Opioid Peptide-Derived Delta Antagonists, Inverse Agonists, and Mixed Mu Agonists/Delta Antagonists

Delta (y) opioid antagonists are of interest as both pharmacological tools and potential therapeutic agents. Obviously, they are required as essential tools in the elucidation of y-opioid receptor mediated in vitro and in vivo effects. Recently, several compounds originally characterized as y-opioid antagonists have been identified as inverse y-agonists. High-affinity inverse y-agonists with high y-selectivity are needed to investigate the spontaneous activity of yopioid receptors in vitro and in vivo.