CA1340084C - Esters of 9-(2-hydroxyethoxymethyl)guanine having antiviral properties - Google Patents

Abstract

2-[(2-Amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl L-isoleucinate and its pharmaceutically acceptable salts may be used in the treatment and prophylaxis of herpes virus infections.

Description

i 3 4 $~

The invention relates to a new ester of 9-(2-hydroxyethoxymethyl)guanine having valuable antiviral properties.
This application is a division of Canadian Patent Application 574,613, filed August 12, 1988.

9-(2-Hydroxyethoxymethyl)guanine, otherwise known as acyclovir, possesses a potent antiviral activity, particularly against herpes viruses (H. J.
Schaeffer et al, "Nature", 272 583-585 (1978), UK Patent Specification 1523865 and U.S. Patent Specification No. 4199574). Acyclovir is however only poorly soluble in water, thereby limiting the formulation of the drug in aqueous pharmaceutical preparations where solubility is required.

., Also acyclovir is only poorly absorbed from the gastrointestinal tract after oral administration ( 15% recovery in the urine when tested in rats and 20% in humans). Such low bioavailability requires the administration of large doses of drug in order to achieve and maintain effective anti-viral levels in the plasma.

' !
European Patent YSpecification 99493 describes amino acid esters of acyclovir, specifically the glycine and alanine esters which show improved water-solubility compared with acyclovir.

It has now been discovered that the L-isoleucine ester of acyclovir, characterised by side-chain branching adjacent to the ~-carbon atom, and which was not disclosed in European Patent Specification 99493, surprisingly has improved bioavailability after oral administration compared with the alanine and glycine esters mentioned therein.

According to one feature of the present invention we provide the compounds of formula (I) c ~ f~
I (I) CH20CH2CH20COCH(Rl)NH2

2 - ~ ~ x O ~ ~ ~

wherein Rl represents a group of fonmula -Cl-l[CH3]CH2CH3 and pharn~ceutically acceptable salts thereof. The compound of fonmula (I) can also be named as 2-(2-amino-1,6-dihydro-6-oxo-9H(purin-9-yl)methoxy)ethyl L-isoleucinate.
The isoleucine moi~ty is in tile L confiqura-~ion.

In tests in rats, measuring the urinary recovery as acyclovir (% dose administered) after oral administration, the compounds of the invention show a large increase in absorption from the gut compared with the other esters and compared with acyclovir. This enables less drug to be adminstered while still providin~ equivalent dru~ levels in the plasma after oral absorption.

In addition to the relatively high bioavailability, the compounds according to the invention possess substantially the same antiviral effect as acyclovir in vitro. The advantageous increase in bioavailability of the compound is thus not gained at the expense of antiviral potency. Indeed, it has been found that in certain clinical applications, e.g. the treatment of stromal keratitis, certain amino acid esters have been found to provide a superior therapeutic effect to acyclovir (EP 99493) The pharmaceutically acceptable salts of the compounds of formula (I) are preferably acid addition salts derived from an appropriate acid, e.g.
hydrochloric, sulphuric, phosphoric, maleic, fumaric, citric, tartaric, lactic, acetic or p-toluenesulphonic acid. Particularly preferred salts are the hydrochloride salts of compounds of formula (I).

In experiments in animals, it was discovered that the oral administration of the compounds of formula (I) above produced measurable levels of acyclovir in the plasma. Thus according to another aspect of the invention we provide a means of generating acyclovir in vivo by administration of a compound of formula (I) above or a pharmaceutically acceptable salt thereof to a mammal.

- 3 - ~ ~400~A

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

Thus, according to a curther feature of the present invention there is provide~
a process for the pr~paration of the compound of formula (I) ~bove and pharma-ceutically acceptable salts thereof which comprises:

a) reacting a compound of formula (II) ~ N
l! /

wherein X is an optionally protected hydroxy group, and Y is an optionally protected amino group with an optionally protected L-isoleucine or a functional equiYalent thereof;
, Y

b) converting a compound of formula (III) ~ ~ (III) I

CH20CH2CH20COCH(Rl)NH2 (wherein Rl 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 amino group; or G represents an amino group and M represents an atom or group that can be replaced by or converted to a hydroxy group) into a compound of formula (I) or a pharmaceutically acceptable salt thereof; or ! ~

- 4 - ~ 3 4 ~ ~ ~

c) reacting a compound of formula (IV) ~ \ ~ (IV) (wherein X and Y are as defined above and Q represents a leaving atom or group) with a compound of formula (V) ACH2~CH2CH2~C~CH(Rl)R2 (V) (wherein Rl is as defined above, A represents a leaving group or atom and R is an optionally protected aDino 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 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), the esterification reaction may be carried out in conventional manner, for example 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 .~.., .~

1 3 ~ 4 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.

