CA1096864A - Intermediates for the preparation of derivatives of guanine and adenine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Intermediates of formula (II):

(II) wherein R1 is hydroxy or , and X1 and X2 are the same or different and each represents an alkyl or phenyl group, and R is hydrogen or

Description

1t)'~6~364 This invention relates to intermediates for synthesising substituted purine compounds in particular 9-(2-hydroxyethoxymethyl) derivatives of the purine~ 2-amino-adenine and guanine, and the preparation of such intermediates.
This application is a division of Canadian Patent Application, Serial No. 285,592, filed August 26, 1977.
. 3-(2-Hydroxyethoxymethyl)derivatives of purines have antiviral activity against various classes of D~A and RNA viruses bot~ ln vitro and in vivo experiments. In particular these compounds are active as antiviral agents .. ; :
against adenovirus, such as adenovirus 5 and rhinovirus.
hey 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 keratitls in rabbit~ and herpetic encephalitis in mice.
Examples:of 9-~2_hydroxyethoxymethyl)derivatives of:purines~showing~particularly:good antiviral activity 20 ~ are~9-~2-hydroxyethoxymethyl~guanine and 2-amino-9-(.2-hydroxyethoxymethyl~ adenlne.: .
A~:number~;of methods:of synthesis are known for 9-t2-hydroxyathoxymoth;yl~) derivatives of purine, for exampl`e~:they~may be~prepared by :the removal of a protective group~from~tha~2~position on tha side chain. Alter-f~ natiYe}y they~can~be~:formed by the~conversion of the 2 and/or 6 ~ubstituant on the purine ring into a different substituant~(sae~Canadian Patent 1,062,257,.Howard J~
Schaefar, i~s~uad Saptamber 11, 1979).

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It has now been found that certain 9-(2-hydroxy-ethoxymethyl) derivatives of purines can be prepared by a new and advantageous synthetic route. In particular it has been found that compoundsof formula (I):

R

N ~

H2~ N N
I

H2~cH2.OH
: .
: wherein R is amino or hydroxy can be prepared in a process :~ ~ which comprises hydrolysing, in the presence of a base, a compound of formula (II~: ~
: .

1~ ~

X~ ~R2 N~ ~ 2 CH 0.CH CH -o-~-X .

2 2 2 whereiA~RI~is~bydroxy or -~R~.Cl~.XI, and Xl and x2 are the same~ or dlferent and each represents an alkyl or phenyl group,~and;~R i9 hydrogen or -CXl provided that when R

is~l;hydroxy,:R2 is hydrogen.

~: ~ : ' ' ' - , 1~6~364 When xl and x 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 lII), in which R is -NR2CXl, and R2 is -CXl, may be completely hydrolysed in O O
one step using, for example, aqueous methylamine. Alter-natively, and more preferably, the intermediate of formula (II) is deacylated in 2-steps, in the first step -a single -C-Xl 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, to remove the remaining -C-Xl groups, is carried out using a stronger O
base such as aqueous methylamine.

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l~q6864 The intermedlates of formula (II) are novel, and the present invention is particularly concerned with such intermediate compounds of formula (II) as defined above.
In another aspect of the invention there is pro-vided a process of preparing the intermediates of formula ~II), as defined above, 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 or, 2-oxa-1,4-butanediol in the presence of a catalytic amount of a strong acid.
:~ Suitable strong acids include sulphuric acid sulphonic acids, for example, E~toluene sulphonic, methanesulphonic, trifluoromethanesulphonic acid, sulphamic aaid and polyphosphoric acid. .

The acyLated purine may in turn be prepared by reactlng the~appropr~iate purine wlth an acid anhydride, for example, acet1c a ~ dride, or other acylating agent, for example~an~acid hal~i~e. : ~ ;. .
To~prepare~the~diester~ of~2-oxa-1,4-butanediol, dioxolane:is~re:acted with~an~acid anhydride in the presence ..
s ~ o~ a~catalytlc amount:of a:strong acid such as one of those acids~listed~ akove~
The~inventlon~will now be lllustrated with re erence-~:to~the following examples: ~

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~96~G4 9-(2-Hydroxyethoxymethyl)~uanine To a mixture of acetic anhydride (102 g), acetic acid (15 g), and p-toluenesulfonic acid (5.0 g) cooled to 10C, dioxolane (70 g) was added with stirring and cooling at such a rate that the pot temperature never exceeded 40C. The mixture was then cooled to room temperature and toluene (300 ml) and diacetyl~uanine (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/O aqueous methyl-amine (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 slurrya 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 9G% pure), m.pt. 255-257C. yield = 56%.

