Regio- and Stereoselective Ribose Modification in Truncated 2,8-Disubstituted Adenosine Scaffold to Develop Highly Potent A2A Adenosine Receptor Antagonists

Previous molecular dynamics simulations of hA_2AAR with 2b and structure-activity relationship (SAR) analyses prompted us to synthesize diol-, deoxy-, fluoro-, and methoxy-derivatives (4) in a regio- and stereoselective manner, modifying the ribose moiety to enhance potency and selectivity at hA_2AAR. SAR analysis revealed that the presence of at least one hydroxyl group at either the R² or R⁴ position is preferred for hA_2AAR binding, and inversion of the R⁴ hydroxyl group significantly reduced binding affinity at hA₃AR. Alteration of the hydroxyl groups in the ribose moiety showed that hA₃AR favored diol derivatives, and the following trend was observed at hA_2AAR: K_i,hA2A, diol ≈ deoxy < fluoro < methoxy. Among the synthesized derivatives, the deoxy derivative 4d demonstrated exceptional in vitro potency at hA_2AAR (K_i,hA2A = 0.36 ± 0.05 nM) and functional efficacy. Additionally, 4d exhibited promising pharmacokinetic properties, and in vivo efficacy assays confirmed its potential as an orally available immune checkpoint inhibitor candidate.