Synthesis of 3β-(4-[18F]fluoromethylphenyl)- and 3β-(2-[18F] fluoromethylphenyl)tropane-2β-carboxylic acid methyl esters: new ligands for mapping brain dopamine transporter with positron emission tomography

The synthesis of two new dopamine transporter ligands, 3β-(4-fluoromethylphenyl)tropane-2β-carboxylic acid methyl ester and 3β-(2-fluoromethylphenyl)tropane-2β-carboxylic acid methyl ester, and their spectral characterization are described. The precursors for these ligands were prepared by TiCl4 catalyzed chloromethylation of 3β-phenyltropane-2β-carboxylic acid methyl ester followed by separation of the isomeric product mixture of 2- and 4-chloromethylphenyltropane derivatives. Reaction of the chloromethyl analogs with no-carrier-added [18F]fluoride ion followed by high performance liquid chromatography purification provided the corresponding [18F]fluoromethyltropanes, in good radiochemical yields, useful for imaging the brain dopamine transporter system in vivo with positron emission tomography