Brominated and Sulfur-Containing Angucyclines Derived from a Single Pathway: Identification of Nocardiopsistins D-F

Antibacterial and cytotoxic angucyclines discovered by heterologous expression of a type II polyketide gene cluster

Three new aromatic polyketides, spirocyclione C (1) and angumycinones E and F (2 and3), were isolated from the heterologous expression of a type II gene cluster in the strain of Streptomyces coelicolor A3(2) assisted by the one strain many compounds (OSMAC) strategy. The structures and absolute configurations of these compounds were elucidated by extensive NMR, MS, theoretical NMR calculations, DP4+ probability analysis, and ECD analyses. Notably, compound 1 represents the first example of an angucycline structure with an unusual oxaspiro[5.4]undecane architecture. Directed by molecular docking and dynamics simulations, the bioactivities of compounds 1-3 were evaluated. Compounds 1 and 2 exhibited promising cytotoxic activity against a panel of human cancer cell lines, and compound 1 showed moderate antibacterial activity against clinical pathogenic strains of B. subtilis, P. vulgaris, B. cereus, M. phlei and MRSA.

Actinomycetes: Treasure trove for discovering novel antibiotic candidates

Actinomycetes are an important source of secondary metabolites such as antibiotics and other active natural products. Many well-known antibiotics, such as streptomycin, oxytetracycline, and tetracycline, are produced by actinomycetes. Different types of antibiotics have distinct mechanisms of action against microorganisms: inhibit protein synthesis, inhibit nucleic acid synthesis, or inhibit cell wall synthesis. For decades, actinomycetes have played a crucial role in clinical treatment for major diseases such as pathogenic bacterial infections, serving as one of the most significant sources of new discoveries. However, due to extensive use of antibiotics, the types and numbers of drug-resistant bacteria, represented by multidrug resistant (MDR) and extensively drug resistant (XDR) bacteria, have increased dramatically in clinical settings, posing a significant threat to human survival. Therefore, there is an urgent need to search for structurally novel antibacterial natural products and develop new antibiotics. In this review, a total of 170 antibacterial secondary metabolites from actinomycetes, published in the 54 literatures (2020 to September 2024) and some synthetic analogs, are discussed with emphasis on their structures and biological activities.

Bioactive Angucyclines/Angucyclinones Discovered from 1965 to 2023

Angucyclines/angucyclinones, a class of polyketides with diverse chemical structures, display various bioactivities including antibacterial or antifungal, anticancer, anti-neuroinflammatory, and anti-α-glucosidase activities. Marine and terrestrial microorganisms have made significant contributions to the discovery of bioactive angucyclines/angucyclinones. This review covers 283 bioactive angucyclines/angucyclinones discovered from 1965 to 2023, and the emphasis is on the biological origins, chemical structures, and biological activities of these interesting natural products.

Heterologous Expression of Type II PKS Gene Cluster Leads to Diversified Angucyclines in Streptomyces albus J1074

Heterologous expression has emerged as an effective strategy in activating Streptomyces cryptic gene clusters or improving yield. Eight compounds were successfully obtained by heterologous expression of the type II PKS gene cluster spi derived from marine Streptomyces sp. HDN155000 in the chassis host Streptomyces albus J1074. The structures with absolute configurations were elucidated using extensive MS and NMR spectroscopic methods, as well as theoretical NMR calculations and electronic circular dichroism (ECD) calculations. Interestingly, compound WS009 Z (2) contains a rare thiomethyl group, angumycinone T (4) has a novel oxo-bridge formed between C12a and C4, and angumycinone X (3) showed cytotoxicity toward K562 and NCI-H446/EP cell lines.

The Chemistry of Angucyclines

Angucyclines and angucyclinones represent a class of natural compounds that belong to the group of aromatic polyketides. They exhibit a wide array of biological properties, such as antimicrobial, antiviral, and cytotoxic. Their considerable therapeutic potential and diverse scaffolds have attracted many synthetic chemists to devise novel strategies to construct their intricate molecular architecture. Over 300 class members have been isolated from natural sources, mainly from bacterial strains of Streptomyces species. This review highlights recent advancements in their synthesis, such as oxidative cyclization, photooxidation, and metal-catalyzed [4+2]-cycloaddition, which has facilitated the efficient and practical total syntheses of various angucycline and angucyclinone natural products.

A Survey of Recently Discovered Naturally Occurring Organohalogen Compounds

The discovery of naturally occurring organohalogen compounds has increased astronomically in the 55 years since they were first discovered─from fewer than 50 in 1968 to a combined 7,958 described examples in three comprehensive reviews. The present survey, which covers the period 2021-2023, brings the number of known natural organohalogens to approximately 8,400. The organization is according to species origin, and coverage includes marine and terrestrial plants, fungi, bacteria, marine sponges, corals, cyanobacteria, tunicates, and other marine organisms.

Targeted Isolation of N-Acetylcysteine-Containing Angucycline Derivatives from Streptomyces sp. MC16 and Their Antiproliferative Effects

Liquid chromatography-mass spectrometry (LC-MS/MS)-based molecular networking analysis was applied to Streptomyces sp. MC16. The automatic classification of the MolNetEnhancer module revealed that its major constituent was an angucycline derivative. By targeted isolation of unique clusters in the molecular network, which showed different patterns from typical angucycline compounds, two new N-acetylcysteine-attached angucycline derivatives (1 and 2) were isolated. The structures were elucidated based on intensive NMR analysis and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). All isolated compounds (1-4) were tested for their inhibitory effects on the proliferation of A431, A549, and HeLa cell lines. Antibiotics 100-1 (3) and vineomycinone B2 (4) showed moderate inhibitory effects on these three cell lines with IC50 values ranging from 18.5 to 59.0 μM, while compounds 1 and 2 with an additional N-acetylcysteine residue showed weak inhibitory effects only on the HeLa cell line with IC50 values of 54.7 and 65.2 μM, respectively.

Sulfur-containing marine natural products as leads for drug discovery and development

Among the large series of marine natural products (MNPs), sulfur-containing MNPs have emerged as potential therapeutic agents for the treatment of a range of diseases. Herein, we reviewed 95 new sulfur-containing MNPs isolated during the period between 2021 and March 2023. In addition, we discuss that the widely used strategies and the emerging technologies including natural product-based antibody drug conjugates (ADCs), small-molecule-based proteolysis targeting chimeras (PROTACs), nanotechnology-based drug carriers, artificial intelligence (AI)-driven drug discovery have been used for improving the efficiency and success rate of NP-based drug development. We also provide perspectives regarding the challenges and opportunities in sulfur-containing MNPs based drug discovery and development and future research directions.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products, such as euphylonoid A from Euphorbia hylonoma.