Synthesis of Intrinsically Disordered Fluorinated Peptides for Modular Design of High-Signal 19 F MRI Agents

Abstract

¹⁹ F MRI is valuable for in vivo imaging due to the only trace amounts of fluorine in biological systems. Because of the low sensitivity of MRI however, designing new fluorochemicals remains a significant challenge for achieving sufficient ¹⁹ F signal. Here, we describe a new class of high-signal, water-soluble fluorochemicals as ¹⁹ F MRI imaging agents. A polyamide backbone is used for tuning the proteolytic stability to avoid retention within the body, which is a limitation of current state-of-the-art perfluorochemicals. We show that unstructured peptides containing alternating N-ϵ-trifluoroacetyllysine and lysine provide a degenerate ¹⁹ F NMR signal. ¹⁹ F MRI phantom images provide sufficient contrast at micromolar concentrations, showing promise for eventual clinical applications. Finally, the degenerate high signal characteristics were retained when conjugated to a large protein, indicating potential for in vivo targeting applications, including molecular imaging and cell tracking.

Keywords: 19F NMR spectroscopy; fluorination; magnetic resonance imaging; molecular imaging; peptides.