# Patent

## Title
C2,8-disubstituted adenosine derivatives and their different uses

## Abstract

Novel C2,8-disubstituted adenosine derivatives disclosed herein have been found to be potent adenosine receptor agonists, in particular for the A2A receptor. The said compounds have biological activity against conditions such as hypertension, ischemic heart disease, ischemic brain disease, psychosis and wound healing. Further, the invention also discloses a process for the preparation of such compounds and pharmaceutical compositions comprising them.

## Background
CROSS-REFERENCE TO RELATED APPLCIATIONS
This application is a 371 national stage application of PCT International application PCT/IL02/00161, filed Mar. 3, 2002.
FIELD OF THE INVENTION
The present invention relates to novel C2,8-disubstituted adenosine derivatives, their process of preparation and different uses.
BACKGROUND OF THE INVENTION
Adenosine mediates a wide variety of effects as a result of its activation of specific membrane-bound receptors called P1-purinoceptors. The three subclasses of P1-purinoceptors are A1, A2 and A3, with A2 further subdivided into A2A and A2B. All adenosine receptors are coupled to the enzyme adenylate cyclase; activation of the A1 and A3 adenosine receptors inhibit the adenylate cyclase, whereas activated A2A and A2B receptors stimulate it. The adenosine A2A receptor can be found throughout the whole body, and A2A receptor agonists might be used to inhibit platelet aggregation in thrombosis, in the diagnosis of diseases in coronary arteries, in ischemia and reperfusion.1 Furthermore, activation of adenosine A2A receptors has been shown to alter the binding characteristics of other receptors. Stimulation of adenosine A2A receptors in rat striatal membranes reduces the affinity of agonist binding to dopamine D2 receptors.2,3 This raises the possibility of using adenosine A2A receptor agonists as a novel therapeutic approach in the treatment of psychosis. However, these desired actions of agonists for the adenosine A2A receptor may be accompanied with serious side effects such as cardiovascular actions, since the receptor is ubiquitously distributed. The design of partial agonists for the adenosine receptors has already been shown to be a useful tool to achieve selectivity of action in vivo by exploitation of the differences in receptor-effector coupling in various tissues.4-7 Hence, partial agonists for the adenosine A2A receptor might then be developed as antipsychotic agents also devoid of undesired cardiovascular actions.
Selectivity for the adenosine A2A receptor can be obtained by the introduction of a C2-substituent, such as a 1-hexynyl or a 1-hexenyl group that have been shown to induce high affinity for the adenosine A2A receptor compared to A1.8-10 Partial agonism for adenosine receptors in general has been achieved by the introduction of alkylthio-substituents at the 5′-position.5,11 However, partial agonism for the adenosine A1 receptor has also successfully been accomplished by introducing alkylamino substituents at the C8-position of adenosine.12 8-Alkylamino substituted CPA derivatives have proven to be adenosine A1 receptor partial agonists in vivo when assessed for cardiovascular activity, although with modest affinities.6,13,14 
LIST OF PRIOR ART
The following is a list of prior art which is considered to be pertinent for describing the state of the art in the field of the invention, all of which are also included in the list of publication provided hereinafter. Acknowledgement of these references herein will be made by indicating the number from the said list list of publications which is also indicated in brackets hereinbelow.

    Cristalli, G., Eleuteri, A., Vittori, S., Volpini, R, Lohse, M. J., Klotz, K.-N., J. Med. Chem., 1992, 35, 2363–2368 (reference no. 8).
    Matsuda, A., Shinozaki, M., Yamaguchi, T., Homma, H., Nomoto, R., Miyasaka, T., Watanabe, Y., Abiru, T., J. Med. Chem., 1992, 35, 241–252 (reference no. 9).
    Vittori, S., Camaioni, E., Di Francesco, E., Volpini, R., Monopoli, A., Dionisotti, S., Ongini, E., Cristalli, G., J. Med. Chem., 1996, 39, 4211–4217 (reference no. 10).
    Matsuda, A., Shinozaki, M., Miyasaka, T., Machida, H., Abiru, T., Chem. Pharm. Bull., 1985, 33, 1766–1769 (reference no. 15).
    Francis, J. E., Webb, R. L., Ghai, G. R., Hutchison, A. J., Moskal, M. A., deJesus, R., Yokoyama, R., Rovinski, S. L., Contardo, N., Dotson, R., Barclay, B., Stone, G. A., Jarvis, M. F., J. Med. Chem., 1991, 34, 2570–2579 (reference no. 20).
    Camaioni; E., DiFrancesco, E., Viffori, S., Volpini, R., Cristalli, G., Bioorg. Med. Chem., 1997, 5, 2267–2275 (reference no. 22).
    Homma, H., Watanabe, Y., Abiru, T., Murayama, T., Nomura, Y., Matsuda, A. J. Med. Chem., 1992, 35, 2881–2890 (reference no. 23).
    Vittori, S., Camaioni, E., Constanzi, S., Volpini, R., Klotz, K.-N., Cristalli, G., Nucleosides and Nucleotides, 1999, 18, 739–740 (reference no. 24).
    Volpini, R., Camaioni, E., Costanzi, S., Vittori, S., Klotz, K.-N., Cristalli, G., Nucleosides and Nucleotides, 1999, 18, 2511–2520 (reference no. 25).
    Klotz, K.-N., Camaioni, E., Volpini, R, Kachler, S., Vittori, S., Cristalli, G., Naunyn-Schmiedeberg's Arch. Pharmacol., 1999, 360, 103–108 (reference no. 26).


SUMMARY OF THE INVENTION
According to the first aspect, the present invention provides C2,8-di-substituted adenosine derivatives having the following general formula (I) (hereinafter referred to at times as the “the compound of the present invention”):




wherein

    
    
        R2 and R3 which may be the same or different, represent a lower alkyl, lower alkenyl, lower alkynyl, lower (ar)alkyl, lower alkoxy, lower alkylidenehydrazino group, cyano, acetoamino, halogen, a group of the general formula —NR4R5 wherein R4 and R5 represent, independently, a hydrogen atom, lower alkyl or (ar)alkyl group or a group of the general formula —SR6, wherein R6 represents a hydrogen, lower alkyl, lower alkanoyl or (ar)alkyl groups,
    
    


or a salt of the above compound, with the provisos that:

    
    
        (i) when R2 represents —NH2, R3 does not represent a halogen, alkyl or alkoxy;
        (ii) when R2 represents an alkythio, R3 does not represent an alkyl;
        (iii) when R2 represents a halogen or alkyl, R3 does not represent, respectively, a halogen or alkyl.
    
    


The term “lower alkyl” as used herein refers to any saturated carbohydrate, either linear or branched chain comprising from one to ten carbon atoms in the backbone of the carbohydrate.
Accordingly, the terms “lower alkenyl” and “lower alkynyl” refer to a linear or branched carbohydrate comprising from two to ten carbon atoms in the backbone, wherein at least two of the carbon atoms are connected via a double or triple bond, respectively.
Thus, it is to be understood that the term “lower” when used for defining a carbohydrate, refers to any carbohydrate chain having no more than 10 carbon atoms.
The compound of the invention also includes salts of the compound of formula (I) and in particular, physiologically acceptable salts. The term “physiologically acceptable salt” refers to any non-toxic alkali metal, alkaline earth metal, and ammonium salts commonly used in the pharmaceutical industry, including the sodium, potassium, lithium, calcium, magnesium, barium ammonium and protamine zinc salts, which are prepared by methods known in the art. The term also includes non-toxic acid addition salts, which are generally prepared by reacting the compounds of this invention with a suitable organic or inorganic acid. The acid addition salts are those which retain the biological effectiveness and properties of the free bases and which are not biologically or otherwise undesirable. Examples include acids are those derived from mineral acids, and include, inter aila, hydrochloric, hydrobromic, sulfuric, nitric, phosphoric, metaphosphoric and the like. Organic acids include, inter alia, tartaric, acetic, propionic, citric, malic, malonic, lactic, fumaric, benzoic, cinnamic, mandelic, glycolic, gluconic, pyruvic, succinic salicylic and arylsulphonic, e.g. p-toluenesulphonic, acids.
The present invention also provides a process for the preparation of the compound of the present invention (i.e. the compound of formula (I) as defined above) or a salt thereof, the process comprising in general treating a compound of the formula (II):




wherein

    
    
        R1 represents a hydrogen atom or methylcarbonyl group; with one or more equivalents of at least one reagent selected from:
        
            PdCl2, triaryl phosphate, CuI and an (ar)alkyn;
            tetrakis(triphenylphosphine)-palladium(0), K2CO3 and (E)-1-borocatechol-1-(ar)alkene, or
            a nucleophile containing an R3 group as defined below;
        
        
    
    


to obtain said compound of general formula (I).
As will be described in detail hereinafter, the process of the present invention may provide a compound wherein R2 and are R3 are the same or different, depending on the amount and number of reagents employed. For example, in order to obtain different substituents at the 2- and 8-positions of the compound of general formula (I), the process is preferably carried out in two steps, each step comprising treatment with 1 equivalent of one of said reagents carrying different substituents.
The invention also provides pharmaceutical compositions comprising as active ingredient an effective amount of one or more of the compounds of the invention as defined hereinbefore.
Evidently, any other use of the novel compounds and compositions disclosed herein are within the scope of the present invention.


DETAILED DESCRIPTION OF THE INVENTION
The present invention is based on the surprising finding that C8-substituted and C2,8-disubstituted adenosine derivatives display higher adenosine A2A receptor affinity and/or A2A selectivity compared to the A1 and A3 receptors.
According to a first aspect, the present invention provides C2,8-disubstituted adenosine derivatives having the following general formula (I):




wherein

    
    
        R2 and R3, which may be the same or different, represent a lower alkyl, lower alkenyl, lower alkynyl, lower aralkyl, lower alkoxy, lower alkylidenehydrazino, cyano, acetoamino, halogen, a group of the general formula —NR4R5 wherein R4 and R5 represent, independently, a hydrogen atom, lower alkyl or (ar)alkyl or a group of the general formula —SR6, wherein R6 represents a hydrogen, lower alkyl, lower alkanoyl or (ar)alkyl;
    
    


or a salt of the above compound, with the provisos that:

    
    
        (i) when R2 represents —NH2, R3 does not represent a halogen, allyl or alkoxy;
        (ii) when R2 represents an alkylthio, R3 does not represent an alkyl;
        (iii) when R2 represents a halogen or alkyl, R3 does not represent, respectively, a halogen or alkyl.
    
