<i>N</i>-Cycloalkyl Derivatives of Adenosine and 1-Deazaadenosine as Agonists and Partial Agonists of the A<sub>1</sub> Adenosine Receptor
作者:Sauro Vittori、Anna Lorenzen、Christina Stannek、Stefano Costanzi、Rosaria Volpini、Adriaan P. IJzerman、Jakobien K. Von Frijtag Drabbe Kunzel、Gloria Cristalli
DOI:10.1021/jm9911231
日期:2000.1.1
A number of cycloalkyl substituents (from C-3 to C-8) have been int-reduced on the 6-amino group of adenosine, 1-deazaadenosine, and 2'-deoxyadenosine, bearing or not a chlorine atom at the 2-position, to evaluate the influence on the A(1) and A(2A) affinity of steric hindrance and lipophilicity. Furthermore, the guanosine 5'-triphosphate (GTP) shift and the maximal induction of guanosine 5'-(gamma-thio)triphosphate ([S-35]GTP gamma S) binding to G proteins in rat brain membranes were used to determine the intrinsic activity of these nucleosides at the A(1) adenosine receptor. All compounds of the ribose-bearing series proved to be full agonists, the 1-deaza derivatives showing affinities for the Al receptor about 10-fold lower than the corresponding adenosines. On the other hand, all the 2'-deoxyribose derivatives bind to the A(1) receptor with affinities in the high nanomolar range, with the 2-chloro substituted compounds showing slightly higher affinities than the 2-unsubstituted counterparts. In terms of the potencies, the most potent compounds proved to be those bearing four- and five-membered rings. Both GTP shifts and [S-35]-GTP gamma S experiments showed that most of the 2'-deoxyadenosine derivatives are partial agonists, The 2'-deoxyadenosine derivatives which were identified as partial agonists consistently detected fewer Az receptors in the high-affinity state than full agonists. However, it is worthwhile noting that there was not a simple Linear relationship between receptor occupancy and activation. These results indicate that a critical density of A(1) adenosine receptors in the high-affinity state is required for G protein activation.