5-Enolpyruvylshikimate-3-phosphate synthase: chemical synthesis of the tetrahedral intermediate and assignment of the stereochemical course of the enzymatic reaction

ORGN 44

Ming An, Ulf Neidlein, Uday Maitra, and Paul A. Bartlett. Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720

The enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase transfers a carboxyvinyl group from phosphoenolpyruvate (PEP) to shikimate-3-phosphate (S3P). This reaction proceeds through an addition-elimination sequence involving a ketal-phosphate tetrahedral intermediate (TI). The addition and elimination steps occur with opposite stereochemistries, i.e. one is syn and one is anti. It is also known that a proton is added to the si-face of PEP during the addition step. Therefore, complete assignment of the stereochemical course of EPSP synthase catalysis only required the knowledge of the absolute configuration of the ketal-phosphate stereocenter of the TI. Here, we report the chemical synthesis of both diastereomers of the enzymatic TI. The demonstration that only the (S)-TI is accepted by the enzyme means that the addition is anti and the elimination is syn. Furthermore, we propose that the syn elimination of the phosphate group occurs in an intramolecular fashion.

Lipids, Biosynthesis, Enzyme Inhibitors, and Mimetics 8:00 AM-11:40 AM, Sunday, September 7, 2003 Sheraton New York -- Royal Ballroom B, Oral Division of Organic Chemistry The 226th ACS National Meeting, New York, NY, September 7-11, 2003