Design and synthesis of novel orexin antagonists via structural simplification of the morphinan skeleton

Herein, we report novel orexin antagonists with a spiro-type piperidine skeleton designed and synthesized via removal of the unnecessary sites of orexin 1 receptor (OX1R) antagonists with a morphinan skeleton for binding to OX1R. In addition, while decahydroisoquinoline compounds with an A-ring did not show antagonistic activity for OX1R, spiro-type piperidine compounds with a dihydroindene structure showed antagonistic activities. This suggests that the lipophilic site corresponding to the A-ring of the morphinan skeleton is important for determining the antagonistic activity toward OX1R.