Synthesis of L-[β-11C]amino acids using immobilized enzymes

L-[β-11C]-3,4-dihydroxyphenylalanine(L-[β-11C]DOPA) and L-[β-11C]-5-hydroxytryptophan(L-[β-11C]-5-HTP) were synthesized in one step with immobilized thermostable enzymes (alanine racemase, D-amino acid oxidase, and β-tyrosinase or tryptophanase) on an aminopropyl-CPG carrier in a single column and by passing D,L-[3-11C]alanine through the column with coenzymes and other substrates. L-[β-11C]DOPA and L-[β-11C]-5-HTP could be obtained at yields of 53% and 60%, respectively, by optimizing the amounts and the ratios of the enzymes used, the reaction temperature, the pH, and the flow rate. Moreover, the same immobilized enzyme column could be used repeatedly.