S-(−)-Dinitrobiphenic Acid:  A Selective Inhibitor of Escherichia coli Chorismate Mutase Based on Prephenate Mimicry

The conversion of chorismate 1 to prephenate 2 in the shikimate biosynthetic pathway is catalyzed by the enzyme chorismate mutase (CM) and represents a rare example of an enzyme-catalyzed pericyclic reaction. X-ray crystallographic analyses of CMs have identified two distinct protein folds that catalyze the rearrangement of 1 to 2, and provided important clues about enzyme mechanism. The mutase reaction has also served as a model for research into fundamental questions of enzymology such as antibody catalysis, combinatorial mutagenesis and selection, and directed evolution. CMs play a central role in the biosynthesis of phenylalanine and tyrosine in microorganisms and plants and are attractive targets for the design of antibiotics and herbicides. Yet limited progress has been made in developing either a highly potent CM inhibitor or one that displays selectivity between mutases. The two most effective CM inhibitors are transition-state mimics 3 and 4, but neither is selective. Oxabicyclic diacid 3 broadly inhibits CMs from the Escherichia coli P- and T-proteins (EcCM), Bacillus subtilis (BsCM), and Saccharomyces cerevisiae (ScCM) with low-micromolar K sub(i) values. In the course of exploring approaches to the design of new mutase inhibitors, we have discovered that the S-enantiomer of 6,6'-dinitrobiphenic acid [S-(-)-DNBA 5] is comparable in potency to 3 as a competitive inhibitor of EcCM (K sub(i) = 13 mu M), but has no effect on BsCM or ScCM at 600 mu M. Here we present kinetic data suggesting that S-5 mimics the reaction product, prephenate 2, and interacts with the prephenate-binding pocket of EcCM (Scheme 1).