1. Synthesis, Characterization, and Computational Modeling of [Co(acacen)L2]+, an Inhibitor of Zinc Finger Proteins
Thomas Williams, Matthew Currier, Timothy Tetrault, and Claudia Willis
University of New Hampshire, Department of Chemistry, Durham, NH
May 4th, 2017
Introduction
Results and Discussion
Future Work
Data was analyzed using 1H NMR, Varying Temperature (VT) NMR, and Spartan Student computational software. Yields of the products were significant but not as high as desired, ranging from 10-40% yield shown in Table 1 above. There was also some difficulty insolating products. Four of the six complexes initially appeared as viscous oils and required extended vacuum condensation. The data in Table 1 also shows the predicted energy of the exchange of 4- methylimidazole (4-MeIm). All of these energies show that an exchange with 4- MeIm is favorable.
Two of the six products were analyzed under 1H NMR and VT NMR. Pictured below, in Figure 1, is the 1H NMR of [Co(acacen)(Py)2] (left) and the exchange shifting of the pyridine (Py) and 4-MeIm under VT NMR at physiological conditions (37°C) (right). The sp2 CH2 peak of the acacen ligand is first situated at 3.48ppm then shifts to 3.29ppm. Characteristic peaks of pyridine in the aromatic region disappeared. In Figure 2 the shift in the 2-MeIm to the 4-MeIm resulted in a shift from 6.73ppm and 7.23ppm to 6.23ppm and 7.23ppm, respectively. A shift of the CH2 peak of the acacen ligand was also observed, moving from 3.49ppm to 3.34ppm. There was not enough time for more spectra.
Table 1: Final mass and percent yields of products along with predicted energies of 4-MeIm exchange
The goal of this project was to create a complex that can manipulate zinc finger proteins. Future chemistry would set that goal into action and reactions of complexes with actual zinc finger proteins could be performed. The Meade group at Northwestern university performed the desired future work using the ammonia complex. That group studies inorganic therapeutic agents and specifically study these complexes as cures for Alzheimer's disease and cancers. They can regulate gene transcription which is a profoundly important biological function.3
Using Spartan computations, it was predicted that the exchange with 4-MeIm with any of the six complexes was favorable. This information makes logical sense as biology is highly efficient and specified. Despite the lack of NMR spectra, exchanges between pyridine and 4-MeIm and 2-MeIm and 4-MeIm were observable; both of which resulted in [Co(acacen)(4-MeIm)2] complexes. These complexes exhibited shifts in the CH2 peak of the acacen ligand as well as shifts due to ligand exchange with 4-MeIm. Unfortunately, due to the lack of time some studies were unachievable; more 1H NMRs and VT exchange NMRs would have been performed, as well as pD studies that were performed in the Manus experiments to fully characterize compounds and exchanges.2
I would like to thank Professors Planalp, Caputo, and Boudreau and the UNH Department of Chemistry as well as our TAs, Luke and Zane
Laity, J. H.; Lee, B. M.; Wright, P.E., Zinc Finger Proteins: New Insight into Structural and Functional Diversity. Curr Opin Struct Biol. 2001, 11(1),
Manus, L. M.; Holbrook, R. J.; Atesin, T. A.; Heffern, M. C.; Harney, A. S.; Eckermann, A. L.; Meade, T. J., Axial Ligand Exchange of N-Heterocyclic Cobalt(III) Schiff Base Complexes: Molecular Structure and NMR Solution Dynamics. Inorg Chem. 2013, 52(2),
Meade, Thomas J., Transcription Factor Inhibition
Cobalt(III) Schiff base complexes that contain the tetradentate ligand bis(acetylacetone)ethylenediamine have important medicinal applications as they can be powerful enzyme and transcription factor inhibitors. Schiff bases are those whose structures rely on an imine group like the one present in bis(acetylacetone)ethylenediamine. In this project, the axial, monodentate ligands of each complex synthesized will be exchanged with 4-methylimidazole and the properties of the resulting complexes will be analyzed. The exchange of ligands explores variations in the preference of the complexes’ binding affinities with histidine residues of zinc finger proteins with profound biological consequences. 4-methylimidazole is an important exchange, as that ligand is analogous to the amino acid residue histidine, which represents a good biological model.1 Zinc finger proteins appear in a relative abundance in the human body and exhibit a wide variety of functions. DNA recognition, RNA packaging, transcriptional activation, regulation of apoptosis, protein folding and assembly, and lipid binding are all key tasks of these proteins which show the vast applications of the manipulation of these molecules.2
Six different cobalt complexes were synthesized each containing different axial ligands and a uniform, singular tetradentate bis(acetylacetone)ethylenediamine (acacen) equatorial ligand. The tetradentate ligand (1) was synthesized through the reaction of acetylacetone and ethylenediamine (Scheme 1). An intermediate product, [Co(acacen)(H2O)2] (2), was synthesized but not isolated using methanol and cobalt bromide (or cobalt chloride in the case of the ammonia ligand) (Scheme 2). A ligand; imidazole, 2-methylimidazole, 4-methylimidazole, N-methylimidazole, pyridine, or ammonia (in the form of ammonia saturated methanol) was added to the solution of the intermediate, then precipitated out using diethyl ether, resulting in product (3) [Co(acacen)(L)2] where L is a ligand (Scheme 3).
Axial Ligands
Mass of Product
Percent Yield ΔE
Imidazole
0.175g
17.5%
-2.80 kJ/mol
2-Methylimidazole
0.103g
10.3%
kJ/mol
4-Methylimidazole
0.422g
26.4%
0.00 kJ/mol
N-Methylimidazole
0.160g
16.0%
-0.29 kJ/mol
Pyridine
0.383g
38.3%
kJ/mol
Ammonia
0.353g
35.3%
-4.13 kJ/mol
Experimental Design
Figure 3: Binding [Co(acacen)(L)2] with zinc finger proteins3
Conclusions
Scheme 1: Synthesis of acacen ligand
Acknowledgements
(1)
Figure 1: 1HNMR of [Co(acacen)(Py)2] (left) and shifts in field directed by exchange with 4-MeIm (middle). An important shift is highlighted (right).
Scheme 2: Synthesis of [Co(acacen)(H2O)2] intermediate
References
(2)
Scheme 3: Synthesis of [Co(acacen)(L)2] product
Figure 2: 1HNMR of [Co(acacen)(2-MeIm)2] (left) and shifts in field directed by exchange 4-MeIm (middle). Important shifts are highlighted (right).
(3)