CRYPTATE MEDIATED NUCLEOPHILIC 18F-FLUORINATION WITHOUT AZEOTROPIC DRYING
Wessmann SH, Henriksen G, Wester HJ. (16-02-2012).Nuklearmedizin.
Research Area B
The radiosynthesis of the vast majority of 18F-labeled tracers rely on azeotropic drying of [18F]fluoride and subsequent cryptate mediated introduction of [18F]fluoride by nucleophilic substitution. The aim of this study was to develop a method for simplification of this process, based on preparation of reactive [K+⊂2.2.2]18F- by solvent drying of [18F]fluoride adsorbed onto an anion exchange resin. Methods: Aqueous [18F]fluoride (0.5-1 ml) obtained from the 18O(p,n)18F nuclear reaction was trapped on a strong anion-exchange (SAX) cartridge. After washing the cartridge with dry CH3CN, [18F]fluoride was eluted with an anhydrous solution of [K+⊂2.2.2]OH- in CH3CN and directly used for nucleophilic fluorination reactions. Results: [18F]Fluoride from target water was quantitatively retained by the SAX cartridge, and water-free [18F]fluoride recovered in an overall yield of 92±5% (n = 10). [18F]Fluoride obtained by this procedure led to radiochemical yields of 70-90% for [18F]FDG, [18F]FET, [18F]FLT, [18F]FAZA and [18F]Fallypride. Conclusion: SAX-resin adsorbed [18F]fluoride can be dried with non-aqueous solvents and eluted with [K+⊂2.2.2]OH- in CH3CN. The reactivity of [K+⊂2.2.2]F- generated by the new method is comparable to that of [18F]fluoride obtained by azeotropic drying. The described procedure facilitates the automated production of 18F-radiopharmaceuticals in general, and may also simplify the use of microfluidic devices for 18F-radiotracer production.