DES—Nα1—ACETYL—α—MELANOTROPIN:

Application of the 2‐methylsulfonylethyloxycarbonyl group for temporary amino protection enables the synthesis from one precursor of des‐Nα1‐acetyl‐α‐MSH, the two mono N‐acetylated forms (in positions I and II) and the diacetyl form of this tridecapeptide amide. The free tridecapeptide amide, although structurally unrelated to the normal substrate, was recognized by an enzyme occurring in calf eye‐lens tissue. The product of the enzymatic reaction was exclusively α‐MSH. Partial sequences derived from the N‐terminus were less rapidly acetylated or not at all, depending on their chain length. The enzyme, therefore, appears to direct its activity to free N‐terminal α‐amino groups of peptides exceeding a certain critical chain length. Acetylation of ‐amino functions did not occur.