Alexandra Nagelski
Dr. Sharon J. N. Burgmayer
Chemistry Department

The Investigation of Pterin Reduction Dynamics in Synthetic Molybdenum Cofactor Models

              Molybdoenzymes catalyze oxygen atom transfer reactions and exist in nearly all organisms. In their catalytic site, molybdoenzymes contain the molybdenum cofactor (Moco). Moco is not stable outside of the protein matrix, therefore the use of small molecule analogues provides an alternate way to study Moco. This research focuses on the molybdopterin (MPT), which describes one or two conserved pyranopterin dithiolene ligands on Moco and its role in the catalytic function of Moco. Although there is little known about the relationship between MPT and the catalytic function of Moco, without MPT, Moco loses its catalytic efficiency. MPT is the most redox active ligand in all of biology, which suggests that the oxidation state may play a role in catalysis. The Burgmayer lab has created the model systems [TEA][Tp*Mo(O)(S2C2(pterin)(C(CH3)2R)], where TEA is tetraethylammonium, Tp* is tris(3,5-dimethylpyrazolyl)hydroborate, Mo exists in the Mo(IV) or Mo(V) oxidation state, and R can be a hydroxyl (1) or methyl (2). In (1), the complex experiences reversible intramolecular cyclization that is dependent upon the dielectric constant of the solvent, producing a pyran ring, as shown in Figure 1. The related complex (2), where the hydroxyl group (depicted in red in Figure 1) is isosterically replaced with a methyl group, prevents this intramolecular cyclization, thereby creating a standard to compare the behavior of (1).

The tetrahydropyranopterin form of (1), which has already been synthesized in our lab, closely resembles the Moco pyranopterin structure observed in molybdoenzymes crystal structures. We hope to achieve the reduced dihydro form and the fully reduced uncyclized tetrahydro form of (1) and (2). From reducing the oxidized pterin in these model complexes, we can learn more about the changes on the catalytic efficiency and the electronics that it may exhibit.

 

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Figure 1: [TEA][Tp*Mo(O)S2BMOPP], where BMOPP is 6-(3-butynyl-2-methyl-2-ol)-2-pivaloyl pterin.