WO2025032082A1

WO2025032082A1 - Process for the preparation of 3-substituted 5-amino-6h-thiazolo[4,5-d]pyrimidine-2,7-dione compounds

Info

Publication number: WO2025032082A1
Application number: PCT/EP2024/072228
Authority: WO
Inventors: Ernesto Santandrea; Isabelle THOMÉ-PFEIFFER
Original assignee: F Hoffmann La Roche AG; Hoffmann La Roche Inc
Current assignee: F Hoffmann La Roche AG; Hoffmann La Roche Inc
Priority date: 2023-08-08
Filing date: 2024-08-06
Publication date: 2025-02-13
Anticipated expiration: 2026-02-08
Also published as: TW202521548A

Abstract

The present invention relates to a novel process for the preparation of a compound of formula (Ia), or a pharmaceutically acceptable salt thereof, (formula (Ia)), wherein R₁ is H or C_1-6 alkyl, R₂ is H or hydroxy.

Description

Process for the preparation of 3-substituted 5-amino-6/7-thiazolo[4,5-rfJpyrimidine-2,7- dione compounds

Field of the invention

The present invention relates to a process for the preparation of a compound of formula (I),

particularly a compound of formula (la),

wherein

Ri is H or Ci-6 alkyl;

R.2 is H or hydroxy; or a pharmaceutically acceptable salt thereof, which is useful for the treatment and/or prevention of a viral disease in a patient relating to hepatitis B infection or a disease caused by hepatitis B infection. Background of the invention

A process for manufacturing a compound of formula (I) or (la) at a large scale was developed and described in document WO 2018/127525.

However, said process is not suitable for large-scale manufacturing due to the following issues: compound (XI) is obtained in low purity due to harsh reaction conditions; compound (XIII) is obtained in low purity, due to the low purity of compound (XI) and used as crude in the following step; compound (la) must be first crystallized as citrate in order to remove process impurities and residual unreacted compound (XV). This is followed by a salt-breaking step;

- the reaction to obtain compound (XIII) has low selectivity for the mono-deacetylation.

Therefore, one object of the invention is to provide a process for the manufacture of a compound of formula (I) or (la) with a higher purity and an improved yield.

Summary of the invention

The present invention relates to a process for the preparation of a compound of formula (la), or a pharmaceutically acceptable salt thereof,

wherein

Ri is H or Ci-6-alkyl,

R.2 is H or hydroxy, comprising: step g) reacting compound of formula (VIII)

with a Grignard reagent in the presence of a copper catalyst to form a compound of formula (IX)

step h) reacting compound of formula (IX) with an acylating agent to form acompound of formula (X)

wherein Ri is H or Ci-6-alkyl; step i) reacting compound of formula (X) with an acylating agent and a catalyst to form a compound of formula (XI)

wherein Ri is H or Ci-6-alkyl; step j) reacting compound of formula (XI) with a compound of formula (XII)

wherein R2 is H or hydroxy, with a silylating agent and a catalyst to form a compound of formula (XIII)

wherein

Ri is H or C1-6 alkyl, R2 is H or hydroxy; step k) reacting compound of formula (XIII) with an acid to form a compound of formula (XIV)

wherein

Ri is H or Ci-6 alkyl, R.2 is H or hydroxy; step 1) reacting compound of formula (XIV) with an aqueous base to form a compound of formula (XV)

wherein

Ri is H or Ci-6 alkyl, R2 is H or hydroxy; step m) performing a selective cleavage of compound of formula (XV) to form a compound of formula (la)

wherein

Ri is H or Ci-6 alkyl, R.2 is H or hydroxy.

Detailed description of the invention

Definitions

The following definitions of the general terms used in the present description apply irrespectively of whether the terms in question appear alone or in combination with other groups.

As used herein, the term “Ci-6-alkyl” signifies a saturated, linear- or branched chain alkyl group containing 1 to 6, particularly 1 to 5 carbon atoms, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl and the like. Particular “Ci-6-alkyl” group is methyl or ethyl.

The term “aryl” means a monovalent, monocyclic or bicyclic, aromatic carboxylic hydrocarbon radical, preferably a 6-10 member aromatic ring system. Preferred aryl groups include, but are not limited to, phenyl, naphthyl, tolyl, and xylyl.

The term “halogen” signifies fluorine, chlorine, bromine or iodine, particularly fluorine or chlorine.

The term “enantiomer” denotes two stereoisomers of a compound, which are non- superimposable mirror images of one another.

The term “diastereomer” denotes a stereoisomer with two or more centers of chirality and whose molecules are not mirror images of one another. The term “pharmaceutically acceptable salt” refers to conventional acid-addition salts or baseaddition salts that retain the biological effectiveness and properties of the compounds of formula I and are formed from suitable non-toxic organic or inorganic acids or organic or inorganic bases. Acid-addition salts include for example those derived from inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfamic acid, phosphoric acid and nitric acid, and those derived from organic acids such as -toluenesul fonic acid, salicylic acid, methanesulfonic acid, oxalic acid, succinic acid, citric acid, malic acid, lactic acid, fumaric acid, and the like. Base-addition salts include those derived from ammonium, potassium, sodium and, quaternary ammonium hydroxides, such as for example, tetramethyl ammonium hydroxide. The chemical modification of a pharmaceutical compound into a salt is a technique well known to pharmaceutical chemists in order to obtain improved physical and chemical stability, hygroscopicity, flowability and solubility of compounds. It is for example described in Bastin R.J., et al., Organic Process Research & Development 2000, 4, 427-435; or in Ansel, H., et al., In: Pharmaceutical Dosage Forms and Drug Delivery Systems, 6th ed. (1995), pp. 196 and 1456- 1457.

The following abbreviations are used in the present text:

MeCN Acetonitrile

BSA N,O-bis(trimethylsilyl)trifluoroacetamide

BSTFA O, M-bistrimethylsilyl trifluoroacetamide

DBU 1 , 8-Diazabicy clo[5.4.0] undec-7-ene

DCM dichloromethane

DIPEA N,N-diisopropylethylamine

DMAP 4-dimethylaminopyridine

EDIPA ethyldiisopropylamine eq Equivalent

IPA Isopropanol

IPAc Isopropyl acetate

EtOAc ethyl acetate

LAH lithium aluminium hydride

MeCy2N N,N-dicyclohexylmethylamine

2-MeTHF 2-Methyltetrahydrofuran

MSA Methanesulfonic acid NMM N-methylmorpholine

PTSA p-Toluenesulfonic acid

TEA Triethylamine

THF tetrahydrofuran

TFA Trifluoroacetic acid

TfzO Trifluoromethanesulfonic anhydride

TMPH Tetramethyl piperidine hydride

TMSOTf Trimethylsilyl trifluoromethanesulfonate

TMSI Trimethyl silyl iodide v/v Volume ratio

Manufacturing processes

wherein

Ri is H or Ci-6-alkyl,

R.2 is H or hydroxy, comprising: step g) reacting compound of formula (VIII)

with a Grignard reagent in the presence of a copper catalyst to form compound of formula (IX)

step h) reacting compound of formula (IX) with an acylating agent to form a compound of formula (X)

wherein

wherein

wherein

wherein

Ri is H or Ci-6 alkyl;

R.2 is H or hydroxy.

In one embodiment, the process as described herein further comprises: step a) reacting compound of formula (II) nd of formula (III)

step b) reacting compound of formula (III) with a reducing agent to form compound of formula (IV)

step c) reacting compound of formula (IV) with an acid to form compound of formula (V)

step d) reacting compound of formula (V) with an acylating agent to form compound of formula (VI)

step e) reacting compound of formula (VI) with MsCl to form compound of formula (VII)

step 1) reacting compound of formula (VII) with a base to form compound of formula (VIII)

In one embodiment, the process as described herein consists of step a) to step m).

