ANTIVIRAL COMPOUNDS

Abstract: Compounds of the general formula (wherein R is a hydroxy or amino group and X is an oxygen or sulphur atom) and their physiologically accept­ able salts and esters have been known to have antiviral activity particularly against herpes viruses. Processes for preparing such compounds are described as well as pharmaceutical and veterinary compositions containing these compounds.

Description: ANTIVIRAL COMPOUNDS This invention relates to antiviral purine derivatives containing an acyclic side chain in the 9-position. The invention also relates to methods of synthesising these compounds, pharmaceutical and veterinary compositions containing them, and their use in the treatment of viral infections in mammals. Ogilvie and Gillen, in Tetrahedron Letters, 21, 1980, 327-330, describe the synthesis of the bis-(hydroxymethyl)methoxymethyl derivatives of adenine but no biological activity was disclosed. In this reference the compound was tested with adenosine deaminase and found it to be a poor substrate for the enzyme and a weak competitive inhibitor. 9-L(2-Hydroxy-1-hydroxymethylethoxy)methylj guanine and the corresponding 6-amino analogue are embraced within the general formula of UK Patent Specification No. 1523865 but are not disclosed specifically therein. UK Patent Specification No. 1523865 discloses a group of acyclic riucleosides, in particular 9-(2-hydroxyethoxymethyl) derivatives of purines, which have been found to have antiviral activity against various classes of DNA and RNA viruses both in vitro and in vivo. In particular these compounds possess activity against the herpes group of viruses which includes H. simplex, H. zoster and H. varicella. These viruses cause such diseases as herpetic keratitis, herpetic encephalitis, cold sores, shingles and genital infections. Of the compounds specifically disclosed in UK Patent Specification No. 1523865, 9 (2-hydroxyethoxymethyl) guanine, otherwise known as acyclovir, has been found to be particularly active against many H. simplex infections but suffers from the disadvantage of being poorly soluble in aqueous systems. It has now been found unexpectedly that the compounds of formula (I) below, in contrast to other compounds disclosed in UK Patent Specification No. 1523865 and heretofore tested, have useful antiviral activity sufficient to treat equine rhinopneumonitis virus in vivo. In experiments in mice, the compounds have also been found to have advantageous activity against herpetic encephalitis. Furthermore these compounds have the selective advantage of greater solubility in water compared with acyciovir which improves the possibility of being able to obtain high levels of the drug in the plasma without the risk of renal complications. According to the present invention there are provided compounds of formula EMI2.1 (wherein R is a hydroxy or amino group and X is an oxygen or sulphur atom) and physiologically acceptable salts and esters thereof. Examples of compounds of formula (I) include 9- L(2 -hydroxy-1 -hydroxymethy le thoxy)methyA7guanine, and 9- -tC2 -hydroxy -1 -hydroxymethylethoxy)methyl7- 2,6 -d iam inopurine. As mentianed above, the compounds of formula (I) have the important advantage of having a greater solubility in water than acyclovir. Thus, the compounds of formula VI) wherein X is an oxygen atom and R is a hydroxy group or amino group have solubilities of 0.4 - 0.5% and 2 - 3% w/w respectively compared with a figure of 014% w/w for acyclovir. Salts of the compounds of formula (I) which may be conveniently used in therapy include physiologically acceptable salts of organic acids such as lactic, acetic, malic or p-toluenesulphonic acid as well as physiologically acceptable salts of mineral acids such as hydrochloric or sulphuric acid. Esters of the compounds of formula (I) which may be conveniently used in therapy include those containing a formyloxy or C1-16 (for example C16) alkanoyloxy (e.g. acetoxy or propionyloxy), optionally substituted aralkanoyloxy (e.g. phenyl-C14alkanoyloxy such as phenyl-acetoxy) or optionally substituted aroyloxy (e.g. benzoyloxy or naphthoyloxy) ester grouping at one or both of the terminal positions of the 9-side chain of the compounds of formula (I). The above-mentioned aralkanoyloxy and aroyloxy ester groups may be substituted, for example by one or more halogen (e.g. chlorine or bromine) atoms or amino, niLrile or suiphamido groups, the aryl moiety of the grouping advantageously containing 6 to 10 carbon atoms. The present invention also includes bioprecursors of the compounds of formula (l) and their physiologically acceptable salts and esters, i.e. compounds which are converted in vivo into compounds of formula (I) and their above-mentioned derivatives. The compounds of formula (I) and their salts and esters may be prepared in conventional manner by analogous processes for preparing compounds of similar structure, such as those methods described in UK Patent Specification No. 1523865. In a second aspect of the present invention there is provided a process for preparing compounds of formula (I) and physiologically acceptable salts and esters thereof, characterised in that: (a) a compound of formula (II) EMI3.1 (wherein X is as defined above and W and W each represent a hydrogen atom or a blocking group, Y is a hydrogen atom or a blocking group and Z is a group of formula -OY or -NHY wherein Y is as defined above providing that at least one of W, W1 and Y represent a blocking group), is deblocked to form a compound of formula (I) or a salt or ester thereof; ; (b) a compound of formula (III) EMI3.2 (wherein X is as defined above and either M is a 6-hydroxy or amino group and G is an atom or group that can be replaced by or converted to an amino group, or G is a 2-amino group and M is an atom or group that can be replaced by or converted to an amino or hydroxy group) or a salt or ester thereof is converted to a compound of formula (I) or a salt or ester thereof; (c) a compound of formula (IV) EMI3.3 (wherein R and X are as defined above) or a salt or ester thereof is reduced by a method known per se; (d) a compound of formula EMI4.1 (wherein R is as defined above and Q is a leaving group or atom) is reacted with a compound of formula EMI4.2 (wherein X is as defined above and A is a leaving group or atom); ; (e) hydrolysis of a compound of formula EMI4.3 (wherein R and X are as,defined above); and optionally effecting one or more of the fdlowing conversions, in any desired sequence:i) where the resulting product is a base, converting the said base into a physiologically acceptable acid addition salt thereof; ii) where the resulting product is an acid addition salt, converting the said salt into the parent base; iii) where the resulting product is a compound of formula (I) or a salt thereof converting the said compound or salt thereof into a physiologically acceptable ester of the said compound or salt; and/or iv) where the resulting product is an ester of a compound of formula (I) converting the said ester into the parent compound of formula (I) or a physiologically acceptable salt thereof. In method a) the blocking groups W, W1 and Y may be selected for example from acyl groups