Antiviral imino-c-nucleoside thienopyrimidine analogues

Abstract

Compounds of the Formula (I), pharmaceutical compositions comprising compounds of the Formula (I), and their use for treating or preventing a viral infection:

Description

[0001] ANTIVIRAL IMINO-C-NUCLEOSIDE THIENOPYRIMIDINE ANALOGUES

[0002] TECHNICAL FIELD

[0003] The invention relates generally to new compounds useful for the treatment or prevention of viral infections. In particular, the invention relates to imino-C-nucleosides having a thieno[3,4-cf]pyrimidine ring system rather than the purine ring system of adenosine and guanosine. The invention also relates to pharmaceutical compositions comprising these compounds, and their use as antiviral agents.

[0004] BACKGROUND OF THE INVENTION

[0005] Broad-spectrum antiviral drugs are essential medicines to combat viral infections. They have saved the lives of millions of people, prevented unnecessary suffering and are extremely important in a pandemic setting caused by a novel virus, particularly when no vaccine is available. Nucleoside analogues, a major class of antiviral drugs, have achieved significant success in treating viral infections. However, the emergence of drug resistance highlights the need for more robust versions of these medicines.

[0006] Novel strains of influenza virus have resulted in four notable pandemics since the early 1900s: H1N1 (1918), H2N2 (1957), H3N2 (1968) and H1N1 (2009), leading to millions of deaths globally.1By May 2023, the COVID-19 pandemic had seen more than 765 million people infected, with at least 6.8 million lives ended prematurely worldwide.2

[0007] Currently, there are only four-FDA approved antiviral drugs recommended for the treatment of influenza. Three of these - oseltamivir, zanamivir and peramivir - are neuraminidase inhibitors while baloxavir targets viral endonuclease activity.3Resistance has been observed against the neuraminidase class4'5and also against baloxivir.6

[0008] The Emergency Use Authorisation of nucleoside antivirals remdesivir and molnupiravir for the treatment of acute SARS-CoV-2 infection7'8has highlighted the usefulness of nucleoside compounds as well as the value of novel broad-spectrum antivirals being in-hand for future pandemics.9'10

[0009] In addition to viral pandemics, viruses endemic to certain parts of the world are a significant cause for concern. Flaviviruses are single-stranded RNA viruses that are transmitted primarily by arthropod vectors and can cause severe illnesses or death in humans.

[0010] For example, the Aedes mosquito-borne dengue virus (DENV) is a significant public health threat to over half of the global population. Climate change has resulted in a dramatic increase in dengue fever reports over the last five years, along with alarming expansion into areas previously unable to support the mosquito vector's lifecycle, including Northern Europe.11In 2019, one study estimated 57 million dengue cases worldwide, resulting in over 36,000 deaths.12Despite this clinical burden, there are currently no specific antivirals available for dengue infection and the two clinically approved DENV vaccines (Dengvaxia and Qdenga) have limited approvals and availability.13There is thus also a need for new, safe antivirals to treat DENV infections.

[0011] The adenosine analogue NITD008 is an example of a nucleoside with antiviral activity against flaviviruses with submicromolar inhibition, including against DENV, YFV and ZIKV.14However, preclinical safety concerns from animal models have prevented this compound's development.14'15More recently, another antiviral nucleoside AT-752 has been reported to be effective against flaviviruses in vitro,16'17progressing to stage two clinical trials for dengue fever.18However, given the uncertainty surrounding the progression of promising drug candidates to the clinical setting, there continues to be a need for new, safe antivirals to treat flavivirus infections.

[0012] There is also an unmet medical need to treat infections cause by respiratory syncytial virus (RSV). RSV is a leading cause of hospitalisation for children under the age of five and is a significant burden on elderly populations. Another virus that mainly affects children is enterovirus-D68 (EV-D68) - causing flu-like symptoms, while infection from enteroviruses affect millions of people worldwide, causing wide-ranging symptoms.

[0013] Imino-C-nucleosides (iminovirs) differ from conventional nucleosides in that they contain a nitrogen atom in place of the ribose ring-oxygen.19The promising antiviral activity exhibited by iminovirs warrants further development of this class of antiviral compounds.27

[0014] Thieno[3,4-cf]pyrimidine C-nucleoside I20was reported to exhibit mediocre inhibition of hepatitis C virus in cell-based assays. However, its activity was improved when administered as the 5'-prodrug 2 exhibiting low micromolar activity (EC50 = 2.9 pM, HCV). No other antiviral data has been reported for compounds 1 and 2. The thieno[3,4- cf]pyrimidine motif is an under-explored variant of adenosine C-nucleoside mimics, that has found its main application to date as an intrinsically fluorescent probe in RNA research.21'22This prompted the applicant to synthesise imino-C-nucleoside version of this compound, imino C-nucleoside 3. It is well-known that a subtle modification in chemical structure of nucleoside analogues can lead to a complete loss of antiviral activity.23Surprisingly however, the applicant found the iminovir analogue 3 to be far more active as an antiviral in cellular assays than riboside 1, although its riboside version 4 was previously found to be highly toxic (e.g. CC50 = 5-9 nM) to certain cell lines.22Even more surprising was that analogue 3 was more active than prodrug 2, and is inherently non-toxic.

[0015] C-ribonucleoside 4

[0016] The generally accepted pathway by which a nucleoside analogue inhibits a virus relies on the conversion of a nucleoside to the "active" triphosphate form inside cells where viruses reside. The triphosphate is then a substrate for the viral replication machinery, with downstream inhibition of the replication process occurring by numerous different mechanisms of action.

[0017] It is also well-established that purine analogues closely resembling adenosine can be toxic to host cells,24as host cellular machinery may not discriminate between ATP and the adenosine mimic-TP "active"-form sufficiently to avoid deleterious interference in cellular processes. Attempts to temper this toxicity have previously involved including substitutions on the ribose ring or on the nucleobase moiety.

[0018] In the search for iminovirs that exhibit both strong antiviral activity and low toxicity, the applicant investigated alteration of the 5,6-bicyclic structure of the 9-deazapurine moiety in galidesivir30to an analogous thieno[3,4-cf]pyrimindine structure, as depicted below.

[0019] 9-Deazapurine Thieno[3,4-d]pyrimidine

[0020] The applicant overcame challenges to the chemical synthesis of such compounds and surprisingly found that certain iminovir compounds having the thieno[3,4-cf]pyrimidine base structure showed broad-spectrum antiviral activity and acceptably low toxicity levels.

[0021] SUMMARY OF THE INVENTION

[0022] In one aspect the invention provides a compound of the Formula (I): wherein:

[0023] R1is H or R6CO; where R6is C1-20 alkyl, C6-12 aryl, C1-6 alkyl-Ce-aryl, where R7is the side group of a natural amino acid;

[0024] R2and R3are each independently selected from H, R6CO and Ci-4 alkyl; where R6is as defined above;

[0025] R4and R5are each independently selected from H, C1-6 alkyl, cycloalkyl, C6-12 aryl and heteroaryl, or R4and R5together form C3-6 heterocycloalkyl;

[0026] X is H, deuterium, C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C6-12 aryl, heteroaryl, CN, C(=O)Z, halogen, amidine, hydroxy amidine, carboxime or CHR8OH; where Z is H, OH, OR9, C1-6 alkyl, NH2, NR9H, N(R9)2or SR9;

[0027] R8is H, C1-6 alkyl, C6-12 aryl or C1-6 alkyl-Ce-aryl; and R9is C1-6 alkyl, cycloalkyl, C6-12 aryl, or heteroaryl;

[0028] A is H, F, Cl, NH2, or CH3; or a pharmaceutically acceptable salt thereof.

[0029] In certain embodiments of the invention A is H.

[0030] In certain embodiments of the invention R4and R5are each independently selected from H, C1-6 alkyl, cycloalkyl, C6-12 aryl and heteroaryl.

[0031] In certain embodiments of the invention R4and R5are both H.

[0032] In certain embodiments of the invention R4is CH3 and R5is H.

[0033] In certain embodiments of the invention R1is H.

[0034] In certain embodiments of the invention R1is R6CO.

[0035] In certain embodiments of the invention R6is C1-12 alkyl.

[0036] In certain embodiments of the invention R6is isobutyroyl and R2and R3are both H.

[0037] In certain embodiments of the invention R6is: wherein R7is the side group of a natural amino acid.

[0038] In certain embodiments of the invention R1, R2and R3are all H.

[0039] In certain embodiments of the invention R1, R2, R3, R4and R5are all H.

[0040] In certain embodiments of the invention X is H.

[0041] In certain embodiments of the invention X is I.

[0042] In certain embodiments of the invention X is CN.

[0043] In certain embodiments of the invention X is C(=O)NH2.

[0044] In certain embodiments of the invention X is deuterium.

[0045] Preferred compounds of the invention include, but are not limited to, the following compounds:

[0046]

[0047] In a second aspect of the invention there is provided a pharmaceutical composition comprising a compound of the invention and a pharmaceutically acceptable carrier.

[0048] In a third aspect of the invention there is provided a method of treating or preventing a viral infection comprising administering to a human in need an effective amount of a compound of the invention.

[0049] In a further aspect of the invention there is provided the use of a compound of the invention in the manufacture of a medicament for treating or preventing a viral infection. In another aspect of the invention there is provided a composition comprising a compound of the invention for use in treating or preventing a viral infection.

[0050] DETAILED DESCRIPTION

[0051] Definitions

[0052] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the inventions belong. Although any assays, methods, devices and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, various assays, methods, devices and materials are now described.

[0053] It is intended that reference to a range of numbers disclosed herein (for example 1 to 10) also incorporates reference to all related numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0054] As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to".

[0055] The term "alkyl" means any saturated hydrocarbon radical and is intended to include both straight- and branched-chain alkyl groups. The term "Ci-Ce alkyl" means any saturated hydrocarbon radical having up to 6 carbon atoms. Examples include, but are not limited to methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, t-butyl, n-pentyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, 2-ethylpropyl, n-hexyl and l-methyl-2-ethylpropyl.

[0056] The term "cycloalkyl" means a cyclic alkyl group. The term "C4-Cs cycloalkyl" means any cyclic alkyl group having 4 to 8 carbon atoms. Examples include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.

[0057] The term "heteroalkyl" means an alkyl group where one or more carbon atoms have been replaced by an atom other than carbon, such as nitrogen, oxygen or sulfur.

[0058] The term "heterocycloalkyl" means a saturated or unsaturated cycloalkyl group where one or more carbon atoms have been replaced by an atom other than carbon, such as nitrogen, oxygen or sulfur. Examples include azetidinyl, pyrrolidinyl, piperidinyl and morpholinyl.

[0059] The term "alkenyl" means any hydrocarbon radical having at least one double bond and is intended to include both straight- and branched-chain alkenyl groups. Examples of alkenyl groups include, but are not limited to, ethenyl, n-propenyl, / so-propenyl, n-butenyl, / so-butenyl, sec-butenyl, n-pentenyl, 1,1-dimethylpropenyl, 1,2-dimethylpropenyl, 1- ethylpropenyl, 2-ethylpropenyl, n-hexenyl and l-methyl-2-ethylpropenyl.

[0060] The term "alkynyl" means any hydrocarbon radical having at least one carboncarbon triple bond and is intended to include both straight- and branched-chain alkynyl groups. Examples of alkynyl groups include, but are not limited to, ethynyl, n-propynyl and n-butynyl.

[0061] The term "aryl" means an aromatic radical having 5 to 12 carbon atoms and includes optionally substituted aryl radicals. Examples include monocyclic groups, as well as fused groups such as bicyclic groups and tricyclic groups. Examples include, but are not limited to, phenyl, 1-naphthyl, 2-naphthyl and biphenyl. Optional substituents for aryl radicals include, but are not limited to, halide substituents such as bromine, chlorine, fluorine, and iodine; alkyl substituents such as methyl, ethyl, and propyl; and alkoxy substituents such as methoxy and ethoxy.

[0062] The term "heteroaryl" means an aryl group where one or more carbon atoms has been replaced by an atom other than carbon, such as nitrogen, oxygen or sulfur.

[0063] The term "alkoxy" means an OR group, where R is alkyl as defined above.

