NO145404B - ANALOGUE PROCEDURE FOR THE PREPARATION OF THERAPEUTICALLY EFFECTIVE PURINE COMPOUNDS AND SALTS THEREOF - Google Patents

Description

The present invention, which is a further development in accordance with Norwegian explanatory document no. 144,216, relates to the production of therapeutically effective, substituted purine compounds with the formula:

where R is a hydroxy or aruino group. It has been discovered that these compounds have antiviral activity against pro-

different classes of DNA viruses in vitro. The compounds are particularly active against influenza, vaccinia and herpes viruses,

including simplex, zoster and varicella, in mammals, which cause such diseases as e.g. herpetic keratitis in rabbits and herpetic encephalitis in mice. A connect-

else with formula I where R is hydroxy or a salt thereof,

is preferred.

Salts which are particularly suitable for therapeutic

tical application are salts of pharmaceutically acceptable organic acids such as lactic acid, acetic acid, malic acid or p-toluenesulphonic acid, as well as salts of pharmaceutically acceptable mineral

acids, such as hydrochloric or sulphonic acid. Other salts can also be prepared and then converted into salts that are directly suitable for treatment purposes.

The compounds of formula I are prepared according to the invention by

a) converts a compound with the formula:

where either both M and G are a halogen atom, a mercapto, hydroxy, amino, alkylthio, alkoxy, azide or hydra-zino group, provided that both M and G are not amino except when M is to be converted to hydroxy, and provided that M is not hydroxy when G is amino except when M is to be converted to amino, to a compound of formula I by hydrolysis, aminolysis or reduction, or

b), reacts a compound with the formula:

where Q is hydrogen, with a compound of the formula:

where A is carboxylate, or

c) esterifies an alcohol with the formula:

where R has the meaning given above, when trading with

formic acid, or

d) a compound of the formula:

where RQ is -OX or -NHX, and X is a lower trialkylsilyl group, preferably trimethylsilyl group, is converted to a compound of formula I by hydrolysis or solvolysis;

and, if desired, when the product of the above reaction is a base, converting a compound of formula I into an acid addition salt thereof, or, if desired, when the product is a salt of a compound of formula I, converting this salt into its base or another salt thereof.

Conversion of a compound of formula II by means of method a) can be achieved in several different ways. The group M can e.g. is converted to a hydroxy group by hydrolysis, and

G and/or M. can be converted to amino by aminolysis. Such methods are well known and are described in "Heterocyclic compounds - Fused Pyrimidines", part II Purines by D.J. Brown (197i), Wiley-Interscience.

Conversion can alternatively be effected by the use of enzymes and adenosine deaminase converts e.g. efficiently a 2,6-diamino compound to the required guanine compound in an aqueous suspension at about 37°C and an initial pH of about 7.0.

The compounds which contain precursors for hydroxy and amino groups and can be converted into compounds of formula I can be regarded as intermediate products in the synthesis of such compounds.

In method b), the atom or group A which is split off is a reactive residue of an organic or inorganic acid and can therefore be a halogen atom or a carboxylate group, and Q is hydrogen or acyl. The preferred method involves the condensation of a purine compound having the desired 2- and 6-substitution with a formyl-blocked 2-haloalkbxy-ethanol, e.g. 2-formyloxyethoxymethyl chloride, in a strongly polar solvent such as dimethylformamide (DMF) or hexamethylphosphoramide, and in the presence of a proton acceptor such as a base, e.g. triethylamine or potassium carbonate. The reaction is preferably carried out at room temperature over a longer period of time, i.e. several days may be necessary to achieve reasonable yields.

One can alternatively carry out a thermal condensation, i.e. a fusion reaction, to obtain the product directly. For this reaction, an appropriately substituted purine compound is heated together with formyloxy-methylcarboxylate in the presence of a catalytic amount of a strong acid such as sulfuric acid. Temperatures in excess of 100°C are generally necessary, but the temperature should preferably not exceed approx. 200°C to minimize decomposition. The temperature should be chosen so that the mixture of reactants melts before they are subjected to de-composition.

