(8-Naphthalen-1-ylmethyl-4-oxo-1-phenyl-1,3,8-triaza-spiro[4. 5]dec-3-yl)-acetic acid methyl ester (NNC 63-0532) is a novel potent nociceptin receptor agonist

Spiroxatrine was identified as a moderately potent (K:(i)=118 nM) but non-selective agonist at the human nociceptin/orphanin FQ receptor, ORL1. This compound was subject to chemical modification and one of the resulting compounds, (8-naphthalen-1-ylmethyl-4-oxo-1-phenyl-1,3,8-triaza-s piro[4. 5]dec-3-yl)-acetic acid methyl ester (NNC 63-0532) was shown to have high affinity for ORL1 (K:(i)=7.3 nM). NNC 63-0532 showed only moderate affinity for the following receptors (K:(i) values in parentheses): mu-opioid (140 nM), kappa-opioid (405 nM), dopamine D(2S) (209 nM), dopamine D(3) (133 nM) and dopamine D(4.4) (107 nM) out of 75 different receptors, ion-channels and transporters. In functional assays, NNC 63-0532 was shown to be an agonist at ORL1 (EC(50)=305 nM), a much weaker agonist at the mu-opioid receptor (EC(50)>10 microM) and an antagonist or weak partial agonist at dopamine D(2S) (IC(50)=2830 nM). Thus, NNC 63-0532 is a novel non-peptide agonist with approximately 12 fold selectivity for ORL1 and may be useful for exploring the physiological roles of this receptor owing to its brain-penetrating properties.