    


According to one embodiment, the substituent R2 represents a halogen atom, a C2–C10 alkenyl or C2–C10 alkynyl or (ar)alkylamine. More preferably, the alkenyl or alkynyl groups are, respectively C6-alkenyl or C6-alkynyl, the halogen atom is iodine and the (ar)alkylamine group is benzylamine.
According to one more specific embodiment, R2 is a halogen atom, preferably an iodine atom.
According to another specific embodiment, R2 is 1-hexenyl or 1-hexynyl, the former preferably representing the (E) 1-hexenyl isomer.
The R3 substituent preferably represents an alkylamine, aralkylamine, alkynyl or alkynyl group. The alkylamine is preferably selected from methylamine, ethylamine, propylamine, butylamine, the alkynyl is prefereably 1-hexynyl, and the (ar)alkylamine is preferebly benzylamine, however, the latter may also include anilines and substituted arylamines.
As will be detailed in the following specific examples, it has been found that the compounds of the present invention are biologically active.
The term “biologically active” indicates that the compound of the present invention has some sort of a biological activity, for example, a measurable effect on a target receptor. As will be detailed hereinafter, the compound of the present invention may induce adenosine receptor activity, preferably acting as adenosine receptor agonists and more preferably as adenosine A2A receptor agonists.
The term “agonist” refers to a biologically active ligand, which binds to its complementary biologically (active) receptor and activates the latter either to cause a biological response in the receptor or to enhance preexisting biological activity of the receptor. The agonist in fact mimics the effect of the natural ligand, in the present case, adenosine, or at times, even increases or prolongs the duration of the biological effect obtained as compared to the effect induced by the natural ligand.
The compounds of the present invention were specifically found to activate adenosine receptors, with a higher selectivity and affinity for the adenosine A2A receptor. Thus, the compounds of the present invention may be recognized as adenosine A2A receptor agonists. More preferably and as will be shown in the following Specific Examples, the compounds of the present invention are partial agonists of the adenosine A2A receptor.
receptor if it produces (or induces (e.g. when increased in concentration) the maximal possible response achievable by activation of this receptor.
A compound according to the invention is considered a “partial agonist” if it is unable to produce maximal activation of the receptor to which it binds no matter how high is its concentration.
Preferred compounds according to the present invention include:

    2-iodo-8-methylaminoadenosine (compound 7 hereinafter);
    2-iodo-8-ethylaminoadenosine (compound 8 hereinafter);
    2-iodo-8-propylaminoadenosine (compound 9 hereinafter);
    2-iodo-8-butylaminoadenosine (compound 10 hereinafter);
    2-iodo-8-benzylaminoadenosine (compound 11 hereinafter);
    2-(1-hexynyl)-8-methylaminoadenosine (compound 12 hereinafter);
    2-(1-hexynyl)-8-ethylaminoadenosine (compound 13 hereinafter);
    2-(1-hexynyl)-8-propylaminoadenosine (compound 14 hereinafter);
    2-(1-hexynyl)-8-butylaminodenosine (compound 15 hereinafter);
    2-(1-hexynyl)-8-benzylaminoadenosine (compound 16 hereinafter);
    2-((E)-1-hexenyl)-8-methylaminoadenosine (compound 17 hereinafter);
    2-((E)-1-hexenyl)-8-ethylaminoadenosine (compound 18 hereinafter);
    2-((E)-1-hexenyl)-8-propylaminoadenosine (compound 19 hereinafter);
    2-((E)-1-hexenyl)-8-butylaminoadenosine (compound 20 hereinafter);
    2-((E)-1-hexenyl)-8-benzylaminoadenosine (compound 21 hereinafter);
    2,8-di-(1-hexynyl)adenosine (compound 22 hereinafter);
    2,8-di-benzylaminoadenosine (compound 23 hereinafter);


By a second of its aspects, the present invention provides a process for the preparation of a compound of the general formula (I):




in which

    
    
        R2 and R3 which may be the same or different, represent a lower alkyl, lower alkenyl, lower alkynyl, lower (ar)alkyl, lower alkoxy, lower alkylidenehydrazino, cyano, acetoamino, halogen, a group of the general formula —NR4R5 wherein R4 and R5 represent, independently, a hydrogen atom, lower allyl or aralkyl group or a group of the general formula —SR6, wherein R6 represents a hydrogen, lower alkyl, lower alkanoyl or (ar)alkyl groups, or a salt of said compound, with the provisos that:
        (i) when R2 represents —NH2, R3 does not represent a halogen, alkyl or alkoxy;
        (ii) when R2 represents an alkylthio, R3 does not represent an alkyl;
        (iii) when R2 represents a halogen or alkyl, R3 does not represent, respectively, a halogen or alkyl;
    
    


the process comprises treating a compound of the general formula (II):




wherein

    
    
        R1 represents a hydrogen atom or methylcarbonyl group; with one or more equivalents of at least one reagent selected from:
        
            PdCl2, triaryl phosphate, CuI and an (ar)alkyn; and/or
            tetrakis(triphenylphosphine)palladium(0), K2CO3 and (E)-1-borocatechol-1-(ar)alkene, and/or
            a nucleophile containing an R3 group as defined above.
        
        
    
    


The process of the invention may be carried out in a single step reaction, according to which two or more equivalents of the reagent selected are applied on the starting compound, or in two steps.
When performing the reaction in a single step, the resulting compound may contain the same or different substituents in R2 and R3 depending on the amount of reagent employed. For example, when using only one equivalent of the reagent, a compound of the following general formula (III) is obtained in which only C8 is substituted, while when using two or more equivalents of the reagent a compound in which C2 and C8 are substituted with the same group is obtained.
When carrying out the process in two steps, it is possible to obtain a product in which R2 and R3 are different. To this end, the two sequential reactions steps employ each about one equivalent of different reagents selected from:

    
    
        PdCl2, triaryl phosphate, CuI and an (ar)alkyn; or
        tetrakis(triphenylphosphine)-palladium(0), K2CO3 and (E)-1-borocatechol-1-(ar)alkene, or
        a nucleophile containing an R3 group as defined;
    
    


As an intermediate product, i.e. after applying one equivalent of the reagent, a compound of the following general formula (III) is obtained:




    
    
        in which R3 is as defined, which is then further reacted with one equivalent of a reagent selected from:
        
            PdCl2, triaryl phosphate, CuI and an (ar)allyn; or
            tetrakis(triphenylphosphine)-palladium(0), K2CO3 and (E)-1-borocatechol-1-(ar)alkene, or
            a nucleophile containing an R3 group, in which R3 is as defined;

the reagent in the second reaction step being different from that applied in the first reaction step.

        
        
    
    


Using two (or more) equivalents of the reagents in a single step reaction results in the same substitution in the 2- and 8-position, as opposed to a two step process, by which it is possible to obtain a compound with two different substituents on these positions, depending on the substituents and reagents used in each step.
The starting compound of formula (II) employed by the process of the present invention may be obtained, for example, by reacting with bromine, in the presence of a base, a compound of the following formula (V):




in which R1 are the same or different and represent a hydrogen atom or a methylcarbonyl group. However, it should be clear that any other method of obtaining the starting compound is applicable in the method of the present invention.
The compounds obtained by the process of the invention are preferably those in which R2 represents a halogen atom, a lower alkenyl or lower alkynyl and R3 is an alkylamine, (ar)alkyl amine or alkynyl.
According to one embodiment, R2 is iodine or a C6-alkenyl or C6-alkynyl group, the latter being respectively, in preference, 1-hexenyl or 1-hexynyl, the 1-hexenyl group being preferably the (E) 1-hexenyl isomer.
In case R3 is an alkylamine group, it is preferably a lower alkylamine selected from the group consisting of methylamine, ethylamine, propylamine, butylamine, while in case R3 is an (ar)alkylamine it is in preference benzylamine.
According to one embodiment, R2 is 1-hexynyl. Yet, according to another embodiment, R2 is (E)1-hexenyl. In both embodiments R3 is preferably selected from methylamine, ethylamine, propylamine and butylamine.
The general process for the preparation of the C2,8-disubstituted adenosine derivatives 3–5, 7–23 is depicted in the following non-limiting scheme I:




