Identification of RC-33 as a potent and selective σ1 receptor agonist potentiating NGF-induced neurite outgrowth in PC12 cells. Part 2: g-Scale synthesis, physicochemical characterization and in vitro metabolic stability

Strong pharmacological evidences indicate that sigma 1 receptors are implicated in the pathophysiology of all major CNS disorders. In the last years our research group has conducted extensive studies aimed at discovering novel sigma 1 ligands and we recently selected (R/S)-RC-33 as a novel potent and selective sigma 1 receptor agonist. As continuation of our work in this field, here we report our efforts in the development of this new sigma 1 receptor agonist. Initially, we investigated the binding of (R) and (S) enantiomers of RC-33 to the sigma 1 receptor by in silico experiments. The close values of the predicted affinity of (R)-RC-33 and (S)-RC-33 for the protein evidenced the non-stereoselective binding of RC-33 to the sigma 1 receptor; this, in turn, supported further development and characterization of RC-33 in its racemic form. Subsequently, we set-up a scaled-up, optimized synthesis of (R/S)-RC-33 along with some compound characterization data (e. g., solubility in different media and solid state characterization by thermal analysis techniques). Finally, metabolic studies of RC-33 in different biological matrices (e. g., plasma, blood, and hepatic S9 fraction) of different species (e. g., rat, mouse, dog, and human) were performed. (R/S)-RC-33 is generally stable in all examined biological matrices, with the only exception of rat and human liver S9 fractions in the presence of NADPH. In such conditions, the compound is subjected to a relevant oxidative metabolism, with a degradation of approximately 65% in rat and 69% in human. Taken together, our results demonstrated that (R/S)-RC-33 is a highly potent, selective, metabolically stable sigma 1 agonist, a promising novel neuroprotective drug candidate. (C) 2013 Elsevier Ltd. All rights reserved.