WO2019237297A1

WO2019237297A1 - Processes for preparing compounds/intermediates useful in the treatment of viral infections

Info

Publication number: WO2019237297A1
Application number: PCT/CN2018/091196
Authority: WO
Inventors: Koen Peeters; Cheng Yi Chen; Ulrich Georg Weigl; Ioannis Nicolaos Houpis; Sébastien Francois Emmanuel Lemaire; Hongjiao ZHANG; Simon Albert WAGSCHAL
Original assignee: Janssen Pharmaceuticals, Inc.; Johnson & Johnson (China) Investment Ltd.
Priority date: 2018-06-14
Filing date: 2018-06-14
Publication date: 2019-12-19

Abstract

An improved process for preparing the compound (I) is provided: which may be used in the synthesis of e.g. AL-335; AL-355 is a nucleoside inhibitor of NS3B polymerase, which plays an important role in the replication of the hepatitis C virus.

Description

PROCESSES FOR PREPARING COMPOUNDS/INTERMEDIATES USEFUL IN THE TREATMENT OF VIRAL INFECTIONS

Field of the invention

The present invention relates to an improved process for preparing certain compounds (and/or intermediates) useful in the treatment of viral infections, e.g. HCV. More particularly, disclosed herein and methods/processes for preparing a phosphoramidate nucleotide analogue, which can be useful in treating diseases/conditions such as viral infections, e.g. HCV.

Background of the Invention

Hepatitis C virus (HCV) , a member of the Flaviviridae family of viruses in the hepacivirus genus, is the leading cause of chronic liver disease worldwide. Recent estimates report the global hepatitis C prevalence at around 2.4%with up to 170 million people thought to be chronically infected. Although the development of diagnostics and blood screening has considerably reduced the rate of new infections, HCV remains a global health burden due to its chronic nature and its potential for long-term liver damage. It is now known that HCV has the ability to incorporate into the host’s genome.

The hepatitis C virus genome is a small positive-sense single stranded RNA enclosed in a nucleocapsid and lipid envelope. It consists of 9.6 kb ribonucleotides, which encodes a large polypeptide of about 3,000 amino acids (Dymock et al. Antiviral Chemistry &Chemotherapy 2000, 11, 79) . Following maturation, this polypeptide is processed into at least ten proteins. NS3/4A serine protease is responsible for the cleavage of the non-structural downstream proteins. NS5A is a zinc-binding proline-rich hydrophilic phosphoprotein which has no apparent enzymatic activity yet has an important function mediating the interaction with other nonstructural viral and cellular proteins. NS5B is an enzyme with polymerase activity that is involved in the synthesis of double-stranded RNA from the single-stranded viral RNA genome, which serves as the template.

NS3/4A serine protease, NS5A and NS5B polymerase are essential for viral replication, and inhibitors are important drug candidates for HCV treatment.

HCV is mainly transmitted by blood contact. Following initial acute infection, a majority of infected individuals develop chronic hepatitis because HCV replicates preferentially in hepatocytes, but is not directly cytopathic. Over decades, a considerable number of infected persons develop fibrosis, at least 30%develop cirrhosis, 1-4%develop hepatocellular carcinoma, and chronic HCV infection is the leading cause for liver transplantation. HCV is responsible for 50-76%of all liver cancer cases and two thirds of all liver transplants in the developed world. This and the number of patients involved has made HCV the focus of considerable medical research.

A huge amount of research has gone into discovery of a number of types of direct-acting antivirals against HCV, including NS5B polymerase inhibitors. Within this category, there exists both non-nucleoside and nucleoside types, and in relation to the latter category the following compound, also known as AL-335 (adafosbuvir) has been discovered and is currently in development:

Various processes are already known to prepare AL-335, including those described in e.g. international patent applications WO 2014/100505 and WO 2015/200216 and US patent application US 2015/0368286, where amongst other routes the following synthetic schemes are disclosed:

In the first step, the main challenges lie in yield and reaction conditions, which can both be improved.

In the second step, the main challenges lie in the selectivity at the phosphorous atom. AL-335 is a single enantiomer with several chiral centres, and indeed the configuration at the phosphorous atom is absolute –the main challenge is the diastereoselectivity at the phosphorous (where it is desired, in order to increase productivity) to obtain as high a diastereoisomeric ratio as possible (so the desired S _p : R _p ratio is above 90: 10) . As can be seen from the above scheme, 1.3 equivalents of a Grignard reagent were employed in the presence of THF at a temperature of between -10℃ and 0℃, using 2 equivalents of the chloro-phosphoramidate side chain component.

