CA1340083C

CA1340083C - Esters of 9-(2-hydroxyethoxymethyl)guanine having antiviral properties

Info

Publication number: CA1340083C
Application number: CA000574613A
Authority: CA
Inventors: Lilia Marie Beauchamp
Original assignee: Wellcome Foundation Ltd
Current assignee: Wellcome Foundation Ltd
Priority date: 1987-08-15
Filing date: 1988-08-12
Publication date: 1998-10-13
Anticipated expiration: 2015-10-13
Also published as: PH29943A; US4957924A; ES2065914T3; HU210815A9; AP9000238A0; DD282229A5; ZA885995B; PH29942A; DE3852682D1; DE3852682T2; GB8719367D0; ATE116648T1; LT2063B; HK39595A; DE19575021I2

Abstract

The present invention relates to certain amino acid esters of the purine nucleoside acyclovir, pharmaceutically acceptable salts thereof and their use in the treatment and prophylaxis of herpes virus infections. The invention also includes pharmaceutical formulations and processes for the preparation of such compounds.

Description

4~08~

The invention reiates to a new ester of 9-(2-hydroxyethox! meth) l)guanine having valuable antiviral properties.
9-(2-Hydroxyetho~methyl)guanine, otherwise known as acyclovir. possesses a potent antiviral activity, particularly against herpes viruses (H. J. Schaeffer et al, "Nature", ~2 ~83-~85 (1978), UK Patent Specification 152386~ and U.S. Patent Specification No.
4199574). Acyclovir is however only poorly soluble in water, thereby limiting the forrnulation of the drug in aqueous pharrnaceutical preparations where solubility is required.
Also acyclovir is only poorly absorbed from the gastrointestinal tract after oral ~1ministration ( 1~% recovery in the urine when tested in rats and 20% in humans). Such low bioavailability requires the ~lminictration of large doses of drug in order to achieve and m~int~in effective anti-viral levels in the plasma.
European Patent Specification 99493 and Journal of Medicinal Chemistry, vol. 26, no.4, 04/83, p.602-604 describes amino acid esters of acyclo~ir, specifically the glycine and alanine esters which show improved water-solubilit compared with acyclovir.
We have now discovered that the L-valine ester of acyclovir, characterised by side-chain branching adjacent to the a-carbon atom, and which were not disclosed in European Patent Specification 9949~ and the Journal of Medicinal Chemistry reference, surprisingly has improved bioavailability after oral ~lmini.stration compared with the alanine and glycine esters mentioned therein.
According to one feature of the present invention we provide the compound of formula (I) OH

CH20CH2CH20COCH(R j~H2 D

~ ~ 34~83 wherein Rl represents a group of forrnu~a -CH[CH3]~ the ester group -OCOCH(RI)NHo bein_ in the L-confinuration and pharmaceutically acceptable salts thereof. The compound of forrnula (I) can aiso be named as 2-((2-arnino- 1 ,6-dihydro-6-o~;o-9H-purin-9-yl)-methoxy)ethyl L-valinate.

In tests in rats, measuring the urinary recovery as acyclovir (% dose a-lmini~tered) after oral ~lministration, 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 ~lministered while still providing equivalent drug levels in the plasma after oral absorption. The L-valinate compound is especially preferred by virtue of its particularly good absorption from the ~ut.

In addition to the relatively high bioavailabilitv, the compound according to the invention possess substantially the sarne antiviral effect as acyclovir in vitro. The advantageous increase in bioavailabili~ 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 forrnula (I) are preferably acid addition salts derived from an approp,iate acid, e.g. hydrochloric, sulphuric, phosphoric, maleic, fumaric, citric, tartaric, lactic, acetic or p-toluenesulphonic acid. A particularly preferred salt is hydrochloride salt of the compound of formula (I).

In experiments in animals, it was discovered that the oral ~mini.~tration of the compound of formula (I) above produced measurable levels of acyclovir in the plasma. Thusaccording to another aspect of the invention we provide a means of generating acyclovir in vivo by ~iministration of a compound of formula (I) above or a pharrnaceuticallyacceptable salt thereof to a marnrnal.

The compounds according to the invention may be prepared in conventional manner, e.g.
by a process as described belo~s Thus, according to a further feature of the present invention we provide a process for the preparation of the compound of forrnula (I) above and pharmaceutically acceptable salts D

.. . , . . , .. .,, " ,. . . .. .. . . . .. .. .

