Positron Emission Tomography
Using Light to Radiolabel Molecules
Positron Emission Tomography (PET) is a cutting-edge imaging technique used to study metabolic processes, in vivo therapeutic uptake, neuroimaging and disease detection. The technique uses unstable isotopes, most commonly 18F which has a half life of ~110 min, that emit positrons. Using MRI, molecules labeled using PET can be tracked in real time in vivo. The challenge for organic chemists - how do you perform synthetic reactions fast enough on a recalcitrant ion like fluoride? We think one way to do so is to use organic photoredox catalysis. We collaborate with Professor Zibo Li, Director of the Cyclotron Facility in the Department of Radiology at UNC on developing new radiolabeling catalytic methods and novel radiotracers. Li and Nicewicz have also formed a company, LED Radiofluidics, which provides imaging services and automated PET tracer modules.
Direct 18F Labeling of (Hetero)Aromatics
We have tamed the reactivity of cation radicals to realize the first C-H/C-18F functionalization of aromatics using 18F fluoride and organic photoredox catalysis. This catalytic method allowed a range of 18F labeling of therapeutic molecules. Aromatic ethers can also be utilized as radiolabeling precursors in photoredox-catalyzed nucleophilic aromatic substitution reactions with 18F anions.
18F Radiolabeling via Aromatic Halide Interconversion
Tracer candidates and therapeutics that contain an aromatic fluoride are excellent candidates for introduction of a radiolabel. What if you could use the fluoroaromatic drug as the radiolabeling precursor? We have reported just such a transformation - 18F radiolabeling via halide interconversion by organic photoredox catalysis - that makes it simple to introduce an 18F radiolabel at the same position it appears in the molecule of interest.