Synthesis of racemic [3-11C]-labelled alanine, 2-aminobutyric acid, norvaline, norleucine, leucine and phenylalanine and preparation of L-[3-11C]alanine and L-[3-11C]phenylalanine

The syntheses of racemic [3-11C]-labelled alanine, 2-amino-butyric acid, norvaline, norleucine, leucine and phenylalanine are reported. The reactions were performed by a phase-transfer alkylation reaction on N-(diphenylmethylene)-glycine tert-butyl ester with the appropriate 11C-alkyl iodides followed by acidic hydrolysis and the labelled amino acids were obtained in 10-55 % radiochemical yield. L-[3-11C]-Alanine and L-[3-11C]phenylalanine were obtained in 99 % enantiomeric excess after treatment of the corresponding racemic mixture by D-amino acid oxidase immobilized on glutaral-dehyde-activated glass beads. In a typical run starting with 120 mCi [11C]carbon dioxide, 25 mCi [1-11C]benzyl iodide was prepared and used to give 6 mCi of DL-[3-11C]phenylalanine within 50 minutes. Following treatment with D-amino acid oxidase, 0.3 mCi of L-[3-11C]phenylalanine was obtained after a total synthesis time of about 100 minutes. (author)