title: Xanthine functionalized congeners as potent ligands at A2-adenosine receptors.
abstract: Amide derivatives of a carboxylic acid congener of 1,3-dialkylxanthine, having a 4-[(carboxymethyl)oxy]phenyl substituent at the 8-position, have been synthesized in order to identify potent antagonists at A2-adenosine receptors stimulatory to adenylate cyclase in platelets. Distal structural features of amide-linked chains and the size of the 1,3-dialkyl groups have been varied. 1,3-Diethyl groups, more than 1,3-dimethyl or 1,3-dipropyl groups, favor A2 potency, even in the presence of extended chains attached at the 8-(p-substituted-phenyl) position. Polar groups, such as amines, on the chain simultaneously enhance water solubility and A2 potency. Among the most potent A2 ligands are an amine congener, 8-[4-[[[[(2-aminoethyl)amino]carbonyl]methyl]oxy]phenyl]- 1,3-diethylxanthine, and its D-lysyl conjugate, which have KB values of 21 and 23 nM, respectively, for the antagonism of N-ethyl-adenosine-5'-uronamide-stimulated adenylate cyclase activity in human platelet membranes. Strategies for the selection and tritiation of new radioligands for use in competitive binding assays at A2-adenosine receptors have been considered.
mesh_terms: D000262:Adenylyl Cyclases / Q000097:blood; D001792:Blood Platelets / Q000378:metabolism; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D011983:Receptors, Purinergic / Q000187:drug effects* / Q000378:metabolism; D013329:Structure-Activity Relationship; D014970:Xanthines / Q000138:chemical synthesis* / Q000378:metabolism
chemical_list: D011983:Receptors, Purinergic; D014970:Xanthines; D000262:Adenylyl Cyclases