Design, synthesis and biological evaluation of 2-hydrazinyladenosine derivatives as A_2A adenosine receptor ligands

To obtain potential A_2A adenosine receptor agonists, a series of 2-hydrazinyladenosine derivatives were synthesized and assayed for adenosine receptors activity using radioligand binding activity assays. The binding activity of the subtypes was examined, and the structure-activity relationship of this class of compounds at the A_2A receptor was investigated. A fragment-based computer-aided design method was used to modify the 2-position side chain structures with different structural fragments, and the newly generated molecules were docked to the A_2A receptor to assess scoring and screening activity. To synthesize compounds with better scoring activity, the newly synthesized compounds were tested for in vitro receptor binding activity. 2-Hydrazinyladenosine derivatives of 32 new structural types were designed and synthesized, with the most potent adenosine derivative 23 exhibiting a K_i value of 1.8 nM for A_2AAR and significant selectivity for the A_2A receptor compared to the A₁ receptor. In addition to, compound 23, 24, 30, 31, and 42 also exhibited potent A_2A receptor selectivity, with Ki values for the A_2A receptor of 6.4, 20, 67 and 6.3 nM, respectively. We also found that compound 35 has a high A₁ receptor selectivity, with a K_i value for the A₁ receptor of 4.5 nM. Further functional assays also demonstrated that these compounds have potent A_2A receptor agonist activity. The study shows the applicability of an in silico fragment-based molecular design for rational lead optimization in A_2AAR.