The above-mentioned route has several disadvantages, for instance the selectivity at the phosphorous is 90: 10, and yield and reliability could also be improved. It is therefore an object of the invention to provide an alternative and/or improved process to preparing AL-355 and intermediates thereto. Manufacturing routes that are suitable for scale-up are particularly desired.

Description of the Invention

There is now provided a process of preparing a compound of formula (I)

or a pharmaceutically acceptable salt/solvate thereof, wherein each PG independently represents a suitable silyl protecting group, and which process comprises reaction of a compound of formula (II)

or a pharmaceutically acceptable salt/solvate thereof, wherein each PG is as defined above, with a compound of formula (III)

or a pharmaceutically acceptable salt/solvate thereof (in an embodiment, it is preferred that at least 1.5 equivalents of compound (III) is employed compared to compound (II) ) , wherein LG represents a suitable halo group, such as chloro; and

wherein, compared to the compound of formula (II) , at least 1.5 equivalents of a Grignard reagent are employed in the presence of an appropriate solvent (e.g. a polar aprotic solvent, such as THF) at a temperature of between about -35℃ to 0℃ (e.g. between about -25℃ to -5℃) ,

which process may be referred to herein as “the process of the invention” .

The advantages of the process of the invention lie in the increased diastereoselectivity obtained at the phosphorous atoms, for instance at least a ratio of 95: 5 (S _p : R _p) e.g. about 97: 3 or higher. Hence, the process of the invention may be characterised in that the selectivity at the phosphorous atom of the compound of formula (I) so formed is greater than 90: 10, for instance greater than 95: 5 or about 97: 3 or higher. Put another way, the selectivity is greater than 20: 1 in favour of the (S) -configuration compared to the (R) -configuration (e.g. the selectivity is greater than 30: 1) at the phosphorous atom. For the avoidance of doubt, where the terms S _p and R _p are employed in the context of selectivity, then this refers to the S or R-configuration at the relevant phosphorous atom, and hence 90: 10 (S _p : R _p) means that at the phosphorous atom, there is a 90: 10 ratio of S: R configuration. In a similar way, the other ratios mentioned here refer to the ratio of S: R at that atom. All this is notwithstanding the fact there the compound (s) contain (s) (an) other chiral centre (s) at which there may also be specific configurations (e.g. in the compound of formula (III) , there is a chiral centre in which the methyl substituent is in a specific configuration and in the compound of formula (I) , which is the compound in which the specific configuration at the phosphorous atom is introduced, there are several other chiral centres with specific configurations) . In this context, in relation to such other chiral centres, what is meant by “specific configurations” is that those chiral centres favour the configuration depicted by a ratio of at least 90: 10, for instance at least 95: 5 and, in an embodiment, in a ratio of at least 99: 1 or in an amount where substantially all of that particular configuration is present in favour of the configuration not depicted (i.e. about or near 100: 0) .

Another advantage is that the compound of formula (III) need not have any specific configuration at the phosphorous atom, and the selectivity in the desired compound of formula (I) can still be achieved.

This process of the invention will now be described in a number of different alternative embodiments.

In an embodiment, each protecting group (represented by “PG” in the compounds of formula (I) and (II) ) may be any suitable silyl protecting group that can be attached to the hydroxy moieties of the relevant compound (s) . For instance, those which may be mentioned in e.g. Protective Groups in Organic Synthesis, Wiley-Interscience, New York, 1999, by T.W. Green and P.G.M. Wuts, Carey and Sundberg, Chapter 13.1, and may be such that each protecting group independently and together with the hydroxy moiety together may form a:

- a silyl ether (e.g. where PG represents -Si (R ^t1) (R ^t2) R ^t3, wherein each of R ^t1, R ^t2 and R ^t3 are independently selected from alkyl (e.g. C _1-6 alkyl) and aryl (e.g. phenyl) so forming for instance tri-alkyl silyl, triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl ether or the like.

