Synthesis and functional analysis of deferriferrichrysin derivatives: application to colorimetric pH indicators

Deferriferrichrysin belongs to the siderophore peptide family which are Fe(III)-coordinating cyclic peptides. The common structure of this family is three consecutive hydroxamate moieties, such as N(δ)-acetyl-N(δ)-hydroxy-l-ornithine (Aho). We have designed two deferriferrichrysin derivatives where three Aho residues were arranged as: cyclo(-Aho-Gly-Aho-Gly-Aho-Gly-) and cyclo(-Aho-Ser-Aho-Ser-Aho-Ser-). Comparative evaluation of the physicochemical properties of their Fe(III) complexes revealed that naturally occurring deferriferrichrysin formed a more stable Fe(III) complex when compared with the two derivatives. This result shows that three consecutive Aho residues are indispensable for high affinity Fe(III) binding by deferriferrichrysin. Of note, the observed pH-dependent chromogenic response of the Fe(III) complexes of the derivatives suggests that these two derivatives should function as sensitive pH indicators in acidic environments.