IE950194L - Therapeutic nucleosides - Google Patents

Description

8051 3 Therapeutic Nucleosides The Invention relates to a new ester of 9-(2-hydroxyethoxyaethyl)guanine having valuable antiviral properties. 9-(2-hydroxyethoxyaethyl)guanine, otherwise known as acyclovir, possesses a 5 potent antiviral activity, particularly against herpes viruses (H. J. Schaeffer et al. -Nature", 222 583-585 (1978), UK Patent Specification 1523865 and U.S. Patent Specification No. 4199574). Acyclovir is however only poorly soluble in water, thereby Halting the fornulatlon of the drug in aqueous pharmaceutical preparations where solubility Is required.

Also acyclovir is only poorly absorbed froa the gastrointestinal tract after oral administration ( 15% recovery in the urine when tested in rata and 20% in huaans). Such low bioavailability requires the adalnlstratlon of large doses of drug in order to achieve and aalntaln effective anti-viral levels in the plasaa.

European Patent Specification 99493 and Journal of Medicinal Chemistry, Vol. 26, re>. 4 p602-604 describes amino acid esters of acyclovir, specifically the glycine and alanine esters tAich shew mproved water—solubility ccnpared with acyclovir.

Ve have now discovered that the L-isoleucine ester of acyclovir, characterised by side-chain branching adjacent to the a-carbon atoa, and 20 which were noc disclosed in European Patent Specification 99493, surprisingly have laproved bioavailability after oral adalnlstratlon coapared with Che alanine and glycine esters aentloned therein.

According to one feature of the present invention we provide the compound of foraula (I) on (I) ch2och2ch2ococh(Rj)nh2 - 2 • 8051 3 wherein R| represents a group of formula -CHtCHjlCI^CHj the ester group (-0C0CH(R|)NH2) being in the L-configuration and pharmaceutical^ acceptable salts thereof. The compound of formula (I) can also be named as 2-(2-amino-I,6-dihydro-6-oxo-9]l(purin-9-yl)methoxy)-ethy 1 5 L-isoleucinate.

In Casts In racs, measuring che urinary recovery as acyclovir (% dose administered) after oral administration, che compounds of the invention show a large increase in absorpcion from the gut compared with the other escers and conpared with acyclovir. This enables less drug to be 10 adminstered while still providing equivalent drug levels in the plasma after oral absorption.

In addition to the relatively high bioavailability, the compounds according to the invention possess substandally che same antiviral effect as acyclovir la vitro. The advantageous increase in bioavailability of the compound is thus not gained at the expense of antiviral potency. Indeed, It has been found thac in cercaln clinical applicacions, e.g. che creacment of stromal keratitis, certain amino acid esters have been found to provide a superior therapeutic effect to acyclovir (EP 99493).

The pharmaceutlcally acceptable salts of the compounds of formula (I) ere 20 preferably acid addldon salts derived from an appropriace acid, e.g. hydrochloric, sulphuric, phosphoric, malelc, fumarlc, citric, tartaric, lactic, acetic or p*Coluenesulphonlc acid. A particularly preferred salt is the hydrochloride salts of compounds of formula (I).

In experiments in animals, it was discovered that the oral administration 2^ of the compound of formula (I) above produced measurable levels of acyclovir in the plasaa. Thus according to another aspect of the invention ve provide a means of generating iii vivo by administration of the compound of formula (I) above or a pharmaceutlcally acceptable salt thereof co a mammal.

The compounds according Co che invention may be prepared in conventional manner, e.g. by a process as described below.