In an embodiment of the invention, each PG independently (together with the relevant hydroxy moiety) forms a silyl ether. Hence, PG represents, in an embodiment, -Si (R ^t1) (R ^t2) R ^t3, in which it is preferred that each of R ^t1, R ^t2 and R ^t3 is as defined above and preferably independently represents alkyl, e.g. C _1-6 alkyl, and in a preferred embodiments each of these represents ethyl, so forming a -Si (ethyl) ₃ group. In an embodiment, each PG in the compound of formula (II) (and hence in the compound of formula (II) so prepared) is the same (for instance, in an embodiment, both PG groups in each of formula (II) and (I) represent a -Si (ethyl) ₃ group.

In an embodiment, LG in the compound of formula (III) may represent any suitable leaving group, for instance halo. In a preferred embodiment the halo group is chloro.

In an embodiment, for the maximum reaction efficiency and yields, at least one equivalent of compound of formula (III) is employed, compared to (or relative to) compound (II) . In an embodiment, it is preferred that at least 1.5 equivalents of compound (III) are employed compared to compound (II) ) , and in a further embodiment, at least 1.8 equivalents, such as, in an embodiment, at least 2 equivalents (e.g. between 2 and 3 equivalents) are employed. For the avoidance of doubt, when equivalents are referred to herein, it is meant molar equivalents.

Grignard agents that may be employed in the process of the invention include any suitable agent, for instance any suitable alkyl, vinyl or aryl-magnesium halide, where: the halide may be bromo, fluoro or chloro, and in an embodiment in this aspect of the invention, it is preferred that it is chloro; and in a preferred embodiment it is alkyl-magnesium halide in which the alkyl moiety is preferably C _1-6 alkyl (such as a branched C _3-6 alkyl group, e.g. isopropyl) .

As indicated hereinbefore, compared to (or relative to) the compound of formula (II) , at least 1.5 equivalents of Grignard reagent are employed. In an embodiment, between about 1.5 and 3 equivalents (e.g. between about 1.7 and 2.7 equivalents) of Grignard reagent are employed and in a further embodiment about 2.3 equivalents or about 2.65 equivalents are employed.

The process of the invention may be conducted in a suitable solvent. In an embodiment, the solvent is a polar aprotic solvent (such as an ether, for example tetrahydrofuran) . In an embodiment, the compound of formula (II) is first added to the solvent and then the Grignard reagent is added to it. In an embodiment, the Grignard reagent is added to such mixture over a period of time (e.g. over at least 10 minutes, for instance over at least 30 mins and can be added over about one hour or at least one hour, for instance on a large scale it can be added over a period of about 12 hours) . The compound of formula (III) can then be added to the reaction mixture, for instance, in an embodiment, it can be added dropwise over a period of time. In an embodiment, such addition may be at the lower temperature of the range (e.g. -35℃ or -25℃) and the reaction mixture so formed may be stirred for a period of time (e.g. over a period of at least one hour, for instance at least three hours (e.g. between three and ten hours or between three and six hours) , and in an embodiment might be over a period of about five hours) . After the reaction mixture is stirred for this period of time, in an embodiment, the reaction mixture is warmed up or allowed to warm (e.g. to the highest point in the temperature range, such as to about -5℃) and stirred for an additional period of time (e.g. for at least one hour, or at least three hours, for instance between about three and 15 hours or between 5 and 12 hours) . Upon completion the reaction can be warmed, quenched and the desired product separated (although it need not be isolated for use in the next step) . The solvent employed in the process of the reaction may be removed and/or switched (e.g. to acetonitrile) , and may be used in that form directly in the next step. As indicated in the experimental section hereinafter, the addition of reagents may also be changed without significantly impacting yield or selectivity.

In an embodiment, there is provided the conversion of a compound of formula (I) as prepared by (any of the embodiments of) the process of the invention to AL-335, which may involve removal of the protecting groups defined by PG. For instance, silyl protecting groups may be removed using suitable acid conditions (e.g. using HCl) , for instance as described hereinafter. There is also provided a process for preparing a pharmaceutical formulation comprising the preparation of AL-335 prepared as defined herein, followed by conversion to a suitable formulation (e.g. by bringing that product into contact with a suitable carrier, excipient and/or diluent, etc) .

