New approach for the synthesis of [18F]fluoroethyltyrosine for cancer imaging: simple, fast, and high yielding automated synthesis.

O-(2-[(18)F]fluoroethyl)-L-tyrosine ([(18)F]FET) is one of the first (18)F-labeled amino acids for imaging amino acid metabolism in tumors. This tracer overcomes the disadvantages of [(18)F]fluorodeoxyglucose, [(18)F]FDG, and [(11)C]methionine, [(11)C]MET. Nevertheless, the various synthetic methods providing (18)F[FET] exhibit a big disadvantage concerning the necessity of two purification steps during the synthesis including HPLC purification, which causes difficulties in the automation, moderate yields, and long synthesis times >60 min. A new approach for the synthesis of [(18)F]FET is developed starting from 2-bromoethyl triflate as precursor. After optimization of the synthesis parameters including the distillation step of [(18)F]-FCH(2)CH(2)Br combined with the final purification of [(18)F]FET using a simple solid phase extraction instead of an HPLC run the synthesis [(18)F]FET could be significantly simplified, shortened, and improved. The radiochemical yield (RCY) was about 45% (not decay corrected and calculated relative to [(18)F]F(-) activity that was delivered from the cyclotron). Synthesis time was only 35 min from the end of bombardment (EOB) and the radiochemical purity was >99% at the end of synthesis (EOS). Thus, this simplified synthesis for [(18)F]FET offers a very good option for routine clinical use.

Simplified fast and high yielding automated synthesis of [18F]fluoroethylcholine for prostate cancer imaging.

(11)C- and (18)F-labeled choline analogues are successful tracers for prostate cancer imaging using positron emission tomography (PET). Due to the practical advantages of the longer-living radioisotope (18)F (t(1/2)=110 min) instead of (11)C (t(1/2)=20 min), [(18)F]fluoroethylcholine has been introduced to increase the opportunity of widespread clinical application. Nevertheless, the various known synthetic methods provide [(18)F]fluoroethylcholine for human use only in moderate overall yields of up to 30% so far. Here, a new simplified and high yield two-step-synthesis for [(18)F]fluoroethylcholine is described for potential clinical applications starting from 2-bromoethyl triflate (BETfO) using a modified, commercially available fully automated synthesis module. All synthesis parameters were subsequently optimized resulting in a total yield of 47+/-5% (not decay corrected) in only 40min. [(18)F]fluoroethylcholine could be obtained ready for human use as physiological solution after fixation on Sep-Pak Accell Light cartridges (waters((R))) and formulation with saline without the need of GC or HPLC purification. Radiochemical purity was >99.9% and no contamination of the sterile solution with chemicals used during the synthesis was detected.