In one embodiment, Ri is methyl and R2 is H or hydroxy.

In a preferred embodiment, Ri is methyl and R2 is hydrogen. In one embodiment, the Grignard reagent in step g) is selected from MeMgCl, MeMgBr and MeMgl and the copper catalyst is selected from CuCl, Cui and CuBr.

In one embodiment, the acylating agent in step h) is selected from alkylacyl anhydride, alkylacyl chloride, arylacyl anhydride and arylacyl chloride.

In a preferred embodiment, wherein the acylating agent in step h) is AC2O.

In one embodiment, step h) is performed in the presence of a catalyst selected from AcOH, TfOH, MSA, TFA, H3PO4, H2SO4, a mixture of AcOH and H₂SO₄, H3BO3, MgCl₂, Na₂SO₄, and DMAP.

In a preferred embodiment, the catalyst in step h) is DMAP.

In one embodiment, the acylating agent in step i) is selected from alkylacyl anhydride, alkylacyl chloride, arylacyl anhydride and arylacyl chloride.

In a preferred embodiment, the acylating agent in step i) is AC2O.

In one embodiment, the catalyst in step i) is selected from AcOH, H2SO4, H3PO4, MeSO4H, a mixture of AcOH and H2SO4, MgCh, Na2SO4, B(OMe)s, B2O3, H3BO3, and a mixture of AcOH and H3BO3.

In a preferred embodiment, the catalyst in step i) is a mixture of AcOH and H3BO3.

In one embodiment, the silylating agent in step j) is selected from trimethylchlorosilane, trimethylbromosilane, trimethyliodosilane, hexamethyldisilazane, O. -bistri methylsilyl trifluoroacetamide (BSTFA) and O. -bistrmrethylsilylacetamide (BSA).

In a preferred embodiment, the silylating agent in step j) is bistrimethylsilylacetamide (BSA).

In one embodiment, the catalyst in step j) is selected from SnCU TMSOTf, TMSI and HI.

In one embodiment, the amount of the silylating agent in step j) is 1.9-2.8 eq.

In one embodiment, the acid in step k) is selected from D-glutamic acid, L-mandelic acid, 1- hydroxy-2-naphthoic acid, citric acid, 4-aminosalicylic acid, L-tartaric acid, hippuric acid, malonic acid, glutaric acid, oxalic acid, fumaric acid, succinic acid, 4-aminobenzoic acid, 2,5- dihydroxybenzoic acid, L-malic acid, salicylic acid, maleic acid, (lS,3R)-(-)-camphoric acid, pamoic acid, mucic acid, palmitic acid, oleic acid and lactobionic acid.

In a preferred embodiment, the acid in step k) is selected from oxalic acid and maleic acid.

In a preferred embodiment, the acid in step k) is maleic acid.

In one embodiment, the aqueous base in step 1) is an aqueous solution of a base selected from sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium phosphate, potassium phosphate, sodium acetate, potassium acetate, sodium hydroxide, potassium hydroxide, ammonium hydroxide, EDIP A, tributylamine and triethylamine.

In a preferred embodiment, the aqueous base in step 1) is triethylamine.

In one embodiment, step m) is performed in the presence of a catalyst selected from NaOH, KOH, MeONa, MeOK, K2CO3, ammonia, ammonium hydroxide, K2HPO4, MgO, DBU, methylamine and MOO2CI2.

In a preferred embodiment, the catalyst in step m) is MeONa.

In one embodiment, step m) is performed in a solvent selected from methanol, ethanol, 2- propanol, a mixture of methanol and ethanol, a mixture of THF and methanol, and a mixture of 2-MeTHF and methanol.

In a preferred embodiment, step m) is performed in methanol.

The process for the preparation of a compound of formula (la) according to the invention is depicted in scheme 1. In one embodiment, the present invention provides a process for the preparation of a compound of formula (la) comprising the preparation of a compound of formula (VIII) as depicted in scheme 2.

wherein

Ri is H or Ci-6 alkyl;

R.2 is H or hydroxy.

Scheme 2

wherein

Ri is H or Ci-6 alkyl, R.2 is H or hydroxy.

Another embodiment of this invention is that compound of formula (I) can also be synthesized in analogy to Scheme 1 and Scheme 2 with racemic starting material.

Step a) Formation of compound of formula (III)

Compound of formula (III) is obtained by reacting compound of formula (II) in the presence of a base and TfzO in a solvent. In one embodiment, the solvent is selected from DCM, CHCh, benzene, THF, 2-MeTHF, fluorobenzene, pyridine, toluene and xylene. In a preferred embodiment, the solvent is toluene.

In one embodiment, the base is selected from TEA, DIPEA, TMPH, MeCy2N, NMM, pyridine, K2CO3, Na2COs and CS2CO3. In a preferred embodiment, the base is pyridine. In one embodiment, the reaction is performed between -40 °C and 25 °C, particularly between 0 °C and 10 °C.

Step b) Formation of compound of formula (IV)

Compound of formula (IV) is obtained by reacting compound of formula (III) with a reducing agent in a solvent.

In one embodiment, the reducing agent is selected from sodium borohydride, lithium borohydride, sodium cyanoborohydride, triacetoxyborohydride, tetraalkyl ammonium borohydride, LAH, Red-Al, hydrogenation with Pd/C and Raney nickel. In a particularly preferred embodiment, the reducing agent is nBmNBFL.

In one embodiment, the solvent is selected from benzene, THF, 2-MeTHF, fluorobenzene, xylene and toluene. In a preferred embodiment, the solvent is toluene.

In one embodiment, the reaction is performed between -20 °C and 100 °C. In a preferred embodiment, the reaction is performed between 65 °C and 75 °C.

Step c) Formation of compound of formula (V)

Compound of formula (V) is obtained by reacting compound of formula (IV) with an acid in a solvent.

In one embodiment, the acid is selected from HC1, H2SO4, H3PO4, MSA, TFA, HCOOH, acetic acid and Lewis acid (such as iodine). In a preferred embodiment, the acid is H2SO4.

In one embodiment, the solvent is selected from water, a mixture of methanol and water, a mixture of ethanol and water and a mixture of acetonitrile and water. In a preferred embodiment, the solvent is a mixture of methanol and water.

In one embodiment, the reaction is performed between -5 °C and 50 °C, particularly between 5 °C and 15 °C.

Step d) Formation of compound of formula (VI)

Compound of formula (VI) is obtained by reacting compound of formula (V) in the presence of a base, an acylating agent and a catalyst in a solvent. In one embodiment, the acylating agent is selected from alkylacyl anhydride, alkylacyl chloride and arylacyl chloride. In a preferred embodiment, the acylating agent is selected from isobutyryl chloride, acetyl chloride, methylbenzoyl chloride and benzoyl chloride. In a particularly preferred embodiment, the acylating agent is benzoyl chloride.

In one embodiment, the amount of acylating agent is between 1.0 eq. and 2.0 eq., particularly between 1.4 eq. and 1.5 eq.

In one embodiment, the catalyst is selected from DMAP, MgCh and Bu2SnO. In a preferred embodiment, the catalyst is Bu2SnO.

In one embodiment, the amount of catalyst is between 0.001 eq. and 0.2 eq., particularly 0.05 eq.

