CHIRAL LIPOPHILIC LIGANDS .4. METALLOMICELLES MADE OF CU(II) COMPLEXES OF ALPHA-AMINO-AMIDE-TYPE LIGANDS AS CATALYSTS OF THE CLEAVAGE OF ALPHA-AMINO-ACID ESTERS

A new series of lipophilic ligands, 1-3, featuring an alpha-amino amid o (1) or a dipeptide amido (2) moiety as chelating subunit and a hydro xy function (except for 3) close to the coordination centre, have been synthesized and their copper(II) complexes investigated as catalysts for the cleavage of p-nitrophenylalanine in aqueous comicelles of CTAB r. Rate acceleration up to two orders of magnitude have been observed. The most effective complexes are those with ligands 1 that are the be st suited for the formation of a ternary complex ligand-Cu(II)-substra te, in which the hydroxyl activated by the metal ion (pK(a)=6.8) may a ct as a nucleophile in the cleavage of the ester. Using chiral 1b,c, 2 b and the enantiomers of the substrate, sizable enantioselectivity (up to 2.4) has been observed only in the case of ligands 1b,c. These eff ects are suggested to arise from a different partitioning of the two d iastereomeric ternary complexes within the aggregate.