Chiral effect of a Phe residue in position 3 of the Dmt¹-l (or d)-Tic² analogues on opioid functional activities

In this letter, we describe a structure-activity relationships study, specifically related to the chirality of third amino acid residue in our H-Dmt-l(or d)-Tic analogues, of which C-terminus is attached to a piperidinyl moiety. Observed selectivities and functional activities of these analogues demonstrated that the chiralities of the second and third position residues are crucial for determining whether these ligands act as antagonists or agonists at the δ opioid receptor, but not at the μ opioid receptor.