EST64454: a Highly Soluble σ Receptor Antagonist Clinical Candidate for Pain Management.

The synthesis and pharmacological activity of a new series of pyrazoles that led to the identification of 1-(4-(2-((1-(3,4-difluorophenyl)-1-pyrazol-3-yl)methoxy)ethyl)piperazin-1-yl)ethanone (, EST64454) as a σ receptor (σR) antagonist clinical candidate for the treatment of pain are reported. The compound is easily obtained through a five-step synthesis suitable for the production scale and shows an outstanding aqueous solubility, which together with its high permeability in Caco-2 cells will allow its classification as a BCS class I compound. It also shows high metabolic stability in all species, linked to an adequate pharmacokinetic profile in rodents, and antinociceptive properties in the capsaicin and partial sciatic nerve ligation models in mice.