Synthesis of (R)-(-)- and (S)-(+)-4-fluorodeprenyl, (R)-(-)- and (S)-(+)-[N-11C-methyl]-4-fluorodeprenyl and PET studies in baboon brain

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Abstract
(R)-(-)- and (S)-(+)-.alpha.-methyl-.beta.-4-(fluorophenyl)-N-methyl-N-propynylethylamine ((R)-(-)- and (S)-(+)-4-fluorodeprenyl) were synthesized via the reaction of 4-fluorobenzaldehyde with nitroethane followed by reduction with lithium aluminium hydride to produce racemic 4-fluoroamphetamine, which was resolved by recrystallization with L- or D-N-acetylleucine to yield (R)-(-)-4-fluoroamphetamine or (S)-(+)-fluoroamphetamine in > 96% enantiomeric excesses and in yields of 42 and 39% respectively. Alkylation with propargyl bromide gave (R)-(-)- or (S)-(+)-4-fluoronordeprenyl which was reductively methylated (Borch conditions) to produce (R)-(-)- or (S)-(+)-4-fluorodeprenyl. Alkylation of (R)-(-)- or (S)-(+)-4-fluoronordeprenyl with carbon-11 labeled methyl iodide gave (R)-(-)- or (S)-(+)-[N-11C-methyl]-4-fluorodeprenyl in a radiochemical yield of 30-40%. Comparative PET studies of the two labeled enantiomers in baboons showed a significantly lower retention of radioactivity in the striatum for the (S)-(+) enantiomer relative to the (R)-(-) enantiomer.