Applications of NMR Spectroscopy

Breast cancer (BC) has the highest occurrence and mortality of all cancers that affect women with more than one million new cases each year across the globe. BC accounts for about one-quarter of all cancer-related deaths. Even though breast cancer is an aggressive and fatal disease, early detection and treatment can result in increased survival in more than three-quarters of diagnosed patients. In general, traditional diagnostic methods, such as ultrasonography and mammography, considerably increase t survival rates due to early disease detection. Although these traditional methods are useful, new strategies for early detection of breast cancer would likely reduce breast cancer mortality rates. Additional diagnostic imaging modalities, such as Computer Tomography (CT), Positron Emission Tomography (PET), and other types of scintigraphy techniques, have been used to identify the primary source of the cancer in metastatic cases, but none of these techniques is yet in routine clinical use. Among other imaging methodologies, Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy (MRS) and Nuclear Magnetic Resonance (NMR) approaches are powerful tools for uncovering cancer biomarkers. In this review, we consider the current capabilities of magnetic resonance techniques in breast cancer research and highlight some milestones that are necessary to move early detection of breast cancer using such approaches into mainstream health care modalities.

Dietary polyphenols represent a large class of naturally occurring phenolic compounds which have been well investigated as antioxidants, radical scavengers and other health-promoting agents. For structural elucidation of any new polyphenol isolated from the food matrix, nuclear magnetic resonance (NMR) spectroscopy has become a powerful and routinely used analytical tool. Moreover, NMR spectroscopy also finds many other applications in food science and technology, such as quality control and metabolomics studies. With the aid of NMR technology, fundamental understanding of the polyphenol chemistry and reactivity has also been gradually disclosed, which sheds light on a better understanding of the structure-property relationship of polyphenols.

Recent advancements in NMR spectroscopy have been pivotal to the discovery of molecules that hold promise as human drugs. A sizeable portion of these newly discovered bioactive compounds are natural products, organic molecules produced by living things such as plants and microorganisms. Natural products provide an ideal vantage point for examining recent NMR advancements, because these molecules pose myriad structure elucidation challenges resulting from their diverse structures and low abundances within complex mixtures. This chapter discusses recent developments in NMR technologies and methods, as applied toward discovery of novel natural products that may hold potential as pharmaceuticals. Discussion of NMR advancements focuses on several areas that have recently emerged or matured, highlighting (1) higher magnetic fields and improved probes (e.g., microprobes and cryoprobes) that have dramatically enhanced the sensitivity of NMR during the past decade and opened doors for structure determination of minute quantities of highly bioactive natural products, (2) hyphenated NMR methods (e.g., LC-NMR, GC-NMR, CE-NMR) for structure elucidation of low abundance or unstable metabolites and dereplication of known natural products, and (3) approaches for the direct identification of molecules within mixtures, including metabolomics-based strategies for metabolite discovery. Each of these highlighted advancements in NMR-based drug discovery is presented in the context of one or more natural product exemplars.

Fluorine NMR is a useful probe of protein structure, conformation and folding in fluorinated proteins, owing to the high sensitivity, large chemical shift of the ¹⁹F nucleus and the lack of high background signal to be suppressed. Protein NMR studies using fluorinated amino acids are a valuable addition to the existing suite of experiments with isotopically enriched nuclei. Recently, there have been several efforts to develop novel methods of biosynthetically tagging proteins to contain ¹⁹F labels using fluorinated amino acids. Each fluorine signal in the resultant protein then becomes a reporter of the protein’s structure and conformational dynamics. ¹⁹F NMR relaxation times (including T1 relaxation and homonuclear and heteronuclear NOE relaxation) can give detailed structural information. The ¹⁹F CSA mechanism is an important relaxation mechanism at high magnetic fields and several novel experiments have been designed, to determine the complete ¹⁹F CSA tensor. Several groups are also trying to apply ¹⁹F NMR techniques to study membrane proteins and intrinsically disordered proteins which have a fluorinated tag. This chapter will focus on novel NMR techniques using fluorine as a probe and their application to structure determination and conformational dynamics of fluorinated biomolecules.

Nuclear Magnetic Resonance (NMR) spectroscopy has advanced as an important tool in support of several studies of pharmacological interest. In this chapter, the following sections are discussed: the history of NMR spectroscopy, the enaminone derivatives and their NMR, the use of molecular modeling techniques as an adjunct to NMR analysis, and a newer class of compounds, the sulfonamide enaminones and their intermolecular forces determined via NMR and X-ray crystallography. The history of NMR spectroscopy details the field of NMR, its origin, and utilization in the area of structure identification. The section on NMR spectroscopy of the enaminones gives a detailed look into the use of NMR in the area of analyzing various enaminone analogs, including our library of anticonvulsant enaminones. Examples of enaminones and NMR include the work of Zhou in noting the correlation between the 17O (which has natural abundance) chemical shifts of the carbonyl atom and the 1H chemical shifts. Our work on enaminones analogs was complemented by NMR spectroscopy with examples of how reactions were determined by NMR analyses. The section on molecular modeling aspects as an adjunct to the NMR field explains how the use of Gaussian 03 performs suitable functions in determining the final structure and gives reason to why some compounds in a series are more potent than others. The final section illustrates the newer sulfonamido enaminones now being researched as potential anticonvulsant agents and how their pharmacological profile (having 6 Hz ‘psychomotor’ activity) differs from the previously investigated anticonvulsant enaminone derivatives.

Intermolecular and intramolecular interactions are crucial for almost all processes in chemistry, biology and biochemistry, and one of the most powerful techniques for monitoring these interactions is NMR spectroscopy. Many NMR experiments study biomolecules or small organic molecules under non-natural conditions, but these are still very similar to the native environments. In this chapter, our aim is to discuss NMR spectroscopy applications to drug design, enzyme inhibition, and the monitoring of host-guest interactions during the development of some novel drug formulations. In addition, other important protein-ligand and proteinprotein interactions will be discussed. Two NMR approaches are conducted for monitoring these interactions: one of these is based on the isotopic labeling of proteins and the other is based on the study of small molecules. Both techniques have a high impact on the examined cases. Finally, intermolecular and intramolecular interactions are used to study different metabolic pathways, and one very important NMR spectroscopy application includes metabolomics, where elucidation of characteristic chemical fingerprints for various biochemical processes can be achieved; this technique can be used to compare symptomatic, infected and healthy subjects.