In recent years, plants, microorganisms, and their products have been the focus of an increasing number of studies. The broad structural diversity of natural products attracts the attention of chemists, cell biologists, chemical engineers, analytical chemists, pharmaceuticals, and microbiologists, stimulated by the need for new therapeutics to address existing and emerging infectious diseases. Natural products (NPs) and their structural analogues have historically made a major contribution to pharmacotherapy, especially for cancer and infectious diseases. Nevertheless, natural products also present challenges for drug discovery, such as technical barriers to screening, isolation, characterization, and optimization, which contributed to a decline in their pursuit by the pharmaceutical industry from the 1990s onwards. Primary and secondary metabolites are the two major classes of NPs that help in cell development, where antimicrobial activity is closely linked with secondary metabolites. To capitalize on the effects of secondary metabolites, co-culture methods have often been used to develop an artificial microbial community that promotes the action of these metabolites. Natural extracts are usually composed of hundreds to thousands of metabolites, whereby the bioactivity of natural extracts can be represented by synergism between several metabolites. However, isolating every single compound from a natural extract is not always possible due to the complex chemistry and presence of most secondary metabolites at very low levels. The potential use of a natural extract or an isolated compound is closely related to their composition determination and structure, respectively. The analytical tools which contribute to gain the molecular characterization of mixtures or isolated NPs are not numerous and are dominated by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. To unravel the complexity of NPs and identify the entities of interest, they are usually coupled with high-resolution separation techniques (i.e. HPLC or capillary electrophoresis) and with chemo-informatics approach to simplify the results and interpret them. Liquid Chromatography-Mass Spectrometry (LC-MS) and Gas Chromatography (GC)-MS are commonly used for metabolite separation while Nuclear Magnetic Resonance (NMR) and Mass Spectrometry (MS) have been used as tools to elucidate the structure of compounds.

Magnetic resonance techniques, such as NMR (nuclear magnetic resonance), MRI (magnetic resonance imaging), and EPR (electron paramagnetic resonance), have become highly useful in a huge number of innovative applications that have emerged and been established over recent years, i.e. absorption spectroscopic techniques that help in structural elucidation and have a wide range of applications in various fields such as drug discovery and development, metabolomics, combinatorial chemistry, and food sciences.

In this Special Issue, we aim to address the roles and effectiveness of various magnetic resonance techniques in the structural elucidation, profiling, and tracing of the biosynthetic pathways of various natural metabolites. This process can ultimately lead to the discovery of new drug entities that may be useful or significant for pharmaceutical industries combating serious diseases. Additionally, metabolomics based on the profiling of natural constituents could serve as a powerful tool in the prevention of the adulteration of various medicinal agents derived either from plants or marine organisms, thereby preventing changes to their biological activity. Original research and review articles are welcome.

Potential topics include but are not limited to the following:

• Using various magnetic resonance techniques for isolation and structural elucidation of secondary metabolites from nature/plants
• Magnetic resonance techniques applied to the identification of metabolites obtained from different microorganisms and their derivatives
• Magnetic resonance techniques applied to the identification of metabolites obtained from marine organisms and their derivatives
• Profiling of phytoproducts using magnetic resonance techniques
• Chemometrics used in quality control and discrimination of plant metabolites employing magnetic resonance techniques
• The tracing of the biosynthetic pathways of various secondary metabolites using the different magnetic resonance techniques
• Various applications of NMR, MRI, and EPR in the exploration and modification of natural metabolites
• The importance of different magnetic resonance techniques in tissue culture and biotransformation of secondary metabolites