NUCLEOPHILIC AROMATIC SUBSTITUTION OF ACTIVATED CATIONIC GROUPS BY 18F-LABELED FLUORIDE. A USEFUL ROUTE TO NO-CARRIER-ADDED (NCA) 18F-LABELED ARYL FLUORIDES

Article abstract of DOI:10.1016/S0022-1139(00)84987-8

A method is described for the rapid preparation of no-carrier-added (NCA) 18F-labeled aryl fluorides by treatment of the corresponding aryltrimethylammonium perchlorates with 18F-labeled fluoride in DMSO.The basic features of the 18F-for-⁺NMe3 displacement process are evaluated as a function of the experimental variables and compared with related substitution routes to NCA 18F-labeled aryl fluorides.The relative nucleofugicity of the ammonium group in the nucleophilic substitution reactions surpasses that of the best neutral leaving groups, including NO2 and F itself.In contrast, radiofluoride incorporation into aromatic rings via other cationic substrates, such as aryldimethylsulfonium perchlorates, is prevented by the fast methyl group transfer from the starting compound to the nucleophiles present.The use of the ammonium function as a leaving group in nucleophilic substitutions by 18F^- may give access to the rapid preparation of novel NCA 18F-radiopharmaceuticals by facilitating the synthesis and the purification of their labeled precursors.