DESC:“AN IMPROVED PROCESS FOR THE PREPARATION OF MOLNUPIRAVIR”
FIELD OF THE INVENTION:
The present invention relates to an improved one-pot, environment-friendly and large-scale industrial process for the preparation of ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate (also known as Molnupiravir, EIDD-2801 and MK-4482) and purification thereof.
BACKGROUND OF THE INVENTION:
Molnupiravir (MK-4482 and EIDD-2801) is orally active and was developed for the treatment of influenza at Emory University by the university's drug innovation company, Drug Innovation Ventures at Emory (DRIVE), but was reportedly abandoned for mutagenicity concerns. 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 of the SARS-CoV-2 virus.
Molnupiravir is chemically known as ((2R,3S,4R,5R)-3,4-dihydroxy-5-(4-(hydroxyamino)-2-oxopyrimidin-1(2H)-yl)tetrahydrofuran-2-yl)methyl isobutyrate and is structurally represented as below.

The drug was developed at Emory University by the university's drug innovation company, Drug Innovation Ventures at Emory (DRIVE). It was then acquired by Miami-based company Ridgeback Biotherapeutics, who later partnered with Merck & Co. to develop the drug further and is undergoing clinical development.
WO2016/106050 first disclosure Molnupiravir and analogues (Markush structure) and their use as antivirals.
WO2019/113462 reports the synthetic route of Molnupiravir. It uses uridine as the starting material reacting in presence of H2SO4 (sulfuric acid) and acetone, then esterification with isobutyric anhydride in presence of triethylamine (TEA) and 4-dimethylaminopyridine (DMAP), and then reacts with 1,2,4-triazole in acetonitrile (ACN) followed by the addition of ?,?-diethylethanamine under the action of phosphorus oxychloride (POCl3), and then reacts with hydroxylamine in isopropylalcohol (IPA), and finally de-protection of acetonide in presence of formic acid to obtain the final product Molnupiravir. The route is as follows:

SCHEME-1
The main issue of the above process is that it uses hazardous chemical such as sulfuric acid. Sulfuric acid is a highly corrosive chemical that is potentially explosive in concentrated form. It can cause severe skin burns, can irritate the nose and throat and cause difficulties in breathing if inhaled, can burn the eyes and possibly cause blindness, and can burn holes in the stomach if swallowed. An another issue regarding this reaction is that it is not suitable for large-scale industrial process as the process involves many steps.
A convenient and cost efficient route suitable for "one-pot" synthesis of Molnupiravir; By Hu, Tianwen; Xie, Yuanchao; Liu, Yin; Xue, Haitao; Zhu, Fuqiang; Aisa, Haji A.; Shen, Jingshan; From ChemRxiv (2021), 1-5. This journal article discloses cytidine reacting in presence of DMF-DMA (N,N-dimethylformamide dimethyl acetal) and pyridine, then esterification with isobutyric anhydride, TEA, DMAP, dichloromethane (DCM), and then reacts with ethanol and acetic acid to remove N-protection, and then reacts with hydroxylamine sulfate and 70% isopropylalcohol (IPA) aqueous solution to obtain the final product Molnupiravir. The reaction sequence may be schematically represented as following:

