected from the MgCl2; however, these reagents need to be used in conjunction with base such as Piperidine or Triethylamine and solvent selected from Acetonitrile or DMF or mixture of Acetonitrile and DMF or mixture thereof.

In a preferred process according to the invention, the coupling process reaction may include suitable coupling reagents are selected from the MgCl2; however, these reagents need to be used in conjunction with base such as Piperidine or Triethylamine and solvent selected from ACN, DMF or mixture thereof.

In one of the embodiment of the present invention of improved process whereby the coupling process is completed in with higher purity and controlled the impurity of Rp Isomer when the base is Piperidine or Triethylamine and solvent selected from Acetonitrile or DMF or mixture of Acetonitrile and DMF. Typically, a 0.5%v/v to about 8.0%v/v solution of base in solvent for the coupling process step.

Coupling is achieved by base, such as Piperidine or Triethylamine, Coupling is achieved by base, such as Piperidine in range of about 0.5%v/v to about 8.0%v/v in Acetonitrile or DMF or mixture of Acetonitrile and DMF. Coupling is achieved by base, most Triethylamine in DMF and in an amount of 2.5%v/v to 5.0%v/v.

In various embodiments, the solvent is pentane, pentanes, hexane, hexanes, heptane, heptanes, petroleum ether, cyclopentanes, cyclohexanes, benzene, toluene, xylene, trifluoromethylbenzene, halobenzenes such as chlorobenzene, fluorobenzene, dichlorobenzene and difluorobenzene, methylene chloride, chloroform, acetone, ethyl acetate, diethyl ether, tetrahydrofuran, acetonitrile, dimethylformamide (DMF) or combinations thereof. In some embodiments, the solvent can be Acetonitrile or DMF or mixture of Acetonitrile and DMF.

The reaction mixture of the method can be at any suitable temperature. For example, the temperature of the reaction mixture can be of from about -78°C to about 100°C, or of from about -50°C to about 100°C, or of from about -25°C to about 50°C, or of from about -10°C to about 25°C, or of from about 0°C to about 2°C. In some embodiments, the temperature of the reaction mixture can be of from about 0°C to about 20°C.

The coupling agent can be present in any suitable amount. For example, the coupling agent can be present in an amount of at least 1.0 to 10.0 eq. (mol/mol) to the compound of Formula (II), such as about 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, or about 10.0 eq. (mol/mol). The coupling agent can also be present in an amount of from about 1.0 to about 10.0 eq. (mol/mol) to the compound of Formula (II), such as about 1.0 to about 5.0eq. (mol/mol), or of from about 1.0 to about 2.0eq. (mol/mol). In some embodiments, the coupling agent can be present in an amount of from about 1.0 to about 5.0 eq. (mol/mol) to the compound of Formula (II). In some embodiments, the coupling agent can be present in an amount of from about 1.0 to about 2.0 eq. (mol/mol) to the compound of Formula (II).

Any suitable coupling agent can be used in the method of making the compound of Formula IV. The coupling agent can be a lithium coupling agent, a sodium coupling agent, a magnesium coupling agent, or others. For example, the coupling agent can be a deprotonating agent such as n-butyl lithium (n-BuLi), sodium hydride (NaH), lithium aluminum hydride (LAH or LiAIH4), and others. The coupling agent such as, but not limited to, magnesium chloride (MgCl2), isopropyl magnesium chloride (iPrMgCl), isopropyl magnesium chloride-lithium chloride (iPrMgCl—LiCl), tert-butyl magnesium chloride (t-BuMgCl), phenyl magnesium chloride (PhMgCl), Cerium chloride, Zinc chloride (ZnCl2), Cupric chloride (CuCl2), Cu(OAc)2, copper iodide (CuI), cuprous oxide (Cu2O), Nickel(II) acetate (Ni(OAc)2), lithium chloride (LiCl) or combinations thereof. Most preferable coupling agent is magnesium chloride (MgCl2).

According to above embodiment, 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro [3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy) phosphoryl)-L-alaninate compound of formula (IV) is isolated in high purity greater than 92.0% preferably greater than 94.0% without any further purification refer figure 3 and figure 4.

The following table summarizes the impact of various base used for Coupling, on the yield and quality of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro [3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy) phosphoryl)-L-alaninate compound of formula (IV) is shown to provide better results.