In a further aspect of the invention, there is provided, a process to prepare a compound of formula (III) (e.g. in which LG represents chloro) as specified above (which process may be employed as a first step preceding the process described above to prepare the compound of formula (I) ) , which process comprises reaction of a compound of formula (IV)

or a pharmaceutically acceptable salt/solvate thereof (e.g. a HCl salt) , with a compound of formula (V)

PhO-P (=O) Cl ₂ (V)

or the like, wherein the reaction is performed at a temperature of -40℃ or higher (for instance up to 20℃; but in an embodiment up to 10℃) , in the presence of a suitable base (for instance, at least 1.5 equivalents of an amine base) ,

which process may also be referred to herein as “the process of the invention” .

In this aspect of the invention a number of embodiments have been envisioned.

In an embodiment, this aspect of the process of the invention is conducted in the in the presence of a non-halogenated solvent (e.g. a polar aprotic solvent such as THF, MeTHF) . In a further embodiment, cyclohexane (or the like) is employed as a solvent.

This aspect of the process of the invention is conducted in the presence of base, which is preferably an amine base (in an embodiment, a tertiary amine) such as triethylamine or diispropylamine/DIPEA (which base may be used in the number of equivalent specified hereinafter) . However, any suitable tertiary amine may be employed. In this aspect of the invention, the number of equivalents of base may be at least 1.5 equivalents (compared to the Compound of formula (IV) ) , for instance, in an embodiment, between 1.5 and 2.5 equivalents of base may be employed. In a further embodiment, the base (for instance the tertiary amine, e.g. DIPEA) may be added together or, in an embodiment, over a period of time e.g. at least 1 minute or longer, e.g. dropwise addition over 1 hour (addition, e.g. dropwise, over a period of more than 10 minutes, e.g. more than 30 minutes, are preferred embodiments) or longer, for instance, the addition time may be key to control the removal of the base. HCl (e.g. tertiary amine: HCl salt, which specifically may be triethylamine. HCl salt or DIPEA. HCl salt) , given that it can control the particle size, for instance addition over 7 hours (i.e. longer addition) led to larger crystal/particle size being formed, and hence easier separation by filtration and/or centrifugation –hence, in an aspect of the invention, there is provided a more convenient process as described herein as such, which involves convenient removal or separation of the impurities from the main product.

This aspect of the process of the invention (i.e. preparation of the compound of formula (III) by reaction of compound (IV) with compound (V) ) may be carried out in the presence of any suitable solvent or mixture of solvents. For instance, in an embodiment the solvent may be a polar aprotic solvent (e.g. THF or MeTHF or the like) dichloromethane and/or a cycloalkane or a mixture of different cycloalkanes (e.g. cyclohexane) or any mixtures thereof. In an embodiment the amount of solvent employed may be between 5V and 50V (although any suitable amount will suffice) , for instance between 10V and 30V, e.g. about 20V) . For instance, in a specific embodiment, the solvent may be a mixture of THF (e.g. about 10V) and cyclohexane (e.g. about 10V) . In an embodiment, the solvent that may be employed in this aspect of the invention may be added in portions, for example the compound of formula (IV) may first be dissolved in one portion of solvent (e.g. 10V THF) , the compound of formula (V) may be added, the base (e.g. tertiary amine base, such as triethylamine/DIPEA may then added, for instance over a period of time; see above) and after stirring for a period of time such as between 10 mins and 4 hours (e.g. about 30 mins) , the second portion of solvent (e.g. 10V cyclohexane) may then be added and the reaction mixture stirred for a further period of time, e.g. between 10 mins and 4 hours (e.g. about 30 mins) .

This aspect of the process of the invention should also be carried out at a suitable temperature, within the range specified (-40℃ or higher) , for instance, between -40℃ and -20℃, e.g. between -40℃ and -10℃, and in an embodiment between -20℃ and 0℃ (and in a very specific embodiment, at a temperature of about -10℃ including -8℃; in this instance, the solvent employed in the process of the reaction may be added in stages/portions as indicated above and, for instance in an embodiment, this aspect of the process of the invention need not be carried out at the same temperature (although the range (s) mentioned herein will still apply) , for instance in the embodiment mentioned above where the solvent is added in portions/phases, during the first phase (e.g. where compound of formula (IV) is dissolved in 10V THF, and compound of formula (V) is added, along with base) , this part of the reaction may be carried out at a range between -20℃ to 0℃, such as between -15℃ to -5℃, e.g. about -10℃, then after the second portion of solvent (e.g. 10V cyclohexane) is added, the second phase may be carried out at a temperature range between -10℃ to 10℃, such as between -5℃ to 5℃, e.g. about 0℃.