3 ~ 8 ~

thereof which comprises a) reactinC a compound of forrnula (II) (II) Y 1~ 9 wherein X is an optionally protected hvdroxy group, and Y is an optionally protected arnino group with an optionally protected L-valine or a functional equivalent thereof;

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

CH20CH2CH20COCH(R )NH2 D

4 L~no~

(wherein R is as defined above; and M represents a hydro~y group and G represents an atom or group that can be replaced by or converted to an amino group; or G represents an arnino group and M represents an atom or group that can be replaced by or converted to a hydroxy group) into a compound of forrnula (I) or a pharrnaceutically acceptable salt thereof; or c) reacting a compound of formula (IV) ~N /\N

(wherein X and Y are as defi~ed above and Q represents a lea~ing atom or group) with a compound of formula (V) ACH2~CH2CH2~C~CH(Rl )R2 ~) (wherein R1 is as defined above, A represents a leaving group or atom and R is an optionally protected amino group); and optionally effecting one or more of the following conversions, in anv desired sequence:-i) removal of any protecting groups;
ii) where the resulting product is a compound of formula (r), conversion of the said r~
V

. ,, ., " . ., , ... , ,. ,. . ~ , . .. . .. . .. . .

-S- 13-~08~

compound into a pharmaceutically acceptable salt thereof; and iii) where the resulting product is a pharrnaceuticallv 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 dimethylforrnarnide 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 exarnple 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-valine ~ se, a functional equivalent of the acid may be employed, e.g. an acid halide such as the acid chloride, or an acid anhvdride. In such a case in order to avoid undesirable side-reactions, it is advantageous to use an arnino-protected derivative. Examples of preferred arnino-protecting groups including acyl, e.g.
C1 4alkanoyl such as acetyl and aryloxycarbonyl, e.g. benzyloxy carbonyl. A suitable arnino-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 forrnula (I), 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, usin_ a suitable catalyst such as palladium on carbon. Alternatively, G may each represent a halogen atom or an alkvlthio 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 exarnple, hydrogen in the presence of palladium on carbon. For the preparation of the compound of forrnula (I), a compound of forrnula (III) wherein M is an arnino group may be converted to a hydroxy group for exarnple b,v treatment with a ~e~rnin~ting enzyme such as adenosine de~min~ce.

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 _roup or an aroyl group such as a benzovl ~roup; or a tri-CI 4alkylsilyl group such as a trimethvlsilyl group. The group A
in forrnula (V) may, for example, represent a halo~en atom (e.g. chlorine) or an acyloxy group wherein the acvl moiety may be, for exampleja Cl 4alkanoyl group such as acetyl or an aroyl group such as benzoyl. The group R may represent an arnino-protecting group such as for example, Cl 4alkanoyl (e.g. acetyl) or arvloxycarbanoyl (e.g.
benzyloxycarbonyl) it may also represent an azido group. The reaction may be conveniently effected in a strong polar solvent such as dimethylformarnide or hexamethylphosphoramide, advantageously in the presence of a base such as triethylamine or potassium carbonate. Alternativel-, a therrnal condensation may be effected by heating the compounds of forrnulae (IV) and (V) in the presence of a catalytic amount of a strong acid, e.g. sulphuric acid.

Compounds of forrnulae (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 rnay be available commercially, or prepared accordin_ to techniques which are well known ~ se and which are disclosed in the literature such as the aforementioned text-book. Thus, for exarnple, compounds of forrnula (III) ma- be generally prepared by using an analogous procedure to that of process (c), i.e. reactin~ 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, remo~al 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 ~ido group, e.g. by catalytic hydrogenation, e.g. using a palladiurn catalyst, are preferred. ~ith regard to protection of the groups in the 2- and/or 6-positions of purine nucleus, these may be selected for e~;ample from arylmethyl groups e.g benzyl;
or tri-Cl 4alkylsilyl e.g. trimethylsilyl. Arylmethyl blocking groups, may be removed for e~;arnple by hvdrogenolysis, e.g. bv hydrogenation in the presence of Raney nickel or a palladium catalyst. Trialkvlsilyl blocking groups may be removed for example by solvolysis e.g. by alcoholysis.