SCHEME-2
The main disadvantage of the above "one-pot" synthesis of molnupiravir is that it uses hazardous chemical such as pyridine. Pyridine can affect you when breathed in and by passing through your skin. Breathing pyridine can irritate the nose and throat causing coughing and wheezing. Pyridine can cause nausea, vomiting, diarrhea, abdominal pain, headache, fatigue, dizziness, lightheadedness, confusion, and even coma and death. It may cause a skin allergy. If allergy develops, very low future exposure can cause itching and a skin rash. It may damage the liver and kidneys and may affect the brain. It may damage the developing fetus.
Furthermore, most of the prior art processes involves protection of hydroxyl group and in the end one need to remove the hydroxyl group protection. Accordingly, all the prior arts require longer duration, more use of reagents and solvents. It is not suitable for synthesis of Active Pharmaceutical Ingredient (API). Therefore, all the processes of the prior-arts are deemed to be time consuming and produce expensive final product due to extra stage. In addition, we are using combination of water and methyl tert-butyl ether (MTBE) for purification of Molnupiravir [I]. Water used in the process give many advantages which mainly include cost-effective final product and environment-friendly large-scale process. In view of above, there is an unmet need to develop an industrially advantageous, cost effective as well as environment-friendly process for the preparation of Molnupiravir.
Thus, the present invention fulfills the above need by providing a process for the preparation of Molnupiravir wherein use of expensive and hazardous reagents such as sulfuric acid and pyridine or another reagent are avoided.
Hence, the inventors of the present invention have developed an alternative improved one-pot process but yet simple, efficient and industrially advantageous process for the preparation of Molnupiravir with high yield and high purity. The present invention also entails an economical and environment-friendly large-scale industrial process for the preparation of Molnupiravir. Furthermore, the present invention comprises use of water and methyl tert-butyl ether for purification of Molnupiravir.
OBJECTIVE OF THE INVENTION:
The principal object of present invention is to provide an industrially advantageous and cost-effective process for the synthesis of Molnupiravir.
One more object of the present invention is to provide an improved one-pot process for the synthesis of Molnupiravir.
Another object of the present invention is to provide an industrially advantageous process for the preparation of Molnupiravir which circumvent the use of hazardous reagents such as H2SO4 and pyridine.
Another object of the present invention is to provide an industrially advantageous process for the purification of Molnupiravir which uses combination water and solvent to give an environment-friendly purification process.
Yet another object of present invention is to provide an efficient process for the preparation of Molnupiravir with high yield & purity.
Another object of the present invention is to provide large-scale advantageous process for the preparation of Molnupiravir with lesser step in shorter span to produce cost-effective final product.
One more object of present invention is to provide process for preparation of N-[(dimethylamino)methylene] Cytidine using N,N-dimethylformamide dimethyl acetal, toluene & cytidine.
SUMMARY OF THE INVENTION:
One aspect of the present invention relates to one-pot preparation of N4-hydroxycytidine nucleoside derivatives comprising the reaction steps as below.
a) adding cytidine of formula-[II] in one or more suitable organic solvents, followed by addition of N,N-dimethylformamide dimethyl acetal;
b) dissolving step-a in one or more suitable organic solvents, adding suitable catalyst and base followed by slowly addition of isobutyric anhydride;
c) adding one or more suitable organic solvents followed by addition of suitable reducing agents;
d) purified by one or more suitable organic solvents to obtain of N4-hydroxycytidine nucleoside derivatives.

