Synthesis and evaluation of 18F- and 11C-labelled 9,10-ethanobenzo[b]quinolizinium derivatives for imaging of the NMDA receptor at the TCP-binding site

Derivatives of 9,10-ethanobenzo[b]quinolizinium are potent antagonists for the TCP-site of the NMDA receptor. Two fluoroethyl-substituted analogues were labelled with fluorine-18 by displacement of the tosylate with [F-18]fluoride, followed by a Diels-Alder reaction. A methoxy-substituted analogue labelled with carbon-ii was obtained by O-methylation of the corresponding hydroxy precursor with [C-11]iodomethane. In biodistribution studies in mice with these three radioligands, it was found that they have little ability to penetrate the blood-brain barrier.