Carbon-11 choline: synthesis, purification, and brain uptake inhibition by 2-dimethylaminoethanol.

We report an improved method for the synthesis and purification of [11C]methylcholine from the precursors [11C]methyliodide and 2-dimethylaminoethanol (deanol). Preparation time, including purification, is 35 min postbombardment. Forty millicuries of purified injectable [11C]choline were produced with a measured specific activity of greater than 300 Ci/mmol and a radiochemical purity greater than 98%. The decay corrected radiochemical yield for the synthesis and purification was approximately 50%. Residual precursor deanol, which inhibits brain uptake of choline, is removed by a rapid preparative high performance liquid chromatography (HPLC) method using a reverse phase cyano column with a biologically compatible 100% water eluent. Evaporation alone did not completely remove the deanol precursor. Brain uptake of the [11C]choline product was six times greater after HPLC removal of deanol because doses of less than 1 microgram/kg significantly inhibit [14C]choline brain uptake.