Radiosynthesis of [11C]DHTP. (a) i [11C2H3]methyl iodide, KOH, DMF; ii solvent removal by SPE; iii HCl. (b) Tris, pH 8.3 to 9.0, d-amino acid oxidase (D-AAO)/catalase, glutamic pyruvic transaminase (GTP). (c) i Tryptophanase (TPase), 5-hydroxyindole; ii HCl; iii filtration; iv semi-preparative HPLC purification.