such as C1 4alkanoyl groups e.g. acetyl, aroyl groups, e.g. benzoyl; arylmethyl groups e.g. benzyl; or tri-C1 4 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 or by the use of sodium in liquid ammonia. Acyl blocking groups may be removed for example by hydrolysis using for example an amine such as methylamine or triethylamine, advantageously in an aqueous medium. Trialkylsilyl blocking groups may be removed for example by solvolysis e.g. with alcoholic or aqueous ammonia, or by alcoholysis. Conversion of a compound of formula (III) into a compound of formula (I), by method b), can be achieved by various means. For example M and/or G may each represent an azide group which can be reduced to an amino group by catalytic hydrogenation using a suiLable catalyst such as palladium. Alternatively, M and/or G may each represent a halogen atom or an alkylthio or alkylsulphonyl group which can be converted to an amino group by aminolysis using for example ammonia. For the preparation of the compound of formula (I) wherein R is a hydroxy group, a compound of formula (III) wherein M is an amino group may be converted for example by treatment with nitrous acid. Alternatively, a compound of formula (III) wherein M is a mercapto or alkylthio group may be converted into a compound of formula (I) wherein R is a hydroxy group by oxidation and hydrolysis in-conventional manner. Also, a c ound o ormu a (III) wherein Dil is halogen can be converted into a compound of formula (I) wherein R is hydroxy by treatment with 2-mercaptoethanol and an alkali metal alkoxide, e.g. sodium methoxide. These processes together with other conventional processes are described in Fused Pyrimidines, Part II, Purines Ed. by O. J. Brown (1971), Wiley lnterscience. In a further alternative a compound of formula (III) wherein M is an amino group may be converted into a compound of formula (I) wherein R is a hydroxy group by treatment with a deaminating enzyme such as adenosine deaminase. Reduction of a compound of formula (IV) in process (c), may be achieved for example by reaction with an appropriate aldehyde reducing agent such as sodium borohydride, sodium cyanoborohydride, te traethylammonium borohydride or pyridine/diborane/tetrahydrofuran/trifluoroacetic acid. In process (d), the group Q in formula (V) may for example represent a hydrogen atom; an acyl group, e.g. a C1 4alkanoyl group such as an acetyl group or an aroyl group such as a benzoyl group; or a tri- C14alkylsilyl group such as a trimethylsilyl group. The group A in formula (VI) may for example represent a halogen atom (e.g. chlorine) or an acyloxy group wherein the acyl moiety may be for example a C1 4alkanoyl group such as acetyl or an aroyl group such as benzoyl. 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 (V) and (VI) in the presence of a catalytic amount of a strong acid, e.g. sulphuric acid. In process (e), hydrolysis of the compound of formula (VII) may be effected for example under basic conditions, e.g. by treatment with an organic amine such as methylamine or triethylamine. In a process incorporating processes a) and b) above, a compound of formula (VII) EMI6.1 wherein W; W1, X and Z are as defined above and G represents a halogen atom can be treated with alcoholic ammonia to give the desired end-product of formula (I). Compounds of formula (II) to (VIII) employed as intermediates in the synthesis of the compounds of formula (I) can be prepared in conventional manner, e.g. by procedures described in UK 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 formulae (II) and (III) may be generally prepared by using an analogous procedure to that of process (d), i.e. reacting an appropriate purine wherein the 2-, 6-, and/or 9- positions are optionally protected, e.g. by acyl or trialkylsilyl groups of the type described above, with a compound of formula (VI) wherein the terminal hydroxy groups are optionally protected by acyl or trialkylsilyl groups of the type described, and subsequently, as necessary and/or desired, removing any of the said protecting groups, prior to use in processes (a) or-(b). Alternatively, a compound of formula (II) wherein W and W1 each represent a benzoyl blocking group can be prepared for example by treatment of a corresponding 9-bis(chloromethyl)methoxy (or thio) methyl purine analogue with a benzoylating agent, e.g. sodium benzoate the starting purine analogue being prepared for example by treatment of a compound of formula (V), optionally protected in the 2-and/or 6-positions, with a compound of formula EMI7.1 (wherein A and X are as described above). Compounds of formula (IV) may be prepared in conventional manner, e.g. as herein described in Example 3 of the present invention or by analogous procedures. The present invention also provides compounds of formula (I) and physiologically acceptable salts and esters thereof for use 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 or zoster, cytomegalovirus as well as diseases caused by hepatitis B or Epstein-Barr viruses. The compounds of formula (I) can also be used for the treatment or prophylaxis of papilloma or wart virus infections. In addition to their use in human medical therapy, the compounds of formula (I) can administered to other animals for treatment or prophylaxis of viral diseases, e.g. in other mammals. For example, the compounds of formula (I) 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 physiologically acceptable salt or ester thereof. The compounds of formula (I) and the physiologically acceptable salts and esters thereof (hereafter collectively referred to as the active ingredients) 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 indirations 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 250mg per kilogram bodyweight of recipient per day, preferably in the range 1 to 100mg per kilogram bodyweight per day and most preferably in the range 5 to 20mg per kilogram bodyweight per day; an optimum dose is about lûmg per kilogram bodyweight per day. (Unless otherwise indicated all weights of active ingredient are calculated as the parent compound of formula (I): for salts and esters 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 1000mg, preferably 20 to 500mg and most preferably 100 to 400mg of active ingredient per unit dosage form. While it is possible for the active ingredients to be administered alone it is prefreable 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 there for and optionally other therapeutic ingredients. The carrier(s) must be "acceptable" in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient thereof. The formulations include those suitable for oral, rectal, nasal, topical (including buccal and sublingual), vaginal or parenteral (including subcutanous, intramuscular, intravenous, intradermal, intrathecal and epidural) administration. The formulations may conveniently be presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. In general the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers of finely divided solid carriers or both, and then, if necessary, shaping the product. Formulations of the 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 or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active ingredient in a free-flowing form such as a powder or granules, optionally mixed with a binder, lubricant, inert diluent, preservative, surface active or dispersing agent. Moulded tablets may be made by moulding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent. The tablets may optionally be coated or scored and may be formulated so as to provide slow or controlled release of the active ingredient therein. For infections of the eye or other external tissues e.g. mouth and skin, the formulations are preferably applied as a topical ointment or cream containing the active ingredient in an amount of, for example, 0.075 to 20% w/w, preferably 0.2 to 15% w/w and most preferably 0.5 to 10% w/w. When formulated in an ointment, the active ingredients may be employed with either paraffinic or a water-miscible ointment base. Alternatively, the active ingredients may be formulated in a cream with an oil-in-water cream base. 