title: The alkenyl migration mechanism catalyzed by extradiol dioxygenases: a hybrid DFT study.
abstract: 6-Hydroxymethyl-6-methylcyclohexa-2,4-dienone is a mechanistic probe which when incubated with an extradiol dioxygenase yields a 2-tropolone product. This observation was originally interpreted as evidence supporting a direct heterolytic 1,2-alkenyl migration mechanism for a ring expansion reaction catalyzed by this class of Fe(II)-dependent nonheme enzymes (Xin and Bugg in J Am Chem Soc 130:10422-10430, 2008). In the work reported in this contribution we used quantum chemical methods to test whether such a mechanism is energetically possible and we found that it is not, neither for the mechanistic probe nor for the native catalytic cycle intermediate. Models of increasing complexity were used to calculate energy barriers to the heterolytic 1,2-alkenyl migration and alternative radical mechanisms. It was found that the former involves substantially higher barriers than the latter. A tentative radical mechanism that accounts for the transformation of the probe substrate to 2-tropolone was also proposed, and it involves acceptable barriers.
authors.affiliation: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Cracow, Poland. ncborows@cyf-kr.edu.pl
authors.forename: Tomasz
authors.initials: T
authors.lastname: Borowski
authors.forename: Anna
authors.initials: A
authors.lastname: Wójcik
authors.forename: Anna
authors.initials: A
authors.lastname: Miłaczewska
authors.forename: Valentin
authors.initials: V
authors.lastname: Georgiev
authors.forename: Margareta R A
authors.initials: MR
authors.lastname: Blomberg
authors.forename: Per E M
authors.initials: PE
authors.lastname: Siegbahn
mesh_terms: D000480:Alkynes / Q000737:chemistry / Q000378:metabolism*; D055162:Biocatalysis; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000378:metabolism*; D011789:Quantum Theory; D014334:Tropolone / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism
chemical_list: D000480:Alkynes; D005290:Ferric Compounds; D014334:Tropolone; D010105:Oxygenases; C439587:extradiol dioxygenase