SNC 80 and Related δ Opioid Agonists

The discovery of the selective delta (δ) opioid agonists SNC 80 and BW373U86, which possess a diarylmethylpiperazine structure unique among opioids, was a major advance in the field of δ-opioid ligands. Much research has been performed to uncover the structure-activity relationships (SAR) of this class of ligands and also to compare the diarylmethylpiperazines with the traditional morphinan-based d opioids. This review focuses on the development of the SAR of this unique series of ligands, and discusses questions which remain unanswered.