| Abstract
| - A new, highly potent, selective, and water-solubleantagonist of the hA3 adenosine receptor was synthesized andtested in binding and functional assays. Compound 4 (5-[[(4-pyridyl)amino]carbonyl]amino-8-methyl-2-(2-furyl)-pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine hydrochloride) displayedhigh water solubility (15 mM) and the highest affinity (Ki =0.01 nM) and selectivity for the hA3 versus A1, A2A, and A2Breceptors (>10000-fold) ever reported. A Schild analysis of theantagonism by 4 of agonist-induced inhibition of cAMP production in CHO cells expressing the hA3 receptor indicated aKB value of 0.20 nM.
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