Calderon SN. Nonpeptidic delta (delta) opioid agonists and antagonists of the diarylmethylpiperazine class: what have we learned? Top Curr Chem. 2011;299:121-40. Review. PubMed
Kaczor A, Matosiuk D. Non-peptide opioid receptor ligands - recent advances. Part I - agonists. Curr Med Chem. 2002 Sep;9(17):1567-89. Review. PubMed