GB1567671A

GB1567671A - Preparation of purine compounds

Info

Publication number: GB1567671A
Application number: GB35914/77A
Authority: GB
Original assignee: Wellcome Foundation Ltd
Current assignee: Wellcome Foundation Ltd
Priority date: 1976-08-27
Filing date: 1977-08-26
Publication date: 1980-05-21
Also published as: YU202277A; NL7709458A; SE8304549D0; ATA620177A; SE7709606L; SE447113B; CS196384B2; SE8304549L; NO147186B; DK380377A; CA1096863A; NO147186C; FI64160B; SE432764B; CH634843A5; DD131856A6; DK147857C; NO772959L; NO822502L; NO150119C

Abstract

9-(2-Hydroxyethoxymethyl) derivatives of 2-amino-adenine and guanine of formula I are prepared by hydrolysis from compounds of formula II. The reaction is carried out in the presence of a base. The symbols in formula I and II have the meanings given in Patent Claim 1. The novel compounds of formula II are prepared by reacting the guanine or 2-aminoadenine, wherein the 2- and 9-positions, or the 2-, 6- and 9-positions, are acylated, with a diester of 2-oxa-1,4-butanediol. This reaction is carried out in the presence of a catalytic amount of an acid. The 9-(2-hydroxyethoxymethyl) derivatives of 2-aminoadenine and guanine are novel and exhibit an antiviral action, especially against the classes of the DNA- and RNA-viruses. <IMAGE>

Description

(54) IMPROVEMENTS IN AND RELATING TO THE PREPARATION OF PURINE COMPOUNDS (71) We, THE WELLCOME FOUN DATION LIMITED, of 183-193 Euston Road, London, N.W.I, a Company incorporated in England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of synthesising substituted purine compounds, in particular 9 - (2 - hydroxyethoxymethyl) derivatives of the purines 2- amino adenine and guanine.

9 - (2 - Hydroxyethoxymethyl) derivatives of purines have antiviral activity against various classes of DNA and RNA viruses both in vitro and in vivo experiments.

In particular these compounds are active as antiviral agents against adenovirus, such as adenovirus 5, and rhinovirus. They are especially active as an antiviral agent against, vaccinia, and herpes viruses, including simplex, zoster and varicella, in mammals, which viruses cause such diseases as herpetic keratitis in rabbits and herpetic encephalitis in mice.

Examples of 9 - (2 - hydroxyethoxymethyl) derivatives of purines showing particularly good antiviral activity are 9 (2 - hydroxyethoxymethyl)guanine and 2 amino - 9 - (2 - hydroxyethoxymethyl) adenine.

A number of methods of synthesis are known for 9 - (2 - hydroxyethoxymethyl) derivatives of purine, for example they may be prepared by the removal of a protective group from the 2 position on the side chain.

Alternatively they can be formed by the conversion of the 2 and/or 6 substituent on the purine ring into a different substituent (see U.K. Patent No. 1,523,865).

It has now been found that certain 9 (2 - hydroxyethoxymethyl) derivatives of purines can be prepared by a new and advantageous synthetic route. Thus, according to the present invention there is provided a process for preparing a compound of formula (I):

wherein R is amino or hydroxy; comprising hydrolysing in the presence of a base a compound of formula (II):

wherein R1 is hydroxy or

Xl and X2 are the same or different and each represent an alkyl or phenyl group; and R2 is hydrogen or

provided that when R' is hydroxy then R2 is hydrogen. When X' and X2 are alkyl groups they preferably have 1 to 4 carbon atoms, most preferably they are the same and each represent a methyl group.

The base used in the hydrolysis may be an aqueous or alcoholic primary or secondary aliphatic amine, an alkoxide in alcohol, or an aqueous or alcoholic hydroxide, for example sodium alkoxide or hydroxide, the preferred base being an aqueous primary aliphatic amine for example aqueous methylamine. Depending on the base used, the hydrolysis can be carried out at a temperature from room temperature up to that of a steam bath. In general the lower the reaction temperature, the longer the reaction time but the fewer the side reactions.

An intermediate of formula (II), in which R' is

and R2 is

may be completely hydrolysed in one step using for example aqueous methylamine.

Alternatively, and more preferably, the intermediate of formula (II) is deactylated in 2-steps; in the first step a single

group is removed from the 2 and 6-positions on the purine ring by mild hydrolysis at room temperature using, for example, butylamine in a lower alcohol.

The second step of the hydrolysis, i.e. to remove the remaining

group, is carried out using a stronger base such as aqueous methylamine.

The intermediates of formula (II) are novel, and therefore according to a second aspect of the invention there is provided a compound of formula (II) as defined above.

