A synthetic model of the nonheme iron–superoxo intermediate of cysteine dioxygenase

Fischer, Anne A.; Lindeman, Sergey V.; Fiedler, Adam T.

doi:10.1039/c8cc06247a

Cited by 34 publications

(40 citation statements)

References 35 publications

(33 reference statements)

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“…Reaction of 1 – 2 with O 2 should lead to the formation of an Fe III –superoxo species. 19 Attack of the bound O 2 on the sulfur center initiates S-oxygenation, 74 giving an Fe(sulfinate) species, which can undergo esterification in MeOH to give the methylsulfinate ester in the case of 1 . Esterification of sulfinic acids in the presence of Lewis acids is documented.…”

Section: Resultsmentioning

confidence: 99%

“…To date there are no Fe II thiol dioxygenase model complexes that utilize the non-native abt substrate. 19 Herein we describe four new Fe II (N 4 S(thiolate)) complexes that incorporate abt and a CF 3 -substituted derivative and include the same triazacyclononane (TACN) scaffold. These complexes form a series of closely related 5-coord and 6-coord Fe II complexes in which the N 4 S ligand set is held constant, but where the sixth site is either unoccupied, or contains counterion or solvent.…”

Section: Introductionmentioning

confidence: 99%

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Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases

et al. 2018

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The synthesis of four new FeII(N4S(thiolate)) complexes as models of the thiol dioxygenases are described. They are composed of derivatives of the neutral, tridentate ligand triazacyclononane (R3TACN; R = Me, iPr) and 2-aminobenzenethiolate (abtx; X = H, CF3), a non-native substrate for cysteine dioxygenase (CDO). The coordination number of these complexes depends on the identity of the TACN derivative, giving 6-coordinate (6-coord) complexes for FeII(Me3TACN)(abtx)(OTf) (1: X = H; 2: X = CF3), and 5-coordinate (5-coord) complexes for [FeII(iPr3TACN)(abtx)](OTf) (3: X = H; 4: X = CF3). Complexes 1 – 4 were examined by UV-vis, 1H/19F NMR, and Mössbauer spectroscopies, and density functional theory (DFT) calculations were employed to support the data. Mössbauer spectroscopy reveals that the 6-coord 1 – 2 and 5-coord 3 – 4 exhibit distinct spectra, and these data are compared with that for cysteine-bound CDO, helping to clarify the coordination environment of the cys-bound FeII active site. Reaction of 1 or 2 with O2 at −95 °C leads to S-oxygenation of the abt ligand, and in the case of 2, a rare di(sulfinato)-bridged complex, [Fe2III(µ-O)(O2S(NH2)C6H3CF3)2](OTf)2 (5), was obtained. Parallel enzymatic studies on the CDO variant C93G were carried out with the abt substrate, and show that reaction with O2 leads to disulfide formation, as opposed to S-oxygenation. The combined model and enzyme studies show that the thiol dioxygenases can operate via a 6-coord FeII center, in contrast to the accepted mechanism for nonheme iron dioxygenases, and that proper substrate chelation to Fe appears to be critical for S-oxygenation..

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases

et al. 2018

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“…An aryl thiolate-ligated Fe–O 2 •− was recently reported; however, the sulfur lone pair is tied up in π -bonding to the aryl carbon in one of its resonance forms making it less reactive. 23 Although it has yet to be demonstrated with a superoxo, π -back-donation by an electron rich alkyl thiolate has been shown to facilitate the cleavage of strong C–H bonds by increasing the basicity of an iron oxo. 25 Herein, we report the synthesis and structure of an alkyl thiolate-ligated iron complex that reacts with O 2 to afford a spectroscopically observable reactive intermediate.…”

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confidence: 99%

Formation of a Reactive, Alkyl Thiolate-Ligated Fe^III-Superoxo Intermediate Derived from Dioxygen

et al. 2019

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Herein, we describe an alkyl thiolate-ligated iron complex that reacts with dioxygen to form an unprecedented example of an iron superoxo (O2•−) intermediate, [FeIII(S2Me2N3(Pr,Pr))(O2)] (4), which is capable of cleaving strong C–H bonds. A cysteinate-ligated iron superoxo intermediate is proposed to play a key role in the biosynthesis of β-lactam antibiotics by isopenicillin N-synthase (IPNS). Superoxo 4 converts to a metastable putative Fe(III)–OOH intermediate, at rates that are dependent on the C–H bond strength of the H atom donor, with a kinetic isotope effect (kH/kD = 4.8) comparable to that of IPNS (kH/kD = 5.6). The bond dissociation energy of the C–H bonds cleaved by 4 (92 kcal/mol) is comparable to C–H bonds cleaved by IPNS (93 kcal/mol). Both the calculated and experimental electronic absorption spectra of 4 are comparable to those of the putative IPNS superoxo intermediate, and are shown to involve RS− → Fe–O2•− and O2•− → Fe charge transfer transitions. The π-back-donation by the electronrich alkyl thiolate presumably facilitates this reactivity by increasing the basicity of the distal oxygen. The frontier orbitals of 4 are shown to consist of two strongly coupled unpaired electrons of opposite spin, one in a superoxo π*(O–O) orbital, and the other in an Fe(dxy) orbital.

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“…Modelling of the facial 3‐His coordination has been accomplished through various nitrogen donor ligands such as 1,4,7‐triazacyclononane ( tacn ), [4] tris(2‐pyridyl)methane, [5] trispyrazolyl variants namely trispyrazolylborates, [6] trispyrazolylmethanes [7] and trisimidazolylphosphines ( TIP ) [8] . Some of these facially coordinating ligands have been used to prepare Fe‐based O 2 derived oxidants, such as superoxo and oxo species [9,10,11,12,13,14] and in catalysis [15,16] …”

Section: Figurementioning

confidence: 99%

A Facially Coordinating Tris‐Benzimidazole Ligand for Nonheme Iron Enzyme Models

et al. 2021

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Herein, we report a new tripodal tris‐benzimidazole ligand (Tbim) that structurally mimics the 3‐His coordination environment of certain nonheme mononuclear iron oxygenases. The coordination chemistry of Tbim was explored with iron(II) revealing a diverse set of coordination modes. The aerobic oxidation of biomimetic model substrate diethyl‐2‐phenylmalonate was studied using the Tbim−Fe and Fe(OTf)2.

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A synthetic model of the nonheme iron–superoxo intermediate of cysteine dioxygenase

Cited by 34 publications

References 35 publications

Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases

Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases

Formation of a Reactive, Alkyl Thiolate-Ligated Fe^III-Superoxo Intermediate Derived from Dioxygen

A Facially Coordinating Tris‐Benzimidazole Ligand for Nonheme Iron Enzyme Models

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A synthetic model of the nonheme iron–superoxo intermediate of cysteine dioxygenase

Cited by 34 publications

References 35 publications

Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases

Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases

Formation of a Reactive, Alkyl Thiolate-Ligated FeIII-Superoxo Intermediate Derived from Dioxygen

A Facially Coordinating Tris‐Benzimidazole Ligand for Nonheme Iron Enzyme Models

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Formation of a Reactive, Alkyl Thiolate-Ligated Fe^III-Superoxo Intermediate Derived from Dioxygen