Synthesis of carbon-11-labeled bivalent β-carbolines as new PET agents for imaging of cholinesterase in Alzheimer's disease

Carbon-11-labeled bivalent β-carbolines, 9,9′-(pentane-1,5-diyl)bis(2-[11C]methyl-9H-pyrido[3,4-b]indol-2-ium)iodide ([11C]2a), 9,9′-(nonane-1,9-diyl)bis(2-[11C]methyl-9H-pyrido[3,4-b]indol-2-ium)iodide ([11C]2b), 9,9′-(dodecane-1,12-diyl)bis(2-[11C]methyl-9H-pyrido[3,4-b]indol-2-ium)iodide ([11C]2c) and 1,9-bis(2-[11C]methyl-3,4-dihydro-1H-pyrido[3,4-b]indol-9(2H)-yl)nonane ([11C]3), were prepared by N-[11C]methylation of their corresponding amine precursors using [11C]CH3I and isolated by either a simplified solid-phase extraction (SPE) method or HPLC in 40–60% radiochemical yields based on [11C]CO2 and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 20–30 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 185–370 GBq/μmol.