The present invention relates to novel compounds which are of potential use as antiviral agents, to processes for their preparation and to their use as pharmaceuticals.

EP-A-319228 and EP-A-353955 (Beecham Group p.l.c.) disclose a group of purine derivatives containing a 9-[2-(phosphonomethoxy)alkoxy] substituent, which are described as having antiviral activity.

EP-A-206459 (Ceskoslovenska akademie ved) discloses a group of 9-(phosphonomethoxyalkyl)adenines, which are described as having antiviral activity.

'Nucleotide Analogues as Antiviral Agents' ACS Symposium Series 401, Editor J.C. Martin, published by the American Chemical Society, Washington DC (1989) Chapters 4 and 5 discloses, a number of (phosphonomethoxyalkyl) derivatives of purines and pyrimidines and their antiviral activity.

Particular compounds of interest are adenine or guanine having a 9- substituent as follows:

(HO) ₂ POCH ₂ OCH ₂ CH2θ- Ex.l, EP-A-319228

(HO) ₂ POCH ₂ OCH2CH(CH ₂ OH)0- Ex.16, EP-A-206459

(HO) ₂ POCH ₂ OCH ₂ CH ₂ - PMEA/PMEG

(HO) ₂ POCH ₂ OCH(CH ₂ OH)CH ₂ - HPMPA/HPMPG

It has now been discovered that certain derivatives of these compounds are prodrugs therefore, having improved gastrointestinal absorption properties.

Accordingly, the present invention provides a compound of formula (I), or a pharmaceutically acceptable salt thereof:

(I)

wherein

Xis -CH ₂ 0, -CH ₂ or -CH(CH ₂ ORs)0 where Rg is hydrogen or acyl; Yis O or S;

R is hydroxy or amino; R ₂ is amino or hydrogen;

R3 is hydrogen or, when X is CH ₂ 0 and Y is 0, R3 may be CH2O 9 where R9 is hydrogen or acyl; R4 and R5 are both hydrogen or the same Cχ_ alkyl group; and Rg and R7 are independently C ₂ _7 alkanoyloxy or benzoyloxy wherein the phenyl moiety is optionally substituted.

When Ri is hydroxy and R ₂ is amino, the compound of formula (I) is a guanine derivative;

When R^ is amino and R ₂ is hydrogen, the compound of formula (I) is an adenine derivative;

When R is hydroxy and R is hydrogen, the compound of formula (I) is a hypoxanthine derivative; and

When Rx and R are both amino groups, the compound of formula (I) is a 2,6-c aminopurine derivative.

Often, the compound of formula (I) is a guanine or adenine derivative.

Suitable examples of R4 and R5 include hydrogen, methyl, ethyl, n- and iso-propvl. preferably hydrogen or methyl.

Suitable examples of Rg and R7 when alkanoyloxy include acetoxy, propionyloxy, butanoyloxy, pentanoyloxy and hexanoyloxy, straight chain or branched; in particular pivaloyloxy. Rg and R7 when benzoyloxy may be optionally substituted as defined below for RQ/RC, benzoyl.

Suitable examples of Rg/Rg when, acyl include carboxylic acyl, such as Cι_7 alkanoyl and benzoyl optionally substituted in the phenyl ring by one, two or three groups or atoms selected from halogen, such as fluoro, chloro, bromo, and Cχ_4 alkyl or C1.4 alkoxy wherein the alkyl moiety is selected from methyl, ethyl, n- and iso-propyl, n-, sec-, iso- and tert-butvl. Preferred acyl groups include acetyl, propionyl, butyryl, heptanoyl and hexanoyl.

There are groups of compounds of interest wherein:

i) X is -CH ₂ 0 and R3 is hydrogen.

ii) X is -CH ₂ 0 and R3 is CH2OR9 as defined.

iii) X is -CH ₂ (CH ₂ ORg)0 as defined and R3 is hydrogen.

iv) X is -CH ₂ and R3 is hydrogen.

v) X is -CH ₂ and R3 is CH2OR9 as defined.

Y is preferably 0.

Examples of pharmaceutically acceptable salts of the compound of formula (I) are acid addition salts formed with a pharmaceutically acceptable acid such as hydrochloric acid, orthophosphoric acid and sulphuric acid. Pharmaceutically acceptable salts also include those formed with organic bases, preferably with amines, such as ethanolamines or diamines; and alkali metals, such as sodium and potassium.

