WO1990015064A1

WO1990015064A1 - Therapeutic nucleosides

Info

Publication number: WO1990015064A1
Application number: PCT/GB1990/000867
Authority: WO
Inventors: Saad George Rahim; Kenneth Powell
Original assignee: The Wellcome Foundation Limited
Priority date: 1989-06-06
Filing date: 1990-06-05
Publication date: 1990-12-13
Also published as: EP0475992A1; JPH04505920A; GB8912972D0

Abstract

Esters of (E)-5-(2-bromovinyl)-1-β-D-arabinofuranosyluracil and salts thereof; their preparation and use in medical therapy particularly in the treatment of viral infections.

Description

Therapeutic Nucleosides

The invention relates to therapeutic nucleosides in particular esters of (E)-5-(2-Bromovinyl)-l-3-D-arabinofuranosyluracil having valuable antiviral properties.

(E) -5-(2-Bromovinyl)-l-/S-D-arabinofuranosyluracil, otherwise known as BVAraU, possesses a potent antiviral activity against herpes viruses (J. Reefschlaeger et al. Antiviral Res.3 (3) 175-87 (1983), EP Publication No. 31128). The tri-acetate ester of BVAraU is also disclosed in the J. Reefschlaege reference mentioned above as an intermediate in the synthesis of BVAraU. BVAraU is however only poorly soluble in water, thereby limiting the formulation of the drug in aqueous pharmaceutical preparations where solubility is required.

Also BVAraU is only poorly absorbed from the gastrointestinal tract after oral administration. Such low bioavailability requires exposing the patient to unnecessary amounts of drug in order to achieve and maintain effective antiviral levels in the plasma.

We have now discovered that esters of BVAraU, which have not previously been disclosed, surprisingly have improved bioavailability after oral administration compared with the parent compound BVAraU.

According to one feature of the present invention the compounds of formula (I) are provided:

wherein R , R and R which may be the same or different each represent a hydroxy group or a pharmaceutically acceptable ester group

1 2 3 provided that at least one of R , R and R represents such an ester

1 2 3 group and (b) all of R , R and R do not represent acetoxy groups; and pharmaceutically acceptable salts thereof.

Preferred esters are those wherein one or more of R 1, R2 and R3 represent a carboxylic acid ester group in which the non-carbonyl moiety is selected from C. - alkyl, c_ , cycloalkyl, C. , alkoxy, C. , alkoxyalkyl (e.g. methoxymethyl) , C. _fi carboxyalkyl (e.g. carboxyethyl) , aralkyl (e.g. benzyl), C- , aryloxyalkyl (e.g. phenoxymethyl) , aryl (e.g. phenyl) optionally substituted by halogen, C. , alkyl or C. , alkoxy; or wherein one or more of R 1, R2 and R3 represent an amino acid ester group (for example, L-valyl or

L-isoleucyl) ; a phosphate ester group (e.g. mono-, di- or t^'ri- phosphate) ; or a sulphonate ester group such as an alkyl-or ar lkyl-sulphonyloxy (e.g. me hanesulphonyloxy) group.

Where reference is made to an alkyl moiety this includes methyl, ethyl, propyl, butyl, pentyl and hexyl.

Particularly preferred esters are those wherein R 1, R2 and R3 each represent a carboxylic acid ester group in which the non-carbonyl moiety is C. - alkyl.

1 2 Most preferred is a compound wherein R and R are hydroxy groups and

3 R is a carboxylic acid ester group in which the non-carbonyl moiety of the ester group is C- _fi alkyl, for example tert-butyl namely,

(E)-5-(2-Bromovinyl)-1-((5-0-pivaloyl)-3-D-arabinofuranosyl)-uracil.

The pharmaceutically acceptable salts of the compounds of formula (I) include base salts such as alkali metal salts for example sodium salts. In tests in rats, measuring the urinary recovery as BVAraU (% dose administered) after oral administration, the compounds of the invention (the compounds of formula (I) and pharmaceutically acceptable salts thereof) show a large increase in absorption from the gut compared with the parent compound BVAraU. This enables less drug to be adminstered while still providing equivalent drug levels in the plasma after oral absorption.

In addition to the relatively high bioavailability, the compounds of the present invention possess substantially the same antiviral effect as BVAraU in vitro. The advantageous increase in bioavailability of the compound is thus not gained at the expense of antiviral potency.