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 dimethylsuiphoxide and related analogues. The oily phase of the emulsions of this invention may be constituted from known ingredients in a known manner. While the phase may comprise merely an emulsifier (otherwise known as an emulgent), it desirably comprises a mixture of at least one emulsifier with a fat or an oil or with both a fat and an oil. Preferably, a hydrophilic emulsifier is included together with a lipophilic emulsifier which acts as a stabliser. It is also preferred to include both an oil and a fat. Together, the emulsifier(s) with or without stabiliser(s) make up the so-called emulsifiying wax, and the wax together with the oil and/fat make up the so-called emulsifying ointment base which forms the oily dispersed phase of the cream formulations. Emulgents and emulsion stabilisers suitable for use in the formulation of the present invention include Tween 60, Span 80, cetostearyl alcohol, myristyl alcohol, glyceryl mono-stearate and sodium lauryl sulphate. The choice of suitable oils or fats for the formulation is based on achieving the desired cosmetic properties, since the solubility of the active compound in most oils likely to be used in pharmaceutical emusion formulations is very low. Thus the cream should preferably be a non-greasy, non-staining and washable product with suitable consistency to avoid leakage from tubes or other containers. Straight or branched chain, mono- or-dibasic'alkyl esters such as di-isoadipate, isocetyl sterate, propylene glycol diester of coconut fatty acids, isopropyl myristate, decyloleate, isopropyl palmitate, butyl stearate, 2-ethylhexyl palmitate or a blend of branched chain esters known as Crodamol CAP may be used, the last three being preferred esters. These may be used alone or in combination depending on the properties required. Altermatively, high melting point lipids such as white soft paraffin and/or liquid paraffin or other mineral oils can be used. Formulations suitable for topical administration to the eye also include eye drops wherein the active ingredient is dissolved or suspended in a suitable carrier, especially an aqueous solvent for the active ingredient. The active ingredient is preferably present in such formulations in a concentration of 0.5 to 20%, advantageously 0.5 to 10% particularly about 1.5% w/w. Formulations suitable for topical administration in the mouth include lozenges comprising the active ingredient in a flavoured basis, usually sucrose and acacia or tragacanth; pastilles comprising the active ingredient in an inert basis such as gelatin and glycerine, or sucrose and acacia; and mouthwashes comprising the active ingredient in a suitable liquid carrier. Formulations for rectal administration may be presented as a suppository with a suitable base comprising for example cocoa butter or a salicylate. Formulations suitable for nasal administration wherein the carrier is a solid include a coarse powder having a particle size for example in the range 20 to 500 microns which is administered in the manner in which snuff is taken, i.e. by rapid inhalation through the nasal passage from a container of the 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, cream, gels, pastes, foams or spray formulations containing in additon 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 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. 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 rgard to the type of formulation in question, for example those suitable for oral administration may include flavouring agents. The present invention further provides veterinary compositions comprising at least one active ingredient as above defined together with a veterinary carrier therefor. Veterinary carriers are materials useful for the purpose of administering the composition and may be solid, liquid or gaseous materials which are otherwise inert or acceptable in the veterinary art and are compatible with the active ingredient. These veterinary compositions may be administered orally, parenterally or by any other desired route. For oral administration the compositions can be in th 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. A paste may be formulated by suspending the active ingredient in a liquid diluent A stiffening or thickening agent may be included together with a wetting agent or a humectant if the liquid diluent is water. If an emulsion paste is needed then one or more surface active agents should desirably be included. From 25 to 80% by weight of these paste formulations may comprise the active ingredient. In feed supplements the active ingredient is generally present in large amounts relative to the accessory ingredients, and the supplements may be added directly or after intermediate blending or dilution. Examples of accessory ingredients for such formulations include solid, orally ingestible carriers such as corn meal, soya flour, wheat shorts, soya grits, edible vegetable materials and fermentation residues. The active ingredient is usually incorporated in one or more of the accessory ingredients and intimately and uniformly dispersed by grinding, tumbling or stirring with conventional apparatus. Formulations containing 1 to 90% by weight of the active ingredient are suitable for adding to feeds. For the treatment of herpes infections in horses, an oral or parenteral dose of from 0.1 to 250 mg per kg body weight per day, preferably from 2 to 100 mg per kg per day may be required. The dose may be split up into discrete units administered at regular intervals during the day, and repeated daily for up to 14 days or until the infection is cleared. For viral infections in other animals the dose may vary depending on the size and metabolism of the animal. The compositions may be administered in unit dosage form, such as a tablet a few times daily in the amount of 10 to 1000 mg per unit dose. The invention will now be illustrated by reference to the following Examples. Example 1 9-ff2-hydroxy-1-hydroxymethylethoxy)methyJquanine Hydrogen chloride gas was passed into a chilled (ooh) mixture of 1,3-dibenzyloxypropanol (20.725 g) (J. Chem. Soc. 445 (1931) A. Fairbourne) and paraformaldehyde (2.28 g) in dry dichloromethane (100 ml) until the solution