Direct Site Selective 19F- and 18F-labelling of Peptides and Proteins Towards "Zero Size - Zero Background" Bioimaging

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Non-invasive imaging techniques now dominate disease diagnosis and can, in principle, provide vital knowledge of disease states at the molecular level. In this was accurate diagnosis will allow more appropriate and successful treatment plans. A myriad of imaging methods, perhaps more prominently magnetic resonance imaging, optical imaging, ultrasonography, positron emission tomography and X-ray computed tomography have become established over the past decades. In parallel, a range of small molecules, molecular complexes, micro- and nanoscale materials used as tracers, targeting or contrast agents has undergone intense diversification to support these technologies by enhancing signal. However, despite this remarkable progresses, there is a surprising lack in the use of molecular imaging agents - agents that not only give a better signal but also tell us about the molecular events associated with the disease. As a result, there has been slower progress towards the fundamental understanding of molecular processes in biology and diseases. We aim to bridge this 'disconnect' between the molecular and medicinal sciences through the development of a general method that will allow creation of innovative chemical tools to produce superior probes for 'molecular imaging'. Access to precisely fluorine(F)-modified peptides and proteins is incredibly useful to allow the visualisation of biological phenomena in complex matrices including cellular lysates, whole cells, and even whole organisms. 19F Nuclear Magnetic Resonance (NMR) spectroscopy is a valuable tool in medicinal chemistry driving early lead discovery efforts, and 19F Magnetic Resonance Imaging (MRI) has been applied in proof-of-principle studies to cell tracking and for molecular imaging of biomarkers in preclinical models. In nuclear medicine, positron emission tomography (PET) is a powerful non-invasive imaging technique that can visualise whole organisms providing that one can access 18F-labelled mall molecules, peptides and proteins. 18F is a cyclotron-produced radioisotope that presents a range of advantageous physical properties including reasonable half life (just under two hours) and clean decay profile (97% positron emission). These remarkable applications have encouraged many scientists to develop methodologies to access fluorine-labelled biologics. From a reactivity viewpoint, fluorine is a "challenging"element of the periodic table, that has prevented the development of effective, precise and reproducible direct fluorine-peptide or fluorine-protein bond construction. To circumvent these difficulties, chemists have opted to modify firstly the peptide or protein to be labelled with a so-called prosthetic that is amenable to fluorine incorporation. However, such prosthetics can modify the structure of the native biologics to such a degree that function is affected in a detrimental way. As a result, direct, effective, precise and easy to implement methods for protein fluorination are in urgent demand. Here, we propose to develop such a method to precisely fluorine-label peptide and proteins by pooling the expertise of the two applicants who together have extensive knowledge of fluorine chemistry and peptide/protein chemistry within the context of chemical biology and chemical medicine. The novelty of our approach is the development of a linker-prosthetic free technology that modifies peptide and proteins with the unnatural CH2SCF3 and CH2CF3 side-chains for application in bioimaging with the minimal symmetrical multi-fluorine group that is possible: CF3. Our proposed late stage 19F- and 18F-trifluoromethylation of peptide and proteins that relies on the availability of so-called 19F- and18F-Umemoto reagents is not only highly novel but could prove transformatory to imaging science as a tool.