Discovery and Structure-Activity Relationship Studies of Novel Adenosine A1 Receptor-Selective Agonists

A series of benzyloxy and phenoxy derivatives of the adenosine receptor agonists N6-cyclopentyl adenosine (CPA) and N6-cyclopentyl 5 '-N-ethylcarboxamidoadenosine (CP-NECA) were synthesized, and their potency and selectivity were assessed. We observed that the most potent were the compounds with a halogen in the meta position on the aromatic ring of the benzyloxy-or phenoxycyclopentyl substituent. In general, the NECA-based compounds displayed greater A1R selectivity than the adenosine-based compounds, with N6-2-(3-bromobenzyloxy)cyclopentyl-NECA and N6-2-(3-methoxyphenoxy)cyclopentyl-NECA showing similar to 1500-fold improved A1R selectivity compared to NECA. In addition, we quantified the compounds' affinity and kinetics of binding at both human and rat A1R using a NanoBRET binding assay and found that the halogen substituent in the benzyloxy-or phenoxycyclopentyl moiety seems to confer high affinity for the A1R. Molecular modeling studies suggested a hydrophobic subpocket as contributing to the A1R selectivity displayed. We believe that the identified selective potent A1R agonists are valuable tool compounds for adenosine receptor research.

Automated summary

A series of benzyloxy and phenoxy derivatives of adenosine receptor agonists were synthesized, and their potency and selectivity were evaluated. The compounds with a halogen substituent in the meta position showed the highest potency. NECA-based compounds demonstrated greater A1R selectivity compared to adenosine-based compounds, with certain compounds exhibiting significantly improved selectivity. The presence of a halogen substituent in the benzyloxy or phenoxy group seemed to contribute to high affinity for A1R. Molecular modeling studies suggested the involvement of a hydrophobic subpocket in the observed A1R selectivity.