Synthesis, characterization, and spectroscopy of model molybdopterin complexes

Abstract

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 or −C(OH)(CH 3 ) 2 ). 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 dithiolene with electron-withdrawing substituents and simple dithiolate 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).

Study of Molybdenum(4+) Quinoxalyldithiolenes as Models for the Noninnocent Pyranopterin in the Molybdenum Cofactor

“…Our strategy for exploring the possibilities created by a Mo-pterin-dithiolene partnership has been to develop the reaction chemistry of pterin- and quinoxaline-substituted dithiolene complexes of molybdenum to serve as small molecule analogues for studying the effects of these N-heterocycles on dithiolene properties. 27 …”

Molybdenum cofactor biosynthesis in plants and humans

“…In contrast to cPMP, dihydropterins are characterized by a high sensitivity to oxygen with half-lives of minutes [29] while tetrahydropterins such as biopterin are more stable at physiological pH (t 1/2 = 10-20 min) [30]. Studies with different synthetic pyranopterins demonstrated a remarkable increase in stability of pyranopterins in comparison to dihydro and tetrahydropterins [31,32], which fits much better with the observed stability of cPMP. The chemical structure of cPMP was clarified using high resolution mass spectrometry and 1 H NMR spectroscopy [33].…”

Recent developments in the study of molybdoenzyme models

“…24 Surprisingly, the Magnetic Circular Dichroism and Electron Paramagnetic Resonance spectra exhibited by Tp*MoO(bdt) and Tp*MoO(pterin-dithiolene) complexes have nearly identical parameters suggesting the pterin substituent has little effect on the molybdenum environment. 24 …”

“…65 A notable piece of data from this study is the 95,97 Mo hyperfine value, whose small value (11 G) was interpreted as consistent with a highly covalent Mo-(pterin-dithiolene) system with a HOMO based on the C and S atoms of the dithiolene. 24, 66 …”

“…10, B), where the R-group can be a variety of hydroxyalkyl, aryl and, under current investigation, alkyl substituents. 24 In the case of the Tp*MoX(pterin-dithiolenes) (X = S,O; R = aryl), it was concluded that the most significant effect of pterin substitution was to shift the Mo(5+/4+) redox potential considerably in the positive direction compared to simpler model complexes bearing 1,2-benzene dithiolate (bdt) or ethanedithiolate (edt). 24 Surprisingly, the Magnetic Circular Dichroism and Electron Paramagnetic Resonance spectra exhibited by Tp*MoO(bdt) and Tp*MoO(pterin-dithiolene) complexes have nearly identical parameters suggesting the pterin substituent has little effect on the molybdenum environment.…”