Ibogaine and its congeners are σ2 receptor-selective ligands with moderate affinity

Abstract

Ibogaine (12-methoxyibogamine) exhibited moderate affinity for σ2 sites (Ki = 201 nM) and low affinity for σ1 sites (Ki = 8554 nM), thus showing 43-fold selectivity for σ2 receptors. Tabernanthine (13-methoxyibogamine) and (±)-ibogamine had σ2Ki = 194 nM and 137 nM, respectively. However, they showed 3- to 5-fold higher σ1 affinity compared to ibogaine, resulting in about 14-fold selectivity for σ2 sites over σ1. A potential ibogaine metabolite, O-des-methyl-ibogaine, had markedly reduced σ2 affinity relative to ibogaine (Ki = 5,226 nM) and also lacked significant affinity for σ1 sites. (±)-Coronaridine ((±)-18-carbomethoxyibogamine) and harmaline (1-methyl-7-methoxy-3,4-dihydro-β-carboline) lacked significant affinity for either σ subtype. Thus, σ2 receptors could play a role in the actions of ibogaine.