We have developed a system for the automatic synthesis of L-[beta-11C]amino acids for i.v.injection by means of enzyme-mediated reactions from 11CO2 via 11CH3I and D,L-[beta-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+/-0.5GBq of 5-hydroxy-L-[beta-11C]tryptophan with a radiochemical purity of 97.1+/-0.6% and a specific activity of 39.6+/-8 GBq/mumol 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-[beta-11C} dihydroxyphenylalanine (L-[beta-11C]DOPA) was also synthesized using this system
