DESC:FORM 2

THE PATENTS ACT 1970
(SECTION 39 OF 1970)

&

THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(Section 10 and Rule 13)

AN IMPROVED PROCESS FOR THE PREPARATION OF INTERMEDIATE AND ITS USE IN THE PREPARATION OF ANTIVIRAL COMPOUND

We, Viruj Pharmaceuticals Private Limited.,
a company incorporated under the companies act, 1956 having address at B-4, IDA Gandhinagar, Hyderabad – 500037, Telangana, India.

The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of a compound useful in the preparation of anti-viral compound.

The present invention specifically relates to an improved process for the preparation of Molnupiravir oxime ester of the formula (I).
Formula (I)

The present invention also relates to a process for preparation of Molnupiravir or its salts.

BACKGROUND OF THE INVENTION
Molnupiravir is an experimental antiviral drug which is orally active and was developed for the treatment of influenza. It is a prodrug of the synthetic nucleoside derivative N4-hydroxycytidine, and exerts its antiviral action through introduction of copying errors during viral RNA replication.

It is the first oral, direct-acting antiviral shown to be highly effective at reducing nasopharyngeal SARS-CoV-2 infectious virus and viral RNA and has a favorable safety and tolerability profile. Molnupiravir increases the frequency of viral RNA mutations and impairs SARS-CoV-2 replication in animal models and in humans.

The chemical name of Molnupiravir is [(2R,3S,4R,5R)-3,4-dihydroxy-5-[(4Z)-4-(hydroxyimino)-2-oxo-1,2,3,4-tetrahydropyrimidin-1-yl]oxolan-2-yl]methyl 2-methylpropanoate, its molecular formula is C13H19N3O7, having molecular structure of:

ChemRxiv, 2021, pg. 1-8 (published on-line on January 11, 2021) discloses a process for the preparation of Molnupiravir which is shown in the scheme given below:

ACS Omega, 2021, Volume 6, issue 15, pg. 10396–10402, (published on April 08, 2021) disclose a process for the preparation of Molnupiravir is shown in the scheme given below:

In view of the importance of Molnupiravir in reducing the infection of SARS-CoV-2 virus, there is a need for develop a process for preparing Molnupiravir with simple, economical, cost effective and environmental friendly process at relatively high yields and high purity without using hazardous and expensive materials. Further, the importance lies in getting the product with correct stereochemistry and enantiomeric purity.

Surprisingly, the inventors of the present application were able to develop a novel route for synthesis of Molnupiravir or its salts, which is environmental friendly, economical, convenient, efficient, and less time consuming.

OBJECTIVE OF THE INVENTION
The main objective of the present invention is to provide an improved process for the preparation of a compound useful in the preparation of anti-viral compound.

In another objective of the present invention is to provide to an improved process for the preparation of Molnupiravir oxime ester of the formula (I).

In another objective of the present invention is to provide a simple, economical and commercially feasible process for preparing Molnupiravir or its salts with good chiral, high chemical purity and high yield.

SUMMARY OF THE INVENTION
Accordingly, the present invention provide an improved process for the preparation of Molnupiravir oxime ester of the formula (I).
Formula (I)

or its salts, wherein the process comprises reacting N-hydroxy cytidine of Formula (II)
Formula (II)
with isobutyric acid anhydride using an enzyme in a solvent.

In another aspect, the present invention provides an improved process for the preparation of highly pure Molnupiravir of Formula (III) which comprises:
(a) reacting N-hydroxy cytidine of Formula (II)
Formula (II)
with isobutyric acid anhydride using an enzyme in a solvent to yield Molnupiravir oxime ester of the formula (I),
(b) converting compound of formula (I) to Molnupiravir using hydroxylamine in present of a solvent.

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a novel process for preparing of Molnupiravir or its salts, which is high yielding as the unwanted impurity (diacetyl compound) which is also an intermediate in the process, is controlled. Further the process involves use of enzyme wherein the chirality of the starting material is retained, thereby yielding the final Molnupiravir with chemical and chiral purity.