These compounds can be prepared by resting guanine, or 2-amino adenine in which the 2 and 9, or 2, 6 and 9 positions respectively are acylated, with a diester of 2 - oxa - 1,4 - butanediol in the presence of a catalytic amount of a strong acid such as sulphuric acid, sulphonic acids such as ptoluenesulphonic, methanesulphonic or trifluoromethanesulphonic acid, sulphamic acid, bis -(p- nitrophenyl)phosphate or polyphosphoric acid.

The acylated purine may in turn be prepared by reacting the appropriate purine with an acid anhydride such as acetic anhydride, or other acylating agent for example an acid halide.

To prepare the diester of 2 - oxa - 1,4 butanediol, dioxolane is reacted with an acid anhydride in the presence of a catalytic amount of a strong acid such as one of those acids listed above.

The invention will now be illustrated with reference to the following examples.

Example 1 9 - (2 - Hydroxyethoxymethyl)guanine To a mixture of acetic anhydride (102 g), acetic acid (15 g), and p-toluenesulfonic acid (5.0 g) cooled to 100C, dioxolane (70 g) was added with stirring and cooling at such a rate that the pot temperature never exceeded 400 C. The mixture was then cooled to room temperature and toluene (300 ml) and diacetylguanine (50 g) added.

The reaction mixture was then heated at reflux with stirring for 16 hours. It was then cooled to room temperature, chloroform (50 ml) was added and the solid product removed by filtration. The filter cake was thoroughly washed with chloroform and dried, The dried filter cake was added to 40% aqueous methylamine (350 ml) and the mixture was heated at reflux with stirring for 40 minutes, cooled and filtered. The filtrate was evaporated under reduced pressure to a thick slurry. The slurry was cooled and filtered, and the filter cake was washed with ethanol and dried to give 9 - (2 - hydroxyethoxymethyl)guanine (27 g, greater than 90% pure), m.pt. 255-2570C, yield=56%.

Example 2 9 - (2 - Hydroxyethoxymethyl)guanine A mixture of diacetylguanine (50 g), 2 oxa - 1,4 - butanediol diacetate (59.8 g), and p-toluene sulfonic acid (1.2 g) in toluene (350 ml) was heated with stirring at reflux for 16 hours. The mixture was cooled to room temperature, filtered and the filter cake thoroughly washed with toluene. The filter cake was dried and added to 40% aqueous methylamine (350 ml). The mixture was heated at reflux with stirring for 40 minutes, cooled to room temperature and filtered. The filtrate was evaporated under reduced pressure to give a thick slurry.

Ethanol (200 ml) was added to the slurry which was then cooled, filtered, washed with ethanol and dried to give 9 - (2 - hydroxyethoxymethyl)guanine (36 g, greater than 90 /n pure), yield=75%.

EXAMPLE 3 2 - Acetamido - 9 - (2 - acetyloxyethoxy methyl)hypoxanthine A mixture of diacetylguanine (1.0 g), 2 oxa - 1,4 - butanediol diacetate (0.82 g) and p-toluenesulfonic acid (23 mg) in mineral oil (4 g) was heated at 1 150C with stirring at reduced pressure overnight. The mineral oil was decanted off. The residue was triturated with chloroform and then extracted with boiling methanol. The methanol extract was concentrated to 50 ml, chilled, and filtered.

The filtrate was evaporated to dryness, giving a solid residue (0.43 g). The solid was purified by column chromatography (silica gel, 10 g, in chloroform; eluted with 1:1 chloroform:acetone) followed by recrystallisation from ethanol to give 2 acetamido - 9 - (2 - acetyloxyethoxymethyl)hypoxanthine (0.14 g), m.p. 202.5- 204.5"C.

EXAMPLE 4 2 - Amino - 9 - (2 - hydroxyethoxy methyl)adenine (a) 2-Formamido adenine (89.0 g) was placed in a 5-liter flask equipped with an airstirrer and reflux condenser (CaC12 drying tube), to which acetic anhydride (4 1) were added. The mixture was brought to reflux and held for 60 hours. At the end of this time, the excess anhydride was removed by distillation at atmospheric pressure until approximately 3.5 1 of distillate had been obtained. The distillation was continued under reduced pressure to remove most of the remaining anhydride. The dark brown pot residue became a viscous gummy mass upon cooling to room temperature and was then dissolved in dichloromethane, filtered to remove any suspended solids, and the solvent removed in vacuo to give 211.0 g ( > 100%) of 2,6 - bis - (diacetylamino) - 9 acetyl purine. The assayed yield was 96.7 based upon the nmr with the balance of the material being acetic anhydride.

