N6-substituted C5′-modified adenosines as A1 adenosine receptor agonists

Adenosines bearing 5'-modification in conjunction with an N-6-substituent have previously been shown to act as partial agonists at the A(1) adenosine receptor. Our current work investigates the effect of modifying the 5'-position in conjunction with efficacious bicyclic and tricyclic N-6-substituents. Several highly potent agonists for the A(1) adenosine receptor were identified; however, all of these compounds behaved as full agonists. In keeping with previous reports, 5'-halogen and 5'-sulfide derivatives of N-6-(endo-norborn-2-yl) adenosine were, in general, low nanomolar agonists of the A(1) adenosine receptor. The known partial agonist, N-6-cyclopentyl-5'-deoxy-5'-ethylthioadenosine (2), also behaved as a full agonist in our assay. (C) 2007 Elsevier Ltd. All rights reserved.