Enzyme as used in the reaction of N-hydroxy cytidine with isobutyric acid anhydride may be lipase which is selected from Addzyme, triacylglycerol lipase, fungal lipase, CALB (Novozyme),

Solvent as defined in the present invention are selected from water or "alcohol solvents" such as methanol, ethanol, n-propanol, isopropanol, n-butanol and t-butanol and the like or "hydrocarbon solvents" such as benzene, toluene, xylene, heptane, hexane and cyclohexane and the like or "ketone solvents" such as acetone, ethyl methyl ketone, diethyl ketone, methyl tert-butyl ketone, isopropyl ketone and the like or "esters solvents" such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, and the like or "nitrile solvents" such as acetonitrile, propionitrile, butyronitrile and isobutyronitrile and the like or "ether solvents" such as di-tert-butylether, dimethylether, diethylether, diisopropyl ether, 1,4-dioxane, methyl tert-butylether, ethyl tertbutyl ether, tetrahydrofuran, 2-methyl tetrahydrofuran, 2-methoxyethanol and dimethoxyethane, or “Amide solvents” such as formamide, DMF, DMAC, N-methyl-2- pyrrolidone, N-methylformamide, 2-pyrrolidone, 1-ethenyl-2-pyrrolidone, haloalkanes such as dichloromethane, 1,2-dichloroethane and chloroform, “Amine solvents” selected from diethylenetriamine, ethylenediamine, morpholine, piperidine, pyridine, quinoline, tributylamine, diisopropyl amine and/or mixtures thereof.

The solvent preferably is water, 2-methyl tetrahydrofuran, Methyl tertiary butyl ether, Toluene, 1,4-dioxane, xylene.

The novelty and inventive step of the process involves in using isobutyric acid anhydride which is commercially available unlike 2-acetone isobutyl oxime use disclosed in the prior-art. Acetone isobutyl oxime has to be synthesized prior-to use which adds on to the total cost of the product. Further the process of the prior-art results in mixture of compounds of the following formula

Intermediate / Impurity as per the process of 2-acetone isobutyl oxime As per the process of the present invention (intermediate stage) As per the process of the present invention (API stage)

Final ~ 3% (Initial IPC Appr 2.0 %) Not Detected <0.15%

Final 0.8% (Initial IPC 67%) 97.68% 0.1%
Final ND (Initial 1.5%) 1.8% ND

Final ~95% (Initial IPC 29.5%) 0.5% 99.9%

The process of the present invention upon reaction of N-hydroxy cytidine with isobutyric acid anhydride selectively results in Molnupiravir oxime ester in 99.0% yield.

The Molnupiravir oxime ester formed in the present invention may or may not be isolated. Any of the above reactions may be carried out in-situ reactions. If any of the above compounds are isolated they can be isolated as salts or free bases and if the above compounds are isolated as salts they are converted to their free bases first and used for further reactions.

Molnupiravir oxime ester prepared by the process of the present invention is converted to Molnupiravir oxime using hydroxylamine of less concentration.

Further the process of present invention consumes less time / solvents for work-up compared to the known procedures which is commercially feasible / industrially scalable and Molnupiravir in high yield.

The present invention is further illustrated by the following examples which are provided merely to be exemplary of the inventions and is not intended to limit the scope of the invention. Certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

EXAMPLES
Example 1: Preparation of 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate

A Mixture of 4-amino-1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl) pyrimidin-2(1H)-one (4.5kg), Hydroxylamine sulfate (4.4kg) and water (6.75lit) was heated to 65-75°C.and stirred for 8-10hrs. HPLC showed as 3.98% 4-amino-1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl) pyrimidin-2(1H)-one, 92.41% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate and 2.18% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)pyrimidine-2,4(1H,3H)-dione. Then the reaction was cooled to 25-35°C and stirred for 2hrs, then further cooled to 0-10°C and stirred for about 3hrs. Filtered the solid through nustche filter and washed the solid with chilled water twice(4.5lit*2). Suck dried the solid for 3hrs and dried the solid at 45-50°C under vacuum for 8-10hrs to obtain 4.6kg of white 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate (89.6% yield, 99.7% purity by HPLC, 99.5% assay by HPLC, 6.7% Moisture Content, Residue on ignition 0.1%).

