7-Azabicyclo[2.2.1]heptane as a scaffold for the development of selective sigma-2 (σ2) receptor ligands

A series of N-substituted 7-azabicyclo[2.2.1]heptanes (12-17 and 22-25) and similarly substituted pyrrolidines (32-36 and 41-44) were synthesized as sterically-reduced, achiral analogs of adamantane- and trishomocubane-derived σ ligands. In vitro competition binding assays against σ receptors revealed that arylalkyl N-substituents conferred selectivity for the σ2 subtype, while alicyclic or polycarbocyclic substituents imparted high affinity for both subtypes. The σ2 binding and subtype selectivities of N-arylalkyl-7-azanorbornanes was generally greater than the analogously-substituted pyrrolidines, indicating that steric bulk and conformational restriction around the nitrogen atom are likely important for subtype discrimination.