It will be appreciated that some of the compounds of formula (I), especially

those wherein R3/R4/R5, is other than hydrogen, have an asymmetric centre, and therefore are capable of existing in more than one stereoisomeric form. The invention extends to each of these forms individually and to mixtures thereof, including racemates. The isomers may be separated conventionally by chromatographic methods or using a resolving agent. Alternatively, the individual isomers may be prepared by asymmetric synthesis using chiral intermediates.

The compounds of formula (I) including their alkali metal salts may form solvates such as hydrates and these are included wherever a compound of formula (I) or a salt thereof is herein referred to.

It will be appreciated that, when R^ is hydroxy in formula (I) the compound exists in the predominant tautomeric form of structure (IA):

O

(IA)

The invention also provides a process for the preparation of a compound of formula (I), or a pharmaceutically acceptable salt thereof, which process comprises reacting a compound of formula (II):

(II)

with RgR4CHQ and R7R5CHQ wherein Q is a leaving group and R^, R , R3, R4, R5, Rg and R7 are as defined in formula (I), and thereafter optionally forming a pharmaceutically acceptable salt thereof.

The compound of formula (II) is preferably in the form of a suitable salt, such as the tetrabutylammonium salt, the tetramethylammomum salt and those with lower alkylamines such as triethylamine, hydroxy-lower alkylamines such as 2-hydroxyethylamine, bis-(2-hydroxyethyl)amine or tris-(2-hydroxyethyl)amine. The triethylamine salt is preferred.

Suitable values for Q include halo, such as chloro.

The reaction takes place in a suitable inert solvent such as N,N-dimethyl- formamide (DMF) OR l,3-dimethyl-3,4,5,6-tetrahydro-2(lH)pyrimidinone (DMPU), at elevated temperatures 20-100°C, preferably 30-80°C.

Suitable examples of protecting groups and their removal, are as described in EP-A-242482. A particularly suitable protecting group is the t-butyldiphenylsilyl group removable by conventional methods.

It will be appreciated that the above conversions may take place in any desired or necessary order, having regard to the final desired compound of formula (I).

Compounds of the formula (II) are prepared as described in EP-A-313289 and the aforementioned publications, the subject matter of which are incorporated herein by reference.

When Rg/Rg is hydroxy, appropriate selective protection may be required, eg using acetate.

Pharmaceutically acceptable salts may be prepared in conventional manner, for example, in the case of acid addition salts, by reaction with the appropriate organic or inorganic acid.

It will be appreciated that the invention provides a process for the preparation of a compound of formula (I) wherein Rg/Rg is hydrogen which process comprises the deprotection of a corresponding compound of

formula (I) wherein Rg/Rg is protected hydroxy.

Preferred methods for deprotection, as hereinbefore described, include removal of the acetyl group.

The compounds of the invention are of potential use in the treatment of infections caused by viruses, in particular DNA viruses and retroviruses. Examples of DNA viruses include herpesviruses such as herpes simplex types 1 and 2, varicella-zoster virus, Epstein-Barr virus and cytomegalovirus. Examples of retroviruses include lentiviruses such as visna virus and human immunodeficiency virus (strains 1 and 2).

The compounds may also be inhibitors of tumorogenic viruses and/or of potential use in the treatment of neoplastic diseases, i.e. cancer.

Compounds of the invention may be formulated for use in a pharmaceutical composition. Accordingly, in a further aspect of the invention, there is provided a pharmaceutical composition which comprises a compound of formula (I) or pharmaceutically acceptable salt thereof together with a pharmaceutically acceptable carrier or excipient.

A composition which may be administered by the oral route to humans may be compounded in the form of a syrup, tablet or capsule. When the composition is in the form of a tablet, any pharmaceutical carrier suitable for formulating such solid compositions may be used, for example magnesium stearate, starch, lactose, glucose, rice, flour and chalk. The composition may also be in the form of an ingestible capsule, for example of gelatin, to contain the compound, or in the form of a syrup, a solution or a suspension. Suitable liquid pharmaceutical carriers include ethyl alcohol, glycerine, saline and water to which flavouring or colouring agents may be added to form syrups. The compounds may also be presented with a sterile liquid carrier for injection.

The composition may also be formulated for topical application to the skin or eyes.

For topical application to the skin, the composition may be in the form of a cream, lotion or ointment. These formulations may be conventional

formulations well known in the art, for example, as described in standard books of pharmaceutics and cosmetics, such as Harry's Cosmeticology published by Leonard Hill Books and the British Pharmacopaeia.

