One-step efficient synthesis of F-18-labeled rhodamine 6G

Objectives We previously demonstrated that F-18-labeled rhodamine 6G is a promising agent for myocardial perfusion imaging. Previously, however, all syntheses were carried out using an inefficient two-step synthesis method. The objective of this study was, therefore, to develop a one-step synthesis of F-18-labeled rhodamines.

Methods A new rhodamine 6G tosylate precursor was synthesized and used in a manual single-step F-18 labeling reaction. The reaction conditions were optimized for solvent, temperature, reaction time, precursor mass. The optimized labeling reaction worked well in anhydrous DMSO with 1 mg/ml precursor concentration, a reaction temperature of 100 °C, and a reaction time of 30 min. The final product was purified by using semi-preparative HPLC, and the radiochemical yield and purity were measured by analytical HPLC and TLC.

Results F-18 labeled rhodamine 6G was synthesized manually using a one-step reaction with rhodamine 6G tosylate as the precursor. The radiochemical yield was >70% (decay corrected to SOS), the radiochemical purity was more than 99%, and the specific activity was >1,000mCi/umol. The total reaction time was less than 30 min.

Conclusions We developed an efficient one-step synthesis for F-18-labeled rhodamine 6G. Compared with the two-step synthesis used in previous studies, the one-step reaction requires only 30 min reaction time, (vs. more than 70 min for the two-step method), the overall radiochemical yield was also improved to >70% (vs. 30% for the two-step method), and the specific activity is higher. More importantly, in contrast to the earlier two-step method, the new method is compatible with the automated synthesis systems.

Research Support 5R01HL108107, Children’s Hospital Radiology Foundation