Epiquinamide: A Poison That Wasn't from a Frog That Was

Article abstract of DOI:10.1021/np8005452

In 2003, we reported the isolation, structure elucidation, and pharmacology of epiquinamide (1), a novel alkaloid isolated from an Ecuadoran poison frog, Epipedobates tricolor. Since then, several groups, including ours, have undertaken synthetic efforts to produce this compound, which appeared initially to be a novel, β2-selective nicotinic acetylcholine receptor agonist. Based on prior chiral GC analysis of synthetic and natural samples, the absolute structure of this alkaloid was established as (15,9aS)-1-acetamidoquinolizidine. We have synthesized the (1.R*,9aS*)-isomer (epiepiquinamide) using an iminium ion nitroaldol reaction as the key step. We have also synthesized ent-1 semisynthetically from (-)-lupinine. Synthetic epiquinamide is inactive at nicotinic receptors, in accord with recently published reports. We have determined that the activity initially reported is due to cross-contamination from co-occurring epibatidine in the isolated material.