Novel highly potent mu-opioid receptor antagonist based on endomorphin-2 structure4392, Fichna, J., do-Rego J.C., Janecki T., Staniszewska R., Poels J, J. Broeck Vanden, Costentin J., Schiller P.W., and Janecka A.E. , Bioorg.Med.Chem.Lett., 15/2/2008, Volume 18, Issue 4, Number 1353, p.1350 - 1353, (2008)