Intramolecular general base-catalyzed ester hydrolyses by the imidazolyl group.

Abstract

Intramolecular general base catalysis by the imidazolyl group was found in the hydrolyses of endo-5-[4''(5'')-imidazolyl]-bicyclo[2.2.1]hept-endo-2-yl trans-cinnamate and endo-5-[4''(5'')-imidazolyl]bicyclo[2.2.2]oct-endo-2-yl trans-cinnamate in which the imidazolyl and trans-cinnamoyl groups are bound in close proximity to each other by rigid bicyclic rings. The rate constants for the intramolecular general base-catalyzed hydrolyses at 60.degree. are 6.4 .times. 10-7 s-1 for the former and 1.8 .times. 10-7 s-1 for the latter, and the D2O solvent isotope effects are 3.0 for both. No intramolecular catalytic participation of the imidazolyl group was observed in the hydrolyses of the endo-exo isomers, exo- 5-[4''(5'')-imidazolyl]bicyclo[2.2.1]hept-endo-2-yl trans-cinnamate and endo-5-[4''(5'')-imidazolyl]bicyclo[2.2.2]oct-exo-2-yl trans-cinnamate, in which the imidazolyl groups are located far from the trans-cinnamoyl groups. Intramolecular general base-catalyzed hydrolyses by the imidazolyl groups in endo-5-[4''(5'')-imidazolyl]bicyclo[2.2.1]hept-endo-2-yl trans-cinnamate and endo-5-[4''(5'')-imidazolyl]bicyclo[2.2.2] oct-endo-2-yl trans-cinnamate can serve as models of serine esterase-catalyzed hydrolyses.