Fluorescein-labelled peptides

A compound comprising a peptidic vector and at least one fluorescein dye, wherein the peptidic vector and the fluorescein dye are coupled, and wherein said peptidic vector is defined by formula I:

• Ra—C(═O)—X1—X2—X3-G-D-X4—X5—X6—X7 (I)
• wherein Formula I comprises two cyclising bridges, and wherein
• Ra represents —(CH2)n— or —(CH2)n—C6H4— forming a bridge to one of X2, X4 or X6, wherein
• n represents a positive integer from 1 to 10, and
• X1 represents a bond or 1, 2, 3, 4 or 5 amino acid residues, wherein one amino acid residue is optionally functionalised with a spacer moiety, or said amino acid residue possesses a functional side-chain chosen from an acid or amine group,
• X2 is an amino acid residue forming a cyclising bridge to one of Ra, X4 or X6;
• X3 represents arginine or N-methylarginine,
• G represents glycine,
• D represents aspartic acid,
• X4 is an amino acid residue forming a cyclising bridge to one of Ra, X2 or X6;
• X5 represents a hydrophobic amino acid, and
• X6 represents an amino acid residue forming a cyclising bridge to either Ra, X2 or X4, and
• X7 represents a spacer or biomodifier moiety or is absent, wherein said biomodifier comprises a monodisperse polyethylene glycol (PEG) building block comprising 1 to 10 units of said building block;
• and,
• wherein at least one of the fluorescein dye is linked to one or more of the groups X1, X6, or X7 optionally via a spacer group.