Activity of N6-substituted 2-chloroadenosines at A1 and A2 adenosine receptors.

Radioligand binding studies of N6-substituted adenosines at the A1 and A2 adenosine receptors of rat brain cortex and rat brain striatum, respectively, show that a 2-chloro substituent does not consistently change the affinity or the selectivity of these analogues for the A1 receptor. A 2-chloro substituent lowers the characteristic stereoselectivity of the A1 receptor toward the R diastereomer of N6-(1-phenyl-2-propyl)adenosine. A 2-chloro substituent consistently increases potency of N6-substituted adenosines as agonists at an adenosine A2 receptor stimulatory to adenylate cyclase in PC12 cell membranes.