[0064] The term "acyl" means a -(C=O)R group, where R is alkyl, alkenyl, alkynyl, aryl as defined above.

[0065] The term "acyloxy" means an -O(C=O)R group, where R is alkyl, alkenyl, alkynyl, aryl as defined above.

[0066] The term "aryloxy" means an OR group, where R is aryl as defined above.

[0067] The term "alkylene" means a diradical corresponding to an alkyl group and is intended to include straight chain alkyl groups. Examples of alkylene groups include, but are not limited to, methylene and ethylene.

[0068] The term "amidine" means a group having the general structure -C(=NH)-NH2, -C(=NH)-NHR, -C(=NH)-NRR, -C(=NR)-NH2, -C(=NR)-NHR, or -C( = NR)-NRR where each R is typically an alkyl group.

[0069] The term "hydroxy amidine", also known as an / V'-hydroxycarbamimidoyl group, means a group having the general structure -C(=N-OH)-NH2, -C(=N-OH)-NHR, or -C(=N-OH)-NR2 where each R is typically an alkyl group.

[0070] The term "carboxime" means a group having the general structure -C(=N-OH)-H.

[0071] The term "protecting group" means a group that selectively protects an organic functional group, temporarily masking the chemistry of that functional group and allowing other sites in the molecule to be manipulated without affecting the functional group. Suitable protecting groups are known to those skilled in the art and are described, for example, in Protective Groups in Organic Synthesis (3rdEd.), T. W. Greene and P. G. M. Wuts, John Wiley & Sons Inc (1999). Examples of protecting groups include, but are not limited to, O-benzyl, O-benzhydryl, O-trityl, O-t-butyldimethylsilyl, O-t-butyldiphenylsilyl, 0-4-methylbenzyl, O-acetyl, O-chloroacetyl, O-methoxyacetyl, O-benzoyl, 0-4- bromobenzoyl, 0-4-methylbenzoyl, O-fluorenylmethoxycarbonyl and O-levulinoyl.

[0072] The term "side group of a natural amino acid" means the 2-substituent of a naturally occurring amino acid. Examples are a methyl (alanine), propan-2-yl (valine), propan-l-yl (norvaline), 2-methylpropan-l-yl(leucine), 1-methylpropan-l-yl (isoleucine), butan-l-yl (norleucine), tert-butyl (2-tert-butylglycine), phenyl (2-phenylglycine), benzyl (phenylalanine), p-hydroxybenzyl (tyrosine), indol-3-ylmethyl (tryptophan), imidazol-4- ylmethyl (histidine), hydroxymethyl (serine), 2 -hydroxyethyl (homoserine), 1- hydroxyethyl (threonine), mercaptomethyl (cysteine), methylthiomethyl (S-methylcysteine), 2- mercaptoethyl (homocysteine), 2-methylthioethyl (methionine), carbamoylmethyl (asparagine), 2-carbamoylethyl (glutamine), carboxymethyl (aspartic acid), 2 -carboxyethyl (glutamic acid), 4-aminobutan-l-yl (lysine), 4-amino-3-hydroxybutanl-yl (hydroxylysine), 3-aminopropan-l-yl(ornithine), 3-guanidinopropan-l-yl (arginine), 3-ureidopropan-l-yl (citrulline). Preferred -a mi no acid side groups are methyl (alanine), propan-2-yl (valine), 2- methylpropan-l-yl (leucine), benzyl (phenylalanine), imidazol-4-ylmethyl (histidine), hydroxymethyl (serine), 1- hydroxyethyl (threonine), 4-aminobutan-l-yl(lysine), 3- aminopropan-l-yl (ornithine), 2-aminoethyl (2,4-diaminobutyric acid), aminomethyl (2,3- diaminopropionic acid), 3-guanidinopropan-l-yl (arginine).

[0073] The term "tautomer" means compounds that can exist as two or more interconvertable species. Tautomers generally exist in equilibrium and attempts to isolate an individual tautomer usually produces a mixture whose chemical and physical properties are consistent with a mixture of compounds. The position of the equilibrium is dependent on chemical features within the molecule. One example of tautomerism is indicated below showing hydroxy- and oxo-tautomers.

[0074] The term "pharmaceutical composition" means a mixture of one or more of the compounds of the invention, or pharmaceutically acceptable salts, or hydrates thereof, with other chemical components, such as physiologically acceptable carriers and excipients. The purpose of a pharmaceutical composition is to facilitate administration of a compound to an organism.

[0075] The term "carrier" refers to a diluent, adjuvant, excipient, or vehicle with which a compound is administered. Non-limiting examples of such pharmaceutical carriers include liquids, such as water and oils, including those of petroleum, animal, vegetable or synthetic origin, such as peanut oil, soybean oil, mineral oil, sesame oil and the like. The pharmaceutical carrier may also be saline, gum acacia, gelatin, starch paste, talc, keratin, colloidal silica, urea, and the like. In addition, auxiliary, stabilizing, thickening, lubricating, and colouring agents may be used. Other examples of suitable pharmaceutical carriers are described in "Remington's Pharmaceutical Sciences" by E.W. Martin, herein incorporated by reference.

[0076] The term "pharmaceutically acceptable salt" refers to any salt of a compound provided herein which retains its biological properties and which is not toxic or otherwise undesirable for pharmaceutical use and is intended to include salts derived from inorganic or organic acids including, for example hydrochloric, hydrobromic, sulfuric, nitric, perchloric, phosphoric, formic, acetic, lactic, maleic, fumaric, succinic, tartaric, glycolic, salicylic, citric, methanesulfonic, benzenesulfonic, benzoic, malonic, trifluoroacetic, trichloroacetic, naphthalene-2 sulfonic and other acids. Pharmaceutically acceptable salt forms may also include forms wherein the ratio of molecules comprising the salt is not 1: 1. For example, the salt may comprise more than one inorganic or organic acid molecule per molecule of base, such as two hydrochloric acid molecules per molecule of compound of formula (I).

[0077] The terms "treatment", "treating" and the like include the alleviation of one or more symptoms, or improvement of a state associated with the disease or disorder.

[0078] The terms "preventing", "prevention" and the like include the prevention of one or more symptoms associated with the disease or disorder.

[0079] Synthesis of compounds

[0080] The compounds of the invention may be prepared by any suitable method. One suitable method involves addition of a heterocyclic Grignard reactant to a suitably substituted nitrone. For example, Scheme 1 below outlines the synthesis of thienopyrimidine imino-C-nucleosides:

[0081]

[0082] Scheme 1

[0083] Addition to nitrone A-l of a suitable organometallic derivative of iodide A-2 can afford hydroxylamine A-3. Reduction of the hydroxylamine functionality followed by protection with a suitable protecting group can afford thienopyrimidines A-4. Treatment of A-4 with an excess of an amine HNR4R5can afford A-5 that can be deprotected to yield compounds of the invention A-6. Alternatively, A-5 can be further substituted at the 5- position of the aromatic heterocycle through iodination, chlorination, bromination, or fluorination. Then, as required, further substituted by suitable palladium-mediated coupling reactions with suitable reacting partners to afford intermediates A-7. A-7 can be deprotected to yield compounds of the invention A-8. Alternatively, A-7 can be selectively deprotected at the 5'-position to form alcohol A-9, which can then be acylated to form ester

[0084] A-1O (where R1= R6CO). Deprotection yields compounds of the invention A-ll.

[0085] Alternatively, alcohol A-9 can be converted to triol A-12 that can be selectively acylated or alkylated at R1, R2and / or R3using a suitable protecting-group strategy.

[0086] Scheme 2

[0087] Thiophene ester A-14 can be condensed with a suitable nucleophile to afford fused heterocycles A-15 where A can be an alkyl-, hydroxy- or amino-substitution. When A is a hydroxy-group in A-15 (or its equivalent tautomeric form), it can be converted to chlorosubstituents where the chloro at the 4-position can be selectively substituted with amines HNR4R5to afford thienopyrimidines A-16. Alternatively in A-15; where A is NH2, the amino-group can be substituted by a suitable fluoride nucleophile via diazotization to afford A-16 with A = a fluoro-substituent. Heterocycles A-16 can be iodinated to afford the pro-nucleophile A-17 suitable for organometallic addition to nitrone A-l to afford hydroxylamines A-18. Compounds of the invention A-19 can be prepared from hydroxylamines A-18 by the transformations described for A-3 outlined above in Scheme 1.

[0088] The following are specific examples of the synthesis of thieno[3,4-cf]pyrimidine iminovir compounds.

[0089]

[0090] Scheme 3 Reagents and conditions-, a) formamidinium acetate, EtOH, A, 16 h, 89%; b) Lawesson's reagent, toluene, 4-16 h, A; c) 40wt% NaOH, 0 °C, pH >12; d) Mel, 0 °C, 2 h. 73% over three steps; e) NIS, DMF, 40 h, 75%; f) iodide 8, 1.3 M i-PrMgCI ■ LiCI in THF, -16 °C, nitrone A-l, THF, 83%; g) Mo(CO)6, MeCN, A, 16 h; h) BoczO, NEt3, 2-24 h. 46% over two steps; i) 7 N NH3 in MeOH, 70 °C, sealed tube, 16 h. 51% (35% r.s.m); j)

[0091] 1 : 1 v / v 2 N HCI / THF, 2 h. 23 °C, cone, in vacuo at 40 °C, 57%.

[0092] Amino-thiophene 5 was efficiently condensed with formamidinium acetate in ethanol under reflux overnight. Pyrimidone 6 was isolated by filtration, dried, then converted to a crude pyrimidin-4-thione with Lawesson's reagent, converted to its sodium salt with concentrated sodium hydroxide, and methylated with iodomethane to afford thioether 7. Conversion to iodide 8 was achieved with NIS in DMF. The anhydrous iodide 8 was treated with 'Turbo-Grignard' reagent at low temperature followed by addition of nitrone A-l.25The resulting hydroxylamine A-3 was reduced with molybdenum hexacarbonyl in acetonitrile under reflux and the intermediate amine protected with Boc-anhydride to afford carbamate 9. The thioether was displaced in methanolic ammonia at elevated temperature in a sealed tube to afford 4-amino-thienopyrimidine 10. Final deprotection was achieved with 1: 1 v / v HCI aq. / THF to afford the bis(hydrochloride) salt of compound 3 as a light-yellow solid.

[0093] sealed tube, 40 min, 90%; b) 10 equiv. azetidine, in abs. ethanol, 80 °C, microwave, 30 min. 93%; c) 1 : 1 v / v 2 N HCI / EtOH or 1,4-dioxane, 2 h., 23 °C, cone, in vacuo at 40 °C,

[0094] 12: 89%, 14: 70%.

[0095] Thioether 9 was reacted with methylamine and azetidine in ethanol at elevated temperature in sealed tubes to afford 4-methylamino-thienopyrimidine 11 and 4-azetidinyl- thienopyrimidine 13, respectively. Deprotection was achieved with 1: 1 v / v HCI aq. / EtOH (1,4-dioxane was used in place of ethanol for azetidine 13) to afford the bis(hydrochloride) salts of compound 13 and 14 as light-yellow solids.

[0096] Scheme 5 Reagents and conditions-, a) 1 M TBAF, THF, 16 h., 93%; b) excess isobutyryl anhydride, 4-DMAP, DCM, 16 h. 73%; c) MeOH, sealed tube, 105 °C, 3 h. 82%; d) 1 : 1 v / v 2 N HCI I 1,4-dioxane, 2 h. 23 °C, cone, in vacuo at 40 °C, 18: 67%; in a ~7 : 3 ratio of ester 18 : 3 alcohol.

[0097] Silyl ether 10 was deprotected with excess TBAF in THF to afford alcohol 15. To avoid formation of a mixture of acylated products, alcohol 15 was treated with excess isobutyryl anhydride to afford the double acylated ester 16 in high yield. Subsequent heating of amide 16 in methanol under pressure selectively formed amino-ester 17 in high yield. Final deprotection was achieved with 1: 1 v / v HCI aq. / 1,4-dioxane to afford the bis(hydrochloride) salts of ester 18 and the free alcohol 3, in a circa 7:3 ratio, that could be readily separated by flash chromatography.