As an alternative to the use of L-isoleucine 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. Cl 4alkanoyl 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), by method b), can be achieved by various means. For example G may represent an azid,el group which can be reduced to an amino group by catal~tic hydro~enation~ usin~ a suitable catalYst such as ~alladium 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 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 M is an amino group may be converted to a hydroxy group for example by treatment with a deaminating enzyme such as adenosine deaminase.

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

In process (c), the group Q in formula (IV) may, for example, represent a hydrogen atom; an acyl group, e.g. a Cl 4alkanoyl group such as an acetyl group or an aroyl group such an a benzoyl group; or a tri-Cl 4alkylsilyl 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 W

1 3 4 ~

wherein the acyl moiety may be, for example, a C~ ,,alkanoyl group such as acetyl or an aroyl group such as benzoyl- The group R2 may represent an amino-protecting group such as for example, Cl 4 alkanoyl (e.g. acetyl) or aryloxycarbanoyl (e.g. benzyloxycarbonyl) and it may also represent an azido group. The reaction may be conveniently effected in a strong polar solvent such as dimethylformamide or hexamethylphosphoramide, 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 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 ~ se and which are disclosed in the literature~such as the aforementioned text-book. Thus, for example, compounds of formu~a (III) may be generally prepared by using an analogous procedure to that of process (c), i.e. reacting an appropriate purine with a compound of formula (V) The optional conversions i), ii) and iii) may be effected in conventional manner. Thus, for example, removal of protecting groups in conversion i) may be effected by hydrolysis, solvolysis or hydrogenolysis as appropriate.
With regard to removal of protecting groups on the amino acid acyl radicals, hydrogenolysis, 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 the purine nucleus, these may ~e selected for example from arylmethyl groups e.g. benzyl; or tri-Cl ~ alkylsilyl e.g.
trimethylsilyl. Arylmethyl blocking groups may be removed for example by hydrogenolysis, e.g. by hydrogenation in the presence of Raney nickel or a palladium catalyst. Trialkylsilyl blocking groups may be removed for example by solvolysis e.g by alcoholysis.

~'.~

- 7 ~ q~

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 solut~on.

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

The present invention also provides the compound of formula (I) and pharmaceutically 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, variceIla zoster, cytomegalovirus as well aq diseases caused by hepatitis B or Epstein-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 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 rhinopneumonitis.

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 comprises administering to the animal an effective antiviral amount of a compound of formula (I) or a pharmaceutic,ally 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, - 8 - ~ 8 -~

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 5 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 carrier(s) must be "acceptable" in the sense 9 1 ~ 4 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 present 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 ormore 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~

lo .t 3 ~ , 4 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 for~ulated 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 asolid 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. 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 andnon- aqueous sterile injection solutions which may contain anti-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 orunit 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 ~t' ~ni.stered orally, parenterally or by any other desired route.

For oral A~lni~tration 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 Exam~le 1 2-(2-Amino-1.6-dihydro-6-oxo-9H(purin-9-yl)methoxy)ethyl L-isoleucinate hydrochloride a) 2-~(2-Amino-1.6-dihydro-6-oxo-9H-purin-9-yl)methoxylethyl-N-~(benzyloxy)carbonyll L-isoleucinate A mixture of acyclovir (1.0 g, 4.4. mmol; Burroughs ~ellcome Co.), 4-dimethylaminopyridine (74 mg, 0.6 mmol; Aldrich Chemical Co. and Chem.Ber. 89 2921-33 [1956]), 1,3-dicyclohexylcarbodiimidide (1.6 g, 8.0 mmol; Aldrich Chemical Co. and US 2656383), .., ~
. ~

- 13 - I 3~ ii84 N-carbobenzoxy-L-isoleucine (1.8 g, 6.6 mmol; Sigma Chemical Co. and Bull.Chem.Soc. Jap (1966) 39 947 or Tetrahedron 40 (24) 5207-11 [1984]), and molecular sieves (0.3 g, Davison type 3A; Fisher Scientific, Co.) in dry N,N-dimethylformamide (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-isoleucine (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-l2-Amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl-~-[(benzyloxy)carbonyl]-_-isoleucinate 0.8 g, 45%) as a white solid; mp 155-157 C;

W (MeOH); ~ max 255 nm (~17700) ~ sh 279 (9800), ~ min 230 (6100) NMR (200MHz, ME2SO-d6): 0.73-0.80 ppm (m, 6H), 1.13-1.33 (m, 2H), 1.66-1.70 (m, lH), 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, lH), 7.78 (s, lH), 10.59 (br s, lH);

MS (Cl/CH4; 70 C)) m/z 473 (1.0%, M+l), 347 (23.2, M-125), 225 (100.0, M-247); [~] 20 C~ 3.07~ (c 0.488, 6N HCl).

