Development of an automated, GMP compliant FASTlab TM radiosynthesis of [ 18 F]GE-179 for the clinical study of activated NMDA receptors.

N-(2-chloro-5-(S-2-[F-18]fluoroethyl)thiophenyl)-N'-(3-thiomethylphenyl)-N'-methylguanidine, ([F-18]GE-179), has been identified as a promising positron emission tomography (PET) ligand for the intra-channel phencyclidine (PCP) binding site of the N-methyl-D-aspartate (NMDA) receptor. The radiosynthesis of [F-18]GE-179 has only been performed at low radioactivity levels. However, the manufacture of a GMP compliant product at high radioactivity levels was required for clinical studies. We describe the development of a process using the GE FASTlab (TM) radiosynthesis platform coupled with HPLC purification. The radiosynthesis is a two-step process, involving the nucleophilic fluorination of ethylene ditosylate, 11, followed by alkylation to the deprotonated thiol precursor, N-(2-chloro-5-thiophenol)-N'-(3-thiomethylphenyl)-N'-methyl guanidine, 8. The crude product was purified by semi-preparative HPLC to give the formulated product in an activity yield (AY) of 7 +/- 2% (n = 15) with a total synthesis time of 120 minutes. The radioactive concentration (RAC) and radiochemical purity (RCP) were 328 +/- 77 MBq/mL and 96.5 +/- 1% respectively and the total chemical content was 2 +/- 1 mu g. The final formulation volume was 14 mL. The previously described radiosynthesis of [F-18]GE-179 was successfully modified to deliver an process on the FASTlab (TM) that allows the manufacture of a GMP quality product from high starting radioactivitity (up to 80 GBq) and delivers a product suitable for clinical use.