Thus, according to a further feature of che presenc invention we provide a process for the preparation of che compounds of formula (I) above and 5 pharmaceutically acceptable sales chereof which comprises a) reacting a compound of formula (II) X (II) CH2OCH2CH2OH wherein X is an optionally protected hydroxy group, and Y is an optionally protected amino group with an opcionally L-isoleucine or a functional 10 equivalent thereof; b) converting a compound of formula (III) (wherein is as defined above; and M represents a hydroxy group and G represents an atom or group that can be replaced by or converted to an 15 amino group; or C represents an amino group and M represents an acom or group chac can be replaced by or converced Co a hydroxy group) inco a compound of formula (I) or a pharmaceutlcally acceptable sale chereof; or c) reacting a compound of formula (IV) * (wherein X and Y are as defined above and Q represents a leaving atom or group) with a compound of formula (V) ach2och2ch2ococh(Rl)r2 (V) (wherein R. is as defined above, A. represents a leaving group or atom and 2 R is an optionally protected amino group); 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 pharmaceutlcally acceptable salt thereof; and Hi) where the resulting product is a pharmaceutlcally acceptable salt of a compound of formula (I), conversion of the said salt into the parent compound.

With regard to process a), the escerification reaction may be carried out in conventional manner, for example in a solvent such as pyridine or dimethylformaaide in the presence of a coupling agent such as N,N'-dicyclohexylcarbodiimlde, optionally in the presence of a catalytic base such as 4-dimethylaminopyridine. The water formed during the reaction ■ay, 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.

As an alternative to the use of L-isoleucine or per se, a functional equivalent of the acid may be employed, e.g. an acid halide such as the acid chloride, or an acid anhydride. In such a case in order to avoid undesirable side-reactions, it is advantageous to use an amino-protected derivative. Examples of preferred amino-protecting groups including acyl, e.g. ^alkanoyl such as acetyl and aryloxycarbonyl, e.g. benzyloxy carbonyl. A suitable amino-protected derivative, for example, is one wherein the amino group of the amino acid is replaced by an azido group.

Conversion of a compound of formula (III) into a compound of formula (I), IS by method b), can be achieved by various means. For example G may represent an azide group which can be reduced to an amino group by catalytic hydrogenation, using a suitable catalyst such as palladium on carbon. Alternatively, G may represent a halogen atom or an alkylthio or alkylsulphonyl group which can be converted to an azide group which in 20 turn can be converted to an amino group by catalytic hydrogenation using, for example, hydrogen in the presence of palladium on carbon. For the preparation of the compound of formula (I), a compound of formula (III) wherein H is an amino group may be converted to a hydroxy group for example by treatment with a deaninating enzyme such as adenosine deaminase.

These processes together with other conventional processes are described in Fused Pyrlmldlnes, Part II, Purines, Ed. by D.J.Brown (1971), Wiley-Intersclence.

In process (c), the group Q in formula (IV) may, for example, represent a hydrogen atom; an acyl group, e.g. a ^alkanoyl group such as an acetyl 30 group or an aroyl group such as a benzoyl group; or a tri-C^ ^alkylsllyl group such as a trimethylsilyl group. The group A in formula (V) may, for example, represent a halogen atom (e.g. chlorine) or an acyloxy group wherein the acyl moiety may be, for example, a Cj^alkanoyi group such as acetyl or an aroyl group such as banzoyl. The group R2 lay represent an amlno-protectlng group such as for example, ^ alkanoyl (e.g. acetyl) or aryloxycarbanoyl (e.g. benzyloxycarbonyl) and it may also represent an azido 5 group. The reaction may be conveniently effected In a strong polar solvent such as dime thy lformaalde or hexaaethylphosphoranlde, advantageously In the presence of a base such as triethylamine or potassium carbonate. Alternatively, a thermal condensation may be effected by heating the compounds of formulae (IV) and (V) in the presence of a catalytic amount of 10 a strong acid, e.g. sulphuric acid.

Compounds of formulae (II) to (V), employed as intermediates in the synthesis of the compound of formula (I), can be prepared in conventional manner, e.g. by procedures described in U.K. Patent Specification No. 1523865. These methods rely on intermediates prepared from simply ^ substituted purines, which may be available commercially, or prepared according to techniques which are well known per se and which are disclosed in the literature such as the aforementioned text-book. Thus, for example, compounds of formula (III) may be generally prepared by using an analogous procedure to that of process (c), i.e. reacting an appropriate purine with 20 « compound of formula (V).

