A HIGHLY STEREOSELECTIVE SYNTHESIS OF (E)-ALKENE DIPEPTIDE ISOSTERES VIA ORGANOCYANOCOPPER - LEWIS ACID MEDIATED REACTION

A stereoselective synthesis of protected (E)-alkene dipeptide isosteres by the reaction of the mesylates of homochiral delta-aminated gamma-hydroxy (E)-alpha,beta-enoates with either RCu(CN)Li.BF3 or RCu(CN)MgX.BF3 reagent is described. The degree of diastereoselectivity has been found to be uniformly high except for the serine- and threonine-derived acetonides 77 and 81. The synthesis permits the introduction of sterically hindered appendages such as isopropyl and tert-butyl groups at the alpha position to the ester group. This methodology provides a new route to a wide range of modified (E)-alkene peptide mimics that may have biological importance.