Molecular Probes for the A2A Adenosine Receptor Based on a Pyrazolo(4,3-e)(1,2,4)triazolo(1,5-c)pyrimidin-5-amine Scaffold

Abstract Pyrazolo[4,3- e ][1,2,4]triazolo[1,5- c ]pyrimidin-5-amine derivatives such as SCH 442416 display high affinity and selectivity as antagonists for the human A 2A adenosine receptor (AR). We extended ether-linked chain substituents at the p -position of the phenyl group using optimized O-alkylation. The conjugates included an ester, carboxylic acid and amines (for amide condensation), an alkyne (for click chemistry), a fluoropropyl group (for 18 F incorporation), and fluorophore reporter groups (e.g., BODIPY conjugate 14 , K i 15 nM). The potent and A 2A AR-selective N -aminoethylacetamide 7 and N -[2-(2-aminoethyl)-aminoethyl]acetamide 8 congeners were coupled to polyamidoamine (PAMAM) G3.5 dendrimers, and the multivalent conjugates displayed high A 2A AR affinity. Theoretical docking of an AlexaFluor conjugate to the receptor X-ray structure highlighted the key interactions between the heterocyclic core and the binding pocket of the A 2A AR as well as the distal anchoring of the fluorophore. In conclusion, we have synthesized a family of high affinity functionalized congeners as pharmacological probes for studying the A 2A AR.