Elucidating the Stereochemistry of Enzymatic Benzylsuccinate Synthesis with Chirally Labeled Toluene. Issue 38 (9th August 2016)

• Record Type: Journal Article
• Authors: Seyhan, Deniz; Friedrich, Peter; Szaleniec, Maciej; Hilberg, Markus; Buckel, Wolfgang; Golding, Bernard T.; Heider, Johann
• Is Part Of: Angewandte Chemie international edition. Volume 55:Issue 38(2016)
• Page Start: 11664
• Page End: 11667
• Publication Date: 2016-08-09
• Subjects: benzylsuccinate synthase -- chiral methyl groups -- glycyl radicals -- stereochemistry -- toluene; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201605197
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Benzylsuccinate synthase is a glycyl radical enzyme that initiates anaerobic toluene metabolism by adding fumarate to the methyl group of toluene to yield ( R )‐benzylsuccinate. To investigate whether the reaction occurs with retention or inversion of configuration at the methyl group of toluene, we synthesized both enantiomers of chiral toluene with all three H isotopes in their methyl groups. The chiral toluenes were converted into benzylsuccinates preferentially containing 2 H and 3 H at their benzylic C atoms, owing to a kinetic isotope effect favoring hydrogen abstraction from the methyl groups. The configuration of the products was analyzed by enzymatic CoA‐thioester synthesis and stereospecific oxidation using enzymes involved in benzylsuccinate degradation. Assessment of the configurations of the benzylsuccinate isomers based on loss or retention of tritium showed that inversion of configuration at the methyl group occurs when the chiral toluenes react with fumarate. Abstract : Attack from the back : Radical‐based enzymatic addition of fumarate to the methyl group of toluene by benzylsuccinate synthase occurs with inversion of configuration, as shown experimentally by using both enantiomers of chiral toluene. This result is consistent with the predicted structure of a modeled transition‐state complex for initial hydrogen abstraction from toluene.