2-chloro-N.sup.6 -substituted adenosines, their pharmaceutical compositions, and activity in treating ischemias

Adenosine compounds having the following structure ##STR1## wherein X is halogen, perhalomethyl, acetamido, cyano, C.sub.1-6 -alkoxy, C.sub.1-6 -alkylthio or C.sub.1-6 -alkylamino; and R.sup.1 is --NR.sup.2 R.sup.3 or YR.sup.4, wherein Y is oxygen or sulfur; R.sup.2 is phenyl, C.sub.1-6 -alkyl or substituted C.sub.1-6 -alkyl; and R.sup.4 is naphthyl, partly saturated naphthyl; optionally phenyl or phenoxy substituted C.sub.1-6 -alkyl wherein the phenyl and phenoxy substituents are also optionally substituted, or optionally phenyl or phenoxy substituted C.sub.3-8 -cycloalkyl and their pharmaceutically acceptable salts are useful in the treatment of myocardial and cerebral ischemias.

The present invention relates to modified adenosine derivatives having a 
substituent at the 6-position containing sulphur, oxygen or nitrogen, 
further substituted at the purine 2-position as well as pharmaceutically 
acceptable addition salts thereof having central nervous system (CNS) 
properties. Also covered are processes for preparation of the above 
derivatives and their pharmaceutical compositions as well as methods for 
using the compounds and compositions as drugs primarily for CNS ailments. 
BACKGROUND OF THE INVENTION 
Adenosine can be considered to be a hormone which has been shown to have a 
number of significant effects on the mammalian central nervous system 
[Annual Reports in Medicinal Chemistry, 1988, 23, 39-48; International 
Review of Neurobiology (Smythies, J. R. and Bradley, R. J., eds.) Academic 
Press Inc., 1985.27, 63-139], especially under conditions of neuronal 
stress where the compound appears to act as an endogenous neuroprotectant 
(Progress in Neurobiology, 1988, 31,85-108, Trends in Pharmacological 
Sciences, 1983, 9, 193-194). For example, the concentration of adenosine 
has been demonstrated to rise greatly in certain brain regions following 
epileptic seizures or ccnditions of neuronal ischaemia/anoxia (Brain 
Research 1990, 516, 248-256). 
It has been established for some years now that centrally acting adenosine 
receptor agonists or compounds which increase extracellular adenosine 
levels can exhibit what is termed neuromodulator activity. Such substances 
influence the release of neurotransmitters in regions of the central 
nervous system (Annual Review of Neuroscience, 1985, 8, 103-124; Trends in 
Neurosciences, 1984, 164-168), with particular inhibitory effects on the 
release of the excitatory amino acid glutamic acid (glutamate) (Nature, 
1985, 316, 148-150, Journal of Neurochemistry, 1992, 58, 1683-1689). 
There are several CNS ailments for which this adenosine receptor mediated 
neuromodulator activity could be of clear therapeutic benefit. Examples of 
these would include the treatment of convulsive disorders (European 
Journal of Pharmacology, 1991, 195, 261-265; Journal of Pharmacology and 
Experimental Therapeutics, 1982, 220, 70-76), prevention of 
neurodegeneration under conditions of brain anoxia/ischaemia (Neuroscience 
Letters, 1987, 83, 287-293; Neuroscience, 1989, 30, 451-462; Pharmacology 
of Cerebral Ischaemia 1990 (Kriegelstein, J. and Oberpichler, H., Eds., 
Wissenschaftliche Verlagsgesellschaft mbH: Stuttgart, 1990, pp 439-448) or 
the use of a purinergic agent in the treatment of pain (European Journal 
of Pharmacology, 1989, 162, 365-369; Neuroscience Letters, 1991, 121, 
267-270). In addition, the antiischaemic effect of the compounds described 
within this invention may be useful in protecting against cardiac 
ischaemia. 
