title: Radiosynthesis of 4-[(18)F]fluoro-L-tryptophan by isotopic exchange on carbonyl-activated precursors.
abstract: Several (18)F-labeled aromatic amino acids have been developed primarily for tumor imaging with positron-emission-tomography (PET). Also, (18)F-labeled tryptophan derivatives were synthesized by electrophilic (18)F-fluorination or by introducing a [(18)F]fluoroalkyl group. Here, a 3-step method for a nucleophilic radiosynthesis of 4-[(18)F]fluoro-L-tryptophan was developed. A carbonyl activated precursor containing a chiral amino acid building block was radiofluorinated by isotopic exchange, followed by removal of the activating formyl group by reductive decarbonylation and subsequent cleavage of the building block under acidic conditions. The title compound was obtained within 100 min with a radiochemical yield of about 13%, a molar activity of >70 MBq/mmol and an enantiomeric excess of >99%.
authors.affiliation: Institut für Neurowissenschaften und Medizin, INM-5: Nuklearchemie, Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: Philipp S
authors.initials: PS
authors.lastname: Weiss
authors.affiliation: Institut für Neurowissenschaften und Medizin, INM-5: Nuklearchemie, Forschungszentrum Jülich, 52425 Jülich, Germany. Electronic address: j.ermert@fz-juelich.de.
authors.forename: Johannes
authors.initials: J
authors.lastname: Ermert
authors.affiliation: Institut für Neurowissenschaften und Medizin, INM-5: Nuklearchemie, Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: Johnny
authors.initials: J
authors.lastname: Castillo Meleán
authors.affiliation: Institut für Neurowissenschaften und Medizin, INM-5: Nuklearchemie, Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: Dominique
authors.initials: D
authors.lastname: Schäfer
authors.affiliation: Institut für Neurowissenschaften und Medizin, INM-5: Nuklearchemie, Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: Heinz H
authors.initials: HH
authors.lastname: Coenen
mesh_terms: D024322:Amino Acids, Aromatic; D005462:Fluorine Radioisotopes / Q000737:chemistry*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis*; D013237:Stereoisomerism; D014364:Tryptophan / Q000031:analogs & derivatives*
chemical_list: D024322:Amino Acids, Aromatic; D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals; D014364:Tryptophan
keywords: 4-Fluoro-l-tryptophan; Aromatic amino acids; Fluorine-18; Fluoroindoles; Isotopic exchange; Radiofluorination