IB-00208, a new cytotoxic polycyclic xanthone produced by a marine-derived Actinomadura. II. Isolation, physico-chemical properties and structure determination

Discovery of Kebanmycins with Antibacterial and Cytotoxic Activities from the Mangrove-Derived Streptomyces sp. SCSIO 40068

Mangrove derived actinomycetes are a rich reservoir of bioactive natural products and play important roles in pharmaceutical chemistry. In a screen of actinomycetes from mangrove rhizosphere sedimental environments, the isolated strain Streptomyces sp. SCSIO 40068 displayed strong antibacterial activity. Further fractionation of the extract yielded four new compounds kebanmycins A-D (1-4) and two known analogues FD-594 (5) and the aglycon (6). The structures of 1-6 were determined based on extensive spectroscopic data and single-crystal X-ray diffraction analysis. 1-3 featured a fused pyranonaphthaxanthene as an integral part of a 6/6/6/6/6/6 polycyclic motif, and showed bioactivity against a series of Gram-positive bacteria and cytotoxicity to several human tumor cells. In addition, the kebanmycins biosynthetic gene cluster (keb) was identified in Streptomyces sp. SCSIO 40068, and KebMT2 was biochemically characterized as a tailoring sugar-O-methyltransferase, leading to a proposed biosynthetic route to 1-6. This study paves the way to further investigate 1 as a potential lead compound.

A review on marine source as anticancer agents

This review investigates the potential of natural compounds obtained from marine sources for the treatment of cancer. The oceans are believed to contain physiologically active compounds, such as alkaloids, nucleosides, macrolides, and polyketides, which have shown promising effects in slowing human tumor cells both in vivo and in vitro. Various marine species, including algae, mollusks, actinomycetes, fungi, sponges, and soft corals, have been studied for their bioactive metabolites with diverse chemical structures. The review explores the therapeutic potential of various marine-derived substances and discusses their possible applications in cancer treatment.

Chemistry and biology of specialized metabolites produced by Actinomadura

Covering: up to the end of 2022In recent years rare Actinobacteria have become increasingly recognised as a rich source of novel bioactive metabolites. Actinomadura are Gram-positive bacteria that occupy a wide range of ecological niches. This review highlights about 230 secondary metabolites produced by Actinomadura spp., reported until the end of 2022, including their bioactivities and selected biosynthetic pathways. Notably, the bioactive compounds produced by Actinomadura spp. demonstrate a wide range of activities, including antimicrobial, antitumor and anticoccidial effects, highlighting their potential in various fields.

Chemistry and biosynthesis of bacterial polycyclic xanthone natural products

Covering: up to the end of 2021Bacterial polycyclic xanthone natural products (BPXNPs) are a growing family of natural xanthones featuring a pentangular architecture with various modifications to the tricyclic xanthone chromophore. Their structural diversities and various activities have fueled biosynthetic and chemical synthetic studies. Moreover, their more potent activities than the clinically used drugs make them potential candidates for the treatment of diseases. Future unraveling of structure activity relationships (SARs) will provide new options for the (bio)-synthesis of drug analogues with higher activities. This review summarizes the isolation, structural elucidation and biological activities and more importantly, the recent strategies for the microbial biosynthesis and chemical synthesis of BPXNPs. Regarding their biosynthesis, we discuss the recent progress in enzymes that synthesize tricyclic xanthone, the protein candidates for structural moieties (methylene dioxygen bridge and nitrogen heterocycle), tailoring enzymes for methylation and halogenation. The chemical synthesis part summarizes the recent methodology for the division synthesis and coupling construction of achiral molecular skeletons. Ultimately, perspectives on the biosynthetic study of BPXNPs are discussed.

Isolation, Biosynthesis, and Biological Activity of Polycyclic Xanthones From Actinomycetes

Natural products from actinomycetes serve as a crucial source of clinical pharmaceuticals, especially antibiotics and anticancer agents. Among them, polycyclic xanthones belong to a growing group of highly oxygenated aromatic polyketides with a xanthone-containing angular hexacyclic framework. These biosynthetically unique small molecules are of great interest due to their wide spectrum of biological activities, especially the remarkable antibacterial activity against gram-positive bacteria and the significant antineoplastic effects toward various cancer cells at nanomolar concentrations. Their complex structures and significant bioactivities have aroused considerable attention in the chemical and biological communities in recent decades. This review covers the isolation, the biosynthesis, and the biological studies toward these structurally complex and biologically active molecules.

Natural Products from Actinobacteria as a Potential Source of New Therapies Against Colorectal Cancer: A Review

Colorectal cancer (CRC) is a common, and deadly disease. Despite the improved knowledge on CRC heterogeneity and advances in the medical sciences, there is still an urgent need to cope with the challenges and side effects of common treatments for the disease. Natural products (NPs) have always been of interest for the development of new medicines. Actinobacteria are known to be prolific producers of a wide range of bioactive NPs, and scientific evidence highlights their important protective role against CRC. This review is a holistic picture on actinobacter-derived cytotoxic compounds against CRC that provides a good perspective for drug development and design in near future. This review also describes the chemical structure of 232 NPs presenting anti-CRC activity with the being majority of quinones, lactones, alkaloids, peptides, and glycosides. The study reveals that most of these NPs are derived from marine actinobacteria followed by terrestrial and endophytic actinobacteria, respectively. They are predominantly produced by Streptomyces, Micromonospors, Saliniospors and Actinomadura, respectively, in which Streptomyces, as the predominant contributor generating over 76% of compounds exclusively. Besides it provides a valuable snapshot of the chemical structure-activity relationship of compounds, highlighting the presence or absence of some specific atoms and chemical units in the structure of compounds can greatly influence their biological activities. To the best of our knowledge, this is the first comprehensive review on natural actinobacterial compounds affecting different types of CRC. Our study reveals that the high diversity of actinobacterial strains and their NPs derivatives, described here provides a new perspective and direction for the production of new anti-CRC drugs and paves the way to innovation for drugs discovery in the future. The knowledge obtain from this review can help us to understand the pivotal application of actinobacteria in future drugs development.

