Design, synthesis, and biological properties of highly potent cyclic dynorphin A analogues. Analogues cyclized between positions 5 and 11.

We have recently reported the synthesis of several cyclic disulfide bridge-containing peptide analogues of dynorphin A (Dyn A), which were conformationally constrained in the putative address segment of the opioid ligand. Several of these analogues, bridged between positions 5 and 11 of Dyn A 1-11 -NH 2 , exhibited unexpected selectivities for the κ and μ receptors of the central over the peripheral nervous systems. In order to further investigate the conformational and topographical requirements for the residues in positions 5 and 11 of these analogues, we have synthesized a systematic series of Dyn A 1-11 -NH 2 analogues incorporating the sulfydryl containing amino acids L- and D-Cys and L- and D-Pen in positions 5 and 11, thus producing 16 cyclic peptides