Synthesis of "no-carrier-added" alpha-[11C]methyl-L-tryptophan

Described here is a synthesis of "no-carrier-added" alpha-[11C]methyl-L-tryptophan based on alkylation with 11CH3I of an anion generated by reacting the Schiff base of L-tryptophan methyl ester with di-isopropylamine. The synthesis requires approximately 30 min after the end of 11CO2 collection and gives alpha-[11C]methyl-L-tryptophan in a 20-25% radiochemical yield calculated at the end of the synthesis and without correction for radioactive decay. The specific activity of the final radiopharmaceutical, measured at the end of the synthesis, was around 2,000 Ci/mmol. Data confirming the stereospecificity of the synthesis are also presented.