Synthesis of partially modified retro and retroinverso psi[NHCH(CF3)]-peptides

Asymmetric conjugate additions of chiral alpha-amino esters to chiral 4-CF3 Michael-acceptors were exploited to prepare a small library of enantiomeri cally pure partially modified retropeptides having a psi[NHCH(CF3)] unit as a possible mimic of the classical psi(NHCO) retropeptide unit. Yields were nearly quantitative, and the stereoselectivity, which is controlled mainly by the nitrogen nucleophile, was progressively higher with increasing the steric bulk of the alpha-amino ester side-chain R-1.