As will be shown herewinafter, the compound 2-(1-Hexynyl)adenosine (3) was prepared (in good yield (85%)) by reacting 2-iodoadenosine (1) with 1-hexyn.8,15 Compound 4 was prepared by reacting 1 with (E)-1-(borocatechol)-1-hexene.10 To obtain the C2,8-disubstituted derivatives, either unprotected 2-iodoadenosine (1) or 2′,3′,5′-tri-O-acetyl-2-iodoadenosine (2) was brominated at the C8-position.16 
Subsequently, different amines may be introduced at this position by stirring either 5 or 6 with the appropriate amine overnight. Under these reaction conditions the acetyl protecting groups, when present, were readily removed and compounds 7–11 were obtained (in good yields (70–91%)).
Finally, the 1-hexynyl and the (E)-1-hexenyl substituents were introduced at the 2-position as described above for compounds 3 and 4. Compounds 22 and 23 were obtained by treating 8-bromo-2-iodoadenosine (5) with an excess of either 1-hexyn or benzylamine.
According to another aspect, the present invention provides pharmaceutical compositions comprising as active ingredient a therapeutically effective amount, including a prophylactically effective amount, of one or more of the compounds of formula (I), or a salt of said compound, and a pharmaceutically acceptable additive. Preferred compounds employed in the compositions of the present invention are as defined above.
The term effective amount for the purposes described herein is that determined by such considerations as are known to those versed in the art. The amount must be sufficient to achieve a desired therapeutic effect, e.g. to treat a disease or a disorder. The effective amount is typically determined in appropriately designed clinical trials (e.g. dose range studies) and the person versed in the art will know how to properly conduct such trials in order to determine the effective amount. As generally known, an effective amount depends on a variety of factors including the affinity of the ligand to the receptor, its distribution profile within the body, a variety of pharmacological parameters such as half life in the body, on undesired side effects, if any, on factors such as age and gender, etc.
The pharmaceutical compositions of the invention are preferably for the treatment of diseases associated with the function of adenosine A2A receptor.
The term “treatment” as used herein refers to the administering of a therapeutic amount of the compound or composition of the present invention which is effective to ameliorate undesired symptoms associated with a disease, to prevent the manifestation of such symptoms before they occur, to slow down the progression of a disease, to slow down the deterioration of symptoms, to slow down the irreversible damage caused by the chronic stage of a disease, to lessen the severity or cure a disease, to improve survival rate or more rapid recovery, to prevent the disease from occurring, or a combination of two or more of the above. Treatment according to the invention preferably includes activation by one or more of the compounds of the present invention of an adenosine receptor (or elevation of an already active receptor) and preferably of the adenosine A2A receptor.
The term “pharmaceutically acceptable additives” used herein refers to any substance combined with said compound and include, without being limited thereto, diluents, excipients, carriers, solid or liquid fillers or encapsulating materials which are typically added to formulations to give them a form or consistency when it is given in a specific form, e.g. in pill form, as a simple syrup, aromatic powder, and other various elixirs. The additives may also be substances for providing the formulation with stability, sterility and isotonicity (e.g. antimicrobial preservatives, antioxidants, chelating agents and buffers), for preventing the action of microorganisms (e.g. antimicrobial and antifungal agents, such as parabens, chlorobutanol, phenol, sorbic acid and the like) or for providing the formulation with an edible flavor etc.
Preferably, the additives are inert, non-toxic materials, which do not react with the active ingredient of the invention. Yet, the additives may be designed to enhance the binding of the active agent to its receptor. Further, the term additive may also include adjuvants, being substances affecting the action of the active ingredient in a predictable way.
The additives can be any of those conventionally used and are limited only by chemico-physical considerations, such as solubility and lack of reactivity with the compound of the invention, and by the route of administration.
The active agent of the invention is preferably administered orally to the patient. Conventional methods such as administering the compound/s in tablets, suspensions, solutions, emulsions, capsules, powders, syrups and the like are usable.
For oral administration, the composition of the invention may contain additives for facilitating oral delivery of the compound/s of the invention. Formulations suitable for oral administration can consist of (a) liquid solutions, such as an effective amount of the compound dissolved in diluents, such as water, saline, or orange juice; (b) capsules, sachets, tablets, lozenges, and troches, each containing a predetermined amount of the active ingredient, as solids or granules; (c) powders; (d) suspensions in an appropriate liquid; and (e) suitable emulsions. Liquid formulations may include diluents, such as water and alcohols, for example, ethanol, benzyl alcohol, and the polyethylene alcohols, either with or without the addition of a pharmaceutically acceptable surfactant, suspending agent, or emulsifying agent. Capsule forms can be of the ordinary hard- or soft-shelled gelatin type containing, for example, surfactants, lubricants, and inert fillers, such as lactose, sucrose, calcium phosphate, and corn starch. Tablet forms can include one or more of lactose, sucrose, mannitol, corn starch, potato starch, alginic acid, microcrystalline cellulose, acacia, gelatin, guar gum, colloidal silicon dioxide, croscarmellose sodiumk talc, magnesium stearate, calcium stearate, zinc stearate, stearic acid, and other excipients, colorants, diluents, buffering agents, disintegrating agents, moistening agents, preservatives, flavoring agents, and pharmacologically compatible carriers. Lozenge forms can comprise the active agent in a flavor, usually sucrose and acacia or tragacanth, as well as pastilles comprising the active ingredient in an inert base, such as gelatin and glycerin, or sucrose and acacia, emulsions, gels, and the like. Such additives are known in the art.
Alternatively, the compound/s may be administered to the patient parenterally. In this case, the composition will generally be formulated in a unit dosage injectable form (solution, suspension, emulsion). Pharmaceutical formulation suitable for injection may include sterile aqueous solutions or dispersions and sterile powders for reconstitution into sterile injectable solutions or dispersions. The carrier can be a solvent or dispersing medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, lipid polyethylene glycol and the like), suitable mixtures thereof and vegetable oils such as cottonseed oil, sesame oil, olive oil, soybean oil, corn oil, sunflower oil, or peanut oil; a fatty acid esters such as ethyl oleate and isopropyl myristate and variety of other solvent systems as known per se. The carrier may be chosen based on the physical and chemical properties of the active agent.
In case the active ingredient has a poor water solubility, and an oily carrier is therefore used proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants.
Suitable fatty acids for use in parenteral formulations include oleic acid, stearic acid, and isostearic acid. Ethyl oleate and isopropyl myristate are examples of suitable fatty acid esters.
Suitable soaps for use in parenteral formulations, in case the active ingredient has a poor water solubility, include fatty alkali metal, ammonium, and triethanolamine salts, and suitable detergents include (a) cationic detergents such as, for example, dimethyl dialkyl ammonium halides, and alkyl pyridinium halides, (b) anionic detergents such as, for example, alkyl aryl, and olefin sulfonates, alkyl, olefin, ether, and monoglyceride sulfates, and sulfosuccinates, (c) nonionic detergents such as, for example, fatty amine oxides, fatty acid alkanolamides, and polyoxy-ethylenepolypropylene copolymers, (d) amphoteric detergents such as, for example, alkyl-β-aminopriopionates, and 2-alkyl-imidazoline quaternary ammonium salts, and (3) mixtures thereof.
