Exploring the Role of N-Substituents in Potent Dual Acting 5'-C-Ethyltetrazolyladenosine Derivatives: Synthesis, Binding, Functional Assays, and Antinociceptive Effects in Mice ∇.

Structural determinants of affinity of N-substituted-5'-C-(ethyltetrazol-2-yl)adenosine and 2-chloroadenosine derivatives at adenosine receptor (AR) subtypes were studied with binding and molecular modeling. Small N-cycloalkyl and 3-halobenzyl groups furnished potent dual acting AAR agonists and AAR antagonists. 4 was the most potent dual acting human (h) AAR agonist (K = 0.45 nM) and AAR antagonist (K = 0.31 nM) and highly selective versus A; 11 and 26 were most potent at both h and rat (r) AAR. All N-substituted-5'-C-(ethyltetrazol-2-yl)adenosine derivatives proved to be antagonists at hAAR but agonists at the rAAR. Analgesia of 11, 22, and 26 was evaluated in the mouse formalin test (AAR antagonist blocked and AAR agonist strongly potentiated). N-Methyl-5'-C-(ethyltetrazol-2-yl)adenosine (22) was most potent, inhibiting both phases, as observed combining AAR and AAR agonists. This study demonstrated for the first time the advantages of a single molecule activating two AR pathways both leading to benefit in this acute pain model.