The conversion of a compound of formula (l) into a pharrnaceutically acceptable salt may 7 lt~c ~-OQ~

be effected in conventional manner for e~;ample, by treatment of the compound with an appropriate acid to form an acid addition salt? for e~arnple~ by Iyophilsation of a methanolic solution of the parent ester with an acid solution.

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

The present invention also provides the compound of formula (I) and pharmaceuticaly acceptable salts thereof (hereinafter identified as "the active compounds") for use in medical therapy e._ in the treatrnent or prophylaxis of a viral disease in an animal, e.g. a m~mmal 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, ~aricella zoster, cytomegalovirus as well as diseases caused by hepatitis B or Epstein-Barr viruses or hurnan herpes virus -6 (HHV-6). The active compounds can also be used for the treatInent or prophylaxis of retrovirus infections such as HIV infections and papilloma or wart virus infections. In addition to their use in hurnan medical therapy, the compounds of forrnula (I) can be ~lministered to other animals for treatrnent or prophylaxis of viral diseases, e.g. in other m~mm~.s. For exarnple, the active compounds are especiallv 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 m~mm~l such as man, which comprises ~mini~tering to the animal an effective antiviral amount of a compound of formula (I) or a pharmaceutically 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 aflmini.~tered by any route appropriate to the condition to be treated, suitable routes including oral, rectal, nasal, topical (including buccal and sublingual) va~inal 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 abo~e-indicated utilities and indications the amount required of an active D

~ -8- 1~ 08~

ingredient (as abo~e 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 as 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 2~0mg per kilograrn bodyweight of recipient per d~y, preferably in the ran2e 1 to ] OOmg per kilograrn bodyweight per day and most preferablv in the range 5 to 20mg per kilograrn body~eight per day; an optimurn dose is about lOmg per kilograrn bodyweight per day. (Unless otherwise indicated, all weights of acti~ e ingredient are calculated as the parent compound of forrnula (I): for salts thereof the figures would be increased proportionately). The desired dose is preferably presented as two, three, four or more sub-doses a~lmini~tered at appropriate intérvals tllroughout the day. These sub-doses rnay be ~ministered in unit dosa_e forrns, for example, containing 10 to lOOOmg, preferably 20 to ~OOmg and most preferably 100 to 400mg of active ingredient per unit dosage form.

The compounds of the present invention may be atlministered 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 a-1mini~tered alone, it is preferably to present them as pharmaceutical forrnulations. The formulations, both for veterinary and for human use, of the present invention comprise at least one active inoredient, 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 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 subcutaneous, intramuscular, intravenous, intraderrnal, intrathecal and epidural) a~mini~tration. The formulations may conveniently be presented in unit dosage forrn and may be prepared by any of the methods well known in the art of pharmacy. Such methods include the step of brin_ing into association the active in~redient with the carrier which constitutes one or more accessory ingredients. In general, the formul.~tions are prepared by uniforrnly and intimately bringing into association the active in~redient with liquid carriers of finely divided solid carriers or both, V

9 ~ 00 and the, if necessar~ . shaping the product.

Forrnulations of the present in~ ention 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 b~ made by compression or moulding, optionally with one or more accessory ingredients. Compresses tablets may be prepared by compressing in a stuiable m~chine the active ingredient in a free-f~owing 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 forrnulated so as to provide slow or controlled release of the active ingredient therein.

For infections of the eye or other extemal tissues e.g. mouth and skin, the forrnulations are preferably applied as a topical ointment or cream containing the active ingredient in an arnount of, for exarnple, 0.075 to 20% w/w, preferably 0.2 to 1~% w/w and most preferably 0.5 to 10% w/w. When forrnulated 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 crearn with an oil-in-water crearn base. In addition topical applications may be made transderrnally by means of an iontophoretic device.

If desired, the aqueous phase of the cream base may include, for exarnple, at least 30%
w/w of a polyhydric alcohol, i.e. an alcohol having t~vo or more hydroxyl groups such as propylene glvcol, butane 1,~-diol, mannito], sorbitol, glycerol and polyethylene glycol and mixtures thereof. The topical forrnulations may desirably include a compound which enhances absorption or penetration of the active ingredient through the skin or other affected areas. Exarnples of such derrnal penetration enhancers include dimethylsulphoxide and related analogues.

- 10 - i ~J'' i~

Forrnulations suitable for topical administration to the eye also include eye drops wherein the acti~e 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 forrnulations in a concentration of 0.5 to 20%, advantageously 0.5 to 10% particularly about 1.~% w/w.