An another aspect of the present invention relates to one-pot preparation of Molnupiravir [I] comprising the reaction steps as below.
a) adding cytidine of formula-[II] in toluene, followed by addition of N,N-dimethylformamide dimethyl acetal;
b) dissolving step-a in dichloromethane and adding 4-Dimethylaminopyridine and triethylamine followed by slowly addition of Isobutyric anhydride;
c) adding isopropyl alcohol and water followed by addition of hydroxylamine sulfate;
d) purified by water and methyl tert-butyl ether produce Molnupiravir of formula-[I].
In another aspect of the present invention, the one-pot process of the present invention may be depicted as a whole in below scheme-3.
SCHEME-3
DETAILED DESCRIPTION OF THE INVENTION:
Accordingly, the present invention relates to an improved one-pot, economic and environment-friendly large-scale industrial process for the preparation of Molnupiravir.
One embodiment of the present invention provides a one-pot process for the preparation of Molnupiravir of formula [I] by reacting intermediate of formula [II] with suitable reducing agents; wherein, suitable reducing agents are selected from hydroxylamine sulfate, hydroxylamine hydrochloride and the like and one or more suitable organic solvents; wherein, suitable organic solvents are selected from water, methanol, ethanol, n-propanol, isopropyl alcohol and mixture thereof.
In another embodiment of the present invention provides a process for the preparation of intermediate of formula [II] by the esterification of intermediate of formula [III] with using Isobutyric anhydride, suitable organic base; Wherein, suitable organic base is selected from ammonia, triethylamine, N,N-diisopropylethylamine and the like, in presence of suitable catalyst; wherein, suitable catalyst is selected from 4-dimethylaminopyridine, dicyclohexylcarbo-diimide, hydroxybenzotriazole and the like and one or more suitable organic solvents; wherein, suitable organic solvents are selected from dichloromethane, trichlorethylene, perchlorethylene, carbon tetrachloride, chloroform, methyl chloroform and the like.
One more embodiment of the present invention provides a process for the preparation of Intermediate of formula [III] by reacting cytidine of formula [IV] with N,N-dimethylformamide dimethyl acetal and one or more suitable organic solvents; wherein, suitable organic solvents are selected from toluene, tetrahydrofuran, dimethyl sulfoxide, xylene, dimethylformamide, methyl tetrahydrofuran and the like.
Yet another embodiment of the present invention provides a one-pot process for the preparation of Molnupiravir of formula [I] by reacting intermediate of formula [II] with hydroxylamine sulfate and aqueous solution of isopropyl alcohol.
Another embodiment of the present invention provides a process for the preparation of intermediate of formula [II] by the esterification of intermediate of formula [III] with using Isobutyric anhydride, triethylamine, 4-Dimethylaminopyridine and dichloromethane.
In another embodiment of the present invention provides a process for the preparation of Intermediate of formula [III] by reacting cytidine of formula [IV] with N,N-dimethylformamide dimethyl acetal and toluene.
Yet another embodiments of the present invention charging cytidine of formula [IV] at 25-30°C along with suitable solvent like toluene and stirred the reaction mixture for 10-15 minutes. Then, the reaction mixture was heated at 110-115°C and allowed to stir for 2 hr. Then, reaction mixture was distilled off azeotropically and the temperature was decreased to 50-55°C and suitable reagents are added which can include but not limited to N,N-dimethylformamide dimethyl acetal into the reaction mixture at 50-55°C. Again, the temperature is raised to 90-95°C and allowed to stir for 12 hr. After checking for completion of the reaction, reaction mixture was cooled to 50-55°C. Then, distilled off the solvent under vacuum to get compound of formula [III].

Another embodiment of the present invention involves esterification of compound of formula [III] by degassing crude compound of formula [III] for 1 hr. Reaction mixture was cooled to 25-30°C and stirred for 5-10 min under dry nitrogen atmosphere. Dichloromethane was charged and stirred for 5-10 min to make homogenous mixture. After this, 4-Dimethylaminopyridine was charged and stirred for 5-10 min and triethylamine charged and stirred for 5-10 min followed by slow addition of isobutyric anhydride and allowed to stir at 25-30°C for 1 hr. After checking for completion of the reaction, industrial solvent was added and reaction mixture was allowed to stir at 25-30°C for 2 hr. Then, activated carbon was charged into the reaction mixture and stirred at 25-30°C for 30 min. Filtered the reaction mixture through hyflo bed and washed with dichloromethane. Distilled off the solvent under vacuum at 45-50°C to get oily compound of formula [II].

In another embodiment of the present invention involves formation of Molnupiravir of formula [I] by degassing crude compound of formula [II] for 30 min. After this, aqueous solution of isopropyl alcohol and hydroxylamine sulfate were added and reaction mixture was allowed to stir at 45-50°C for 10-15 min. Then, the reaction mixture was heated at 75-80°C and allowed to stir for 18 hr. After checking for completion of the reaction, reaction mixture was cooled to 25-30°C. After this, purified water was charged into the reaction mixture at 25-30°C and stirred for 15-20 min. After this, reaction mixture was allowed to settle for 45 min, organic layer and aqueous layer were separated and 30% brine solution was added into the organic layer and stirred for 15-20 min. After this, reaction mixture was allowed to settle, organic layer and aqueous layer were separated. Isopropyl alcohol was added into the brine layer and stirred for 15-20 min. After this, reaction mixture was allowed to settle, organic layer and aqueous layer were separated. Both the organic layers were combined. Then, activated carbon and sodium sulfate were added at 25-30°C for 30 min. Reaction mixture was filtered through hyflo bed and washed with isopropyl alcohol. Distilled off the organic layer under vacuum at 45-50°C. Isopropyl acetate (IPOAc) was added to the reaction mixture, reaction mixture was allowed stir for 5-10 min and distilled off the organic layer under vacuum at 45-50°C. After this, purified water and isopropyl acetate were added at 45-50°C and stirred for 15-20 min and the temperature was decreased to 25-30°C and allowed to stir for 8 hr. Then, reaction mass was filtered and washed with isopropyl acetate and dried well to get crude Molnupiravir of formula [I].