[0098] Scheme 6: Reagents and conditions-, a) 1.0 equiv. 1,3,5-trichoroisocyanuric acid, CHCI3, 16 h. 19, 53%; b) 1.0 equiv. 1,3-dibromoisocyanuric acid, CHCI3, 16 h. 20, 20%; c) 6 equiv. / V-iodosuccinimide, 5 equiv. AcOH, CHCI3, 16 h. 21, 53%; d) 1 : 1 v / v 2 N HCI I THF, 2 h. 23 °C, cone, in vacuo at 40 °C, 22: 57%, 23: 59%, 24: 60%.

[0099] 4-Amino-thienopyrimidine 10 was halogenated with the use of the appropriate electrophilic reagents: Strict control of stoichiometry was required for chlorination and bromination, with 1,3,5-trichloroisocyanuric acid and 1,3-dibromocyanuric acid respectively, to avoid over oxidation or decomposition of the desired halides 19 and 20. Iodination with multiple equivalents of / V-iodosuccinimide (NIS) with glacial acetic acid was required to form iodide 21 in good yield. No overoxidation was observed in this case. Standard deprotection conditions afforded the three 5-halo-species 22, 23 and 24 as their bis-hydrochloride salts.

[0100]

[0101] Scheme 7: Reagents and conditions-, a) Zn(CN)2, Pc dbas, Xantphos, DMF, 60 °C, 30 min. microwave, 83%; B) 30wt% H2O2, K2CO3, DMSO, 30 mins, 66%; C) hydroxylamine. HCI, NEts, EtOH, 2 h, 80 °C, microwave, 20%; d) 1: 1 v / v 2 N HCI I THF, 2 h. 23 °C, cone, in vacuo at 40 °C, 26: 97%, 29: 85%, 30: 99%.

[0102] Iodide 21 was the subject of further elaboration using palladium coupling chemistry: In the first instance, a Negishi cross coupling reaction with zinc cyanide afforded 5-cyano- thienopyrimidine 25 in good yield. Facile hydrolysis of nitrile 25 to carboxamide 28 was achieved with 30wt% H2O2 in DMSO with K2CO3. Treatment of nitrile 25 with hydroxylamine also afforded / V-hydroxy amidine 27 in good yield. The established deprotection conditions were applied to nitrile 25, carboxamide 28, and hydroxy amidine 27 to afford iminoribitol test compounds 26, 29, and 30 as their hydrochloride salts.

[0103]

[0104] Scheme 8: Reagents and conditions-, a) 31, Pd(PPh3)2Cl2, DMF, 120 °C, 30 min. microwave, 32: 44%, 33: <56%; b) excess 1.0 M TBAF in THF, 16 h., 47%; c) 1: 1 v / v 2 N HCI / THF, 2 h. 23 °C, cone, in vacuo at 40 °C, 98%.

[0105] Attempts to extend the substrate scope of palladium coupling chemistry with iodide 21 to heterocyclic coupling partners were unsuccessful under Suzuki conditions. However, Stille coupling with heteroaryl-stannane 31 afforded a mixture of the de-tritylated imidazole 32 and trityl-protected 33. Deprotected imidazole 32 was de-silylated with excess TBAF in THF, to further assist in organotin removal and afford alcohol 34. The standard acidic deprotection afforded iminoribitol salt 35 as a dark-brown powder.

[0106] Antiviral activity

[0107] Compound 3 was found to be an excellent candidate for further development as a broad-spectrum agent, displaying sub-micromolar inhibition against Rift Valley Fever Virus (RVFV), Yellow Fever Virus (YFV), Zika Virus (ZIKV), Dengue Virus 2 (DENV-2), SARS Coronavirus 2 (SARS-CoV-2), Influenza A Virus (IAV) with good selectivity index (SI50) values of between 13 to 240 (Tables 1 and 2). Of note is the performance of compound 3 against broader influenza strains. For example, the EC90 values of compound 3 against IAV H5N1, IAV H3N2 and IBV are <32 nM, 43 nM and 120 nM respectively with good SI90 values of >690, 698 and 210, respectively. Low micromolar activity was exhibited against Junin virus (JUNV) and Enterovirus D68 (EV-D68). Low micromolar activity was observed against Middle Eastern Respiratory Virus (MERS) albeit with a low SI50 of 4.5. Low micromolar inhibition observed with West Nile Virus (WNV), and Respiratory Syncytial Virus (RSV) with low selectivity indices.

[0108] Table 1: Antiviral activity of compound 3 and iminovirs A, B and C aECso (in piM).bNo CC50 data given. Tested on IAV H1N1 (Strain A / WSN / 33) with the RPMI 2650 cell line at 500 p.M (see ref 29). Tested on PS cell line.

[0109] The new thienopyrimidine-scaffold of compound 3 has activity superior to that of the known iminovirs A26(galidesivir) and B27(an isomer of galidesivir) (see Table 1) with equivalent to superior selectivity indices. In other words, compound 3 is more potent and less toxic than iminovirs A and B, respectively. This is the right direction for the development of an antiviral agent. The comparison of iminovir C28with iminovir B illustrates how the activity and selectivity index of the broader iminovir class can be improved further through substitutions on the nucleobase moiety.

[0110] An important advantage of this class of compounds is that the thienopyrimidine scaffold possesses multiple accessible positions for substitutions and therefore facilitates the synthesis of a variety of compounds of this type. Alterations at the C-2, C-5, and C-4-NH2 positions increases the scope for novel compounds. See below for numbering in compound 3.

[0111] A number of additional compounds having the above thienopyrimidine scaffold were also found to be very active against a range of viruses. These include compounds 12, 18, 24, 29, 30 and 35. See Examples 9 to 14.

[0112] Compared with compound 3, Compound 24 displayed an improved safety profile in cell-based assays with CC50 values of greater than 100 pM, while retaining high activity against certain viruses like IAV H1N1 and DENV with EC90 values of 0.36 pM and 1.03 pM respectively (Example 9). Compound 29 exhibited strong activity against RSV with an EC90 value of 230 nM and an SI90 value of 360 (Example 10). Compound 18 was active against IAV H1N1 and DENV with EC50 values of 0.38 pM and 0.30 pM respectively, with corresponding SI50 values of 110 and >330 respectively (Example 11). Compound 12 was found to be highly active against RSV with an EC90 value of 1.3 pM and an SI90 value of 360 (Example 12). Compounds 30 and 35 exhibited good antiviral activity against IAV H1N1 with EC50 values of 1 pM and 7.9 pM respectively. Compounds 30 and 35 also exhibited antiviral activity against and RSV, with EC50 values of 30 pM and 18 pM respectively. See Examples 13 and 14.

[0113] Formulations and administration

[0114] The compounds of the invention may be administered to a patient by a variety of routes, including orally, parenterally, by inhalation spray, topically, rectally, nasally, buccally or via an implanted reservoir. For parenteral administration, injections may be given intravenously, intra-arterially, intramuscularly, or subcutaneously.

[0115] The amount of a compound of the invention to be administered to a patient will vary widely according to the nature of the patient and the nature and extent of the disorder to be treated. Typically, the dosage for an adult human will be in the range of about 0.01 pg / kg to about 1 g / kg, and preferably about 0.01 mg / kg to about 100 mg / kg. The specific dosage required for any particular patient will depend upon a variety of factors, such as the patient's age, body weight, general health, gender, and diet. Optimal doses will depend on other factors such as mode of administration and level of progression of the disease or disorder. Doses may be given once daily, or two or more doses may be required per day. For example, a dosage regime for a patient might require one dose in the morning and one in the evening. Alternatively, a dosage regime for such a patient might require four hourly doses.

[0116] For oral administration the compounds can be formulated into solid or liquid preparations, for example tablets, capsules, granules, powders, solutions, suspensions, syrups, elixirs and dispersions. Such preparations are well known in the art as are other oral dosage regimes not listed here.

[0117] For parenteral administration, compounds of the invention can be formulated into sterile solutions, emulsions and suspensions.

[0118] Compounds of the invention may be mixed with suitable vehicle and then compressed into the desired shape and size. The compounds may be tableted with conventional tablet bases such as lactose, sucrose, and corn starch, together with a binder, a disintegration agent and a lubricant. The binder may be, for example, corn starch or gelatin, the disintegrating agent may be potato starch or alginic acid, and the lubricant may be magnesium stearate. For oral administration in the form of capsules, diluents such as lactose and dried cornstarch may be employed. Other components such as colourings, sweeteners or flavourings may be added. Tablets, capsules, or powders for oral administration may contain up to about 99% of a compound of the invention.

[0119] When liquid preparations are required for oral use, a compound of the invention may be combined with a pharmaceutically acceptable carriers such as water, an organic solvent such as ethanol, or a mixture of both, and optionally other additives such as emulsifying agents, suspending agents, buffers, preservatives, and / or surfactants may be used. Colourings, sweeteners, or flavourings may also be added.

[0120] The compounds may also be administered by injection in a pharmaceutically acceptable diluent such as water or saline. The diluent may comprise one or more other ingredients such as ethanol, propylene glycol, an oil, or a pharmaceutically acceptable surfactant. The compounds of the invention may also be administered topically. Carriers for topical administration of the compounds include mineral oil, liquid petrolatum, white petrolatum, propylene glycol, polyoxyethylene, polyoxypropylene compound, emulsifying wax and water. The compounds may be present as ingredients in lotions or creams, for topical administration to skin or mucous membranes. Such creams may contain the active compounds suspended or dissolved in one or more pharmaceutically acceptable carriers. Suitable carriers include mineral oil, sorbitan monostearate, polysorbate 60, cetyl ester wax, cetearyl alcohol, 2-octyldodecanol, benzyl alcohol, and water.

[0121] The compounds of the invention may further be administered by means of sustained release systems. For example, they may be incorporated into a slowly dissolving tablet or capsule.

[0122] * * * *

[0123] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0124] The invention is further described with reference to the following Examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these Examples.

[0125] EXAMPLES

[0126] Example 1: Preparation of (lR)-l-(4-Aminothieno[3,4-d]pyrimidin-7-yl)-l,4- dideoxy-l,4-imino-D-ribitol bis( hydrochloride) (3)

[0127] Example 1.1: Thieno[3,4-d]pyrimidin-4(3H)-one (6)

[0128] Methyl 4-aminothiophene-3-carboxylate hydrochloride 5 (5.1 g, 24.6 mmol) and formamidinium acetate (8.3 g, 79.7 mmol, 3.2 equiv.) were heated under reflux in abs. ethanol (50 mL) for 16 hours. After cooling to room temperature, the precipitate was removed by filtration and washed with ethanol (x 5). The filtrate was concentrated in vacuo and triturated with deionised water to afford a second crop of product. The combined solids were washed with water and dried under high vacuum to afford the title compound as an olive green solid (3.33 g, 89%).XH NMR (500 MHz, DMSO) 6 11.63 (s, 1H), 8.46 (d, J = 3.3 Hz, 1H), 7.79 (d, J = 3.3 Hz, 1H), 7.78 (s, 1H).13C NMR (126 MHz, DMSO) 6 157.8, 148.5, 143.7, 127.8, 126.4, 118.2. HRMS: (ESI) m / z calculated for (C6H5N2O2S+): 153.0117

[0129] Found: 153.0121; m / z calculated for (C6H4N2O2SNa+): 174.9937 Found: 174.9939

[0130] Example 1.2: 4-(Methylthio)thieno[3,4-d]pyrimidine (7)

