A series of novel 4-phenylpiperidinyl and (4-phenylpiperazinyl)alkyl 1-phenylcyclopentanecarboxylates was synthesized and evaluated for affinity at σ1 and σ2 sites by inhibition of [3H]-(+)-pentazocine (PENT) and [3H]-1,3-di(2-tolyl)guanidine (DTG) binding in guinea pig brain. The phenylpiperidines were more potent σ ligands than the corresponding piperazines. Structural modifications varying the optimal spatial distance between the piperidine nitrogen and ester functions led to the identification of the propyl compound 24 ([3H]PENT Ki = 0.50 nM; [3H]DTG Ki = 1.17 nM) and the butyl derivative 32 ([3H]PENT Ki = 0.51 nM; [3H]DTG Ki = 0.69 nM) as novel high-affinity σ-selective agents. An ethylene spacer was optimum with para-substituted analogs. A notable finding was the discovery of 2-(4-phenylpiperidinyl)ethyl 1-(4-nitrophenyl)-cyclopentanecarboxylate hydrochloride (15) (RLH-033), which demonstrated potent affinity for the [3H]PENT-defined σ site with a Ki of 50 pM, selectivity for σ1 over muscarinic M1 (> 17 600-fold), M2 (> 34 200-fold), dopamine D1 (> 58 000-fold), and D2 (> 7000-fold) receptors, and inactivity at phencyclidine, NMDA, and opioid receptors. RLH-033 is a valuable tool which will aid further in understanding the biology of the σ recognition site. Information from this research has further defined the topography of the σ recognition site, which may provide an explanation for the diverse structures which bind with relatively high affinity.
All Science Journal Classification (ASJC) codes
- Molecular Medicine
- Drug Discovery