On the Mechanism of Rearrangement of Chorismic Acid and Related Compounds

Abstract

The thermal reactions of the biochemically important molecule chorismic acid are studied in solution. It undergoes two competitive reactions, one is an unusually facile Claisen rearrangement, and the other an elimination to give p-hydroxybenzoic acid and pyruvic acid. Attempts are made to understand the factors responsible for the facility of the Claisen rearrangement by preparation of a variety of analogues of chorismate. Correlations of rate with structure as well as determinations of solvent and isotope effects are undertaken. The data from these experiments lead to the conclusion that chorismic acid and related molecules undergo the rearrangement and, where it occurs, the elimination, by reactions whose transition structures are dissociative in nature, i.e., there is substantial cleavage of the C-O bond linking the sidechain to the ring but little bond formation at the terminus of the sidechain. The roles of radical and zwitterionic structures are discussed, as are the implications of this work for the mechanism of enzyme catalysis of the chorismate to prephenate conversion. © 1987, American Chemical Society. All rights reserved.