Novel Peptides Bearing Pyrene and Coumarin Units with or without β-Cyclodextrin in Their Side Chains Exhibit Intramolecular Fluorescence Resonance Energy Transfer

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Abstract
Novel peptides bearing the pyrene/coumarin FRET pair in their side chains have been designed and synthesized. Peptide 1 having endogenous β-cyclodextrin (β-CD) in the side chain exhibits FRET in aqueous solution, indicating that coumarin, being accommodated into the CD cavity, is separated from pyrene. Guest-induced quenching of the fluorophores in 1 indicates that coumarin, being excluded from the CD cavity, comes into close contact with pyrene. Peptide 2 shows FRET only after addition of external β-CD that again reflects the idea that β-CD surely caps the coumarin unit in its hydrophobic cavity, and, therefore, quenching of the fluorophores can be prevented in FRET peptide probes. With this strategy, various peptide-based FRET probes can be developed that would be useful for studying biological phenomena in living cells.