Adenosine receptors represent a subclass (P1) of the group of purine 
nucleotide and nucleoside receptors known as purinoreceptors. This 
subclass has been further classified into two distinct receptor types 
which have become known as A1 and A2. Extensive research has been carried 
out in a quest to identify selective ligands at these sites [see, for 
example, Comprehensive Medicinal Chemistry Volume 3, (Hansch, C., Sammes, 
P. G. and Taylor, J. B., Eds., Pergamon Press PLC: 1990, pp 601-642)]. 
Selective ligands exist for A1 and A2 adenosine receptors and the 
structure-activity relationships of the various reference ligands have 
been reviewed (Biochemical Pharmacology, 1986, 35, 2467-2481) together 
with their therapeutic potential (Journal of Medicinal Chemistry, 1992, 
35, 407-422). Among the known adenosine receptor agonists most selective 
for the A1 receptor over the A2 receptor are the examples where the 
adenine nucleus is substituted with a cycloalkyl group on the amino 
function, for example N-cyclopentyladenosine and N-cyclohexyladenosine 
(Journal of Medicinal Chemistry, 1985, 28, 1383-1384) or 
2-chloro-N-cyclopentyladenosine (Naunyn-Schmiedeberg's Arch pharmacal. 
1988, 337, 687-689). 
Examples of adenosine derivatives in the chemical literature with the 
heteroatoms, oxygen or nitrogen bonded directly to the 6-amino substituent 
are summarised below. 
Examples with hydrogen at the purine 2-position include N-aminoadenosine, 
N-[(N-methyl-N-phenyl)amino]adenosine, N-hydroxyadenosine, 
N-methoxyadenosine and N-benzyloxyadenosine (Journal of Medicinal 
Chemistry, 1985, 28, 1636-1643); N-ethoxyadenosine (Chemical and 
Pharmaceutical Bulletin, 1973, 21, 1676-1682; ibid., 1973, 21, 1835-1838); 
N-(methylamino)adenosine and N-[(N-hydroxy-N-methyl)amino]adenosine 
(Journal of Medicinal Chemistry, 1968, 11, 521-523). 
Examples of adenosine derivatives with oxygen or nitrogen atoms bonded to 
the 6-amino substituent, containing an additional purine 2-substituent are 
2-amino-N-hydroxyadenosine (Journal of Medicinal Chemistry, 1972, 15, 
387-390); 2-amino-N-aminoadenosine (Chemical and Pharmaceutical Bulletin, 
1969, 17, 2373-2376); 2-amino-N-methoxyadenosine (Chemical and 
Pharmaceutical Bulletin, 1975, 23, 464-466); 2-chloro-N-hydroxyadenosine 
(Journal of Medicinal Chemistry, 1991, 34, 2226-2230), 
2-fluoro-N-aminoadenosine (Journal of Medicinal Chemistry, 1970, 13, 
427-430) and 2-fluoro-N-hydroxyadenosine (Journal of Medicinal Chemistry, 
1971, 14, 816-819). 
In the above scientific articles, no mention is made of any pharmacological 
effects of the compounds concerned on the central nervous system. 
In U.S. Pat. No. 3,819,613, substituted adenosine analogues with hydrazone 
derivatives on the 6-amino function are disclosed as hypotensive agents. 
In GB 1,351,501, adenosine and 2-aminoadenosine derivatives having a 
--NH--R.sub.2 group joined to the 6-amino function are disclosed as 
coronary dilators and platelet aggregation inhibitors. In EP A 152,944, a 
series of 2-, 6- and 8-substituted adenosine derivatives are described 
having activity as anti-allergy agents. In EP A 253,962, adenosine and 
2-haloadenosine analogues having an alkyl, cycloalkyl or an aralkyl group 
attached to the 6-amino function are described with activity as 
anti-dementia agents. In EP 402,752A, derivatives of adenosine 
unsubstituted in the 2-position are described which have a substituted 
heteroaromatic 1-pyrrolyl moiety attached to the 6-amino group. In WO 
91/04032, methods of preventing neural tissue damage in neurodegenerative 
diseases by increasing extracellular concentrations of adenosine are 
described. Examples are given of prodrug esters of AICA riboside 
(5-amino-1-.beta.-D-ribofuranosyl)imidazo-4-carboxamide) which are claimed 
to be centrally acting neuroprotective agents. In WO 92/02214, analogs of 
AICA riboside are revealed for the treatment of myocardial and cerebral 
ischaemias. In WO 90/05526, 2-(alkylalkynyl)adenosine derivatives are 
described for treatment of ischaemic disease of the heart and brain. 
The present invention relates to new adenosine analogues having potent 
binding in vitro to the adenosine A1 receptor, and at the same time 
showing selectivity for A 1 receptor binding in vitro over that to the A2 
receptor subtype. In addition, many of the novel compounds contained in 
this invention have a relatively high lipophilicity, especially when 
compared to adenosine analogues and adenosine itself which are not 
substituted on the 6-amino group or the purine 2-position. This latter 
property may make these compounds suitable for passage across the blood 
brain barrier. 