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

Forrnulations for rectal ~mini.stration may be presented as a suppository with a suitable base comprising for exarnple cocoa butter or a salicylate.

Formulations suitable for nasal ~lmini.stration wherein the carrier is a solid include a coarse powder having a particle size for exaTnple in the range ~0 to ~00 microns which is ~imini~tered in the manner in which snuff is taken, i.e. bv 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, includè aqueous or oily solutions of the active ingredient.

Formulations suitable for vaginal ~ministration may be presented as pessaries, tampons, creamst 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 ~lministration include aqueous and non-aqueous steriie injection solutions which may contain anti-oxidants, buffers, bacteriostats and solutes which render the forrnulation isotonic with the blood of the intended recipient; arld 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 (Iyophilized) 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 r~

- ] ~ 0 8 ~

pre~iously 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 ~minictration may include flavouring aoents.

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 materaials useful for the purpose of a~minictering the composition and may be solid, liquid or gaseous materials which are otherwise inert or acceptable in the veterinary art and are compatible uith the active ingredient. These veterinary compositions may jbe ~rlmini.ctered orallv, parenterally or by any other desired route.

For oral ~mini.ctration 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 ~minictered 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 dispensing agent are included.
These forrnulations preferably contain from 15 to 85% of the active ingredient.

The following Examples illustrate the present invention F.xarnple lA

2-(?-Amino- 1 .6-dihvdro-6-oxo-9H(purin-9-v])methoxv)ethvl T .-valinate a) ?-~f2-Amino-1.6-dihvdro-6-oxo-9H-purin-9-yl)methoxv]ethyl-~-[(ben7yloxv)carbonyl] L-valinate - I 7 - i i.,~ 3 A suspension of acvclovir (~.000~; Burroughs Wellcome Co.) in dry dimethylfomlamide (DMF) ( ] 50ml) was ~armed to 60 C to give a colorless solution. CBZ-L-valine (3.017g; Sigma Chemicals, St. Louis MO and J.Arn.Chem.Soc, 79, 5697 (1957), 4-dimethylaminopyri- dine (154mg; DMAP, Chem.Ber. 89 2921-33 [1956] and dicyclohexyl- carbodiimide (2.998g; DCC, US
Patent 2656~83) were added to the warrn solution. The faint yellow solution was allowed to cool to room temperature and stirred overnight. A white precipitate was observed after 30 minutes. The reaction mixture was recharged with the above arnounts of CBZ-L-valine, DMAP and DCC and the cloudy suspension stirred at room temperature for 2 days. The suspension was filtered to remove 1.418g, of a white solid. The colorless filtrate was concentrated to give a light yellow oil. The oil was purified by flash chromatography on silica gel, eluting with a methanol in dichloromethane gradient (0.15%) to yield the title compound as 3.751g (92.1%) of a white solid.

b) ~-[(2-,4 mino- 1.6-dihvdro-6-oxo-9H-purin-9-vl)methoxv]ethvl T -valin~

A mixture of 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)meth- oxy]ethyl 1~-~benzyloxy)carbonyl] L-valinate (5.0g), 5% palladiurn on carbon catalyst - 50%
water (2g), and dimethylforrnamide (50ml), was shaken on a Parr a~ Llls under 40 psi H~ for 3 hours. The reaction rnixture was filtered through a pad of Celite and evaporated in vacuo to give an oil. A solid was crystallised from water/ethanol (1 :3v/v) and recrystallised to yield l .5g of title compound;
Analysis Calcd. C, 48.14; H, 6.22, N, 25.91 Found C, 47.84; H, 6.26; N, 25.75 Fxarnple lF~

