title: Synthesis and structure-activity relationship of pyrazolo[3,4-d]pyrimidines: potent and selective adenosine A1 receptor antagonists.
abstract: A series of 12 substituted 1-phenylpyrazolo[3,4-d]pyrimidines were synthesized and evaluated for rat brain adenosine A1 and A2a receptor binding affinity. Substituents at C-4 and C-6 were varied in order to define these regions in terms of molecular recognition by the receptor subtypes. At C-4, the effects of a mercapto, methylthio, and amino substituent were evaluated, while at C-6, amides with varying alkyl groups extending from the alpha-carbon were examined. This study identified both potent and selective adenosine A1 receptor antagonists. The most potent of the 12 compounds was alpha-[(4-amino-1-phenylpyrazolo[3,4-d]pyrimidin-6-yl)thio]hexanamide (14); with an A1 Ki of 0.939 nM and an A2a Ki of 88.3 nM, this compound is 94-fold A1 selective. The most selective of the 12 compounds was alpha-[[4-(methylthio)-1-phenylpyrazolo[3,4-d]pyrimidin-6-yl]thio]hex anamide (10); with an A1 Ki of 6.81 nM and an A2a Ki > 40 000 nM, this compound is > 5900-fold A1 selective. The structure-activity relationships for the complete series has identified discrete structural differences between the A1 and A2a receptors with respect to the binding of pyrazolo[3,4-d]pyrimidines. This study resulted in prediction that increased A1 affinity could be achieved by incorporation of NH-alkyl substituents at C-4. This was confirmed by synthesis of alpha-[[4-(methylamino)-1-phenylpyrazolo[3,4-d]pyrimidin-6-yl]thiol] hexanamide (15) which was found to have an A1 Ki of 0.745 nM.
authors.affiliation: Queensland Pharmaceutical Research Institute, Griffith University, Brisbane, Australia.
authors.forename: S A
authors.initials: SA
authors.lastname: Poulsen
authors.forename: R J
authors.initials: RJ
authors.lastname: Quinn
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D010627:Phenethylamines / Q000378:metabolism; D010660:Phenylisopropyladenosine / Q000378:metabolism; D058915:Purinergic P1 Receptor Antagonists; D011720:Pyrazoles / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D011743:Pyrimidines / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D010627:Phenethylamines; D058915:Purinergic P1 Receptor Antagonists; D011720:Pyrazoles; D011743:Pyrimidines; C101889:alpha-((4-(methylamino)-1-phenylpyrazolo(3,4-d)pyrimidin-6-yl)thio)hexanamide; C101888:alpha-((4-amino-1-phenylpyrazolo(3,4-d)pyrimidin-6-yl)thio)hexanamide; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D010660:Phenylisopropyladenosine; D000241:Adenosine