A new nucleophilic fluorine-18 labeling method for aliphatic mesylates: reaction in ionic liquids shows tolerance for water.

[see text for equation] Nucleophilic [(18)F]fluorination of some halo- and mesyloxyalkanes to the corresponding [(18)F]fluoroalkanes with fluoride-18 obtained from an (18)O(p,n) [(18)F]F reaction, using an ionic liquid as a reaction medium, has been studied as a new method for fluorine-18 labeling. Of the various ionic liquids, 1-butyl-3-methylimidazolium triflate ([bmim][OTf]) in the presence of Cs(2)CO(3), gave the highest radiochemical yields. This method is rapid and particularly convenient because [(18)F]fluoride in H(2)O can be added directly to the reaction media, obviating the careful drying that is typically required for currently used radiofluorination methods. As a model reaction, [(18)F]fluorination of 2-(3-methanesulfonyloxypropoxy)naphthalene was found to provide the corresponding [(18)F]fluoro product in 93+/-1.2% (n=3) radiochemical yield, after reaction at 120 (o)C for 5-10 min under optimized conditions. Thus, we anticipate that this method will be very useful in the labeling of various molecules with [(18)F]fluoride in a convenient manner.