An efficient synthesis of [ring-14C]-L-tyrosine from [U-14C ]-phenol

The title compound was prepared in good overall yield and high enantiopurity via a five step route beginning with [U-14C]-phenol, 4. Benzyl ether 5 was prepared from 4 under standard conditions and underwent selective iodination at the 4-position in the presence of iodine and mercuric oxide. Palladium catalysed cross coupling of the resulting aryl iodide 6 and the organozinc intermediate derived from N-tert-butoxycarbonyl-3-iodo-alanine methyl ester, 7, proceeded smoothly to give 8. Debenzylation and acid hydrolysis afforded the deprotected amino acid as the hydrochloride salt. Purification (flash chromatography) was necessary in only two of the five steps in the synthesis.