The optional conversions 1), 11) and ill) may be effected in conventional manner. Thus, for example, removal of protecting groups In conversion 1) may be effected by hydrolysis, solvolysis or hydrogenolysls as appropriate. Vlth regard to removal of protecting groups on the amino acid acyl 25 radicals, hydrogenolysls, e.g. of aryloxycarbonyl protecting groups, and conversion of azido group, e.g. by catalytic hydrogenation, e.g. using a palladium catalyst, are preferred. With regard to protection of the groups in the 2* and/or 6-positions of purine nucleus, these may be selected for example from arylmethyl groups e.g. benzyl; or trl-C^ ^ alkylsllyl e.g. 30 trlmethylsllyl. Arylmethyl blocking groups, may be removed for example by hydrogenolysls, e.g. by hydrogenation In the presence of Raney nickel or a palladium catalyst. Trlalkylsllyl blocking groups may be removed for example by solvolysis e.g. by alcoholysis.

The conversion of a compound of formula (I) into a pharmaceutlcally 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 5 ester with an acid solution.

Similarly, conversion of a salt into the parent compound of formula (I) may be effected in conventional manner.

The present invention also provides the compounds of formula (I) and pharmaceutlcally acceptable salts thereof (hereinafter identified as "the active compounds") for use in medical therapy e.g. in the treatment or prophylaxis of a viral disease in an animal, e.g. 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 veil as 15 diseases caused by hepatitis B or Epsteln-Barr viruses or human herpes virus -6 (HHV-6). The active compounds can also be used for the treatment or prophylaxis of retrovirus infections such as HIV Infections and papilloma or wart virus infections. In addition to their use in human medical therapy, the compounds of formula (I) can be administered to other 20 animals for treatment or prophylaxis of viral diseases, e.g. in other mammals. For example, the active compounds are especially useful for the treatment of equine rhinopneumonltls.

The present invention also provides a method for the treatment or prophylaxis of a viral disease in an animal, e.g. a mammal such as man, which conprlses administering to the animal an effective antiviral amount of a compound of formula (I) or a pharmaceutlcally acceptable salt thereof.

The present invention also provides the use of a compound of formula (I) in the manufacture of a medicament for the treatment or prophylaxis of a viral infection.

The active compounds 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 (as above defined) 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 S to 20 mg per kilogram bodyweight per day; an optimum dose is about 10 mg per kilogram bodyweight per day. (Unless otherwise indicated, all weights of active ingredient are calculated as the parent compound of formula (I): for salts thereof the figures would be increased proportionately.) 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 unit 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 unit dosage form.

The compounds of the present invention may be administered alone or in combination with other therapeutic agents, for example, with 9-(2-hydroxyethoxymethyl)guanine (acyclovir) used to treat herpes virus infections in particular HSV (I), and with zidovudine used to treat retroviral infections in particular HIV Infections.

While it is possible for the active Ingredients to be administered alone, it is preferable to present them 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 acceptable carriers therefor and optionally other therapeutic ingredients. The carrler(s) must be "acceptable" in the sense of being compaclble with the other ingredient* 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 veil known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient vith the carrier which constitutes one or '0 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 present invention suitable for oral administration may 15 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 oll-in-water liquid emulsion or a water-in-oil liquid emulsion. The active ingredient may also be presented as a bolus, 20 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 vith an inert liquid diluent. The tablets may optionally be coated or scored and may be formulated so as to provide slov 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, 0.07S to 20% v/v, preferably 0.2 Co 15% v/v and mosc preferably 0.5 to 10% v/v. When formulated in an ointment, the active ingredients may be employed vith either paraffinic or a vater-misclble ointment base. Alternatively, the active ingredients may be formulated in a cream vith an oil-in-vater cream 5 base. In addition topical applications may be made transdermally by means of an iontophorecic device.