2-e-Amino-]~6-dihvdro-6-oxo-9H(purin-9-yl)methoxv)ethv~L-va1inate hydrochloride monohvdrate a) 2-[f2-Amino-~6-dihvdro-6-oxo-9H-~unn-9-vl)methoxv]ethvl ~-[fbenzv]oxv)carbonvl] T-valinate A suspension of ac~clo~ir (~.OOOg; Burroughs Wellcome Co.) in dry dimethylformamide (DMF) (150ml) ~as warrned to 60 C to give a colorless solution. CBZ-L-~aline (3.01~g; Sigma Chemicals, St. Louis MO and J.Am.Chem.Soc, 79, 5697 (1957), 4-dimethylaminopyri- dine (154mg; DMAP, Chem.Ber. 89 2921-33 [1956] and dicyclohexyl- carbodiimide (2.998g; DCC, US
2656383) were added to the warm solution. The fain yellow solution was allowed to cool to room temperature and stirred overnight. A white precipitate was obsenJedafter 30 minutes. The reaction mixture was recharged with the above amounts of CBZ-L-valine, D~AP and DCC and the c]oudy suspension stirred at room temperature for 2 days. The suspension was filtered to remove 1.418g, of a whitesolid. The colorless filtrate was concentrated to give a light yellow oil. The oil was purified by flash chromatography on silica gel, eluting with a methanol in dichloromethane gradient (0-15%) to yield the title compound as 3.751g (92.1%) of a white solid.

b) 2-[(~-Amino- 1 ~6-dihvdro-6-oxo-9H-purin-9-v3)methoxv]eth~ 1 r -v~lin~t~
l~vdrochloride monohvdrate A mixture of 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl ~I.-[benzyloxy)carbonyl] L-valinate, (3.730g), 5% palladium on carbon catalyst (377mg), methanol (lOOml), tetrahydrofuran (THF) (lOOml) and a 0.5 M aqueous HC1 solution (18ml) was sha~cen on a Parr a~p~dLus under 60 psi H for one day.
The reaction mixuture w as filtered through a pad of Celite*then concentrated to give a white solid. This solid was recrystallized from water/ethanol to yield the title compound as 1.762g (60.0%) of a white powder; mp 150 C (solid shrinks), gradually changes to oil and decomposes with foaming at 195 C.
Analysis Calcd. C, 41.22; H, 6.12; N,22.19; Cl, 9.36 Found C,41.09;H,6.10;N,22.12;CI,9.28 Example 2 Tablet Fonnulations The following formulations A, B and C are prepared by wet granulation of the ingredients with a so]ution of providone. followed by addition of magnesium stearate and compression.
* Trade Mark Forrnulation A
m~/tabletmo/tablet Active Ingredient 2jO 250 Lactose B.P. 210 26 Povidone B.P. I
Sodium StarchGlycollate 20 1 Magnesiurn Stearate 5 3 iOO ~00 Formulation B
m~/tabletm~/tab]et Active Ingredient2jO 250 Lactose 1 50 Avicel PH 101 60 26 Povidone B.P. 1 j 9 Sodium St2rch Glycollate 20 12 Magnesium Stearate Formulation C
mg/tablet Active Ingredient 100 Lactose 200 Starch 50 Povidone B.P. 5 Magnesium Stearate _4 The following forrnulations D and E, are prepared by direct compression of the admi~:ed in_redients. The lactose in forrnulation E is of the compression type.

* Trade Mark 'L~

- 15~ $~

FormuJation D
m~/tablet Active Ingredient 250 Avicel * I S0 Magnesium Stearate 4 Forrnulation E
m~/tablet Active Ingredient 250 Lactose 150 Avicel 1 00 MagnesiD Stearate 5 Forrnulation F (Controlled Release Forrnulation~

The formulation is prepared by wet granulation of the ingredients (below) with asolution of povidone followed by the addition of magnesiurn stearate and compression.
m~/tablet Active Ingredient 500 Hydroxypropylmethylcellulose 1 12 (Methocel K4M Premium) Lactose B.P. 53 Povidone B.P. 28 Magnesium Stearate 7 Example 3: Capsule Formulations Forrnulation A
* Trade Mark ~D-A capsule formulation is prepared admixing the ingredients of Fonnulation D in Example 2 above and filling into a two-part hard gelatin capsule. Formulation B
(infra! is prepared in a similar manner.

Fonnulation B
mg/capsule Active Ingredient 50 Lactose B.P. 143 Sodium Starch Glycollate 25 Magnesiurn Stearate Forrnulation C
m~lcaps Active Ingredient 250 Macrogol 4000 B.P. ~Q

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.

Formul~tion D

Active Ingredient 250 Lecithin l 00 Arachis Oil l oo Capsules are prepared by dispersing the active ingredient in the lecithin and arachis oil and filling the dispersion into soft, elastic gelatin capsules.