The melting reaction can also be carried out under substantially de

same conditions as stated above, with possibly somewhat lower temperatures, between a 9-acylpurine compound and an alkoxymethylcarboxylate or halide. Alternatively, the fusion reaction can be carried out using the diester, e.g. 2-Formyloxyethoxymethyl acetate.

In method d), the amino and hydroxy groups can be reversibly blocked, e.g. with trimethylsilyl groups. Such a compound would be the product of the condensation of a trimethylsilylated purine and an ester or diester. Such blocking groups are very labile and can be removed by solvolysis with alcoholic or aqueous ammonia, or by alcoholysis.

Alternatively, the mercury chloride salt of a purine compound can be prepared in the presence of alkali and then condensed with a halogen ether in an aromatic organic type solvent. Before producing the salt, however, all reactive substituents on the purine compound must be blocked and the last step in this method therefore consists in removing the blocking groups.

A pharmaceutical preparation comprises in particular a compound of formula I in an effective unit dose form. The term "effective unit dose" used denotes a specific antiviral amount which is sufficient to be effective against viral organisms in vivo. Pharmaceutically acceptable carriers are materials that are useful for the purpose of administering the drug, and can be solid, liquid or gaseous materials which are otherwise inert and medically acceptable bg are compatible with the active constituents.

These pharmaceutical preparations can be given parenterally,

orally, used as a suppository or pessary, applied topically as an ointment, cream, aerosol, powder or given as eye or nose drops, etc., depending on whether the preparation is used for the treatment of internal or external viral infections.

For internal infections, the preparations are administered orally or parenterally at dosage levels calculated as the free base, of 0.1-250 mg/kg body weight, and used in humans in a unit dosage form, sometimes administered in an amount of 1-250 mg/unit dose.

For oral administration, fine powders or granules may contain diluents, dispersants and/or surfactants, and may be given in a drink, in water or in a syrup; in capsules or dragees, in the dry state or in a non-aqueous solution or suspension, in which suspending agents may be included; tablets which may include binders and lubricants; or in a suspension in water or a syrup. Where it is desirable or necessary, flavourings, preservatives, suspending agents, thickeners or emulsifiers can be used. Tablets and granules are preferred, and these can be coated.

For parenteral administration or for administration in the form of drops, such as for eye infections, the compounds can be presented in aqueous solution at a concentration of 0.1-10%, preferably 0.1-7%, and preferably 0.2% w/v . The solution may contain antioxidants, buffer substances, etc.

For infections of the eye or other external tissues, e.g. mouth and skin, the preparations are preferably applied to the infected part of the patient's body in the form of a topical ointment or cream. The compounds can be present in an ointment, e.g. with a water-soluble ointment base, or in a cream, e.g. with an oil in a water-cream base, in a concentration of 0.1-10%, preferably 0.1-7% and preferably 1% w/v.

Of the compounds of formula I, 9-(2-formyloxyethoxymethyl)guanine is preferred because this compound has very high antiviral activity against Herpes.

In the treatment of viral infections in mammals, an effective antiviral amount of a compound of formula I or a pharmaceutically acceptable salt thereof is administered. The administration is preferably carried out by topical application or ad oral or parenteral route.

In what follows, the invention will be illustrated with reference to the examples below.

Example 1

A solution of 9-(2-hydroxyethoxymethyl)guanine (4.73 g) in 97% formic acid (24 mL) was stirred at room temperature overnight. The amber solution was diluted with about 200 ml of dried ether and cooled. The resulting white precipitate was filtered, dried and recrystallized from dry dimethylformamide to give 9-(2-phoriuyloxyethoxymethyl)-guanine (3.6 g, mp 225-275°C).

Example 2

A solution of 2-amino-9-(2-hydroxyethoxymethyl)-adenine (0.5 g) in 97% formic acid (2.5 ml) was stirred in an ice bath for 3 hours, and then at room temperature overnight. Dry ether (80 mL) was added and the mixture cooled. The solid was removed by filtration and dissolved in hot acetonitrile (125 mL); residual solids were removed by filtration. The filtrate was placed on a column containing silica gel (14 g) in acetonitrile. The column was eluted with dry acetone. The eluent was evaporated and the remaining solid recrystallized from acetonitrile to give 2-amino-9-(2-formyloxyethoxymethyl)adenine (93 mg), m.p. 238-240°C.

