title: Iron(II) complexes of sterically bulky alpha-ketocarboxylates. structural models for alpha-ketoacid-dependent nonheme iron halogenases.
abstract: Reaction of the sterically hindered alpha-ketocarboxylate 2,6-di(mesityl)benzoylformate (MesBF) with the iron(II) complexes LFeCl 2 [L = N, N, N', N'-tetramethylpropylenediamine (Me 4pda) or 6,6'-dimethyl-2,2'-bipyridine (dmby)] yielded LFe(Cl)(MesBF) ( 1 or 2). X-ray crystal structures of these complexes showed that they closely model the active site structure of the nonheme iron halogenase enzyme SyrB2. A similar synthetic procedure using benzoylformate with L = dmby yielded (dmby)Fe[(O 2CC(O)Ph)] 2 ( 3) instead, demonstrating the need for the sterically hindered alpha-ketocarboxylate to assemble the halogenase model compounds. In order to make reactivity comparisons among the structurally related iron(II) complexes of benzoylformates of varying steric properties, the complexes [LFe(O 2CC(O)Ar)] n ( 4- 6) were prepared, where L' = tris(pyridylmethyl)amine (tpa) and Ar = 2,6-dimesitylphenyl, 2,6-di p-tolylphenyl, or 2,4,6-trimethylphenyl, respectively. X-ray structures for the latter two cases ( 5 and 6) revealed dinuclear topologies ( n = 2), but UV-vis and (1)H NMR spectroscopy indicated that all three complexes dissociated in varying degrees to monomers in CH 2Cl 2 solution. Although compounds 1- 6 were oxidized by O 2, oxidative decarboxylation of the alpha-ketocarboxylate ligand(s) only occurred for 3. These results indicate that the steric hindrance useful for structural modeling of the halogenase active site prohibits functional mimicry of the enzyme.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA.
authors.forename: Seth J
authors.initials: SJ
authors.lastname: Friese
authors.forename: Benjamin E
authors.initials: BE
authors.lastname: Kucera
authors.forename: Victor G
authors.initials: VG
authors.lastname: Young
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que
authors.forename: William B
authors.initials: WB
authors.lastname: Tolman
mesh_terms: D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D007651:Keto Acids / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D019159:Nonheme Iron Proteins / Q000737:chemistry* / Q000378:metabolism; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
chemical_list: D005290:Ferric Compounds; D007651:Keto Acids; D019159:Nonheme Iron Proteins; D009942:Organometallic Compounds; D010088:Oxidoreductases