Exploration of ring size in a series of cyclic vicinal diamines with σ1 receptor affinity

Imidazolidine and 1,4-diazepane analogs of N-(2-benzofuranyl)methyl-N′-(4-alkoxybenzyl)piperazines were prepared to explore the effect of ring contraction and expansion on σ receptor affinity and subtype selectivity within a series of cyclic diamines. In vitro receptor binding assays revealed that all cyclic vicinal diamines possessed affinity and selectivity for σ1 receptors. The imidazolidines possessed nanomolar σ1 affinities (Ki = 6.45-53.5 nM), and relatively low levels of subtype selectivity (σ2/σ1 = 58-237). However, the piperazines and diazepanes achieved picomolar σ1 interactions, with Ki ranges of 0.05-10.28 and 0.10-0.194 nM, respectively. Moreover, the piperazines and diazepanes showed excellent discrimination over the σ2 receptor, with σ1 selectivities of 143-16140 and 220-11542, respectively.