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 hA2AAR 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 hA2AAR. SAR analysis revealed that the presence of at least one hydroxyl group at either the R2 or R4 position is preferred for hA2AAR 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 hA2AAR: Ki,hA2A, diol ≈ deoxy 4d demonstrated exceptional in vitro potency at hA2AAR (Ki,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.