Synthesis and biological actions of highly potent and prolonged acting biotin-labeled melanotropins

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Abstract
Biocytin derivatives of a superpotent analog of .alpha.-melanotropin, [Nle4,D-Phe7]-.alpha.-MSH, were prepared. [N.alpha.-Bct-Ser1,Nle4,D-Phe7]-.alpha.-MSH and [12-Bct-N.alpha.-dodecanoyl-Ser1,Nle4,D-Phe7]-.alpha.-MSH were synthesized by solid-phase techniques, and the coupling of biotin and 12-aminododecanoic acid was achieved through their succinimido esters. These melanotropins possessed almost identical actions to [Nle4,D-Phe7]-.alpha.-MSH as determined by several melanocyte bioassays. Both biocytin derivatives were highly potent agonists and exhibited prolonged biological activity as determined in the frog and lizard skin bioassays. Both biotinylated peptides were at least equipotent to .alpha.-MSH in stimulating Cloudman S91 mouse melanoma tyrosinase activity. The analogs were resistant to inactivation by .alpha.-chymotrypsin.