Example 2: Preparation of 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate
A Mixture of 4-amino-1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl) pyrimidin-2(1H)-one (165kg), Hydroxylamine sulfate (189.29kg) and water (247.5lit) was heated to 65-75°C.and stirred for 8-10hrs. HPLC showed as 3.98% 4-amino-1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl) pyrimidin-2(1H)-one, 92.41% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate and 2.18% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)pyrimidine-2,4(1H,3H)-dione. Then the reaction was cooled to 25-35°C and stirred for 2hrs, then further cooled to 0-10°C and stirred for about 3hrs. Filtered the solid through Centrifuge and washed the solid with chilled water twice (165lit). Suck dried the solid for 3hrs and unload the wet compound about 172kg and load the wet compound (172kg) and add 165 lit water and was heated to 65-75°C and stirred for 30-45min. Then the reaction was cooled to 25-35°C and stirred for 2hrs, then further cooled to 0-10°C and stirred for about 3hrs. Filtered the solid through Centrifuge and washed the solid with chilled water twice(165lit). Suck dried the solid for 3hrs and unload the wet compound about 168kg and dried the solid at 45-50°C under vacuum for 8-10hrs to obtain 162kg of white 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate (86.6% yield, 99.7% purity by HPLC, 99.5% assay by HPLC, 6.7% MC, ROI 0.1%).

Example 3: Preparation of ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate

A mixture of 2-methyl tetrahydrofuran (20.0Lit), 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate(1.33kg) and Addzyme-015(200.0g) was cooled to 0-10°C. 3.04kg of 2-Methylpropionic anhydride was added slowly for 3-4hr. Heated the reaction to 40-45°C and stirred for 18hrs. HPLC showed as ~1.8% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-((isobutyryloxy)amino) pyrimidin-2(1H)-one compound and 97.68% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate compound. Then cooled the reaction was cooled to 25-35°C and filtered the addzyme-015. Then to filtrate added 17% Hydroxylamine (4.0lit) solution at 0-10°c for 2hrs.Then raised the temperature to 25-35°C and stirred for 2-3hrs and submitted to Analysis. HPLC showed as 1.5% of 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one, 97.07% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate and 0.41% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate. Then separated the layers and washed the 2-methyl tetrahydrofuran with (4.0lit) water. Then 2-methyl tetrahydrofuran was distilled out completely under vacuum at below 50°C to obtain white solid. To the solid Methyl tertiary butyl ether (1.33lit) was added and distilled out completely under vacuum at below 50°C. To the solid (4.0lit) Methyl tertiary butyl ether was added at same temperature and cooled the temperature to 25-35°C followed by 0-10°C. Stirred the reaction for 3hrs and filtered the solid through nustche filter. Washed the solid with Methyl tertiary butyl ether (1.33lit) and suck dried the solid for 1hr. Crude 1.5kg ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl) tetrahydrofuran-2-yl) methyl isobutyrate. Charged crude into reactor and added water (2.4Lit) then raised the temperature to 65-75°C and stirred for 30mins. Cooled the reaction temperature to 25-35°C followed by 0-10°C. Stirred for 3hrs. and filtered the solid and dried the solid for 8hrs at 50°C under vacuum to obtain ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate (Yield 76%, Purity by HPLC 99.9%, assay by HPLC 99.9%, Specific Optical rotation -8.217°C, Moisture Content 0.36%w/w, Residue on ignition 0.12%w/w).

Example 4: Preparation of ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate

A mixture of Toluene (20.0Lit), 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate(1.33kg) and Addzyme-015(200.0g) was cooled to 0-10°C. 3.04kg of 2-Methylpropionic anhydride was added slowly for 3-4hr.Heated the reaction to 40-45°C and stirred for 18hrs. HPLC showed as 2.2% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-((isobutyryloxy)amino) pyrimidin-2(1H)-one compound and 96.22% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate compound. Then cooled the reaction was cooled to 25-35°C and filtered the addzyme-015. Then to filtrate added 17% Hydroxylamine (4.0lit) solution at 0-10°c for 2hrs.Then raised the temperature to 25-35°C and stirred for 2-3hrs and submitted to Analysis. HPLC showed as 1.25% of 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one, 96.2% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate and 0.31% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate. Then separated the layers and washed the 2-methyl tetrahydrofuran with (4.0lit) water. Then 2-methyl tetrahydrofuran was distilled out completely under vacuum at below 50°C to obtain white solid. To the solid Methyl tertiary butyl ether (1.33lit) was added and distilled out completely under vacuum at below 50°C. To the solid (4.0lit) Methyl tertiary butyl ether was added at same temperature and cooled the temperature to 25-35°C followed by 0-10°C. Stirred the reaction for 3hrs and filtered the solid through nustche filter. Washed the solid with Methyl tertiary butyl ether (1.33lit) and suck dried the solid for 1hr. Crude 1.45kg ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl) tetrahydrofuran-2-yl) methyl isobutyrate. Charged crude into reactor and added water (2.4Lit) then raised the temperature to 65-75°C and stirred for 30mins. Cooled the reaction temperature to 25-35°C followed by 0-10°C. Stirred for 3hrs and filtered the solid and dried the solid for 8hrs at 50°C under vacuum to obtain ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate (Yield 70%, Purity by HPLC 99.9%, assay by HPLC 99%).

