Extended N6 substitution of rigid C2-arylethynyl nucleosides for exploring the role of extracellular loops in ligand recognition at the A3 adenosine receptor

Abstract

2-Arylethynyl-(N)-methanocarba adenosine 5′-methyluronamides containing rigid N6-(trans-2-phenylcyclopropyl) and 2-phenylethynyl groups were synthesized as agonists for probing structural features of the A3 adenosine receptor (AR). Radioligand binding confirmed A3AR selectivity and N6-1S,2R stereoselectivity for one diastereomeric pair. The environment of receptor-bound, conformationally constrained N6 groups was explored by docking to an A3AR homology model, indicating specific hydrophobic interactions with the second extracellular loop able to modulate the affinity profile. 2-Pyridylethynyl derivative 18 was administered orally in mice to reduce chronic neuropathic pain in the chronic constriction injury model.

Structure-Based Scaffold Repurposing for G Protein-Coupled Receptors: Transformation of Adenosine Derivatives into 5HT2B/5HT2C Serotonin Receptor Antagonists

“…Concerning the activity at the hA 1 and hA 3 ARs exhibited by 5′-methylamide derivatives, we expect binding modes similar to the previously discussed poses of (N)-methanocarba adenosines 21,33 envisaging the placement of the scaffold perpendicular to the membrane plane with the pseudo-sugar pointing toward the intracellular side. In this binding mode, the C2′ and C3′ OH groups interact with the sidechains of the conserved His 7.43 and Ser 7.42 , respectively, and the NH group of the 5′-methylamide engages in an H-bond interaction with Thr 3.36 .…”

Chronic Morphine-Induced Changes in Signaling at the A3Adenosine Receptor Contribute to Morphine-Induced Hyperalgesia, Tolerance, and Withdrawal

“…Figure 1), we have achieved >1000-fold receptor subtype selectivity for A3AR over other adenosine receptor. The selectivity for A3AR of these second generation A3AR agonists greatly exceeds the selectivity of IB-MECA and Cl-IB-MECA, which display 50-to 250-fold selectivity over the other three receptor subtypes in rodents (Tosh et al, 2014;Tosh et al, 2015). MRS5698…”

Repurposing of a Nucleoside Scaffold from Adenosine Receptor Agonists to Opioid Receptor Antagonists

“… d K i (μM), inhibition of binding of [ 3 H] 104 at NET: 50 , 8.66; 51 , 2.8. 6 e A 3 AR binding data from Tosh et al 3 , 34 , 35 Representative binding inhibition at hA 1 AR is (% at 10 μM) 49 , 18%; 50 , 36%; 51 , 30%; representative binding inhibition at hA 2A AR is (% at 10 μM, or K i ) 47 , 670 nM; 49 , 18%; 50 , 42%; 51 , 22%; determined as reported. 37 Values are expressed as the mean ± SEM of N = 3 assays performed in duplicate.…”

“…Values are expressed as the mean ± SEM of N = 2–4 assays performed in duplicate. c A 3 AR binding data from Tosh et al 2 , 3 , 6 , 34 , 35 , 37 Representative binding K i values at hA 1 AR (nM): 55 , 1300 ± 290; 56 , 650 ± 71; determined as reported. 37 Values are expressed as the mean ± SEM of N = 3 assays performed in duplicate.…”