Synthesis, enantiomeric separation and docking studies of spiropiperidine analogues as ligands of the nociceptin/orphanin FQ receptor

A series of triazospirodecanone derivatives were synthesized as potential NOP ligands. 8-(Chroman-4-yl)-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (4) and its 5-fluoro analogue (18) proved to be active as agonists with EC50 values in the submicromolar range. Single enantiomers of compound 4 were separated and tested as NOP agonists; the eutomer R-(+)-4 showed a pEC50 of 7.34. Finally docking studies were performed on the NOP receptor to identify the most significant stereospecific interactions.