[en] The labelled dehydroamino acid, 2-N-acetylamino-3-(2-naphthyl)-3-[¹⁴C]-acrylic acid was prepared at 52.8 mCi/m mol from Ba¹⁴CO₃. Asymmetric reduction of this precursor with hydrogen in the presence of the chiral homogeneous catalyst (S,S) BPPMRh⁺ afforded N-acetyl-D-3-(2-naphthyl)-3-[¹⁴C]-alanine in greater than 98% optical yield. This unnatural amino acid was used in a solution phase synthesis of 2 ¹⁴C-labelled LHRH analogs, [N-Ac-D-3[¹⁴C]Nal¹ D-p-Cl-Phe², D-Trp³, D-hArg(Et₂)⁶, D-Ala¹⁰] LHRH and [D-3-[¹⁴C] Nal⁶] LHRH having specific activities in excess of 50 mCi/mmol. (author)