Efficient microwave-assisted direct radiosynthesis of [(18)F]PR04.MZ and [(18)F]LBT999: selective dopamine transporter ligands for quantitative molecular imaging by means of PET.

PR04.MZ 8-(4-fluoro-but-2-ynyl)-3-p-tolyl-8-aza-bicyclo[3.2.1]octane-2-carboxylic acid methyl ester (1) and LBT999 8-((E)-4-fluoro-but-2-enyl)-3b-p-tolyl-8-aza-bicyclo[3.2.1]octane-2beta-carboxylic acid methyl ester (2) are selective dopamine reuptake inhibitors, derived from cocaine. Compounds 1 and 2 were labelled with fluorine-18 at their terminally fluorinated N-substituents employing microwave enhanced direct nucleophilic fluorination. K[(18)F]F(-) Kryptofix 222 cryptate, tetrabutyl ammonium [(18)F]fluoride and caesium [(18)F]fluoride were compared as fluoride sources under conventional and microwave enhanced conditions. Fluorination yields were remarkably increased under microwave irradiation for all three fluoride salts. Radiochemically pure (>98%) [(18)F]PR04.MZ (0.95-1.09GBq, 42-135GBq/micromol) was obtained within 34-40min starting from 3.0GBq [(18)F]fluoride ion in 32-36% non-decay-corrected overall yield using K[(18)F]F(-)Kryptofix 222 cryptate in MeCN.