LABELING OF THE CFC-ALTERNATIVE, 2H-HEPTAFLUOROPROPANE (HFC 227EA), WITH F-18

Various reactions of no-carrier-added K+-aminopolyether 2.2.2-[F-18]fl uoride were examined for labelling the CFC-altemative, 2H-heptafluorop ropane (HFC 227ea), with the positron-emitting radioisotope, fluorine- 18 (t(1/2) = 109.7 min). Reaction with 2H-hexafluoroisopropyl tosylate incorporated less than 2% of the radioactivity into [2-F-18] HFC 227e a and about 12% into three other volatile products. Reaction with hexa fluoropropene led to a high incorporation of fluorine-18 (80%) into fo ur radioactive products, namely the desired [1-F-18] HFC 227ea, [F-18] hexafluoropropene, [F-18] perfluoro-isohex-2-ene and an unknown, in a molar ratio of 5:4:38:3, respectively. Although reaction with 1-iodo- 2H-hexafluoropropane gave [1-F-18]HFC 227ea in a much higher radiochem ical yield (50% decay-corrected), the best radiochemical yield (80% de cay-corrected) was obtained by exchange with HFC 227ea. The mechanisti c bases of the results are discussed. An efficient fully shielded and automated procedure was devised for labelling HFC 227ea with fluorine- 18 in high radioactivity, based on the successful exchange reaction an d GC purification. [1-F-18] HFC 227ea was obtained in high radiochemic al purity ( > 99%) and high chemical purity ( > 98.4%) at 80 min from the start of radiosynthesis. This product is suitable for studies of t he disposition of HFC 227ea in vivo.