[0131] 6 7

[0132] Lawesson's reagent (27.5 g, 68 mmol) was added to a slurry of thieno[3,4- cf]pyrimidin-4(3H)-one 6 (7.0 g, 46 mmol, 1.5 equiv.) in anhydrous toluene (200 mL) under an argon atmosphere. The mixture was heated under reflux for 16 hours, cooled to room temperature, then concentrated in vacuo at 40 °C to afford an amber-tinted white solid. Residual volatiles were removed under high vacuum, the solids were suspended in deionised water (320 mL), and the slurry cooled to 0 °C for 10 mins. Freshly made 40wt% NaOH (50 mL) was slowly added to pH 14, with solid residue attached to the flask wall mechanically removed into suspension. The result was a diminishment of suspended solids within a dark brown aqueous solution. The brown slurry was filtered through diatomaceous earth to remove precipitates. lodomethane (5.0 mL, 80 mmol, 1.75 equiv.) was added to the filtrate in one portion with vigorous stirring. After two hours, the precipitate formed was isolated by filtration and dried under high vacuum overnight to afford the title compound 7 as an off- white solid (6.1 g, 73%).XH NMR (500 MHz, CDCI3) 6 8.65 (s, 1H), 8.01 (d, J = 3.3 Hz, 1H), 7.83 (dd, J = 3.3, 0.5 Hz, 1H), 2.70 (s, 3H).13C NMR (126 MHz, CDCI3) 6 168.2, 151.8, 148.2, 127.5, 120.0, 117.7, 12.0. HRMS: (ESI) m / z calculated for (C7H7N2S2+): 183.0045 Found: 183.0053

[0133] Example 1.3: 7-Iodo-4-(methylthio)thieno[3,4-d]pyrimidine (8)

[0134] / V-Iodosuccinimide (5.71 g, 25.4 mmol, 1.1 equiv.) was added to a 4-(methylthio)thieno[3,4-cf]pyrimidine 8 (4.08 g, 22.4 mmol) in anhydrous DMF (50 mL) under an argon atmosphere. After 40 hours, the reaction mixture was poured onto a solution of excess Na2SO3 in 0.01 M NaOH aq. (400 mL). The precipitate was isolated by filtration and washed with deionised water (x 3). The solids were partially dissolved in chloroform, filtered through diatomaceous earth, and concentrated in vacuo to afford the title compound 8 as a bronze-coloured solid (5.16 g, 75%).XH NMR (500 MHz, CDCI3) 6 8.74 (s, 1H), 8.29 (s, 1H), 2.71 (s, 3H).13C NMR (126 MHz, CDCI3) 6 168.7, 152.9, 150.1, 127.5, 125.9, 71.6, 12.2. HRMS: (ESI) m / z calculated for (C7H6N2S2I+): 308.9012 Found:

[0135] 308.9015

[0136] Isopropylmagnesium chloride-lithium chloride complex (1.40 mL, 1.8 mmol, 1.7 equiv.) was added dropwise over four minutes to a solution of 7-iodo-4- (methylthio)thieno[3,4-cf]pyrimidine 8 (523 mg, 1.7 mmol, 1.6 equiv.) in anhydrous THF (20 mL) at -16 °C. Nitrone A-l (320 mg, 1.06 mmol) in THF (5 mL) was added by syringe pump over three minutes. After 12 minutes additional reaction time, TLC analysis confirmed full consumption of the nitrone. The reaction was removed from the cooling bath then quenched by the rapid addition of saturated NH4CI aq. The organic phase was separated from the aqueous phase and the aqueous material further extracted with ethyl acetate three times. The combined organic phases were dried over MgSCk and concentrated in vacuo to afford a dark brown viscous oil. The crude material was purified by automated by reversephase, flash column chromatography (gradient elution, 10-100% MeCN in water on C-18, loaded as DMSO solution) to afford the title compound A-3 as a yellow foam (426 mg, 83%).XH NMR (500 MHz, CDCI3) 6 8.52 (s, 1H), 7.86 (s, 1H), 7.17 (s, 1H), 4.82 - 4.76 (m, 1H), 4.56 - 4.47 (m, 2H), 3.90 - 3.82 (m, 2H), 3.29 - 3.21 (m, 1H), 2.60 (s, 3H), 1.55 (d, J = 0.7 Hz, 3H), 1.25 (d, J = 0.7 Hz, 3H), 0.82 (s, 9H), 0.02 (s, 3H), 0.00 (s, 3H).13C NMR (126 MHz, CDCI3) 6 168.6, 151.2, 144.6, 135.4, 128.3, 128.2, 118.5, 114.0, 83.3, 77.9, 73.5, 71.3, 62.3, 27.4, 25.9, 25.4, 18.4, 12.0, -5.2, -5.3. HRMS: (ESI) m / z calculated for (C2iH34N3O4S2Si+): 484.1755 Found: 484.1776

[0137] Example 1.5: (lR)-N-tert-Butyloxycarbonyl-l-(4-(methylthio)thieno[3,4-d]pyrimidin-7-yl)- 5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (9)

[0138] Hydroxylamine A-3 (425 mg, 0.88 mmol) was dissolved in LCMS-grade acetonitrile

[0139] (30 mL) in a 100 mL round bottom flask. Molybdenum hexacarbonyl (369 mg, 1.7 mmol, 1.9 equiv.) was added in one portion and the slurry was sparged with argon, through an immersed needle, while under sonication for 10 minutes. An argon flushed condenser was fitted to the flask and the reaction was heated under reflux overnight. Reaction monitoring by LCMS was used to confirm complete reduction to the intermediate amine. BoczO (270 mg, 1.2 mmol, 1.4 equiv.) was added in a single portion under argon with the reaction mixture stirred for 64 hours. After confirmation of reaction completion by LCMS, the reaction mixture was concentrated in vacuo to afford a dark brown glassy solid. The material was re-suspended in ethyl acetate, with insoluble material removed by filtration through diatomaceous earth, and concentrated in vacuo to afford a dark amber oil. The crude material was purified by automated reverse-phase, flash column chromatography (gradient elution 10-100% MeCN in water on C-18, loaded as DMSO solution) to afford the title compound 9 as a colourless oil (229 mg, 46%).XH NMR (500 MHz, CDCI3) Rotamers: 6 8.65 (s, 1H), 7.85 (s, 1H), 5.70 (d, J = 2.2 Hz, 1H), 5.49 - 5.11 (m, 1H), 4.97 - 4.76 (m, 1H), 4.39 - 4.14 (m, 1H), 3.94 - 3.61 (m, 2H), 2.69 (s, 3H), 1.63 - 1.55 (m, 3H), 1.54 - 1.42 (m, 4H), 1.39 (s, 3H), 1.36 - 1.19 (m, 5H), 0.82 (s, 9H), 0.06 - -0.07 (m, 6H).13C NMR (126 MHz, CDCI3) Rotamers: 6 168.0, 154.2, 150.9, 143.5, 137.9, 128.2, 116.8, 112.1, 86.6, 81.9, 80.6, 66.0, 64.0, 63.1, 28.3, 27.5, 25.9, 25.6, 18.3, 11.9, -5.3, -5.4. HRMS: (ESI) m / z calculated for (C26H42N3O5S2Si+): 568.2330 Found: 568.2332

[0140] Example 1.6: (lR)-N-tert-Butyloxycarbonyl-l-(4-aminothieno[3,4-d]pyrimidin-7-yl)-5-O- tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (10)

[0141] Methyl thioether 9 (190 mg, 0.33 mmol) was dissolved in 7 N methanolic ammonia (25 mL, 175 mmol, 530 equiv.) in a sealed tube and heated to 65 °C over 21 hours. Monitoring by LCMS indicated a circa 2: 1 ratio of product to starting material. The solution was concentrated in vacuo at 40 °C and the product separated from the mixture by automated normal-phase, flash column chromatography (gradient elution 10-100% EA in PE on SiO2, loaded as CHCI3 solution) to afford returned starting material (67 mg, 35%) and the title compound 10 as a colourless oil (91 mg, 51%).XH NMR (500 MHz, CDCI3) Rotamers: 6 8.35 - 8.10 (m, 1H), 7.89 - 7.52 (m, 1H), 6.32 (v. br. s, 2H), 5.80 - 5.56 (m, 1H), 5.30 - 5.06 (m, 1H), 4.84 (dd, J = 5.8, 1.2 Hz, 1H), 4.34 - 4.05 (m, 1H), 3.81 (dd, J = 9.9, 4.3 Hz, 1H), 3.79 - 3.67 (m, 1H), 1.55 (s, 3H), 1.53 - 1.38 (m, 5H), 1.35 (s, 3H), 1.33 - 1.11 (m, 4H), 0.83 (s, 9H), 0.01 (br. s, 6H).13C NMR (126 MHz, CDCI3) Rotamers: 6 157.9, 154.5, 154.3, 153.2, 145.6, 135.8, 133.6, 120.7, 117.0, 116.6, 112.0, 86.3, 85.4, 82.4, 81.9, 80.8, 80.5, 66.4, 66.0, 63.6, 63.0, 28.4, 28.3, 27.5, 27.4, 25.9, 25.5, 18.3, -5.30, -5.35. Underlined peaks are rotameric pairs. HRMS: (ESI) m / z calculated for (C25H4iN4O5SSi + ): 537.2561 Found: 537.2563

[0142] Example 1.7: (lR)-l-(4-Aminothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4-imino-D-ribitol bis(hydrochloride) (3)

[0143] Carbamate 10 (26.9 mg, 50 pmol) was dissolved in THF (6 mL) with freshly prepared 2 M HCI aq. (6 mL) added dropwise with vigorous stirring. After two hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight. A minor impurity (circa 5 mol%) was removed by automated reverse-phase, flash column chromatography (isocratic elution, 10% MeCN in water on C-18, 20 g, loaded as H2O / D2O solution), collecting the cleanest fraction, to afford the title compound 3 as a light-yellow powder (10.1 mg, 57%).XH NMR (500 MHz, D2O) 6 8.97 (d, J = 0.9 Hz, 1H), 8.25 (d, J = 0.9 Hz, 1H), 5.42 (d, J = 8.7 Hz, 1H), 4.88 (ddd, J = 9.1, 4.9, 0.9 Hz, 1H), 4.50 (dd, J = 4.9, 2.9 Hz, 1H), 4.04 - 3.97 (m, 3H).13C NMR (126 MHz, D2O) 6 153.8, 144.2, 143.3, 130.7, 124.7, 117.5, 75.0, 70.8, 66.1, 58.5, 56.9. HRMS: (ESI) m / z calculated for (C11H15N4O3S+): 283.0859 Found: 283.0859

[0144] Example 2: Preparation of (lR)-l-[4-(Methylamino)thieno[3,4-d]pyrimidin-7-ylJ- l,4-dideoxy-l,4-imino-D-ribitol bis(hydrochloride) (12) and (lR)-l-[4-(Azetidin-l-yl)thieno[3,4-d]pyrimidin-7-yl]-l,4-dideoxy-l,4-imino-D- ribitol bis(hydrochloride) (14)

[0145] Example 2.1.1: (lR)-N-tert-Butyloxycarbonyl-l-[4-(methylamino)thieno[3,4-d]pyrimidin-7- yl]-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (11)

[0146] Methyl thioether 9 (55 mg, 0.1 mmol) was dissolved in 33wt% methylamine in absolute ethanol (3.5 mL, 37 mmol, 370 equiv.) and heated in a microwave reactor at 80 °C for 40 mins. The solution was concentrated in vacuo at 40 °C and the product purified by automated normal-phase, flash column chromatography (gradient elution 10-100% EA in PE on SiO2, loaded as CH2CI2 solution) to afford the title compound 11 as a colourless solid (48 mg, 90%).XH NMR (500 MHz, CDCI3) 6 8.50 - 8.22 (m, 1H), 7.79 - 7.29 (m, 1H), 6.66 - 5.81 (m, 1H), 5.67 (s, 1H), 5.29 - 4.98 (m, 1H), 4.85 (dd, J = 5.9, 1.2 Hz, 1H), 4.41 - 4.05 (m, 1H), 3.82 (dd, J = 9.9, 4.4 Hz, 1H), 3.79 - 3.71 (m, 1H), 3.22 - 3.00 (m, 3H), 1.56 (s, 3H), 1.54 - 1.39 (m, 5H), 1.35 (s, 3H), 1.33 - 1.19 (m, 4H), 0.90 - 0.74 (m, 9H), 0.12 - -0.09 (m, 2 x 3H).13C NMR (126 MHz, CDCI3)13C NMR (126 MHz, CDCI3) 6 156.9, 154.6, 153.9, 145.4, 121.5, 114.9, 114.6, 112.0, 85.4, 82.4, 80.7, 66.4, 63.5, 63.0, 28.4, 27.9, 27.5, 25.9, 25.5, 18.3, -5.28, -5.33. Underlined peaks are rotameric pairs. One quaternary 13C signal was not observed by NMR. LRMS done: (ESI) m / z calculated for (C26H43N4O5SSi+): 551.3 Found: 551.2

