DESC: “A PROCESS FOR THE PURIFICATION OF MOLNUPIRAVIR WITH SUBSTANTIALLY FREE FROM IMPURITIES”

FIELD OF THE INVENTION
The present invention provides an efficient process for the purification of Molnupiravir with substantially free from impurities such as Dimethyl dioxol impurity (I), Acetyl impurity (II) and N-Hydroxycytidine impurity (III).

BACKGROUND OF THE INVENTION
Molnupiravir (development codes MK-4482 and EIDD-2801) 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. Activity has also been demonstrated against coronaviruses including SARS, MERS and SARS-CoV-2.
In April 2020, a whistleblower complaint by former Head of US Biomedical Advanced Research and Development Authority (BARDA) Rick Bright revealed concerns over providing funding for the further development of Molnupiravir due to similar drugs having mutagenic properties (producing birth defects). A previous company, Pharmasset, that had investigated the drug's active ingredient had abandoned it. These claims were denied by George Painter, CEO of DRIVE, noting that toxicity studies on Molnupiravir had been carried out and data provided to regulators in the US and UK, who permitted safety studies in humans to move forward in the spring of 2020. Also at this time, DRIVE and Ridgeback Biotherapeutics stated they planned future safety studies in animals.
After being found to be active against SARS-CoV-2 in March 2020, Molnupiravir was tested in a preliminary human study for "Safety, Tolerability, and Pharmacokinetics" in healthy volunteers in the UK and US. In June 2020, Ridgeback Bio therapeutics announced it was moving to Phase II trials to test the efficacy of the drug as a treatment for COVID-19. Two trials of small numbers of hospitalized and non-hospitalized patients in the US and the UK were underway in July. In late July 2020, and without yet releasing any medical data, Merck, which had been partnering with Ridgeback Biotherapeutics on developing the drug, announced its intention to move Molnupiravir to late stage trials beginning in September 2020. On October 19 2020, Merck began a one-year Stage 2/3 trial focused on hospitalized patients.

On December 3rd, 2020, an article was published in the journal Nature on the results of a study on the treatment with Molnupiravir of ferrets infected with Covid-19. The study found that the drug was "efficacious" when administered orally to infected ferrets, and that it blocked the transmission of the virus between ferrets after 24 hours following administration of the drug. Molnupiravir structural formula is as follows:

Molnupiravir is reported in US 20200276219 by Emory University, discloses a solid formed in the flask, which was collected by filtration, rinsed with isopropyl alcohol and MTBE, and dried in vacuum to an additional crop of desired product.
Synlett (2021), 32(3), 326-328, discloses Molnupiravir was purified by silica gel column chromatography in 8% MeOH/CHCl3.
The main drawback of the prior art purification process of Molnupiravir by using silica gel column chromatography. Hence, it’s not feasible for industrial scale of production.

Moreover, the prior art processes do not disclose preparation of pure Molnupiravir, substantially free from impurities. The removal of the impurities form the final API is very essential.

In view of this, our scientists have developed the present invention; it has now surprisingly been found that the pure Molnupiravir have numerous advantages over the reported processes.

OBJECTIVE OF THE INVENTION

The main objective of the present invention relates to an efficient process for the purification of Molnupiravir with substantially free from impurities.

SUMMARY OF THE INVENTION

The present invention provides an efficient process for the purification of Molnupiravir substantially free from impurities such as Dimethyl dioxol impurity (I), Acetyl impurity (II) and N-Hydroxycytidine impurity (III).

In an embodiment of the present invention provides a process for the purification of Molnupiravir with substantially free from impurities, which process comprises the steps of:
a) Molnupiravir is dissolved in a suitable solvent,
b) optionally, filtering the resulting solution,
c) adding an anti-solvent to the resulting solution, and
d) isolate the pure Molnupiravir.
In yet another embodiment of the present invention provides a process for the purification of Molnupiravir with substantially free from impurities, which process comprises the steps of:

a) Molnupiravir is dissolved in a suitable solvent or mixture of solvents,
b) Optionally, treating the solution with carbon,
c) isolate the pure Molnupiravir by evaporation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an efficient process for the purification of Molnupiravir with substantially free from impurities such as Dimethyl dioxol impurity (I), Acetyl impurity (II) and N-Hydroxycytidine impurity (III).

In an embodiment of the present invention provides a process for the purification of Molnupiravir with substantially free from impurities, which process comprises the steps of:
a) Molnupiravir is dissolved in a suitable solvent,
b) optionally, filtering the resulting solution,
c) adding an anti-solvent to the resulting solution, and
d) isolate the pure Molnupiravir.

