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. 2019 Jan 1;1317(4):71-83.
doi: 10.1021/bk-2019-1317.ch004. Epub 2019 Jul 12.

A Biomimetic System for Studying Salicylate Dioxygenase

Atanu Banerjee  1 , Jia Li  1 , Monika A Molenda  1 , William W Brennessel  2 , Ferman A Chavez  2
Affiliations

A Biomimetic System for Studying Salicylate Dioxygenase

Atanu Banerjee et al. ACS Symp Ser Am Chem Soc. .

Abstract

We report the characterization of [Fe(T1Et4iPrIP)(sal)] (2) (T1Et4iPrIP = tris(1-ethyl-4-isopropyl-imidazolyl)phosphine; sal2- = salicylate dianion), which serves as a model for substrate-bound salicylate dioxygenase (SDO). Complex 2 crystallizes in the monoclinic space group P21/n with a = 10.7853(12) Å, b = 16.5060(19) Å, c = 21.217(2) Å, β = 94.489(2)°, and V = 3765.5(7) Å3. The structure consists of FeII bonded in distorted square pyramidal geometry (τ = 0.32) with two salicylate oxygens and two T1Et4iPrIP nitrogens serving as the base and the apical position occupied by the other ligand nitrogen. [Fe(T1Et4iPrIP)(OTf)2] (1), the precursor for 2, catalyzes the cleavage of 1,4-dihydroxy-2-naphthoate in the presence of O2. Complex 1 is also capable of cleaving the salicylate aromatic ring in the presence of H2O2. The progression of this reaction toward product formation involves an FeIII-phenoxide species.

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Figures

Figure 1.
Figure 1.
X-ray structure for the active site of GDO (PDB 3BU7) and SDO with bound gentisate (PDB 3NL1), salicylate (PDB 3NJZ), and naphthoate (PDB 3NKT).
Figure 2.
Figure 2.
Oak Ridge thermal ellipsoid plot of 2 (50% probability). H-atoms have been removed for clarity.
Figure 3.
Figure 3.
Initial UV–vis spectrum of 1 and bis(tetraethylammonium) salicylate at a ratio of 1:1 in methanol (−), spectrum in methanol after addition of 20 equiv H2O2 (⋯), and spectrum after 10 min (- - -).
Figure 4.
Figure 4.
1H NMR spectra (25 °C) of extracted reaction mixtures in CDCl3. Fe(OTf)2·2CH3CN (control, top) and 1 reacted with 1 equiv bis(tetraethylammonium) salicylate and 20 equiv H2O2 in methanol. After 14 h, reactions were acidified with 1 N HCl and extracted with CH2Cl2. The CH2Cl2 was removed in vacuo and the residues were redissolved in CDCl3 for analysis.
Scheme 1.
Scheme 1.
Class III dioxygenase enzymes: GDO, SDO, and HNDO.
Scheme 2.
Scheme 2.
Proposed mechanism for dioxygenation of gentisate by GDO (23).
Scheme 3.
Scheme 3.
Structures of T1Et4iPrIP and [Fe(T1Et4iPrIP)(OTf)2] (1).
Scheme 4.
Scheme 4.
Dioxygenation of 1,4-dihydroxy-2-naphthoate (33).
Scheme 5.
Scheme 5.
Proposed mechanism for the dioxygenation of 1,4-dihydroxy-2-naphthoate (33).
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