Further, in order to minimize or eliminate irritation at the site of injection, the compositions may contain one or more nonionic surfactants having a hydrophile-lipophile balance (HLB) of from about 12 to about 17. Suitable surfactants include polyethylene sorbitan fatty acid esters, such as sorbitan monooleate and the high molecular weight adducts of ethylene oxide with a hydrophobic base, formed by the condensation of propylene oxide with propylene glycol.
The choice of an additive will be determined in part by the particular compound of the present invention, as well as by the particular method used to administer the composition.
Notwithstanding the above, the composition of the present invention may include one or more of the compounds of the present invention and may be comprise other biologically active substances, to provide a combined therapeutic effect.
As indicated hereinbefore, the compounds of the present invention were found to be capable of binding and activating or inducing the activity of adenosine receptors, particularly, of the adenosine A2A receptor. Accordingly, the composition of the present invention is preferably for the treatment of a disease or a disorder, which require for their treatment activation or induction of the activity of the adenosine A2A receptor present on a target cell. For example, the compound or composition of the present invention may be useful as therapeutic or prophylactic agents for circulatory diseases, such as hypertension and ischemic heart or brain disease. Also, the compounds or compositions of the present invention may be useful as neuroleptic agents, e.g. for the treatment of psychosis, or for wound healing.
The compounds and compositions of the present invention as set forth hereinabove and below are administered and dosed in accordance with good medical practice, taking into account the clinical conditions of the individual patient, the site and method of administration, scheduling of administration, individual's age, sex body weight and other factors known to medical practitioners.
The dose may be single daily dose or multiple doses over a period of several days. The treatment generally has a length proportional to the length of the disease process and drug effectiveness and the individual species being treated. Suitable doses and dosage regimens can be determined by conventional range-finding techniques known to those of ordinary skill in the art. Generally, treatment is initiated with smaller dosages, which are less than the optimum dose of the compound. Thereafter, the dosage is increased by small increments, until the optimum effect under the circumstances is reached. Exemplary dosages range from about 0.001 mg/kg body weight to about 10 mg/kg body weight of the subject being treated/day.
The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the is nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teaching. It is therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described hereinafter.
Throughout the description various publications are referred to by corresponding reference numbers. Full citations of the publications are listed hereinafter.
SPECIFIC EXAMPLES
Materials and Methods
Chemicals and Solvents All reagents were from standard commercial sources and of analytic grade. [3H]DPCPX (1,3-dipropyl-8-cyclopentylxanthine), [3H]CGS 21680 and [125 I]AB-MECA were purchased from NEN (Hoofddorp, The Netherlands).
Chromatography Thin-layer chromatography (TLC) was carried out using aluminum sheets (20×20 cm) with silica gel F254 from Merck. Spots were visualized under UV (254 nm). Preparative column chromatography was performed on silica gel (230–400 mesh ASTM).
Instruments and Analyses. Elemental analyses were performed for C, H, N (Department of analytical Chemistry, Leiden University, The Netherlands). 13C NMR spectra were measured at 50.1 MHz with a JEOL JNM-FX 200 spectrometer equipped with a PG 200 computer operating in the Fourier-transform mode. 1H NMR spectra were measured at 200 MHz, using the above mentioned spectrometer, or at 300 MHz, using a Bruker WM-300 spectrometer equipped with an ASPECT-2000 computer operating in the Fourier-transform mode. Chemical shifts for 1H and 13C NMR are given in ppm (δ) relative to tetramethylsilane (TMS) as internal standard.
All high resolution mass spectra were measured on a Finnigan MAT900 mass spectrometer equipped with a direct insertion probe for EI experiments (70 eV with resolution 1000) or on a Finnigan MAT TSQ-70 spectrometer equipped with an electrospray interface for ESI experiments. Spectra were collected by constant infusion of the analyte dissolved in 80/20 methanol/H2O. ESI is a soft ionization technique resulting in protonated, sodiated species in positive ionization mode and deprotonated species in the negative ionization mode.
Resolution of the compounds was achieved by reverse-phase HPLC (Gilson HPLC system, 712 system controller software. Gilson Netherlands, Meyvis en Co BV, Bergen op Zoom, the Netherlands) using as a mobile phase either: Eluent A: 20% CH3CN in H2O—100% CH3CN in 35 minutes or Eluent B: 30% MeOH in H2O—100% MeOH in 40 minutes; an Alltima C18 5μ (250 mm×4.6 mm) column (Alltech Nederland BV, Breda, the Netherlands) at a flow rate of 1 mL/min. The peaks were defined by measurement of UV absorbance (254 nm). Retention-times are given.
Melting points were determined in a Böchi capillary melting point apparatus.
Synthesis Procedures (In the following description the compounds are referred to at times by their number as defined in brackets after they first appear)
2-Iodoadenosine (compound 1) was prepared according to literature.17 Yield 80%; mp 185–187÷C; Rf0.21 (10% MeOH in CH2Cl2).
2′,3′,5′-tri-O-Acetyl-2-iodoadenosine (Compound 2). To a suspension of 2-iodoadenosine (1, 400 mg, 1.02 mmol) and dimethylaminopyridine (DMAP, 9.32 mg, 0.08 mmol) in a mixture of acetonitrile (13 ml) and Et3N (0.56 ml, 4.04 mmol) is added acid anhydride (0.34 ml, 3.60 mmol) at room temperature. After stirring for 1 hr the solution became clear. Methanol (5 ml) was added and stirring was continued for 5 min. The mixture was concentrated in vacuo. The residu was extracted with H2O (15 ml) and EtOAc (15 ml). The organic layer was dried (MgSO4), concentrated and purified further by column chromatography (eluens EtOAc).
Yield 434 mg (0.84 mmol, 82%), Rƒ0.70 (10% MeOH in CH2Cl2); 1H NMR)(DMSO-d6) δ 8.29 (s, 1H, H-8), 7.79 (bs, 2H, NH2), 6.12 (d, 1H, J=5.15 Hz, H-1′), 5.84 (t, 1H, J=5.84 Hz, H-2′), 5.59 (t, 1H, J=5.14 Hz, H-3′), 4.40–4.25 (m, 3H, H-4′,5′), 2.11 (s, 3H, COCH3), 2.04 (s, 3H, COCH3), 1.98 (s, 3H, COCH3) ppm.
2-iodo-8-bromoadenosine (Compound 5). 2-Iodoadenosine (1, 2.93 g, 7.45 mmol) was dissolved in NaOAc buffer (1.0 M, pH 4, 50 ml) at 50° C. The solution was cooled to room temperature and bromine (0.46 mL, 8.94 mmol) was added. After stirring overnight at room temperature, adding NaHSO3 destroyed the excess of bromine and the pH of the solution was adjusted to 7 with NaOH solution (5 M). The reaction mixture was kept at 4° C. for 5 hr and the precipitate was filtered. The white solid was washed with water and dried. Yield 2.43 mg (5.14 mmol, 69%), Rƒ 0.69 (10% MeOH in EtOAc); 1H NMR (DMSO-d6) δ 7.91 (s, 2H, NH2), 5.77 (d, 1H, J=6.52 Hz, H-1′), 5.47 (d, 1H, J=5.84 Hz, OH-2′), 5.24 (d, 1H, J=4.80 Hz, OH-5′), 5.03–4.84 (m, 2H, OH-3′, H-2′), 4.20–4.09 (m, 1H, H-3′), 3.97–3.88 (m, 1H, H-4′), 3.71–3.42 (m, 2H, H-5′) ppm.
2′,3′,5′-tri-O-Acetyl-2-iodo-8-bromoadenosine (Compound 6). To an aqueous Na2HPO4 solution (10% w/v, 10 mL) was added bromine (83.5 μL). The mixture was stirred vigorously for 15 min. until most of the bromine had dissolved. Then 2.6 mL of the decanted bromine solution was added to 2′,3′,5′-tri-O-acetyl-2-iodoadenosine (2, 132 mg, 0.25 mmol) in dioxane (2.6 ml) cooled in an ice/water bath. After 20 min. the ice bath was removed and the reaction mixture was stirred overnight at room temperature. The mixture was cooled again (ice bath) and NaHSO3 (1.8 M) was added dropwise until it became colorless. The water layer was extracted with CH2Cl2 (1×25 ml) and EtOAc (2×20 ml). The combined organic layers were dried (MgSO4), filtered and concentrated in vacuo. The residue was purified by column chromatography (eluents EtOAc). Yield 94.2 mg (0.16 mmol, 63%), Rƒ 0.61 (5% MeOH in CH2Cl2); 1H NMR (DMSO-d6) δ 7.95 (bs, 2H, NH2), 6.01–5.99 (m, 2H, H-1′,2′), 5.75–5.73 (m, 1H, H-3′), 4.37–4.17 (m, 3H, H-4′,5′), 2.10, 2.08, 1.97 (3×s, 9H, 3×COCH3) ppm.