was saturated. The cloudy colorless solution was dried over molecular seives and calcium chloride, filtered and the filtrate evaporated in vacuo. The 1,3-bis(benzyloxy)-2-(chloromethoxy)propane formed as a residual yellow oil, and had satisfactory IR (absence of OH group) and H-NMR spectra. A solution of 13mM of 2,6,9-tris-trimethylsilylguanine, 1,3-bis(benzyloxy)2-(chloromethoxypropane (5.45 g) and dry triethylamine (4 ml (29 mM)) in dry toluene (10 ml) was refluxed under nitrogen forts hours. The reddish amber solution was evaporated in vacuo and digested on a steam bath with methanol for thirty minutes. The solvent was removed by flash evaporation and the oily residue purified by column chromatography on silica gel; the desired 9-(2-benzyloxy-1gbenzyloxymethyl)ethoxymethyl) guanine, containing about 104b of the 7-isomer, was obtained by elution of the column with acetone and recrystallization from acetonitrile, m.p. 173-80 C. To a suspension of 9-(2-benzyloxy-1gbenzyloxymethyl)ethoxymethyl) guanine (3.88 g) in liquid ammonia (300 ml) at temperatures of 45 to -300C (acetonedry ice bath) was added, with magnetic stirring, sodium chips (1.54 g) in portions over a period of 15 minutes. The mixture was stirred 30 minutes longer and the excess sodium destroyed with methanol. The solvents were removed by evaporation in vacuo, the residue dissolved in a minimum of water, chilled and the pH adjusted to 6.0 with glacial acetic acid. The mixture was re-evaporated in vacuo and recrystallized twice from water. A final recrystallization from methanol gave analytically pure 9-/(2-hydroxy 1 -hy droxy methylethoxy)methyl/guan ine m. p. = 2500C with resolidification. Example 2 a) 9-if2-Benzoyloxy -l -benzoyloxymethyl)ethoxymethylJguanine To a cold (ooh) solution of acetylating mixture (prepared by combining acetic anhydride (7 ml), glacial acetic acid (3 ml) and concentrated sulfuric acid (0.1 ml)) was added, with magnetic stirring, tetrabenzoyl-methylenebis-2-glycerol (1.0 g). A.T. Ness, R.M. Hann & C.S. Hudson, J. Amer. Chem. Soc, Nov 1943, 2215. The solution was stirred at temperatures of 30 to 1000 for thirty minutes, then poured into a mixture of 260 ml of ice and water. The acidic solution was extracted three times with chloroform, and the organic extracts washed with brine and dried over sodium sulfate. The filtered chloroform solution was evaporated in vacuo and the residual oil purified by column chromatography on silica gel. Elution with dichloromethane yielded 2-0-(acetoxymethyl) 1,3-bis(O-benzoyl) glycero-l. The proton and carbon-13 NMR spectra were consistent with the desired structure. A mixture of 2,9-diacetylguanine (0.49 g), 2-O-(aceto xyme thyl)-1,3-b is(O- benzoyl)glycerol (1.22 g), p-toluenesulfonic acid (0.01-3 g) in dry toluene (30 ml) was refluxed with stirring for 18 hours. The solvent was removed by flash evaporation and the residue dissolved in boiling methanol (35 ml). n-Butanol (1 ml) was added and the mixture refluxed for five minutes, to hydrolyze the 2-acetamido group. The mixture was evaporated in vacuo at a bath temperature of 30 C and recrystallized once from methanol and once from formamide to yield 9-/(2-benzoyloxy-1-benzoyloxymethyl)ethoxymethyl/ guanine. The elemental analysis showed the product contained 0.75 mole of formamide and the NMR spectrum was consistent with the structure. TLC on silica gel with 20% methanol in chloroform gave one spot Rf = 0.49. Mpt = 220-222 C. b) 9-K2 -Hydroxy-1 -hydroxymethylethoxy)methyl7quanine. 942-Benzoyloxy-1gbenzoylaxymethyl)ethoxymethyl)guanine (0.6 g) is heated in a mixture of 1:1 methanol and 40% aqueous methylamine on a steam bath for one hour. The solvents are removed in vacuo and the residue recrystalliz ed twice from water to give 9-/(2-hydroxy-1 -hydroxyme thylethoxy)methyl/guanine as a one quarter hydrate. m.p. dec. 2300C. Example 3 9-/(2 -Hydroxy-1 -hydroxymethylethoxy)methvl7guanine A mixture of 1,4-dichlorobutane-2,3-diol (111.8 g), paraformaldehyde (42.2 g) and boron trifluoride-ethereate r22 ml) in dry acetonitrile (460 ml) was refluxed with stirring until the solids had dissolved. Molecular seives were added and the reaction mixture was refluxed for a further three hours. The mixture was cooled and dried by the addition of more sieves, filtered and evaporated in vacuo. The oily residue was added to saturated sodium bicarbonate solution (250 ml) and extracted three times with equal volumes of purified ether. The ethereal extracts were dried over sodium sulfate, filtered and evaporated in vacuo. The residual liquid was distilled with water aspirator (16 mm) pressure and the fraction boiling at 99-109 C collected to give 4,5-bis(chloromethyl)1,3dioxolane. A mixture of 4,5-bis(chloromethyl)1,3-dioxolane (76.5 g), and sodium benzoate (258 g) in dry dimethylformamide (1500 ml) was stirred with heating at temperature of 1420C for eighteen hours. The mixture was cooled, filtered and the solids washed with ether The mother liquors and washings were evaporated in vacuo to dryness and partitioned between dichloromethane and water, three times. The organic layers were washed with water and dried over sodium sulfate. After filtering and flash evaporation, the residue was purified by flash chromatography on silica gel in dichloromethane to give 4,5-bis(benzoyloxymethyl)-1,3-dioxolane as a thick oil. An analytical sample was obtained by allowing an aliquot of the oil to crystallize in air, mpt = 66.5-680C. To a chilled (ooh) solution of acetic anhydride (100 ml) and concentrated sulfuric acid (0.3 ml) was added portionwise 4,5-bis(benzoyloxymethyl)1,3-dioxolane (114.2 g) while maintaining an internal temperature of 0-5 C. The solution was allowed to come to room temperature and then heated for three hours at steam bath temperature (internal temperature 920C). After cooling, the solution was poured onto 600 ml of ice and water and extracted three times with purified ether. The ethereal extracts were washed once with water, once with 5% sodium bicarbonate solution and finally with brine. The ethereal extracts were dried (Na2S04) and the clear amber solution, filtered and evaporated in vacuo to yield 2-acetoxy-3-acetoxymethoxy-1,4-butanediyl dibenzoate. An analytical sample was obtained by recrystallization from benzene-hexane. Mpt. 56-58 c. A mixture of 2,6-dichloropurine (5.75 g) and 2-acetoxy-3-acetoxymethoxy- 1,4-butanediyldibenzoate (14.1 g) was heated at 1400C under water aspirator pressure until the mixture had formed a liquid melt. After 10 minutes further heating, the reaction mixture was cooled and p-toluenesulfonic acid (150 mg) added with stirring. Heating under aspirator pressure was resumed for twenty minutes, then the reaction solution was cooled and partitioned between dichloromethane and water three times. The organic extracts were washed once with saturated sodium bicarbonate solution, twice with water and finally once with brine. After drying over sodium sulfate, and filtering, the solvent was removed by flash evaporation and the residual yellow foam purified by column chromatography. After elution with dichloromethane to remove non-purinic by-products, elution with 50% ethyl acetate hexane yielded, on evaporation, a colorless