LIPASE-CATALYZED HYDROLYSIS OF CROWNED ESTER SUBSTRATES - METAL CATION-ENHANCED REACTIVITY AND ENANTIOSELECTIVITY OF 12-CROWN-4 ESTER

Lipase from Pseudomonas cepacia was first applied in hydrolysis of est er substrates which had crown ether, azacrown, and acyclic polyether m oieties as cation binding sites. The reaction behaviors of these crown ed ester substrates were changed by addition of alkali metal salts. In particular, 12-crown-4 ester offered enhanced reactivity and enantios electivity in the presence of sodium salt. FAB MS, C-13 NMR, and compu tational studies revealed that the ester formed a diastereomeric compl ex in which Na+ cation was sandwiched between two chiral crowned subst rates. The lipase reaction was effectively controlled by ''host-guest chemistry'' of the crowned ester substrate.