If desired, the aqueous phase of the cream base may include, for example, at least 30% v/v of a polyhydric alcohol, i.e. an alcohol having tvo or more hydroxyl groups such as propylene glycol, butane 1,3-diol, mannicol, 10 sorbitol, glycerol and polyethylene glycol and mixtures thereof. The topical formulations may desirably include a compound vhich 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 vherein 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 20 1.5% v/v.

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 25 scacia; and mouthvashes comprising the active ingredient in a suitable liquid carrier.

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

Formulations suitable for nasal administration vherein the carrier is a 30 solid Include a coarse povder having a particle size for example In che range 20 Co 500 microns vhlch is administered in che manner in vhich snuff - 11 is taken, i.e. by rapid inhalation through the nasal passage from a container of powder held close up to the nose. Suitable 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 ant1-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 15 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 (lyophillzed) 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 20 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 25 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 30 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 vhich are othervise inert or acceptable in the veterinary art and are compatible vith 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 veil known techniques of vet 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 vith vater 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 folloving Examples illustrate the present invention.

Example 1 2 - ( 2 - Amino -1.6 - dlhvdro - 6 - oxo - 9H (pur in- 9 -vl)me thoxv) e thvl L-lsoleuclnate hydrochloride a) 2-f (2-Amlno-1.6-dlhvdro-6-oxo-9H-purln-9-vl)methoxv1ethvl-N- f(benzvloxv)carbonvl1 L-lsoleucinate A mixture of acyclovir (1.0 g, 4.4. mmol; Burroughs Wellcome Co.), 4-dimethylamlnopyrldlne (74 mg, 0.6 anol; Aldrich Chemical Co. and Chem.Ber. £2 2921-33 [1956]), 1,3-dlcyclohexylcarbodlimldlde (1.6 g, 8.0 mnol; Aldrich Chemical Co. and US 2656383), . 13 N-carbobenzoxy-L-lsoleucine (1.8 g, 6.6 mmol; Sigma Chemical Co. and Bull.Chem.Soc. Jap (1966) 21 947 or Tetrahedron 4fi (24) 5207-11 [1984]), and molecular sieves (0.3 g, Davison type 3A; Fisher Scientific, Co.) in dry N.N-dimethylformamlde (80 ml) was stirred at room temperature under nitrogen. After 4 days, additonal 1,3-dicyclohexylcarbodiimide (1.6 g, 8.0 mmol) and N-carbobenzoxy-L-lsoleucine (1.8 g, 6.6 mmol) were added. Stirring at room temperature was continued for 7 days. The resulting mixture was filtered and the clear filtrate was concentrated in vacuo to a semi-solid residue. Elution of the residue from silica gel 60 (EM, 230-400 mesh; 8.5x14 cm) with 2.5-5% methanol/methylene chloride gave 2 - [ 2 - Amino -1,6- dihydro - 6 - oxo - 9U - purin-9-yl)methoxy]ethyl-fi- [ (benzyloxy)carbonyl] -L-lsoleucinate 0.8 g, 45%) as a white solid; mp 155-157°C; UV (MeOH); X max 255 nm (cl7700) X sh 279 (9800), X min 230 (6100) NMR (200MHz, ME^O-dg): 0.73-0.80 ppm (m, 6H), 1.13-1.33 (m, 2H), 1.66-1.70 (m, 1H), 3.64 (t,2H), 3.92 (t,lH), 4.16 (m, 2H), 5.00 (s, 2H), 5.32 (s,2H) 6.47 (br s. 2H), 7.33 (s, 5H), 7.65 (d, j-8 Hz, 1H), 7.78 (s, 1H), 10.59 (br s, 1H); MS (C1/CH4; 70®C): m/z 473 (1.0%, M+l), 347 (23.2, M-125), 225 (100.0, M-247); [a],20 C -3.07° (c 0.488, 6N HC1).

TLC: one spot on silica gel with 10% MeOH/CH^Clj. R^- 0.38 HPLC: one peak on Supelco LCg with 50% MeOH/H^O; 100% K'-7.02 Anal Calcd for C22H28N6°6.H20: C, 53.87; H, 6.16; N, 17.13.

