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.
Pirrung, Michael C.,Chen, Jrlung,Rowley, Elizabeth G.,McPhail, Andrew T.
Stereoconvergent Synthesis of Monofluoroalkenes via Photoinduced Dual Decarboxylative Cross-Coupling of α-Fluoroacrylic Acids with Redox-Active Esters
Herein, a new strategy for the synthesis of monofluoroalkenes via employing α-fluoroacrylic acids and N-hydroxyphthalimide (NHPI) redox-active esters as coupling partners has been developed. This decarboxylative reaction enabled the formation of C(sp2)-C(sp3) bonds to provide a practical and efficient approach for the construction of a variety of monofluoroalkenes, which are key structural motifs in organic chemistry, under mild reaction conditions. The protocol exhibited excellent functional group compatibility and delivered monofluoroalkene products with excellent Z-stereoselectivity. This work also provides a platform for the modification of complex biologically active molecules containing carboxylic acids.