Synthesis and evaluation of 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-[11C]ethyl-1,3-dihydro-2H-benzimidazol-2-one as a brain ORL1 receptor imaging agent for positron emission tomography.

1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-[(11)C]ethyl-1,3-dihydro-2H-benzimidazol-2-one ([(11)C]CPEB) was synthesized by [(11)C]N-ethylation and evaluated as a potential brain ORL1 receptor imaging agent by positron emission tomography. The uptake of [(11)C]CPEB in the mouse brain was 1.9% dose/g, 2 min post-injection, and gradually decreased with time. Receptor-specific binding was observed, however, the contribution of other receptors was observed and the non-specific binding of [(11)C]CPEB was too high for imaging receptors in vivo. Therefore, [(11)C]CPEB is not a suitable tracer for in vivo ORL1 receptor imaging. Copyright 2002 Elsevier Science Inc.