Covalent and Visible‐Light Photoswitchable Derivatives of the Potent Synthetic Opioid Isotonitazene and Other Nitazenes

Isotonitazene belongs to a potent class of m-opioid receptor (µOR) ligands, known as nitazenes. The lack of knowledge surrounding this agonist and others in its class has sparked thorough re-investigations. To aid in these investigations, the purportedly covalent yet underexplored nitazene BIT was biochemically re-evaluated in this work, along with a newly synthesized analogue, Iso-BIT. Moreover, in the pursuit of understanding the mechanism, function, and interactions of µOR, this study involved developing photoswitchable derivatives of nitazene as potential probe molecules. Converting known ligands into azo-containing photoswitchable derivatives offers the opportunity to modulate ligand structure with light, allowing for photocontrol of compound activity. While photocontrol of µOR activity could not be entirely achieved, photophysical evaluation of these arylazobenzimidazole derivatives revealed a novel photoswitch scaffold that responds to visible light. Furthermore, azo-containing 2e and 3e emerged as promising nitazene derivatives that were able to form an exceptionally high fraction of covalent-ligand receptor complexes with wild-type µOR at physiological pH.