Note: Descriptions are shown in the official language in which they were submitted.
363
This invention relates to a method of synthesising
substituted purine compounds in particular 9-(2-hydrGxy-
ethoxymethyl) derivatives of the purines 2-amino-adenine and
guanine.
9-(2-Hydroxyethoxymethyl)derivatives of purines
have antiviral activity against various classes of D~A and
RNA viruses both 1n vitro and ln vivo experiments. In parti-
cular these compounds are active as antiviral ~gents 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-hydroxy-
ethoxymethyl) 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 Canadian Patent 1,062,257, Howard J~ Schaeffer, issued
September 11, 1979).
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~q6~63
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It has no;~ been found that certain 9-(2-hydroxy-
ethoxymethyl) 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 pre-
paring compounds of formula (I):
R
~ N
N
H2N N
CH2~o cH2~cH2~OH
whPrein R is amlno or hydroxy, comprising hydrolysing in
the presence of a base a compound of formula (II)
X -C-~R ~ o (II)
~ 2
- CH2 O CH2CH2-O-C X
wherein Rl is hydroxy or _NR2.C.Xl, and Xl and x2 are the
O
same or different and each represents an alkyl or phenyl
group, and R2 is hydrogen or -CXl provided that when
is hydroxy, R is hydrogen~ When Xl 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.
~: :
,
' ' : , ,- ,' :.
-
1(~46863
The base used in the hydrolysis m~y be anaqueous or alcoholic primary or secondary aliphatic amine,
an alko~ide 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 Rl
i9 -~R2CXl, and R is -IXl, may be completely hydrolysed in
O. O
~- one step using for example a~ueous 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-X
O
20~ ~groups,~is carried out uslng a stronger base such as
aqyeous methy1amlre.
.
~96863
-- 5 --
The intermediates of formula (II) are novel,
and therefore according to a second aspect of the
invention there is provided intermediate compounds of
formula (II) as defined above. These compounds ran
be prepared by reacting guanine, or 2-amino ~denine 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
such as sulphuric acid, sulphonic acids, SUC~ as E~toluene-
sulphonic, methanesulphonic or trifluoromethanesulphonic
acid, sulphamic acid or polyphosphoric acid.-
The acylated purine may in turn be preparedby reacting the appropriate purine with an acid anhydride
- ~ such as acetic anhydride, or other acylating agent for
examplè an acid halide.
To p~epare the diester of 2-oxa-1,4-butane-
diol, dioxolane is reacted with an acid anhydride in the
presence of a catalytic amount of a strong acid such as
one of those acids Iisted above.
20 ~ ~ The invention will now ~e illustrated with
~ reference to the following examples.
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~C~96863
-- 6
EXAMPLE 1
- 9-(2-Hydroxyethoxymethyl)quanine
To a mixture of acetic anhydride (102 g),
acetic acid (15 g), and ~-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 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 ml3 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 40/0 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 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 9G% pure), m.pt. 255-257C. yield = 56%.
363
EXAMPLE 2
9-(2-Hydroxyethoxymethyl)~uanine
A mixture of diacetylguanine (50 g), 2-oxa-1,4-
butanediol diacetate (59.8 g), and ~-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 4~/O aqueous methylamine (350 ml~. The mixture was
heated at reflux with stirring or 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~9~/O pure), yield = 75%.
EXAMPLE 3
2-Acetam}do-9-(2-acetylo ~ethoxyme~thyl)hypoxanthine
A mixture of diacetylguanine (1.0 g), 2-oxa-1,4-
~ butanediol diacetate (0.82 g) and E~toluenesulfonic acid
(23 mg)~in mlneral o11 (4 g) was~heated at llSC with
9tirring~at reduced pressure overnight. The mineral oil
;was~decanted off. ~The residue was triturated with chloro-
form: and~ then extracted with boiling methanol. The
methanol~extract was concentrated to~50 ml, chilled, and
~iltered.~The filtrate w~as evaporated to dryness, giving
a solid~residue (0.43 g). `The solid was purified by
:''' ~ ' ' - ~ ' ' ~ -' :
:
: '- ,
,
'15~C'6863
-- 8 --
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.
202.5-204.5C.
EXAMPLE 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
condenser (CaC12 drying tube), to which acetic anhydride
(4 1) were added. The mixture was brought to reflux
and held for 60 hour~. 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 coollng to room temperature and was then
d1ssolved in~dichloromethane, filtered to remove any
suspended solids,~and the soLvent removed ln vacuo to
give ~211;.0 g (> 10~/o) of 2,6-bis-(dlacetylamino)-9-
acetyl purine.;~The ~assayed yield wss 96.7% based upon
the~ nmr ~with the~balance of the material being acetic
3nhydride.~
' `~ ' : '
~ - . . : : -
~ : ' .
863
-- 3
(b) The ~enta-acetyl p~rine (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
mixture 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
then added in one portion and heating was continued
_ 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. I
(c) The fusion product (208.5 ~) 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) 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 30C. 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 x 500 ml) and refiltered. This was dried ln vacuo
at 65C for 3 hours and then at room temperature overnight
to give 154.2 g (91.P/o) of a light brown hard solid.
6863
-- 10 --
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.~/o) 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 raised 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 ln vacuo on a water ~ath at 45 50C to
give a thick mass of brown crystals. This was then
slurried with acetone (545 ml, 7 ml/g) for 15 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 (96.0%) of crude, hydrated 2-amino-9-(2-
hydroxyethoxymethyl)adenine as light brown crystals.
mese were dried in vacuo at 80C for 18 hours to give
69.3 g. (39.~) of dry pr duct.