In experiments in animals, it was discovered that the oral administra¬ tion of the compounds of the invention produced measurable levels of BVAraU in the plasma. Thus according to another aspect of the invention there is provided a method of generating BVAraU .in vivo by administration of a compound of formula (I) or a pharmaceutically acceptable salt thereof to a mammal.

The invention also provides the compounds of formula (I) and pharmaceutically acceptable salts thereof for use in medical therapy for example in the treatment or prophylaxis of a viral infection in an animal, for example a mammal such as man. The compounds are especially useful for the treatment or prophylaxis of diseases caused by various DNA viruses, such as herpes infections, for example herpes simplex, varicella zoster, cytomegalovirus as well as diseases caused by hepatitis B or Epstein-Barr viruses or human herpes virus-6 (HHV-6) .

Additionally, the invention provides a method for the treatment of a viral disease in an animal, for example a mammal such as man, which comprises administering to the animal an effective antiviral amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof. The invention further provides the use of a compound of formula (I) or a pharmaceutically acceptable salt thereof in the manufacture of a medicament for the treatment or prophylaxis of a viral infection.

Furthermore the invention provides (E)-5-(2-bromovinyl)-1- ((2,3,5-tri-0-acetyl)-3-D-arabinofuranosyl)uracil for use in medical therapy for example in the treatment or prophylaxis of a viral disease particularly a herpes viral infection.

The compounds of the invention may be prepared in conventional manner, for example by a process as described below.

Thus, according to a further feature of the invention a process for the preparation of the compounds of formula (I) above and pharmaceutically acceptable salts thereof is provided, which comprises:

a) reacting a compound of formula (II)

OH

1 2 3 wherein Z is leaving group, and R , R and R are as defined above with a compound to inti-oduce the side-group CH=CHBr or b) esterifying a compound of formula (III)

1 2 3 to form a compound of formula (I) wherein R , R and R are as defined above;

c) reacting a compound of formula (IV)

1 2 3 wherein R , R and R are as hereinbefore defined and B is a purine or pyrimidine base, with (E)-5-(2-bromovinyl)uracil; and optionally effecting one or more of the following conversions, in any desired sequence:-

i) removal of any protecting groups; ** ii) where the resulting product is a compound of formula (I) , conversion of the said compound into a pharmaceutically acceptable salt thereof; and

iii) where the resulting product is a pharmaceutically acceptable salt of a compound of formula (I) , conversion of the said salt into the parent compound.

With regard to process a) a compound of formula (I) may be prepared from corresponding compounds of formula (II) where Z represents a halogen, advantageously iodo, by reaction with an ester of acrylic

4 acid to give a compound of formula (II) where Z represents CH-CHC0„R

4

(R may represent any conventional carboxyl protecting group, conveniently methyl) . The reaction may be carried out with a transition metal complex formed in situ from palladium (II) acetate and triphenylphosphine in the presence of an organic base such as triethylamine in a solvent such as alcohol for example methanol, acetonitrile or preferentially dioxane at a temperature range of

50-110 C. The ester protecting group of the compound of formula (II)

4 4 where Z represents CH-CHC0„R (where R is as previously defined) may be removed by conventional means such as base hydrolysis conveniently by reaction with aqueous sodium hydroxide in the temperature range

0-30 C. This reaction may or may not be accompanied by hydrolysis of

1 2 3 ester groups R , R and R , where present, to give compound of formula

1 2 3 (II) where Z represents CH-CHCO H and R -R -=R -OH. The compound of formula (I) may be prepared from the compound of formula (II) were Z represents CH-=CHC0_H by reaction with a brominating agent followed by re-esterification as necessary using process b) . The reaction may be carried out using a suitable brominating agent such as N-bromosuccini- mide in the presence of a alkali metal salt such as potassium acetate in water as the solvent or in the absence of a base in organic solvents such as alcohol, halogenated hydrocarbons or a substituted amide eg. N-N-dimethylformamide in the temperature range 20-100 C.

This process is exemplified by A.S. Jones et al, Tetrahedron lett..

