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

O-(2-[F-18]fluoroethyl)-L-tyrosine ([(18)]FET) is one of the first F-18-labeled amino acids for imaging amino acid metabolism in tumors. This tracer overcomes the disadvantages of [F-18]fluorodeoxyglucose, [F-18]FDG, and [C-11]methionine, [C-11]MET. Nevertheless, the various synthetic methods providing F-18[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 [F-18]FET is developed starting from 2-bromoethyl triflate as precursor. After optimization of the synthesis parameters including the distillation step of [F-18]-FCH2CH2Br combined with the final purification of [F-18]FET using a simple solid phase extraction instead of an HPLC run the synthesis [F-18]FET could be significantly simplified, shortened, and improved. The radiochemical yield (RCY) was about 45% (not decay corrected and calculated relative to [F-18]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 [F-18]FET offers a very good option for routine clinical use. (C) 2009 Elsevier Ltd. All rights reserved.