(b) The penta-acetyl purine (174 g) was combined with 1,4 - diacetoxy - 2 oxabutane A (126.8 g) in a flask equipped with an air-stirrer and drying tube. This mixture was then placed in an oil bath at 1300C and stirred for a few minutes to homogenize the batch. The acid catalyst, para toluenesulphonic acid (2.74 g), was then added in one portion and heating was continued in vacuo for 4 hours at which time nearly quantitative conversion to products was observed. The reaction mixture was then cooled to room temperature and stored under dry nitrogen.

(c) The fusion product (208.5 g) was dissolved in ethanol (5 mUg) at room temperature and transferred to flask equipped with a dropping funnel, air-stirrer, and thermometer. The n-butylamine (140.4 g) was then added dropwise over a 2 hour period and the exothermic reaction was controlled with the use of a water bath. The maximum temperature which the reaction was allowed to reach being only 300 C. The product began to separate from the reaction mixture during the course of the addition.

After completion of the addition, the mixture was stirred at room temperature for 3 hours and then placed in the cold room overnight. The product was removed by filtration to give a pasty mass which was slurried with acetone (1 x500 ml) and refiltered. This was dried in vacuo at 650C for 3 hours and then at room temperature overnight to give 154.2 g (91.7%) of a light brown hard solid. The product was purified by dissolving it in hot dimethylformamide (10 mg/g) at 100 110 C to give an opaque brown solution. After cooling overnight at 5"C, the product was removed by filtration, washed with acetone (1 x250 ml) and air dried to give 121.7 g (78.8%) of 2,6 diacetamido - 9 - (2 - acetoxyethoxymethyl)purine.

(d) The 2,6 - diacetamido - 9 - (2 acetoxyethoxymethyl)purine (121.7 g) was added to a stirred solution of aqueous methylamine (608.5 ml of 40% solution) over a 5-minute period. The addition was accompanied by a mild exotherm which raised the temperature of the mixture to 35"C and all of the solid material dissolved in a few minutes. After stirring for 2+ hours the tlc of the mixture indicated completion of the reaction. the mixture was then concentrated in vacuo on a water bath at 45 50"C to give a thick mass of brown crystals.

This was then slurried with acetone (545 ml, 7 mVg) for 15 minutes to remove N-methyl acetamide and vacuum filtered. The cake was rinsed with acetone (I x200 ml) and airdried to give 74.7 g (96.0%) of crude, hydrated 2- amino - 9 - (2 - hydroxyethoxymethyl)adenine as light brown crystals. These were dried in vacuo at 800C for 18 hours to give 69.3 g (89.0%) of dry product.

WHAT WE CLAIM IS: 1. A process for preparing a compound of formula (I)

wherein R is amino or hydroxy, comprising hydrolysing in the presence of a base a compound of formula (II)

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

hydroxyethoxymethyl)guanine (36 g, greater than 90 /n pure), yield=75%.

EXAMPLE 3 2 - Acetamido - 9 - (2 - acetyloxyethoxy methyl)hypoxanthine A mixture of diacetylguanine (1.0 g), 2 oxa - 1,4 - butanediol diacetate (0.82 g) and p-toluenesulfonic acid (23 mg) in mineral oil (4 g) was heated at 1 150C with stirring at reduced pressure overnight. The mineral oil was decanted off. The residue was triturated with chloroform and then extracted with boiling methanol. The methanol extract was concentrated to 50 ml, chilled, and filtered.

The filtrate was evaporated to dryness, giving a solid residue (0.43 g). The solid was purified by column chromatography (silica gel, 10 g, in chloroform; eluted with 1:1 chloroform:acetone) followed by recrystallisation from ethanol to give 2 acetamido - 9 - (2 - acetyloxyethoxymethyl)hypoxanthine (0.14 g), m.p. 202.5- 204.5"C.

EXAMPLE 4

2 - Amino - 9 - (2 - hydroxyethoxy methyl)adenine (a) 2-Formamido adenine (89.0 g) was placed in a 5-liter flask equipped with an airstirrer and reflux condenser (CaC12 drying tube), to which acetic anhydride (4 1) were added. The mixture was brought to reflux and held for 60 hours. At the end of this time, the excess anhydride was removed by distillation at atmospheric pressure until approximately 3.5 1 of distillate had been obtained. The distillation was continued under reduced pressure to remove most of the remaining anhydride. The dark brown pot residue became a viscous gummy mass upon cooling to room temperature and was then dissolved in dichloromethane, filtered to remove any suspended solids, and the solvent removed in vacuo to give 211.0 g ( > 100%) of 2,6 - bis - (diacetylamino) - 9 acetyl purine. The assayed yield was 96.7 based upon the nmr with the balance of the material being acetic anhydride.