As per one embodiments of the present invention Molnupiravir can be purified to enhance purity and/or to remove impurity in the product. Process for purification of Molnupiravir involve arranging 1.0 L assembly equipped with mechanical stirrer, condenser and water bath. Crude Molnupiravir and purified water were charged into glass assembly under stirring at 25-30°C and allowed to stir for 10 min. Then, the reaction mixture was heated at 70-75°C and allowed to stir for 20-30 min. Then, reaction mass was filtered through Whatman filter paper and washed with hot purified water. Reaction mixture was gradually cooled to 25-30°C. Further, cooled to 5-10°C and stirred the reaction mixture for 1 hr. After this, Reaction mixture was filtered and washed with methyl tert-butyl ether and dried well to get pure Molnupiravir of formula [I].
EXAMPLES:
Having described the invention with reference to certain preferred embodiments, other aspects will become apparent to one skilled in the art from consideration of the specification. The invention is further defined by reference to the following examples describing in detail by the preparation of the compounds of the invention. It will be apparent to those skilled in the art that many modifications, both to materials and methods, may be practiced without departing from the scope of the invention.
The following examples are provided for illustrative purpose only and these examples are in no way limitative on the present invention.
Example-1: One-pot Preparation of Crude Molnupiravir [I]

Cytidine of formula [IV] (100 gm) was charged at 25-30oC along with suitable solvent like toluene (1200 ml) and was stirred for 10-15 minutes. Then, the reaction mixture was heated at 110-115°C and allowed to stir for 2 hr. Then, reaction mixture was distilled off azeotropically and the temperature was decreased to 50-55°C and N,N-dimethylformamide dimethyl acetal (197.2 gm) are added. Again, the temperature is raised to 90-95°C and allowed to stir for 12 hr. After this reaction mixture was cooled to 50-55°C and distilled off the solvent under vacuum to get compound of formula [III]. After this, crude compound of formula [III] was degas for 1 hr. Reaction mixture was cooled to 25-30°C and stirred for 5-10 min under dry nitrogen atmosphere. Dichloromethane (1000 mL) was charged and stirred for 5-10 min to make homogenous mixture. After this, 4-Dimethylaminopyridine (1.25 gm) was charged and stirred for 5-10 min and triethylamine (125 gm) charged and stirred for 5-10 min followed by slow addition of isobutyric anhydride (81.3 gm) and allowed to stir at 25-30°C for 1 hr. Industrial solvent (500 mL) was added and reaction mixture was allowed to stir at 25-30°C for 2 hr. Then, activated carbon (5 gm) was charged into the reaction mixture and stirred at 25-30°C for 30 min. Filtered the reaction mixture through hyflo bed and washed with dichloromethane (100 mL). Distilled off the solvent under vacuum at 45-50°C to get oily compound of formula [II]. After this, crude compound of formula [II] for 30 min. isopropyl alcohol (1800 mL), purified water (600 mL) and hydroxylamine sulfate (240 gm) were added and reaction mixture was allowed to stir at 45-50°C for 10 min. Then, the reaction mixture was heated at 75-80°C and allowed to stir for 18 hr. Purified water (400 mL) was charged into the reaction mixture at 25-30°C and stirred for 15-20 min. After this, reaction mixture was allowed to settle for 45 min, organic layer and aqueous layer were separated and 30% brine solution [sodium chloride (300 gm) in purified water (1000 mL)] was added into the organic layer and stirred for 15-20 min. After this, reaction mixture was allowed to settle, organic layer and aqueous layer were separated. Isopropyl alcohol (300 mL) was added into the brine layer and stirred for 15-20 min. After this, reaction mixture was allowed to settle, organic layer and aqueous layer were separated. Both the organic layers were combined. Then, activated carbon (2.5 gm) and sodium sulfate (10 gm) were added at 25-30°C for 30 min. Reaction mixture was filtered through hyflo bed and washed with isopropyl alcohol (100 mL). Distilled off the organic layer under vacuum at 45-50°C. Isopropyl acetate (IPOAc) was added to the reaction mixture, reaction mixture was allowed stir for 5-10 min and distilled off the organic layer under vacuum at 45-50°C. After this, purified water (100mL) and isopropyl acetate (400 mL) were added at 45-50°C and stirred for 15-20 min and the temperature was decreased to 25-30°C and allowed to stir for 8 hr. Then, reaction mass was filtered and washed with isopropyl acetate (200 mL) and dried well to get crude Molnupiravir (90-135 gm) of formula [I].
Yield Calculation:
Practical Yield (gm) : 90-135 gm
Theoretical Yield (gm) : 135.40 gm
Percentage Yield (%) : 66.47% - 99.70%
Yield (w/w) : 0.66-0.99
Example-2: Purification of Molnupiravir [I]
Crude Molnupiravir (100 gm) and purified water (250 mL) were charged into glass assembly under stirring at 25-30°C and allowed to stir for 10 min. Then, the reaction mixture was heated at 70-75°C and allowed to stir for 20-30 min. Then, reaction mass was filtered through Whatman filter paper and washed with hot purified water (20 mL). Reaction mixture was gradually cooled to 25-30°C. Further, cooled to 5-10°C and stirred the reaction mixture for 1 hr. After this, Reaction mixture was filtered and washed with methyl tert-butyl ether (200 mL) and dried well to get pure Molnupiravir (70-80 gm) of formula [I].
Yield Calculation:
Practical Yield (gm) : 70-80 gm
Theoretical Yield (gm) : 100 gm
Percentage Yield (%) : 70.00% - 80.00%
Yield (w/w) : 0.70-0.80
The invention described herein comprises in various objects and their description as mentioned above, with respect to characteristics and processes adopted. While these aspects are emphasised in the invention, any variations of the invention described above are not to be regarded as departure from the spirit and scope of the invention as described.
,CLAIMS:We claim:
1. An improved one-pot process for preparation of Molnupiravir [I], which comprises;

