title: Mechanistic basis for the enantioselectivity of the anaerobic hydroxylation of alkylaromatic compounds by ethylbenzene dehydrogenase.
abstract: The enantioselectivity of reactions catalyzed by ethylbenzene dehydrogenase, a molybdenum enzyme that catalyzes the oxygen-independent hydroxylation of many alkylaromatic and alkylheterocyclic compounds to secondary alcohols, was studied by chiral chromatography and theoretical modeling. Chromatographic analyses of 22 substrates revealed that this enzyme exhibits remarkably high reaction enantioselectivity toward (S)-secondary alcohols (18 substrates converted with >99% ee). Theoretical QM:MM modeling was used to elucidate the structure of the catalytically active form of the enzyme and to study the reaction mechanism and factors determining its high degree of enantioselectivity. This analysis showed that the enzyme imposes strong stereoselectivity on the reaction by discriminating the hydrogen atom abstracted from the substrate. Activation of the pro(S) hydrogen atom was calculated to be 500 times faster than of the pro(R) hydrogen atom. The actual hydroxylation step (i.e., hydroxyl group rebound reaction to a carbocation intermediate) does not appear to be enantioselective enough to explain the experimental data (the calculated rate ratios were in the range of only 2-50 for pro(S): pro(R)-oriented OH rebound).
authors.affiliation: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Kraków, Poland. Electronic address: ncszalen@cyfronet.pl.
authors.forename: Maciej
authors.initials: M
authors.lastname: Szaleniec
authors.affiliation: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Kraków, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Dudzik
authors.affiliation: Department of Organic Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland.
authors.forename: Bartłomiej
authors.initials: B
authors.lastname: Kozik
authors.affiliation: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Kraków, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Borowski
authors.affiliation: Laboratory for Microbial Biochemistry, Philipps University of Marburg, Karl-von-Frisch Strasse 8, D-35043 Marburg, Germany.
authors.forename: Johann
authors.initials: J
authors.lastname: Heider
authors.affiliation: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Kraków, Poland.
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Witko
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry*; D020134:Catalytic Domain; D006860:Hydrogen Bonding; D006900:Hydroxylation; D008956:Models, Chemical; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory; D043362:Rhodocyclaceae / Q000201:enzymology; D013237:Stereoisomerism; D013379:Substrate Specificity; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D001555:Benzene Derivatives; D010088:Oxidoreductases; C121602:ethylbenzene dehydrogenase; D010100:Oxygen
keywords: Chiral chromatography; DFT; Enantioselective reaction; Ethylbenzene dehydrogenase; Molybdenum enzymes; QM:MM