Synthesis of alpha-MSH fragments containing phenylalanine mustard for receptor studies

For chemical affinity labeling of the melanotropin receptor several alpha-MSH fragments containing phenylalanine mustard were synthesized in solution. Tested in the frog skin bioassay the derivatives roughly preserved the biological activity of the corresponding natural sequences. Alkylating peptides with prolonged biological activity containing phenylalanine mustard in place of arginine, phenylalanine or methionine are inhibitors of alpha melanotropin, suggesting an irreversible binding to reactive nucleophiles on the part of the MSH receptor, where the Met-Glu-His-Phe-Arg sequence is attached.