Synthesis of chiral 1-[omega-(4-chlorophenoxy)alkyl]-4-methylpiperidines and their biological evaluation at sigma1, sigma2, and sterol delta8-delta7 isomerase sites

Sumitomo's patented sigma ligand 1-[3-(4-chlorophenoxy)propyl]-4-methylpiperidine (15), which has been claimed as agent for CNS disorders and neuropathies, and its lower homologue 12 were prepared along with related chiral (4-chlorophenoxy)alkylpiperidines. They were tested at sigma1, sigma2, and sterol Delta8-Delta7 isomerase (SI) sites by in vitro radioligand binding assays, to evaluate the influence of a chiral center in the alkyl chain on the selective sigma(1) binding relative to other sigma family sites. Generally high sigma1-site affinities were found, so that the chirality introduced by a methyl substitution resulted in slight differences. Nevertheless, the shorter oxyethylenic chain was beneficial to increase sigma1 selectivity. However, the (-)-(S)-4-methyl-1-[2-(4-chlorophenoxy)-1-methylethyl]piperidine ((-)-(S)-17) reached the highest sigma1 affinity (K(i) = 0.34 nM) and the best selectivity relative to the sigma2 site (547-fold). Compound (-)-(S)-17 displayed also a moderate selectivity (11-fold) relative to the SI site.