[0147] Example 2.1.2: (1R)-1 -[4-(Methylamino)thieno[3,4-d]pyrimidin-7-yl]-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (12)

[0148] Carbamate 11 (30 mg, 54 pmol) was dissolved in EtOH (6 mL) with freshly prepared 2 M HCI aq. (6 mL) added dropwise with vigorous stirring. After an hour, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 12 as a light-yellow powder (18 mg, 89%). 1H NMR (500 MHz, D2O) 6 8.83 (d, J = 1.0 Hz, 1H), 8.31 (d, J = 1.1 Hz, 1H), 5.41 (dd, J = 9.1, 1.1 Hz, 1H), 4.89 - 4.81 (m, 3H), 4.49 (dd, J = 4.8, 2.6 Hz, 1H), 4.05 - 3.96 (m, 3H), 3.30 (d, J = 1.1 Hz, 3H).13C NMR (126 MHz, D2O) 6 153.3, 144.7, 142.1, 129.2, 123.5, 118.1, 75.1, 70.8, 66.2, 58.5, 56.7, 28.8. HRMS: (ESI) m / z calculated for (C12H17N4O3S+) : 297.1016 Found: 297.1016 Example 2.2.1 : (lR)-N-tert-Butyloxycarbonyl-l-[4-(azetidin-l -yl)thieno[3,4-d]pyrimidin-7- yl]-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (13)

[0149] Methyl thioether 9 (53 mg, 0.1 mmol) was dissolved in anhydrous ethanol (1.5 mL) under argon in a microwave reaction vial. Azetidine (100 ptL, 1.5 mmol, 15 equiv.) was added by autopipette, immediately forming a red-amber solution. The reaction was heated in a microwave reactor at 80 °C for 30 mins. The resulting light-yellow solution was concentrated in vacuo at 40 °C and the product purified by automated normal-phase, flash column chromatography (gradient elution 10-100% EA in PE on SiO2, loaded as CH2CI2 solution) followed by automated reverse-phase, flash column chromatography (gradient elution 10-100% MeCN in H2O on C-18, loaded as DMSO solution) to afford the title compound 13 as a light-amber oil (50 mg, 93%).XH NMR (500 MHz, CDCI3) 6 8.26 (s, 1H), 7.59 (s, 1H), 5.60 (d, J = 2.0 Hz, 1H), 5.54 - 5.09 (m, 1H), 4.97 - 4.78 (m, 1H), 4.78 - 4.32 (m, 4H), 4.32 - 4.01 (m, 1H), 3.87 - 3.60 (m, 2H), 2.53 (p, J = 7.6 Hz, 2H), 1.55 (s, 3H), 1.50 - 1.39 (m, 4H), 1.36 (s, 3H), 1.34 - 1.21 (m, 5H), 0.83 (s, 9H), 0.005 (s, 3H), 0.001 (s, 3H).13C NMR (126 MHz, CDCI3) 6 156.7, 154.2, 153.5, 146.2, 120.5, 117.9, 117.4, 111.8, 86.3, 84.8, 82.8, 81.9, 81.7, 79.5, 66.6, 66.0, 63.7, 63.4, 62.9, 52.8, 50.2, 28.31, 28.27, 28.23, 28.0, 27.4, 25.9, 25.5, 18.3, 17.1, -5.3, -5.4. Underlined peaks are rotameric pairs. HRMS: (ESI) m / z calculated for (C28H45N40sSiS-i-): 577.2880 Found: 577.2879.

[0150] Example 2.2.2: (lR)-l-[4-(Azetidin-l-yl)thieno[3,4-d]pyrimidin-7-yl]-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (14)

[0151] Carbamate 13 (25 mg, 43 pmol) was dissolved in EtOH (2 mL) with freshly prepared 2 M HCI aq. (2 mL) added dropwise with vigorous stirring. After 90 mins, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight. The product mixture was purified by reverse-phase, flash column chromatography (10-100% MeCN in H2O, loaded as an aqueous solution) to afford the title compound 14 as a light-yellow powder (12 mg, 70%).XH NMR (500 MHz, D2O) 6 7.84 (s, 1H), 7.83 - 7.81 (m, 1H), 4.59 - 4.39 (m, 2H), 4.21 - 4.11 (m, 3H), 4.04 (dd, J = 5.7, 4.2 Hz, 1H), 3.77 - 3.58 (m, 2H), 3.31 - 3.24 (m, 1H), 2.49 - 2.39 (m, 2H). 1H signal obscured by HDO peak at 4.79 ppm.13C NMR (126 MHz, D2O) 6 155.6, 152.9, 145.3, 131.0, 122.3, 119.3, 77.6, 72.0, 64.6, 62.9, 58.2, 53.4, 51.0, 16.4. LRMS: (ESI) m / z calculated for (C14H19N4O3S+): 323.1 Found: 323.1

[0152] Example 3: Preparation of (lR)-l-(4-Aminothieno[3,4-d]pyrimidin-7-yl)-5-O- isobutyryl-l,4-dideoxy-l,4-imino-D-ribitol bis( hydrochloride ) (18)

[0153] Example 3.1 : (IR)-N-tert-Butyloxycarbonyl-l -(4-aminothieno[3,4-d]pyrimidin-7-yl)-l,4- dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (15)

[0154] TBDMS ether 10 (300 mg, 0.56 mmol) was dissolved in anhydrous THF (8 mL) under an argon atmosphere and cooled to 0 °C. Excess TBAF in THF (4.0 mL, c = 1.0 M, 7 equiv.) was added by syringe with cooling maintained for an hour. Monitoring by LCMS indicated a circa 2: 1 ratio of product to starting material. After stirring at room temperature overnight (16 h.), the solution was concentrated in vacuo and the product separated from the mixture by automated normal-phase, flash column chromatography (gradient elution 10-100% (3: 1 v / v EA / EtOH) in PE on SiO2, loaded as CHCI3 solution) to afford the title compound 15 as a light amber solid (220 mg, 93%).XH NMR (500 MHz, CDCI3) 6 8.22 - 7.98 (m, 1H), 7.91 - 7.56 (m, 1H), 5.07 - 4.90 (m, 2H), 4.90 - 4.76 (m, 1H), 4.42 - 4.14 (m, 2H), 3.75 (d, J = 12.0 Hz, 1H), 1.62 (s, 3H), 1.37 (br. s, 5H), 1.34 (s, 3H), 1.07 (br. s, 4H).13C NMR (126 MHz, CDCI3) 6 159.0, 154.8, 153.0, 143.5, 133.5, 132.5, 121.0, 117.8, 117.0, 112.2, 86.1, 85.5, 82.2, 81.8, 80.9, 80.5, 66.3, 66.2, 65.5, 65.3, 63.3, 62.9, 28.5, 28.3, 28.2, 25.7. Underlined peaks are rotameric pairs. LRMS: (ESI) m / z calculated for (C19H27N4O5S+): 423.2 Found: 423.1

[0155] Example 3.2: (IR)-N-tert-Butyioxycarbonyl-l -(4-[isobutyrylamido ]thieno[3,4-d]pyrimidin- 7-yl)-5-O-isobutyryl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (16)

[0156] Alcohol 15 (105 mg, 0.25 mmol) and 4-DMAP (2 mg, 16 ptmol, 6 mol%) were dissolved in anhydrous DCM (10 mL) under an argon atmosphere. Excess isobutyryl anhydride (250 uL, 1.5 mmol, 6 equiv.) was added by syringe. After stirring for 16 hours, the solution was concentrated in vacuo and the product separated from the mixture by automated normal-phase, flash column chromatography (gradient elution 0-100% EA in PE on SiO2, loaded as CH2CI2 solution) to afford the title compound 16 as a light amber oil (102 mg, 73%).XH NMR (500 MHz, CDCI3) 6 8.57 - 8.34 (m, 1H), 8.19 (br. s, 1H), 5.65 (br. s, 1H), 5.43 - 5.07 (m, 1H), 4.82 (br. s, 1H), 4.58 - 4.07 (m, 3H), 2.92 (br. s, 1H), 2.45 (hept, J = 7.0 Hz, 1H), 1.56 (s, 3H), 1.51 - 1.30 (m, 9H), 1.36 (s, 3H), 1.29 - 1.23 (m, 6H), 1.10 (dd, J = 7.0, 6.1 Hz, 6H).13C NMR (126 MHz, CDCI3) 6 182.1, 176.7, 153.9, 153.7, 135.5, 123.2, 112.4, 86.2, 85.3, 82.8, 82.2, 81.1, 63.6, 63.2, 38.0, 33.8, 28.2, 27.3, 25.4, 19.33, 19.31, 19.0, 18.7. Underlined peaks are rotameric pairs. C-4a, C-7, and C-7a in thienopyrimidine were not observed. LRMS: (ESI) m / z calculated for (C27H39N4O7S+) : 563.3 Found: 563.3

[0157] Example 3.3: (lR)-N-tert-Butyloxycarbonyl-l-(4-aminothieno[3,4-d]pyrimidin-7-yl)-5-O- isobutyryl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (17)

[0158] Amide 16 (64.7 mg, 115 pimol) was dissolved in methanol (3.5 mL) in a microwave reaction vial under an argon atmosphere. The solution was heated under microwave irradiation (pressure 5.0 to 2.3 Bar) at 105 °C for three hours, concentrated in vacuo and purified by automated normal-phase, flash column chromatography (gradient elution 10-100% EA in PE on SiO2, loaded as CH2CI2 solution) to afford the title compound 17 as a light amber oil (46.4 mg, 82%).XH NMR (500 MHz, CDCI3) 6 8.22 (s, 1H), 7.93 - 7.55 (m, 1H), 6.45 (s, 2H), 5.77 - 5.48 (m, 1H), 5.48 - 5.16 (m, 1H), 4.85 (dd, J = 6.0, 1.2 Hz, 1H), 4.62 - 4.12 (m, 3H), 2.45 (hept, J = 7.0 Hz, 1H), 1.54 (s, 3H), 1.52 - 1.37 (m, 9H), 1.36 (s, 3H), 1.12 - 1.07 (m, 6H).13C NMR (126 MHz, CDCI3) 6 176.8, 158.1, 154.2, 153.5, 145.8, 133.8, 132.7, 120.9, 117.1, 112.3, 85.9, 85.2, 82.7, 82.4, 81.1, 63.7, 63.7, 63.2, 33.8, 28.3, 27.3, 25.4, 19.0, 18.8. Underlined peaks are rotameric pairs. HRMS: (ESI) m / z calculated for (C23H33N4O6S+): 493.2097 Found: 493.2129.

[0159] Ester 17 (28.6 mg, 58 pmol) was dissolved in 1,4-dioxane (2 mL) with freshly prepared 2 M HCI aq. (2 mL) added dropwise with vigorous stirring. After two hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight. The de-esterified impurity circa 25 mol%) was removed by automated reverse-phase, flash column chromatography (5-100% MeCN in water on C-18, 12 g, loaded as an H2O solution) followed by lyophilisation of the dry residue from a circa 10 mM HCI aq. solution to afford the title compound 18 as a colourless powder (16 mg, 67%).XH NMR (500 MHz, D2O) 6 8.54 - 8.45 (m, 1H), 8.13 - 8.06 (m, 1H), 5.01 (dd, J = 7.6, 1.2 Hz, 1H), 4.38 (ddd, J = 7.6, 5.0, 1.2 Hz, 1H), 4.29 (d, J = 1.4 Hz, 1H), 4.29 - 4.27 (m, 1H), 4.27 - 4.23 (m, 1H), 3.78 - 3.71 (m, 1H), 2.65 - 2.47 (m, 1H), 1.11 - 1.04 (m, 6H).13C NMR (126 MHz, D2O) 6 179.8, 157.8, 149.5, 140.7, 128.9, 125.8, 118.6, 76.8, 71.7, 64.2, 61.9, 58.5, 33.9, 18.2, 18.0. HRMS: (ESI) m / z calculated for (C15H21N4O4S+) : 353.1284 Found: 353.1282.

