Synthesis of [11C-methyl]-alpha-aminoisobutyric acid (AIB).

Alpha-aminoisobutyric acid (AIB) labeled with the cyclotron-produced, positron-emitting radionuclide 11C has been synthesized with the label in the alpha-methyl group. Our previously published synthesis of [11C] AIB in the carboxyl position from [11C] HCN requires a rigorous quality assurance program to ensure that the concentration of cyanide in the final product is below certain levels. This can be avoided using the method described here with [11C] CH3I. The radiochemical yield calculated to end of bombardment (EOB) was 45-55% from [11C] CO2 with radiochemical purity of [11C-methyl] AIB exceeding 99%. Synthesis times from [11C] CO2 were about 55 min. Specific activities of 1 Ci/mumol were achieved on average. It has been shown that [11C-carboxyl] AIB is a useful imaging agent in patients with soft tissue cancers and melanoma, and it demonstrates tumor uptake in a spectrum of other animal tumor models. Because AIB is a nonmetabolized amino acid, [11C-methyl] AIB should be equally as useful. Either agent can be employed for the quantification of the A-type amino acid transport system in vivo with PET.