Synthesis of a Double Marker Synthon (NMR and Fluorescent) for Peptide Labeling

摘要

Multimodality imaging can non-invasively monitor the distribution of peptide-based imaging nrobes in vivo Fluorescent dyes are major tools for biomolecules labeling. They are applied in fluorescence microscopy [1], confocal microscopy [2], flow cytometry [3] and other fluorescent techniques. Paramagnetic Gd~(III) chelates can achieve high proton relaxivity [4] as contrast agents in magnetic resonance imaging (MRI). Our intention was to combine those two markers (fluorescence and MRI) into one unit ready to couple to biomolecules such as neotides We propose the synthesis of a double marker building block with bis-axmao acids as Ivsine ornithine, 2, 4-diaminobutric acid or 2, 5-diaminopropionic acids in the core (Fisure 1) A tris-t-butyl ester DOTA chelator (in free acid form) for ~(68)Ga (positron emission tomo apriy PET) or Gd (MRI) is coupled on N-amine site and other β,γ,δ and s-amino group of selected bis amino acids were coupled with a fluorescent agent (fluorescein) via thiourea link. Use of p, y, § and s-amino site for isothiocyanate coupling fits perfectly with requirements for stable thiourea bond formation [5]. As fluorescent agents we used FITC, but other fluorescent agents could easy be used instead if they are resistant to peptide cleavage conditions Synthesis on chlorotrityl resin results in building blocks ready to couple to a selected peptide. Naturally occurring protein amino acid lysine (I) in peptide sequence at N-terminus of labeled peptide would be the most appropriate as synthon. In some cases other more enzymatically resistant bis-amino acids [ornithine (II), 2,3-diaminopropionic acid (HI) or 2 4-diaminobutric acid (IV)] were used.