a) reacting compound of formula [IV] with N,N-dimethylformamide dimethyl acetal in presence of one or more suitable organic solvents to obtain compound of formula [III]

b) reacting compound of formula [III] with isobutyric anhydride in presence of one or more suitable organic solvents, catalyst and organic base to obtain compound of formula [II]

c) converting compound of formula [II] into Molnupiravir [I] in presence of suitable reducing agent and one or more suitable organic solvents.

2. The improved one-pot process for preparation of Molnupiravir as claimed in claim 1, step (a), wherein suitable organic solvents are selected from toluene, tetrahydrofuran, dimethyl sulfoxide, xylene, dimethylformamide and methyl tetrahydrofuran.
3. The improved one-pot process for preparation of Molnupiravir as claimed in claim 1, step (b), wherein suitable organic solvents are selected from dichloromethane, trichlorethylene, perchlorethylene, carbon tetrachloride, chloroform and methyl chloroform.
4. The improved one-pot process for preparation of Molnupiravir as claimed in claim 1, step (b), wherein suitable catalyst is selected from 4-dimethylaminopyridine, dicyclohexylcarbo-diimide and hydroxybenzotriazole.
5. The improved one-pot process for preparation of Molnupiravir as claimed in claim 1, step (b), wherein suitable organic base is selected from ammonia, triethylamine and N,N-diisopropylethylamine.
6. The improved one-pot process for preparation of Molnupiravir as claimed in claim 1, step (c), wherein suitable reducing agent is selected from hydroxylamine sulfate and hydroxylamine hydrochloride.
7. The improved one-pot process for preparation of Molnupiravir as claimed in claim 1, step (c), wherein suitable organic solvents are selected from water, methanol, ethanol, n-propanol, isopropyl alcohol and mixture thereof.
8. The improved one-pot process for preparation of Molnupiravir as claimed in claim 2, step (a), wherein suitable organic solvent is toluene.
9. The improved one-pot process for preparation of Molnupiravir as claimed in claim 3 to 5, step (b), wherein suitable organic solvent is dichloromethane, suitable catalyst is 4-dimethylaminopyridine and suitable organic base is triethylamine.
10. The improved one-pot process for preparation of Molnupiravir as claimed in claim 6 and 7, step (c), wherein suitable reducing agent is hydroxylamine sulfate and suitable organic suitable organic solvents are isopropyl alcohol and water.