Base Solvent Metal complex used in coupling R-isomer Remdesivir
DMAP DMF MgCl2 17.65 54.92
NMM DMF MgCl2 26.56 53.18
Imidazole DMF MgCl2 3.97 13.68
Potassium carbonate DMF MgCl2 8.11 19.45
TEA DMF MgCl2 5.92 86.37
TEA DMF ZnCl2 6.64 56.42
TEA DMF CuCl2 1.06 6.94
TEA DMF Cu(OAc)2 3.05 7.76
TEA DMF CuI 3.75 17.54
TEA DMF Cu2O NA 1.67
TEA DMF Ni(OAc)2 NA 0.87
Pyridine DMF MgCl2 NA 2.26
Pyrrolidine DMF MgCl2 2.67 84.83
Piperidine DMF MgCl2 0.77 89.6
Piperazine DMF MgCl2 1.29 89.43
Pyrrole DMF MgCl2 NA 1.46
Diethylamine DMF MgCl2 1.3 88.62
Piperidine DMF MgCl2 0.65 90.63
Piperidine MDC MgCl2 8.78 55.2
Piperidine Ethyl acetate MgCl2 7.76 26.53
Piperidine DMF Cerium chloride 2.37 27.49
Piperidine DMF LiCl 8.4 25.9
Piperidine THF MgCl2 19.62 48.07
Piperidine Acetone MgCl2 1.42 72.99
Piperidine 1,4-Dioxan MgCl2 2.69 16.44
Piperidine IPA MgCl2 1.28 20.05
Piperidine Xylene MgCl2 12.64 59.25
Piperidine ACN MgCl2 0.06 88.31
DIPEA ACN MgCl2 2.74 76.68

From the Table 1 it is concluded that suitable base is Piperidine and coupling agent is MgCl2 for the preparation of compound of Formula IV and solvent can be Acetonitrile or DMF or mixture of Acetonitrile and DMF. The Process for preparation of of compound of Formula IV in presences of base is Piperidine and coupling agent is MgCl2 and solvent as Acetonitrile and DMF for controlling isomer ration in the reaction, this process are advantageous as process does not require prep HPLC for further purification.

Preparation of Remdesvir treating 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy) phosphoryl)-L-alaninate compound of formula IV to obtain 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy} (phenoxy)phosphoryl]amino} propanoate of formula I.

Purification of Remdesvir Crude: Remdesvir of formula I crude is purified using solvent selected from chlorobenzene, fluorobenzene, dichlorobenzene and difluorobenzene, methylene chloride, chloroform, acetone, ethyl acetate, diethyl ether, tetrahydrofuran, acetonitrile, dimethylformamide (DMF) or combinations thereof and preferably Acetone to obtain pure (S)-2-ethylbutyl 2-(((S)-(((2R.3S.4R.5R)-5-(4-aminopyrrolor 2.1- firi,2,41 triazin-7-yl)-5-cvano-3,4-ditivdroxytetratiydrofuran-2- yl) methoxy)( phenoxy)phosphoryl) amino) propanoate of formula I.

Major advantages realized in the present invention are high purity and high yields. The formation of impurity of R-isomer at 0.98 RRT has been restricted by making use of selective base and solvent system with coupling agent wherein base is selected form Piperidine, TEA solvent is selected form DMF, ACN and coupling agent is selected form MgCl2, Cu2O, Ni(OAc)2. This avoids the use of tedious and cumbersome technique i.e. chromatographic purification as additional step of purification.

The stage I isomeric impurity R-isomer is removed from 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy) phosphoryl)-L-alaninate compound of formula IV by making use of selective base and solvent system with coupling agent wherein base is selected form Piperidine, TEA solvent is selected form DMF, ACN and coupling agent is selected form MgCl2, Cu2O, Ni(OAc)2.

The above process is represented stepwise as shown below:
Scheme

The process of the invention is illustrated with reference to the following Examples and is not intended to limit the scope of the invention. Any permutations and modifications in the process are possible keeping in mind the scope of the invention.

Example 1: preparation of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro [3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy) pho- sphoryl)-L-alaninate:

(3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydro- xymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile- (12 g; 36.2 mmol) was charged into acetonitrile under nitrogen atmosphere. 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate (24g; 48.44 mmol; 1.33 mol eq) was charged in to the clear solution. Charged Magnesium chloride (2.5 g) into the solution. Added Piperidine (6g; 68 mmol; 1.9 mol eq) to the reaction mixture at temperature below 0°C. The reaction mixture was stirred for 15 hours at ambient temperature. The reaction mixture was quenched in citric acid solution. The product was extracted in ethyl acetate (3x100 ml). The combined organi layer was washed with brine. The organic layer was distilled to get residue (25 g). The residue was taken for next step without purification.

Example 2: preparation of 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f] [1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2yl]metho- xy}(phenoxy) phosphorryl]amino} propanoate:

2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy) (phenoxy)phosphoryl)-L-alaninate (25g) was charged in to acetonitrile. The solution was cooled to 10-20°C. Conc. Hydrochloric acid (75 ml) was added at temperature 10-20°C. Stirring was continued for 12 hrs at room temperature. The reaction mixture was neutralized with saturated sodium bicarbonate solution. The product was extracted with ethyl acetate (3 x 100 ml). The combined organic layer was washed with saturated brine solution. The organic layer was distilled to residue. The residue was dissolved in fresh ethyl acetate (100 ml). The solution was made particle free by passing through 0.45µ filter. The filtrate was seeded with 100 mg of remdesivir. Stirred the suspension for 24hrs to get a slurry. The solids were filtered and washed with ethyl acetate. The solid was dried in vacuum oven at temperature below 50°C under vacuum to get a white solid (8 g); purity by HPLC-99.6%; Rp isomer 0.1%.

