Identification of potent, selective, CNS-targeted inverse agonists of the ghrelin receptor

The optimization for selectivity and central receptor occupancy for a series of spirocyclic azetidine–piperidine inverse agonists of the ghrelin receptor is described. Decreased mAChR muscarinic M2 binding was achieved by use of a chiral indane in place of a substituted benzylic group. Compounds with desirable balance of human in vitro clearance and ex vivo central receptor occupancy were discovered by incorporation of heterocycles. Specifically, heteroaryl rings with nitrogen(s) vicinal to the indane linkage provided the most attractive overall properties.