Automatic synthesis of L-[β-11C]amino acids using an immobilized enzyme column

We have developed a system for the automatic synthesis of image-[β-11C]amino acids for i.v. injection by means of enzyme-mediated reactions from 11CO2 via 11CH3I and image,image-[β-11C]alanine as labeled intermediates. This system, which incorporates an ultrafilter cartridge sterilized by electron beam irradiation and a column packed with immobilized enzymes, was effective for eliminating enzymes and endotoxins that may contaminate the product. Using this system, 1.3±0.5 GBq of 5-hydroxy-image-[β-11C]tryptophan with a radiochemical purity of 97.1±0.6% and a specific activity of 39.6±8 GBq/μmol a pH value of 4 could be obtained in about 32 min (n=3, at EOS). No endotoxin, enzyme, or bacteria was detected in the product. image-[β-11C]dihydroxyphenylalanine (image-[β-11C]DOPA) was also synthesized using this system.