Discovery of Melanocortin Ligands via a Double Simultaneous Substitution Strategy Based on the Ac-His-dPhe-Arg-Trp-NH2 Template

The melanocortin system regulates an array of diverse physiological functions including pigmentation, feeding behavior, energy homeostasis, cardiovascular regulation, sexual function, and steroidogenesis. Endogenous melanocortin agonist ligands all possess the minimal messaging tetrapeptide sequence His-Phe-Arg-Trp. Based on this endogenous sequence, the Ac-His1-dPhe2-Arg3-Trp4-NH2 tetrapeptide has previously been shown to be a useful scaffold when utilizing traditional positional scanning approaches to modify activity at the various melanocortin receptors (MC1–5R). The study reported herein was undertaken to evaluate a double simultaneous substitution strategy as an approach to further diversify the Ac-His1-dPhe2-Arg3-Trp4-NH2 tetrapeptide with concurrent introduction of natural and unnatural amino acids at positions 1, 2, or 4, as well as an octanoyl residue at the N-terminus. The designed library includes the following combinations: (A) double simultaneous substitution at capping group position (Ac) to...