TLC: one spot on silica gel with 10% MeOH/CH2C12. Rf= 0.38 HPLC: one peak on Supelco LC8 with 50~ MeOH/H2O; 100% K'-7.02 Found: C, 53.94; H, 6.20 N, 17.04 b) 2-~(2-Amino-1.6-dihydro-6-oxo-9H-purin-9-yl~ethoxylethyl L-isoleucinate hydrochloride A solution of 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)-methoxy]-l?~ a~

ethyl-N-[(benzyloxy)carbonyl]-L-isoleucinate (1.11 g, 2.2 mmol) in methanol-tetrahydro furan (1:1, 50 ml) was treated 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 psi for 11 hours, filtered through a Celite pad and the filtrate was concentarted in vacuo to give 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl-L-isoleucinate hydrochloride (0.86 g, 92%) as an off-white solid; mp 180-182 C (effervescent softening ca. 150~C):

W (MeOH): ~ max 254 nm (~13400), ~ sh 272 (9000), ~ min 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, lH), 4.14-4.40 (m, 2H), 5.36 (s, 2H), 6.70 (br s, 2H), 7.97 (s, lH), 8.46 (br s, 3H), 10.87 (s, lH);

MS (Cl/CH4; 150 C): m/z 367 (6.9%, M+29), 339 (100, M+l), 225 (92.9, M-113); [~]D20 c + 11.15~ (c 2.0, HOAc)-' !
, ~
TLC: one spot on silica gel with 10% MeOH/CH2C12 Rf-0.12; HPLC: one peak on Versapack C18 with 10% MeOH/H2O/0.1% F3CCOOH;100% K'-3.74.
Anal Calcd for C14H22N6O4. 1.25 HCl. 1.10 MeOH. 0.25 H2O:
C, 42.81; H, 6.70; N, lg.84;; Cl, 10.46 Found C, 42.82; H, 6.50; N, 19.64; Cl, 10.46 Example 2 : Tablet Formulations The following formulations A, B and C are p,repared by wet granulation of the ingredients with a solution of povidone, followed by addition of magnesium stearate and compression.

Formulation A
mg/tablet mg/tablet Active ingredient 250 250 Lactose B.P. 210 26 Povidone B.P. 15 9 Sodium Starch Glycollate 20 12 Magnesium Stearate 5 3 Formulation B

j mg/tablet m~/tablet Active ingredient 250 250 Lactose 150 Avicel PH 101 (Trade Mark) 60 26 Povidone B.P. 15 9 Sodium Starch Glycollate 20 12 Magnesium Stearate 5 ~ormulation C
mg/tablet Active ingredient 100 Lactose 200 Starch 50 Povidone B.P. 5 Magnesium stearate . 4 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.

t Formulation D
mg/tablet Active Ingredient 250 Avicel (Trade Mark) 150 Magnesium Stearate 4 Formulation E
mg/tablet Active Ingredient 250 . ,, Lactose 150 Avicel (Trade Mark) 100 Magnesium Stearate 5 Formulation F (Controlled Release For~ulation) . I
, i ~
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 Hydroxypropylmethylcellulose112 (Methocel K4M Premium Trade Mark) Lactose B.P. 53 Povidone B.P. 28 Magnesium Stearate 7 - 17 - ~ ~ ~ g~ ~ L~

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 tinfra) is prepared in a similar manner.

Formulation B
mg/capsule Active ingredient 250 Lactose B.P. 143 Sodium Starch Glycollate 25 Magnesium Stearate 2 Formulation C
mg/capsule . ~
Active ingredient 250 Macrogol(Trademark) 4000 B.P.350 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.

~, - 18 - ~ 3~

~ormulation D
mg/capsule Active ingredient 250 Lecithin 100 Arachis Oil 100 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 releas~e-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 Example 4 : Ophthalmic Solution Active ingredient 0.5 Propylene Glycol 0.2 g Thiomersal 0.001 g Purified water to 100 ml pH adjusted to 7.5 k ~

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 lOml amber glass vial (type l) and sealed with sterile closures and overseals.

