Synthesis of Partially Modified Retro and Retroinverso ψ[NHCH(CF3)]-Peptides

Abstract
Asymmetric conjugate additions of chiral α-amino esters to chiral 4-CF3 Michael-acceptors were exploited to prepare a small library of enantiomerically pure partially modified retropeptides having a ψ[NHCH(CF3)] unit as a possible mimic of the classical ψ(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 α-amino ester side-chain R1.