The inventors have observed that during the condensation reaction of (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) in presences of Coupling agent base and solvent to obtain 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV) formation of an impurity of R-isomer at 0.98 RRT occurs about 1% to 30% by restricted and selective base and solvent system with coupling agent wherein base is selected form Piperidine, TEA solvent is selected form DMF, ACN and coupling agent is selected form MgCl2, Cu2O, Ni(OAc)2.
The amount of impurity formation varies depending upon reaction conditions, base and solvent system with coupling agent used. It is advantageous to remove impurity at condensation reaction of (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile compound of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) to obtain 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV), otherwise it hinders and remain in the final product of 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl] amino}propanoate compound of formula I. Further after the formation of impurity of R-isomer at 0.98 RRT, it is difficult form purify form the final product, hence difficult to remove. Further it is an isomeric impurity R-isomer of 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy) phosphoryl)-L-alaninate, the inventors have further found that during condensation reaction of (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) in presences of Coupling agent, base and solvent impurity R-isomer at 0.98 RRT is generated. Once the impurity R-isomer at 0.98 RRT is generated in the reaction mixture it is difficult to remove as it is an isomeric impurity. An additional step for purification of impurity is required to obtain purified desired compound. To achieve a high efficiency of the reaction for industrial synthesis of 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I (remdesivir), it is necessary to minimize the formation of the impurities and improve the yields.

,CLAIMS:CLAIMS

We Claim,

1. A novel process for preparation of compound 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of formula I and pharmaceutically acceptable salts thereof

Comprises:
(i) reacting (3aR,4R,6R,6aR)-4-(4-Aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-(hydroxymethyl)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carbonitrile of formula (II) with 2-Ethylbutyl ((S)-(Perfluorophenoxy)(Phenoxy) Phosphoryl)-L-Alaninate of formula (III) in presences of coupling agent, base and solvent to obtain 2-ethylbutyl ((((3aR,4R,6R,6aR)-6-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-6-cyano-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl)methoxy)(phenoxy)phosphoryl)-L-alaninate compound of formula (IV);

(ii) treating of compound of Formula IV to 2-Ethylbutyl (2S)-2-{[(S)-{[(2R,3S,4R,5R)-5-(4- aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl]methoxy}(phenoxy)phosphoryl]amino} propanoate of Formula I;

(iii) purification of the compound of formula I using solvent.

2. The novel process as claimed in claim 1, wherein coupling agent is selected from n-butyl lithium (n-BuLi), sodium hydride (NaH), lithium aluminum hydride (LAH or LiAIH4), magnesium chloride (MgCl2), isopropyl magnesium chloride (iPrMgCl), isopropyl magnesium chloride-lithium chloride (iPrMgCl—LiCl), tert-butyl magnesium chloride (t-BuMgCl), phenyl magnesium chloride (PhMgCl), Cerium chloride, Zinc chloride (ZnCl2), Cupric chloride (CuCl2), Cu(OAc)2, copper iodide (CuI), cuprous oxide (Cu2O), Nickel(II) acetate (Ni(OAc)2), lithium chloride (LiCl) or combinations thereof.

3. The novel process as claimed in claim 1, wherein base is selected from Piperidine or Triethylamine present in an amount of 0.5%v/v to about 8.0%v/v.

4. The novel process as claimed in claim 1, wherein solvent is selected from pentane, pentanes, hexane, hexanes, heptane, heptanes, petroleum ether, cyclopentanes, cyclohexanes, benzene, toluene, xylene, trifluoromethyl benzene, halo benzenes such as chlorobenzene, fluorobenzene, dichlorobenzene and difluorobenzene, methylene chloride, chloroform, acetone, ethyl acetate, diethyl ether, tetrahydrofuran, acetonitrile, dimethylformamide (DMF) or combinations thereof present in an amount 2.5%v/v to 5.0%v/v.

5. The novel process as claimed in claim 1, wherein L is leaving group of compound of Formula III is selected from Pentafluorophenyl or 4-nitrophenyl.

6. The novel process as claimed in claim 1, wherein solvent for purification is selected from chlorobenzene, fluorobenzene, dichlorobenzene and difluorobenzene, methylene chloride, chloroform, acetone, ethyl acetate, diethyl ether, tetrahydrofuran, acetonitrile, dimethylformamide (DMF) or combinations thereof and preferably Acetone.

Dated this 28th November 2022