Novel Synthesis and Pharmacological Characterization of NOP Receptor Agonist 8-[(1<i>S</i>,3a<i>S</i>)-2,3,3a,4,5,6-Hexahydro-1<i>H</i>-phenalen-1-yl]-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (Ro 64-6198)

The nociceptin/orphanin FQ opioid peptide (NOP) receptor is a widely expressed GPCR involved in the modulation of pain, anxiety, and motor behaviors. Dissecting the functional properties of this receptor is limited by the lack of systemically active ligands that are brain permeant. The small molecule NOP receptor-selective, full agonist 8-[(1<i>S</i>,3a<i>S</i>)-2,3,3a,4,5,6-hexahydro-1<i>H</i>-phenalen-1-yl]-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (Ro 64-6198) hydrochloride is an active, brain penetrant ligand, but its difficult and cost-prohibitive synthesis limits its widespread use and availability for animal studies. Here, we detail a more efficient and convenient method of synthesis, and use both in vitro and in vivo pharmacological assays to fully characterize this ligand. Specifically, we characterize the pharmacodynamics of Ro 64-6198 in cAMP and G-protein coupling in vitro and examine, for the first time, the effects of nociceptin/orphanin FQ and Ro 64-6198 in arrestin recruitment assays. Further, we examine the effects of Ro 64-6198 on analgesia, anxiety, and locomotor responses in vivo. This new synthesis and pharmacological characterization provide additional insights into the useful, systemically active, NOP receptor agonist Ro 64-6198