(b) The penta-acetyl purine (174 g) was combined with 1,4 - diacetoxy - 2 oxabutane A (126.8 g) in a flask equipped with an air-stirrer and drying tube. This mixture was then placed in an oil bath at 1300C and stirred for a few minutes to homogenize the batch. The acid catalyst, para toluenesulphonic acid (2.74 g), was then added in one portion and heating was continued in vacuo for 4 hours at which time nearly quantitative conversion to products was observed. The reaction mixture was then cooled to room temperature and stored under dry nitrogen.

(c) The fusion product (208.5 g) was dissolved in ethanol (5 mUg) at room temperature and transferred to flask equipped with a dropping funnel, air-stirrer, and thermometer. The n-butylamine (140.4 g) was then added dropwise over a 2 hour period and the exothermic reaction was controlled with the use of a water bath. The maximum temperature which the reaction was allowed to reach being only 300 C. The product began to separate from the reaction mixture during the course of the addition.

After completion of the addition, the mixture was stirred at room temperature for 3 hours and then placed in the cold room overnight. The product was removed by filtration to give a pasty mass which was slurried with acetone (1 x500 ml) and refiltered. This was dried in vacuo at 650C for 3 hours and then at room temperature overnight to give 154.2 g (91.7%) of a light brown hard solid. The product was purified by dissolving it in hot dimethylformamide (10 mg/g) at 100 110 C to give an opaque brown solution. After cooling overnight at 5"C, the product was removed by filtration, washed with acetone (1 x250 ml) and air dried to give 121.7 g (78.8%) of 2,6 diacetamido - 9 - (2 - acetoxyethoxymethyl)purine.

(d) The 2,6 - diacetamido - 9 - (2 acetoxyethoxymethyl)purine (121.7 g) was added to a stirred solution of aqueous methylamine (608.5 ml of 40% solution) over a 5-minute period. The addition was accompanied by a mild exotherm which raised the temperature of the mixture to 35"C and all of the solid material dissolved in a few minutes. After stirring for 2+ hours the tlc of the mixture indicated completion of the reaction. the mixture was then concentrated in vacuo on a water bath at 45 50"C to give a thick mass of brown crystals.

This was then slurried with acetone (545 ml, 7 mVg) for 15 minutes to remove N-methyl acetamide and vacuum filtered. The cake was rinsed with acetone (I x200 ml) and airdried to give 74.7 g (96.0%) of crude, hydrated 2- amino - 9 - (2 - hydroxyethoxymethyl)adenine as light brown crystals. These were dried in vacuo at 800C for 18 hours to give 69.3 g (89.0%) of dry product.

WHAT WE CLAIM IS: 1. A process for preparing a compound of formula (I)

wherein R is amino or hydroxy, comprising hydrolysing in the presence of a base a compound of formula (II)

wherein R1 is hydroxy or

X' and X2 are the same or different and each represents an alkyl or phenyl group; and R2 is hydrogen or

provided that when R1 is hydroxy then R2 is hydrogen.
2. A process as claimed in Claim 1, wherein the alkyl group represented by X; and/or X2 contains from 1 to 4 carbon atoms.
3. A process as claimed in either Claim 1 or Claim 2, wherein X' and X2 are the same and each represents a methyl group.
4. A process as claimed in any one of the preceding claims, wherein the base is an aqueous or alcoholic primary or secondary aliphatic amine, an alkoxide in alcohol or aqueous or alcoholic hydroxide.
5. A process as claimed in any one of the preceding claims, wherein the compound of formula (II) has been prepared by reacting guanine, or 2-amino adenine in which the 2 and 9, or 2, 6 and 9 positions respectively are acylated, with a diester of 2 - oxa - 1,4 butanediol in the presence of a catalytic amount of a strong acid.
6. A process as claimed in Claim 5, wherein the acid catalyst is ptoluenesulphonic acid.
7. A compound of formula (II)

wherein R' is hydroxy or

X' and X2 are the same or different and each represents an alkyl or phenyl group; and R2 is hydrogen or

provided that when R' is hydroxy then R2 is hydrogen.
8. A compound as claimed in Claim 7 where the alkyl group represented by X' and/or X2 contains from 1 to 4 carbon atoms.
9. A compound as claimed in either Claim 7 or Claim 8, wherein X' and X2 are the same and each represent a methyl group.
10. A process for preparing a compound of formula (II), as claimed in Claim 7, comprising reacting guanine, or 2-amino adenine in which the 2 and 9, or 2, 6 and 9 positions respectively are acylated, with a diester of 2 - oxa - 1,4 - butanediol in the presence of a catalytic amount of a strong acid.
11. A process as claimed in Claim 10, wherein the acid catalyst is ptoluenesulphonic acid.
12. A process as claimed in Claim 1 substantially as hereinbefore described with reference to any one of the Examples.
13. A process as claimed in Claim 10 substantially as hereinbefore described with reference to any one of the Examples.