Facile synthesis of new carbon-11 labeled conformationally restricted rivastigmine analogues as potential PET agents for imaging AChE and BChE enzymes

Rivastigmine is a newer-generation inhibitor with a dual inhibitory action on both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes, and is used for the treatment of AChE- and BChE-related diseases such as brain Alzheimer's disease and cardiovascular disease. New carbon-11 labeled conformationally restricted rivastigmine analogues radiolabeled quaternary ammonium triflate salts, (3aR,9bS)-1-[11C]methyl-1-methyl-6-(methylcarbamoyloxy)-2,3,3a,4,5,9b-hexahydro-1H-benzo[g]indolium triflate ([11C]8) and (3aR,9bS)-1-[11C]methyl-1-methyl-6-(heptylcarbamoyloxy)-2,3,3a,4,5,9b-hexahydro-1H-benzo[g]indolium triflate ([11C]9), were designed and synthesized as potential positron emission tomography (PET) agents for imaging AChE and BChE enzymes. The appropriate precursors were labeled with [11C]CH3OTf through N-[11C]methylation, and the target tracers were isolated by solid-phase extraction (SPE) using a cation-exchange CM Sep-Pak cartridge in 40–50% radiochemical yields decay corrected to end of bombardment (EOB), 15–20 min overall synthesis time, and 148–222 GBq/μmol specific activity at EOB.