Molybdopterin-Modeling: The Synthesis of Pterin Dithiolene Ligands (original) (raw)
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Pterin chemistry and its relationship to the molybdenum cofactor
Coordination Chemistry Reviews, 2011
The molybdenum cofactor is composed of a molybdenum coordinated by one or two rather complicated ligands known as either molybdopterin or pyranopterin. Pterin is one of a large family of bicyclic N-heterocycles called pteridines. Such molecules are widely found in Nature, having various forms to perform a variety of biological functions. This article describes the basic nomenclature of pterin, their biological roles, structure, chemical synthesis and redox reactivity. In addition, the biosynthesis of pterins and current models of the molybdenum cofactor are discussed.
Synthesis, characterization, and spectroscopy of model molybdopterin complexes
Journal of Inorganic Biochemistry, 2007
The preparation and characterization of new model complexes for the molybdenum cofactor are reported. The new models are distinctive for the inclusion of pterin-substituted dithiolene chelates and have the formulation Tp * MoX(pterin-R-dithiolene) (Tp * = tris(3,5,-dimethylpyrazolyl)borate), X = O, S, R = aryl. Syntheses of Mo(4+) and (5+) complexes of two pterin-dithiolene derivatives as both oxo and sulfido compounds, and improved syntheses for pterinyl alkynes and [Et 4 N][Tp * Mo IV (S)S 4 ] reagents are described. Characterization methods include electrospray ionization mass spectrometry, electrochemistry, infrared spectroscopy, electron paramagnetic resonance and magnetic circular dichroism. Cyclic voltammetry reveals that the Mo(5+/4+) reduction potential is intermediate between that for dithiolenes with electron-withdrawing substituents and simple dithiolates chelates. Electron paramagnetic resonance and magnetic circular dichroism of Mo(5+) complexes where X = O, R = aryl indicates that the molybdenum environment in the new models is electronically similar to that in Tp * MoO(benzenedithiolate).
Inorganic Chemistry, 1999
The synthesis and structure of a new molybdenum complex coordinated by a reduced pterin is reported. [MoOCl-(detc)(H 3 dmp)]Cl (1) (where detc is diethyldithiocarbamate and H 3 dmp is 6,7-dimethyl-6,7,8-trihydropterin) is prepared from MoOCl 2 (detc) 2 and H 4 dmp (6,7-dimethyl-5,6,7,8-tetrahydropterin). The X-ray structure determination of [MoOCl(detc)(H 3 dmp)]Cl‚MeOH reveals an octahedral complex where the reduced pterin ligand coordinates through the carbonyl oxygen and pyrazine ring nitrogen atoms. An extensive hydrogen bonding network in the crystal lattice connects adjacent complexes, the chloride counterion, and the molecule of methanol. This hydrogen bonding persists in solution where it is identified by characteristic absorptions in the electronic spectrum. Dimethyl sulfoxide (DMSO) oxidizes [MoOCl(detc)(H 3 dmp)]Cl, producing 1 equiv of dimethylpterin and 1 / 2 equiv of oxidized dithiocarbamate, tetraethylthiuramdisulfide (TETDS), a reaction that constitutes a net five-electron oxidation of the molybdenum complex 1. Pterin oxidation is also observed for 1 in dimethylformamide (DMF) solution where it is believed to result from intermolecular electron transfer mediated by the hydrogen-bonding network.
Inorganic Chemistry, 1999
The coordination of alloxazine and pterins to molybdenum(IV) is demonstrated in this study. The synthesis of MoOCl 3 (pteridineH), where pteridineH is the protonated form of 1,3,7,8-tetramethylalloxazine (tmaz), 2-pivaloyl-6,7-dimethylpterin (piv-dmp), and 6,7-dimethylpterin (dmp), proceeds readily starting from Mo(IV)Cl 4 (acetonitrile) 2 and the pteridine ligand in chloroform or methanol. X-ray crystal structures of MoOCl 3 (tmazH) (1) and MoOCl 3 -(piv-dmpH) (2) show that Mo chelates each pteridine at the carbonyl oxygen and pyrazine nitrogen and that the pteridine ligand is protonated at the other nitrogen in the pyrazine ring. A third X-ray structure for MoOCl 3 (H 3dmp) (4) is included in this work since its determination permits the comparison of metrical parameters for the oxidized and reduced forms of a pterin in identical molybdenum coordination environments. The major difference observed in the structures of 2 as compared to 4 is the Mo-N5 bond length which is significantly shorter in compound 4 containing the reduced form of the pterin. Pteridine protonation is facilitated by molybdenum(IV) coordination due to partial reduction of the pteridine ring through electronic delocalization from Mo to the pteridine ligand. Electronic spectroscopy monitoring the solution reactivity of 1, 2, and MoOCl 3 (dmpH) (3) provides evidence to support this idea. Solution conditions favoring deprotonation of the complexes 1-3 promote pteridine dissociation and complex decomposition.
Helvetica Chimica Acta, 1997
The first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [MoV'02(LN-S,)] (8; LN-S, = pyridine-2,6-bis(methanethiolato)) with 5,6,7&tetrahydropterin (7)'2 HCl (H,Ptr '2 HC1). The complex crystallizes, with a non-coordinating CI-atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4)A,P = 120.36(3)0, a n d Z = 8. Weinterpret 9as [Mo"O(LN-S2)(Hf-q-H,Ptr)]Cl (q = quinonoid; H,Ptr = dihydropterin), i e. , a Mo" monooxo center coordinated by a pyridine-2,6bis(methanethiolat0) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S-coordination. The slightly H20-soluble complex 9 reacts with the natural enzyme subsuate DMSO very slowly, possibly due to the lack ofeasily dissociable ligands at the metal center. ') Name according to IUPAC rules; tetrahydropterin [H4Ptr] = 2-amino-5,6,7,8-tetrahydropteridin-4(3H)-one.
2019
Molybdenum dependent enzymes are involved in essential metabolic transformations in bacteria, plants, and human beings. The extreme instability of the molybdenum cofactor (Moco) prevents its use as an effective treatment for patients with a Moco deficiency. Therefore, the design, develop and execute the artificial molybdenum cofactor models are essential. In the present thesis, the asymmetric molybdopterin (mpt) model precursors with oxygen functionality and various electronic structures and their Moco model complexes mimicking the natural cofactor have been synthesized and comprehensively investigated through multi-nuclear NMR, MS, IR, resonance Raman, X-ray crystallography, UV-Vis, and electrochemical methods. Notably, the asymmetrically substituted dithiolenes in this thesis are confirmed through a significant push-pull effect, which is tuning its electronic structure. The redox behavior of Moco model complexes was investigated by temperature-dependent cyclic voltammetry. Electro...