2-(2-Piperidyl)- and 2-(2-Pyrrolidyl)chromans as Nicotine Agonists:  Synthesis and Preliminary Pharmacological Characterization

As part of an effort to develop a new class of subtype selective nicotine agonists, we have synthesized and tested a group of 12 hydroxylated 2-(2-piperidyl)- and 2-(2-pyrrolidyl)chromans. In rat brain membranes, all 12 compounds displayed poor affinity for [125I]-α-bunagarotoxin binding sites. In contrast, three compounds, 17c, 24, and 26, displayed moderate to high affinity for [3H]cytisine binding sites, while three (17b, 18b,c) and six (17a,d,e and 18a,d,e) compounds showed weak and poor affinity, respectively, for these same sites. In subsequent studies, compounds 17a and 17c were found to stimulate the efflux of 86Rb+ from rat cortical synaptosomes, an indication of agonist activity. Further, both 17c and 26 displayed high intrinsic activity in stimulating the release of [3H]dopamine from striatal synaptosomes; however, only 17c was effective at stimulating the release of [3H]acetylcholine from cortical synaptosomes, suggesting differential selectivity. In cloned human nicotinic acetylcholine receptors (nAChR) expressed in Xenopus oocytes, both 17c and 26 activated α7 and α3β2 receptor subtypes in a dose-dependent manner, but 26 was clearly the more potent agonist. Last, neither compound displayed dose-dependent activation of α4β2 nAChRs. We conclude that 2-(2-azacyclic)chromans appear to be a promising new class of nicotine agonists.