Inversion of an Asymmetric Center in Carbocyclic Inhibitors of 3-Dehydroquinate Synthase: Examining and Exploiting the Mechanism for syn-Elimination during Substrate Turnover

Article abstract of DOI:10.1021/jo00102a025

Conversion of 3-deoxy-D-arabino-heptulosonic acid 7-phosphate (DAHP) into 3-dehydroquinate (DHQ) by the enzyme DHQ synthase has been proposed to proceed through a step where the phosphate monoester of a reactive intermediate mediates its own elimination.This hypothesis was tested by challenging DHQ synthase with a series of carbocyclic substrate analogues possessing an inverted methine carbon relative to the same asymmetric center in substrate DAHP which loses a proton during elimination of inorganic phosphate.Despite the stereochemical alternation, epicarbocyclic substrate analogues 5-<(phosphonooxy)methyl>-5-deoxyquinate, 5-(phosphonomethyl)-5-deoxyquinate, 5-(phosphonoethyl)-5-deoxyquinate, and 3-(phosphonooxy)quinate inhibited DHQ synthase with respective inhibition constants (K_i) of 30 nM, 55 nM, 30 μM, and 53 μM.These inhibitors were synthesized from quinic acid and with the exception of 3-(phosphonooxy)quinate, were assembled via a strategy employing intramolecular, radical cyclization to establish the stereocenter where the (phosphonooxy)methyl, phosphonomethyl, and phosphonoethyl moieties were attached to the carbocyclic ring.The observed diastereomeric promiscuity in the binding of epicarbocyclic substrate analogues by DHQ synthase is consistent with the hypothesized nonenzymic syn-elimination of inorganic phosphate during substrate turnover.