1979, 45, 44-5 and E. De Clercq et al, J. Med. Chem.. 1986, 29, 213. With regard to process b) , the compounds of formula (I) may be prepared from corresponding compounds of formula (III) by esterification using an appropriate acid chloride or anhydride (for example pivaloyl chloride or pivalic anhydride) advantageously in the presence of a base such as pyridine or triethylamine which may also serve as a solvent medium for the reaction, at ambient temperature.

Additionally, the compound of formula (I) may be prepared from the corresponding compound of formula (III) by transesterification using an appropriate ester of the acid (for example, an appropriate ester of pivalic acid) in the presence of a base such as pyridine or triethyl¬ amine which may also serve as a solvent medium for the reaction.

With regard to process c) , group B is preferably a purine or pyrimidine base capable of donating the esterified sugar to a (E)-5-2-(bromovinyl) uracil base using for example an enzyme such as a phosphorylase enzyme in the presence of a phosphate salt at a pH of 5.0-9.0 and a temperature of 15-90°C advantageously 40-60°C.

In addition, the esterification reaction may be carried out in conventional manner using for example an appropriate acid, in a solvent such as pyridine or dimethylformamide in the presence of a coupling agent such as N,N' -dicyclohexylcarbodiimide, optionally in the presence of a catalytic base such as 4-dimethylaminopyridine. The water formed during the reaction may, if desired, be removed in conventional manner, for example by distillation or by the addition of a water-binding substance. Subsequently, the ester obtained as reaction product may be isolated in conventional manner.

The conversion of a compound of formula (I) into a pharmaceutically acceptable salt may be effected in conventional manner, for example, by treatment of the compound with an appropriate acid to form an acid addition salt, for example, by lyophilisation of a methanolic solution of the parent ester with an acid solution. Similarly, conversion of a salt into the parent compound of formula (I) may be effected in conventional manner.

The compounds of the Invention may be administered by any route appropriate to the condition to be treated, suitable routes including oral, rectal, nasal, topical (including buccal and sublingual) vaginal and parenteral (including subcutaneous, intramuscular, intravenous, intradermal, intrathecal and epidural) . It will be appreciated that the preferred route may vary with for example the condition of the recipient.

For each of the above-indicated utilities and indications the amount required of an active ingredient (a compound of the invention) will depend upon a number of factors including the severity of the condition to be treated and the identity of the recipient and will .ultimately be at the discretion of the attendant physician or veterinarian. In general however, for each of these utilities and indications, a suitable effective dose will be in the range 0.1 to 250 mg per kilogram bodyweight of recipient per day, preferably in the range 1 to 100 mg per kilogram bodyweight per day and most preferably in the range 5 to 20 mg per kilogram bodyweight per day; an optimum dose is about 10 mg per kilogram bodyweight per day. The desired dose is preferably presented as two, three, four or more sub-doses administered at appropriate intervals throughout the day. These sub-doses may be administered in dosage forms, for example, containing 10 to 1000 mg, preferably 20 to 500 mg and most preferably 100 to 400 mg of active ingredient per dosage form.

The compounds of the invention may be administered alone or in combination with other therapeutic agents.

While it is possible for the active ingredient to be administered alone, it is preferable to present it as pharmaceutical formulations. The formulations, both for veterinary and for human use, of the present invention comprise at least one active ingredient, as above defined, together with one or more pharmaceutically accept¬ able carriers therefor and optionally other therapeutic ingredients. The carrier(s) must be "acceptable" in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient thereof.

The formulations include those suitable for oral, rectal, nasal, topical (including buccal and sublingual), vaginal or parenteral (including subcutanous, intramuscular, intravenous, intradermal, intrathecal and epidural) administration. The formulations may conveniently be presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers of finely divided solid carriers or both, and then, if necessary, shaping the product.

Formulations of the invention suitable for oral administration may be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient; as a powder or granules; as a solution or a suspension in an aqueous liquid or a non-aqueous liquid; or as an oil-in-water liquid emulsion or a water-in-oil liquid emulsion. The active ingredient may also be presented as a bolus, electuary or paste.

A tablet may be made by compression or moulding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active ingredient in a free-flowing form such as a powder or granules, optionally mixed with a binder, lubricant, inert diluent, preservative, surface active or dispersing agent. Moulded tablets may be made by moulding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent. The tablets may optionally be coated or scored and may be formulated so as to provide slow or controlled release of the active ingredient therein.