Example 5: Preparation of ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate

A mixture of 1,4-dioxane(200.0mL), 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate(10.0g) and Addzyme-015(2.0g) was cooled to 0-10°C. 23.5g of 2-Methylpropionic anhydride was added slowly for 3-4hr. Heated the reaction to 40-45°C and stirred for 18hrs. HPLC showed as 2.1% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-((isobutyryloxy)amino) pyrimidin-2(1H)-one compound and 96.35% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate compound. Then cooled the reaction was cooled to 25-35°C and filtered the addzyme-015. Then to filtrate added 17% Hydroxylamine (40mL) solution at 0-10°c for 2hrs.Then raised the temperature to 25-35°C and stirred for 2-3hrs and submitted to Analysis. HPLC showed as 1.01% of 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one, 97.2% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate and 0.41% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate. Then separated the layers and washed the 2-methyl tetrahydrofuran with (40mL) water. Then 2-methyl tetrahydrofuran was distilled out under vacuum at below 50°C to obtain white solid. To the solid Methyl tertiary butyl ether (10 mL) was added and distilled out under vacuum at below 50°C. To the solid (40mL) Methyl tertiary butyl ether was added at same temperature and cooled the temperature to 25-35°C followed by 0-10°C. Stirred the reaction for 3hrs and filtered the solid through nustche filter. Washed the solid with Methyl tertiary butyl ether (50mL) and suck dried the solid for 1hr. Crude 14.8g ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl) tetrahydrofuran-2-yl) methyl isobutyrate. Charged crude into reactor and added water (20 mL) then raised the temperature to 65-75°C and stirred for 30mins. Cooled the reaction temperature to 25-35°C followed by 0-10°C. Stirred for 3hrs. and filtered the solid and dried the solid for 8hrs at 50°C under vacuum to obtain ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate (Yield 68%, Purity by HPLC 99.1%, assay by HPLC 99.2%).

Example 6: Preparation of ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate

A mixture of xylene(20mL), 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate(1g) and Addzyme-015(0.2g) was cooled to 0-10°C. 3g of 2-Methylpropionic anhydride was added slowly for 3-4hr. Heated the reaction to 40-45°C and stirred for 18hrs. HPLC showed as 1.5% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-((isobutyryloxy)amino) pyrimidin-2(1H)-one compound and 97.35% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate compound. Then cooled the reaction was cooled to 25-35°C and filtered the addzyme-015. Then to filtrate added 17% Hydroxylamine (4mL) solution at 0-10°c for 2hrs.Then raised the temperature to 25-35°C and stirred for 2-3hrs and submitted to Analysis. HPLC showed as 1.19% of 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one, 97.32% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate and 0.41% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate. Then separated the layers and washed the 2-methyl tetrahydrofuran with (4mL) water. Then 2-methyl tetrahydrofuran was distilled out under vacuum at below 50°C to obtain white solid. To the solid Methyl tertiary butyl ether (1.3mL) was added and distilled out under vacuum at below 50°C. To the solid (4 mL) Methyl tertiary butyl ether was added at same temperature and cooled the temperature to 25-35°C followed by 0-10°C. Stirred the reaction for 3hrs and filtered the solid through nustche filter. Washed the solid with Methyl tertiary butyl ether (1.33mL) and suck dried the solid for 1hr. Crude 1.36g ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl) tetrahydrofuran-2-yl) methyl isobutyrate. Charged crude into reactor and added water (2 mL). then raised the temperature to 65-75°C and stirred for 30mins. Cooled the reaction temperature to 25-35°C followed by 0-10°C. Stirred for 3hrs. and filtered the solid and dried the solid for 8hrs at 50°C under vacuum to obtain ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate (Yield 66%, Purity by HPLC 99.2%, assay by HPLC 98.6.%).

