1. Cyclohexylpuromycin, an anlogue of puromycin in which a cyclohexane ring replaces the aromatic benzene ring of the L-phenylalanyl moeity of the nucleoside., has been synthesized and examined for its ability to release N-acetylphenylalanine from tRNA attached to rat liver ribosomes. 2.dl-Cyclohexylpuromycin was active in reacting with N-[3H]acetylphenylalanyl-tRNA on rat liver ribosomes to form N-E13H]lacetylphenylalanycyclohexypuromycin. 3. The reaction product N-acetylphenylalanylcyclohexylpuromycin and the corresponding analogue N-acetylphenylalanylpuromycin were chemically synthesized for evaluation of the structure of the released N-acetylphenylalanyl-containing material. 4. The results obtained suggest that the model of Raacke (1971) for purmycin reactivity needs further examination with regard to the role played by the aromatic ring system of the Lphenylalanyl moiety of the nucleoside
