Fast Route To Radiolabeled Formaldehyde

Scientists and doctors may soon have access to a greater number of radiotracer compounds for positron emission tomography (PET), thanks to a new method for making radiolabeled formaldehyde. Compounds containing carbon-11 are popular radiotracers for PET scans, but the radionuclide's 20-minute half-life presents a challenge to chemists: The process of generating a ¹¹C labeling reagent, synthesizing a tracer molecule, and then purifying that compound so that it can be injected into a patient waiting for a PET scan must all take place before the radioactive signal decays. Methylation with [¹¹C]methyl iodide is the most common radiolabeling reaction, but this restricts radiotracers to compounds with pendant methyl groups. A team led by Jacob M. Hooker of Brookhaven National Laboratory now has developed a simple and rapid route to [¹¹C] formaldehyde, thereby expanding the types of radiolabeling reactions (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200800991). The synthesis uses [¹¹C] methyl iodide to methylate trimethylamine N-oxide. [¹¹C] formaldehyde is subsequently generated via elimination of trimethylamine. Hooker's group was able to make the reaction work with radiolabeled reagents in a matter of minutes under mild conditions.