Preparation of No-Carrier-Added 6-[$^{18}$ F]Fluoro- l -tryptophan via Cu-Mediated Radiofluorination

18F-Labeled aromatic amino acids exhibit great potential for diagnostic applications using positron emission tomography. However, the introduction of 18F into aromatic compounds remains challenging, and novel fluorination methods facilitating easy access to 18F-labeled arenes are highly sought after. In recent years, novel metal-mediated fluorination methods have been reported and transferred into radiochemistry. Based on Cu-mediated radiofluorination, a two-step synthesis of no-carrier-added (n.c.a.) 6-[18F]fluoro-l-tryptophan was developed. 6-[18F]Fluoro-l-tryptophan was synthesized with an overall radochemical yield of 16 ± 4% within 110 min and a specific activity of 280 GBq µmol–1. The radiochemical purity was more than 99 %. The developed method allowed access to radiofluorinated tryptophan derivatives in high radiochemical yields and opens new ways to provide radiofluorinated amino acids. Furthermore, the reaction conditions were optimized to facilitate automation