Catalyst selection is very important in step d) to achieve high conversion as well as high selectivity. If only a base, such as TEA, is used in this step, the reaction would result in low conversion and poor selectivity (mono-/bis-benzoylated product = 11:1). Although DMAP as catalyst could improve the conversion (>90%), poor selectivity (desired bis-protected: by-product = 3:2) is still expected. Surprisingly, Bu2SnO served as the catalyst is found to achieve almost complete conversion with significantly increased selectivity (desired bis-protected: byproduct >97:3).

In one embodiment, the solvent is selected from DCM, CHCh, THF, 2-MeTHF, toluene and xylene. In a preferred embodiment, the solvent is DCM.

In the literature (eg. Carbohydrate Research; 261 (1994); 149-156), pyridine is used as solvent which is highly toxic and difficult to work up. DCM used in the current step is more operationally friendly for scale up.

In one embodiment, the base is selected from TEA, DIPEA, NMM, pyridine, Na2COs and K2CO3. In a preferred embodiment, the base is TEA.

In one embodiment, the reaction is performed between -20 °C and 45 °C, particularly between 0 °C and 10 °C.

Compound of formula (VII) is obtained by reacting compound of formula (VI) with a sulfonating agent and a base in a solvent. In one embodiment, the sulfonating agent is selected from alkylsulfonic anhydride, alkylsulfonic chloride, arylsulfonic anhydride and arylsulfonic chloride. In a preferred embodiment, the sulfonatig agent is selected from methanesulfonic anhydride, 4- methylbenzenesulfonic anhydride, MsCl and TfzO. In a particularly preferred embodiment, the sulfonating agent is MsCl.

In one embodiment, the solvent is selected from DCM, CHCh, benzene, THF, 2-MeTHF, fluorobenzene, pyridine and toluene. In a preferred embodiment, the solvent is toluene.

In one embodiment, the base is selected from TEA, DIPEA, TMPH, MeCy2N, NMM, pyridine, K2CO3, Na2COs and CS2CO3. In a preferred embodiment, the base is TEA.

In one embodiment, the reaction is performed between -10°C and 25 °C, particularly between 0 °C and 5 °C.

Step f) Formation of compound of formula (VIII)

Compound of formula (VIII) is obtained by reacting compound of formula (VII) with a base in a solvent.

In one embodiment, the base is selected from NaOH, KOH, MeONa, MeOK, t-BuOK and t-BuONa. In a preferred embodiment, the base is MeONa.

In one embodiment, the solvent is selected from a mixture of DCM and methanol, a mixture of DCM and ethanol and a mixture of THF and methanol. In a preferred embodiment, the solvent is a mixture of DCM and methanol.

In one embodiment, the reaction is performed between -10 °C and 25 °C, particularly between 10 °C and 15 °C.

Step g) Formation of compound of formula (IX)

Compound of formula (IX) is obtained by reacting compound of formula (VIII) with a Grignard reagent in the presence of a copper catalyst.

In one embodiment, the Grignard reagent is selected from MeMgCl, MeMgBr and MeMgl. In a preferred embodiment, the Grignard reagent is MeMgCl. In one embodiment, the Grignard reagent is added between -70 °C and 30 °C, particularly between -5 °C and 0 °C.

In one embodiment, the copper catalyst is selected from CuCl, Cui and CuBr. In a preferred embodiment, the catalyst is CuCl.

In one embodiment, the amount of catalyst is between 0.05 eq. and 0.5 eq., particularly 0.05 eq.

Step h) Formation of compound of formula (X)

Compound of formula (X) is obtained by reacting compound of formula (IX) with an acylating agent with or without a catalyst in a solvent

In one embodiment, the acylating agent is selected from alkylacyl anhydride, alkylacyl chloride, arylacyl anhydride and arylacyl chloride. In a preferred embodiment, the acylating agent is selected from AcCl and AC2O. In a particularly preferred embodiment, the acylating agent is AC2O.

In one embodiment, the catalyst is selected from AcOH, TfOH, MSA, TFA, H3PO4, H2SO4, a mixture of AcOH and H2SO4, H3BO3, MgCh, Na2SO4, and DMAP. In a preferred embodiment, the catalyst is DMAP.

In one embodiment, the amount of catalyst is between 0.001 eq. and 0.5 eq., particularly 0.05 eq.

In one embodiment, the solvent is selected from DCM, CHCI3, 2-MeTHF, toluene, xylene, IPAc and EtOAc. In a preferred embodiment, the solvent is toluene.

In one embodiment, the reaction is performed between -10 °C and 110 °C, particularly between 0 °C and 70 °C, more particularly at 60 °C.

Step i) Formation of compound of formula (XI)

Compound of formula (XI) is obtained by reacting compound of formula (X) with an acylating agent and a catalyst in a solvent.

In one embodiment, the catalyst is selected from AcOH, H2SO4, H3PO4, MeSO4H, a mixture of AcOH and H2SO4, MgCh, Na2SO4, B(OMe)s, B2O3, H3BO3, and a mixture of AcOH and H3BO3. In a preferred embodiment, the catalyst is a mixture of AcOH and H3BO3.

In one embodiment, the amount of AcOH is between 0.01 eq. and 10 eq. In a preferred embodiment, the amount of AcOH is between 1.0 eq. and 3.0 eq.

In one embodiment, the amount of H3BO3 is between 0.005 eq. and 1 eq. In a preferred embodiment, the amount of H3BO3 is between 0.1 eq. and 0.3 eq.

In one embodiment, the reaction is performed between -10 °C and 110 °C, particularly between 0 °C and 70 °C, more particularly between 70 °C and 80 °C.

In document WO 2018/127525 Al, the transformation of compound of formula (IX) into compound of formula (XI) was performed in a one-pot procedure. However, this procedure resulted in the formation of some process impurities in compound (XI). Surprisingly, in the present invention, it was possible to address that issue and increase the purity of compound of formula (XI) from 92-93% to 98-99%. This increased purity surprisingly facilitated the purification and the isolation of the subsequent intermediates.

Step j) Formation of compound of formula (XIII)

Compound of formula (XIII) is obtained by reacting compound of formula (XI) with compound of formula (XU) and a silylating agent in the presence of a catalyst in a solvent.

In one embodiment, the silylating agent is selected from trimethylchlorosilane, trimethylbromosilane, trimethyliodosilane, hexamethyldisilazane, 61 M-bistri methylsilyl trifluoroacetamide (BSTFA), 61M-bistrimethylsilylacetamide (BSA). In a preferred embodiment, the silylating agent is BSA. In one embodiment, the amount of silylating agent is between 1.9 eq. and 2.8 eq. In a preferred embodiment, the amount of silylating agent is between 2.0 eq. and 2.2 eq. In a particularly preferred embodiment, the amount of silylating agent is 2.08 eq.

In one embodiment, the catalyst is selected from SnCh, TMSOTf, TMSI and HI. In a preferred embodiment, the catalyst is TMSOTf.

In one embodiment, the amount of catalyst is between 0.05 eq. and 1.2 eq. In a preferred embodiment, the amount of catalyst is 0.10 eq.

In one embodiment, the solvent is selected from DCM, CHCh, benzene, THF, 2-MeTHF, fluorobenzene, xylene, 1,4-di oxane and toluene. In a preferred embodiment, the solvent is toluene.

Step k) Formation of compound of formula (XIV)

Compound of formula (XIV) is obtained by reacting compound of formula (XIII) with an acid in an organic solvent.

