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Browsing by Author "Bandar, Jeff, committee member"

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    Ring-conversion and functionalization of nitrogen-containing heterocycles
    (Colorado State University. Libraries, 2024) Josephitis, Celena M., author; McNally, Andrew, advisor; Bandar, Jeff, committee member; Chung, Jean, committee member; Reisfeld, Bradley, committee member
    Pyridines and related azines are ubiquitous in pharmaceuticals and agrochemicals development. Chemist rely on the development of new synthetic methods to modify these heterocycles. Described herein are the development of methods to functionalize azines and convert pyridines and diazines into new heterocycles. Novel hydrogenation and molecular editing strategies were designed and leveraged to accomplish this goal. Chapter one introduces the importance of pyridines and related heterocycles in pharmaceuticals as well as methods to access and functionalize these molecules. Both classical and contemporary methods for functionalization and hydrogenation of pyridines are discussed to provide context for this work. Chapter two describes a novel method to selectively reduce pyridines to dihydropyridines, tetrahydropyridines, and piperidines. This method offers a complementary alternative to current hydrogenation or reduction methods, in which the degree of saturation cannot be controlled, and applies to complex azine starting materials. Chapter three explains the importance of structure-activity relationship (SAR) studies and its implications on the drug-discovery process. It also describes classical and contemporary strategies that apply to SAR diversification including de novo heterocycle synthesis and molecular editing strategies. Finally, chapter four presents a novel method for SAR diversification of pyrimidine containing molecules using a deconstruction/reconstruction approach.
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    Site-selective pyridine functionalization via nucleophilic additions to activated pyridiniums
    (Colorado State University. Libraries, 2024) Nguyen, Hillary M. H., author; McNally, Andrew, advisor; Bandar, Jeff, committee member; Chung, Jean, committee member; Shoemaker, Mark, committee member
    Pyridines and diazines are important heterocycles commonly found in pharmaceuticals, agrochemicals, ligands, and various other organic molecules. Pyridines existing in these molecules usually have multiple bonds connected to them that contribute to their reactivity and characteristics. Therefore, there are ongoing efforts l to find new methods to functionalize these heterocycles. Our lab has contributed to this field by developing methods to functionalize pyridines directly from the C–H bond through phosphonium salts or Zincke imines. Chapter One gives an overview of the current methods for pyridine functionalization and their limitations. Chapter Two describes the synthesis of N-Tf Zincke imines and their use for regioselective 3-position pyridine functionalization. Bipyridines and pyridine-piperidine coupled products are accessed through this method. Chapter Three discusses using N-Tf Zincke imines to form 15N pyridines and coupled with deuteration forms higher mass isotopologues. Chapter Four describes the formation of N-alkyl pyridinium salts from N-Tf Zincke imines. This chapter focuses on optimizing the ring-opening of 2-ester pyridines and ring-closing them with amino esters to access pipecolic esters for macrocyclization. Chapter Five highlights direct nucleophile additions to the 4-position of N-Tf pyridinium salts for pyridine functionalization. 4-aminated pyridines are formed with both aliphatic amines and anilines from the C–H bond. The regioselectivity of this amination is controlled by the basicity of the reaction. In addition, 4-NH2 pyridines are achieved through this method by adding benzophenone imine, an ammonia surrogate. This reaction extends to adding in heteroatom nucleophiles including alcohols, thioesters, amides, and sulfonamides.
