SAR and biological evaluation of 3-azabicyclo[3.1.0]hexane derivatives as µ opioid ligands.

3-Azabicyclo[3.1.0]hexane compounds were designed as novel achiral µ opioid receptor ligands for the treatment of pruritus in dogs. In this paper, we describe the SAR of this class of opioid ligand, highlighting changes to the lead structure which led to compounds having picomolar binding affinity, selective for the µ receptor over δ and κ subtypes. Some subtleties of functional activity will also be described.