In one embodiment, the acid is selected from D-glutamic acid, L-mandelic acid, 1- hydroxy-2-naphthoic acid, citric acid, 4-aminosalicylic acid, L-tartaric acid, hippuric acid, malonic acid, glutaric acid, oxalic acid, fumaric acid, succinic acid, 4-aminobenzoic acid, 2,5- dihydroxybenzoic acid, L-malic acid, salicylic acid, maleic acid, (lS,3R)-(-)-camphoric acid, pamoic acid, mucic acid, palmitic acid, oleic acid and lactobionic acid. In a preferred embodiment, the acid is selected from oxalic acid and maleic acid. In a particularly preferred embodiment, the acid is maleic acid.

In one embodiment, the solvent is selected from MeOH, EtOH, /7-propanol. IP A, MeCN, acetone, THF, 2-MeTHF, toluene, or mixtures thereof. In a preferred embodiment, the solvent is a mixture of toluene and 2-MeTHF.

Step k) is critical for the whole process in terms of purity improvement. In document WO 2018/127525 Al, compound of formula (XIII) was not isolated and the process was completely telescoped without solid isolation from compound of formula (IX) to compound of formula (la). The purity of crude compound of formula (la) was only 75-90%. Compound of formula (la) was isolated in the presence of a suitable acid. Surprisingly, in the present invention it was possible to isolate and purify compound of formula (XIV) from compound of formula (XIII) in the presence of a suitable acid. This provides compound of formula (XIV) in high yield and >99% purity. Surprisingly, when compound of formula (XIV) was isolated, the subsequent compound (I) or (la) could be obtained in >97% crude purity and could be isolated in its free form in >99% purity and high yield.

Step 1) Formation of compound of formula (XV)

Compound of formula (XV) is obtained by reacting compound of formula (XIV) with an aqueous base in a solvent.

In one embodiment, the aqueous base is an aqueous solution of a base selected from sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium phosphate, potassium phosphate, sodium acetate, potassium acetate, sodium hydroxide, potassium hydroxide, ammonium hydroxide, EDIP A, tributylamine and tri ethyl amine. In a preferred embodiment, the aqueous base is an aqueous solution of triethylamine.

In one embodiment, the solvent is selected from DCM, CHCh, benzene, 2-MeTHF, fluorobenzene, xylene and toluene. In a preferred embodiment, the solvent is toluene.

In one embodiment, the reaction is performed between -10 °C and 80 °C, particularly between 60 °C and 70 °C.

Step m) Formation of compound of formula (la)

Compound of formula (la) is obtained by performing a selective cleavage of compound of formula (XV) in the presence of a catalyst in a solvent.

In one embodiment, the catalyst is selected from NaOH, KOH, MeONa, MeOK, K2CO3, ammonia, ammonium hydroxide, K2HPO4, MgO, DBU, methylamine and MOO2CI2. In a preferred embodiment, the catalyst is MeONa.

In one embodiment, the amount of catalyst is between 0.005 eq and 5 eq. In a preferred embodiment, the amount of catalyst is 0.0375 eq.

In one embodiment, the solvent is selected from methanol, ethanol, 2-propanol, a mixture of methanol and ethanol, a mixture of THF and methanol, and a mixture of 2-MeTHF and methanol. In a preferred embodiment, the solvent is methanol. In one embodiment, the reaction is performed between -20 °C and 70 °C. In a preferred embodiment, the reaction is performed at -15 °C.

Surprisingly, in the present invention it was possible to increase the selectivity of this reaction and suppress the over-reaction of compound of formula (la), which forms process impurities. In WO 2018/127525 Al, compound of formula (la) was isolated in the form of a salt or co-crystal with a suitable acid to increase purity and crystallizability, as the free form of a compound of formula (la) could not be obtained directly in a solid form. However, this isolation required the use of additional solvents and was laborious. Furthermore, it required an additional salt-breaking step to obtain compound of formula (la) as a free base. Surprisingly, in the present invention it was found that compound of formula (la) can be isolated in the free form in high purity, directly from the reaction medium. This simplifies the process, reduces the solvent usage and makes it more amenable for technical scale-up.

Examples

The invention will be more fully understood by reference to the following examples. They should not, however, be construed as limiting the scope of the invention.

Example 1

Preparation of [(3aR,5R 6S, 6aR)-5-[(4R)-2,2-dimethyl-l , 3-dioxolan-4-yl] -2,2-dimethyl- 3a, 5, 6, 6a-tetrahydrofuro[2, 3-d] [1, 3 ]dioxol-6-yl ] trifluoromethanesulfonate (III)

To a 1500 L glass-lined reactor was charged (3aR,5S,6S,6aR)-5-[(4R)-2,2-dimethyl-l,3- dioxolan-4-yl]-2,2-dimethyl-3a,5,6,6a-tetrahydrofuro[2,3-d][l,3]dioxol-6-ol (compound II, 60.0 kg, 231 mol), toluene (600 L) and pyridine (36.4 kg, 460 mol) at 5 °C-15 °C. After cooled to 0 °C-10 °C, the reaction mixture was then charged with TfzO (78.0 kg, 276 mol) dropwise at 0 °C- 10 °C over 2 hours and stirred at 0 °C-10 °C for another 4 hours. The reaction was then quenched by adding water (180 L) at 0 °C-10 °C slowly. After phase separation, the organic phase was washed with 10% AcOH (240 L, three times), sat. NaHCCh (240 L, twice) and water (180 L), dried with Na2SO4 (60 kg) for 4 hours. The solid was removed by vacuum filtration and the wet cake was washed with toluene (30 L). The combined organic phase (solution A) was used in the next step without further purification.

Example 2

Preparation of (3aR, 5S, 6aR)-5-[(4R)-2, 2-dimethyl-l, 3-dioxolan-4-yl] -2, 2-dimethyl-3a, 5, 6, 6a- tetrahydrofuro[2, 3-d] [1, 3 ] dioxole (IV)

To a 3000 L glass-lined reactor was charged nBruNBTU (119 kg, 462 mol) and toluene (240 L) at 5 °C- 15 °C. After heated to 65 °C-75 °C, to the reaction mixture was then added solution A from previous step dropwise while the reaction temperature was controlled at 65 °C-75 °C. After addition, the reaction mixture was stirred at 65 °C-75 °C for 8 hours and then cooled to 0 °C- 10 °C, quenched by adding water (600 L) slowly while the mixture temperature was controlled at 0 °C-10 °C. The resulting mixture was then stirred at 0 °C-10 °C for another hour. After phase separation, the aqueous phase was extracted with 1 : 1 toluene/n-heptane (600 L, twice). The combined organic phase was washed with 20% NaCl aqueous solution (200 L), then concentrated to form an oil (64.0 kg; 50.4 kg of compound IV based on assay result) which was used in the next step without further purification.

In the present invention, toluene is used as solvent for step a) in order to telescope steps a) and b). The procedure of addition of compound of formula (III) in toluene solution into BU4NBH4 solution is designed so that it is easy to control the reaction temperature of step b) with higher yield and less by-products. Example 3

Preparation of (lR)-l-[( 3aR, 5S, 6aR)-2, 2-dimethyl-3a, 5, 6, 6a-tetrahydrofu.ro [2, 3-d][l,3]dioxol- 5-yl]ethane-l ,2-diol (V)

To a 3000 L glass-lined reactor was charged (3aR,5S,6aR)-5-[(4R)-2,2-dimethyl-l,3-dioxolan-4- yl]-2,2-dimethyl-3a,5,6,6a-tetrahydrofuro[2,3-d][l,3]dioxole (compound IV, 64.0 kg crude, 50.4 kg by weight assay, 206 mol) and methanol (830 L) at 5 °C-15 °C. To the reaction mixture was then added 0.8% aq. H2SO4 solution (224 L) while the reaction temperature was controlled at 5 °C-15 °C. After addition, the reaction mixture was heated to 25 °C-30 °C and stirred at this temperature for 16 hours, then cooled to 10 °C-20 °C and quenched by adding 2N NaOH solution (~20 kg) to adjust to pH = 7-8. The reaction mixture was concentrated to remove all the volatiles and to the left residue was charged DCM (900 kg), and the resulting organic solution was dried with Na2SC>4 (250 kg) for 8 hours. The solid was removed by vacuum filtration and the solution (34.1 kg of compound V by weight assay) was used for next step without further purification.

