Synthesis and quality assurance of [11C]alpha-aminoisobutyric acid (AIB), a potential radiotracer for imaging and amino acid transport studies in normal and malignant tissues.

Carbon-11 labeled alpha-aminoisobutyric acid (AIB), a synthetic amino acid, was prepared by the modified Bucherer-Strecker amino acid synthesis from acetone, ammonium carbonate and [11C]KCN in the presence of carrier KCN. This method results in the labeling of AIB in the carboxyl group. The label is stable in this position because AIB is not a metabolized after cellular uptake. AIB is rapidly accumulated in viable cells including malignant cells. Since it is a non-metabolized amino acid, AIB offers the possibility of studying amino acid transport in vivo without interference by radiolabeled metabolic products. Radiochemical yields of [11C]AIB of 35-60% have been obtained in 70-80 min with radiopurities greater than 99%. Carrier added syntheses gave 15-25 mCi of [11C]AIB with specific activities of 0.3 Ci/mmol. Our quality control program which insures that [11C]AIB is suitable for imaging studies in patients with cancer includes HPLC analyses of product identity and purity, apyrogenecity and isotonicity assays, and a sensitive test for cyanide.