Semiautomatic synthesis of 3′-deoxy-3′-[18F]fluorothymidine using three precursors

To facilitate clinical studies with [18F]FLT, we modified 2-vessel [18F]FDG synthesis module (manufactured by CTI) to produce [18F]FLT. Three thymidine derivatives were used as precursors for [18F]FLT synthesis. Among these precursors, 3-N-t-butoxycarbonyl-[5′-O-(4,4′-dimethoxytrityl)-2′-deoxy-3′-O-(4-nitrobenzenesulfonyl)-β-d-threopentofuranosyl]thymine (thymidine derivative II) gave the best radiochemical yield (37.9%) when the reaction was carried out at 140 °C for 5 min. This semiautomatic synthesis system was not only simple and convenient, but also showed good reproducibility. The total synthesis time was 50 minutes from the end of bombardment (EOB) by the use of this modified synthesizer (including the manual process).