Example 4

Preparation of [(2R)-2-[( 3aR, 5S, 6aR)-2, 2-dimethyl-3a, 5, 6, 6a-tetrahydrofuro[2, 3-d] [1, 3]dioxol- 5-yl]-2-hydroxy-ethyl] benzoate (VI)

To a 1500 L glass-lined reactor was charged (!R)-l-[(3aR,5S,6aR)-2,2-dimethyl-3a,5,6,6a- tetrahydrofuro[2,3-d][l,3]dioxol-5-yl]ethane-l,2-diol (compound V, 63.9 kg by weight assay, 313 mol) in DCM solution, TEA (47.5 kg, 318 mol) and Bu2SnO (3.9 kg, 15.7 mol, 0.05 eq). After cooled to -10 °C-0 °C, the reaction mixture was then charged with BzCl (61.8 kg, 440 mol, 1.4 eq) dropwise at -10 °C-0 °C, then stirred at 0 °C- 10 °C for 1 hour. The reaction was quenched by adding water (50 L) at -10 °C-15 °C slowly, then neutralized with 2 N aq. HC1 (~9 L) to adjust to pH = 6-7 at -10 °C-15 °C and stirred for 20 minutes. After phase separation, the organic phase was washed with sat. NaHCCh (100 L) and 20% NaCl (100 L). The resulting organic phase was dried with Na2SO4 (25 kg) for 8 hours. The reaction mixture was filtered through a pad of celite (20 kg) and the organic solution was concentrated under vacuum to remove all the volatiles. The resulting crude mixture was suspended in EtOAc (128 L) and n-heptane (512 L) at 15 °C-25 °C, then heated to 50 °C and stirred for 2 hours. The reaction mixture was then cooled to 10 °C-20 °C over 2 hours and stirred at this temperature for 1 hour. The suspension was separated via centrifuge and the wet cake was dried in vacuum oven (30 mmHg, 50 °C) for 18 hours to afford compound VI (66.5 kg, 69.0% yield).

Compound VI: 'H NMR (400 MHz, DMSO) > ppm: 8.05-8.08 (m, 2H), 7.61 (m, 1H), 7.46 (m, 2H), 5.85 (d, J= 3.60 Hz, 1H), 4.80 (t, J= 4.20 Hz, 1H), 4.47-4.52 (dd, J= 11.40, 3.60 Hz, 1H), 4.32-4.39 (m, 2H), 4.21-4.26 (m, 1H), 2.53 (br.s., 1H), 2.11-2.17 (dd, J= 13.20, 4.50 Hz, 1H), 1.92-2.02 (m, 1H), 1.53 (s, 3H), 1.34 (s, 3H).

Example 5

Preparation of [(2R)-2-[( 3aR, 5S, 6aR)-2, 2-dimethyl-3a, 5, 6, 6a-tetrahydrofuro[2, 3-d] [1, 3]dioxol- 5-yl]-2-hydroxy-ethyl] benzoate (VII)

To a 300 L glass-lined reactor was charged [(2R)-2-[(3aR,5S,6aR)-2,2-dimethyl-3a,5,6,6a- tetrahydrofuro[2,3-d][l,3]dioxol-5-yl]-2-hydroxy-ethyl] benzoate (compound VI, 25 kg, 81.1 mol), DCM (250 L), DMAP (198 g, 1.62 mol) and TEA (12.3 kg, 82.4 mol). After cooled to 0 °C-5 °C, the reaction mixture was then charged with MsCl (11.2 kg, 97.8 mol) at 0 °C-5 °C over 2 hours and stirred at 0 °C-5 °C for 1 hour. The reaction was then quenched by adding water (50 kg) at 0 °C- 10 °C. The reaction mixture was then charged with 1 N HC1 (~12 L) to adjust to pH = 5-6 and stirred for 20 minutes. After phase separation, the organic phase was washed with sat. NaHCCti (50 L) and 20% NaCl (50 L). The resulting organic phase was dried with NaiSCti (20 kg) for 2 hours. The solid was removed by vacuum filtration and the organic solution was used in the next step without further purification.

Example 6

Preparation of (3aR, 5S, 6aR)-2,2-dimethyl-5-[(2S)-oxiran-2-yl]-3a, 5, 6, 6a-tetrahydrofuro[2, 3- d][ 1, 3] dioxole (VIII)

To a 300 L glass-lined reactor was charged MeOH (50 L) and NaOMe (9.8 kg, 181 mol). After cooled to 5 °C-10 °C, the reaction mixture was charged with [(2R)-2-[(3aR,5S,6aR)-2,2- dimethyl-3a, 5, 6, 6a-tetrahydrofuro[2, 3-d] [ 1 , 3] dioxol-5-yl] -2 -hydroxy-ethyl] benzoate (compound VII) in DCM solution from last step dropwise at 5 °C-10 °C. The reaction mixture was stirred at 10 °C-15 °C for 2 hours and then quenched by adding water (100 L). After phase separation, the aqueous phase was extracted with DCM (50 L) and the combined organic phase was washed with 20% NaCl (50 L), and then concentrated under vacuum to remove all the volatiles. The residual was then purified by column chromatography to afford crude compound VIII (8.4 kg). The crude compound VIII was then suspended in n-heptane (5 L). Vacuum filtration and the wet cake was dried under vacuum for 8 hours to afford compound VIII (7.76 kg, 51% yield). The reaction time and temperature are critical for this step otherwise overreaction to form the methoxy adduct of the epoxide would take place.

Compound VIII: 'H NMR: (300 MHz, CDC1₃) > > Dppm: 5.87 (d, J= 3.76 Hz, 1H), 4.77 (t, J = 4.00 Hz, 1H), 4.20-4.28 (m, 1H), 3.14-3.20 (m, 1H), 2.83-2.88 (m, 1H), 2.63 (dd, J= 5.00, 2.80 Hz, 1H), 2.09 (dd, J= 12.00, 4.00 Hz, 1H), 1.69-1.79 (m, 1H), 1.52 (s, 3H), 1.34 (s, 3H).