The possibility that some of the compounds may be substrates for 
nucleoside-specific active transport systems into the CNS across the blood 
barrier is, however, not excluded. These useful properties support the 
notion that some of the examples may have potential as candidate drugs for 
treatment of the CNS ailments mentioned within this invention in humans. 
The compounds of the invention are purine derivatives of formula I, or a 
pharmaceutically acceptable salt thereof: 
##STR2## 
wherein 
X represents hydrogen, halogen, amino, perhalomethyl, acetamido, cyano, 
C.sub.1-6 -alkyl, C.sub.1-6 -alkoxy, C.sub.1-6 -alkylthio or C.sub.1-6 
-alkylamino; 
R.sup.1 is --NR.sup.2 R.sup.3, --YR.sup.4, 
wherein Y is oxygen or sulphur; 
R.sup.2 is C.sub.1-6 alkyl; 
R.sup.3 is phenyl or C.sub.1-6 -alkyl, which may be substituted with phenyl 
or phenoxy; 
R.sup.4 is naphthyl; 
partly saturated naphthyl; 
C.sub.1-6 -alkyl, which may be substituted with phenoxy or phenyl, which 
may be substituted with nitro, halogen or amino; 
or C.sub.3-8 -cycloalkyl, which may be substituted with phenyl or phenoxy; 
In certain examples, the group R.sup.1 can contain one or more asymmetric 
carbon atoms in addition to those asymmetric centres already present in 
the molecule. In examples where this is the case, this invention includes 
all resulting diastereoisomers and mixtures thereof. 
Various salts of compounds of formula (I) can be prepared which can be 
considered physiologically acceptable. These include addition salts 
derived from inorganic or organic acids, for example, acetates, fumarates, 
glutarates, glutaconates, lactates, maleates, methanesulphonates, 
phosphates, salicylates, succinates, sulphates, sulphamates, tartrates and 
paratoluenesulphonates. In some cases, solvates of either the free 
nucleosides or the acid addition salts can be isolated and these solvates 
may, for example, be hydrates or alcoholates. 
Compounds of formula (I), which act as adenosine receptor agonists, are 
found to be useful in the treatment of central nervous system conditions 
such as anxiety, neuronal ischaemia/anoxia, convulsive disorders 
(epilepsy) and neurodegeneration (including Parkinson's disease). 
Further, the compounds of formula (I) are found to be useful as analgesic 
agents, in lowering plasma free fatty acid (FFA) levels or as 
cardiovascular agents and also have application to myocardial ischaemia. 
The invention also relates to methods of preparing the above mentioned 
compounds. These methods comprise: 
Method A 
A compound of formula (i) may be prepared by reacting a substance of 
formula (II), wherein L represents a leaving group such as a halogen atom 
(e.g. a chlorine or bromine atom) or a trimethylsilyloxy group, P.sup.1, 
P.sup.2 and P.sup.3 are the same or different and represent hydrogen or a 
protecting group such as benzoyl-, p-toluoyl-, lower alkanoyl- (e.g. 
acetyl-), a substituted silyl group (e.g. a trimethylsilyl or 
t-butyldimethylsilyl group) or in the case of P.sup.3, a triarylmethyl 
group, or in the case of P.sup.1 and P.sup.2, a 
2',3'-O-(1-methyl)ethylidene derivative, with an O-alkylated hydroxylamine 
or a functionalised hydrazine derivative of general formula (III) 
##STR3## 
giving the compound of formula (IV) as the reaction product. In cases 
where P.sup.1, P.sup.2 and P.sup.3 are not hydrogen an additional step 
will be required to remove protecting groups from (IV); in cases where the 
groups P.sup.1, P.sup.2 and P.sup.3 are for example acetyl or benzoyl, 
suitable conditions for deprotection include methanolic ammonia, an alkali 
metal carbonate in methanol, an alkali metal alkoxide in the corresponding 
alcohol. Where the protecting groups are for example alkylsilicon or 
arylsilicon derivatives, suitable methods for deprotection include for 
example treatment with tetraalkylammonium fluorides or aqueous hydrolysis 
in the presence of acid or base. Where the P.sup.1 and P.sup.2 groups 
comprise a 2',3'-O-(1-methyl)ethylidene group, or P.sup.3 comprises a 
triarylmethyl group, suitable conditions for deprotection include, for 
example, hydrolysis with aqueous mineral acid. 
