Labelling of the CFC-alternative, 2H-heptafluoropropane (HFC 227ea), with fluorine-18

Article abstract of DOI:10.1016/0022-1139(95)03306-X

Various reactions of no-carrier-added K(+)-aminopolyether 2.2.2-<18F>fluoride were examined for labelling the CFC-alternative, 2H-heptafluoropropane (HFC 227ea), with the positron-emitting radioisotope, fluorine-18 (t1/2 = 109.7 min).Reaction with 2H-hexafluoroisopropyl tosylate incorporated less than 2percent of the radioactivity into <2-18F>HFC 227ea and about 12percent into three other volatile products.Reaction with hexafluoropropene led to a high incorporation of fluorine-18 (80percent) into four radioactive products, namely the desired <1-18F>HFC 227ea, <18F>hexafluoropropene, <18F>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 <1-18F>HFC 227ea in a much higher radiochemical yield (50percent decay-corrected), the best radiochemical yield (80percent decay-corrected) was obtained by exchange with HFC 227ea.The mechanistic 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 and GC purification. <1-18F>HFC 227ea was obtained in high radiochemical purity (>99percent) and high chemical purity (>98.4percent) at 80 min from the start of radiosynthesis.This product is suitable for studies of the disposition of HFC 227ea in vivo. - Keywords: 2H-Heptafluoropropane; HFC 227ea; Fluorine-18; Exchange labelling; Mass spectrometry; Reaction mechanisms