Effects of linker elongation in a series of N-(2-benzofuranylmethyl)-N'-(methoxyphenylalkyl)piperazine σ₁ receptor ligands.

In our continued exploration of disubstituted piperazine derivatives as sigma (σ) receptor ligands with central nervous system (CNS) activity, a series of N-(2-benzofuranylmethyl)-N'-(methoxyphenylalkyl)piperazines (16-21 and 26-31) were synthesized, anticipating that these ligands would better suit the structural requirements of the current σ(1) pharmacophore. Affinities of these ligands for σ(1) and σ(2) receptors were investigated by means of radioligand binding assays, with the identification of N-(2-benzofuranylmethyl)-N'-[3-(4-methoxyphenyl)propyl]piperazine (29, K(i)=3.1 nM, σ(2)/σ(1)=45) as a selective σ(1) ligand. The σ(1) affinities and subtype selectivities of piperazines 16-21 and 26-31 were generally comparable to the corresponding benzylic analogs. Additionally, the affinities of 16-21 and 26-31 for the 5-HT(2B) receptor were much lower than the relatively nonselective methoxybenzylic analogs 2-4, indicating that elongation of the alkyl tether generally improved selectivity for σ(1) receptors.