The composition for application to the eyes may be a conventional eye-drop composition well known in the art, or an ointment composition.

Preferably, the composition of this invention is in unit dosage form or in some other form that may be administered in a single dose. A suitable dosage unit might contain from 50 mg to 1 g of active ingredient, for example 100 to 500 mg.

Such doses may be administered 1 to 4 times a day or more usually 2 or 3 times a day. The effective dose of compound will in general be in the range of from 1.0 to 20 mg/kg of body weight per day or more usually 2.0 to 10 mg/kg per day.

No unacceptable toxicological effects are indicated at the above described dosage levels.

The invention also provides a method of treating viral infections in a human or non-human animal, which comprises administering to the animal an effective, non-toxic amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof.

The invention also provides a compound of formula (I) or a pharmaceutically acceptable salt thereof for use as an active therapeutic substance, in particular for the treatment of viral infections.

The compounds of the invention are also believed to exhibit a synergistic antiviral effect in conjunction with interferons; and combination products comprising these two components for sequential or concomitant administration, by the same or different routes, are therefore within the ambit of the present invention.

The following examples illustrate the invention.

gxampigg

The following compounds of formula (I) were prepared:

R _x R ₂ R3 R4 R5 R6 R7 X Y

NH ₂ H H H H (CH ₃ ) ₃ C-COO -CH ₂ 0 O

NH ₂ H H CH3 CH3 (CH ₃ ) ₃ C-COO -CH ₂ 0 O NH ₂ H H CH3 CH3 (CH ₂ ) CHCOO -CH ₂ 0 O

Example 1

9-r2-πBis(pivaloyloxymethoxy)phosphorylmethoxylethoxy1ad enine

To a suspension of 9-[2-(phosphonomethoxy)ethoxy]adenine (3.8mmol, l.lg) in diniethylformamide (10ml) triethylamine (7.6mmol, 1.06ml) was added. The resulting mixture was stirred at room temperature for 5 min. and chloromethyl pivalate (15.21mmol, 2.19ml) was added. The reaction mixture was stirred at 60°C for 2h, then the solvent was evaporated under reduced pressure and the residue dissolved in chloroform (200ml). The chloroform solution was washed with aqueous sodium hydrogen carbonate (2x40ml), water (40ml) and dried (MgSC . After evaporation of chloroform the residue was purified by column chromatography on silica gel (eluting with 4% ethanol in chloroform) to give the product as a colourless oil (0.81g, 41%); 5H[(CD ₃ ) ₂ SO] 1.16 (18H, s, 2x(CH ₃ ) ₃ C), 3.86 (2H, s, CH ₂ ), 4.04 (2H, d, J 7.7, CH ₂ P), 4.51 (2H, m, 4.51, CH ₂ ON), 5.66 (4H, d, J 12.65, 2xCH ₂ OP), 7.38 (2H, br s, D ₂ 0 exchangeable, NH ₂ ), 8.14 (1H, s), 8.33 (1H, s). (Found: C, 45.87; H, 6.29; N, 13.37; C oH3 N ₅ OgP.0.3 H 0 requires C, 45.89; H, 6.29; N, 13.34).

Example 2

9-r2-IΕis(l-pivaloyloxyethoxy)phosphorylmethoxy1ethoxy1a denine

To a suspension of 9-[2-(phosphonomethoxy)ethoxy)]adenine (1.52mmol, 0.440g) in ά metliylformamide (5ml), trieihyla ine (3.03mmol, 0.42ml) was added. The resulting mixture was stirred at room temperature for 5 min. and 1-chloroethyl pivalate (6.08mmol, 1.0ml) was added. The

reaction mixture was stirred at 80°C for 6h, then the solvent was evaporated under reduced pressure and the residue dissolved in dichloromethane (100ml). The dichloromethane solution was washed with aqueous sodium hydrogen carbonate (2x30ml), water (1x30ml) and dried (MgS04). After evaporation of dichloromethane the residue was purified by column chromatography on silica gel (eluting with 6% ethanol in chloroform) to give 25mg of the faster diastereomer, 50mg of the mixture of diastereomers and 75mg of the slower diastereomer, total yield 18%); 5H[(CD ) ₂ SO] the faster diasteromer: 1.14 (18H, s, 2x(CH3)3θ, 1.60 (6H, d, 2xCH ₃ ), 3.82 (2H, m, CH ₂ ), 3.95 (2H, d, J 7.42, CH P), 4.48 (2H, m,