For infections of the eye or other external tissues e.g. mouth and skin, the formulations are preferably applied as a topical ointment or cream containing the active ingredient in an amount of, for example, 0.075 to 20% w/w, preferably 0.2 to 15% w/w and most preferably 0.5 to 10% w/w. When formulated in an ointment, the active ingredients may be employed with either paraffinic or a water-miscible ointment base. Alternatively, the active ingredients may be formulated in a cream with an oil-in-water cream base. In addition topical applications may be made transdermally by means of an iontophoretic device.

If desired, the aqueous phase of the cream base may include, for example, at least 30% w/w of a polyhydric alcohol, i.e. an alcohol having two or more hydroxyl groups such as propylene glycol, butane 1,3-diol, mannitol, sorbitol, glycerol and polyethylene glycol and mixtures thereof. The topical formulations may desirably include a compound which enhances absorption or penetration of the active ingredient through the skin or other affected areas. Examples of such dermal penetration enhancers include dimethylsulphoxide and related analogues.

Formulations suitable for topical administration to the eye also include eye drops wherein the active ingredient is dissolved or suspended in a suitable carrier, especially an aqueous solvent for the active ingredient. The active ingredient is preferably present in such formulations in a concentration of 0.5 to 20%, advantageously 0.5 to 10% particularly about 1.5% w/w.

Formulations suitable for topical administration in the mouth include lozenges comprising the active ingredient in a flavoured basis, usually sucrose and acacia or tragacanth; pastilles comprising the active ingredient in an inert basis such as gelatin and glycerine, or sucrose and acacia; and mouthwashes comprising the active ingredient in a suitable liquid carrier.

Formulations for rectal administration may be presented as a suppository with a suitable base comprising for example cocoa butter or a salicylate.

Formulations suitable for nasal administration wherein the carrier is a solid include a coarse powder having a particle size for example in the range 20 to 500 microns which is administered in the manner in which snuff is taken, i.e. by rapid inhalation through the nasal passage from a container of powder held close up to the nose. Suit¬ able formulations wherein the carrier is a liquid, for administration as for example a nasal spray or as nasal drops, include aqueous or oily solutions of the active ingredient.

Formulations suitable for vaginal administration may be presented as pessaries, tampons, creams, gels, pastes, foams or spray formulations containing in addition to the active ingredient such carriers as are known in the art to be appropriate.

Formulations suitable for parenteral administration include aqueous and non- aqueous sterile injection solutions which may contain an i-oxidants, buffers, bacteriostats and solutes which render the formulation isotonic with the blood of the intended recipient; and aqueous and non-aqueous sterile suspensions which may include suspending agents and thickening agents. The formulations may be presented in unit-dose or multi-dose containers, for example sealed ampoules and vials, and may be stored in a freeze-dried (lyophilized) condition requiring only the addition of the sterile liquid carrier, for example water for injections, immediately prior to use. Extemporaneous injection solutions and suspensions may be prepared from sterile powders, granules and tablets of the kind previously described. Formulations for intramuscular administration are particularly preferred.

Preferred unit dosage formulations are those containing a daily dose or unit daily sub-dose, as herein above recited, or an appropriate fraction thereof, of an active ingredient.

It should be understood that in addition to the ingredients particularly mentioned above the formulations of this invention may include other agents conventional in the art having regard to the type of formulation in question, for example those suitable for oral administration may include flavouring agents.

The present invention further provides veterinary compositions comprising at least one active ingredient as above defined together with a veterinary carrier therefor.

Veterinary carriers are materials useful for the purpose of administering the composition and may be . solid, liquid or gaseous materials which are otherwise inert or acceptable in the veterinary- art and are compatible with the active ingredient. These veterinary compositions may be administered orally, parenterally or by any other desired route.

For oral administration the compositions can be in the form of a tablet, granule drench, paste, cachet, capsule or feed supplement. Granules may be made by the well known techniques of wet granulation, precompression or slugging. They can be administered to animals in an inert liquid vehicle so as to form a drench, or in a suspension with water or oil base. Preferably further accessory ingredients such as a dispensing agent are included. These formulations preferably contain from 15 to 85% of the active ingredient. The following Examples illustrate the present invention. Hereinafter the compounds of Formula I may be referred to as active ingredients.

