REMARKABLY ENHANCED ENANTIOSELECTIVE HYDR OLYSIS OF AMINO-ACID ESTERSWITH TRIPEPTIDE CATALYST IN MICELLAR SYSTEMS

Stereoselective hydrolysis of the long-chain substrate (p-nitrophenyl ester of N-dodecanonyl-D and L-phenylalanine: C12-D(L)-Phe-PNP) cataly zed by the active tripeptide yloxycarbonyl-L-phenylalanyl-L-histidyl-L -leucine: Z-PheHisLeu) in the micellar systems (cationic hexadecyltrim ethylammonium bromide (CTAB); nonionic alpha-[4-(1,1,3,3-tetramethylbu thyl) phenyl]-omega-hydroxydecakis (oxyethylene) (Triton X-100), polyo xyethylene (20) sorbitan monolaurate (Tween 20), alpha-tetradecyl-omeg a-hydroxyheptakis (oxyethylene) (C-14(EO)7); anionic sodium dodecylsul fate (SDS)) was found to be controlled by changing the concentration a nd structure of surfactants. The noteworthy aspects are as follows: Wi th respect to the rate-enhancement, (a) the apparent rate constant (k( a,obsd)) is markedly enhanced around critical micelle concentration (C MC) and the head group in micellar surfactants takes an important role for the enhancement of rate (cationic CTAB much-greater-than nonionic surfactants (C-14 (EO)7, Triton X-100, Tween 20) much-greater-than an ionic SDS). On the other hand, with respect to the stereospecificity, (b) kinetic enantioselectivity is exclusively favored for the L-substr ate and the enantioselectivity (reflected in k(a, obsd)L/k(a, obsd)D) is kept constant above CMC in all of micellar systems in this study. T he head group in micelles also take an important role to enhance the e nantioselectivity (nonionic surfactants (Triton X-100, Tween 20, C-14( EO)7) > anionic SDS > cationic CTAB). In particular, a remarkably high enantioselectivity (k(a, obsd)D/k(a, obsd)D = 77) was attained around CMC in the C-14(EO)7 micellar system.