NCA 16α-[¹⁸F]fluoroestradiol-17β: The effect of reaction vessel on fluorine-18 resolubilization, product yield, and effective specific activity

Although the reported synthesis of the title compound resulted in a high radiochemical yield (43% based on resolubilized ¹⁸F), the effective specific activity at EOS was low (166 Ci/mmol). Reduction in the amount of carrier fluoride in the target water improved the effective specific activity of the product, but with a concommitant decrease in the resolubilized yield of the fluoroestradiol (12.7%). A re-examination of the labeling parameters was performed to determine the conditions that would increase the yield of the fluoroestrogen and maintain a high effective activity for the product. Since the amount of resolubilized ¹⁸F in THF is important in obtaining high specific activity compounds in this type of synthesis, several types of vessels were investigated to determine their effect on the evaporation of the [¹⁸O]H₂O target water and subsequent resolubilization of ¹⁸F into THF. Of these vessels (Pt crucible, borosilicate glass, siliconized borosilicate glass, Vacutainer^R), the Vacutainer afforded the highest resolubilization of ¹⁸F into THF (90%), resulting in an improved resolubilized yield for the fluoroestradiol (28%) and an increased effective specific activity at EOS for the product (1600-3939 Ci/mmol).