Iron binding β-hairpin peptides.

Posttranslational modification of tyrosine to 3,4-dihydroxyphenylalanine (dopa) yields a unique functional group in biomolecular systems. Oxidation produces a quinone, which can undergo cross linking while deprotonation is well suited to metal binding. Mussels, tunicates and bacteria chelate iron and other metals with multiple dopa subunits. Solution equilibria between catechols and iron indicate favorable assembly though this interaction has not been studied with highly structured biomolecules, such as peptides, despite their widespread biological applications. Here, a series of β-hairpin peptides are generated. Dopa is involved in an aromatic interaction as the edge position. Despite the presence of the surrounding secondary structure dopa readily undergoes oxidation and cross linking. Formation of bispeptide:iron complexes also occur in the presence of mild to significant aromatic interactions.