Enantioselective hydrolysis of long chain α-amino acid esters by chiral sulfur-containing macrocyclic metallomicelles

Abstract

A novel chiral lipophilic sulfur-containing macrocyclic ligand 5 with bis-pendant alcohols in the proximity of the coordination center has been synthesized. Its metal ion complexes have been investigated as catalysts for the enantioselective hydrolysis of long chain α-amino acid esters in aqueous comicellar solution with Brij35. Large rate accelerations (up to 220 times) and moderate enantioselectivities (up to 4.85 (k S/k R)) employing the macrocyclic 5-Cu 2+ have been observed, whereas the acyclic 3-Cu 2+ exhibits less reactivity and stereoselectivity. Taking the analogous ligand 4, lacking the hydroxy groups leads to a dramatic rate decrease, and an inversion of enantioselectivity is observed. The pKa value of the hydroxyl bound to Cu 2+ is determined to be pKa=7.2 under our micellar reaction conditions.