Isolation and characterization of erythramide from Hyperbaena prioriana: Nicotinic receptor pharmacology of erythramide and erythroculines

In the course of our studies aimed at the isolation of novel nicotinic acetylcholine receptor ligands from natural sources, we recently examined two species of Hyperbaena (Menispermaceae, moonseed family). We have isolated erythramide (1) as the major lipophilic alkaloid from Hyperbaena prioriana (Miers) and found it to bind nicotinic receptors in brain with high affinity using [³H]-epibatidine binding. The identity of the alkaloid was confirmed by 1D and 2D NMR and GC-MS. In 2006, we reported the isolation of two erythroculine derivatives, 2 and 3, from Hyperbaena valida (Miers) and identified them as nicotinic receptor ligands, similar to other erythrina alkaloids, such as dihydro-β-erythroidine (DHβE), a well-known nicotinic antagonist with selectivity for β2 containing receptors. We describe herein the detailed nicotinic receptor pharmacology of 1 and compare it to that of 2, 3, and DHβE.