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Erschienen in:
01.09.2007 | Short Communication
Simple and highly efficient synthesis of 3′-deoxy-3′-[18F]fluorothymidine using nucleophilic fluorination catalyzed by protic solvent
Erschienen in: European Journal of Nuclear Medicine and Molecular Imaging | Ausgabe 9/2007
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Purpose
The aim of this study was to develop a method of radiochemical synthesis of 3′-deoxy-3′-[18F]fluorothymidine ([18F]FLT) with an improved radiochemical yield using nucleophilic substitution catalyzed by protic solvent.
Methods
We introduced t-butanol (t-BuOH) as a new reaction solvent for nucleophilic [18F]fluorination with [18F]fluoride using (5′-O-DMTr-2′-deoxy-3′-O-nosyl-β-D-threo-pentofuranosyl)-3-N-BOC-thymine to synthesize [18F]FLT. [18F]F− was eluted with (1) tetrabutylammonium bicarbonate (TBAHCO3), (2) Cs2CO3 and kryptofix 2.2.2 (K222) after trapping of [18F]F− on an ion exchange cartridge, or (3) addition of tetrabutylammonium hydroxide (TBAOH) and [18F]F− to the reactor without trapping [18F]F− on an ion exchange cartridge. We optimized [18F]fluorination conditions with t-butanol and then applied them to automatic synthesis using commercially available radiochemistry modules (TracerLab MX, GE Healthcare).
Results
We achieved a high radiochemical yield of 85.3 ± 3.5% by radio-TLC with TBAHCO3 as an elution solvent and 20 mg of precursor at 100°C (n = 4). With the same labeling conditions, use of Cs2CO3 and K222 with t-BuOH and TBAOH with t-BuOH generated radiochemical yields of 57.1 ± 22.5% and 55.0 ± 18.8% by radio-TLC, respectively (n = 3 for each condition). Automated synthesis with TBAHCO3 and 20 mg of precursor at 120°C for 10 min of [18F]fluorination led to radiochemical yields of 60.2 ± 5.2% after HPLC purification with an MX module (n = 10). Synthesized [18F]FLT was stable for 6 h.
Conclusion
[18F]FLT was synthesized with a significantly improved radiochemical yield by nucleophilic substitution catalyzed by protic solvent with mild reaction conditions and a short preparation time.