Synthesis of 11C-labeled 5-hydroxytryptamine for the measurement of pulmonary endothelial cell function

[11C]3-β-Aminoethyl-5-hydroxy-indole labeled in the β position of the ethyl group ([11C]5-hydroxytryptamine, ([11C]-5-HT), [11C]serotonin) was synthesized from hydrogen [11C]cyanide in a three-step procedure: [11C]cyanide was first added to the cold precursor 5-methoxygramine methylsulfate by a phase-transfer catalyst supported nucleophilic substitution to give [11C]5-methoxy-3-acetonitrile-indole; secondly, the methoxy group was cleaved with boron tribromide to give [11C]5-hydroxy-3-acetonitrile-indole; thirdly, the nitrile was reduced to give [11C]5-HT which was finally purified by reverse phase high pressure liquid chromatography. The overall radiochemical yield was 13%. 410 ± 140 MBq of [11C]5-HT (sp. act. 5.1 GBq/μmol, radiochemical purity >96%) were ready for injection after the 78 min procedure.