Example 1(a) :

(E)-5-(2-Bro ovinyl -1-(5-0-pivalσyl-θ-D-arabinofuranosyl)uracil

To a stirred solution of (E)-5-(2-bromovinyl)-1-(^-D-arabino furanosyl)uracil (0.3g, 0.86mmol) in dry pyridine (8mL) at 0°C was slowly added pivaloyl chloride (0.127mL, 1.03mmol) and the mixture stirred at ambient temperature for 5 hours. A further aliquot of trimethylacetyl chloride (0.06mL, 0.48mmol) was added at 0°C and after stirring for 4 hours at ambient temperature, the solvent was evaporated and residual pyridine co-evaporated with portions of ethanol. The remaining residue was triturated with water, the solid filtered and recrystallised from isopropanol to give two crops of the title compound.

Yield 0.204g, 55% M.pt 213-214°C(d)

Microanalysis: Calculated C, 44.38; H, 4.85: N, 4.46% Found C, 44.63; H, 4.66; N, 6.24%

Example Kb) :

(E)-5-(2-Bromovinyl)-l-(5-0-(2-ethylbutyryl) -g-D-arabinofuranosyl uracil

To a solution of (E)-5-(2-bromovinyl)-1-(5-0-(2-ethylbutyryl) -β-Ω-

3 arabinofuranosyl) uracil (l.Og, 2.86 x 15 mol) in dry pyridine (24 ml) at 0 C was added the acid chloride, 2-ethylbutyryl chloride

(0.42g, 1.1 eqv) . The mixture was stirred at room temperature for 4 hours. The resulting solution was concentrated in vacuo (Temp - 40 C, - 14mmtlg) to a gum. Residual pyridine was evaporated with portions of ethanol (3x20ml) under vacuo. Finally the residue was concentrated under vacuo with water (20ml) . A solid residue resulted.

The solid was column chromatographed and the product was isolated and recrystallised to give a white solid. (solvent system CHC1_ to a gradient 10% MEOH/CHCl.,) . An NMR, a CHN and an I.R. were recorded. A

m.pt 190-192°C with decomposition.

Example 1(c) :

5-(2-Bromovinyl)-1-(5-O-butyryl-θ-D-arabinofuranosyl) uracil

(E)-5-(2-Bromovinyl)-l-(5-D-arabinofuranosyl)uracil 0.7g was dissolved in 20ml dry pyridine and stirred at 0 C under Nitrogen. Butyryl chloride (0.25ml) was added and washed in with a little more pyridine. The mixture was stirred and allowed to warm to room temperature. Stirring continued at room temperature for a further 5-6 hours. The pyridine was evaporated off on Buchi. Residual oil was evaporated down several times wtih EtOH. A residual brown oil was formed of which was 'flash' columned in 8% MeOH/CH Cl-. Flasks 13-22 were pooled and evaporated. Residual solid was triturated with a small volume of neat CH„C1„ and stood in a fridge. White crystalline solid was filtered off, washed with CH-C1„ and dried.

m.pt 194-196°C

Example 2 : Tablet Formulations

The following formulations A, B and C are prepared by wet granulation of the ingredients with a solution of povidone, followed by addition of magnesium stearate and compression. Formulation A mg/tablet me/tablet

Active ingredient 250 250

Lactose B.P. 210 26

Povidone B.P. 15 9

Sodium Starch Glyco Hate 20 12

Magnesium Stearate 5 3

500 300

Formulation B mg/tablet mp/tablet

Active ingredient 250 250

Lactose 150 -

Avicel PH 101 60 26

Povidone B.P. 15 9

Sodium Starch Glycollate 20 12

Magnesium Stearate 5 3

500 300

Formulation C mg/tablet

Active ingredient 100

Lactose 200

Starch 50

Povidone B.P. 5

Magnesium stearate 4

359

The following formulations, D and E, are prepared by direct compress¬ ion of the admixed ingredients. The lactose in formulation E is of the compression type. Formulation D mp/tablet

Active Ingredient 250

Avicel 150

Magnesium Stearate 4

404

Formulation E mg/tablet

Active Ingredient 250

Lactose 150

Avicel 100

Magnesium Stearate 5

505

Formulation F (Controlled Release Formulation)

The formulation is prepared by wet granulation of the ingredients (below) with a solution of povidone followed by the addition of magnesium stearate and compression.

me/tablet

Active Ingredient 500

Hydroxypropylmethylcellulose 112

(Methocel K4M Premium)

Lactose B.P. 53

Povidone B.P. 28

Magnesium Stearate "/7

700 Example 4 : Capsule Formulations

Formulation A

A capsule formulation is prepared by admixing the ingredients of Formulation D in Example 3 above and filling into a two-part hard gelatin capsule. Formulation B (infra) is prepared in a similar manner.