[0160] Example 4: Preparation of

[0161] 4.1 (lR)-l-(4-Amino-5-chlorothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (22) and

[0162] 4.2 (lR)-l-(4-Amino-5-bromothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (23) and

[0163] 4.3 (lR)-l-(4-Amino-5-iodothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (24)

[0164] Example 4.1.1: (IR)-N-tert-Butyioxycarbonyi-l -(4-amino-5-chiorothieno[3,4-d]pyrimidin-7- yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (19)

[0165] Thienopyrimidine 10 (166 mg, 0.31 mmol) was dissolved in AR CHCI3 (20 mL) under an argon atmosphere. 1,3,5-Trichloroisocyanuric acid (25.2 mg, 1.05 equiv.) was added in a single portion under an argon atmosphere and the reaction flask covered in aluminium foil to exclude light. After stirring at room temperature for 16 h, the solution was quenched with half-saturated, aqueous sodium sulfite, the organic layer was separated, the aqueous layer extracted with DCM (x 3) with the combined organic fractions dried over MgS04and concentrated in vacuo. The crude product was purified by automated normal-phase, flash column chromatography (gradient elution 10-100% EA in PE on SiO2, loaded as CHCI3 solution) to afford the title compound 19 as a light amber oil (94 mg, 53%).XH NMR (500 MHz, CDCI3) 6 9.14 - 8.88 (m, 1H), 7.92 - 7.73 (m, 1H), 7.64 - 7.49 (m, 1H), 5.73 - 5.45 (m, 1H), 5.05 - 4.85 (m, 1H), 4.77 (d, J = 5.7 Hz, 1H), 4.36 - 4.08 (m, 1H), 3.85 (dd, J = 10.1, 4.0 Hz, 1H), 3.82 - 3.64 (m, 1H), 1.58 (s, 3H), 1.53 - 1.40 (m, 5H), 1.36 (s, 3H), 1.34 - 1.19 (m, 4H), 0.86 (s, 9H), 0.12 - 0.01 (m, 2 x 3H).13C NMR (126 MHz, CDCI3) 6 154.6, 154.2, 151.6, 140.2, 139.8, 139.1, 138.6, 136.5, 122.5, 120.0, 112.1, 86.7, 86.0,

[0166] 82.3, 81.7, 81.0, 80.6, 66.0, 65.6, 63.6, 63.4, 63.2, 28.4, 27.5, 25.9, 25.5, 18.4, 18.3, -

[0167] 5.3. Underlined peaks are rotameric pairs. HRMS: (ESI) m / z calculated for (C25H40N4O5SiS35CI+): 571.2177 Found: 571.2175; m / z calculated for (C25H40N4O5SiS37CI + ): 573.2148 Found: 573.2154.

[0168] Example 4.1.2: (1R)-1 -(4-Amino-5-chlorothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (22)

[0169] Carbamate 19 (26.9 mg, 50 pmol) was dissolved in EtOH (3 mL) with freshly prepared 2 M HCI aq. (3 mL) added dropwise with vigorous stirring. After 2.5 hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 22 as a light-yellow powder (10.8 mg, 57%).XH NMR (500 MHz, D2O) 6 8.09 (d, J = 0.8 Hz, 1H), 5.27 (d, J = 9.1 Hz, 1H), 4.41 - 4.31 (m, 1H), 3.90 (q, J = 2.9 Hz, 3H). 1H peak obscured by HDO peak at 4.79 ppm.13C NMR (126 MHz, D2O) 6 153.3, 143.6, 143.3, 135.9, 121.9, 114.2, 74.9, 70.8, 66.3, 58.5, 56.5. LRMS: (ESI) m / z calculated for

[0170] (CnHi4N4O3S35CI+): 317.0 Found: 317.0 (100); m / z calculated for

[0171] (C11H14N4O3S37CI+): 319.0 Found: 319.1 (38).

[0172] Example 4.2.1 : (IR)-N-tert-Butyloxycarbonyl-l -(4-amino-5-bromothieno[3,4-d]pyrimidin- 7-yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (20)

[0173] Thienopyrimidine 11 (99 mg, 0.18 mmol) was dissolved in AR CHCI3 (8 mL) under an argon atmosphere. 1,3-Dibromoisocyanuric acid (31 mg, 1.2 equiv.) was added in a single portion under an argon atmosphere and the reaction flask covered in aluminium foil to exclude light. After stirring at room temperature for 16 h, the solution was quenched with half-saturated, aqueous sodium sulfite, the organic layer was separated, the aqueous layer extracted with DCM (x 3) with the combined organic fractions dried over MgSCh and concentrated in vacuo. The crude product was purified by automated normal-phase, flash column chromatography (gradient elution 10-100% EA in PE on SiO2, loaded as CHCI3 solution) to afford the title compound 20 as a light amber oil (23 mg, 20%).XH NMR (500 MHz, CDCI3) 6 8.02 (s, 1H), 5.55 (s, 1H), 5.13 - 4.85 (m, 1H), 4.71 (br. s, 1H), 4.40 - 4.13 (m, 1H), 3.87 - 3.66 (m, 2H), 1.57 (s, 3H), 1.51 - 1.39 (m, 5H), 1.37 (s, 3H), 1.34 - 1.16 (m, 4H), 0.80 (s, 9H), 0.01 (s, 3H), -0.01 (s, 3H).13C NMR (126 MHz, CDCI3) 6 154.4, 153.7, 141.5, 141.3, 115.8, 112.4, 111.41, 111.37, 86.9, 86.3, 85.9, 85.9, 85.5, 82.4, 81.8, 81.7, 81.4, 81.2, 80.7, 66.2, 66.0, 65.8, 64.2, 63.7, 63.3, 62.8, 28.4, 28.3, 27.5, 25.89, 25.85, 25.5, 18.3, -5.35, -5.40. Underlined peaks are rotameric pairs. HRMS: (ESI) m / z calculated for (C25H4oN40sSiS79Br+): 615.1672 Found: 615.1672; m / z calculated for (C25H40N4O5SiS81Br+): 617.1652 Found: 617.1654

[0174] Example 4.2.2: (lR)-l-(4-Amino-5-bromothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (23) Carbamate 20 (17.2 mg, 28 pmol) was dissolved in EtOH (3 mL) with freshly prepared 2 M HCI aq. (3 mL) added dropwise with vigorous stirring. After four hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 23 as a brown powder (9.0 mg, 59%).XH NMR (500 MHz, D2O) 6 8.10 (d, J = 0.7 Hz, 1H), 5.27 (d, J = 9.2 Hz, 1H), 4.42 - 4.30 (m, 1H), 3.93 - 3.78 (m, 3H). An 1H proton multiplet was partially obscured by HDO peak at 4.80 ppm.13C NMR (126 MHz, D2O) 6 153.7, 144.2, 143.4, 125.1, 118.6, 116.1, 74.9, 70.8, 66.3, 58.5, 56.7. LRMS: (ESI) m / z calculated for (CnHi4N4O3S79Br+): 361.0 Found: 360.9 (100); m / z calculated for

[0175] (CnHi4N4O3S81Br+): 363.0 Found: 363.0 (94).

[0176] Example 4.3.1 : (IR)-N-tert-Butyloxycarbonyl-l -(4-amino-5-iodothieno[3,4-d]pyrimidin-7- yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (21)

[0177] Thienopyrimidine 11 (290 mg, 0.54 mmol) was dissolved in AR CHCI3 (15 mL) under an argon atmosphere. / V-Iodosuccinimde (773 mg, 6.4 equiv.) was added in a single portion under an argon atmosphere and the reaction flask covered in aluminium foil to exclude light. Glacial acetic acid (160 pL, 5.2 equiv.) was added by autopipette after which the light-amber slurry immediately turned a vivid crimson colour. After stirring at room temperature for 16 h, the solution was quenched with half-saturated, aqueous sodium sulfite, the organic layer was separated, the aqueous layer extracted with DCM (x 3) with the combined organic fractions dried over MgSCk and concentrated in vacuo. The crude product was purified by automated normal-phase, flash column chromatography (gradient elution 10-100% EA in PE on SiO2, loaded as CHCI3 solution) to afford the title compound 21 as a light amber oil (189 mg, 53%).XH NMR (500 MHz, CDCI3) 6 8.23 (s, 1H), 5.62 (d, J = 2.2 Hz, 1H), 5.37 - 4.96 (m, 1H), 4.93 - 4.69 (m, 1H), 4.42 - 4.02 (m, 1H), 3.98 - 3.54 (m, 2H), 1.56 (s, 3H), 1.52 - 1.40 (m, 4H), 1.37 (s, 3H), 1.35 - 1.26 (m, 4H), 0.82 (s, 9H), 0.02 (s, 3H), 0.01 (s, 3H).13C NMR (126 MHz, CDCI3) 6 157.9, 154.2, 152.8, 145.7, 142.0, 140.3, 122.6, 116.3, 112.1, 111.9, 86.4, 85.1, 82.4, 81.6, 80.6, 66.4, 65.9, 64.3, 63.9, 63.3, 63.2, 63.0, 28.3, 27.4, 25.8, 25.5, 18.2, -5.39, -5.43. Underlined peaks are rotameric pairs. HRMS: (ESI) m / z calculated for (C25H4oN40sSISi-i-): 663.1533 Found: 663.1532. Example 4.3.2: (lR)-l-(4-Amino-5-iodothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4-imino-

[0178] D-ribitol bis(hydrochloride) (24)

[0179] Carbamate 21 (40.9 mg, 62 pmol) was dissolved in EtOH (3 mL) with freshly prepared 2 M HCI aq. (3 mL) added dropwise with vigorous stirring. After 2.5 hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 24 as a lightbrown powder (17.9 mg, 60%).XH NMR (500 MHz, D2O) 6 8.21 (d, J = 0.7 Hz, 1H), 5.36 (d, J = 9.1 Hz, 1H), 4.82 - 4.80 (m, 1H), 4.46 (dd, J = 4.8, 2.6 Hz, 1H), 4.05 - 3.90 (m, 3H).13C NMR (126 MHz, D2O) 6 154.2, 144.7, 143.2, 129.9, 119.5, 82.1, 74.8, 70.8, 66.2, 58.5, 56.9. HRMS: (ESI) m / z calculated for (C11H14N4O3SI+): 408.9831 Found: 408.9832.