The reaction time of this aspect of the process of the invention, may be at least one hour, for instance between 1 and 5 (e.g. between 1 and 3 hours) . Further in the embodiment above where this aspect of the process of the invention is carried out in phases, each reaction phase may be between 15 mins and 2 hours, for instance about 30 mins.

In an aspect of the invention, the compound of formula (III) may be derivatized in order to prepare a compound, for which the yield may be measured. In this respect, the compound of formula (III) so formed may be brought into contact (e.g. the corresponding compound in which LG represents chloro) with an amine (e.g. a primary amine, such as n-propylamine) so forming for example an amine (e.g. an n-propylamine) adduct of a compound of formula (III) . Hence, in a further aspect of the invention, there is provided the following compound of formula (IIIA) :

Experimental

Preparation of Compound 3

Compound 1 (1.0 equiv) was dissolved in THF (10 L/kg) and cooled down to -8℃. Compound 2 (1.0 equiv) was then added to the mixture. Triethylamine was then added dropwise slowly (the longer the period over which triethylamine is added, the better the filtration will be vis-à-vis scale) . The reaction was left stirring 30 minutes after the end of addition and then warmed up to 0℃. Cyclohexane (10 L/kg) was then added to the reaction mixture and stirred for 30 min. The heterogenous mixture was then filtered, concentrated to 6V and cooled down to 0℃. After one hour stirring, the mixture was filtered, assayed and stored under nitrogen. The Compound 3 (as a mixture of configurations at the phosphorous atoms) so formed was thus used as such in the next step, without any further purification.

The process as depicted on the scheme may be followed with variations, for instance:

- another amine base may be employed

- the number of equivalents of base may be modified, although at least 1.5 equivalents (compared to Compound 1) should be used, for instance between 1.5 and 2.5 equivalents of base may be employed

- the base (e.g. triethylamine) may be added together or, in an embodiment, over a period of time e.g. at least 1 minute or longer, e.g. dropwise addition over 1 hour (addition, e.g. dropwise, over a period of more than 10 minutes, e.g. more than 30 minutes, are preferred embodiments)

- the amount of THF and cyclohexane can be varied (although 10V of each is preferred)

- as an alternative to THF, another solvent may be employed such as dichloromethane (DCM) and/or MeTHF

- the temperature may be varied, although it should remain -40℃ or higher, for instance, between about -20℃ and 20℃

- the reaction time may be, in an embodiment, at least one hour, for instance between 1 and 3 hours

- in addition to the variation of base (and duration of base addition) , solvent (THF and/or cyclohexane) , temperature and reaction time, all other parameters (e.g. amounts of Compound 1, Compound 2, solvent (THF/cyclohexane) can be varied by +/-15%without impacting the next step

For instance, with variations the following yields were obtained:

Where: (i) Et ₃N was used as the base; (ii) Cy represents cyclohexane

As indicated herein, Compound 3 may be converted to the n-propylamine adduct in order to determine the yield.

Duplicate samples of 2.0 mg/ml of Compound 3 were prepared for identification/impurity/assay:

50 mg of the Compound 3 sample was weighed and transferred to a 25 ml brown volumetric flask to which 10 ml acetonitrile (previously mixed with 0.3 ml of n-propylamine) was added. The sample was dissolved and diluted to volume with the diluent (acetonitrile) . If needed, it may be sonicated to dissolve. It was mixed well and each sample was labelled.

For “In Process Control” (IPC) (2.0 mg/ml as target concentration of Compound 3) : 1 ml of IPC solution was transferred to a 50 ml volumetric flask to which 10 ml acetonitrile (previously mixed with 0.3 ml of n-propylamine) was added. The sample was dissolved and diluted to volume with the diluent (acetonitrile) .

High Performance Liquid Chromatography (HPLC) was then conducted to assay and determine impurities (and yield) of Compound 3, for instance using the following parameters:

- Column: Waters Xbridge C18 (150 mm x 4.6mm, 3.5μm)

- Wavelength: For information 220 nm; IPC/purity/assay 260 nm

- Column Oven Temp. 20℃

- Flow Rate: 1.0 ml/min

- Injection volume: 10 μl

- Mobile Phases: A –0.05%TFA in water, v/v; B –0.05%TFA in acetonitrile, v/v

- Gradient Program:

Re-equilibration time: 6 mins

- Run Time: 21 mins

- Diluent: acetonitrile (ACN)

- Needle wash solvent: ACN: water (8/2, v/v)

Note: The above conditions are established in accordance with the Shimadzu LC-20A system. Certain non-critical parameters such as re-equilibration time can be adjusted when other instruments are utilized.

