Design, Synthesis, and Biological Evaluation of C2-(N-Substituted Amino) Truncated 4′-Thioadenosine Derivatives as A _2A AR and A ₃ AR Dual Ligands

Dual modulation of adenosine A_2A and A₃ receptors (ARs) is an emerging strategy for disorders involving receptor interplay. We designed and synthesized truncated 4'-thioadenosines bearing a C2-NH-R linker to enable dual A_2A/A₃ AR engagement. Structure-activity trends showed that aryl amine analogues tended to display affinity toward both A_2A and A₃ receptors, whereas aliphatic ones were inactive at both receptors. Ortho substitution in aryl amine analogues consistently enhanced binding affinity relative to meta or para substitution. Lead <b>4q</b> (σ-morpholinophenyl) exhibited high affinity for hA_2AAR and hA₃AR (<i>K</i> _i = 15.0 ± 1.2 nM; 4.5 ± 0.5 nM). Computational modeling supported orthosteric binding at both receptors, and cAMP assays revealed inverse agonism at hA_2AAR (-19%) and antagonism at hA₃AR (69% inhibition of the NECA response). These findings suggest that the C2-NH-R-modified, truncated 4'-thioadenosine as a compact scaffold for A_2A/A₃ binding and highlight <b>4q</b> as a dual ligand that may contribute to future AR ligand research.