[0180] Example 5: Preparation of

[0181] 5.1 (lR)-l-(4-Amino-5-cyanothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (26) and

[0182] 5.2 (lR)-l-(4-Amino-5-carboxamidothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy- 1,4-imino-D-ribitol bis(hydrochloride) (29) and

[0183] 5.3 (lR)-l-(4-Amino-5-[(E / Z)-N'-hydroxycarbamimidoyl]thieno[3,4- d]pyrimidin-7-yl)-l,4-dideoxy-l,4-imino-D-ribitol bis(hydrochloride) (30)

[0184] Example 5.1.1: (IR)-N-tert-Butyloxycarbonyl-l -(4-amino-5-cyanothieno[3,4-d]pyrimidin-7- yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (25)

[0185] Zinc cyanide (170 mg, 1.45 mmol, 4 equiv.), Xantphos (10.2 mg, 18 pirnol, 5.0 mol%), and tris(dibenzalacetone)dipalladium(0) (7.2 mg, 16 pirnol, 4.3 mol%) were placed in a 10 mL microwave reactor tube and flushed with argon under a septum. Iodide 21 (240 mg, 0.36 mmol) was dissolved in DMF (4 mL) and added by syringe to the reaction tube. The resulting slurry was sparged with argon (bubbled through, with vigorous stirring) for 20 mins. The tube was sealed under argon and heated under microwave irradiation to 60 °C for 30 mins. Completion of the reaction was confirmed by LCMS of the crude mixture. The crude product was purified by automated reverse-phase, flash column chromatography (gradient elution 10-100% MeCN in H2O on C-18, the filtered reaction mixture was directly loaded as a DMF solution) to afford the title compound 25 as a light-amber solid (170 mg, 83%).XH NMR (500 MHz, CDCI3) Rotamers: 6 8.43 (s, 1H), 6.28 (br. s, 2H), 5.69 (d, J = 2.5 Hz, 1H), 5.29 - 4.99 (m, 1H), 4.86 - 4.65 (m, 1H), 4.49 - 4.17 (m, 1H), 3.96 - 3.68 (m, 2H), 1.59 (s, 3H), 1.54 - 1.41 (m, 4H), 1.39 (s, 3H), 1.37 - 1.19 (m, 5H), 0.78 (s, 9H), -0.01 (br. s, 3H), -0.03 (br. s, 3H).13C NMR (126 MHz, CDCI3) Rotamers 6 156.9, 154.7, 154.3, 154.0, 147.7, 146.7, 145.9, 125.1, 114.8, 112.4, 97.1, 96.8, 86.6, 85.1, 82.5, 81.7, 81.3, 66.4, 66.0, 65.2, 64.7, 63.6, 28.2, 27.5, 25.8, 25.5, 18.2, -5.44, -5.45. Underlined peaks are rotameric pairs. Italicized peaks at 147.7 ppm and 145.9 ppm are rotameric pairs. LRMS: (ESI) m / z calculated for (CzeH^NsOsSSi-i-): 562.3 Found: 562.3

[0186] Example 5.1.2: (1R)-1 -(4-Amino-5-cyanothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy-l,4- imino-D-ribitol bis(hydrochloride) (26)

[0187] Carbamate 25 (27.0 mg, 48 pmol) was dissolved in 1,4-dioxane (4 mL) with freshly prepared 2 M HCI aq. (4 mL) added dropwise with vigorous stirring. After three hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 26 as a lightorange powder (17.7 mg, 97%).XH NMR (500 MHz, D2O) 6 8.36 (d, J = 1.1 Hz, 1H), 5.43 (dd, J = 9.3, 1.1 Hz, 1H), 4.85 (ddt, J = 9.3, 5.0, 1.5 Hz, 1H), 4.47 (ddd, J = 4.8, 2.5, 1.0 Hz, 1H), 4.05 - 3.97 (m, 3H).13C NMR (126 MHz, D2O) 6 152.5, 145.5, 144.3, 133.7, 122.3, 111.8, 108.8, 75.1, 70.7, 66.8, 58.4, 56.8. LRMS: (ESI) m / z calculated for (C12H14N5O3S+) : 308.1 Found: 308.1

[0188] Example 5.2.1: (1 R)-N-tert-Butyloxycarbonyl-l -(4-amino-5-carboxamidothieno[3,4- d]pyrimidin-7-yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene- D-ribitol (28)

[0189] Nitrile 25 (58.1 mg, 103 pmol) was dissolved in DMSO (1.5 mL) in the presence of K2CO3 (41.4 mg, 300 pmol, 2.9 equiv.). 30wt% Hydrogen peroxide (388 pL, 16.5 mmol, 160 equiv.) was added dropwise by autopipette to the slurry. The rapid evolution of gas and heat was observed. After 30 mins, the reaction was confirmed to be complete by LCMS. The crude product was purified by automated reverse-phase, flash column chromatography (gradient elution 10-100% MeCN in H2O on C-18, the filtered reaction was directly loaded as a DMSO solution) to afford the title compound 28 as a light-amber oil (39.3 mg, 66%).XH NMR (500 MHz, CDCI3) 6 8.28 (s, 1H), 6.19 (br. s, 2H), 5.87 - 5.53 (m, 1H), 5.53 - 4.99 (m, 1H), 4.99 - 4.58 (m, 1H), 4.47 - 4.03 (m, 1H), 4.03 - 3.57 (m, 2H), 1.83 (s, 2H), 1.58 (s, 3H), 1.53 - 1.41 (m, 4H), 1.41 - 1.35 (m, 3H), 1.35 - 1.13 (m, 5H), 0.81 (s, 9H), 0.01 (s, 3H), -0.01 (s, 3H). LRMS: (ESI) m / z calculated for (C26H42N5O6SSi+): 580.3 Found: 580.3

[0190] Example 5.2.2: (1R)-1 -(4-Amino-5-carboxamidothieno[3,4-d]pyrimidin-7-yl)-l,4-dideoxy- 1,4-imino-D-ribitol bis(hydrochloride) (29)

[0191] Carbamate 28 (42 mg, 72 pmol) was dissolved in ethanol (3 mL) with freshly prepared 2 M HCI aq. (3 mL) added dropwise with vigorous stirring. After two hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 29 as a lightorange powder (24.5 mg, 85%).XH NMR (500 MHz, D2O) 6 8.25 (s, 1H), 5.42 (d, J = 9.2 Hz, 1H), 4.86 (dd, J = 9.2, 4.8 Hz, 1H), 4.49 (dt, J = 4.9, 1.3 Hz, 1H), 4.04 - 4.00 (m, 3H).13C NMR (126 MHz, D2O) 6 164.3, 152.9, 147.1, 142.9, 136.3, 128.1, 118.9, 75.0, 70.7, 66.5, 58.5, 56.9. HRMS: (ESI) m / z calculated for (C12H16N5O4S+): 326.0923 Found: 326.0920. Example 5.3.1: (lR)-N-tert-Butyloxycarbonyl-l-(4-amino-5-[(E / Z)-N'-hydroxy- carbamimidoyl]thieno[3,4-d]pyrimidin-7-yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4- imino-2,3-O-isopropylidene-D-ribitol (27)

[0192] Nitrile 25 (65 mg, 0.11 mmol) and triethylamine (35 .L, 4.8 mmol, 40 equiv.) was dissolved in Abs EtOH (2 mL). Hydroxylamine. HCI (15.0 mg, 0.22 mmol, 1.9 equiv.) was added and the suspension was heated in a sealed tube under microwave irradiation to 80 °C for two hours. Volatiles were removed in vacuo and the crude product was purified by automated reverse-phase, flash column chromatography (gradient elution 10-100% MeCN in H2O on C-18, loaded as a DMSO solution) to afford the title compound 27 as a lightyellow solid (13.9 mg, 20%).XH NMR (500 MHz, CDCI3) 6 8.39 - 8.04 (m, 1H), 5.67 (s, 1H), 5.10 (d, J = 30.7 Hz, 2H), 4.82 (d, J = 36.6 Hz, 1H), 4.47 - 4.08 (m, 1H), 3.82 (d, J = 66.4 Hz, 2H), 1.64 - 1.53 (m, 3H), 1.53 (s, 4H), 1.38 (s, 3H), 1.35 - 1.14 (m, 5H), 0.83 (s, 10H), 0.02 (s, 2H), 0.02 (s, 3H), 0.01 - 0.00 (m, 1H).13C NMR (126 MHz, CDCI3) Rotamers and isomers:13C NMR (126 MHz, CDCI3) 6 158.2, 157.7, 154.5, 154.3, 153.0, 152.8, 152.8, 148.4, 147.7, 145.6, 136.3, 133.9, 126.9, 120.5, 118.0, 117.7, 112.1, 112.0, 86.5, 85.1, 82.6, 81.8, 81.0, 80.6, 66.6, 65.7, 63.8, 63.2, 63.0, 28.3, 27.5, 25.89, 25.86, 25.5, 18.3, - 5.28, -5.30, -5.34. HRMS: (ESI) m / z calculated for (C26H43N6O6SiS+): 595.2733 Found: 595.2734

[0193] Example 5.3.2: (lR)-l-(4-Amino-5-[(E / Z)-N'-hydroxycarbamimidoyl]thieno[3,4- d]pyrimidin-7-yl)-l,4-dideoxy-l,4-imino-D-ribitol bis(hydrochloride) (30)

[0194] Carbamate 27 (10.4 mg, 22 pmol) was dissolved in ethanol (3 mL) with freshly prepared 2 M HCI aq. (3 mL) added dropwise with vigorous stirring. After two hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 30 as a lightorange powder (9.0 mg, 99%).XH NMR (500 MHz, D2O) 6 8.87 (d, J = 0.8 Hz, 0.2H), 8.15 (d, J = 0.8 Hz, 0.2H), 8.11 (d, J = 0.7 Hz, 0.8H), 5.32 (dd, J = 9.1, 1.8 Hz, 1H), 4.80 - 4.74 (m, 1H), 4.39 (dd, J = 4.8, 2.3 Hz, 1H), 4.00 - 3.83 (m, 3H).13C NMR (126 MHz, D2O) 6 153.1, 148.8, 146.4, 142.7, 137.5, 130.7, 124.7, 115.0, 74.93 (minor), 74.88, 70.77 (minor), 70.74, 66.3, 66.1 (minor), 58.49 (minor), 58.46, 56.87 (minor), 58.84. Isomeric pairs underlined. HRMS: (ESI) m / z calculated for (C12H17N6O4S+): 341.1032 Found: 341.1028

[0195] Example 6: Preparation of (lR)-l-(4-Amino-5-[lH-imidazol-4-yl]thieno[3,4- d]pyrimidin-7-yl)-l,4-dideoxy-l,4-imino-D-ribitol bis(hydrochloride) (35)

[0196] Example 6.1: (lR)-N-tert-Butyloxycarbonyl-l-(4-amino-5-[lH-imidazol-4-yl]thieno[3,4- d]pyrimidin-7-yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-

[0197] D- ribitol (32) and

[0198] (lR)-N-tert-Butyloxycarbonyl-l-(4-amino-5-[l-trityl-imidazol-4-yl]thieno[3,4-d]pyrimidin-

[0199] 7-yl)-5-O-tert-butyldimethylsilyl-l,4-dideoxy-l,4-imino-2,3-O-isopropylidene-D-ribitol (33)

[0200] Pd(PPh3)2Cl2 (20.2 mg, 29 pimol, 15 mol%) and 4-(tributylstannyl)-l-tritylimidazole 31 (163 mg, 0.27 mmol, 1.4 equiv.) were placed in a 10 mL microwave reactor tube and flushed with argon under a septum. Iodide 21 (126 mg, 0.19 mmol) was dissolved in DMF (2 mL) and added by syringe to the reaction tube. The reaction solution was sparged with argon (bubbled through, with vigorous stirring) for 20 mins. The tube was sealed under argon, then heated under microwave irradiation to 110 °C for 40 mins. Completion of the reaction was confirmed by LCMS of the crude mixture. The crude product was purified by automated reverse-phase, flash column chromatography (gradient elution 10-100% MeCN in H2O on C-18, filtered reaction was directly loaded as a DMF solution) to afford the de- tritylated title compound 32 as an amber oil (49.9 mg, 44%). The / V-trityl protected product 33 (70 mg, <56%) was contaminated with stannane impurities, so was placed into storage. / V-H compound 32:XH NMR (500 MHz, CDCI3) 6 11.32 (s, 1H), 8.12 (s, 1H), 7.35 - 7.27 (m, 1H), 7.19 - 7.02 (m, 1H), 5.75 - 5.59 (m, 1H), 5.33 - 5.10 (m, 1H), 4.96 - 4.75 (m, 1H), 4.34 - 4.06 (m, 1H), 3.94 - 3.65 (m, 2H), 1.54 (s, 3H), 1.52 - 1.40 (m, 5H), 1.37 (s, 3H), 1.34 - 1.16 (m, 4H), 0.90 - 0.78 (m, 9H), 0.06 - 0.00 (m, 2 x 3H). HRMS: (ESI) m / z calculated for (C28H43N6O5SSH-): 603.2785 Found: 603.2792.