1~ 64 9-(2-Hydroxyethoxymethyl)quanine 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 40YO aqueous methylamine (350 ml). The mixture was heated at reflux with stirring for 40 minutes, cooled to room temperature and filtered. me filtrate was evaporated under reduced pres~ure to give a thick slurry. Ethanol (200 ml) was added to the ~lurry which was then cooled, filtered, washed with ethanol and dried to give 9-(2-hydroxyethoxymethyl~)guanine (36 g, greater than 9G%~ pure), yield = 75%.
EXAMPLE~3 :
2-Acetami:do-9-~(2-aaetyloxyethoxvmethvl)hYpoxanthine ; A mixture of~diacetylguanine (1.0 g), 2-oxa-1,4-~butanediol diacetate (0.82 g) and E~toluenesulfonic acid (23 mg) in mineral~oil (4 g) was~heated at 115C with stirri~ng at~reduced~préssure overnight. The mineral oil was~decanted off.; The residue was triturated with chloro-form~and~;then~extr~cted~with boillng methanol. The methanol~extract~was~concentrated to 50 ml, chilled, and filtered.~ The filtrate was evaporated to dryness, giving a~olid~residue (0.43~g). The solid was purified by . ~. -. ~: : : :

: - :

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9~36~

column chromatography (~ilica gel, 10 g, in chloroform,eluted with 1:1 chloroform:acetone) followed by recrystalli~;ation from ethanol to give 2-acetamido-9-(2-acetyloxyethoxymethyl)hypoxanthine (0.14 g), m.p.
202.5-204.5C.
~AMPLE 4 2-Amino-9-(2-hydroxyethoxymethyl)adenine (a) 2-Formamido adenine (89.0 g) was placed in a 5-liter flask equipped with an air-stirrer and reflux 10 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 di~tillate 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 `~ gun~ny mass upon cooling to room temperature and was then dis801ved in dichloromethane, filtered to remove any 20 ~ suspended 901ids,~and the solvent removed in vacuo to give 211.0 g (~ 100%) of 2,6-bi~-(diacetylamino)-9-acetyl purine. The assayed yield was 96.7% based upon the nmr with the balance of the material being acetic anhydride.

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~S~64 (b) The penta-acetyl purine (174 g) was combined with 1,4-diacetoxy-2-oxabutane (126.8 g) in a flask equipped with an air-stirrer and drying tube. This mi.xture was then placed in an oil bath at 130C and stirred for a few minutes to homogenize the batch. The acid catalyst, para toluenesulphonic acid (2.74 g), was thèn 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 ml/g) at room temperature and transferred to :~: :
flask equipped with a dropping funnel, air-stirrer, and thermometer, The n-butylamine (140.4 g) wae 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 30C. ~The product began to separate from the 20~ reaction mixture~during the cour~oe 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 x~SOO~ml)~and~refiltered. Thls~was dried in vacuo at~65~C~for 3~hour~s~and~then at room temperature overnight ~ to~give 154.2~g (91.P~) of a~light brown hard solid.

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9 _ The product was purified by dissolving it in hot dimethyl-formamide (10 ml/g) at 100-110C to give an opaque brown solution. After cooling overnight at 5C, the product was removed by filtration, washed with acetone (1 x 250 ml) and air dried to give 121.7 g (78.8%) of 2,~-di-acetamido-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 4~/O solution) over a 5-minute period. The addition was accompanied by a mild exotherm which raiced the temperature of the mixture to 35C and all of the solid material dissolved in a few minutes.
After stirring for 2-1/2 hours the tlc of the mixture indicated completion of the reaction. The mixture was ;~ ~ then concentrated 1n vacuo on a water bath at 45-50C to give a thick mass of brown crystals. This was then slurried with acetone (545 ml, 7 ml/g) for l5 minutes to remove N-methyl acetamide and vacuum filtered. The cake was rinsed with acetone (1 x 200 ml) and air-dried to give 74.7 g (96.0Yo) of crude, hydrated 2-amino-9-(2-hydroxyethoxymethyl)adenine as light brown crystals.
ese~were dried in vacuo at 80C for 18 hours to give 69.3~g. ~89.0~ of dry product.

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Claims (11)

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

1, A process for preparing a compound of formula (II):

(II) wherein R1 is hydroxy or , and X1 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 R2 is hydrogen comprising reacting guanine, or 2-amino adenine in which the 2 and 9, and 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.

2. A process as claimed in claim 1, wherein the acid catalyst is p-toluenesulphonic acid.

3. A process as claimed in claim 1, wherein the alkyl group contains from 1 to 4 carbon atoms.

4. A process as claimed in claim 1, wherein X1 and X2 are both methyl groups.

5, A process as claimed in claim 1, wherein is hydroxy.

6. A process as claimed in claim 1, wherein R1 is said group.

7. A compound of formula (II), as defined in claim 1, whenever prepared by the process of claim 1 or 2, or by an obvious chemical equivalent.

8. A compound of formula (II), as defined in claim 3, whenever prepared by the process of claim 3, or by an obvious chemical equivalent.

9. A compound of formula (II), as defined in claim 1, wherein X1 and X2 are both methyl groups, whenever prepared by the process of claim 4, or by an obvious chemical equivalent.

10. A compound of formula (II), as defined in claim 1, wherein R1 is hydroxy, whenever prepared by the process of claim 5, or by an obvious chemical equivalent.

11. A compound of formula (II) as defined in claim 1, wherein R1 is said: group, whenever prepared by the process of claim 6, or by an obvious chemical equivalent.