Amination of compound 5 or 6 to obtain the 8-alkylamino-2-iodoadenosines 7–10 was generally as follows: to 8-bromo-2-iodoadenosine (5) or 2′,3′,5′-tri-O-acetyl-2-iodo-bromoadenosine (6) (0.17 mmol) the appropriate alkylamine was added (excess) and the mixture was stirred overnight at room temperature. The reaction mixture was concentrated in vacuo and the product was crystallised from water.
2-Iodo-8-methylaminoadenosine (Compound 7). The reaction was performed with 2′,3′,5′-tri-O-acetyl-2-iodo-8-bromoadenosine (6, 100 mg, 0.17 mmol) and methylamine (16 ml, 40% w/v in water). Yield 54.6 mg (0.13 mmol, 77%), mp 162–164÷C; 1H NMR (DMSO-d6) δ 7.02 (d, 1H, J=5.15 Hz, NH), 6.93 (s, 2H, NH2), 5.77 (d, 1H, J=7.56 Hz, H-1′), 5.66 (t, 1H, J=4.81 Hz, OH-2′), 5.31 (d, 1H, J=6.52 Hz, OH-5′), 5.18 (d, 1H, J=4.46 Hz, OH-3′), 4.56 (q, 1H, J=5.15 Hz, H-2′), 4.09–4.04 (m, 1H, H-3′), 3.98–3.91 (m, 1H, H-4′), 3.68–3.57 (m, 2H, H-5′), 2.86 (d, 3H, J=4.46 Hz, CH3); MS m/z 423 (M+H)+; Anal. (C11H15IN6O4) C, H, N.
2-iodo-8-ethylaminoadenosine (Compound 8). The reaction was performed with 2-iodo-8-bromoadenosine (5, 90 mg, 0.19 mmol) and ethylamine (2.5 ml, 70% w/v in water). Yield 58.3 mg (0.13 mmol, 70%), mp 205–207÷C, Rƒ 0.15 (10% MeOH in CH2Cl2); 1H NMR (DMSO-d6) δ 6.97 (t, 1H, J=5.15 Hz, NH), 6.89 (s, 2H, NH2), 5.79 (d, 1H, J=7.56 Hz, H-1′), 5.65–5.61 (m, 1H, OH-2′), 5.30 (d, 1H, J=6.18 Hz, OH-5′), 5.18 (d, 1H, J=3.77 Hz, OH-3′), 4.55 (q, 1H, J=6.17 Hz, H-2′), 4.08–4.04 (m, 1H, H-3′), 3.94 (bs, 1H, H-4′), 3.65–3.61 (m, 2H, H-5′), 2.49 (m, 2H, CH2), 1.16 (t, 3H, J=7.21 Hz, CH3); MS m/z 437 (M+H)+; Anal. (C12H17IN6O4) C, H, N.
2-Iodo-8-propylaminoadenosine (Compound 9): The reaction was performed with 2-iodo-8-bromoadenosine (5, 90 mg, 0.19 mmol) and propylamine (2.5 ml, 70% w/v in water). Yield 68.8 mg (0.15 mmol, 80%), mp 160–162÷C, Rƒ 0.20 (10% MeOH in CH2Cl2); 1H NMR (DMSO-d6) δ 6.99 (t, 1H, J=4.80 Hz, NH), 6.87 (s, 2H, NH2), 5.80 (d, 1H, J=8.24 Hz, H-1′), 5.67–5.63 (m, 1H, OH-2′), 5.30 (d, 1H, J=6.18 Hz, OH-5′), 5.18 (d, 1H, J=3.77 Hz, OH-3′), 4.56–4.51 (m, 1H, H-2′), 4.09–4.03 (m, 1H, H-3′), 3.96–3.94 (m, 1H, H-4′), 3.62–3.59 (m, 4H, H-5′, NHCH2), 1.57 (q, 2H, J=7.20 Hz, CH2CH3), 0.88 (t, 3H, J=7.50 Hz, CH3); MS m/z 451 (M+H)+; Anal. (C13H19IN6O4) C, H, N.
2-Iodo-8-butylaminoadenosine (Compound 10): The reaction was performed with 2-iodo-8-bromoadenosine (5, 1.15 g, 2.44 mmol) and n-butylamine (25 ml). Some drops of water were added to dissolve everything. Yield 0.92 g (1.98 mmol, 81%), mp 142–144÷C, Rƒ 0.23 (10% MeOH in CH2Cl2); 1H NMR (DMSO-d6) δ 6.94–6.86 (m, 3H, NH, NH2), 5.79 (d, 1H, J=7.56 Hz, H-1′), 5.67–5.62 (m, 1H, OH-2′), 5.30–5.16 (m, 2H, OH-3′,5′), 4.54–4.49 (m, 1H, H-2′), 4.07–4.04 (m, 1H, H-3′), 3.95–3.92 (m, 1H, H-4′), 3.64–3.57 (m, 2H, H-5′), 2.49–2.42 (m, 2H, NHCH2), 1.55–1.26 (m, 4H, CH2CH2CH3), 0.88 (t, 3H, J=7.21 Hz, CH3); MS m/z 464 (M+H)+; Anal. (C14H21IN6O4) C, H, N.
2-iodo-8-benzylaminoadenosine (Compound 11): 8-Bromo-2-iodoadenosine (5, 1.28 g, 2.14 mmol) was dissolved in benzylamine (21.4 mmol, 2.34 ml) and some drops of water were added to dissolve everything. The mixture was stirred overnight at 60° C. and concentrated in vacuo. The white solid was stirred in CH2Cl2, filtered and dried. Yield 0.97 g (1.95 mmol, 91%), mp 128–130÷C, Rƒ 0.19 (5% MeOH in EtOAc); 1H NMR (DMSO-d6) δ 7.65 (t, 1H, NH), 7.37–7.21 (m, 5H, phenyl), 6.91 (bs, 2H, NH2), 5.86 (d, 1H, J=7.90 Hz, H-1′), 5.63 (t, 1H, J=3.43 Hz, OH-2′), 5.37 (d, 1H, J=6.52 Hz, OH-5′), 5.20 (d, 1H, J=3.77 Hz, OH-3′), 4.65–4.55 (m, 3H, H-2′, NHCH2), 4.12–4.07 (m, 1H, H-3′), 4.07–3.97 (m, 1H, H-4′), 3.64–3.61 (m, 2H, H-5′); MS m/z 498 (M+H)+; Anal. (C17H19IN6O4) C, H, N.
The general procedure for the introduction of an 1-hexyn group at derivatives 1 and 7–11 to obtain compounds 3 and 12–16 is as follows: To a solution of 2-iodoadenosine (1) or the appropriate 2-iodo-8-(ar)alkylaminoadenosine (7–11) (0.65 mmol) in dry acetonitrile (5 ml) and Et3N (5 ml) under an atmosphere of nitrogen were added CuI (9.3 mg, 48.8 μmol), PdCl2 (6.0 mg, 33.8 μmol), Ph3P (19.5 mg, 74.3 μmol) and 1-hexyn (3.15 mmol, 362 μl). The mixture was stirred overnight at room temperature under an atmosphere of nitrogen. The mixture was filtered, concentrated and purified by column chromatography.
2-(1-hexynyl)adenosine (Compound 3).8 The reaction was performed with 2-iodoadenosine (1, 255 mg, 0.65 mmol) and 1-hexyn (3.15 mmol). The mixture was purified by column chromatography (5% MeOH in CH2Cl2). Yield 192 mg (0.55 mmol, 85%), mp 106–109÷C; Rƒ 0.10 (10% MeOH in CH2Cl2); 1H NMR (DMSO-d6) δ 8.37 (s, 1H, H-8), 7.41 (bs, 2H, NH2), 5.84 (d, J=6.18 Hz, 1H, H-1′), 5.45 (d, J=6.18 Hz, 1H, OH-2′), 5.22–5.16 (m, 1H, OH-5′), 5.22–5.16 (m, 1H, OH-3′), 4.52 (q, J=5.15 Hz, 1H, H-2′), 4.11 (q, J=3.43 Hz, 1H, H-3′), 3.93 (pd, J=3.43 Hz, 1H, H4′), 3.65–3.48 (m, 2H, H-5′), 2.39 (t, J=6.86 Hz, 2H, ≡CCH2), 1.51–1.39 (m, 4H, CH2CH2), 0.90 (t, J=6.87 Hz, 3H, CH3); MS m/z 348 (M+H)+; Anal. (C16H21N5O4 0.22 CH2Cl2) C, H, N.
2-(1-Hexynyl)-8-methylaminoadenosine (Compound 12). The reaction  was performed with 2-iodo-8-methylaminoadenosine (7, 50 mg, 0.12 mmol) and 1-hexyn (0.58 mmol). The mixture was purified by column chromatography (5% MeOH in CH2Cl2). Yield 36 mg (0.09 mmol, 79%), mp 161–163÷C; Rƒ 0.23 (5% MeOH in CH2Cl2); 1H NMR (DMSO-d6) δ 7.01 (d, 1H, J=4.81 Hz, NH), 6.61 (s, 2H, NH2), 5.84 (d, 1H, J=7.55 Hz, H-1′), 5.78 (t, 1H, J=4.47 Hz, OH-2′), 5.26 (d, 1H, J=6.87 Hz, OH-5′), 5.15 (d, 1H, J=4.12 Hz, OH-3′), 4.58 (q, 1H, J=5.83 Hz, H-2′), 4.10–4.03 (m, 1H, H-3′), 3.95 (bs, 1H, H-4′), 3.62 (bs, 2H, H-5′), 2.87 (s, 3H, J=4.46 Hz, NHCH3), 2.36 (t, 2H, J=6.87 Hz, ≡CCH2), 1.53–1.39 (m, 4H, CH2CH2), 0.89 (t, 3H, J=6.87 Hz, CH3); MS m/z 376 (M+H)+; Anal. (C17H24N6O4) C, H, N.
2-(1-hexynyl)-8-ethylaminoadenosine (Compound 13). The reaction was performed with 2-iodo-8-ethylaminoadenosine (8, 67 mg, 0.15mmol) and 1-hexyn (0.73 mmol). The mixture was purified by column chromatography (EtOAc-10% MeOH in EtOAc). Yield 49 mg (0.12 mmol, 83%), mp230–232÷C; 1H NMR (DMSO-d6) δ 6.97 (t, 1H, J=4.80 Hz, NH), 6.57 (s, 2H, NH2), 5.86 (d, 1H, J=7.55 Hz, H-1′), 5.74 (t, 1H, J=4.80 Hz, OH-2′), 5.25 d, 1H, J=6.52 Hz, OH-5′), 5.15 (d, 1H, J=4.12 Hz, OH-3′), 4.57 (q, 1H, J=6.18 Hz, H-2′), 4.08 (m, 1H, H-3′), 3.95 (m, 1H, H4′), 3.64–3.60 (m, 2H, H-5′), 3.05 (m, 2H, NHCH2), 2.36 (t, 2H, J=7.21 Hz, ≡CHCH2), 1.51–1.40 (m, 4H, CH2CH2CH3), 1.16 (t, 3H, J=7.20 Hz, NHCH2CH3), 0.89 (t, 3H, J=5.15 Hz, CH3); MS m/z 391 (M+H)+; Anal. (C18H26N6O4) C, H, N.
2-(1-Hexynyl)-8-propylaminoadenosine (Compound 14). The reaction  was performed with 2-iodo-8-propylaminoadenosine (9, 68 mg, 0.15 mmol) and 1-hexyn (0.73 mmol). The mixture was purified by column chromatography (EtOAc-10% MeOH in EtOAc). Yield 49 mg (0.12 mmol, 80%), mp 184–186÷C; Rƒ 0.60 (10% MeOH in EtOAc); 1H NMR (DMSO-d6) δ 6.98 (t, 1H, J=5.15 Hz, NH), 6.54 (bs, 2H, NH2), 5.87 (d, 1H, J=7.55 Hz, H-1′), 5.75 (t, 1H, J=4.46 Hz, OH-2′), 5.26 (d, 1H, J=6.86 Hz, OH-5′), 5.15 (d, 1H, J=4.12 Hz, OH-3′), 4.55 (q, 1H, J=6.86 Hz, H-2′), 4.06 (m, 1H, H-3′), 3.96 (bs, 1H, H4′), 3.61 (bs, 2H, H-5′), 2.49 (m, 2H, NHCH2), 2.36 (m, 2H, ≡CCH2), 1.60–1.42 (m, 6H, NHCH2CH2CH3, CH2CH2), 0.89 (t, 6H, J=7.55 Hz, 2×CH3); MS m/z 405 (M+H)+; Anal. (C19H28N6O4) C, H, N.
2-(1-hexynyl)-8-butylaminoadenosine (Compound 15). The reaction was performed with 2-iodo-8-butylaminoadenosine (10, 200 mg, 0.43 mmol) and 1-hexyn (2.08 mmol). The mixture was purified by column chromatography (5% MeOH in CH2Cl2). Yield 111 mg (0.26 mmol, 62%), mp 182–184÷C; 1H NMR (DMSO-d6) δ 6.95 (t, 1H, J=5.49 Hz, NH), 6.55 (bs, 2H, NH2), 5.87 (d, 1H, J=7.90 Hz, H-1′), 5.77–5.72 (m, 1H, OH-2′), 5.26 (d, 1H, J=6.52 Hz, OH-5′), 5.15 (d, 1H, J=4.12 Hz, OH-3′), 4.54 (q, 1H, J=5.84 Hz, H-2′), 4.09–4.04 (m, 1H, H-3′), 3.95–3.93 (m, 1H, H-4′), 3.64–3.59 (m, 2H, H-5′), 3.09 (m, 2H, NHCH2), 2.36 (m, 2H, ≡CCH2), 1.51–1.30 (m, 8H, 2×CH2CH2), 0.89 (t, 6H, J=,7.55 Hz, 2×CH3); MS m/z 419 (M+H)+; Anal. (C20H30N6O4) C, H, N.