Formulation F ~Controlled Rel~ Capsule) * Trade Mark D

~ ' 17 ~ nQ~'~

The following controlled release capsule forrnulation is prepared by extruding ingredients a, b and c using an ext;uder, followed by spheronisation of the extrudate and drying. The dried pellets are then coated with release-controlling membrane (d) and filled into a t~,vo-piece, hard gelatin capsule.
m~/capsule Active Ingredient 250 Microcrystalline Cellulose 125 Lactose B.P. 125 Ethyl Cellulose 13 Fx~ le 4: Ophth~lmic Solution Active Ingredient 0.5 Propylene Glycol 0.2 g l~iomersal 0.001 g Purified water to pH adjusted to 7.5 - 100 rnl Fx~ le 5: Tn~lectable Forrnulation Active Ingredient 0.200 g Sterile, pyrogen free citrate buffer (pH 7.0) to 10 ml o o rhe active ingredient is dissolved in most of the citrate buffer (3 5 -40 C), then made up to volurne and filtered through a sterile rnicropore filter into a sterile l Oml ~rnber glass vial (type l) and sealed with sterile closures and overseals.

F.x~ le 6: Intr~-nusc~llar Ir~ection Active Ingredient 0.20 g Benzyl Alcohol 0.10 g Glycofiurol 75 1.45 g Water for Injection q.s. to 3.00 ml r~ .

- 18- ~ 3~;QO~

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

F.~;amp]e 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 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.

~x~n~le 8: Slu;positorv Active Ingredient (63,u m)* 250 Hard Fat, BP (Witepsol H~ j - Dynarnit NoBel) 1700 * The active ingredient is used as a powder wherein at least 90% of the particles are of 6311m diameter or less.
** o One-fifth ofthe Witepsol H15 is melted in a steamjacketed pan at 45 C maxirnum. The active ingredient is sifted through a 20011m 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 4j C, the rern~inin~ Witepsol H15 is added to the suspension and stirred to ensure a homogenous mix. The entire suspension is passed through a 25011m 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.
llle suppositories are allowed to cool to room temperature.
** Trade Mark ~FD

19- L~J~

Example 9: Pessaries Active Ingredient 631m 250 Anhydrous Dextrose 543 Starch 200 Magnesiurn Stearate 7 The above ingredients are mixed directly and pessaries prepared by direct compression of the resulting mixture.

Fxan~le l 0 a) Antiviral Activitv Herpes Simplex Virus (HSV l) was assayed 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 1, and then overlaid with nutrient agarose in the form of a gel to ensure that there was no spread of virtue throughout the culture. A range of concentrations of cor~pound of known molarity was incorporated in the nutrient agarose overlay. Plaque nurnbers at each concentration were expressed as percentages of the control and a dose-response cur~e was drawn. From this curve the 50% inhibitory concentration (IC50) was estim~te,1 Corr~ol]n~ 0,~.~

Example l B 0.84 Acyclovir 0.08 - 0.1 b) r)etermination of Oral Bioavailabilitv Long Evans Rats were ~(lministered the compound to be tested by gavage at a doseequivalent to 25mg/}~g acyclovir. The urine was collected for 24 and 48 hours post-dose, ultrafiltered, and analysed by reverse-phase high-pressure liquid ~.. .
s, ~
~.

~ . :

-20~ 0~3 chromatography. ~he oral bioavaiiability of the compoud was expressed as the percent of the dose e~;creted in the urine as acyclovir.

Cgmpound I Jrinarv Recoverv (% of dose) as acvclo~ir Example 1 63 Acyc]ovir (ACV) 15 Glycyl ester of ACV 30 L -alanyl ester of ACV 34 d) Toxicitv Data Deterrnin~tion of Growth Jnhibition of Uninfe~ted M~mm~lian Cellc The capability of candidate compounds to inhibit the growth of D98 cells (human)and L cells (murine) was measured by det~rmin~tion of cell nurnber following three days exposure of a standard number of ceIls to various dilutions of compound (Rideout, J.L., Krenitsky, T.A. Koszalka7 G.W., Coh, N.K., Chao, E.Y. Elion, G.B., Latter, V.S., and Williams, R.B. (1982) J.Med.Chem. 25: 1040-1044). The cell nurnber was then compared to the number obtained in the ~bsen~e of compound.
Cell enumeration was performed by either direct particle counts followillg trypsinization of the monolayer, or b,v spectrophotometric determin~tion of the amount of vital stain taken up by the cells. Comparable results were obtained with both methods.

