Reliable preparation of [11C]GR205171, a selective NK1 radioligands for noninvasive imaging

Abstract

[11C]GR205171, a Neurokinin 1 (NK1) radioligand, has been known as such a promising PET probe forquantitation of NK1 receptors in the brain by positron emission tomography (PET) imaging. First trial tosynthesis of [11C]GR205171 was to use methylene chloride and tetrabutylammonium hydroxide for preactivationof precursor, but the result was not successful in radiochemical yield (0~25%) and unreliable. 7years later, inorganic base (Cs2CO3) was tried to achieve higher radiochemical yield, and they showed higheryield (~53%). We have tried to repeat the same synthesis method, but it did not work properly, becausethere were the lack of the detail procedure and still reproducibility in radiochemical yield. Here we report theimproved synthesis protocol to produce [11C]GR205171 in high yield via commercial automated synthesizer. The sonicator which combines water heating bath was used to activate desmethyl-GR205171, and this methodshowed high efficiency and reasonable yields (4.7 ± 0.6%, non-decay corrected from molecular sieve trap) with>95% radiochemical purity.