Method B 
A compound of formula (I) (wherein X represents --NH.sub.2, --NH--C.sub.1-6 
-alkyl, or --O--C.sub.1-6 -alkyl, or S--C.sub.1-6 -alkyl) may be prepared 
by reacting a substance of general formula (V) 
##STR4## 
(where L is a leaving group as defined in method (A)) with a nucleophile, 
for example C.sub.1-3 -alkylamino (optionally in the presence of a 
suitable base) or with the anion (C.sub.1-6 -alkoxide or C.sub.1-6 
-thioalkoxide) to afford the product (IV). In cases where P.sup.1, P.sup.2 
and P.sup.3 are hydrogen, compound (I) can be obtained directly. However, 
in cases where P.sub.2 and P.sub.3 are not hydrogen an additional step 
will be involved to remove protecting groups from (IV); examples of 
conditions for removal of protecting groups are given in process (A). In 
some reactions involving (V) with the anion C.sub.1-6 -alkoxide or 
C.sub.1-6 -thioalkoxide, where P.sup.1, P.sup.2 and P.sup.3 are for 
example acetyl- or benzoyl-, partial or full deprotection may take place. 
In cases where only partial deprotection has taken place, deprotection can 
be completed under conditions described in method (A). 
Method C 
A compound of formula (I) may be prepared by reacting a substance of 
general formula (VI) (where B represents --NH--R.sup.1 or L as defined 
previously) with a diazotising agent (such as, for example, 3-methylbutyl 
nitrite) to form an intermediate species which can be reacted further with 
a variety of substrates as exemplified below in order to introduce the 
group -X into the product (VII). 
##STR5## 
In the case where B represents a leaving group L, a further displacement 
reaction with for example (III) will be required in order to obtain the 
product (IV). In cases where the groups P.sup.1, P.sup.2 and P.sup.3 are 
not hydrogen, or not all hydrogen, another step will be required to remove 
protecting groups from (IV); conditions for removing protecting groups are 
described in method A. Alternatively, where B represents HN--R.sup.1, 
direct deprotection of intermediate (VII) can be carried out to provide 
(I). 
Methods for assessing adenosine receptor binding in vitro have been 
reviewed [Adenosine Receptors, Cooper, D.M.F. and Londos, C., Eds., Alan 
R. Liss, Inc.: New York, 1988, 43-62]. 
Evaluation of these compounds in established animal models has indicated 
that the compounds according to the invention possess desirable central 
nervous system properties. For example, they act as anticonvulsant agents, 
are effective in animal models of pain, and show cerebroprotective effects 
in laboratory test animals subjected to simulated cerebral ischaemia. In 
addition, the compounds may have efficacy as neuroprotective agents in 
cases of cerebral oedema and traumatic head injury. 
Evaluation of in vitro binding to adenosine A1 and A2 receptors 
The affinity of the novel compounds described in this invention for the 
adenosine A1 receptor was determined essentially as described in the 
literature using [.sup.3 H]-R-PIA as a radioligand (Naunyn-Schmiedeberg's 
Archives of Pharmacology, 1980, 313, 179-187). Affinity for the A2 
receptor was measured using the radioligand [.sup.3 H]-CGS 21680 (European 
Journal of Pharmacology, 1989, 168, 243-246), and the values for 
representative compounds is given in the table below. 
Test results obtained by testing some compounds employed in the present 
invention are included in table I. 
TABLE I 
______________________________________ 
A1 receptor A2 receptor 
Adenosine agonist 
binding binding Ratio 
tested (Ki.sub.50, nM) 
(Ki.sub.50, nM) 
A2/A1 
______________________________________ 
Example 3 18 1659 92 
Example 7 6.7 2876 429 
Example 8 21 1154 55 
______________________________________ 
The compounds of the invention, together with a conventional adjuvant, 
carrier or diluent, and if desired in the form of a pharmaceutically 
acceptable acid addition salt thereof, may be placed into the form of 
pharmaceutical compositions and unit dosages thereof, and in such form may 
be employed as solids, such as tablets of filled capsules, or liquids, 
such as solutions, suspensions, emulsions, elixirs, or capsules filled 
with the same, all for oral use, in the form of suppositories for rectal 
administration; or in the form of sterile injectable solutions for 
parenteral use (including subcutaneous administration and infusion). Such 
pharmaceutical compositions and unit dosage forms thereof may comprise 
conventional ingredients in conventional proportions, with or without 
additional active compounds or principles, and such unit dosage forms may 
contain any suitable effective amount of the adenosine receptor agonist 
commensurate with the intended daily dosage range to be employed. Tablets 
containing ten (10) milligrams of active ingredient or, more broadly, ten 
(10) to hundred (100) milligrams, per tablet, are accordingly suitable 
representative unit dosage forms. 
