ENANTIOSELECTIVE HYDROLYSIS OF LONG-CHAIN ALPHA-AMINO-ACID ESTERS BY CHIRAL SULFUR-CONTAINING MACROCYCLIC METALLOMICELLES

A novel chiral lipophilic sulfur-containing macrocyclic ligand 5 with bis-pendant alcohols in the proximity of the coordination center has b een synthesized. Its metal ion complexes have been investigated as cat alysts for the enantioselective hydrolysis of long chain alpha-amino a cid esters in aqueous comicellar solution with Brij35. Large rate acce lerations (up to 220 times) and moderate enantioselectivities (up to 4 .85 (k(S)/k(R))) employing the macrocyclic 5-Cu2+ have been observed, whereas the acyclic 3-Cu2+ exhibits less reactivity and stereoselectiv ity. Taking the analogous ligand 4, lacking the hydroxy groups leads t o a dramatic rate decrease, and an inversion of enantioselectivity is observed. The pKa value of the hydroxyl bound to Cu2+ is, determined t o be pKa=7.2 under our micellar reaction conditions. (C) 1998 Elsevier Science Ltd. All rights reserved.