oil with a satisfactory NMR spectrum for the desired 9-/(2-acetoxy-3-(2,6-dichloro-9H-purin-9-yl)-methoxy1,4-butanediyl dibenzoate. A mixture of 2-acetoxy-3-(2,6-dichloro-9H-purin-9-yl)methoxy-1,4-butanediyldi- benzoate (11.5 g) and sodium azide (2.6 g) in 50 ml of 1:1 v/v ethanol-water was heated with stirring at reflux for four hours. The heterogeneous mixture was evaporated in vacuo and the residue partitioned between ether and water. Two additional washings of the aqueous phase and evaporation of the combined, dried ethereal extracts gave 2-acetoxy 3-(2,6-diazido-9H-purin-9-yl)methoxy-1,4-butanediyldibenzoate. The NMR and IR spectra were consistent with the desired structure. A solution of 2-acetoxy-3-(2,6-diazido-9H-purin-9-yl)methoxy-1,4-outanediyl- dibenzoate (5.0 g) in tetrahydrofuran (200 ml) and methanol (20 ml) containing 190 mg of 5% palladium on charcoal catalyst was shaken under 50 p. s. i. of hydrogen at room temperature for three days. The mixture was filtered through a pad of Celite and the solution evaporated in vacuo. The syrupy residue was recrystallized from methanol to give 2-acetoxy-3-(2,6-diamino 9H-purin-9-y l)methoxy-1,4-bu taned iy ld ib enz oate, mpt. 192 -4 OC, 2-Acetoxy-3-(2,6-diamino-9H-purin-9-yl)methoxy-1,4-butanediyldibenzoate (2.0 g) in methanol (100 ml) and 40% aqueous methylamine (35 ml) were heated on a stearn bath for one hour, then the solution evaporated in vacuo. The residue was triturated with ether to remove the N-methylbenzamide, and recrystallized from ethanol to yield 3-(2,6-diamino-9H-purine-9-yl)methoxy 1,2,4-butanetriol, mpt. 167-9 C. A solution of 3-(2,6-diamino-9H-purine-9-yl)methoxy-1 ,2,4-butanetriol (0.7 g (2.4 mM)) and sodium periodate (0.6 g (2.8 mM)) in water (50 ml) was stirred at room temperature for 3.5 hours. A precipitate formed within 5 minutes of combining the two reactants. The mixture was chilled, filtered and washed with water yielding 2-L(2- amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxyJ-3-hydroxypropanal. A mass spectrum of this product gave m/e M+) = 253. To a suspension of the aldehyde derivative (150 mg (0.592 mM)) in water (20 ml) was added in portions, sodium borohydride (18 mg (0.47 mM)). The solution was stirred at room temperature overnight, chilled and the pH adjusted to 6 with 4N aqueous hydrochloric acid. The resulting precipitate was filtered to give 9-L(2-hydroxy-1-hydroxymethylethoxy)methygguanine. m.p. 248-2500C. Example 4 9-/(2-Hvdroxy-1-hvdroxymethylethoxy)methyl7guanine To a solution of 2,6-d iamino-9-/(2-hydroxy-l-hydroxymethylethoxy)methyl/purine (0.5 g) in double distilled water (10 ml) is added approximately 600 ul of calf intestinal mucosa adenosine deaminase suspension in ammonium sulphate (Sigma). The mixture is incubated at 370C and monitored by u.v. until the reaction was complete (26 days). At intervals, the reaction mixture is evaporated in vacuo at room temperature and redissolved in water to remove the ammonia formed and thus keep the pH of the solution between 7-7.5. The solution is evaporated in vacuo and the residue is recrystallised once from methanol and twice from water to yield 9J±2-hydroxy-l-hydroxymethyl- ethoxy)methyjiguanine as a one quarter hydrate m.p. dec. 2300C. Example 5 9-g2-hydroxv-1-hydroxymethylethoxy)methyll-2.ó-diarnino purine a) 9-g2-benzoyloxy-1-benzoyloxymethylethoxy)methvl/-2,6-dichloropurine. A mixture of 1.16 g (6 mM) of 2,6 dichloropurine and 2.7 g (7.3 mM) of 2-0-(acetoxy methyl)-1,3-bis-(0-benzyl)glycerol was heated with magnetic stirring under water aspirator pressure at an oil bath temperature of 15500 for approximately 25 minutes. The resultant clear yellow liquid was cooled and the thick yellow glass which formed was dissolved in benzene and purified by flash chromatography on a silica gel column (diam = 6 cm). Initial elution with 1:1 benzene-dichloromethane, and dichloromethane alone, removed by-products and the desired 9-/(2-benzoyloxy-l -benzoyloxymethylethoxy)methyl/-2,6 dichloropurine was obtained by elution with 1:1 dichloromethane-ether (1.77 g). An additional prop of the 9- isomer contaminated with 7- isomer was eluted using 100% purified ether. The H'-NMR spectrum and TLC (silica gel in dichloromethane) showed a slight amount of impurity in the main batch which is a white-yellow foam. b) 9-i(2-Benzoyloxy-l-benzoyloxymethylethoxy)methviT2,6-diazidopurine. A heterogeneous mixture of 1.77 g (3. 53mM) of 9-/(2-benzoyloxy-1-benzoyloxy- methyl)ethoxy)methyl/-2,6-dichloropurine and 0.45 g (6.88 mM) of sodium azide in 10 ml of 1:1 v/v water-ethanol was refluxed with magnetic stirring for three hours. The solvents were removed by flash evaporation and the residual oil triturated with water to remove the sodium chloride. The oil was taken up in hot alcohol and cooled to yield, after filtration, a white solid with a pinkish tinge after drying. Mpt = 144-50C. An additional crop was obtained from the mother liquor by evaporation and trituration with ethanol to give material sufficient purity to combine with the initial precipitate for the next step. NMR and u.v. spectra were consistent with the postulated structure. Qual. u.v. peaks: pH 1.0max = 240, 305, 275 (shdr) pH 13.0Nmax = 300, 270 (sdr) c) 9-/t2-Hydroxy-1-hydroxymethvlethoxyDmethyl/-2,6-diaminopurine. A mixture of 1.68 g (3.26 mM) of the product of stage b) in 120 ml of 1:1 v/v tetrahydrofuran - methanol was shaken with 118 mg of 5% palladium on charcoal catalyst under an inital pressure of 50 p.s.i. H2 for 72 hours at room temperature. The mixture was filtrated through a pad of Celite and the solvents removed by flash evaporation. The residual oil was taken up in hot benzene and hexane which caused soldification to occur. After chilling, the solid was filtered to yield 9-/(2.benzoyloxy.1-benzoyloxymethyl- ethoxy)methyl/-2,6-diaminopurine, which gave a satisfactory NMR (H) spectrum. The solid was dissolved in a minimum amount of methanol and stirred with an equal volume of 40% aqueous methylamine at room temperature until TLC (silica gel in 40% methanol-dichloromethane) showed complete hydrolysis had occurred. The solution was evaporated in vacuo and the residue recrystallised from ethanol-acetone to yield 9-/(2-hydroxy- 1-hydroxymethylethoxy)methyl/-2,6-diaminopurine which gave satisfactory H'-NMR spectrum and elemental analysis. ,Mpt = 182-4 C. Example 6 2,6-Diamino-9-ff2-hydroxy-1-hydroxymethylethoxy)methyU-9H-purine A mixture of 33.69 (0.2M) of 2,6-diminopurine hydrate in 400 ml of xylene was refluxed with water separation in a Dean Stark trap. Acetic anhydride, 63.849 (0.625M) was added and the reaction mixture was heated to distill off a mixture of acetic acid and xylene (head temperature 1150C). The temperature was raised to 12500 at the end of a four hour reaction time. To the mixture was added O.g5g (0.005M) of para toluenesulfonic acid hydrate and 2-0-(acetoxymethyl)-1,3-bis(O-acetyl)glycerol, 74.479 (0.3M) and the reaction mixture heated to distill off a mixture of xylene and acetic acid at 12500. The distillation temperature was raised to 13500 at the end of a three hour reaction time. The reaction mixture was cooled, and the crude product was obtained by flash evaporation and trituration