ExamDle 6: 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 7 : SyruD 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.

s ' , ~C~

- 20 - ~

Example 8 : SuPpository mg/suppository Active Ingredient (63~m)* 250 Hard Fat, BP (Witepsol H15 (Trade Mark) - 1700 Dynamit Nobel ) *The active ingredient is used as a powder wherein at least 90~ of the particles are of 63~m 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 200~m sieve and added to the molten base with mixing, using a silverson fitted with a cutting head, until a smooth dispersion is achieved. Maint~ining the mixture at 45 C, the remaining Witepsol Hl5 is added to the suspension and stirred to ensure a homogenous mix. The entire suspension is passed through a 250~m stainless steel sc~reen and, with continuous stirring, is allowed to cool to 40 C. At a tempe~rYature 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 9: Pessaries mg~pessary Active ingredient 63~m250 Anhydrous Dextrose 543 Starch 200 Magnesium Stearate 7 The above ingredients are mixed directly and pessaries prepared by direct compression of the resulting mixture.

- 21 - 1 3 ~ ~

Example IO

a) Antiviral Activity Herpes Simplex Virus (HSV l) was asssayed in monolayers of Vero cells in multiwell trays. Activity of compounds was determined in the plaque reduction assay, in which a cell monolayer was infected with a suspension of HSV l, 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 expressed as percentages of the control and a dose-response curve was drawn. From this curve the 50% inhibitory concentration (IC50) was estimated.

Compound IC50 ~M

Example l 3.8 Acyclovir ~ 0.08 - 0.1 b) Determination of Oral Bioavailability Long Evans Rats were adminstered the compound to be tested by gavage at a dose equivalent to 25 mg/kg acyclovir. 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 acyclovir.

ComDound Urinary Recovery (~ of dose) as acyclovir Example l 50 Acyclovir (ACV) 15 Glycyl ester of ACV 30 L -alanyl ester of ACV 34 .~.
.~

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. 25: 1040-1044). The cell number was then compared to the number obtained in the absence of compound. Cell enumeration was performed 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.

~ ~ I

~,~

) g ~

Data Analysis The concentration 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 the 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.

Example Cell Toxicity (% of control at lOO~m) D-98 Cells L-Cells ACV (acyclovir) 99 72 1 .~ 80 83 ~1 ,,

Claims (26)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

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

2. A salt of L-isoleucinate of claim 1, wherein the salt is an acid addition salt.

3. A salt of 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.

5. 2-[2-Amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl L-isoleucinate.

6. A compound of claim 1, 2, 3, 4 or 5, for use in the treatment or prophylaxis of a virus infection.

7. A compound of claim 1, 2, 3, 4 or 5, for use in the treatment or prophylaxis of a herpes simplex virus infection.

8. A pharmaceutically acceptable salt of claim 1, 2 or 3, for use in the treatment or prophylaxis of a viral infection.

9. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of a virus infection.

10. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of a herpes virus infection.

ll. Use of a compound of claim 1, 2, 3, 4 or 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 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of a herpes simplex type 1 infection.

13. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of a varicella zoster virus infection.

14. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of varicella.

15. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of zoster.

16. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of a cytomegalovirus infection.

17. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of an Epstein-Barr virus infection.

18. Use of a compound of claim 1, 2, 3, 4 or 5, in the manufacture of a medicament for the treatment or prophylaxis of a hepatitis B virus infection.

19. A pharmaceutical composition comprising as active ingredient a pharmacologically effective amount of a compound of claim 1, 2, 3, 4 or 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 capsule contains from 10 to 1000 mg of said compound.

23. A pharmaceutical composition according to claim 21, wherein the tablet or capsule contains from 20 to 500 mg of said compound.

24. Use of a compound of claim 1, 2, 3, 4 or 5, in combination with zidovudine in the manufacture of a medicament for use in the treatment or prophylaxis of HIV infection.

25. An antiviral pharmaceutical composition comprising an acceptable, antivirally effective amount of a compound of claim 1, 2, 3, 4 or 5, in association with a pharmaceutically acceptable carrier.

26. An anti-retroviral pharmaceutical composition for treatment or prophylaxis of HIV
infection comprising an acceptable, anti-retrovirally effective amount of a compound of claim 1, 2, 3, 4 or 5, in combination with zidovudine, and a pharmaceutically acceptable carrier.