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.

2-[(18)F]Fluoro-L-phenylalanine and 2-[(18)F]fluoro-L-tyrosine have been developed as promising radiopharmaceuticals for molecular imaging using positron emission tomography (PET). However, the lack of a convenient radiosynthetic pathway has limited their practical use. In this work a new three-step nucleophilic synthesis of these compounds starting from [(18)F]fluoride is described. Corresponding precursors (1a and 1b) were (18)F-fluorinated by isotopic exchange, followed by the removal of an activating formyl group with Rh(PPh(3))(3)Cl and subsequent hydrolysis of protecting groups in acidic medium. All reactions were carried out using both conventional and microwave heating. Conventional heated reactions yielded the desired products 2-[(18)F]Fphe and 2-[(18)F]Ftyr in 43% and 49% whereas radiochemical yields of 34% and 43%, respectively, were obtained when they were heated by microwaves. Under optimized conditions the enantiomeric purity was ≥94% for both radiopharmaceuticals.

No abstract

No abstract

No abstract