Antcamphorols A-K, Cytotoxic and ROS Scavenging Triterpenoids from Antrodia camphorata

Metabolic Blockade-Based Genome Mining of Sea Anemone-Associated Streptomyces sp. S1502 Identifies Atypical Angucyclines WS-5995 A-E: Isolation, Identification, Biosynthetic Investigation, and Bioactivities

Marine symbiotic and epiphyte microorganisms are sources of bioactive or structurally novel natural products. Metabolic blockade-based genome mining has been proven to be an effective strategy to accelerate the discovery of natural products from both terrestrial and marine microorganisms. Here, the metabolic blockade-based genome mining strategy was applied to the discovery of other metabolites in a sea anemone-associated Streptomyces sp. S1502. We constructed a mutant Streptomyces sp. S1502/Δstp1 that switched to producing the atypical angucyclines WS-5995 A-E, among which WS-5995 E is a new compound. A biosynthetic gene cluster (wsm) of the angucyclines was identified through gene knock-out and heterologous expression studies. The biosynthetic pathways of WS-5995 A-E were proposed, the roles of some tailoring and regulatory genes were investigated, and the biological activities of WS-5995 A-E were evaluated. WS-5995 A has significant anti-Eimeria tenell activity with an IC50 value of 2.21 μM. The production of antibacterial streptopyrroles and anticoccidial WS-5995 A-E may play a protective role in the mutual relationship between Streptomyces sp. S1502 and its host.

Development of Integrated Vectors with Strong Constitutive Promoters for High-Yield Antibiotic Production in Mangrove-Derived Streptomyces

It is important to improve the production of bioactive secondary products for drug development. The Escherichia coli-Streptomyces shuttle vector pSET152 and its derived vector pIB139 containing a strong constitutive promoter ermEp* are commonly used as integrative vectors in actinomycetes. Four new integrative vectors carrying the strong constitutive promoter kasOp*, hrdBp, SCO5768p, and SP44, respectively, were constructed and proven to be functional in different mangrove-derived Streptomyces host strains by using kanamycin resistance gene neo as a reporter. Some biosynthetic genes of elaiophylins, azalomycin Fs, and armeniaspirols were selected and inserted into these vectors to overexpress in their producers including Streptomyces sp. 219807, Streptomyces sp. 211726, and S. armeniacus DSM 43125, resulting in an approximately 1.1-1.4-fold enhancement of the antibiotic yields.

Visible-Light-Enabled Catalytic Approach to N,O-Spirocycles through Amidyl Radical Addition/Cyclization

A rational combination of photoredox catalyst anthraquinone and hydrogen atom transfer (HAT) catalyst methyl thioglycolate allows for the rapid and straightforward conversion of a range of 2-amidated acetylenic alcohols to multifunctional N,O-spirocycles under visible light irradiation. With oxygen as the sole terminal oxidant, these reactions can be carried out efficiently at room temperature without the involvement of transition metals or strong oxidants. The successful application of this mild catalytic strategy in the late-stage functionalization of bioactive skeletons further highlights its practical value.

Enhancing armeniaspirols production through multi-level engineering of a native Streptomyces producer

BACKGROUND

Nature has provided unique molecular scaffolds for applications including therapeutics, agriculture, and food. Due to differences in ecological environments and laboratory conditions, engineering is often necessary to uncover and utilize the chemical diversity. Although we can efficiently activate and mine these often complex 3D molecules, sufficient production of target molecules for further engineering and application remain a considerable bottleneck. An example of these bioactive scaffolds is armeniaspirols, which are potent polyketide antibiotics against gram-positive pathogens and multi-resistance gram-negative Helicobacter pylori. Here, we examine the upregulation of armeniaspirols in an alternative Streptomyces producer, Streptomyces sp. A793.

RESULTS

Through an incidental observation of enhanced yields with the removal of a competing polyketide cluster, we observed seven-fold improvement in armeniaspirol production. To further investigate the improvement of armeniaspirol production, we examine upregulation of armeniaspirols through engineering of biosynthetic pathways and primary metabolism; including perturbation of genes in biosynthetic gene clusters and regulation of triacylglycerols pool.

