N-methylpiperidinemethyl, N-methylpyrrolidyl and N-methylpyrrolidinemethyl esters as PET radiotracers for acetylcholinesterase activity.

The N-[(11)C]methylpiperidinyl esters are used as radiopharmaceuticals for measuring brain cholinesterase activity. We have synthesized a series of N-methylpiperidinemethyl (1), N-methylpyrrolidinyl (2) and N-methylpyrrolidinemethyl (3) esters and examined the effects of sterric constraint and stereochemistry on cholinesterase-mediated cleavage. Acetylcholinesterase exhibited a preference for primary esters 1 and for the R-isomers of both 1 and 2. Biological data for (S)-N-[(11)C]methyl-2-piperidinemethyl acetate (1a) were similar to [(11)C]AMP. These data better define the structure-activity relationships for cholinesterase radiotracers and provide lead compounds for (18)F- labeling.