Synthesis and biological evaluation of 1-(4-[18f]fluorobenzyl)-4-[(5,6-dimethoxy-1-oxoindan2-yl)methyl]piperidine for in vivo studies of acetylcholinesterase

The muscarinic cholinergic receptor ligands N-[11C]ethyl-4-piperidyl benzilate (4-EPB) and N-[11C]propyl-4-piperidyl benzilate (4-PPB) were developed and evaluated in comparison with N-[11C]methyl-4-piperidyl benzilate (4-MPB) in the conscious monkey brain using positron emission tomography (PET). Time-activity curves of [11C]4-EPB, unlike [11C]4MPB, showed peaks within 91 min in regions rich in muscarinic receptors. [11C]4-PPB showed no specific binding even in the regions rich in these receptors. These observation demonstrated that increases in [11C]alkyl chain length could alter the kinetic properties of receptor ligands for PET.