Natural products from marine actinomycetes remain an important resource for drug discovery, many of which are produced by the genus, Streptomyces. However, in standard laboratory conditions, specific gene clusters in microbes have long been considered silent or covert. Thus, various stress techniques activated latent gene clusters leading to isolation of potential metabolites. This study focused on the analysis of two new angucycline antibiotics isolated from the culture filtrate of a marine Streptomyces pratensis strain NA-ZhouS1, named, stremycin A (1) and B (2) which were further determined based on spectroscopic techniques such as high resolution time of flight mass spectrometry (HR-TOF-MS), 1D, and 2D nuclear magnetic resonance (NMR) experiments. In addition, four other known compounds, namely, 2-[2-(3,5-dimethyl-2-oxo-cyclohexyl)-6-oxo-tetrahydro-pyran-4yl]-acetamide (3), cyclo[l-(4-hydroxyprolinyl)-l-leucine] (4), 2-methyl-3H-quinazoline-4-one (5), and menthane derivative, 3-(hydroxymethyl)-6-isopropyl-10,12-dioxatricyclo[7.2.1.0]dodec-4-en-8-one (6) were obtained and elucidated by means of 1D NMR spectrometry. Herein, we describe the “Metal Stress Technique” applied in the discovery of angucyclines, a distinctive class of antibiotics that are commonly encoded in microbiomes but have never been reported in “Metal Stress” based discovery efforts. Novel antibiotics 1 and 2 exhibited antimicrobial activities against Pseudomonas aeruginosa, methicillin resistant Staphylococcus aureus (MRSA), Klebsiella pneumonia, and Escherichia coli with equal minimum inhibitory concentration (MIC) values of 16 µg/mL, while these antibiotics showed inhibition against Bacillus subtilis at MIC value of approximately 8–16 µg/mL, respectively. As a result, the outcome of this investigation revealed that metal stress is an effective technique in unlocking the biosynthetic potential and resulting production of novel antibiotics.

Polysaccharides are important biomolecules, which play a key role in biological, medical, and industrial processes due to their diverse structures and important functions. This paper looks into the significant progress made in the structural and functional analysis of polysaccharides by nuclear magnetic resonance (NMR) spectroscopy. NMR spectroscopy, including solution-state and solid-state technology, has revolutionized this field through detailed molecular insights into the structure, conformation, and dynamics of polysaccharides at the molecular level. There have been some important historical breakthroughs in 1D and 2D NMR, which have led to modern methods like multidimensional NMR and nuclear dynamic polarization (DNP). These modern methods offer a high level of resolution and sensitivity and have made it easier to come up with innovative applications. The applications range from the structural elucidation of microbial and plant structures of polysaccharides to improving food texture, developing therapies, and creating sustainable materials. Despite challenges such as signal overlap and limited sensitivity, emerging solutions are making significant progress. Computational modeling, isotope labeling, and integrated methods that combine complementary technologies are driving the boundaries of polysaccharide research. This review demonstrates the transformative role of NMR in revealing the complexity of polysaccharides and its potential to promote future discoveries and new ideas in the dynamic field.

Nuclear magnetic resonance (NMR) spectroscopy is gaining prominence as a vital quantitative method for sample analysis, with significant progress being made in the investigation of heteronuclei like phosphorus, a key element in numerous physiological functions. This paper provides a comprehensive review of the principles, methodologies, and applications of quantitative ³¹P nuclear magnetic resonance (qNMR) spectroscopy. It begins with an introduction to the fundamental principles of NMR spectroscopy, highlighting the specific advantages of qNMR and the unique properties of the ³¹P nucleus, including its high natural abundance and broad chemical shift range. While ¹H qNMR is widely used, signal overlap in complex mixtures can limit its accuracy. Additionally, this work explores diverse applications of ³¹P qNMR across fields such as food analysis, pharmaceuticals, and biology, emphasizing its contributions to real-time drug quantification, metabolomics, and environmental analysis. A key advantage of ³¹P NMR is its ability to provide exclusive detection and direct quantification of phosphorus in phosphorus-containing compounds. The internal standard method is favored for its simplicity, as it avoids the need for calibration curves, while the external standard method is better suited for natural products with established reference materials. This review aims to consolidate the applied prospects of ³¹P qNMR, emphasizing its potential to expand the horizons of quantitative detection technologies and facilitate advancements in future research and practical applications.