Synthesis of optically pure (D)-phenyl[3-14C]alanine

Lithium aluminium hydride reduction of methyl [7-C-14]benzoate gave [7-C-14]benzyl alcohol which was transformed (HBr, H2SO4) to [7-C-14]benzyl bromide. The latter was reacted with lithium N-(bis-methylthiomethylenimino)-acetyl-(2R)-bornane-10,2-sultam (Oppolzer chiral synthon) followed by hydrochloric acid then lithium hydroxide hydrolysis and chromatography on a Dowex 50 column to give (D)-phenyl[3-C-14]alanine with 40% overall yield. The molar activity was higher than 50 mCi/mmol and e.e. >99% as measured by the Marfey method and a modified Marfey method with TLC scanning. The latter method is suitable for the measurement of the optical purity of any amino acid.