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    Static and dynamic study of metal salt hydrates of weakly-coordinating fluoroanions by vibrational spectroscopy, gravimetry, and an analysis of previously published x-ray structures
    (Colorado State University. Libraries, 2021) Lacroix, Matthew R., author; Strauss, Steven H., advisor; Chen, Eugene, committee member; Bandar, Jeff, committee member; Ridley, John, committee member
    Eighteen metal salt hydrates (Li(H2O)4(Al(OC(CF3)3)4), Li(H2O)(B(3,5-C6H3(CF3)2)4), Li(H2O)n(Ga(C2F5)4), Li(H2O)(PF6), Na(H2O)(PF6), Li2(H2O)4(B12F12), Na2(H2O)2(B12F12), K2(H2O)2(B12F12), Rb2(H2O)2(B12F12), Cs2(H2O)(B12F12), Mg(H2O)6(B12F12), Ca(H2O)n(B12F12), Sr(H2O)n(B12F12), Ba(H2O)n(B12F12), Co(H2O)6(B12F12), Ni(H2O)6(B12F12), Zn(H2O)6(B12F12), and Li2(H2O)2(TiF6)) containing weakly coordinating anions were analyzed using room temperature ATR-FTIR spectroscopy. The goal was to investigate the relative strengths of water–anion hydrogen bonds in the solid-state. In all but one case, these hydrogen bonds take the form of O–H···F hydrogen bonds. The one exception is in the salt Li2(H2O)4(B12F12) where there are both O–H···F and O–H···O hydrogen bonds present. Based on the magnitude of the redshift of the ν(OH) band(s) a qualitative scale for the comparison of the relative hydrogen bond strength is constructed. Included in this scale are additional metal salt hydrates taken from the literature. This spectroscopic study has produced some of the only room temperature spectra for water participating in hydrogen bonding in the solid-state where the νasym(OH) and νsym(OH) bands are individually resolvable. The weak nature of the O–H···F hydrogen bonds allows for resolution of ν(OH) bands only 5 cm−1 apart in some cases. The two metal salt hydrates (Li(H2O)4(Al(OC(CF3)3)4) and Li(H2O)(B(3,5-C6H3(CF3)2)4) are shown to possess the weakest O–H···F hydrogen bonds observed in the solid state at room temperature. The salt Li2(H2O)4(B12F12) contains a cyclic (H2O)4 water cluster, also known as the R4 cluster, is presented, and discussed in the context of the FTIR spectrum of water clusters. Due to the nature of the weak O–H···F hydrogen bonding between the cluster and the surrounding anions the E and B fundamental vibrations for the cluster were able to be determined. The peak-to-peak separation, and relative intensities of these two bands are consistent with computational results from the literature. This is the first time that the R4 water cluster has been successfully studied via FTIR spectroscopy without the presence of other clusters leading to ambiguity in the results. Finally, direct observation of the effect of cation acidity on the relative strength of water–anion hydrogen bonding has been directly observed for the first time in the metal hexahydrate salts M(H2O)6(B12F12) (M = Mg, Co, Ni, Zn). These results, along with the correlation curves constructed in this work, show that it is not possible to assign relative hydrogen bond strength based on O–H···X bond length, nor is it possible to accurately approximate O–H···X bond length based on degree of ν(OH) redshift. Instead, it is shown that the relative basicity of the anion is the primary factor governing the relative hydrogen bond strength, and thus the degree of redshifting experienced by the ν(OH) band(s). The cation acidity also is shown to have a lesser, but observable, effect on the relative strength of O–H···X hydrogen bond. In addition to broadening our fundamental understanding of hydrogen bonding in the solid state, this work also shows that FTIR spectroscopy can be a useful tool for rapidly assigning relative basicity of new weakly coordinating anions without need the for complex protonation experiments.
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    Synthetic control of magnetic resonance properties towards metal-based electron paramagnetic resonance imaging
    (Colorado State University. Libraries, 2023) Campanella, Anthony John, author; Zadrozny, Joseph, advisor; Shores, Matthew, committee member; Bandar, Jeff, committee member; Wu, Mingzhong, committee member
    Electron paramagnetic resonance imaging (EPRI) is the electron-spin analogue to conventional biological (nuclear) magnetic resonance imaging (MRI) whereby unpaired electron spins are probed in order to generate an image. The greater sensitivity of electron spins to their environment can thus be leveraged to capture detailed chemical information from the surroundings, producing an image of the local physiology that adds an extra dimension to the already powerful anatomical information gained from MRI. To move EPRI a step closer to common utilization, paramagnetic probes must be developed to sense the local environment using safe low-frequency microwaves at high (ca. 1.5 T) magnetic fields. Paramagnetic metal complexes are ideal candidates due to their electronic structures but have not been investigated for such purposes. The goal of this dissertation is to develop fundamental design principles to improve the utility of metal complexes as EPRI probes. Presented herein is the first comprehensive collection of experimental investigations to this end. Firstly, a method for improving signal sharpness is investigated, where exhaustive spectroscopic and computational studies suggest differences in relaxation dynamics as being a key factor in spectral linewidth (Chapters 2 and 3). A highly tunable clathrochelate structure is developed, inducing an unusual coordination geometry around the Ni(II) ion affording an 11 cm−1control of zero-field splitting (Chapter 4). The temperature dependence of zero-field splitting is examined in a series of Mn(II) complexes where an unusually high temperature sensitivity is found in the solid state (Chapter 5). Finally, the utility of metal complexes as environmental sensors is demonstrated with a pair of Mn(II) complexes showing that increasing magnetic anisotropy is a design strategy for enhancing microviscosity sensitivity (Chapter 6). The learned design principles will serve as a foundation for the design of metal-based EPRI agents towards improving the non-invasive diagnostic capabilities.