Retention Time (RT) of Compound 3: 9.2 mins

Preparation of Compound 5

Compound 4 may be prepared in accordance with the procedures described in international patent application WO 2015/200216. Compound 4 (1.0 equiv) was then dissolved in THF (10 L/kg) and cooled down to -25℃. iPrMgCl (2M in THF) was added slowly over one hour and the resulting mixture was stirred for one hour. The Compound 3 solution previously made (see above) was then added dropwise at -25℃ and the mixture was stirred for 5h at that temperature before being warmed to -5℃ and stirred for 10 additional hours at that temperature. Once the reaction was complete, the reaction was warmed up to 5℃ and an aqueous solution of NH ₄Cl (5L/kg -9 w/w%) was added slowly over 30 minutes. After phase separation, the organic layer was washed with aqueous NaHCO ₃ solution (5L/kg -10 w/w%) and twice with aqueous NaCl solution (5L/kg -10 w/w%) . After solvent switch to acetonitrile, the reaction was assayed and stored under nitrogen and used as such in the next step.

Variations to the above general process may also be made, for instance as specified in the table:

As can be seen from the above table:

- compared to the Compound 4, at least one 1.5 equivalents of Compound 3 are employed, for instance at least 1.8 equivalents, such as, in an embodiment, at least 2 equivalents (e.g. between 2 and 3 equivalents)

- any suitable Grignard reagent may be employed, such as iPrMgCl

- compared to the Compound 4, at least 1.5 equivalents of Grignard agent is employed, e.g. between about 1.5 and 3 equivalents (e.g. between about 1.7 and 2.7 equivalents) ; in an embodiment about 2.3 equivalents or about 2.65 equivalents is employed

- as indicated in the table the temperature may be varied

- the order of addition could also be reversed within significantly impacting yield or selectivity

Reverse Additions using other specific conditions

As above, using: (i) 2.1 equivalents of Compound 3; (ii) 1.8 equivalents of iPrMgCl Grignard reagent; (iii) temperature of -25℃ to -5℃, where the following results were obtained:

250 mg of Compound 5 was weighed and transferred (e.g. in a portion of acetonitrile) to a 50 ml volumetric flask. The sample was dissolved and diluted to volume with the diluent (acetonitrile) and mixed well. If needed, it may be sonicated to dissolve.

High Performance Liquid Chromatography (HPLC) was then conducted to assay and determine impurities (and yield) of Compound 5, for instance using the following parameters:

- Column: Zorbax SB-CN (150 mm x 4.6mm, 3.5μm)

- Wavelength: For information 220 nm; IPC/purity/assay 260 nm

- Column Oven Temp. 20℃

- Flow Rate: 1.0 ml/min

- Injection volume: 10 μl

- Gradient Program:

Re-equilibration time: 6 mins

- Run Time: 30 mins

- Diluent: acetonitrile (ACN)

- Needle wash solvent: ACN: water (8/2, v/v)

Retention Time (RT) of Compound 5: 17.1 mins

Calculation of diastereoselectivity at the phosphorous of Compound 5, determined using the following HPLC technique:

- Column: Chiralpak IC (4.6mm x 250 mm, 5μm)

- Wavelength: 260 nm

- Column Oven Temp. 30℃

- Flow Rate: 1.0 ml/min

- Injection volume: 10 μl

- Gradient Program:

Re-equilibration time: 9 mins

- Run Time: 20 mins

- Diluent: acetonitrile (ACN)

Retention times (RTs) : the desired S _p diastereoisomer –6.9 mins; and the other R _p diastereoisomer –7.4 mins

A similar HPLC technique may also be used to determine the diastereoselectivity of Compound 4 (although Compound 4 need not have any particular configuration at the phosphorous in the process of the invention) .

Preparation of the compound of AL-335 (adafosbuvir) :

Compound 5 prepared above is essentially a compound of formula (I) as defined herein. The relevant protecting group (e.g. tri-alkyl-silyl group) may be cleaved off under appropriate conditions (e.g. using acid conditions, e.g. HCl conditions, e.g. in between 2 to 2.6 equivalents) to prepare the compound AL-335, also known as adafosbuvir:

Various conditions may also be used to crystallise the final product (for instance, crystallisation in a mix of solvents such as acetone/heptane.

