Design, synthesis and biological activity of cyclic GHRP-6 analogues

Growth Hormone (GH) secretion is normally stimulated by GHRH. In 1984 C.Y. Bowers and F.A. Momany synthesized the hexa-peptide Growth Hormone Releasing Peptide (GHRP-6) and discovered its ability to stimulate GH release in various species [1]. With the aim to identify the bioactive conformation of GHRP-6, a series of constrained monocyclic analogs were prepared. The cyclizations involved the termini and/or the side chains and, in some of the analogs, a reduced peptide bond was also introduced.