Example 7

Preparation of (!S)-l-[(3aR,5S, 6aR)-2,2-dimethyl-3a,5, 6, 6a-tetrahydrofu.ro [2, 3-d] [1, 3]dioxol-5- yl] propan- l-ol (IX)

To a 300 L glass-lined reactor was charged CuCl (520 g, 5.25 mol. 0.05 eq) and THF (71 kg). After cooled to -5 °C-0 °C, the reaction mixture was charged with 3N MeMgCl in THF solution (46 kg) dropwise at -5 °C-0 °C and then stirred for 30 minutes at -5 °C-0 °C. Then (3aR,5S,6aR)- 2,2-dimethyl-5-[(2S)-oxiran-2-yl]-3a,5,6,6a-tetrahydrofuro[2,3-d][l,3]dioxole (compound VIII, 19.3 kg, 104 mol) in THF (71 kg) solution was added slowly at 0 °C-10 °C. The reaction mixture was stirred for 1 hour at 0 °C- 10 °C, then added into a 1000 L glass-lined reactor containing aq. NH4CI (13.5 kg in 121.15 kg water) solution at 0 °C-5 °C over 2 hours, extracted with EtOAc (90 kg) twice. The combined organic phase was washed with 5% NH3 H2O aq. solution (7.5 kg), 5% NH3 H2O aq. solution (2.5 kg) and 15.6% NaCl aq. solution (30 kg) twice. The organic phase was then concentrated under vacuum to remove all the volatiles. To the residue was then charged with n-heptane (5.13 kg), and the resulting mixture was stirred at 50 °C for 30 minutes to form a clear solution, which was slowly cooled to 20 °C-30 °C over 4 hours, and then further cooled to 0 °C-5 °C over 2 hours. The reaction mixture was stirred at 0 °C-5 °C for 30 minutes, then the solid was removed by vacuum filtration and the wet cake was dried in vacuum oven (~30 mmHg, 50 °C) for 6 hours to afford compound IX (4.77 kg, 87.8% yield)

Compound IX: 'H NMR (400 MHz, CDCh) > > Dppm: 5.83 (d, J = 3.76 Hz, 1H), 4.81 - 4.73 (m, 1H), 4.26-4.19 (m, 1H), 3.91-3.82 (m, 1H), 2.08-2.02 (m, 1H), 1.93 - 1.89 (m, 1H), 1.54 (s, 3H), 1.49-1.39 (m, 2H), 1.34 (s, 3H), 1.02 (t, J= 7.53 Hz, 3H).

Example 8

Screening of conditions for the synthesis of compound Xia

This example provides a comparison study with the process disclosed in WO 2018/127525. The purity of compound Xia is pivotal to increase the purity and yield of compound XIHa. Reaction conditions were screened, in order to increase the purity of the crude compound Xia.

Conditions for direct conversion of compound IXa to compound Xia are summarized in the table below.

The direct conversion of compound IXa into compound Xia was proven possible. However, under those optimized conditions a purity of only 92-93% area (GC) of the crude compound Xia was achieved. Therefore, the reaction was split into two subsequent stages:

1. Formation of compound Xa from compound IXa

2. Conversion of crude compound IXa into compound Xia.

The screening of the conditions is summarized in the table below.

By spliting the reaction in two steps and using a combination of HBCh/AcOH, compound Xia could be obtained in high purity. In the absence of acetic acid (Entry 12) the reaction proceeded very slowly and was not complete after 23h. In presence of substoichiometric acetic anhydride or in its absence (Entry 13), the conversion of compound Xa into compound Xia did not occur. Therefore, both components are required for this reaction to take place. Based on the experiments above, the protocols described in Example 8 and Example 9 were developed.

Example 9

Preparation of [(lS)-l-[(3aR,5S, 6aR)-2,2-dimethyl-3a,5, 6, 6a-tetrahydrofuro[2, 3-d][l,3]dioxol- 5 -y I] propyl] acetate (Xa)

To a 2 L glass-lined reactor was charged (!S)-l-[(3aR,5S,6aR)-2,2-dimethyl-3a,5,6,6a- tetrahydrofuro[2,3-d][l,3]dioxol-5-yl]propan-l-ol (IX) (100 g, 0.494 mol, 1.0 eq.), DMAP (3.2 g, 0.025 mol, 0.05 eq.) and toluene (475 ml). Acetic anhydride (88.3 g, 0.865 mol, 1.75 eq.) was charged and the addition line was rinsed forward with toluene (25 ml). The resulting mixture was heated to 60°C and stirred for 30 minutes. Water (125 g) was charged and the mixture was stirred for 15 minutes. The aqueous phase was discarded, and the organic phase was concentrated under reduced pressure to 3.75 volumes and diluted with toluene (193 ml). The solution of crude product was used without further purification.

Example 10

Preparation of [(3R5S)-2-acetoxy-5-[(lS)-l-acetoxypropyl]tetrahydrofuran-3-yl] acetate (Xia)

To the solution of crude compound Xa in toluene was added acetic acid (62.4 g, 1.04 mol, 2.1 eq.), acetic anhydride (121.1 g, 1.19 mol, 2.4 eq.) and boric acid (9.17 g, 0.148 mol, 0.3 eq.). The addition funnel and lines were rinsed forward with toluene (35 ml). The mixture was heated to 75 °C and stirred for 5h. The resulting solution was cooled to 0 °C and a 14% w/w aqueous solution of tripotassium phosphate (1.46 kg, 0.99 mol, 2.0 eq.) was charged. The mixture was warmed to room temperature and stirred for 30 minutes. The phases were separated and the aqueous layer was discarded. The organic layer was extracted with water (100 g), and then concentrated under reduced pressure to 3.75 vol. The residue was polish-filtered and the reactor and filter were rinsed forward with toluene (25 ml). The crude product solution (37.5% w/w assay, yield: 97.9% mol, purity: 98.81% area, GC) was used without further purification.

Example 11

Preparation of [(2R, 3R,5S)-5-[(lS)-l-acetoxypropyl]-2-(5-amino-2-oxo-thiazolo[4,5- d]pyrimidin-3-yl)tetrahydrofuran-3-yl] acetate (Xllla)

To a IL glass-lined reactor was charged 5-amino-3H-thiazolo[4,5-d]pyrimidin-2-one (Xlla) (35g, 0.21 mol, 1.0 eq.) and toluene (364 ml). BSA (88.1g, .433 mol, 2.08 eq) was added, and the addition funnel was rinsed with toluene (41 ml). The mixture was heated to 85 °C and stirred for 2h. Vacuum was applied and the solution was concentrated to 10 volumes. To the mixture was added TMSOTf (4.63 g, 0.021 mol, 0.1 eq) at 85 °C. The addition line was rinsed with toluene (4 ml). A 37.5% w/w solution of compound Xia in toluene (176.2g, 0.23 mol, 1.1 eq) was added to the reaction mixture in 3h at 85 °C. The mixture was stirred for 2h, and then cooled to 0°C. The reaction mixture is charged slowly to a 5% w/w aqueous solution of sodium sulfate (350 g) at 0 °C. The mixture was heated to 50 °C and the phases were separated. The aqueous phase was discarded. The organic phase was extracted twice with a 5% w/w aqueous sodium sulfate solution. The organic phase was concentrated under reduced pressure to 10 volumes and clarified through a paper filter. The reactor and filter were rinsed forward with toluene (35 ml). The filtrate was diluted to 12 volumes with toluene. A solution of compound Xllla in toluene (399.4 g, purity: 96.05% area, HPLC) was obtained. The crude compound XHIa was used without further purification.

Example 12

Preparation of [(2R, 3R,5S)-5-[(lS)-l-acetoxypropyl]-2-(5-amino-2-oxo-thiazolo[4,5- d]pyrimidin-3-yl)tetrahydrofuran-3-yl] acetate; maleic acid (XlVa)

The toluene solution of crude compound Xllla (399.4g) was heated to 45 °C. A 22.1% w/w solution of maleic acid in 2-MeTHF (41.1 g, 0.078 mol, 0.375 eq.) was added slowly at 45°C. Compound XlVa (0.055g, 0.11 mmol, 0.0005 eq) was charged, and the resulting suspension was stirred for Ih. A 22.1% w/w solution of maleic acid in 2-MeTHF (68.5 g, 0.130 mol, 0.625 eq.) was added in 3.5 h at 45 °C. The suspension was cooled to 0 °C in 4.5 h, stirred for 1 h, and then the solids were isolated by filtration and dried under reduced pressure. 89.2 g of compound XlVa (83.6% yield, 99.4% area, HPLC) was obtained.

