[6- 1 3 C]-(2S,4S)-5-Chloroleucine 12 was prepared in six steps and 26% overall yield from protected l-glutamic acid using 1 3 CH 3 I as the source of isotopic label. On feeding 12 to cultures of L. majuscula no incorporation of isotopic label into the trichlorinated marine natural product barbamide was detected. The synthesis of a novel dichloroleucine derivative 16 is also described.