The role of backbone conformation in deltorphin II binding: a QSAR study of new analogues modified in the 5-, 6-positions of the address domain.

The delta selectivity of the opioid heptapeptides deltorphin I and II has been attributed to the C-terminal 'address' domain, the hydrophobic Val(5)-Val(6) residues apparently playing a topographical role. We now report the synthesis, opioid binding affinities, and a QSAR study of a series of peptides in which one of the valine side chains was altered. QSAR analyses included previously published models for a binding pocket interaction and an optimum size (Schullery, S.