CONCLUSION

With either overexpression of extender unit pathway or late-stage N-methylation, or the deletion of a competing polyketide cluster, we can achieve seven-fold to forty nine-fold upregulation of armeniaspirol production. The most significant upregulation was achieved by expression of heterologous fatty acyl-CoA synthase, where we observed not only a ninety seven-fold increase in production yields compared to wild type, but also an increase in the diversity of observed armeniaspirol intermediates and analogs.

Armeniaspirol analogues disrupt the electrical potential (ΔΨ) of the proton motive force

The armeniaspirol family of natural product antibiotics have been shown to inhibit the ATP-dependent proteases ClpXP and ClpYQ and disrupt membrane potential through shuttling of protons across the membrane. Herein we investigate their ability to disrupt the proton motive force (PMF). We show, using a voltage sensitive, that armeniaspiols disrupt the electrical membrane potential (ΔΨ) component of the PMF and not the transmembrane proton gradient (ΔpH). Using checkerboard assays, we confirm this by showing antagonism, with kanamycin, an antibiotic that required ΔΨ for penetration. By evaluating the antibiotic activity and disruption of the PMF by sixteen armeniaspirol analogs, we find that disruption of the PMF is necessary but not sufficient for antibiotic activity. Analogs that are potent disruptors of the PMF without possessing the ability to inhibit ClpXP and ClpYQ are not potent antibiotics. Thus we propose that the armeniaspirols utilize a dual mechanism of action where they disrupt PMF and inhibit the ATP-dependent proteases ClpXP and ClpYQ. This type of dual mechanism has been observed in other natural product-based antibiotics, most notably chelocardin.

Pyrrole-Containing Alkaloids from a Marine-Derived Actinobacterium Streptomyces zhaozhouensis and Their Antimicrobial and Cytotoxic Activities

Two new alkaloids, streptopyrroles B and C (1 and 2), were discovered through a chemical investigation of the ethyl acetate (EtOAc) extract from a marine-derived actinomycete, Streptomyces zhaozhouensis, along with four known analogs (3–6). The structures of the new compounds were elucidated by spectroscopic analysis (HR-ESIMS, 1D, and 2D NMR) and a comparison of their experimental data with literature values. The new compounds were evaluated for their antimicrobial activity by standard broth dilution assay, and the tested compounds showed significant activity against Gram-positive bacteria with minimum inhibitory concentration (MIC) values ranging from 0.7 to 2.9 µM, and kanamycin was used as a positive control with MIC values ranging from <0.5 to 4.1 µM. Additionally, 1, 3, and 5 were evaluated for their cytotoxicity against six tumor cell lines by sulforhodamine B (SRB) assay, and these compounds displayed cytotoxic activities against all the tested cell lines, with concentration causing 50% cell growth inhibition (GI50) values ranging from 4.9 to 10.8 µM, while a positive control, adriamycin, showed GI50 values of 0.13–0.17 µM.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Plant growth-promoting and antimicrobial chloropyrroles from a rare actinomycete of the genus Catellatospora

Two new chloropyrroles, designated catellatopyrroles A (1) and B (2), along with 2-(2'-hydroxybenzoyl)pyrrole (3), were isolated from a culture extract of an actinomycete of the genus Catellatospora. The structures of 1-3 were elucidated through interpretation of NMR and MS data. Compounds 1 and 2 are the first chloropyrroles substituted by an aliphatic acyl group at the 5-position. Compounds 1-3 promoted root elongation of germinated lettuce seeds at 1-10 μM. While all compounds inhibited the growth of Gram-positive bacteria, activity against Gram-negative bacterium Rhizobium radiobacter and yeasts Candida albicans and Saccharomyces cerevisiae was varied. Compounds 1 and 2 were moderately cytotoxic against P388 cells.