Found: C, 53.94; H, 6.20 N, 17.04 b) 2-f (2-Affllno-1.6-dlhvdro-6-oxo-9H-purln-9-vnmethoxvlethvl L-isoleuclnate hydrochloride A solution of 2-[ (2-amino-l, 6-dlhydro-6-oxo-9H-purln-9-yl)-methoxy] - . 14 . ®thyl-H-[ (benzyloxy)c*rbortyl]-L-lsoleucinate (1.11 g, 2.2 mmol) in methanol-tetrahydro furan (1:1, SO nl) was created with 0.5 N hydrochloric acid (5 ml) and 5% palladium on charcoal (0.30g; MCB Reagents). The mixture was hydrogenated on a Parr hydrogenator at 50 psl for 11 hours, filtered through a Cellte pad and the filtrate was concentrated In vacuo to give 2-[(2-amino-l,6-dlhydro-6-oxo-9tJ-purln-9-yl)nethoxy]ethyl-L-isoleucinate hydrochloride (0.86 g, 92%) as an off-white solid; mp 180-182°C (effervescent softening ca. 150°C): UV (MeOH): X 254 run («13400), X sh 272 (9000), X "in 224 (3600); NMR (200 MHz, Me2SO-d6): 0.77-0.84 ppm (m, 6H), 1.13-1.37 (m, 2H), 1.82 (m,lH), 3.73 (t,2H), 3.87 (br t, 1H), 4.14-4.40 (m. 2H), 5.36 (», 2H), 6.70 (br s, 2H), 7.97 (s, 1H), 8.46 (br s, 3H), 10.87 (s, 1H); MS (C1/CH4; 150°C): m/z 367 (6.9%, M+29), 339 (100, M+l), 225 (92.9, M-113); [o]D20 C ♦ 11.15° (c 2.0, HOAc).

TLC: one spot on silica gel with 10% MeOH/CHjClj Rf-0.12; HPLC: one peak on Versapack C^g with 10% MeOH/HjO/0.1% F^CCOOH;100% K'-3.74.

Anal Calcd for 1.25 HC1. 1.10 MeOH. 0.25 HjO: C, 42.81; H, 6.70; N, 19.84;; CI, 10.46 Found C, 42.82; H, 6.50; N, 19.64; CI, 10.46 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 rcs/tefrlgt Active ingredient 250 Lactose B.P. 210 Povidone B.P. 15 Sodium Starch Glycollate 20 Magnesium Stearate 5 500 Formulation B mg/tablet Active ingredient 250 Lactose 150 Avicel PH 101 60 Povidone B.P. 15 Sodium Starch Glycollate 20 Magnesium Stearate £ 500 Fgrnwlfltlgn C Active ingredient Lactose Starch Povidone B.P. Magnesium stearate mg/tablet 250 26 9 12 300 mg/tablet 250 26 9 12 300 mg/tablet 100 200 50 5 —k 359 The following formulations, D and E, are prepared by direct compression of the admixed Ingredients. The lactose in formulation E is of the compression type. 16 - Formulation D mg/tablet Active Ingredient Avicel Magnesium Stearate fprn>"lfltlpn e mg/tablet Active Ingredient 250 Lactose 150 Avicel 100 Magnesium Stearate £ 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. mg/tablet Active Ingredient 500 Hydroxypropylmethylcellulose 112 (Methocel K4M Premium) Lactose B.P.

Povidone B.P.

Magnesium Stearate 250 150 4 404 53 28 __I 700 17 - Example 3 : Capsule Formulations Formulation A A capsule formulation is prepared by admixing the ingredients of Formulation D in Example 2 above and filling into a two-part hard gelatin capsule. Formulation B I infra) is prepared in a similar manner.