According to the embodiment of the present invention, substantially free we mean that the process produces impurities such as a compound of formula (I) equal to or lower than 0.15% and/or an amount of a compound of formula (II) equal to or lower than 0.15% and/or an amount of a compound of formula (III) equal to or lower than about 0.15%.

According to the embodiment of the present invention, substantially free we mean that the process produces impurities containing an amount of a compound of formula (I) typically equal to or lower than about 0.15% and typically equal to or higher than about 0.0001% and/or an amount of a compound of formula (II) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001% and/or an amount of a compound of formula (III) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001%.

The process of the present invention provides pure Molnupiravir, containing an amount of a compound of formula (I) typically equal to or lower than about 0.15% and typically equal to or higher than about 0.0001% and/or an amount of a compound of formula (II) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001% and/or an amount of a compound of formula (III) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001%.

In an embodiment of the present invention, a mixture comprising a Molnupiravir, and a compound of formula (I) in an amount typically equal to or lower than about 0.15% and typically equal to or higher than about 0.0001%, and/or an amount of a compound of formula (II) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001% and/or an amount of a compound of formula (III) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001%.

The present invention, a pharmaceutical composition comprising a Molnupiravir, and a compound of formula (I) in an amount typically equal to or lower than about 0.15% and typically equal to or higher than about 0.0001%, and/or an amount of a compound of formula (II) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001% and/or an amount of a compound of formula (III) typically lower than or equal to about 0.15% and typically equal to or higher than about 0.0001%, and a pharmaceutically acceptable excipient and/or carrier.

The amount of each impurity of formula (I) or (II) or (III), in a mixture comprising a compound of Molnupiravir, and one or more said impurities of formula (I), formula (II) and formula (III), can be determined according to the usual analytic techniques. By way of example, impurities of formula (I), (II) and (III) can be detected by normal or reversed phase HPLC.

The evaluation of the content in impurities of formula (I), (II) and (III) is crucial, particularly in a process for the purification of Molnupiravir, as it affects the industrial applicability of the process itself.

In particular, a compound of formula (I) and/or a compound of formula (II) and/or a compound of formula (III) can be used as an analytical standard. Therefore, a further object of the present invention is the use of a compound of formula (I), of formula (II) and of formula (III), as an analytical standard in a process for the purification of Molnupiravir.

Therefore, a further the present invention is a process for the preparation of Molnupiravir, as defined above, comprising the use of a compound of formula (I) and/or (II) and/or (III), as an analytical standard.

According to the embodiment of the present invention, it provides purification process for the preparation of Molnupiravir, which comprises the crude Molnupiravir is dissolved in solvent, heating the reaction mixture to 40-60° C and further stirred the reaction mixture up to 30 minutes, preferable 20 minutes. Filtering the resulting solution through micron filter and cooled to 40-45° C. After adding anti-solvent stirred the reaction mixture up to 1-2 hours, preferably 1 hour and cooled to 20-30°C to get pure Molnupiravir.

According to the embodiment of the present invention, after adding suitable solvent in step (a) heating the reaction mixture to 40-60° C., preferable 40-45° C. and further stirred the reaction mixture up to 30 minutes, preferable 20 minutes. Filtering the resulting solution through micron filter and cooled to 40-45° C.

According to the embodiment of the present invention, after adding anti-solvent in step (b) stirred the reaction mixture up to 1-2 hours, preferably 1 hour and cooled to 20-30° C, further it isolates to get purified Molnupiravir.

According to the embodiment of the present invention, suitable solvent used in step (a) is selected from but not limited to methanol, ethanol, propanol, isopropyl alcohol, N, N- dimethylformamide (DMF), ethyl acetate, acetone and/or mixtures thereof.

According to the embodiment of the present invention, anti-solvent used in step (b) is selected from but not limited to water, diisopropyl ether, methyl tert-butyl ether, diethyl ether and/or mixtures thereof.

According to the embodiment of the present invention, isolation of the resulting pure Molnupiravir may involve methods such as removal of solvent by filtration, distillation under vacuum or removal of solvent under reduced pressure.

In yet another embodiment of the present invention provides a process for the purification of Molnupiravir with substantially free from impurities, which process comprises the steps of:
a) Molnupiravir is dissolved in a suitable solvent or mixture of solvents,
b) Optionally, treating the solution with carbon,
c) isolate the pure Molnupiravir by evaporation.
According to the embodiment of the present invention, it provides purification process for the preparation of Molnupiravir, which comprises the crude Molnupiravir is dissolved in solvent or mixture of solvents, heating the reaction mixture to 45-50° C. Thus the obtained solution was treated with carbon and Filtering the resulting solution through micron filter get pure Molnupiravir.