Compound XlVa: 'H NMR (400 MHz, CDCh) 8 ppm: 10.48 - 11.89 (bs, 2 H); 7.99 (s, 1 H); 6.38 (s, 2 H); 5.98 - 5.99 (d, J= 1.61 Hz, 1 H); 5.67 - 5.74 (d, J= 6.72 Hz, 1 H); 4.93 - 5.04 (dt, J= 5.10 Hz, 8.33 Hz, 1 H); 4.29 - 4.40 (m, 1 H); 2.57 - 2.72 (m, 1 H); 2.12 (s, 3H); 2.01 - 2.10 (m, 4 H); 1.55 - 1.75 (m, 2 H); 0.87 - 1.00 (t, J = 7.52 Hz, 3 H).

Example 13

Preparation of [(2R, 3R,5S)-5-[(lS)-l-acetoxypropyl]-2-(5-amino-2-oxo-thiazolo[4,5- d]pyrimidin-3-yl)tetrahydrofuran-3-yl] acetate; oxalic acid (XlVb)

A solution of crude compound Xllla (52.7 g) was heated to 45°C. A solution of oxalic acid (3.57 g, 0.04 mol, 1.0 eq.) in ethyl acetate (107.2 g) was added in 35 minutes. Compound XlVb (0.005 g) was added after ca. 1/3 of the addition. To the resulting suspension was charged n-heptane (24.2 g) in 15 minutes. The mixture was cooled to 20°C in Ih and stirred for 2h. The solids were isolated by filtration and dried under reduced pressure. 16.9 g of compound XlVa (87.9% yield, 96.2% area, HPLC) were obtained.

Compound XlVb: IH NMR (600 MHz, DMSO-d6) 6 ppm 8.36 (s, 1 H), 6.96 (br s, 2 H), 5.87 (d, J=1.7 Hz, 1 H), 5.67 (dd, J=7.0, 1.8 Hz, 1 H), 4.84 (ddd, J=8.8, 5.4, 4.1 Hz, 1 H), 4.22 (dt, J=11.0, 5.5 Hz, 1 H), 2.58 - 2.77 (m, 1 H), 2.06 (s, 2 H), 1.98 (s, 3 H), 1.95 - 1.97 (m, 1 H), 1.93 - 2.01 (m, 1 H), 1.62 (ddd, J=14.2, 7.5, 4.2 Hz, 1 H), 1.44 - 1.58 (m, 1 H), 0.82 (t, J=7.4 Hz, 3 H).

Example 14

Preparation of [(2R, 3R,5S)-5-[(lS)-l-acetoxypropyl]-2-(5-amino-2-oxo-thiazolo[4,5- d]pyrimidin-3-yl)tetrahydrofuran-3-yl] acetate (XVa)

To a 500 ml glass jacket reactor was charged [(2R,3R,5S)-5-[(lS)-l-acetoxypropyl]-2-(5-amino- 2-oxo-thiazolo[4,5-d]pyrimidin-3-yl)tetrahydrofuran-3-yl] acetate; maleic acid (XlVa), 50 g, 97.56 mmol, 1.0 eq) and toluene (410.9 g, 475 ml). To this suspension was charged 20% w/w aqueous NaCl (100 g), and triethylamine (24.68 g, 243.91 mmol, 2.5 eq). The addition line was rinsed forward with toluene (21.6 g, 25 ml). The resulting mixture was heated to 60 °C and stirred. The lower aqueous phase was discarded. The upper organic layer was extracted with 20% w/w aqueous NaCl (100 g) at 60 °C. The lower aqueous phase was discarded. Vacuum was applied to the upper organic layer and water was distilled azeotropically in a Dean-Stark. The organic solution was filtered through a pad of activated charcoal. The filtrate was concentrated under reduced pressure to 2 vol. The solvent was switched to methanol and then diluted with methanol to 9 vol. The crude solution of compound XVa in methanol was used without further purification.

Example 15

Preparation of[(lS)-l-[(2S,4R5R)-5-(5-amino-2-oxo-thiazolo[4,5-d]pyrimidin-3-yl)-4-hydroxy- tetrahydrofuran-2-yl] propyl] acetate (la-a)

The solution of compound (XVa) from Example 14 was cooled to -15°C. A 25% w/w solution of sodium methanolate (0.791g, 3.66 mmol, 0.0375 eq) was added and the resulting solution was stirred for 15h at -15 °C. Acetic acid (0.293 g, 4.88 mmol, 0.05 eq) was added to the solution.

The mixture was heated to 50 °C and concentrated under reduced pressure to 3 vol. The temperature of the residue was adjusted to 35 °C. Water (125 g) was added at 35 °C. Compound la (0.25 g, 0.071 mmol, 0.0072 eq) was added, and the suspension was stirred for Ih at 35 °C. To the suspension was added water (175 g) in lOh. The suspension was stirred at 35 °C for Ih and then cooled to -5 °C in 8h.

Solids were collected by filtration and rinsed with water (2x50 g) and ^-heptane (34.2 g, 50 ml). The wet solids were dried under reduced pressure. Compound la-a was obtained as an off-white solid (yield: 87.9%, purity: 99.72% area, HPLC).

Compound la-a: 'H NMR (400 MHz, ₆-DMSO) > > Dppm: 8.34 (s, IH), 6.91 (br. s„ 2H), 5.82 (s, IH), 5.46-5.58 (m, IH), 4.70-4.82 (m, 2H), 4.14-4.23 (m, IH), 2.42-2.48 (m, IH), 1.98 (s, 3H), 1.78-1.88 (m, IH), 1.55-1.70 (m, IH), 1.34-1.49 (m, IH), 0.82 (t, J = 7.40 Hz, 3H). MS obsd. (ESI⁺) [(M+H)⁺]: 355. Example 16

Preparation of [(2R,3R5S)-5-[(lS)-l-acetoxypropyl]-2-(5-amino-2, 7-dioxo-6H-thiazolo[4,5- d]pyrimidin-3-yl)tetrahydrofuran-3-yl] acetate (Xlllb)

(Xlllb)

To a 250 mL round bottom flask was charged with 5-amino-3,6-dihydrothiazolo[4,5- d]pyrimidine-2, 7-dione (Xllb, 4.3 g, 22.9 mmol) and toluene (80.5 g). The reaction mixture was heated to 110 °C and some toluene (50 g) was removed. After cooled to 75 °C-80 °C, to the mixture was charged with BSA (13.9 g, 68.6 mmol) over a 30 minutes period. The reaction mixture was then stirred at 75 °C-80 °C for 2 hours, then TMSOTf (0.254 g, 1.14 mmol, 0.05 eq) was added, followed by addition of [(3R,5S)-2-acetoxy-5-(l-acetoxypropyl)tetrahydrofuran-3-yl] acetate (7.91 g, 27.4 mmol) in toluene (37.2 g) solution over a 30 minutes period while keeping the temperature at 75 °C-80 °C. The mixture was stirred at 75 °C-80 °C for 6.5 hours then cooled to 0 °C- 10 °C and quenched by adding water (38 g) at 0 °C- 10 °C, followed by addition of IP Ac (35.0 g). After phase separation, the aqueous phase was extracted with IP Ac (35.0 g). The combined organic phases were washed with water (38.0 g), 15.6% NaCl aq. solution (40.5 g), and concentrated under vacuum. The residue was dissolved in 2-MeTHF (20.6 g), and then concentrated again, this process was repeated once. The crude product was used in next step without further purification.

