New synthesis and evaluation of enantiomers of 7-methyl-2-exo-(3'-iodo-5'-pyridinyl)-7-azabicyclo[2.2.1]heptane as stereoselective ligands for PET imaging of nicotinic acetylcholine receptors |
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Authors: | Gao Yongjun Horti Andrew G Kuwabara Hiroto Ravert Hayden T Holt Daniel P Kumar Anil Alexander Mohab Wong Dean F Dannals Robert F |
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Affiliation: | Division of Nuclear Medicine, Department of Radiology, The Johns Hopkins University School of Medicine, 600 North Wolfe Street, Baltimore, MD 21287-0816, USA. yongjgao@yahoo.com |
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Abstract: | A simple and efficient synthesis of nAChR antagonist (+/-)-7-methyl-2-exo-(3'-iodo-5'-pyridinyl)-7-azabicyclo[2.2.1]-heptane ((+/-)-NMI-EPB) has been developed. Both enantiomers of (+/-)-NMI-EPB were separated by semi-preparative chiral HPLC. The enantiomers manifested a substantial difference in their inhibition binding affinities ((+)-NMI-EPB, K(i)=2310, 1680 pM; (-)-NMI-EPB, K(i)=55, 68 pM). The enantiomers were stereoselectively radiolabeled with (11)C. In the distribution studies in the rodent brain [(11)C](-)-NMI-EPB specifically labeled nAChR whereas [(11)C](+)-NMI-EPB exhibited little specific binding. In the baboon PET study [(11)C](-)-NMI-EPB did not reach steady-state within 90 min post-injection suggesting that the radioligand may have some limitations for quantitative imaging. |
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