of the residue with acetone. Recrystallization from ethanol gave the analytically pure intermediate 2,6-diacetamido 9-/(2-acetoxy-1 acetoxymethylethoxy)methyl/purine. The solid was dissolved in methanol and heated with an equal volume of 40% aqueous methylamine for 15 minutes on a steam bath. Flash-evaporation and recrystallization of the residue from ehtanol gave 2,6-diamino-9-/(2 -hydroxy-l- hydroxymethylethoxy)methyl/-9H-purine. Example 7 a) 9-[(2-hydroxy-1-hydroxymethylethoxy)methyl]-2-ch loroadenine A solution of 2.09 (4mM) 9-/(2-benzoyloxy-(l-benzoylkoxymethylethoxy)methyl/- 2,6-dichloropurine in 63 ml of saturated methanolic ammonia was heated in a bomb at 850C for 20 hrs. The solution was evaporated in vacuo and recrystallized twice from ethanol to yield analyticalLy pure 9-/(2-hydroxy-l-hydroxy- methy leth oxy)methyl/-2 -chloroadenine. b) 9-[(2-Hydroxy-1-hydroxymethylethoxy)methyl]-2-chloro-6-hydroxypurine. To a solution of 500mg (1.83mM) of 9-/(2-hydroxy-1-hydroxymethylethoxy)- methyl/2-chloroadenine in 10ml of glacial acetic acid was added 0.639 (9.15mM) of sodium nitrite in portions over a period of 45 mins. The reaction was stirred at room temperature for four hours then evaporated in vacuo to dryness. The residue was recrystallized once from water and once from ethanol to yield analytically pure /C2-hydroxy-l hydroxymethylethoxy)methyi7-2- chloro-6-hydroxypurine. c) 9-jC2-hydroxy-1-hydroxymethylethoxy)methyijguanine A solution of 0.2749 (1mM) of 9-[(2-hydroxy-1-hydroxymethylethoxy)methyl]-2- chloro-6-hydroxypurine in 60ml of saturated methanolic ammonia was heated at 120 C in a bomb for 25 hrs. The cooled solution was evaporated in vacuo and recrystallized twice from water to yield analytically pure 9-t(2-hydroxy-l- hydroxymethylethoxy)methyl7guanine. Mpt. 220-2220C. Example 8 a) 5-Benzyloxy-1,3-dioxan-2-one A solution of 1829 (1M) of 2-0-benzylglycerol (Carbohydrate Research 91 (1981) 85-88 G. Chittenden), 128ml of 2,6-lutidine (1.1M) and 550ml (1.lM) of 20% phosgene in toluene is stirred at room temperature for two days. The solvent was removed in vacuo and the residue purified by factional distillation to give 1579 (7536) of 5-benzyloxy-1,3-dioxan-2-one. b) 5-Hydroxy-1,3-dioxan-2-one A solution of 177g (0.85M) of 5-benzyloxy-1,3-dioxan-2-one in 100ml of 1.1 tetrahydrofuran-ethanol is shaken with 16g of 5% palladium on carbon at atmospheric pressure until the theoretical amount of hydrogen is consumed. The catalyst is filtered off, the filtrate passed through a pad of celite and evaporated in vacuo to yield 94.5J80%) of 5-hydroxy-1,3-dioxan-2-one. c) 5,5-Methylenedioxvbis(1,3-dioxan-2-orie) A mixture of 599 (0.5M) of 5-hydroxy-1,3-dioxan-2-one, 459 (0.5M) of paraformaldehyde and 24ml of boron trifluoride etherate in 80m1 of dry tetrahydrofuran is stirred at room temperature with 309 of 3A molecular series for 18 hrs. The mixture is filtered and the filtrate evaporated in vacuo. The residual oil is dissolved in ether and extracted twice with 5% aqueous sodium bicarbonate and twice with water. The ethereal extracts are dried over sodium sulfate, filtered and evaporated to yield 5,5-methylenedioxybis(1.3-dioxan-2-one). d) (2 -Oxo-1,3-diox an-5-yl)oxymethylacetate To a chilled (ooh) solution of 100ml of actic anhydride and û.3ml of concentrated sulfuric acid is added portionwise 100.4g (0.33M) of 5.5-methylenedioxybis(1,3- dioxan-2-one), while maintaining an internal temperature of 0-SOC. The solution is then stirred at room temperature for 18 hrs. The reaction solution is poured onto 600ml of ice and water and extracted three times with an equal volume of purified ether. The extracts are dried over sodium sulfate, filtered and evaporated to give (2-oxo-1,3-dioxan-5-yl)oxymethyl acetate. e) 2-Acetamido-1,9-dihydro-9-/(2-oxo-1,3-dioxan-5-yl)oxymethyl/-purine -6-one. A mixture of 6.539 (27.8mM) of diacetyl guanine, 0.2179 of para-toluene sulfonic acid monohydrate and 9.16g (48.2mM) of (2-oxo-1,3-dioxan-5-yl)-oxymethyl) acetate in 60 ml of dry xylene is refluxed with stirring for eighteen hours. The solvent is removed by evaporation in vacuo and the residue purified by column chromatography on silica gel, eluting the dried nine isomer with 10% methanol in dichloromethane. Recrystallization from methanol gives 5.49 (60%) of 2-acetamido-1,9-dihydro-9-E2-oxo-1,3-dioxan-5 yl)oxymethyl)-6H-purine-6-one f) 9-L(2-hydroxy-l-hydroxymethylethoxy)methyf7guanine A solution of 0.639 (1.96mM) of 2-acetamido-l,9-dihydro-9-/(2 -oxol,3-dioxan-5- yl)osxymethyl)-6H-purine-6-one in 30ml of 40% aqueous methylamine is heated on a steam bath for 3 hr, then evaporated in vacuo. The residue is recrystallized from water to give 9-112-hydroxy-l-hydroxymethyl)ethoxy- methylUguanine. The following Examples 9 to 13 illustrate pharmaceutical formulations according to the invention where the active compound is a compound of formula (I) or a physiologically acceptable salt or ester thereof. Example 9 Tablet Active compound 100mg Lactose 200mg Starch , 50mg Polyvinylpyrrolidone 5mg Magnesuim stearate 4mg 359mg Tablets were prepared from the foregoing ingredients by wet granulation followed by compression. Example 10 Injectable Solution Active compound 0.775 g Sterile, pyrogen-free, pH 7 phosphate buffer to 25 ml Example 11 Ophthalmic Solution Active compound 1.09 Sodium chloride, analytical grade 0.9 g Thiomersal 0.001 g Purified water to 100 ml pH adjusted to 5.5-7.5 Example 12 Oil based Paste China Clay (solid diluent) 20.0% w/w Mineral Oil* (liquid diluent) 60.0% w/w Active compound 20.0% w/w The components were mixed to provide a paste of uniform consistency. *Mineral oil is a high boiling fraction of a refined petroleum oil containing not less than 96% unsulphonatable material. Example 13 Feed Supplement - Pellets Active compound 1% Cereal Base 99% The two ingredients were mixed and the mixture then fed to any conventional feed stuff pelleting plant. Example 14 In vivo activity of 9-ft -hydroxy-1 -hydroxymethylethoxy)methyfllguanine and acyclovir against equine rhinopneumonitis virus Method Male cream Syrian weanling hamsters, 40-50 g, 21-24 days old, were caged in groups of 5 and given water and food ad lib. Equine rhinopneumonitis virus (EHV-1), hamster adapted Vaccine Strain 'Pneumabort' was used; the vaccine was diluted 10-1 in tissue culture fluid and this stock stored in 1 ml aliquots in sealed glass vials at -700C. On Day 0 hamsters to be infected received 0.2 ml stock vaccine virus, diluted further 2 x 10 1 in phosphate buffered saline, subcutaneously in the left flank. 9-/(2-Hydroxy-1-hydroxymethy lethoxy)methyl/guanine (hereinafter referred to as 759U) and acyclovir were made up as aqueous solutions in sterile distilled water in the concentrations specified below. Experiment 1 Intraperitoneal administration: from Day O to Day 4, inclusive, hamsters received 759U or acyclovir in divided twice daily doses in aqueous solution, the concentration of 759U varying as following, namely 5 mg/ml to give a dose rate of 100 or 50 mg/kg/day, 1.2 mg/ml for 20 mg/kg/day, 0.18 mg/ml for 4 mg/kg/day and 0.036 mg/ml for 2 mg/kg/day. Untreated control hamsters received an equivalent volume of sterile distilled water. Results The results are shown in the following Table: No. in Treatment Day Cumulative mortality group. mg/kg/day intraperitoneal. 