Formulation B mg/ Sodium Starch Glycollate Magnesium Stearate 1 420 250 143 Formulation C my/capsule Active ingredient Macrogol 4000 B.P. 250 m 600 Capsules are prepared by melting active ingredient in the melt and gelatin capsule. the Macrogol 4000 BP, dispersing the filling the melt into a two-part hard 18 - Formulation D mg/capsule Accive ingredient Lecichin 5 Arachis Oil 250 100 100 450 Capsules are prepared by dispersing che accive ingredienc in che lecichin and arachis oil and filling che dispersion inco sofc, 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 spheronisacion of che excrudace and drying. The dried pellecs are Chen coaced wich release-controlling membrane (d) and filled into a two-piece, 15 hard gelacln capsule.

Bg/c»pgylg Accive Ingredienc Mlcrocryscalllne Cellulose Laccose B.P. 250 125 125 JL2 513 Echyl Cellulose Example * ; Oohthalalc Solution Active ingredient Propylene Glycol 0.5 0.2 g 0.001 g 100 ml Thiomersal Purified water co pH adjusted to 7.5 19 Example 5 : 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 vith sterile closures and overseals.

Exwple ? : Intramuscular injection Active Ingredient 0.20 g '0 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 vater 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 7 : Svrup 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 vater and the 25 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. . 20 Example 8 : Supposlt-nrv fflg/syppgsltpurv Accive Ingredienc (63Mm)* 250 Hard Fat, BP (Wlcepsol H15 - Dynamic NoBel) 1700 Magnesium Stearate 1950 *The accive Ingredienc is used as a powder wherein aC lease 90% of che parcicles are of 63j*m diameter or less.

One-flfch of che Wlcepsol H15 is melced in a steam-Jacketed pan aC 45°C maximum. The accive ingredienc is sifted chrough a 200/jm sieve and added Co che molcen base wich 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 che suspension and scirred Co ensure a homogenous mix. The encire suspension is passed chrough a 250pm stainless steel screen and, with continuous stirring, is allowed to cool to 40°C. At a temperacure of 38°C Co 40°C, 2.02g of Che mixcure is filled inco suitable plasCic moulds. The supposicories are allowed Co cool to room temperature.

Example 9 : Pessaries me/pessarv Accive ingredienc 63j*a 250 Anhydrous Dexcrose 543 Starch 200 Magnesium Stearace Z. 1000 The above ingrediencs are mixed direccly and pessaries prepared by direct compression of the resulting mixture. - 21 Example 10 a) Antiviral Activity Herpes Simplex Virus (HSV 1) was assayed in monolayers of Vero cells in multiwell trays. Activity of compounds was determined in the plaque 5 reduction assay, in which a cell monolayer was infected with a suspension of HSV 1, and then overlaid with nutrient agarose in the form of a gel to ensure that there was no spread of virus throughout the culture. A range of concentrations of compound of known molarity was incorporated in the nutrient agarose overlay. Plaque numbers at each concentration were 10 expressed as percentages of the control and a dose-response curve was drawn. From this curve the 50% inhibitory concentration (IC^q) was b) Determination of Oral Bioavailability Long Evans Rats were admlnstered the compound to be tested by gavage at a dose equivalent to 25 ag/kg acyclovir. The urine was collected for 24 and 20 48 hours post-dose, ultraflltered, 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 acyclovir.

Compound Urinary Recovery (% of dose) as acyclovir Example I 50 Acyclovir (ACV) 15 Clycyl ester of ACV 30 L -alanyl ester of ACV 34 estimated.

Compound Example 1 15 Example 2 Acyclovir 0.84 3.8 0.08 - 0.1 d) Toxicity Data Determination of Growth Inhibition of Uninfected Mammalian Cells The capability of candidate compounds to inhibit the growth of D98 cells (human) and L cells (murine) was measured by determination of cell number ^ following three days exposure of a standard number of cells to various dilutions of compound (Rideout, J. L., Krenitsky, T.A. , Koszalka, G.W. , Cohn, N.K., Chao, E.Y. Elion, G.B., Latter, V.S., and Williams, R.B. (1982) J. Med Chem. 22.' 1040-1044). The cell number was then compared to the number obtained in the absence of compound. Cell enumeration was performed 10 by either direct particle counts following trypsinization of the monolayer, or by spectrophotometric determination of the amount of vital stain taken up by the cells. Comparable results were obtained with both methods. - 23 Dpta Analysis The concenCration of compound resulting in 50% of control values (IC50) was calculated either by direct interpolation from graphs of the log of the compound concentration versus che percent of control value, or from a computer program which analyses the data according to the same algorithm. Data in the range of 20% to 80% of control were used in these calculations.

