Studies on Peptides. IX. Synthesis of N-(Histidylphenylalanylarginy1)-5-methoxytryptamine, an Inhibitor of α-Melanocyte-stimulating Hormone in virto

Abstract

The N-acetyl group of melatonin was replaced with a histidylphenylalanylarginyl moiety . The product, N-(histidyenylalanylarginy1)-5-methoxytryptamine, reversed the darkening action of α-melanocyte-stimulating hormone (MSH) on frog-skin in vitro in contrast to the closely related tetrapeptide, histidylphenylalanylarginyltryptophan which exhibits intrinsic MSH activity. The synthetic intermediates, N-arginy1-5-meth-oxytryptamine and N-(phenylalanylarginyl)-5-methoxytryptamine also reversed the action of α-MSH. The color lightening potency of these compounds was about one millionth that of melatonin.