Synthesis and structure-activity relationships of 3,8-diazabicyclo[4.2.0]octane ligands, potent nicotinic acetylcholine receptor agonists

A series of potent neuronal nicotinic acetylcholine receptor (nAChR) ligands based on a 3,8-diazabicyclo[4.2.0]octane core have been synthesized and evaluated for affinity and agonist efficacy at the human high affinity nicotine recognition site (h alpha 4 beta 2) and in a rat model of persistent nociceptive pain (formalin model). Numerous analogs in this series exhibit picomolar affinity in radioligand binding assays and nanomolar agonist potency in functional assays, placing them among the most potent nAChR ligands known for the h alpha 4 beta 2 receptor. Several of the compounds reported in this study (i.e., 24, 25, 28, 30, 32, and 47) exhibit equivalent or greater affinity for the h alpha 4 beta 2 receptor relative to epibatidine, and like epibatidine, many exhibit robust analgesic efficacy in the rat formalin model of persistent pain.