General Base Catalysis of β Elimination by a Steroidal Enzyme Model

Abstract

The water soluble steroid 1 acts as a catalyst for the enolization of the ketones 2a-c. The rate enhancement for 1-catalyzed reaction relative to imidazole-catalyzed reaction (R), increases as the size of the aromatic ring system of the substrate increases; a plot of log Rvs π has a slope of 0.43. This is interpreted in terms of hydrophobic binding between steroid α-surface and aromatic ring system which lowers the free energy level of the transition state for steroid-catalyzed enolization.