New synthetic amino acids for the design and synthesis of peptide-based metal ion sensors

The syntheses of two new nonstandard amino acids, Flu (6) and YBp (20), and a new synthesis of Dmd (12) are reported. These residues exhibit fluorescence, metal-coordination, and fluorescence-quenching properties, respectively. These building blocks have been incorporated into peptides via solid phase peptide synthesis to afford the prototype fur a photoinduced electron transfer-based metal ion chemosensor. The fluorescence of the peptides is modulated upon metal binding. This results from a metal. ion-induced conformational change that brings the side chains of the Flu and Dmd amino acids into proximity, thereby favoring photoinduced electron transfer (PET) fluorescence quenching.