- 2,5′-disubstituted adenosine derivatives: Evaluation of selectivity and efficacy for the adenosine A1, A2A, and A3 receptor
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Novel 2,5′-disubstituted adenosine derivatives were synthesized in good overall yields starting from commercially available guanosine. Binding affinities were determined for rat adenosine A1 and A2A receptors and human A3 receptors. Emax values were determined for the stimulation or inhibition of cAMP production in CHO Cells expressing human adenosine A2A (EC50 values as well) or A3 receptors, respectively. The compounds displayed affinities in the nanomolar range for both the adenosine A2A and A3 receptor, without substantial preference for either receptor. The derivatives with a 2-(1-hexynyl) group had the highest affinities for both receptors; compound 4 (2-(1-hexynyl)adenosine) had the highest affinity for the adenosine A2A receptor with a Ki value of 6 nM (A3/A2A selectivity ratio of approximately 3), whereas compound 37 (2-(1-hexynyl)-5′-S-methyl-5′-thioadenosine) had the highest affinity for the adenosine A3 receptor with a Ki value of 15 nM (A2A/A3 selectivity ratio of 4). In general, compounds with a relatively small 5′-S-alkyl-5′-thio substituent (methyl-5′-thio) displayed the highest affinities for both the adenosine A2A and A3 receptor; the larger ones (n- or i-propyl-5′-thio) increased the selectivity for the adenosine A3 receptor. The novel compounds were also evaluated in cAMP assays for their (partial) agonistic behavior. Overall, the disubstituted derivatives behaved as partial agonists for both the adenosine A2A and A3 receptor. The compounds showed somewhat higher intrinsic activities on the adenosine A2A receptor than on the A3 receptor. Compounds 37, 40 and 45, 48, with either a 5′-S-methyl-5′-thio or a 5′-S-i-propyl-5′-thio substituent had the lowest intrinsic activities on the adenosine A2A receptor. For the A3 receptor, compounds 34, 35, 38, 39, and 46, 47, with a 5′-S-ethyl-5′-thio or a 5′-S-n-propyl-5′-thio substituent had the lowest intrinsic activities.
- Van Tilburg, Erica W.,Von Frijtag Drabbe Künzel, Jacobien,De Groote, Miriam,IJzerman, Ad P.
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p. 420 - 429
(2007/10/03)
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