Armeniaspirol analogues with more potent Gram-positive antibiotic activity show enhanced inhibition of the ATP-dependent proteases ClpXP and ClpYQ

Antibiotics with fundamentally new mechanisms of action such as the armeniaspirols, which target the ATP-dependent proteases ClpXP and ClpYQ, must be developed to combat antimicrobial resistance. While the mechanism of action of armeniaspirol against Gram-positive bacteria is understood, little is known about the structure-activity relationship for its antibiotic activity. Based on the preliminary data showing that modifications of armeniaspirol's N-methyl group increased antibiotic potency, we probed the structure-activity relationship of N-alkyl armeniaspirol derivatives. A series of focused derivatives were synthesized and evaluated for antibiotic activity against clinically relevant pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. Replacement of the N-methyl with N-hexyl, various N-benzyl, and N-phenethyl substituents led to substantial increases in antibiotic activity and potency for inhibition of both ClpYQ and ClpXP. Docking studies identified binding models for ClpXP and ClpYQ that were consistent with the inhibition data. This work confirms the role of ClpXP and ClpYQ in the mechanism of action of armeniaspirol and provides important lead compounds for further antibiotic development.

Total synthesis and mechanism of action of the antibiotic armeniaspirol A

Emerging antimicrobial resistance urges the discovery of antibiotics with unexplored, resistance-breaking mechanisms. Armeniaspirols represent a novel class of antibiotics with a unique spiro[4.4]non-8-ene scaffold and potent activities against Gram-positive pathogens. We report a concise total synthesis of (±) armeniaspirol A in six steps with a yield of 20.3% that includes the formation of the spirocycle through a copper-catalyzed radical cross-coupling reaction. In mechanistic biological experiments, armeniaspirol A exerted potent membrane depolarization, accounting for the pH-dependent antibiotic activity. Armeniaspirol A also disrupted the membrane potential and decreased oxygen consumption in mitochondria. In planar lipid bilayers and in unilamellar vesicles, armeniaspirol A transported protons across membranes in a protein-independent manner, demonstrating that armeniaspirol A acted as a protonophore. We provide evidence that this mechanism might account for the antibiotic activity of multiple chloropyrrole-containing natural products isolated from various origins that share a 4-acylphenol moiety coupled to chloropyrrole as a joint pharmacophore. We additionally describe an efflux-mediated mechanism of resistance against armeniaspirols.

Comparative genomics and proposal of Streptomyces radicis sp. nov., an endophytic actinomycete from roots of plants in Thailand

Strains DS1-2^T and AZ1-7, which were isolated from roots of plants, were taxonomically characterized based on polyphasic taxonomic and taxogenomic approaches. Both strains were Gram-stain-positive and filamentous bacteria which contained LL-diaminopimelic acid in cell-wall peptidoglycan and glucose and ribose in whole-cell hydrolysates. MK-9(H₆), MK-10(H₆), MK-9(H₈), MK-10(H₈) and MK-10(H₄) were major menaquinones; iso-C_16:0 and iso-C_16:1G were predominant cellular fatty acids; diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylinositol mannoside presented as major phospholipids; and the DNA G+C contents of 73.2 mol%. Strains DS1-2^T and AZ1-7 showed 97.6-98.0 % 16S rRNA gene sequence similarity, 81.0-82.0 % ANIb, 84.8-85.3 % ANIm and 22.0-23.1 % digital DDH to their related type strains: S. specialis GW41-1564^T and S. hoynatensis S1412^T. Comparative genomics results of these strains and their related type strains also revealed the differences and distributions of key genes associated with stress responses, environmental variables, plant interactions and bioactive metabolites. Based on the phenotypic, chemotaxonomic and genomic data, strains DS1-2^T and AZ1-7 could be assigned to the novel species within the genus Streptomyces for which the name Streptomyces radicis sp. nov. is proposed. The type strain is DS1-2^T (=JCM 32152^T =KCTC 39738^T =TISTR 2403^T).