2-(1-hexynyl)-8-Benzylaminoadenosine (Compound 16). The reaction was performed with 2-iodo-8-benzylaminoadenosine (11, 230 mg, 0.46 mmol) and 1-hexyn (2.23 mmol). The mixture was purified by column chromatography (EtOAc). Yield 146 mg (0.32 mmol, 70%), mp 141–143÷C; Rƒ 0.26 (5% MeOH in EtOAc); 1H NMR (DMSO-d6) δ 7.64 (t, 1H, J=6.10 Hz, NH), 7.36–7.18 (m, 5H, phenyl), 6.59 (bs, 2H, NH2), 5.92 (d, 1H, J=7.71 Hz, H-1′), 5.77 (t, 1H, J=4.85 Hz, OH-2′), 5.32 (d, 1H, J=6.74 Hz, OH-5′), 5.18 (d, 1H, J=4.18 Hz, OH-3′), 4.64 (q, 1H, J=4.64 Hz, H-2′), 4.58 (t, 2H, J=4.65 Hz, NHCH2), 4.09 (t, 1H, J=4.09 Hz, H-3′), 3.98 (d, 1H, J=1.60 Hz, H-4′), 3.62 (q, 2H, J=2.58 Hz, H-5′), 2.36 (t, 2H, J=6.92 Hz, ≡CCH2), 1.55–134 (m, 4H, CH2CH2), 0.89 (t, 3H, J=7.11 Hz, CH3); MS m/z 453 (M+H)+; Anal. (C23H28N6O4) C, H, N.
(E)-1-(borocatechol)-1-hexene.10 Yield 75%; Rƒ 0.28 (EtOAc:PE40/60 40/60=1:1).
General procedure for the introduction of an (E)-1-hexene group at derivatives 1 and 7–11 to obtain compounds 3 and 17–21 To a solution of 2-iodoadenosine (1) or the appropriate 2-iodo-8-(ar)alkylaminoadenosine (7–11) 0.82 mmol) in 20 ml of CH3CN:DMF (1:1) was added 50 mg of tetrakis(triphenylphosphine)palladium(0) and the mixture was stirred at room temperature for 15 min. Then 500 mg each of K2CO3 and (E)-1-borocatechol)-1-hexene (2.46 mmol) were added, and the suspension was refluxed for 5 hr. The mixture was filtered, concentrated in vacuo and purified by column chromatography.
2-((E)-1-hexenyl)adenosine (Compound 4).10 The reaction was performed with 2-iodoadenosine (1, 150 mg, 0.38 mmol) and (E)-1-borocatechol)-1-hexene (1.14 mmol). The mixture was purified by column chromatography (5–30% MeOH in CH2Cl2). Yield 27 mg (0.08 mmol, 20%), mp 124–127÷C; Rƒ 0.10 (10% MeOH in CH2Cl2); 1H NMR (MeOD-d4) δ 8.18 (s, 1H, H-8), 7.05–6.97 (m, 1H, ═CHCH2), 6.33 (d, 1H, J=15.44 Hz, ═CH), 5.93 (d, 1H, J=6.52 Hz, H-1′), 4.81–4.78 (m, 1H, H-2′), 4.33 (d, 1H, J=4.81 Hz, H-3′), 4.17 (m, 1H, H-4′), 3.81 (dq, 2H, J=18.88 Hz, J=2.41 Hz, H-5′), 2.25 (q, 2H, J=5.84 Hz, ═CHCH2), 1.48–1.36 (m, 4H, CH2CH2), 0.93 (t, 3H, J=6.87 Hz, CH3); MS m/z 350 (M+H)+; HPLC, System A: 20–100% CH3CN in H2O in 35 min., retention time=8.92 min.; System B: 30–100% CH3OH in H2O in 40 min., retention time=20.37 min.
2-((E)-1-Hexenyl)-8-methylaminoadenosine (Compound 17). The reaction was performed with 2-iodo-8-methylaminoadenosine (7, 520 mg, 1.23 mmol) and (E)-1-borocatechol)-1-hexene (3.70 mmol). The mixture was purified by column chromatography (20% MeOH in CH2Cl2). Yield 42 mg (1.11 mmol, 9%), mp 161–166÷C; Rƒ 0.60 (20% MeOH in CH2Cl2); 1H NMR (MeOD-d4) δ 6.91–6.83 (m, 1H, ═CHCH2), 6.29 (d, 1H, J=15.44 Hz, ═CH), 5.98 (d, 1H, J=7.55 Hz, H-1′), 4.81–4.74 (m, 1H, H-2′), 4.29 (t, 1H, J=5.49 Hz, H-3′), 4.13 (m, 1H, H-4′), 3.82–3.79 (m, 2H, H-5′), 2.97 (m, 3H, NHCH3), 2.29–2.22 (m, 2H, ═CHCH2), 1.52–1.36 (m, 4H, CH2CH2), 0.94 (t, 3H, J=6.52 Hz, CH3); MS m/z 379 (M+H)+; HPLC, System A: 20–100% CH3CN in H2O in 35 min., retention time=6.15 min.; System B: 30–100% CH3OH in H2O in 40 min., retention time=18.67 min.
2-((E)-1-hexenyl)-8-ethylaminoadenosine (Compound 18). The reaction was performed with 2-iodo-8-ethylaminoadenosine (8, 740 mg, 1.70 mmol) and (E)-1-borocatechol)-1-hexene (5.09 mmol). The mixture was purfied by column chromatography (10–20% MeOH in CH2Cl2).Yield 23 mg (0.06 mmol, 5%), mp 128–130÷C; Rƒ 0.61 (20% MeOH in CH2Cl2); 1H NMR (MeOD-d4) δ 6.92–6.82 (m, 1H, ═CHCH2), 6.29 (d, 1H, J=14.04 Hz, ═CH), 6.02 (d, 1H, J =7.64 Hz<H-1′), 4.80–4.76 (m, 1H, H-2′), 4.29–4.27 (m, 1H, H-3′), 4.13–4.11 (m, 1H, H4′), 3.81 (q, 2H, J=10.89 Hz, H-5′), 3.42 (q, 2H, J=6.02 Hz, NHCH2), 2.24 (q, 2H, J=6.00 Hz, ═CHCH2), 1.53–1.33 (m, 4H, CH2CH2), 1.28 (t, 3H, J=7.72 Hz, NHCH2CH3), 0.94 (t, 3H, J=7.11 Hz, CH3); MS m/z 393 (M+H)+; HPLC, System A: 20–100% CH3CN in H2O in 35 min., retention time=7.42 min.; System B: 30–100% CH3OH in H2O in 40 min., retention time=20.16 min.
2-((E)-1-hexenyl)-8-propylaminoadenosine (Compound 19). The reaction was performed with 2-iodo-8-propylaminoadenosine (9, 400 mg, 0.89 mmol) and (E)-1-borocatechol)-1-hexene (2.67 mmol). The mixture was purified by column chromatography (10% MeOH in CH2Cl2). Yield 43 mg (0.11 mmol, 12%), mp 170–172÷C; Rƒ 0.41 (10% MeOH in CH2Cl2); 1H NMR (MeOD-d4) δ 6.93–6.82 (m, 1H, ═CHCH2), 6.29 (d, 1H, J=15.48 Hz, ═CH), 6.04 (d, 1H, J=7.65 Hz, H-1′), 4.79–4.74 (m, 1H, H-2′), 4.29–4.26 (m, 1H, H-3′), 4.13–4.12 (m, 1H, H-4′), 3.81 (q, 2H, J=8.24 Hz, H-5′), 3.37–3.32 (m, 2H, NHCH2), 2.24 (q, 21H, J=7.16 Hz, ═CHCH2), 1.89–1.66 (m, 2H, NHCH2CH2), 1.51–1.35 (m, 4H, CH2CH2), 1.02–0.91 (m, 6H, 2×CH3); MS m/z 407 (M+H)+; HPLC, System A: 20–100% CH3CN in H2O in 35 min., retention time=8.10 min.; System B: 30–100% CH3OH in H2O in 40 min., retention time=20.25 min.
2-((E)-1-hexenyl)-8-butylaminoadenosine (Compound 20). The reaction was performed with 2-iodo-8-butylaminoadenosine (10, 380 mg, 0.82 mmol) and (E)-1-borocatechol)-1-hexene (2.46 mmol). The mixture was purified by column chromatography (10% MeOH in CH2Cl2). Yield 42 mg (0.10 mmol, 12%); Rƒ 0.44 (10% MeOH in CH2Cl2); 1H NMR (MeOD-d4) δ 6.94–6.80 (m, 1H, ═CHCH2), 6.28 (d, 1H, J=15.42 Hz, ═CH), 6.02 (d, 1H, J=7.62 Hz, H-1′), 4.81–4.69 (m, 1H, H-2′), 4.31–4.20 (m, 1H, H-3′), 4.20–4.05 (m, 1H, H-4′), 3.87–3.70 (m, 2H, H-5′), 3.35–3.23 (m, 2H, NHCH2), 2.29–2.05 (m, 2H, ═CHCH2), 1.72–1.20 (m, 8H, 2×CH2CH2), 1.00–0.83 (m, 6H, 2×CH3); MS m/z 422 (M+H)+; HPLC, System A: 20–100% CH3CN in H2O in 35 min., retention time=8.53 min.; System B: 30–100% CH3OH in H2O in 40 min., retention time=20.47 min.
2-((E)-1-hexenyl)-8-benzylaminoadenosine (Compound 21). The reaction was performed with 2-iodo-8-benzylaminoadenosine (11, 410 mg, 0.82 mmol) and (E)-1-borocatechol)-1-hexene (2.47 mmol). The mixture was purified by column chromatography (10% MeOH in CH2Cl2). Yield 41 mg (0.10 mmol, 11%), mp 153–155÷C; 1H NMR (MeOD-d4) δ 7.64 (t, 1H, J=6.10 Hz, NH), 7.36–7.18 (m, 5H, phenyl), 6.59 (bs, 2H, NH2), 6.94–6.80 (m, 1H, ═CHCH2), 6.28 (d, 1H, J=15.42 Hz, ═CH), 5.92 (d, 1H, J=7.71 Hz, H-1′), 5.77 (t, 1H, J=4.85 Hz, OH-2′), 5.32 (d, 1H, J=6.74 Hz, OH-5′), 5.18 (d, 1H, J=4.18 Hz, OH-3′), 4.64 (q, 1H, J=4.64 Hz, H-2′), 4.58 (t, 2H, J=4.65 Hz, NHCH2), 4.09 (t, 1H, J=4.09 Hz, H-3′), 3.98 (d, 1H, J=1.60 Hz, H-4′), 3.62 (q, 2H, J=2.58 Hz, H-5′), 2.29–2.05 (m, 2H, ═CHCH2), 1.72–1.20 (m, 4H, CH2CH2), 1.00–0.83 (m, 3H, CH3) ppm; MS m/z 456 (M+H)+; HPLC, System A: 20–100% CH3CN in H2O in 35 min., retention time=9.61 min.; System B: 30–100% CH3OH in H2O in 40 min., retention time=26.10 min.
2,8di-(1-Hexynyl)adenosine (Compound 22). 2-iodo-8-bromoadenosine (5, 150 mg, 0.32 mmol) was dissolved in 3 mL CH3CN and 3 ml Et3N (dry). Then 4.5 mg CuI (23.6 μmol), 2.9 mg PdCl2 (16.4 μmol) and 9.6 mg Ph3P (36.4 μmol) were added. Subsequently, 1.55 mmol (178 μl) 1-hexyn was added and the mixture was stirred under nitrogen atmosphere at room temperature overnight. The mixture was concentrated and purified by column chromatography (10% MeOH in CH2Cl2). Yield 96 mg (0.22 mmol, 70%), mp 146–148÷C; Rƒ 0.48 (10% MeOH in CH2Cl2); 1H NMR (MeOD-d4) δ 7.61 (bs, 2H, NH2), 5.89 (d, 1H, J=6.86 Hz, H-1′), 5.39 (d, 1H, J=6.18 Hz, OH-2′), 5.29–5.22 (m, 1H, OH-5′), 5.16 (d, 1H, J=4.12 Hz, OH-3′), 4.94 (q, 1H, J=5.83 Hz, H-2′), 4.15–4.13 (m, 1H, H-3′), 3.94–3.92 (m, 1H, H-4′), 3.72–3.44 (m, 2H, H-5′), 2.56 (t, 2H, J=6.52 Hz, ≡CCH2), 2.44–2.34 (m, 2H, ≡CCH2), 1.57–1.37 (m, 8H, CH2CH2), 0.93–0.86 (m, 6H, CH3) ppm; MS m/z 429 (M+H)+; Anal. (C22H29N5O4) C, H, N.
2,8-di-benzylaminoadenosine (Compound 23). 8-Bromo-2-iodoadenosine (5, 1.4 g, 2.34 mmol) was dissolved in benzylamine (23.4 mmol, 2.56 ml ) The mixture was heated at 140 C for 2 h. and was poured into CHCl3. A precipitate was formed which was removed by filtration. The filtrate was concentrated and purified by column chromatography (0–10% MeOH in EtOAc). Yield 838 mg (1.76 mmol, 75%), mp 133–135÷C; Rƒ 0.24 (5% MeOH in EtOAc); 1H NMR (MeOD-d4) δ 7.32–6.91 (m, 11H, 2×phenyl, NH), 6.35–6.29 (m, 1H, NH), 6.05 (bs, 2H, NH2), 5.81 (d, 1H, J=6.86 Hz, H-1′), 5.66–5.54 (m, 1H, OH-2′), 5.20 (d, 1H, J=6.18 Hz, OH-5′), 5.04 (d, 1H, J=4.80 Hz, OH3′), 4.75–4.62 (m, 1H, H-2′), 4.56–4.38 (m, 4H, 2×CH2), 4.13–4.04 (m, 1H, H-3′), 3.92–3.84 (m, 1H, H-4′), 3.65–3.52 (m, 2H, H-5′) ppm; MS m/z 479 (M+H)+; Anal. (C24H27N7O4) C, H, N.
The elemental analysis for compounds 1, 3, 7–17, 22 and 23 is provided in the following Table 1:







