ORL1 receptor ligands: Structure–activity relationships of 8-cycloalkyl-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-ones

We have investigated 8-cycloalkyl-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-ones as ligands for the ORL1 receptor. These unsophisticated, achiral compounds show remarkable affinity for the ORL1 receptor. Optimizing for selectivity we show that the maximum of affinity and selectivity versus the other opioid receptors is achieved for 8-cyclodecyl-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-one 2e and 8-(cis-4-isopropyl-cyclohexyl)-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-one 2q. The identified compounds (2e, 2q) are more or less equipotent to the natural ligand itself, both in the binding assay and in the functional GTPγS assay.