The shikimate pathway is the biosynthetic route that is responsible for the production of essential aromatic compounds (1). These include the aromatic amino acids tryptophan, tyrosine, and phenylalanine, folic acid, an essential cofactor for many enzymatic processes, and salicylate, used for the biosynthesis of the siderophores through which bacteria acquire iron (2). The pathway is found in microorganisms and plants and has more recently been discovered in apicomplexan parasites (3, 4). The pathway is absent in higher organisms, making the enzymes of this pathway attractive as targets for the development of antimicrobial agents. Recent gene disruption studies have shown that operation of the shikimate pathway is essential for the viability of Mycobacterium tuberculosis (5), the causative agent of tuberculosis, a disease that remains a significant world-wide health risk (6). Although effective anti-tuberculosis drugs exist, the long treatment times required, the problems of latent or persistent tuberculosis (7), and the proliferation of multidrug-resistant strains of M. tuberculosis (8) have all created an urgent need for the development of new antimycobacterial agents.The first committed step in the shikimate pathway is the stereospecific aldol reaction between phosphoenolpyruvate (PEP) 4 and erythrose 4-phosphate (E4P) to produce 3-deoxy-Darabino-heptulosonate 7-phosphate (DAH7P), catalyzed by the enzyme DAH7P synthase (Fig. 1). DAH7P is converted into chorismate, the product of the main shikimate pathway, via six further enzyme-catalyzed reactions. At this point the pathway to the aromatic amino acids branches, with chorismate converted either to anthranilate by anthranilate synthase or to prephenate by chorismate mutase. Anthranilate ultimately produces Trp, whereas prephenate is converted into Phe and Tyr.As the first enzyme, DAH7P synthase, is a major control point for shikimate pathway flux. Several organisms express two or more isozymes of this enzyme that show different sensitivity to the pathway end products. Escherichia coli and Neurospora crassa each produce three isozymes, with each enzyme individually inhibited by either Phe, Tyr, or Trp (9,10