Formulation B mg/capsule

Active ingredient 250

Lactose B.P. 143

Sodium Starch Glycollate 25

Magnesium Stearate 2

420

Formulation C mg/capsule

Active ingredient 250

Macro D1 4000 B.P. 3_50

600

Capsules are prepared by melting the Macrogol 4000 BP, dispersing the active ingredient in the melt and filling the melt into a two-part hard gelatin capsule.

Formulation D me/capsule

Active ingredient 250 Lecithin 100 Arachis Oil 100 450

Capsules are prepared by dispersing the active ingredient in the lecithin and arachis oil and filling the dispersion into soft, elastic gelatin capsules.

Formulation E (Controlled Release Capsule)

The following controlled release capsule formulation is prepared by extruding ingredients a, b and c using an extruder, followed by spheronisation of the extrudate and drying. The dried pellets are then coated with release-controlling membrane (d) and filled into a two-piece, hard gelatin capsule.

mg/capsule

Active Ingredient 250 Microcrystalline Cellulose 125 Lactose B.P. 125 Ethyl Cellulose 13 513

Example 5 : Ophthalmic Solution

Active ingredient 0.5 Propylene Glycol 0.2 g Thiomersal 0.001 j Purified water to 100 ml pH adjusted to 7.5 Example 6 : Injectable Formulation

Active Ingredient 0.200 g

Sterile, pyrogen free citrate buffer (pH 7.0) to 10 ml

The active ingredient is dissolved in most of the citrate buffer (35 -40 C) , then made up to volume and filtered through a sterile micropore filter into a sterile 10ml amber glass vial (type 1) and sealed with sterile closures and overseals.

Example 7 : Intramuscular injection

Active Ingredient 0.20 g

Benzyl Alcohol 0.10 g

Glycofurol 75 1.45 g

Water for Injection q.s. to 3.00 ml

The active ingredient is dissolved in the glycofurol. The benzyl alcohol is then added and dissolved, and water added to 3 ml. The mixture is then filtered through a sterile micropore filter and sealed in sterile 3 ml amber glass vials (type 1) .

Example 8 : Syrup Suspension

Active Ingredient 0.25 g

Sorbitol Solution 1.50 g

Glycerol 2.00 g

Sodium Benzoate 0.005 g

Flavour, 0.0125 ml

Purified Water q.s. to 5.00 ml

The sodium benzoate is dissolved in a portion of the purified water and the sorbitol solution added. The active ingredient is added and dissolved. The glycerol and flavours are added and mixed in. Water is added to a final volume of 5ml. Example 9 : Suppository mg/suppository

Active Ingredient (63μm)* 250

Hard Fat, BP (Witepsol H15 - Dynamit NoBel) 1700 1950

*The active ingredient is used as a powder wherein at least 90% of the particles are of 63/xm diameter or less.

One-fifth of the Witepsol H15 is melted In a steam-jacketed pan at 45 C maximum. The active ingredient Is sifted through a 200μm sieve and added to the molten base with mixing, using a silverson fitted with a cutting head, until a smooth dispersion is achieved. Maintaining the mixture at 45 C, the remaining Witepsol H15 is added to the suspension and stirred to ensure a homogenous mix. The entire suspension is passed through a 250μm stainless steel screen and, with continuous stirring, is allowed to cool to 40°C. At a temperature of 38 C to 40 C, 2.02g of the mixture is filled into suitable plastic moulds. The suppositories are allowed to cool to room temperature.