The compounds of this invention can thus be used for the formulation of 
pharmaceutical preparation, e.g. for oral and parenteral administration to 
mammals including humans, in accordance with conventional methods of 
galenic pharmacy. 
Conventional excipients are such pharmaceutically acceptable organic or 
inorganic carrier substances suitable for parenteral or enteral 
application which do not deleteriously react with the active compounds. 
Examples of such carriers are water, salt solutions, alcohols, polyethylene 
glycols, polyhyroxyethoxylated castor oil, gelatine, lactose amylose, 
magnesium stearate, talc, silicic acid, fatty acid monoglycerides and 
diglycerides, pentaerythritol fatty acid esters, hydroxymethylcellulose 
and polyvinylpyrrolidone. 
The pharmaceutical preparations can be sterilized and mixed, if desired, 
with auxiliary agents, emulsifiers, salt for influencing osmotic pressure, 
buffers and/or colouring substances and the like, which do not 
deleteriously react with the active compounds. 
For parenteral application, particularly suitable are injectable solutions 
or suspensions, preferably aqueous solutions with the active compound 
dissolved in polyhydroxylated castor oil. 
Ampoules are convenient unit dosage forms. 
Tablets, dragees, or capsules having talc and/or carbohydrate carrier or 
binder or the like, the carrier preferably being lactose and/or corn 
starch and/or potato starch, are particularly suitable for oral 
application. A syrup, elixir or the like can be used in cases where a 
sweetened vehicle can be employed. 
Generally, the compounds of this invention are dispensed in unit form 
comprising 0.05-100 mg in a pharmaceutically acceptable carrier per unit 
dosage. 
The dosage of the compounds according to this invention is 0.1-300 mg/day, 
preferably 10-100 mg/day, when administered to patients, e.g. humans, as a 
drug. 
A typical tablet which may be prepared by conventional tabletting 
techniques contains: 
______________________________________ 
Active compound 5.0 mg 
Lactosum 67.0 mg Ph.Eur. 
Avicel .TM. 31.4 mg 
Amberlite .TM.IRP 88 
1.0 mg 
Magnesii stearas 0.25 mg Ph.Eur. 
______________________________________ 
Owing to activity against pain or convulsive disorders and prevention of 
neurodegeneration under conditions of anoxia/ischaemia the compounds of 
the invention are extremely useful in the treatment of related symptoms in 
mammals, when administered in an amount effective for agonist activity of 
compounds of the invention. The compounds of the invention may accordingly 
be administered to a subject, e.g., a living animal body, including a 
human, in need of adenosine receptor agonist, and if desired in the form 
of a pharmaceutically acceptable acid addition salt thereof (such as the 
hydrobromide, hydrochloride, or sulfate, in any event prepared in the 
usual or conventional manner, e.g., evaporation to dryness of the free 
base in solution together with the acid), ordinarily concurrently, 
simultaneously, or together with a pharmaceutically acceptable carrier or 
diluent, especially and preferably in the form of a pharmaceutical 
composition thereof, whether by oral, rectal, or parenteral (including 
subcutaneous) route, in an effective amount of adenosine receptor agonist, 
and in any event an amount which is effective for the treatment of anoxia, 
traumatic injury, ischemia, migraine or other pain symptoms, epilepsy, or 
neurodegenerative diseases owing to their adenosine receptor agonist 
activity. Suitable dosage ranges are 1-200 milligrams daily, 10-100 
milligrams daily, and especially 30-70 milligrams daily, depending as 
usual upon the exact mode of administration, form in which administered, 
the indication toward which the administration is directed, the subject 
involved and the body weight of the subject involved, and the preference 
and experience of the physician or veterinarian in charge.