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

F-19 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 F-19 signal. Here, we describe a new class of high-signal, water-soluble fluorochemicals as F-19 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-epsilon-trifluoroacetyllysine and lysine provide a degenerate F-19 NMR signal. F-19 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.