2 3 4 5 6 7 10 50/acyclovir 0 1 2 5 6 6 10 100!acyclovir 0 0 1* 2* 2* 3* 10 100í759U 0 0 0 0 0 1* 10 50/759U 0 0 0 0 0 0 10 20/759U 0 0 0 0 0 0 10 4/759U 0 0 0 0 0 0 10 2/759U 0 0 0 0 0 0 10 untreated 0 5 9 10 10 10 * non-virus specific deaths. Conclusion A dose rate of acyclovir at 100 mg/kg/day intraperitoneally for 5 days commencing 5 hours pre-infection, was generally necessary to prevent any virus-induced mortality. In comparison 759U at 2 mg/kg/day intraperitoneally gave complete control. Experiment 2(a) Oral administration with 759U A stock solution of 759U was made in sterile distilled water at 0.304 mg/ml and then diluted in 3-fold steps to 0.101 and 0.034 mg/ml. Hamsters were given medicated drinking water for 5 days commencing 5 hours pre-infection. A control group was supplied with unmedicated water. Results No. in Treatment* Cumulative mortality group mg/kg/day Day 759U oral 2 3 4 5 6 7 10 39 . 0 0 0 0 0 0 10 13 0 0 0 0 0 0 10 3 0 1 1 1 10 untreated 1 5 10 10 10 10 * calculated from the mean daily intake. Experiment 2 (b) Oral administration with acyclovir Acyclovir was dissolved in sterile distilled water at 2 mg/ml with the addition of a little sodium hydroxide and warming to 420C to facilitate solution. Hamsters were given medicated drinking water, containing acyclovir at 2 mg/ml, for 5 days commencing 5 hours pre-infection. Oral treatment resulted in a dose rate of approximately 100 mg/kg/day. A control group supplied with unmedicated water was set up. Results No in Treatment Cumulative mortality group. mg/kg/day Day acyclovir oral. 2 3 4 5 6 12 r 12 untreated 0 6 12 12 12 Conclusion Acyclovir showed poor efficacy against EHV-1 when administered orally at 100 mg/kg/day for 5 days whilst 759U was completely effective orally at 13 mg/kg/day, with only limited mortality at a dose rate of 3 mg/kg/day. Example 15: Comparative in vivo activities of 759U and its 6-amino analogue (457U) against equine rhinooneumonitis virus Materials and Methods Hamsters 50 male WO/CR Syrian hamsters were caged randomly in 10 groups of 5, with water and food (seed mix) ad lib. Hamsters were weighed on Days -3,0,4, andfor at death/sacrifice. Water consumption was recorded over Days -3 to O to 4. Virus and Infection EHV-1 Pneumabort vaccine strain stored as a 10-1 dilution, was further diluted 10'1 in PBS for infection. On Day 0, hamsters in Groups 1-9 received 0.2 ml virus inoculum s/c in the left flank equivalent to about 2 x 105 PFU (plaque-forming units). Compounds and Medication 457U and 759U were dissolved in drinking water at 0.075 mg/ml. Assuming an average daily intake of 134 ml/mg bodyweight, this would result in a daily dose of around 10 mg/kg. Medicated water was provided from approximately 5 hours pre-infection for 96 hours, as below Group Medication 1-3 759U 4-6 457U 7-9 t Untreated/infected 10 Untreated/uninfected Results Cumulative mortality patterns are summarised in the following Table. The drug intake was calculated from the weight of the animals and the water consumption recorded over the period of the experiment. There was only 1 death from virus-induced hepatitis in the 15 457U treated hamsters compared with 14 deaths in 15 untreated controls and no deaths in 15 hamsters receiving 759U. Table Group Water conc. Water conc. Average intake Cumulative mortality of 457U of 759U mg/kg/day (out of 15) on day mg/ml mg/ml 2 3 4+ 1-3 - 0.075 6.6 0 0 0 4-6 0.075 - 6.8 0 1 1 7-9 - 0 - O 9 14 lû* - - - 0 0 0 Conclusions Compound 457U, the diamino derivative of 759U, when administered orally in drinking water at a rate of approximately 7 mg/kg/day, almost completely prevented EHV-1 induced mortality in Syrian hamsters, while 759U completely prevented EHV-1 induced mortality. Example 16 In vitro activity of 759U against Herpes simplex type 1 Method 60mm plastic cell culture dishes were seeded with a VERO cell suspension (6 ml of 2 x 105 cells/ml) in VERO cell growth medium comprising 5% foetal calf serum, 10% Eagles minimal essential medium, 0.11% sodium bicarbonate,0.25% Crystamycin (50,000 units/ml sodium benzyl penicillin B.P. and 50 mg/ml streptomcyin sulphate B.P.). The dishes were gently shaken to ensure the complete dispersion of the cells and then the cultures were incubated at 370C in an atmosphere of 5% C02/air overnight to attain confluency. The growth medium was then replaced with 2 ml of virus (Herpes simplex type 1) inoculum in phosphate buffered saline (PBS). The virus concentration was such as to induce the formation of 200-400 plaques/plate. A period of 1 hour was allowed for virus absorption at 370C in 5% C02air, after which time the plates were drained and overlay medium (8 ml) was added at 420C. The overlay medium consisted of 0.6% agarose, 2% foetal calf serum, 10% Eagle:5 minimal essential medium, 0.11% sodium bicarbonate and 0.25% Crystamycin. Doubling dilutions in micromolarity of active compound were prepared in the overlay and replicate cultures were fed with the maintenance medium overlay containing a range of concentrations of the compound. Untreated virus control cultures and uninfected cultures were also prepared. The overlay was allowed to solidify at room temperature before the cultures were returned to the incubator at 370C in 5% C02/air for 4 days. The cultures were then fixed with 10% formalin in-gBS for 30 minutes to 1 hour; the overlay was removed and the cells were stained with 0.05% w/v methyl violet in 20% methanol. The resultant plaques were counted and expressed as a percentage of the plaque count of the untreated virus control cultures. These values were then plotted against the log10 of the compound concentration and the IC50 values representing the amount of the compound required to reduce the plaque count by 50% was read from the resulting dose-response line. Results 759U Acyclovir IC50 yM 1C509JM Experiment 1 0.09 0.17 Experiment 2 0.05 0.075 Experiment 3 0.036 0.11 Mean 0.059 0.118 Conclusion 759U has greater activity in vitro against Herpes simplex type I than acyclovir. Example 17 In vivo activity of 759U against herpetic encephalitis Preparation of stock virus Swiss mice weighing 12-15 g were anaesthetised with ether and inoculated intracerebrally with 0.025 ml of a tissue culture preparation of type I herpes virus. The mice were examined daily for sign of herpes encephalitis i.e. cerebral irritation leading to paralysis, coma and death. Mice were killed when they showed early signs of cerebral irritation. The viscera of the mice were examined for signs of infection with bacteria or other agents and if no abnormalities were found the brains were removed asceptically and ground to a smooth paste. The homogenate was resuspended in 4 ml of tissue culture maintenance medium to each brain, and mixed with glycerol in the ratio 2:1. Mouse brains weigh approximately 400 mg and the preparation thus represented a dilution of 10 1. The stocks of virus thus prepared were titrated in mice to determine the LD50 titre by inoculating mice intracerebrally with 10-fold dilutions of the stock preparation of virus and subsquently examined twice daily for signs