An All D-Amino Acid Opioid Peptide with Central Analgesic Activity from a Combinatorial Library

A synthetic combinatorial library containing 52,128,400 D-amino acid hexapeptides was used to identify a ligand for the μ opioid receptor. The peptide, Ac-rfwink-NH 2 , bears no resemblance to any known opioid peptide. Simulations using molecular dynamics, however, showed that three amino acid moieties have the same spatial orientation as the corresponding pharmacophoric groups of the opioid peptide PLO17. Ac-rfwink-NH 2 was shown to be a potent agonist at the μ receptor and induced long-lasting analgesia in mice. Analgesia produced by intraperitoneally administered Ac-rfwink-NH 2 was blocked by intracerebroventricular administration of naloxone, demonstrating that this peptide may cross the blood-brain barrier.