Exwaple Cell Toxicity (% of concrol aC 100pm) D-98 Cells L-Cells ACV (acyclovir) 99 72 1 80 83

Claims (27)

1. 2-((2-Amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy)ethyl L-isoleucinate or a pharmaceutlcally acceptable salt thereof.

2. A salt of a compound according to claim 1 wherein the salt is an acid addition salt. 5

3. A salt of a compound according to claim 2 which is derived from hydrochloric, sulphuric, phosphoric, maleic, fumaric, citric, tartaric, lactic, acetic or p-toluenesulphonic acid.

4. 2-((2-Amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy)ethyl L-isoleucinate hydrochloride. 10

5. 2-((2-Amino-l,6-dihydro-6-oxo-9H-purin-9-yl)methoxy)ethyl L-isoleucinate.

6. A compound according to any of the preceding claims for use in medical therapy.

7. A compound according to claim 6 for use in the treatment of prophylaxis of a virus infection.

8. A compound according to claim 7 for use in the treatment or prophylaxis of a herpes 15 simplex vims infection.

9. Use of a compound according to any of claims 1 to 5 in the nsmufacture of a medicament for the treatment or prophylaxis of a vims infection.

10. Use of a compound according to any of claims 1 to 5 in the manufacture of a medicament for the treatment or prophylaxis of a herpes virus infection. .25 •

11. Use of a compound according to any of claims 1 to 5 in the manufacture of a medicament for the treatment or prophylaxis of a herpes simplex virus infection.

12. Use of a compound according to claim 11 in the manufacture of a medicament for the treatment or prophylaxis of a herpes simplex type 1 infection.

13. Use of a compound according to any of claims 1 to 5 in the manufacture of a medicament for the treatment or prophylaxis of a varicella zoster virus infection.

14. Use of a compound according to claim 13 in the manufacture of a medicament for the treatment or prophylaxis of varicella.

15. Use of a compound according to claim 13 in the manufacture of a medicament for the treatment or prophylaxis of zoster.

16. Use of a compound according to any of claims 1 to 5 in the manufacture of a medicament for the treatment or prophylaxis of a cytomegalovirus infection.

17. Use of a compound according to any of claims 1 to 5 in the manufacture of a medicament for the treatment or prophylaxis of an Epstein-Barr virus infection.

18. Use of a compound according to any om of claims 1 Xo 5 in the manufacture of a medicament for the treatment or prophylaxis of a hepatitis B virus infection.

19. A phannaceutical composition comprising as active ingredient a ccnpound according to any of claims I to 5 together with a pharmaceutically acceptable carrier.

20. A pharmaceutical composition according to claim 19 adapted for oral administration.

21. A pharmaceutical composition according to claim 20 in the form of a tablet or capsule.

22. A pharmaceutical composition according to claim 21 wherein the tablet or capsule contains from 10 to lOOQnqg of a compound according to any of claims I to 5.

23. A pharmaceutical composition according to claim 21 wherein the tablet or capsule contain from 20 to 500mg of a compound according to any of claims 1 to 5. .26.

24. Use of the compounds according to claims 1 to 5 in combination with zidovudine in the manufacture of a medicament for use in the treatment or prophylaxis of HIV infection.

25. A compound substantially as hereinbefore described with reference to the Examples.

26. Use of a compound substantially as hereinbefore described with reference to the Examples.

27. A pharmaceutical composition substantially as hereinbefore described with reference to the Examples. CRUICKSHANK & CO.,