^Calderon SN (2011). "Nonpeptidic delta (delta) opioid agonists and antagonists of the diarylmethylpiperazine class: what have we learned?". Top Curr Chem. 299: 121–140. PMID21630509.
^Kaczor A, Matosiuk D (2002). "Non-peptide opioid receptor ligands - recent advances. Part I - agonists". Curr Med Chem. 9 (17): 1567–1589. PMID12171553.