of infection. The LD50 titre was calculated by the Karber method. Method Groups of 5 mice were infected intracerebrally with stock virus diluted to give a dose of around 300 x LD50. The compound under test was administered twice daily as a suspension by the oral route at a dose of 100 mg/kg. The animals were examined twice daily and survival times were recorded to the nearst half-day. Dosing was carried out for 5 days and the total period of observation was 14 days. Survival times were converted to recipocals and the mean survival time was determined for each group L. Bauer, D. J., Brit. J. Exp. Path., 1960, 41, 130). Acyclovir 759U Untreated Mean reciprocal survival time 0.26 0.15 0.33 Conclusion The activity of 759U observed when given orally to intracerebrally infected mice was much greater than acyclovir under the same conditions. Example 18 Comparative in vivo activity of 759U and 457U against herpetic encephalitis 759U and 457U were tested in vivo against herpetic encephalitis in mice in comparison with acylovir and its 6-amino analogue, 2-amino-9-(2-hydroxymethoxymethyl) adenine (134U). Materials and Methods Mice CD.1 mice weighing 16 - 20 gm were obtained from Charles River, Manston, Kent, U.K. The animals were housed in groups of approximately 10 and were given food and water ad lib. Antiviral compounds The compounds namely acyclovir, 134U, 759U and 457U, were prepared as suspensions or solutions in sterile water at a concentration of 20 mg/ml prior to each experiment, and were stored at 40C during the dosing period. Virus The ICI strain of herpes simplex virus type I was used for all experiments at a concentration of 300 L050 (105 pfu)/ml). Dilutions from virus stocks (10 pfu/ml) were prepared in PBS 'Al. Test procedures The test procedure is analoguous to that described in Example 13. Three experiments were performed, in which three routes of compound administration were examined: i) subcutaneous, ii) oral and iii) intraperitoneaI. Compounds were adminstered at 100 mg/ml/dose twice daily for 41 days, commencing 2 - 3 hours after infection. Results The mean reciprocal survival times following oral, subcutanteous (s.c.) and intraperitoneal (i.p) administration of the antiviral compounds are shown in the following Table. Treatment Group Mean reciprocal survival time Oral s.c. i.p. Virus controls 300 LD50 0.334 . 0.344 0.307 Acyclovir 100 mg/kg/dose 0.237 0.174 0.236 134U 100 mg/kg/dose 0.222 0.226 0.231 759U 100 mg/kg/dose 0.146 0.084 0.093 457U 100 mg/kg/dose 0.155 0.102 0.077 Comparing the two groups of therapies, acyclovir and 134U with 759U and 457U, the latter group resulted in the greatest antiviral effect. The differences between the two groups'was highly significant by any of the three routes of administation.

Claims: Claims 1) Compounds of the general formula EMI32.1 (wherein R represents a hydroxy or amino group and X represents an oxygen or sulphur atom) and physiologically acceptable salts and esters thereof. 2) Compounds as claimed in claim 1 wherein X represents an oxygen atom. 3) 9-/(2-Hydroxy-1-hydroxymethylethoxy)methyl/guanine. 4) 9-/(2-Hydroxy -1-hydroxymethyleth oxy)m ethyl/2,6-d iam inopurine. 5) Physiologically acceptable acid addition salts of compounds of formula (I) as claimed in any of the preceding claims. 6) Physiologically acceptable esters of compounds of formula (I) as claimed in any of the preceding claims wherein the esters contain a formyloxy, C1 16 alkanoyloxy, or optionally substituted aralkanoyloxy or aroyl ester grouping. 7) Physiologically acceptable esters as claimed in claim 6 wherein the esters contain an acetoxy or benzoyloxy ester grouping. 8) A process for preparing compounds of formula (I) and physiologically acceptable salts and esters thereof, characterised in that: (a) a compound of formula EMI32.2 (wherein X is as defined above and W and W1 each represent a hydrogen atom or a blocking group, Y is a hydrogen atom or a blocking group and Z is a group of formula -OY or -NHY wherein Y is as defined above providing that at least one of W, W1 and Y represent a blocking group), is deblocked to form a compound of formula (I) or a salt or ester thereof; ; (b) a compound of formula (III) EMI33.1 (wherein X is as defined above and either M is a 6-hydroxy or amino group and G is an atom or group that can be replaced by or converted to an amino group, or G is a 2-amino group and M is an atom or group that can be replaced by or converted to a compound of formula (I) or a salt or ester thereof; (c) a compound of formula (IV) EMI33.2 (wherein R and X are as defined above) or a salt or ester thereof is reduced by a method known per se; (d) a compound of EMI33.3 (wherein R is as defined above and O is a leaving group or atom) is reacted with a compound of formula EMI34.1 (wherein X is as defined above and A is a leaving group or atom); (e) hydrolysis of a compound of formula EMI34.2 (wherein R and X are as defined above); and optionally effecting one or more of the following conversions, in any desired sequence:i) where the resulting product is a base, converting the said base into a physiologically acceptable acid addition salt thereof; ii) where the resulting product is an acid addition salt, converting the said salt into the parent base; iii) where the resulting product is a compound of formula (I) or a salt thereof converting the said compound or salt thereof into a physiologically acceptable ester of the said compound or salt; and/or iv) where the resulting product is an ester of a compound of formula (I), converting the said ester into the parent compound of formula (I) or a physiologically acceptable salt thereof. 9) Pharmaceutical or veterinary formulations comprising, as active ingredient, at least one compound of formula (I) (as defined in claim 1) or a physiologically acceptable salt or ester thereof together with one or more carriers there for. 10) Formulations as claimed in claim 9 wherein the active ingredient comprises 9-/(2-hydroxy-1-hydroxymethylethoxy) methyl/guanine or a physiologically acceptable salt or ester thereof. 11) Formulations as claimed in claim 9 or claim 10 adapted for oral administration. 12) Formulations as claimed in claim 11 in the form of tablets or capsules. 13) Formulations as claimed in claim 9 or claim 10 adapted for parenteral administration. 14) Formulations as claimed in claim 9 or claim 10 adapted for topical administration. 15) A compound of formula (I) (as defined in claim 1) and physiologically acceptable salts and esters thereof for use in the treatment or prophylaxis of a viral disease in an animal. 16) A compound of formula (I) as claimed in claim 15 wherein the said compound is 9-/(2-hydroxy-1-hydroxymethylethoxy) methyl/guanine or 9-/(2-hydroxy 1-hydroxymethylethoxy)methyl/-2,6-diaminopurine. 17) A compound as claimed in claim 15 or claim 16 for use in the treatment or prophylaxis of a herpes viral disease 18) A compound as claimed in any of claims 15 to 17 for the treatment of a viral disease in a human or other animal.

Inventors: SCHAEFFER, HOWARD JOHN
Applicants: THE WELLCOME FOUNDATION LIMITED
Application year: 1982
Main classification: C07D473
IPC codes: C07D473, A61K31, C07D317, C12P17, A61P31, C07D319