N6-Cyclopentyladenosine (CPA) is a potent and selective adenosine A1 receptor agonist, with Ki values of 2.3 nM (A1), 790 nM (A2A), and 43 nM (A3). It is widely used in research to study A1 receptor-mediated signaling, neurotransmission, and cardioprotective effects in both cellular and animal models.