Example 10 : Pessaries mg/pessarv

Active ingredient 63μm 250

Anhydrous Dextrose 543

Starch 200

Magnesium Stearate 7

1000

The above ingredients are mixed directly and pessaries prepared by direct compression of the resulting mixture. Example 11 : Antiviral Activity

Varicella zoster virus (VZV) is assayed in monolayers of either MRC5 cells (human embryonic lung) or Detroit 532 cells (human foreskin fibroblasts) in multiwell trays. Activity of compounds Is determined in the plaque reduction assay, in which a cell monolayer is infected with a suspension of VZV. A range of concentrations of compounds of known molarity are introduced to the cell layer. Plaque numbers of each concentration are expressed as percentage of the control and a dose-response curve is drawn. From this curve the 50% inhibitory concentration (IC_j..) is estimated.

Cell toxicity is assessed in a cell growth inhibition assay. Subconfluent cultures of Vero cells grown on 96-well microtiter dishes are exposed to different dilutions of drug, and cell viability determined daily on replicate cultures using uptake of a tetrazolium dye (MTT) . The concentration required for 1 50% inhibition of cell viability at 96 hours is termed CCID_t-...

The results are shown in the following Table.

TABLE

Example IC_5Q(μM) CCID₅₍₎(μM)

VZV at 96 hours

1 0.04 >500

Determination of Oral Bioavailability

Long Evans Rats were adminstered the compound to be tested by gavage at a dose equivalent to 25 mg/kg BVAraU. The urine was collected for 24 and 48 hours post-dose, ultrafiltered, and analysed by reverse- phase high-pressure liquid chromatography. The oral bioavailability of the compound was expressed as the percent of the dose excreted in the urine as BVAraU.

Compound Urinary Recovery (% of dose) as BVAraU

Example 1 11

Claims

1. A compound of formula (I)

wherein R , R 2 and R 3 which ma^* y be the s represent a hydroxy group, or a pharmaceutically acceptable ester

1 2 3 group provided that (a) at least one of R , R and R represents

1 2 3 such an ester group and (b) all of R , R and R do not represent acetoxy groups; or a pharmaceutically acceptable salt thereof.

2. A compound of claim 1 wherein one or more of R 1, R2 and R3 represent; a carboxylic acid ester group In which the non-carbonyl moiety of the ester group is selected from C.

1-6 alkyl, C. - alkoxy, C. , alkoxyalkyl, C. _fi carboxyalkyl, aralkyl, C. _β aryloxyalkyl, aryl optionally substituted by halogen, C. alkyl or C. , alkoxy; an amino acid ester; a phosphate ester group; or a sulphonate ester group.

3. A compound of claims 1 or 2 wherein one or more of R 1, R2 and R3 and represent a carboxylic acid ester group in which the non-carbonyl moiety of the ester is C- , alkyl.

S A compound of claim 1 or any claim dependent thereon in which R

2 3 and R are hydroxy groups and R is a carboxylic acid ester group in which the non-carbonyl moiety of the ester group is C.

1-6 alkyl.

(E)-5-(2-bromovinyl)-1-((5-0-pivaloyl)-/S-D-arabinofuranosyl) uracil.

6. A compound of claim 1, or any claim dependent thereon for use In medical therapy.

7. Use of a compound of formula (I) as defined In claim 1 or a pharmaceutically acceptable salt thereof in the manufacture of a medicament for the treatment or prophylaxis of a viral infection.

8. Use of a compound of formula (I) as defined in claim 1 or a pharmaceutically acceptable salt thereof in the manufacture of a medicament for the treatment or prophylaxis of a herpes viral infection.

9. A process for the preparation of a compound of formula (I) as defined in claim 1 or a pharmaceutically acceptable salt thereof comprising:

a) reacting a compound of formula (II)

1 2 3 wherein Z is leaving group , and R , R and R are as defined in claim 1 with a compound to introduce the side -group CH-CHBr or

b) esterifying a compound of formula (III)

to form a compound of formula (I) , or

c) reacting a compound of formula (IV)

1 2 3 wherein R , R and R are as defined in claim 1 and B is a purine or pyrimidine base, with (E)-5-(2-bromovinyl)uracil; and optionally effecting one or more of the following conversions, in any desired sequence:-

i) removal of any protecting groups;

ii) where the resulting product is a compound of formula (I) , conversion of the said compound into a pharmaceutically acceptable salt thereof; and iii) where the resulting product is a pharmaceutically acceptable salt of a compound of formula (I) , conversion of the said salt into the parent compound.

10. A pharmaceutical formulation comprising a compound of formula (I) as defined in claim 1 or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable carrier therefor.