Triazene as a powerful tool for solid-phase derivatization of phenylalanine containing peptides: zygosporamide analogues as a proof of concept.

A novel method for the synthesis of para-substituted phenylalanine containing cyclic peptides is described. The main features of this strategy are the coupling of phenylalanine to the solid support through its side chain via a triazene linkage, on-resin cyclization of the peptide chain, cleavage of the cyclic peptide from the resin under mild acidic conditions and further transformation of the resulting diazonium salt. The usefulness of this approach is exemplified by the solid-phase synthesis of some derivatives of the naturally occurring cyclic depsipeptide zygosporamide.