Similar methods to those described herein (for preparing the compound, analysing it and calucating the yield, etc) may be used herein for the preparation of AL-335. Hence, in an aspect of the invention, there is provided a process for preparing a product (AL-335) , which included one of more of the earlier steps of the processes of the invention as described herein, followed by conversion to AL-335 (e.g. by removing the protecting groups, e.g. the silyl protecting groups may be cleaved off, for isntance with acid under known reaction conditions) . Such AL-335 may also be prepared in a form that is crystalline and hence there is further provided the step of converting AL-335 to a suitable form, e.g. by crystallising it (e.g. in a mixture of solvents as described herein) .

In a further aspect, there is provided a process for preparing a pharmaceutical formulation, which comprises a process for preparing AL-335 (or a form, e.g. a crystalline form of AL-335) as descibed herein (e.g. by using one or more of the process steps described herein, followed by conversion to AL-335) by bringing that product into contact with a pharmaceutically acceptable carrrier, excipient and/or diluent.

Claims

A process of preparing a compound of formula (I)

or a pharmaceutically acceptable salt/solvate thereof, wherein each PG independently represents a suitable silyl protecting group, and which process comprises reaction of a compound of formula (II)

or a pharmaceutically acceptable salt/solvate thereof, wherein each PG is as defined above, with a compound of formula (III)

or a pharmaceutically acceptable salt/solvate thereof (in an embodiment, it is preferred that at least 1.5 equivalents of compound (III) is employed compared to compound (II) ) , wherein LG represents a suitable halo group, such as chloro; and wherein, compared to the compound of formula (II) , at least 1.5 equivalents of a Grignard reagent are employed in the presence of an appropriate solvent (e.g. a polar aprotic solvent, such as THF) at a temperature of between about -35℃ to 0℃ (e.g. between about -25℃ to -5℃) .
A process as claimed in Claim 1, where each silyl protecting group (i.e. each PG) independently represents -Si (R ^t1) (R ^t2) R ^t3, wherein each of R ^t1, R ^t2 and R ^t3 are independently selected from alkyl (e.g. C _1-6 alkyl) and aryl (e.g. phenyl) so forming for instance tri-alkyl silyl, triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl ether or the like.
A process as claimed in Claim 1 or Claim 2, wherein in the compound of formula (I) the diasteroselectivity obtained at the phosphorous atoms, is at least a ratio of 95: 5 (S _p : R _p) e.g. about 97: 3 or higher.
A process as claimed in any one of the preceding claims, wherein the compound of formula (III) does not have any specific configuration at the phosphorous atom.
A process as claimed in any one of the preceding claims, which is preceded by a process to prepare a compound of formula (III) as specified in claim, which process comprises reaction of a compound of formula (IV)

or a pharmaceutically acceptable salt/solvate thereof, with a compound of formula (V)

PhO-P (=O) Cl ₂ (V)

or the like, wherein the reaction is performed at a temperature of -40℃ or higher, in the presence of a suitable base.
The process according to any one of the preceding claims, wherein in the process to prepare the compound of formula (I) at least 1.5 equivalents of compound (III) is employed compared to compound (II) .
The process according to claim 6 wherein in the process to prepare the compound of formula (I) the solvent employed is a polar aprotic solvent, such as THF.
The process according to any one of claims 5 or 6 or 7 (as dependent on claim 5) wherein in the process to prepare the compound of formula (III) , at least 1.5 equivalents of an amine base e.g. triethylamine and/or DIPEA is employed.
The process according to any of the preceding claims, wherein in the process in the process to prepare the compound of formula (I) at least 1.7 (e.g. between about 1.7 and 2.7 equivalents) of Grignard reagent is employed relative to the compound of formula (II) .
A process as claimed in any one of the preceding claims, which further comprises a process for the conversion of the compound of formula (I) (e.g. by deprotection) to form the compound AL-335, also known as adafosbuvir:
A process for the preparation of a pharmaceutical composition comprising adafosbuvir preparing as claimed in Claim 10, followed by bringing it into association with a pharmaceutically-acceptable excipient, carrier and/or diluent.