According to the embodiment of the present invention, suitable solvent or mixture of solvents is selected from but not limited to methanol, ethanol, propanol, isopropyl alcohol, N, N- dimethylformamide (DMF), ethyl acetate, acetone, water, diisopropyl ether, methyl tert-butyl ether, diethyl ether and/or mixtures thereof.

According to the embodiment of the present invention, isolation of the resulting pure Molnupiravir may involve methods such as removal of solvent by filtration, distillation under vacuum or removal of solvent under reduced pressure.

According to the embodiment of the present invention, the present invention provides Molnupiravir obtained is in crystalline form.

The following examples illustrate the present invention, but should not be construed as limiting the scope of the invention.

EXAMPLES
Example-1:
Purification of Molnupiravir:
Crude Molnupiravir (200 g) was dissolved in methanol (300 ml) and heated to 40-45°C and stirred for 20 minutes at this temperature. Thus the obtained solution was filtered through micron filter at 40-45°C, further added water (150 ml) to the resultant filtrate at same temperature. Then reaction mass was slowly cooled to 25-30° C and stirred at this temperature for 30-60 minutes. Thereafter, precipitated product was filtered, washed with water and dried at 65-70°C under reduced pressure to obtain purified compound of Molnupiravir.
Yield: 95% (190 g)
Purity: = 99.5%

Example-2:
Purification of Molnupiravir:
Crude Molnupiravir (200 g) was dissolved in dimethylformamide (100 ml) and heated to 40-45°C and stirred for 20 minutes at this temperature. Thus the obtained solution was filtered through micron filter at 40-45°C, further added water (300 ml) to the resultant filtrate at same temperature. Then reaction mass was slowly cooled to 25-30° C and stirred at this temperature for 30-60 minutes. Thereafter, precipitated product was filtered, washed with water and dried at 65-70°C under reduced pressure to obtain purified compound of Molnupiravir.
Yield: 92% (185 g)
Purity: = 99.5%
Example-3:
Purification of Molnupiravir:
Crude Molnupiravir (200 g) was dissolved in mixture of ethyl acetate (100 ml) and water (200ml), heated to 45-50°C and stirred for 20 minutes at this temperature. Thus the obtained solution was treated with carbon and filtered through micron filter at 40-45°C. Then reaction mass was slowly cooled to 25-30° C. Thereafter, precipitated product was filtered, under reduced pressure to obtain purified compound of Molnupiravir.

Yield: 90% (181 g)
Purity: = 99.5%

Example-4:

Purification of Molnupiravir:
Crude Molnupiravir (200 g) was dissolved in mixture of acetone (100 ml) and methanol (100ml), heated to 45-50°C and stirred for 20 minutes at this temperature. Thus the obtained solution was treated with carbon and filtered through micron filter at 40-45°C. The obtained filtrate was concentrated under reduced pressure to obtain purified compound of Molnupiravir.

Yield: 91% (183 g)
Purity: = 99.5%
,CLAIMS:WE CLAIM:

1. A process for the purification of Molnupiravir with substantially free from impurities, which process comprises the steps of:
a) Molnupiravir is dissolved in a suitable solvent,
b) optionally, filtering the resulting solution,
c) adding an anti-solvent to the resulting solution, and
d) isolate the pure Molnupiravir.

2. A process for the purification of Molnupiravir with substantially free from impurities, which process comprises the steps of:
a) Molnupiravir is dissolved in a suitable solvent or mixture of solvents,
b) Optionally, treating the solution with carbon,
c) isolate the pure Molnupiravir by evaporation.
3. The process as claimed in claim 1 and 2, wherein substantially free from impurities such as Dimethyl dioxol impurity (I), Acetyl impurity (II) and N-Hydroxycytidine impurity (III).

4. The process as claimed in claim 1, 2 and 3, wherein substantially free impurities means such as a compound of formula (I) equal to or lower than 0.15% and/or an amount of a compound of formula (II) equal to or lower than 0.15% and/or an amount of a compound of formula (III) equal to or lower than about 0.15%.

5. The process as claimed in claim 1 and 2, wherein the suitable solvent is selected from the group consisting of methanol, ethanol, propanol, isopropyl alcohol, N, N- dimethylformamide (DMF), ethyl acetate, acetone, water, diisopropyl ether, methyl tert-butyl ether, diethyl ether and/or mixtures thereof.

6. The process as claimed in claim 1, wherein the anti-solvent used is selected from water, diisopropyl ether, methyl tert-butyl ether, diethyl ether and/or mixtures thereof.