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

Nucleophilic [ 18F]fluorination of some halo- and mesyloxyalkanes to the corresponding [ 18F]fluoroalkanes with fluoride-18 obtained from an 18O(p,n) [ 18F]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 2CO 3, gave the highest radiochemical yields. This method is rapid and particularly convenient because [ 18F]fluoride in H 2O 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, [ 18F]fluorination of 2-(3-methanesulfonyloxypropoxy)naphthalene [1] was found to provide the corresponding [ 18F]fluoro product in 93±1.2% ( n=3) radiochemical yield, after reaction at 120 oC for 5-10 min under optimized conditions. Thus, we anticipate that this method will be very useful in the labeling of various molecules with [ 18F]fluoride in a convenient manner.