Development of novel phenoxyalkylpiperidines as high-affinity Sigma-1 (σ₁) receptor ligands with potent anti-amnesic...

The sigma-1 (σ₁) receptor plays a significant role in many normal physiological functions and pathological disease states, and as such represents an attractive therapeutic target for both agonists and antagonists. Here, we describe a novel series of phenoxyalkylpiperidines based on the lead compound 1-[ω-(4-chlorophenoxy)ethyl]-4-methylpiperidine (1a) in which the degree of methylation at the carbon atoms alpha to the piperidine nitrogen was systematically varied. The affinity at σ₁ and σ₂ receptors and at Δ⁸-Δ⁷ sterol isomerase (SI) ranged from subnanomolar to micromolar K_i values. While the highest-affinity was displayed at the σ₁, the increase of the degree of methylation in the piperidine ring progressively decreased the affinity. The subnanomolar affinity 1a and 1-[ω-(4-methoxyphenoxy)ethyl]-4-methylpiperidine (1b) displayed potent anti-amnesic effects associated with σ₁ receptor agonism, in two memory tests. Automated receptor-small-molecule ligand docking provided a molecular structure-based rationale for the agonistic effects of 1a and 1b. Overall, the class of the phenoxyalkylpiperidines holds potential for the development of high affinity σ₁ receptor agonists, and compound 1a, that appears as the best in class (exceeding by far the activity of the reference compound PRE-084) deserves further investigation.