[0201] / V-Trityl compound 33:XH NMR (500 MHz, CDCI3) 6 11.06 (s, 1H), 8.15 (s, 1H), 7.57

[0202] - 7.49 (m, 1H), 7.41 - 7.34 (m, 8H), 7.34 - 7.27 (m, 7H), 6.14 - 5.80 (m, 1H), 5.75 - 5.36 (m, 1.5H), 5.20 - 4.66 (m, 1.5H), 4.34 - 4.02 (m, 0.5H), 3.90 - 3.51 (m, 1.5H), 1.59

[0203] - 1.53 (m, 3H), 1.46 - 1.39 (m, 1H), 1.36 (s, 3H), 1.32 - 1.21 (m, 8H), 0.81 - 0.70 (m, 9H), 0.02 - -0.16 (m, 2 x 3H). LRMS: (ESI) m / z calculated for (C47H57N6O5SSi+): 845.4 Found: 845.3

[0204] Example 6.2: (lR)-N-tert-Butyloxycarbonyl-l-(4-amino-5-[lH-imidazol-4-yl]thieno[3,4-

[0205] Silyl ether 32 (49.9 mg, 83 pimol) was dissolved in anhydrous THF (5 mL), cooled to 0 °C and excess 1.0 M TBAF in THF (0.5 mL, 6 equiv.) was added dropwise. The reaction was left in its cooling bath to warm to room temperature overnight. Completion of the reaction was confirmed by TLC analysis of the reaction mixture. Volatiles were removed in vacuo and the crude product was purified by automated reverse-phase, flash column chromatography (gradient elution 10-100% MeCN in H2O on C-18, loaded as a DMF solution) to afford the title compound 34 as a dark-amber solid (19.2 mg, 47%).XH NMR (500 MHz, CDCI3) 6 11.96 (br. s, 1H), 10.94 (br. s, 1H), 7.96 (br. s, 1H), 7.08 (br. s, 1H), 6.93 (br. s, 1H), 5.04 - 4.92 (m, 1H), 4.90 (d, J = 5.2 Hz, 1H), 4.86 (d, J = 5.1 Hz, 1H), 4.36 - 4.19 (m, 2H), 3.76 (dd, J = 12.0, 2.3 Hz, 1H), 2.08 (br. s, 1H), 1.65 (s, 3H), 1.45 (s, 7H), 1.37 (s, 3H), 1.20 - 1.09 (m, 2H).13C NMR (126 MHz, CDCI3) 6 159.5, 155.0, 152.3, 144.2, 134.1, 134.0, 132.9, 127.9, 116.0, 115.3, 112.1, 85.3, 82.1, 81.2, 66.4, 65.5, 62.9, 28.5, 28.0, 25.6. HRMS: (ESI) m / z calculated for (C22H29N6O5S+): 489.1920 Found: 489.1927

[0206] Example 6.3: (lR)-l-(4-Amino-5-[lH-imidazol-4-yl]thieno[3,4-d]pyrimidin-7-yl)-l,4- dideoxy-l,4-imino-D-ribitol bis(hydrochloride) (35)

[0207]

[0208] Alcohol 34 (11.5 mg, 28 pmol) was dissolved in ethanol (4 mL) with freshly prepared 2 M HCI aq. (4 mL) added dropwise with vigorous stirring. After two hours, the reaction was concentrated in vacuo at 40 °C to complete deprotection, redissolved in deionised water, and freeze-dried overnight to afford the title compound 35 as a dark brown powder (10.6 mg, 98%).XH NMR (500 MHz, D2O) 6 8.35 (d, J = 1.2 Hz, 1H), 8.14 (d, J = 1.1 Hz, 1H), 7.93 (q, J = 1.0 Hz, 1H), 5.37 (dd, J = 9.2, 1.3 Hz, 1H), 4.83 (d, J = 4.9 Hz, 1H), 4.47 (dd, J = 4.8, 2.4 Hz, 1H), 4.05 - 3.92 (m, 3H).13C NMR (126 MHz, D2O) 6 153.3, 145.4, 142.8, 138.4, 136.7, 127.9, 122.2, 119.5, 113.2, 74.9, 70.8, 66.2, 58.5, 56.8. HRMS: (ESI) m / z calculated for (C14H17N6O3S+): 349.1080 Found: 349.1083

[0209] Example 7: Antiviral Materials and Methods

[0210] Example 7.1: Reduction of virus-induced cytopathic effect (Primary CPE assay)

[0211] Confluent or near-confluent cell culture monolayers of cells are prepared in 96-well disposable microplates the day before testing. Cells are maintained in MEM supplemented with 5% FBS. For antiviral assays the same medium is used but with FBS reduced to 2% and supplemented with 50-pg / mL gentamicin. Compounds are dissolved in DMSO. The test compound is prepared at four serial logic concentrations, usually 100, 10, 1.0, and 0.1 pg / mL or pM. Five microwells are used per dilution: three for infected cultures and two for uninfected toxicity cultures. Controls for the experiment consist of six microwells that are infected and not treated (virus controls) and six that are untreated and uninfected (cell controls) on every plate. A known active drug is tested in parallel as a positive control drug using the same method as is applied for test compounds. The positive control is tested with every test run.

[0212] Growth media is removed from the cells and the test compound is applied in 0.1 mL volume to wells at 2X concentration. Virus, normally at 30-100 CCID50 (50% cell culture infectious dose), in 0.1 mL volume is added to the wells designated for virus infection. Medium devoid of virus is placed in toxicity control wells and cell control wells. Plates are incubated at 37 °C with 5% CO2 until marked CPE (>80% CPE for most virus strains) is observed in virus control wells. The plates are then stained with 0.011% neutral red for approximately two hours at 37 °C in a 5% CO2 incubator. The neutral red medium is removed by complete aspiration, and the cells may be rinsed IX with phosphate buffered solution (PBS) to remove residual dye. The PBS is completely removed, and the incorporated neutral red is eluted with 50% Sorensen's citrate buffer / 50% ethanol for at least 30 minutes. The dye content in each well is quantified using a spectrophotometer at 540 nm wavelength. The dye content in each set of wells is converted to a percentage of dye present in untreated control wells using a Microsoft Excel-based spreadsheet and normalized based on the virus control. The 50% effective (ECso, virus-inhibitory) concentrations and 50% cytotoxic (CC50, cell-inhibitory) concentrations are then calculated by regression analysis. The quotient of CC50 divided by ECso gives the selectivity index (SI50) value.

[0213] Example 7.2: Reduction of virus yield (Secondary VYR assay)

[0214] This assay is set up similar to the methodology described for the primary CPE assay above, except that eight half-logic concentrations of compound are tested for antiviral activity and cytotoxicity. After sufficient virus replication occurs (generally 3 days for many viruses), a sample of supernatant is taken from each infected well (replicate wells are pooled) and tested immediately or held frozen at -80 °C for later virus titer determination. After maximum CPE is observed, the viable plates are stained with neutral red dye. The incorporated dye content is quantified as described above to generate the ECso and CC50 values.

[0215] The VYR test is a direct determination of how much the test compound inhibits virus replication. Virus yielded in the presence of test compound is titrated and compared to virus titers from the untreated virus controls. Titration of the viral samples (collected as described in the paragraph above) is performed by endpoint dilution.29Serial 10-fold dilutions of supernatant are made and plated into four replicate wells containing fresh cell monolayers of cells. Plates are then incubated, and cells are scored for presence or absence of virus after distinct CPE is observed, and the CCIDso calculated using the Reed-Muench method. The 90% (one logic) effective concentration (EC90) is calculated by regression analysis by plotting the logic of the inhibitor concentration versus logic of virus produced at each concentration. Dividing CC50 by the EC90 gives the SI90 value for this test.

[0216] Example 8: Anti-viral activity of compound 3

[0217] The antiviral activity of compound 3 was assessed against a range of viruses in cellular assays.

[0218] Virus definitions-. Influenza A virus H1N1 (IAV H1N1); Influenza A virus H5N1 (IAV H5N1); Influenza A virus H3N2 (IAV H3N2); Influenza B virus (IBV); Rift Valley fever virus (RVFV); Zika virus (ZIKV); Yellow fever virus (YFV); Dengue virus serotype 2 (DENV-2); West Nile virus (WNV); Middle East respiratory syndrome coronavirus (MERS-CoV); Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); Respiratory syncytial virus (RSV);

[0219] Enterovirus D68 (EV-D68); Junin virus (JUNV).

[0220] Table 2: Antiviral activity of compound 3 a Not determined.

[0221] Example 9: Anti-viral activity of compound 24

[0222] The antiviral activity of compound 24 was assessed against a range of viruses in cellular assays.

[0223] Table 3: Antiviral activity of compound 24

[0224] Example 10: Anti-viral activity of compound 29

[0225] The antiviral activity of compound 29 was assessed against a range of viruses in cellular assays. Table 4: Antiviral activity of compound 29

[0226] Example 11: Anti-viral activity of compound 18

[0227] The antiviral activity of compound 18 was assessed against a range of viruses in cellular assays.

[0228] Table 5: Antiviral activity of compound 18

[0229] Example 12: Anti-viral activity of compound 12

[0230] The antiviral activity of compound 12 was assessed against a range of viruses in cellular assays.

[0231] Table 6: Antiviral activity of compound 12

[0232] Example 13: Anti-viral activity of compound 35

[0233] The antiviral activity of compound 35 was assessed against a range of viruses in cellular assays. Table 7: Antiviral activity of compound 35

[0234] Example 14: Anti-viral activity of compound 30

[0235] The antiviral activity of compound 30 was assessed against a range of viruses in cellular assays.

[0236] Table 8: Antiviral activity of compound 30

[0237] * * *

[0238] Although the invention has been described by way of example, it should be appreciated that variations and modifications may be made without departing from the scope of the invention as defined in the claims. Furthermore, where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred in this specification.

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Claims

CLAIMS1. A compound of the Formula (I):wherein:R1is H or R6CO; where R6is C1-20 alkyl, C6-12 aryl, C1-6 alkyl-Ce-aryl,where R7is the side group of a natural amino acid;R2and R3are each independently selected from H, R6CO and Ci-4 alkyl; where R6is as defined above;R4and R5are each independently selected from H, C1-6 alkyl, cycloalkyl, C6-12 aryl and heteroaryl, or R4and R5together form C3-6 heterocycloalkyl;X is H, deuterium, C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C6-12 aryl, heteroaryl, CN, C(=O)Z, halogen, amidine, hydroxy amidine, carboxime or CHR8OH; where Z is H, OH, OR9, C1-6 alkyl, NH2, NR9H, N(R9)2or SR9;R8is H, C1-6 alkyl, C6-12 aryl or C1-6 alkyl-Ce-aryl; and R9is C1-6 alkyl, cycloalkyl, C6-12 aryl, or heteroaryl;A is H, F, Cl, NH2, or CH3; or a pharmaceutically acceptable salt thereof.

2. A compound as claimed in claim 1, wherein A is H.

3. A compound as claimed in claim 1 or claim 2, wherein R4and R5are each independently selected from H, C1-6 alkyl, cycloalkyl, C6-12 aryl and heteroaryl.

4. A compound as claimed in any one of claims 1 to 3, wherein R4and R5are both H.

5. A compound as claimed in any one of claims 1 to 3, wherein R4is CH3 and R5is H6. A compound as claimed in any one of claims 1 to 5, wherein R1is H.

7. A compound as claimed in any one of claims 1 to 5, wherein R1is R6CO.

8. A compound as claimed in claim 7, wherein R6is C1-12 alkyl.

9. A compound as claimed in claim 7, wherein R6is isobutyroyl and R2and R3are both H.

10. A compound as claimed in claim 7, wherein R6is:wherein R7is the side group of a natural amino acid.

11. A compound as claimed in any one of claims 1 to 6, wherein R1, R2and R3are all H.

12. A compound as claimed in any one of claims 1 to 6, wherein R1, R2, R3, R4and R5are all H.A compound as claimed in any one of claims 1 to 12, wherein X is H.

14. A compound as claimed in any one of claims 1 to 12, wherein X is I.

15. A compound as claimed in any one of claims 1 to 12, wherein X is CN.

16. A compound as claimed in any one of claims 1 to 12, wherein X is C(=O)NH2.

17. A compound as claimed in any one of claims 1 to 12, wherein X is deuterium.

18. A compound as claimed in claim 1 selected from the group comprising:

19. A pharmaceutical composition comprising a compound as claimed in any one of claims 1 to 18 and a pharmaceutically acceptable carrier.

20. A method of treating or preventing a viral infection comprising administering to a human in need an effective amount of compound of any one of claims 1 to 18.

21. A compound of any one of claims 1 to 18 for use in the treatment or prevention of a viral infection.

22. The use of a compound of any one of claims 1 to 18 in the manufacture of a medicament for treating or preventing a viral infection.

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