Example 17

Preparation of [(lS)-l-[(2S,4R,5R)-5-(5-amino-2, 7-dioxo-6H-thiazolo[4,5-d]pyrimidin-3-yl)-4- hydroxy-tetrahydrofuran-2-yl]propyl] acetate (la-b)

To a 250 mL round bottom flask was charged [(2R,3R,5S)-5-[(lS)-l-acetoxypropyl]-2-(5-amino- 2,7-dioxo-6H-thiazolo[4,5-d]pyrimidin-3-yl)tetrahydrofuran-3-yl] acetate (Xlllb, 6.0 g, 14.4 mmol) in 2-MeTHF (20.6 g) solution from last step, 2-MeTHF (32.6 g), powder K2CO3 (2.58 g, 18.7 mmol), PEG-400 (0.06 g) and MeOH (9.5 g). The reaction mixture was stirred at 20 °C-25 °C for 20 hours and the solid was removed through vacuum filtration. The wet cake was washed with IP Ac (28.0 g) and the combined filtrate was washed with water (45.0 g), 15.6% aq. NaCl solution (40.0 g). The organic phase was concentrated under vacuum to remove all the volatile and the residue was purified by silica gel column that eluted with DCM/MeOH 30/1 (v/v). The collected fraction was concentrated under vacuum to remove all the solvent to afford compound (la-b) (2.5 g, 46.3% yield).

Example 18

Screening study of deacetylation conditions for the synthesis of compound la-a

The selectivity of the monodeacetylation of compound XVa is an essential pre-requisite to obtain pure compound la-a in high yield, and allow direct crystallization, without the formation of intermediate salts or co-crystals. The deacetylation can be performed under various conditions by alcoholysis or aminolysis and in the presence of different catalysts. Under all reaction conditions, variable amounts of over-reacted bis-deacetylated side-product (Diol) is observed. The amount of that side-product typically increases upon prolonged reation.

The screening of the experimental conditions for the selective monodeacetylation is reported in the following table. The goal of the screening was to identify conditions in which a high selectivity for the mono-deacetylation at high conversion can be obtained.

While the reaction proceeded under almost all conditions tested, the highest selectivity was obtained by methanolysis in the presence of catalytic MeONa. Under those conditions, the selectivity remains high even upon prolonged stirring.

Claims

1. A process for the preparation of a compound of formula (la), or a pharmaceutically acceptable salt thereof,

wherein

Ri is H or Ci-6-alkyl,

R.2 is H or hydroxy, comprising: step g) reacting compound of formula (VIII)

wherein

wherein

wherein

wherein

Ri is H or Ci-6 alkyl; R.2 is H or hydroxy.

2. The process according to claim 1, further comprising: step a) reacting compound of formula (II) nd of formula (III)

step b) reacting compound of formula (III) with a reducing agent to form compound of formula

(IV)

step I) reacting compound of formula (VII) with a base to form compound of formula (VIII)

3. The process according to claim 2, consisting of step a) to step m).

4. The process according to any one of claims 1 to 3, wherein Ri is methyl and R2 is H or hydroxy.

5. The process according to any one of claims 1 to 4, wherein Ri is methyl and R2 is hydrogen.

6. The process according to any one of claims 1 to 5, wherein the Grignard reagent in step g) is selected from MeMgCl, MeMgBr and MeMgl and the copper catalyst is selected from CuCl, Cui and CuBr.

7. The process according to any one of claims 1 to 6, wherein the acylating agent in step h) is selected from alkylacyl anhydride, alkylacyl chloride, arylacyl anhydride and arylacyl chloride.

8. The process according to any one of claims 1 to 7, wherein the acylating agent in step h)

IS AC2O.

9. The process according to any one of claims 1 to 8, wherein step h) is performed in the presence of a catalyst selected from AcOH, TfOH, MSA, TFA, H3PO4, H2SO4, a mixture of AcOH and H2SO4, H3BO3, MgCh, Na₂SO₄, and DMAP.

10. The process according to claim 9, wherein the catalyst in step h) is DMAP.

11. The process according to any one of claims 1 to 10, wherein the acylating agent in step i) is selected from alkylacyl anhydride, alkylacyl chloride, arylacyl anhydride and arylacyl chloride.

12. The process according to any one of claims 1 to 11, wherein the acylating agent in step i) is AC2O.

13. The process according to any one claims 1 to 12, wherein the catalyst in step i) is selected from AcOH, H2SO4, H3PO4, MeSO4H, a mixture of AcOH and H2SO4, MgCh, Na2SO4, B(OMe)s, B2O3, H3BO3, and a mixture of AcOH and H3BO3.

14. The process according to any one of claims 1 to 13, wherein the catalyst in step i) is a mixture of AcOH and H3BO3.

15. The process according to any one of claims 1 to 14, wherein the silylating agent in step j) is selected from trimethylchlorosilane, trimethylbromosilane, trimethyliodosilane, hexamethyldisilazane, O, -bistrimethylsilyl trifluoroacetamide (BSTFA), O,N,- bistrimethylsilylacetamide (BSA).

16. The process according to any one of claims 1 to 15, wherein the silylating agent in step j) is bistrimethylsilylacetamide (BSA).

17. The process according to any one of claims 1 to 16, wherein the catalyst in step j) is selected from SnCU TMSOTf, TMSI and HI.

18. The process according to any one of claims 1 to 17, wherein the amount of the silylating agent in step j) is 1.9-2.8 eq.

19. The process according to any one of claims 1 to 18, wherein the acid in step k) is selected from D-glutamic acid, L-mandelic acid, 1 -hydroxy-2-naphthoic acid, citric acid, 4- aminosalicylic acid, L-tartaric acid, hippuric acid, malonic acid, glutaric acid, oxalic acid, fumaric acid, succinic acid, 4-aminobenzoic acid, 2,5-dihydroxybenzoic acid, L-malic acid, salicylic acid, maleic acid, (lS,3R)-(-)-camphoric acid, pamoic acid, mucic acid, palmitic acid, oleic acid and lactobionic acid.

20. The process according to any one of claims 1 to 19, wherein the acid in step k) is selected from oxalic acid and maleic acid.

21. The process according to any one of claims 1 to 20, wherein the acid in step k) is maleic acid.

22. The process according to any one of claims 1 to 21, wherein the aqueous base in step 1) is an aqueous solution of a base selected from sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium phosphate, potassium phosphate, sodium acetate, potassium acetate, sodium hydroxide, potassium hydroxide, ammonium hydroxide, EDIP A, tributylamine and triethylamine.

23. The process according to any one of claims 1 to 22, wherein the aqueous base in step 1) is triethylamine.

24. The process according to any one of claims 1 to 23, wherein step m) is performed in the presence of a catalyst selected from NaOH, KOH, MeONa, MeOK, K2CO3, ammonia, ammonium hydroxide, K2HPO4, MgO, DBU, methylamine and MOO2CI2.

25. The process according to claim 24, wherein the catalyst in step m) is MeONa.

26. The process according to any one of claims 1 to 23, wherein step m) is performed in a solvent selected from methanol, ethanol, 2-propanol, a mixture of methanol and ethanol, a mixture of TH F and methanol, and a mixture of 2-MeTHF and methanol.

27. The process according to claim 26, wherein step m) is performed in methanol.

28. The invention as described hereinbefore.