Development of 4-Heteroarylamino-1'-azaspiro[oxazole-5,3'-bicyclo[2.2.2]octanes] as α7 Nicotinic Receptor Agonists.

We describe the synthesis of quinuclidine-containing spiroimidates and their utility as α7 nicotinic acetylcholine receptor (nAChR) partial agonists. A convergent synthetic route allowed for rapid SAR investigation and provided a diverse set of fused 6,5-heteroaryl analogs. Two potent and selective α7 nAChR partial agonists, (1' S ,3' R ,4' S )- N -(7-bromopyrrolo[2,1- f ][1,2,4]triazin-4-yl)-4H-1'-azaspiro[oxazole-5,3'-bicyclo[2.2.2]octan]-2-amine ( 20 ) and (1' S ,3' R ,4' S )- N -(7-chloropyrrolo[2,1- f ][1,2,4]triazin-4-yl)-4H-1'-azaspiro[oxazole-5,3'-bicyclo[2.2.2]octan]-2-amine ( 21 ), were identified. Both agonists improved cognition in a preclinical rodent model of learning and memory. Additionally, 5-HT3A receptor SAR suggested the presence of a steric site that when engaged led to significant loss of affinity at that receptor.