Spectroscopic Techniques for the Structural Characterization of Bioactive Phytochemicals

This chapter deals with the structural elucidation of natural products using UV-visible, FT-IR, NMR (1D and 2D) spectroscopy and Mass spectrometry. Key concepts associated with these techniques are introduced here. Various spectra of natural compounds have been included with a brief discussion of the functional groups and structural features that they reveal. The use of these spectroscopic techniques in drug discovery from natural products has been reviewed, highlighting the advantages of these techniques. The importance of each technique is discussed with suitable examples of natural products obtained from medicinal plants. Some of these techniques, such as FT-IR and NMR spectroscopy, are primarily used for identification purposes; while UV-visible spectroscopy and mass spectrometry are used for the purpose of analysis and structural elucidation. Recent advancements in the isolation techniques such as counter-current chromatography, supercritical fluid chromatography, preparative high-performance liquid chromatography (prep-HPLC), and preparative gas chromatography (prep-GC) have made the availability of novel natural compounds from plants possible for their structural elucidation and biological screening. Development of hyphenated techniques such as LC-NMR, UPLC-MS, and GC-MS have made simultaneous isolation and structural elucidation of natural products achievable. In this chapter, we have summarized basic principles of UVvisible, FT-IR, 1D and 2D NMR spectroscopy and mass spectrometry and their role in the determination of structures of natural compounds citing suitable examples.

Keywords: FT-IR Spectroscopy, Mass Spectrometry, Natural Products, NMR Spectroscopy, UV-visible Spectroscopy, Structural Characterization.