Data An~l,vsis The concentration of compound resulting in ~0% of control values (IC~0~ 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 dataaccording to the same algorithm. Data in the ran~e of 20% to 80% of control were used in these calculations.

fD

-21 I.3 F~rnple Cell Toxicitv (% of control at 100,~7) D-98 Cells L-Cells ACV (acyclovir) 99 7 lB 91 85 ~D

Claims

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

2. A salt of the L-valinate according to 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-valinate hydrochloride.

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

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

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

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

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

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

11. A compound of claim 1, 2, 3, 4 or 5, for use in the treatment or prophylaxis of varicella.

12. A compound of claim 1, 2, 3, 4 or 5, for use in the treatment or prophylaxis of zoster.

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

14. A compound of claim 1, 2, 3, 4 or 5, for use in the treatment or prophylaxis of an Epstein-Barr virus infection.

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

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 viral 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 a herpes viral 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 herpes simplex virus infection.

19. 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 type 1 infection.

20. 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.

21. 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.

22. 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.

23. 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.

24. 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.

25. 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.

26. 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.

27. A pharmaceutical composition according to claim 26, for use in the treatment or prophylaxis of herpes simplex virus infection.

28. A pharmaceutical composition according to claim 26, for use in the treatment or prophylaxis of varicella zoster virus infection.

29. A pharmaceutical composition according to claim 26, for use in the treatment or prophylaxis of a cytomegalovirus infection.

30. A pharmaceutical composition according to claim 26, 27, 28 or 29, in a form for oral administration.

31. A pharmaceutical composition according to claim 30, in the form of a tablet or capsule.

32. A pharmaceutical composition according to claim 31, wherein the tablet or capsule contains from 10 to 1000 mg of said active ingredient.

33. A pharmaceutical composition according to claim 31, wherein the tablet or capsule contains from 20 to 500 mg of said active ingredient.

34. 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.

35. 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.

36. An antiviral pharmaceutical composition comprising an acceptable, antivirally effective amount of 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl L-valinate hydrochloride, in association with a pharmaceutically acceptable carrier.

37. An antiviral pharmaceutical composition comprising an acceptable, antivirally effective amount of 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl L-valinate, in association with a pharmaceutically acceptable carrier.

38. A composition of claim 35, in the form of a tablet.

39. A composition of claim 35, in the form of a capsule.

40. A composition of claim 38 or 39 containing from 10 to 1000 mg of said compound.

41. A composition of claim 38 or 39, containing from 20 to 500 mg of said compound.

42. A composition of claim 36 or 37, in the form of a tablet.

43. A composition of claim 36 or 37, in the form of a capsule.

44. A composition of claim 36, in the form of a tablet containing 10 to 1000 mg of said hydrochloride.

45. A composition of claim 36, in the form of a tablet containing 20 to 500 mg of said hydrochloride.

46. A composition of claim 36, in the form of a capsule containing 10 to 1000 mg of said hydrochloride.

47. A composition of claim 36, in the form of a capsule containing 20 to 500 mg of said hydrochloride.

48. A composition of claim 37, in the form of a tablet containing 10 to 1000 mg of said L-valinate.

49. A composition of claim 37, in the form of a tablet containing 20 to 500 mg of said L-valinate.

50. A composition of claim 37, in the form of a capsule containing 10 to 1000 mg of said L-valinate.

51. A composition of claim 37, in the form of a capsule containing 20 to 500 mg of said L-valinate.

52. 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.

53. A process for the preparation of a compound of formula (I):

wherein R1 represents a group of formula -CH[CH3]2 the ester group (OCOCH(R1)NH2) being in the L-configuration, or a pharmaceutically acceptable salt thereof which comprises:
a) reacting a compound of formula (II):

wherein X is an optionally protected hydroxy group, and Y is an optionally protected amino group with an optionally protected L-valine or a functional equivalent thereof; or b) i) converting G to an amino group in a compound of formula (III):

wherein R1 is as above, M represents a hydroxy group and G represents a halogen atom or an alkylthio or alkylsulphonyl group by converting G to an azide group and converting the azide group to an amino group by catalytic hydrogenation; or ii) converting M to hydroxy in a compound of formula (III) as defined above, wherein R1 is as defined above, G is amino and M is amino, with a deaminating enzyme; 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(R1)R2 (V) wherein R1 is as defined above, A represents a leaving group or atom and R2 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 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.