A multireceptorial binding reinvestigation on an extended class of σ ligands: N-[ω-(indan-1-yl and tetralin-1-yl)alkyl] derivatives of 3,3-dimethylpiperidine reveal high affinities towards σ1 and EBP sites Original Research Article

New 1-[ω-(2,3-dihydro-1H-inden-1-yl)- and (2,3-dihydro-5-methoxy-1H-inden-1-yl)alkyl]- and 1-[ω-(1,2,3,4-tetrahydronaphthalen-1-yl)- and (6-methoxy- or 6-fluoro-1,2,3,4-tetrahydronaphthalen-1-yl)alkyl] derivatives of 3,3-dimethylpiperidine were synthesized, as homologous compounds of an existing series of σ ligands, in order to carry out σ receptor subtypes structure–affinity relationships. The new compounds and some of their related analogues, already reported, were tested in new multireceptorial radioligand binding assays. As reference compounds, the known σ1 ligands SA 4503, BD 1008 and NE 100 were also prepared and tested. All reported compounds showed high σ1 affinity assayed by (+)-[3H]-pentazocine on guinea-pig brain (apparent Ki=1.75–72.2 nM) and moderate or low σ2 affinity by [3H]-DTG on rat liver, in contrast with previous results. One tertiary amine function spaced by a five-membered chain from a phenyl group is the structural feature shared by the most active compounds 26 and 43 and some reference σ1 ligands. The reported σ1 ligands, including reference compounds, also demonstrated a high affinity towards EBP (Δ8–Δ7 sterol isomerase) site (apparent Ki=0.48–14.8 nM) and some of them (37 and 44) were good ligands at L-type Ca++ channel. 1-[4-(2,3-Dihydro-1H-inden-1-yl)butyl]-3,3-dimethylpiperidine (26) was the best mixed σ1 and EBP ligand (apparent Ki=1.75 and 1.54 nM, respectively) with a good selectivity versus σ2 receptor (138- and 157-fold, respectively).