TABLE 1







Elemental Analysis












Atom



No
Mol. Formula
Calculated
Determined













1
C10H12IN5O4.0.33 C2H5CO2C2H5
C 32.18%
C 32.48%




H 3.49%
H 3.10%




N 16.60%
N 16.72%


3
C16H21N5O4.0.22 CH2Cl2
C 53.25%
C 53.31%




H 5.91%
H 5.82%




N 19.15%
N 19.05%


7
C11H15IN6O4.1.9 H2O
C 29.00%
C 29.19%




H 4.14%
H 4.21%




N 18.44%
N 18.18%


8
C12H17IN6O4.1.2 CH3OH
C 33.41%
C 33.11%




H 4.64%
H 4.91%




N 17.68%
N 17.72%


9
C13H19IN6O4.1.8 HCON(CH3)2
C 38.04%
C 37.95%




H 5.49%
H 5.71%




N 18.78%
N 18.80%


10
C14H21IN6O4
C 36.22%
C 36.55%




H 4.56%
H 4.24%




N 18.10%
N 18.22%


11
C17H19IN6O4
C 40.98%
C 40.59%




H 3.84%
H 4.05%




N 16.87%
N 16.50%


12
C17H24N6O4.2.9 H2O
C 47.69%
C 47.66%




H 7.00%
H 7.21%




N 19.63%
N 19.73%


13
C18H26N6O4.0.5 H2O
C 54.21%
C 54.10%




H 6.81%
H 7.01%




N 21.07%
N 21.4%


14
C19H28N6O4.1.6 H2O
C 52.63%
C 52.70%




H 7.26%
H 7.23%




N 19.38%
N 19.19%


15
C20H30N6O4.1.4 H2O
C 54.16%
C 54.11%




H 7.45%
H 7.72%




N 18.95%
N 19.14%


16
C23H28N6O4.1.0 H2O
C 59.43%
C 59.39%




H 6.71%
H 6.69%




N 18.65%
N 18.28%


22
C22H29N5O4.0.8 HCON(CH3)2
C 60.27%
C 60.10%




H 7.18%
H 7.00%




N 16.72%
N 16.46%


23
C24H27N7O4
C 60.37%
C 60.65%




H 5.70%
H 5.37%




N 20.53%
N 20.44%









Radioligand Binding Studies

Measurements with [3H]DPCPX in the absence of GTP were performed according to a protocol published previously.30 Adenosine A2A receptor affinities were determined according to Gao et al.31 Adenosine A3 receptor affinities were determined essentially as described.28,29 Briefly, assays were performed in 50/10/1 buffer (50 mM Tris/10 mM MgCl2/1 mM ethylenediaminetetra-acetic acid (EDTA) and 0.01% 3-([3-cholamidopropyl]-dimethylammonio)-1-propanesulfonate (CHAPS)) in glass tubes and contained 50 μl of a HEK 293 cell membrane suspension (10–30 μg), 25 μL [125I]AB MECA (final concentration 0.15 nM), and 25 μl of ligand. Incubations were carried out for 1 hr at 37° C. and were terminated by rapid filtration over Whatman GF/B filters, using a Brandell cell harvester (Brandell, Gaithersburg, Md.). Tubes were washed three times with 3 ml of buffer. Radioactivity was determined in a Beckman 5500B γ-counter. Nonspecific binding was determined in the presence of 10−5 M R-PIA.
cAMP assay. A2A 
CHO cells expressing the human adenosine A2A receptors were grown overnight as a monolayer in 24 wells tissue culture plates (400 μl/well; 2×105 cells/well). cAMP generation was performed in Dulbecco's Modified Eagles Medium (DMEM)/N-2-hydroxyethylpiperazin-N′-2-ethansulfonic acid HEPES) buffer (0.60 g HEPES/50 ml DMEM pH 7.4). To each well, washed three times with DMEM/HEPES buffer (250 μl), 100 μl DMEM/HEPES buffer, 100 μl adenosine deaminase (final concentration 5 IU/ml) and 100 μl of a mixture of rolipram and cilostamide (final concentration 50 μM each) were added. After incubation for 40 minutes at 37° C., 100 μL agonist was added. After 15 minutes at 37° C., the reaction was terminated by removing the medium and adding 200 μl 0.1 M HCl. Wells were stored at −20° C. until assay.
The amounts of cAMP were determined after a protocol with cAMP binding protein12 with the following minor modifications. As a buffer was used 150 mM K2HPO4/10 mM EDTA/0.2% Bovine Serum Albumine (BSA) at pH 7.5. Samples (20 μl+30 μl 0.1 M HCl) were incubated for at least 2.5 hours at 0° C. before filtration over Whatman GF/B filters. Filters were additionally rinsed with 2×2 ml TrisHCl buffer (pH 7.4, 4° C.). Filters were counted in Packard Emulsifier Safe scintillation fluid (3.5 ml) after 24 hours of extraction.
Biological Evaluation
All compounds prepared were tested in radioligand binding assays to determine their affinities for the adenosine A1 receptor in rat brain cortex, the A2A receptor in rat striatum and the human A3 receptor as expressed in HEK 293 cells (Table 2, hereinafter). The Ki values were computed from the displacement curves obtained by nonlinear regression of the competition curves with the software package Prism (Graph Pad, San Diego, Calif.)
For the adenosine A1 receptor, the tritiated antagonist, [3H]-1,3-dipropyl-8-cyclopentylxanthine ([3H]DPCPX), and for the adenosine A2A receptor, the tritiated antagonist [3H]ZM 241385 were used. Since radiolabeled antagonists are not commercially available for the adenosine A3 receptor, [125I]AB-MECA, an A3 receptor agonist, was used. Displacement experiments were performed in the absence of GTP.
All compounds prepared were also tested in a functional assay. The ability of the compounds (3–5, 7–23) to produce cAMP by activation of human adenosine A2A receptors expressed in CHO cells was assessed and compared to the reference full agonist CGS21680 (100%).
Results and Discussion
Compounds 3 and 4 were synthesized starting from the important intermediate 2-iodoadenosine (1).17 The 2-(1-hexynyl) substituent was successfully introduced via a slightly modified traditional palladium-catalyzed cross-coupling reaction.8 Synthesis of 2-alkenyl derivatives by the reaction of 1 with terminal alkenes in this classical cross-coupling have been shown to be disappointing, with E derivatives obtained in very low yields only.10 An alternative route has been the preparation of a (E)-1-(borocatechol)-1-alkene complexe, by letting catecholborane react with the appropriate terminal alkyn. These (E)-1-(borocatechol)-1-alkene complexes have been coupled successfully with 2-iodoadenosine derivatives.10 Treatment of 1, under similar conditions, with (E)-1-(borocatechol)-1-hexene, gave compound 4 in reasonable yield.
For the synthesis of the C2,8-disubstituted derivatives 12–23, 2-iodoadenosine (1) was brominated at the 8-position prior to the introduction of the 2-substituent. Using a standard bromination procedure, e.g. stirring 2-iodoadenosine (1) or 2′,3′,5′-tri-O-acetyl-2-iodoadenosine (2) in dioxan and adding bromine water (in phosphate buffer, 10% w/v, pH  ̃7),18 yielded the corresponding 8-bromo derivatives. With the use of a different buffer (NaOAc buffer, 1.0 M, pH=4), 2-iodoadenosine (1) readily dissolved (50÷C) and after addition of Br2, stirring overnight and subsequent adjustment of the pH to 7, the 8-brominated compound (5) was obtained as a white solid that could easily be filtered.16 Subsequent amination at the 8-position was straightforward by stirring compound 5 with the appropriate amine (less nucleophilic amines needed some heating), and compounds 7–11 were obtained in good yields (70–91%).19
The introduction of the 1-hexynyl or the (E)-1-hexenyl substituents at the 2-position was achieved as described for compound 1, and yielded the desired compounds 12–21. The alternative synthesis of compounds 12–21 by the introduction of the 2-substituent prior to the 8-substituent failed. In this case, compound 3 was indeed brominated at the 8-position, however, addition of bromine at the triple bond occurred as well. Finally, reacting compound 5 with an excess of either 1-hexyn or benzylamine yielded compounds 22 and 23.
Table 2 displays radioligand binding data for all synthesized C2,8-adenosine derivatives (final products 1, 3–5, 7–23). The affinities of the adenosine analogues at adenosine A1, A2A and A3 receptors is expressed as Ki values (±SEM in nM, n=3) or percentage displacement (n=2, mean value) at 10 μM.







TABLE 2













 


Ki (nM) or % displacement at 10−5 M













No
R2
R3
A1a
A2Ab
A3c
A3/A2A
















1
I
H
36.1%
4200 ± 80
297 ± 17
0.07


3
C≡C(CH2)3CH3
H
63.7%
6 ± 1
16.9 ± 4.1
2.78


4
(E) CH═CH(CH2)3CH3
H
53.1%
26.2 ± 1.8
73.5 ± 7.7
2.78


5
I
Br
21.6%
43.1%
6.2%
—


7
I
NHCH3
35.2%
43.3%
7310 ± 440
—


8
I
NHCH2CH3
35.2%
40.6%
5110 ± 890
—


9
I
NH(CH2)2CH3
40.2%
50.7%
8670 ± 2000
—


10
I
NH(CH2)3CH3
28.2%
3110 ± 1650
43.1%
—


11
I
NHCH2C6H5
35.5%
44.7%
39.5%
—


12
C≡C(CH2)3CH3
NHCH3
31.6%
115 ± 8
5640 ± 780
49.0


13
C≡C(CH2)3CH3
NHCH2CH3
30.9%
253 ± 29
8830 ± 1230
34.9


14
C≡C(CH2)3CH3
NH(CH2)2CH3
47.6%
82 ± 10
2160 ± 120
26.3


15
C≡C(CH2)3CH3
NH(CH2)3CH3
539 ± 380
149 ± 29
64.3%
—


16
C≡C(CH2)3CH3
NHCH2C6H5
756 ± 483
35.4%
7970 ± 610
—


17
(E) CH═CH(CH2)3CH3
NHCH3
17.9%
663 ± 106
13440 ± 2130
20.3


18
(E) CH═CH(CH2)3CH3
NHCH2CH3
30.0%
1840 ± 300
17530 ± 2100
9.53


19
(E) CH═CH(CH2)3CH3
NH(CH2)2CH3
49.5%
678 ± 25
14330 ± 2160
21.1


20
(E) CH═CH(CH2)3CH3
NH(CH2)3CH3
906 ± 264
580 ± 250
47.4%
—


21
(E) CH═CH(CH2)3CH3
NHCH2C6H5
2110 ± 560
26.3%
24.3%
—


22
C≡C(CH2)3CH3
C≡C(CH2)3CH3
50.3%
28.7%
254 ± 34
—


23
NHCH2C6H5
NHCH2C6H5
50.2%
11.6%
54.1%
—





adisplacement of [3H]DPCPX from rat cortical membranes


bdisplacement of [3H]ZM241385 from rat striatal membranes;


cdisplacement of [125I]AB-MECA from the human A3 receptor expressed in HEK 293 cells.






From Table 2 it is clear that most synthesized compounds had low affinities for the adenosine A1 and A3 receptor. The affinities of the compounds for the adenosine A2A receptor were higher, depending on the 2-substituent present. The compounds with an 8-alkylamino group had lower adenosine A2A receptor affinities than the C8-unsubstituted derivatives 3 and 4. The introduction of either an (E)-1-hexenyl or a 1-hexynyl substituent at the 2-position of 8-alkylamino adenosine derivatives led to an increase in affinity for the adenosine A2A receptor, up to approx. 7- or 60-fold, respectively (Table 2). The compounds had adenosine A2A receptor affinities in the nanomolar range, with compound 14 having the highest A2A receptor affinity (Ki value of 82 nM). The introduction of 8-substituents at adenosine decreases the affinity of the resulting compounds for the adenosine receptors compared to adenosine itself. 8-Alkylamino adenosine derivatives had adenosine A1 and A2A receptor affinities in the μM range, without substantial preference for either receptor, whereas introduction of a cyclopentyl group at the N6-position led to an increase in adenosine A1 receptor affinity up to 23-fold.14 The 2-(1-hexynyl) adenosine derivatives 12–16 generally had higher adenosine A2A receptor affinities than the 2-((E)-1-hexenyl)-substituted compounds 17–21, in line with the receptor affinities of compounds 3 and 4. Within both 2-substituted series. (12–16 and 17–21, Table 2), the 8-propylamino substituent seemed to be tolerated best on the adenosine A2A receptor. This is in contrast with the 2-unsubstituted derivatives, for which the 8-methylamino group appeared optimal for adenosine A2A receptor affinity.12 In general, all compounds were more adenosine A2A receptor selective compared to the A1 receptor or the A3 receptor. Exceptions were compounds 16 and 21, containing the large benzylamino group at the 8-position. These compounds displayed higher adenosine A1 receptor affinities compared to A2A and A3, indicating that the adenosine A1 receptor seemed best capable of accommodating this group. A 1-hexynyl group at the 8-position strongly decreased the A2A receptor affinity as well (compounds 3 and 22). The adenosine A3 receptor seemed better able to accommodate the 1-hexynyl group (22) than the benzylamino group at the 8-position (16, 21). Finally, the adenosine A2A receptor affinity of compound 16, with a 1-hexynyl group at the 2-position, was higher than that of the 2-benzylamino-substituted derivative (23), also in line with receptor (functional) data on either 2-(1-hexynyl)-8 or 2-benzylamino-substituted20 derivatives. Other adenosine derivatives substituted at the 8-position have not displayed very high receptor affinities.14 However, as shown herein, 8-alkylamino-substituted adenosine derivatives were obtained with affinities in the low micromolar (17–20) or even nanomolar range (12–15) for the adenosine A2A receptor. Although the adenosine A2A receptor affinity was somewhat decreased with the introduction of the 8-alkylamino groups, the A2A receptor selectivity compared to (A1 and) A3 was increased. Many 2-substituted adenosine derivatives have been described as potent ligands for the A2A receptor, although binding data for the adenosine A3 receptor is often lacking.8,10,21,-23 Some 2-alkynyl adenosine derivatives have been tested on the adenosine A3 receptor.24-26 These compounds, such as HENECA (2-(1-hexynyl)-5′-deoxy-5′-N-ethylcarboxamidoadenosine), had high affinity for the A3 receptor, and were often more selective for the adenosine A3 compared to the A2A receptor. The 8-methylamino (12) and 8-propylamino (14) derivatives of 2-(1-hexynyl)adenosine (3), of the present invention showed high A2A receptor affinities with Ki values of 115 and 82 nM, respectively. Furthermore, the selectivity for the adenosine A2A receptor compared to A3 was approx. 49- and 26-fold, respectively. Although the affinities of the 2-(1-hexenyl)adenosines were somewhat lower, the selectivity for the A2A receptor was also increased.
The nanomolar adenosine A2A receptor affinities of compounds 12–15, and the acceptable A2A receptor affinities of compounds 17–20, indicate that the (fairly large) size of the substituents is not the main determining factor for the affinities of these compounds. The 8-substituents may have an influence on the conformation of the ligand itself (by forcing the ribose ring into the syn conformation). The conformation of 8-bromoadenosine in the crystal structure is syn, suggested to cause the low affinity of this compound for the adenosine receptors.27-29 The bulkiness of 8-alkylamino groups was initially thought to force the ribose ring into the Syn conformation as well. However, from the X-ray structure of 8-(cyclopentylamino)-N6-ethyladenosine it became apparent that the anti conformation is compatible with 8-substitution.14 The difference in energy between the syn and the anti conformation is often not very large, and a direct steric hindrance at the receptor binding site seems to be a more probable explanation. Furthermore, the electronic (hydrogen bond formation) and lipophilic characteristics of the 8-substituents influence receptor affinity too.12 
The effect of the synthesized compounds in cAMP assays was also determined. Table 3 shows the percentage of cAMP production via the human adenosine A2A receptor expressed in CHO cells compared to a reference agonist CGS 21680 (10 μM) (n=2, mean value, both values in percentage). The results are displayed in the following Table 3:







