Conformational studies and receptor binding of delta selective opioid peptides.

Detailed energy-conformation studies of a linear (DTLET) and four cyclic (DPDPE, DPLPE, DPLCE,DCLPE), delta-selective opioid peptides were combined with computer assisted detailed receptor binding studies. The results of these studies have allowed the identification of a low energy conformer common to all of these analogs which could be responsible for their high affinity delta-receptor binding. This conformer contains multiple intramolecular H-bonds and is very different from the beta-II type structure previously postulated to lead to high affinity mu-receptor binding. This mu-binding conformer was found either to have higher energies or be greatly distorted in these delta selective analogs.