MECHANISTIC AND STEREOCHEMICAL STUDY OF PHENYLPYRUVATE TAUTOMERASE

A variety of substrates and potential enol/enolate mimics for the product/transition state of the enzyme phenylpyruvate tautomerase (E.C. 5.3.2.1) have been prepared and studied. Their stereostructures have been secured by a combination of NMR spectroscopy based on vicinal H-F and H-C coupling constants and X-ray crystallography. On the basis of the inhibition by stereoisomeric substituted cinnamates, it has been concluded that the enzyme produces the thermodynamically less stable (E) enol via a syn tautomerization transition state. Free energy profiles for the reaction suggest that vinyl fluorides act as product analogues. Because amide and dicarboxylate enolate mimics are relatively poor inhibitors of the enzyme, it is believed that an enolate is not involved in the tautomerization process.