New CD derivatives as self-assembling contrast agents for magnetic resonance imaging (MRI)

A way to improve Magnetic Resonance Imaging is to deliver a larger number of Imaging Probe units to the target site. Aiming at this objective, we prepared a self-assembling system consisting of: 1) a β-cyclodextrin (β-CD) bearing a covalently bonded Gd complex (DTPA-Lys); 2) a polypeptide containing a high percentage of tyrosine residues (PLT); 3) a second β-CD derivative bearing a covalently bonded peptide vector (CCK8) that can recognize a specific cell-membrane receptor. Both β-CD derivatives can form stable inclusion complexes with the aromatic moieties of the polypeptide. The formation of a supramolecular adduct having a long reorientational correlation time entailed a marked relaxivity increase (per Gd3+ ion), which recommends it as a promising model for detail enhancement procedures at the target site. Out of three different synthetic pathways that could be used for binding a CD to DTPA, the most convenient one involved a micro-wave(MW)-assisted Mannich aminomethylation of a monopropargyl β-CD by the primary amino group of t-butyl-DTPA-Lys.