Readily available protected forms of δ-amino-γ-msyloxy-α,β-enoates can be converted to protecteddipeptideisosteres, Ω[(E)CHCH]Gly, in high yields by reduction with alkenylcopper reagents.
The “higher order” organozinc cuprates, R2Cu(CN)(ZnCl)2·2Mg(X)Cl·nLiCl, derivedfrom admixture of LiCl (1∼2 equiv.), ZnCl2 (1 equiv.), RMgX (1 equiv.), and CuCN (0.5 equiv.) in a mixed solvent of THF and Et2O exhibit high diastereoselection of up to > 99: 1 in the synthesis of (E)-alkene dipeptide isosteres from γ-mesyloxy-α,β-unsaturated esters. Addition of lithium chloride is essential for the preparation
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.