In response to adenosine 5′-diphosphate, the P2Y1 receptor (P2Y1R) facilitates platelet aggregation, and thus serves as an important antithrombotic drug target. Here we report the crystal structures of the human P2Y1R in complex with a nucleotide antagonist MRS2500 at 2.7Å resolution, and with a non-nucleotide antagonist BPTU at 2.2Å resolution. The structures reveal two distinct ligand binding sites, providing atomic details of P2Y1R’s unique ligand binding modes. MRS2500 recognizes a binding site within the seven transmembrane bundle of P2Y1R, which, however, is different in shape and location from the nucleotide binding site in previously determined P2Y12R structure. BPTU binds to an allosteric pocket on the external receptor interface with the lipid bilayer, making it the first structurally characterized selective G protein-coupled receptor (GPCR) ligand located entirely outside of the helical bundle. These high-resolution insights into P2Y1R should enable discovery of new orthosteric and allosteric antithrombotic drugs with reduced adverse effects.

Adenosine derivatives developed to activate adenosine receptors (ARs) revealed µM activity at serotonin 5HT2B and 5HT2C receptors (5HTRs). We explored the SAR at 5HT2Rs and modeled receptor interactions in order to optimize affinity and simultaneously reduce AR affinity. Depending on N6 substitution, small 5′-alkylamide modification maintained 5HT2BR affinity, which was enhanced upon ribose substitution with rigid bicyclo[3.1.0]hexane (North (N)-methanocarba), e.g. N6-dicyclopropylmethyl 4′-CH2OH derivative 14 (Ki 11 nM). 5′-Methylamide 23 was 170-fold selective as antagonist for 5HT2BR vs. 5HT2CR. 5′-Methyl 25 and ethyl 26 esters potently antagonized 5HT2Rs with moderate selectivity in comparison to ARs; related 6-N,N-dimethylamino analogue 30 was 5HT2R-selective. 5′ position flexibility of substitution was indicated in 5HT2BR docking. Both 5′-ester and 5′-amide derivatives displayed in vivo t1/2 of 3–4 h. Thus, we used GPCR modeling to repurpose nucleoside scaffolds in favor of binding at nonpurine receptors, as novel 5HT2R antagonists, with potential for cardioprotection, liver protection or CNS activity.

Substitution of rigidified A 3 adenosine receptor (AR) agonists with a 2-((5-chlorothiophen-2-yl)ethynyl) or a 2-(4-(5-chlorothiophen-2-yl)-1H-1,2,3-triazol-1-yl) group provides prolonged protection in a model of chronic neuropathic pain. These agonists contain a bicyclo[3.1.0]hexane ((N)-methanocarba) ring system in place of ribose, which adopts a receptor-preferred conformation. N 6 -Small alkyl derivatives were newly optimized for A 3 AR affinity and the effects of a 1-deaza-adenine modification probed. 1-Deaza-N 6 -ethyl alkyne 20 (MRS7144, K i 1.7 nM) and 1-aza N 6 -propyl alkyne 12 (MRS7154, K i 1.1 nM) were highly efficacious in vivo. Thus, the presence of N1 is not required for nanomolar binding affinity or potent, long-lasting functional activity. Docking of 1-deaza compounds to a receptor homology model confirmed a similar binding mode as previously reported 1-aza derivatives. This is the first demonstration in nonribose adenosine analogues that the 1-deaza modification can maintain high A 3 AR affinity, selectivity, and efficacy.