Direct incorporation of unprotected ketone groups into peptides during solid-phase synthesis: Application to the one-step modification of peptides with two different biophysical probes for FRET

An amino acid bearing an unprotected ketone group, (2S)-aminolevulinic acid, was incorporated into a synthetic peptide using standard Fmoc-based solid-phase methods. The ketone group remained unharmed during the synthesis and provided a uniquely reactive functional group for covalent modification of the peptide. The ketone and the sulfhydryl group of a cysteine residue elsewhere in the peptide were reacted simultaneously with two different biophysical probes, enabling the site-specific installation of a donor and acceptor pair for FRET in one step without the need for differential side chain protection. (C) 1998 Elsevier Science Ltd. Atl rights reserved.