Development of a reliable remote‐controlled synthesis of β ‐[ 11 C]‐5‐hydroxy‐ L ‐tryptophan on a Zymark robotic system

Precise staging of neuroendocrine tumors (NET) using positron emission tomography (PET) tracers visualizing their specific metabolic activity is of interest. Besides [ 18 F]FDOPA, staging NET with carbon‐11 labeled 5‐hydroxytryptophan (5‐HTP) is reported in recent literature. We implemented the multi‐enzymatic synthesis of enantiomerically pure [ 11 C]‐ L ‐5‐HTP on a Zymark robotic system to compare both tracers in patient studies. [ 11 C]‐5‐HTP can be synthesized in up to 24% radiochemical yields (EOB). Average specific activity is 44 000 GBq/mmol in ca. 50 min from [ 11 C]methyl iodide in radiochemical purities >99 %. The synthesis of 5‐HTP is difficult due to its multi‐enzymatic reaction steps but typical yields can be achieved of ca. 400 MBq. [ 11 C]‐5‐HTP is now reliably used in ongoing studies for staging NET. Copyright © 2006 John Wiley & Sons, Ltd.