Armeniaspirol A: a novel anti-Helicobacter pylori agent

Antibiotic resistance in Helicobacter pylori has been growing worldwide with current treatment regimens. Development of new compounds for treatment of H. pylori infections is urgently required to achieve a successful eradication therapy in the future. Armeniaspirols, a novel class of natural products isolated from Streptomyces armeniacus, have been previously identified as antibacterial agents against Gram‐positive pathogens. In this study, we found that armeniaspirol A (ARM1) exhibited potent antibacterial activity against H. pylori, including multidrug‐resistant strains, with MIC range values of 4–16 μg ml^‐1. The underlying mechanism of action of ARM1 against H. pylori involved the disruption of bacterial cell membranes. Also, ARM1 inhibited biofilm formation, eliminated preformed biofilms and killed biofilm‐encased H. pylori in a dose‐dependent manner. In a mouse model of multidrug‐resistant H. pylori infection, dual therapy with ARM1 and omeprazole showed efficient in vivo killing efficacy comparable to the standard triple therapy, and induced negligible toxicity against normal tissues. Moreover, at acidic pH 2.5, ARM1 exhibited a much more potent anti‐H. pylori activity than metronidazole. Thus, these findings demonstrated that ARM1 is a novel potent anti‐H. pylori agent, which can be developed as a promising drug lead for treatment of H. pylori infections.

Discovery and Biosynthesis of Tetrachlorizine Reveals Enzymatic Benzylic Dehydrogenation via an ortho-Quinone Methide

Ortho-quinone methides (o-QMs) are reactive intermediates in biosynthesis that give rise to a variety of intra- and intermolecular cyclization/addition products in bacteria, fungi, and plants. Herein, we report a new metabolic deviation of an o-QM intermediate in a benzylic dehydrogenation reaction that links the newly described marine bacterial natural products dihydrotetrachlorizine and tetrachlorizine. We discovered these novel dichloropyrrole-containing compounds from actinomycete strain AJS-327 that unexpectedly harbors in its genome a biosynthetic gene cluster (BGC) of striking similarity to that of chlorizidine, another marine alkaloid bearing a different carbon skeleton. Heterologous expression of the homologous flavin-dependent oxidoreductase enzymes Tcz9 and Clz9 revealed their native functions in tetrachlorizine and chlorizidine biosynthesis, respectively, supporting divergent oxidative dehydrogenation and pyrrolizine-forming reactions. Swapping these berberine bridge enzyme-like oxidoreductases, we produced cyclized and dehydrogenated analogs of tetrachlorizine and chlorizidine, including a dearomatized chlorizidine analog that stabilizes an o-QM via conjugation with a 3H-pyrrolizine ring.

Recent progress of antibacterial natural products: Future antibiotics candidates

The discovery of novel antibacterial molecules plays a key role in solving the current antibiotic crisis issue. Natural products have long been an important source of drug discovery. Herein, we reviewed 256 natural products from 11 structural classes in the period of 2016-01/2020, which were selected by SciFinder with new compounds or new structures and MICs lower than 10 μg/mL or 10 μM as criterions. This review will provide some effective antibacterial lead compounds for medicinal chemists, which will promote the antibiotics research based on natural products to the next level.

Halogenating Enzymes for Active Agent Synthesis: First Steps Are Done and Many Have to Follow

Halogens can be very important for active agents as vital parts of their binding mode, on the one hand, but are on the other hand instrumental in the synthesis of most active agents. However, the primary halogenating compound is molecular chlorine which has two major drawbacks, high energy consumption and hazardous handling. Nature bypassed molecular halogens and evolved at least six halogenating enzymes: Three kind of haloperoxidases, flavin-dependent halogenases as well as α-ketoglutarate and S-adenosylmethionine (SAM)-dependent halogenases. This review shows what is known today on these enzymes in terms of biocatalytic usage. The reader may understand this review as a plea for the usage of halogenating enzymes for fine chemical syntheses, but there are many steps to take until halogenating enzymes are reliable, flexible, and sustainable catalysts for halogenation.