CH ₂ ON), 6.47 (2H, m, 2xCHOP), 7.37 (2H, br s, D ₂ 0 exchangeable, NH ₂ ), 8.14 (1H, s), 8.31 (1H, s). (Found: C, 48.05; H, 6.40; N, 12.01; C ₂₂ H3gOgN ₅ P requires C, 48.44; H, 6.65; N, 12.83). (Found: m z (e.i.) 545.2251 C ₂₂ H ₃ gNg0 ₅ P requires M+; 545.2251). δπ [(CD ₃ ) ₃ SO] the slower diastereomer: 1.14 (9H, s, (CH3) ₃ C), 1.16 (9H, s, (CH ₃ ) ₃ C), 1.47 (6H, m, 2xCH ₃ ), 3.85 (2H, m, CH ₂ ), 3.97 (2H, m, CH ₂ P), 4.49 (2H, m, CH ₂ ON), 6.49 (2H, m, 2xCHOP), 7.38 (2H, br s, D ₂ 0 exchangeable, NH ₂ ), 8.14 (1H, s), 8.33 (1H, s). (Found: C, 48.52; H, 6.66; N, 12.31; C ₂₂ H3gOgN ₅ P requires C, 48.44; H, 6.65; N, 12.83). (Found: m/z (e.i.) 545.2251 C ₂₂ H3gOgN ₅ P requires M+; 545.2251).

Example 3

9-r2-rBis-(l-isobutyryloxyethoxy)phosphorylmethoxy1ethoxy l-adenine

To a suspension of 9-[2-(phosphonomethoxy)ethoxy3adenine (1.45mmol, 0.420g) in l,3-dimethyl-3,4,5,6-tetrahydro-2(lH)-pyrimidinone (5ml) triethylamine (3.42mmol, 0.48ml) was added. The mixture was stirred at room temperature for 10 min and 1-chloroethyl isobutyrate (0.5ml) was added together with sodium iodide (1.67mmol, 0.250g). The resulting reaction mixture was stirred at 60°C for 5h after which further sodium iodide (1.67mmol, 0.250g) was added to it and stirring continued for a further lh. The solid was filtered off, washed with dichloromethane, the filtrate concentrated to a small volume and precipitated into hexane at 0°C. The hexane solution was removed by decantation, the resulting oil dissolved in chloroform (150ml) washed with aqueous sodium hydrogen carbonate (30ml), water (30ml), dried (MgS04) and evaporated. The residue was purified by column chromatography on silica gel eluting with

5% ethanol in chloroform to afford the title compound as a mixture of diastereomers. (0.240g, 32%). 5H[(CD ₃ )SO] 1.09 (12H, m, C(CH3) _2> 1.49 (6H, m, CH C), 2.55 (2H, m, CHCO), 3.83 (2H, m, CH ₂ ), 3.97 (2H, m, CH ₂ P), 4.48 (2H, m, CH ₂ 0), 6.5 (2H, m, CH), 7.37 (2H, br s, D ₂ 0 exchangeable, NH ₂ ), 8.14 (IH, s, H-2), 8.33 (IH, s, H-8). (Found: C, 44.13; H, 6.07; N, 12.55%. C oH ₃₂ N ₅ OgP-0.25 CHCI3 requires C, 44.43; H, 5.94; N, 12.79%. (Found: M+, 517.1930 C ₂ oH3 ₂ N ₅ OgP requires M, 517.1938).

Biologjcal Evaluation

Procedures

Compounds were administered as single doses of 0.2mmol/kg in 0.1ml of 1% carboxymethyl cellulose by oral gavage to female Balb/c mice weighing 20g. Food was withheld from the mice for 18 hours prior to the start of the experiment. Blood was collected by cardiac puncture using heparinised syringes 15, 60 and 180 mins after dosing. Equal volumes (0.2ml) from 3 mice were pooled at each time point and 0.6ml of ice-cold ethanol was added. Following chilling at -20°C and centrifugation, 0.5ml of supernatant was dried under reduced pressure. The sample was then reconstituted with 0.5ml of 0.4M NH4OAC (pH 6.0) and analysed by HPLC.

Re l s

Ex.l, EP-A-319228 <1 <1 <1