Example 3

9-[(2-formyloxyethoxy)methyl]2,6-diaminopurine

A solution of 9-[(2-formyloxyethoxy)methyl]-2-azidoadenine (610 mg) in dry dimethylformamide (125 ml) containing 5% palladium (120 mg) on charcoal was hydrogenated at an initial pressure of 3, 5 kg/cm 2 for 24 hours at room temperature. Thin layer chromatography (silica gel in acetone) showed only one spot corresponding to authentic 9-[(2-formyloxyethoxy)methyl]-2,6-diaminopurine and no starting material.

The solution was filtered through a pad of "Celite", the pad was washed with ethyl acetate and the combined washing solutions and filtrate evaporated in vacuo at a bath temperature of 60°C. The resulting yellow solid was purified by column chromatography (silica gel), eluting the desired product with acetone.

Trituration of the evaporated eluates with acetone gave 119 mg (22%) of 9-[(2-formyloxyethoxy)methyl]-2,6-diaminopurine whose U.V. and N.M.R. spectra were consistent with the determined structure, m.p. 238-240°C.

Example 4

9-(2-formyloxyethoxymethyl)guanine

Hydrogen chloride gas was bubbled into a cooled (0°C) suspension of ethylene glycol monoformate (3.6 g, Annalen der chemie, 641, 1 (1961)) and paraformaldehyde (1.2 g) in dry dichloromethane (100 mL) until the mixture was saturated. The oily suspension was dried over molecularly sieved ethanol and anhydrous calcium chloride, filtered and the solvent was removed by evaporation under reduced pressure (bath temperature

<3 0°C). The resulting crude 2-formyloxyethoxymethyl chloride (2.5 g) was added to a solution of tris-(trimethylsilyl)-guanine (4.8 g) in dry toluene (50 mL) and the mixture heated at reflux under nitrogen for 24 h. The solvent was removed under reduced pressure to give 9-(2-formyloxyethoxymethyl)bis-N 2 ,0 6-)-trimethylsilyl)guanine as an oil which was used without purification. An excess of methanol was added to the oil and the mixture stirred for 1 hour. The methanol was removed by evaporation and the residue recrystallized from dimethylformamide and acetonitrile to give 9-(2-formyloxyethoxymethyl)guanine, m.p. 225-227°C.

Example 5

9-(2-formyloxyethoxymethyl)guanine

To a mixture of acetic acid-formic anhydride (1.0 ml) and p_-toluenesulfonic acid (0.1 g) was added, while stirring, to

added dioxolane (1.0 g), and since the reaction is exothermic,

caution was exercised. The solution was allowed to cool for several minutes. Dry toluene (10 mL) and guanine (1.0 g) were added and the reaction heated at 50°C for 24 hours. The toluene was decanted and the residue thoroughly washed with dry toluene (25 mL) and recrystallized twice from dry dimethylformamide to give 9-(2-formyloxyethoxymethyl)guanine,

m.p. 225-227°C.

Claims (1)

Analogy method which is a further development according to Norwegian patent document no. 144 126, for the production of therapeutically effective, substituted purine compounds with the formula: where R is a hydroxy or amino group, or a pharmaceutically acceptable salt thereof, characterized by a) converting a compound with the formula: where either both M and G are a halogen atom, a mercapto, hydroxy, amino, alkylthio, alkoxy, azide or hydra-zino group, provided that both M and G are not amino except when M is to be converted to hydroxy, and provided that M is not hydroxy when G is amino except when M is to be converted to amino, to a compound of formula I by hydrolysis, aminolysis or reduction, or b) reacts a compound of the formula: where Q is hydrogen, with a compound of the formula: where A is carboxylate, or c) esterifies an alcohol with the formula: where R has the above meaning, by reaction with formic acid, or d) a compound with the formula: where Rq is -OX or -NHX, and X is a lower trialkylsilyl group, preferably trimethylsilyl group, is converted to a compound of formula I by hydrolysis or solvolysis; and, if desired, when the product of the above reaction is a base, converting a compound of formula I into an acid addition salt thereof, or, if desired, when the product is a salt of a compound of formula I, converting this salt into its base or another salt thereof.