Synthesis of a hoechst 32258 analogue amino acid building block for direct incorporation of a fluorescent, high-affinity DNA binding motif into peptides

The synthesis of a new versatile "Hoechst 33258-like" Boc-protected amino acid building block for peptide synthesis is described. It is demonstrated that this new ligand is an effective mimic of Hoechst 33258 in terms of DNA affinity and sequence specificity. Furthermore, this minor groove binder was conjugated to a DNA condensing peptide (KSPKKAYK) by continuous solid-phase peptide synthesis, and the conjugate exhibited increased DNA affinity (ca. 10-fold), but similar sequence preference compared to Hoechst 33258 as analyzed by DNaseI footprinting. Finally, the fluorescence quantum yield of the new chromophore is found to increase 30% upon binding to double stranded DNA.