TABLE 3













 










No
R2
R3
% cAMP production hA2A





CGS 21680


100%


 1
I
H
126% (118–134)


 3
C≡C(CH2)3CH3
H
61% (58–64)


 4
(E) CH═CH(CH2)3CH3
H
82% (78–86)


 5
I
Br
n.d.


 7
I
NHCH3
23% (20–25)


 8
I
NHCH2CH3
77% (76–78)


 9
I
NH(CH2)2CH3
4% (3–5)


10
I
NH(CH2)3CH3
28% (27–30)


11
I
NHCH2C6H5
125% (92–157)


12
C≡C(CH2)3CH3
NHCH3
85% (85–86)


13
C≡C(CH2)3CH3
NHCH2CH3
134% (124–143)


14
C≡C(CH2)3CH3
NH(CH2)2CH3
58% (50–66)


15
C≡C(CH2)3CH3
NH(CH2)3CH3
72% (63–82)


16
C≡C(CH2)3CH3
NHCH2C6H5
83% (61–106)


17
(E) CH═CH(CH2)3CH3
NHCH3
54% (49–59)


18
(E) CH═CH(CH2)3CH3
NHCH2CH3
65% (63–66)


19
(E) CH═CH(CH2)3CH3
NH(CH2)2CH3
73% (70–76)


20
(E) CH═CH(CH2)3CH3
NH(CH2)3CH3
36% (33–40)


21
(E) CH═CH(CH2)3CH3
NHCH2C6H5
73% (72–75)


22
C≡C(CH2)3CH3
C≡C(CH2)3CH3
99% (98–99)


23
NHCH2C6H5
NHCH2C6H5
95% (90–100)









For determination of the amount of cAMP produced via the adenosine A2A receptor, all compounds were first tested at a single concentration (approx. 100× the Ki value). Compounds 3 and 4, without an alkylamino group at the 8-position, displayed partial agonism compared to the reference agonist CGS 21680. The intrinsic activity of compound 3 was less than that of compound 4. Compound 1, with iodine at the 2-position, behaved as a full agonist. Introduction of the 8-alkylamino groups to compound 1, led in most cases (except compound 11) to a decrease in intrinsic activity. Compound 9 showed a cAMP production of 4% only, compared to CGS 21680. Within the 2-(hexynyl) series (12–16), compounds 14–16 had similar intrinsic activities as the 8-unsubstituted compound 3, while 12 had a somewhat higher intrinsic activity. They all behaved as partial agonists compared to CGS 21680, whereas compound 13 behaved as a full agonist. Within the 2-(E)-alkenyl substituted series (17–21), the introduction of methyl-, ethyl, and butylamino groups all decreased the intrinsic activity compared to compound 4. The intrinsic activities of compounds 19 and 21 were similar to that of 4 and they all behaved as partial agonists as well. Most compounds with very bulky C8-substituents (11, 16, 22 and 23) behaved as full agonists at the adenosine A2A receptor in this assay. Actually, GCS 21680 seemed a partial agonist here, since its intrinsic activity was lower than that of compounds 1, 11 and 13.
The C2,8-disubstituted adenosine derivatives disclosed herein were synthesized in good overall yields starting from 2-iodoadenosine. Most compounds appear to have adenosine A2A receptor affinities in the low micromolar or nanomolar range. Although the affinity for the adenosine A2A receptor was decreased somewhat with the introduction of the 8-alkylamino substituents, the selectivity for this receptor compared to the A3 receptor was improved significantly. The 8-methylamino (12) and 8-propylamino (14). derivatives of 2-(1-hexynyl)adenosine (3), showed high A2A receptor affinities with Ki values of 115 and 82 nM, respectively, and were 49- and 26-fold selective for the adenosine A2A receptor compared to the A3 receptor. The adenosine A2A receptor seem to accommodate the 8-propyl- or 8-butylamino substituents best, whereas the even larger 8-substituents (8-benzylamino or 8-(1-hexynyl)) were not well tolerated. As for the intrinsic activity, the 8-unsubstituted compounds 3 and 4 displayed a reduced intrinsic activity compared to the reference agonist CGS21680. With the introduction of 8-alkylamino substituents the intrinsic activity was either not affected much, or as in most cases, was further reduced, and most of the compounds behaved as partial agonists. Most of the 8-substituted derivatives of 1 behaved as partial agonists as well.
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## Claims

1. A compound of the general formula (I):




wherein
R2 and R3, which may be the same or different, represent a lower alkyl; a lower alkenyl; a lower alkynyl; a lower (ar)alkyl; a lower alkoxy; a lower alkylidenehydrazino; a cyano; an acetoamino; a halogen; a group of the general formula —NR4R5, wherein R4 and R5 represent, independently, a hydrogen atom, a lower alkyl or an (ar)alkyl group; or a group of the general formula —SR6, wherein R6 represents a hydrogen, a lower alkyl, a lower alkanoyl or an (ar)alkyl group;
or a salt of said compound, with the provisos that:
(i) when R2 represents —NH2, R3 represents a lower alkenyl, a lower alkynyl, a lower (ar)alkyl, a lower alkylidenehydrazino, a cyano, an acetoamino, a group of the general formula —NR4R5; wherein one of —R4 or R5 represents, independently, a hydrogen atom; or wherein R4 and R5 represent, independently, -a lower alkyl or an (ar)alkyl group, or a group of the general formula —SR6; wherein R6 represents a hydrogen, a lower alkyl, a lower alkanoyl or an (ar)alkyl group;
(ii) when R2 represents an alkylthio, R3 does not represent an alkyl;
(iii) when R2 represents a halogen or an alkyl, R3 does not represent, respectively, a halogen or an alkyl.

2. The compound of claim 1, wherein R2 is a halogen atom, an alkenyl group, an alkynyl group or an (ar) alkylamino group.

3. The compound of claim 2, wherein said halogen atom is iodine.

4. The compound of claim 2, wherein said alkenyl group or said alkynyl group is, respectively a C6-alkenyl group or a C6-alkynyl group.

5. The compound of claim 4, wherein said R2 is 1-hexenyl or 1-hexynyl.

6. The compound of claim 5, wherein said 1-hexenyl is the (E)1-hexenyl isomer.

7. The compound of claim 1, wherein R3 represents an alkylamino group, an (ar)alkylamino group or an alkynyl group.

8. The compound of claim 7, wherein said alkylamino group is selected from methylamino, ethylamino, propylamino, and butylamino; and said (ar)alkylamino group is a benzylamino group.

9. The compound of claim 1, wherein said R2 is 1-hexynyl and R3 is selected from a methylamino group, an ethylamino group, a propylamino group and a butylamino group.

10. The compound of claim 1, wherein said R2 is (E)1-hexenyl and R3 is selected from a methylamino group, a thylamino group, a propylamino group and a butylamino group.

11. The compound of claim 1, which is an adenosine A2A receptor agonist.

12. The compound of claim 1, which is a partial adenosine A2A receptor agonist.

13. The compound of claim 1, selected from the group consisting of the following compounds:
2-iodo-8-methyl aminoadenosine;
2-iodo-8-ethyl aminoadenosine;
2-iodo-8-propylaminoadenosine;
2-iodo-8-butylaminoadenosine;
2-iodo-8-benzylaminoadenosine;
2-(1-hexynyl)-8-methylaminoadenosine;
2-(1-hexynyl)-8-ethylaminoadenosine;
2-(1-hexynyl)-8-propylaminoadenosine;
2-(1-hexynyl)-8-butylaminoadenosine;
2-(1-hexynyl)-8-benzylaminoadenosine;
2-((E)-1-hexenyl)-8-methylaminoadenosine;
2-((E)-1-hexenyl)-8-ethylaminoadenosine;
2-((E)-1-hexenyl)-8-propylaminoadenosine;
2-((E)-1-hexenyl)-8-butylaminoadenosine;
2-((E)-1-hexenyl)-8-benzylaminoadenosine;
2,8-di-(1-hexynyl)adenosine; and
2,8-di-benzylaminoadenosine.

14. A pharmaceutical composition comprising as active ingredient an effective amount of a compound of the formula (I):




or a salt thereof,
wherein
R2 and R3 which may be the same or different, represent a lower alkyl; a lower alkenyl; a lower alkynyl; a lower (ar)alkyl; a lower alkoxy; a lower alkylidenehydrazino group-; a cyano; an acetoamino; a halogen; a group of the general formula —NR4R5 wherein R4 and R5 represent, independently, a hydrogen atom, a lower alkyl or an (ar)alkyl group; or a group of the general formula —SR6, wherein R6 represents a hydrogen, a lower alkyl, a lower alkanoyl or an (ar)alkyl group; with the provisos that
when R2 represents —NH2, R3 does not represent a halogen, an alkyl or an alkoxy;
when R2 represents an alkylthio, R3 does not represent an alkyl;
when R2 represents a halogen or an alkyl, R3 does not represent, respectively, a halogen or an alkyl group; and in combination with one or more pharmaceutically acceptable additives.

15. The pharmaceutical composition of claim 14, wherein R2 is a halogen atom, an alkenyl group, an alkynyl group or an (ar)alkylamino group.

16. The pharmaceutical composition of claim 15, wherein said halogen atom is iodine.

17. The pharmaceutical composition of claim 15, wherein said alkenyl group or alkynyl group is a C6-alkenyl group or a C6-alkynyl group.

18. The pharmaceutical composition of claim 17, wherein said R2 is 1-hexenyl or 1-hexynyl.

19. The pharmaceutical composition of claim 18, wherein said 1-hexenyl is the (E) 1-hexenyl isomer.

20. The pharmaceutical composition of claim 14, wherein R3 represents an alkylamino group, an (ar)alkylamino group or an alkynyl group.

21. The pharmaceutical composition of claim 20, wherein said alkylamino group is selected from a methylamino group, an ethylamino group, a propylamino group, and a butylamino group, and wherein said (ar)alkylamino group is a benzylamino group.

22. The pharmaceutical composition of claim 14, wherein said R2 is 1-hexynyl and R3 is selected from a methylamino group, an ethylamino group, a propylamino group and a butylamino group.

23. The pharmaceutical composition of claim 14, wherein said R2 is (E)1-hexenyl and R3 is selected from a methylamino group, an ethylamino group, a propylamino group and a butylamino group.

24. A method for achieving activation of adenosine A2AA receptor in a cell comprising administering to said cell the composition of claim 14.

25. A method according to claim 24, wherein said activation is partial activation.