Peptidyl molecular imaging contrast agents using a new solid-phase peptide synthesis approach

A versatile method is disclosed for solid-phase peptide synthesis (SPPS) of molecular imaging contrast agents. A DO3A moiety was derivatized to introduce a CBZ-protected amino group and then coupled to a polymeric support. CBZ cleavage with Et2AlCl/thioanisole was optimized for SPPS. Amino acids were then coupled to the aminoDOTA-loaded resin using conventional stepwise Fmoc SPPS to create a product with DOTA coupled to the C-terminus of the peptide. In a second study, the DO3A moiety was coupled to a glycine-loaded polymeric support, and amino acids were then coupled to the amino-DOTA-peptide-loaded resin using SPPS to incorporate DOTA within the peptide sequence. The peptide-(Tm3+-DOTA) amide showed a paramagnetic chemical exchange saturation transfer (PARACEST) effect, which demonstrated the utility of this contrast agent for molecular imaging. These results demonstrate the advantages of exploiting SPPS methodologies through development of unique DOTA derivatives to create peptide-based molecular imaging contrast agents.