5‘-<i>O</i>-Alkyl Ethers of<i> N</i>,2-Substituted Adenosine Derivatives: Partial Agonists for the Adenosine A<sub>1</sub> and A<sub>3</sub> Receptors
作者:Erica W. van Tilburg、Pieter A. M. van der Klein、Jacobien von Frijtag Drabbe Künzel、Miriam de Groote、Christina Stannek、Anna Lorenzen、Ad P. IJzerman
DOI:10.1021/jm001114o
日期:2001.8.1
New N,5'-di- and N,2,5'-trisubstituted adenosine derivatives were synthesized in good overall yields. Appropriate 5-O-alkyl-substituted ribose moieties were coupled to 6-chloropurine or 2,6-dichloropurine via Vorbruggen's glycosylation method. Subsequent amination and deprotection of the intermediates yielded compounds 18-35. Binding affinities were determined for rat adenosine A(1) and A(2A) receptors and the human A(3) receptor. The ability of compounds 18-35 to inhibit forskolin-induced (10 muM) cyclic AMP (cAMP) production and their ability to stimulate guanosine 5'-O-(3-[S-35]thio)triphosphate ([S-35]GTP gammaS) binding, via either the adenosine A(1) receptor or the adenosine A(3) receptor, were assessed. N-Cyclopentyl-substituted adenosine derivatives displayed affinities in the low nanomolar range for the adenosine A(1) receptor, whereas N-(3-iodobenzyl)-substituted derivatives had high affinity for the adenosine A(3) receptor. Compound 22 had the highest affinity for the adenosine A(3) receptor (K-i value of 16 nM), and compounds 20 and 26 had the highest affinities for the adenosine A(3) receptor (K-i values of 4 and 3 nM, respectively). A chlorine substituent at the 2-position either did not affect or slightly increased the adenosine A(3) receptor affinity, whereas the A(3) receptor affinity was affected differently, depending on the N-substituent. Furthermore, the introduction of chlorine slightly increased the A(3)/A(1) selectivity ratio. At the 5 ' -position, an O-methyl substituent induced the highest adenosine A(1) receptor affinity, whereas an O-ethyl substituent did so for the A(3) receptor. All compounds showed partial agonistic effects in both the cAMP and [S-35]GTP gammaS assays, although more marked in the latter assay. In general, the 2-chloro derivatives seemed to have lower intrinsic activities compared to the 2-H-substituted compounds on both the adenosine A(1) and the adenosine A(3) receptors. The compounds with an N-(3-iodobenzyl) substituent displayed the lowest intrinsic activities. Finally, all compounds also showed partially antagonistic behavior in the [S-35]GTP gammaS assay.