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

Abstract We have developed a system for the automatic synthesis of l -[ β - 11 C]amino acids for i.v. injection by means of enzyme-mediated reactions from 11 CO 2 via 11 CH 3 I and d , l -[ β - 11 C]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- l -[ β - 11 C]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. l -[ β - 11 C]dihydroxyphenylalanine ( l -[ β - 11 C]DOPA) was also synthesized using this system.