ENANTIOSELECTIVE SYNTHESES OF NCA (S)-L-[BETA-C-11]-4-CHLOROPHENYLALANINE AND (S)-L-(ALPHA-METHYL)-[BETA-C-11]-4-CHLOROPHENYLALANINE

The radiolabeling of (S)-L-4-chlorophenylalanine and (S)-L-(alpha-methyl)-4-chlorophenylalanine were realized with carbon-11 at position B through a radiochemical synthesis relying on the highly enantioselective reaction between 4-chloro[alpha-C-11]benzyl bromide and the lithium enolate of (S)-1-(t-butyloxycarbonyl)-2-(t-butyl)-3-methyl-1,3-imidazolidine-4-one for (S)-L-[beta-C-11]-4-chlorophenylalanine and of (2S,5S)-1-(t-butyloxycarbonyl)-2-(t-butyl)-3,5-dimethyl-1,3-imidazolidine-4-one for (S)-L-(alpha-methyl)-[beta-C-11]-4-chlorophenylalanine. Quantities of about 25-35 mCi were obtained at the end of synthesis, ready for injection, after hydrolysis and HPLC purification with a radiochemical yield of 19% corrected to EOB within 45 min. The enantiomeric excesses were shown to be greater than or equal to 97% for both molecules without chiral separation. The radiochemical and the chemical purities of the final compounds were greater than or equal to 98% and the specific activity at the end of synthesis ranged between 250-800 mCi/mu mol.