Opioid peptides cyclic analogs

Schiller PW, Nguyen TM-D, Maziak LA, Lemieux C. A novel cyclic opioid peptide analog showing high preference for p-receptors. Biochem Biophys Res Commun 1985 127 558-564. 

Wilkes BC, Schiller PW. Theoretical conformational analysis of a p-selective cyclic opioid peptide analog. Biopolymers 1987 26 1431-1444. 

Various peptides from the enkephalin family, or analogs of these molecules, permeate through the blood-brain barrier at different rates, often by different mechanisms [49]. For example, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (a cyclic peptide that binds to jU.-opioid receptors, in which Pen is penicillamine) permeates by diffusion only Tyr-D-Pen-Gly-Phe-D-Pen ([d-Penj -enkephalin, a cyclic Met-enkephalin analog that binds to 5-opioid receptors) permeates by diffusion and a saturable transport mechanism (Tyr-D-Ala-Gly-Phe-NH)2 (biphalin, a dimeric analog that is active at fx-... 

Macrocyclic modulators of the p-opioid reeeptor inelude cyclic p-casomor-phin- and enkephalin- analogs as well as so ealled atypical cyclic peptides derived from endomorphin-1. 

---