Example 7: Preparation of ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate
A mixture of 2-methyl tetrahydrofuran(1280Lit), 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one hydrate(160kg) and Addzyme-015(160.0 kg) was cooled to 0-10°C. 365.20 kg of 2-Methylpropionic anhydride was added slowly for 3-4hr. Heated the reaction to 40-45°C and stirred for 16-18hrs. HPLC showed as 0.65% 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-((isobutyryloxy)amino) pyrimidin-2(1H)-one compound and 99.18% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate compound. Then cooled the reaction was cooled to 25-35°C and filtered the addzyme-015. Then to filtrate added 17% Hydroxylamine (480Lit) solution at 0-10°c for 2hrs.Then raised the temperature to 25-35°C and stirred for 2-3hrs and submitted to Analysis. HPLC showed as 0.2 % of 1-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxymethyl) tetrahydrofuran-2-yl)-4-(hydroxyamino) pyrimidin-2(1H)-one, 99.56% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate and 0.11% ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-((isobutyryloxy)amino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate. Then separated the layers and washed the 2-methyl tetrahydrofuran with (320.0Lit) water. Then 2-methyl tetrahydrofuran was distilled out completely under vacuum at below 50°C to obtain white solid. To the solid added Methyl tertiary butyl ether (160.0Lit) and distilled out completely under vacuum at below 50°C. To the solid added Methyl tertiary butyl ether (160.0Lit) and distilled out completely under vacuum at below 50°C. To the solid added Methyl tertiary butyl ether (160.0Lit) and distilled out completely under vacuum at below 50°C.To the solid added (480.0lit) Methyl tertiary butyl ether at same temperature and cooled the temperature to 25-35°C followed by 0-10°C. stirred the reaction for 3hrs and filtered the solid through nustche filter. Washed the solid with Methyl tertiary butyl ether (160.0lit) and suck dried the solid for 1hr. Crude 170.0 kg ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl) tetrahydrofuran-2-yl) methyl isobutyrate. Charged crude into reactor and added water (340.0Lit) then raised the temperature to 65-75°C and stirred for 30mins. Cooled the reaction temperature to 25-35°C followed by 0-10°C. Stirred for 3hrs. and filtered the solid and dried the solid for 8hrs at 50°C under vacuum to obtain (Yield 76%, Purity by HPLC 99.9%, assay by HPLC 99.9%, Specific Optical rotation -8.217°C, Moisture Content 0.36%w/w, Residue on ignition 0.04%w/w). ,CLAIMS:WE CLAIM
1. An improved process for the preparation of highly pure Molnupiravir of Formula (III) which comprises :
(a) reacting N-hydroxy cytidine of Formula (II)
Formula (II)
with isobutyric acid anhydride using an enzyme in a solvent to yield Molnupiravir oxime ester of the formula (I),
(b) converting compound of formula (I) to Molnupiravir using hydroxylamine in present of a solvent.

2. The process as claimed in claim 1 wherein the enzyme is lipase which is selected from Addzyme, triacylglycerol lipase, fungal lipase, CALB (Novozyme).
3. The process as claimed in claim 1 wherein the solvent is water or "alcohol solvents" such as methanol, ethanol, n-propanol, isopropanol, n-butanol and t-butanol and the like or "hydrocarbon solvents" such as benzene, toluene, xylene, heptane, hexane and cyclohexane and the like or "ketone solvents" such as acetone, ethyl methyl ketone, diethyl ketone, methyl tert-butyl ketone, isopropyl ketone and the like or "esters solvents" such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, and the like or "nitrile solvents" such as acetonitrile, propionitrile, butyronitrile and isobutyronitrile and the like or "ether solvents" such as di-tert-butylether, dimethylether, diethylether, diisopropyl ether, 1,4-dioxane, methyl tert-butylether, ethyl tertbutyl ether, tetrahydrofuran, 2-methyl tetrahydrofuran, 2-methoxyethanol and dimethoxyethane, or “Amide solvents” such as formamide, DMF, DMAC, N-methyl-2- pyrrolidone, N-methylformamide, 2-pyrrolidone, 1-ethenyl-2-pyrrolidone, haloalkanes such as dichloromethane, 1,2-dichloroethane and chloroform, “Amine solvents” selected from diethylenetriamine, ethylenediamine, morpholine, piperidine, pyridine, quinoline, tributylamine, diisopropyl amine and/or mixtures thereof.
4. The process as claimed in claim 1 wherein the solvent is preferably water, 2-methyl tetrahydrofuran, Methyl tertiary butyl ether, Toluene, 1,4-dioxane, xylene.

Dated this Third (3rd) day of October, 2022.

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Dr. S. Padmaja
Agent for the Applicant
IN/PA/883