Flavonoids from Marine-Derived Actinobacteria as Anticancer Drugs

Flavonoids represent a large diverse group of natural products that are used as a traditional medicine against various infectious diseases. They possess many biological activities including antimicrobial, antioxidant, anti-inflammatory, anti-cancer and anti-diabetic activities. Commercially, flavonoids are mainly obtained from plants, however, several challenges are faced during their extraction. Microorganisms have been known as natural sources of a wide range of bioactive compounds including flavonoids. Actinobacteria are the most prolific group of microorganisms for the production of bioactive secondary metabolites, thus facilitating the production of flavonoids. The screening programs for bioactive compounds revealed the potential application of actinobacteria to produce flavonoids with interesting biological activities, especially anticancer activities. Since marine actinobacteria are recognized as a potential source of novel anticancer agents, they are highly expected to be potential producers of anticancer flavonoids with unusual structures and properties. In this review, we highlight the production of flavonoids by actinobacteria through classical fermentation, engineering of plant biosynthetic genes in a recombinant actinobacterium and the de novo biosynthesis approach. Through these approaches, we can control and improve the production of interesting flavonoids or their derivatives for the treatment of cancer.

Antiangiogenic molecules from marine actinomycetes and the importance of using zebrafish model in cancer research

Blood vessel sprouting from pre-existing vessels or angiogenesis plays a significant role in tumour progression. Development of novel biomolecules from marine natural sources has a promising role in drug discovery specifically in the area of antiangiogenic chemotherapeutics. Symbiotic actinomycetes from marine origin proved to be potent and valuable sources of antiangiogenic compounds. Zebrafish represent a well-established model for small molecular screening and employed to study tumour angiogenesis over the last decade. Use of zebrafish has increased in the laboratory due to its various advantages like rapid embryo development, optically transparent embryos, large clutch size of embryos and most importantly high genetic conservation comparable to humans. Zebrafish also shares similar physiopathology of tumour angiogenesis with humans and with these advantages, zebrafish has become a popular model in the past decade to study on angiogenesis related disorders like diabetic retinopathy and cancer. This review focuses on the importance of antiangiogenic compounds from marine actinomycetes and utility of zebrafish in cancer angiogenesis research.

Marine Actinobacteria Bioflocculant: A Storehouse of Unique Biotechnological Resources for Wastewater Treatment and Other Applications

The bioactive compounds produced by actinobacteria have played a major role in antimicrobials, bioremediation, biofuels, enzymes, and anti-cancer activities. Biodegradable microbial flocculants have been produced by bacteria, algae, and fungi. Microbial bioflocculants have also attracted biotechnology importance over chemical flocculants as a result of degradability and environmentally friendly attributes they possess. Though, freshwater actinobacteria flocculants have been explored in bioflocculation. Yet, there is a paucity of information on the application of actinobacteria flocculants isolated from the marine environment. Similarly, marine habitats that supported the biodiversity of actinobacteria strains in the field of biotechnology have been underexplored in bioflocculation. Hence, this review reiterates the need to optimize culture conditions and other parameters that affect bioflocculant production by using a response surface model or artificial neural network.

Bacteria and bacterial anticancer agents as a promising alternative for cancer therapeutics

Cancer is the leading cause of deaths worldwide, though significant advances have occurred in its diagnosis and treatment. The development of resistance against chemotherapeutic agents, their side effects, and non-specific toxicity urge to screen for the novel anticancer agent. Hence, the development of novel anticancer agents with a new mechanism of action has become a major scientific challenge. Bacteria and bacterially produced bioactive compounds have recently emerged as a promising alternative for cancer therapeutics. Bacterial anticancer agents such as antibiotics, bacteriocins, non-ribosomal peptides, polyketides, toxins, etc. These are adopted different mechanisms of actions such as apoptosis, necrosis, reduced angiogenesis, inhibition of translation and splicing, and obstructing essential signaling pathways to kill cancer cells. Also, live tumor-targeting bacteria provided a unique therapeutic alternative for cancer treatment. This review summarizes the anticancer properties and mechanism of actions of the anticancer agents of bacterial origin and antitumor bacteria along with their possible future applications in cancer therapeutics.

Glycosylated Natural Products From Marine Microbes

A growing body of evidence indicates that glycosylated natural products have become vital platforms for the development of many existing first-line drugs. This review covers 205 new glycosides over the last 22 years (1997-2018), from marine microbes, including bacteria, cyanobacteria, and fungi. Herein, we discuss the structures and biological activities of these compounds, as well as the details of their source organisms.

Natural Products and Their Mimics as Targets of Opportunity for Discovery

Diverse structural types of natural products and their mimics have served as targets of opportunity in our laboratory to inspire the discovery and development of new methods and strategies to assemble polyfunctional and polycyclic molecular architectures. Furthermore, our efforts toward identifying novel compounds having useful biological properties led to the creation of new targets, many of which posed synthetic challenges that required the invention of new methodology. In this Perspective, selected examples of how we have exploited a diverse range of natural products and their mimics to create, explore, and solve a variety of problems in chemistry and biology will be discussed. The journey was not without its twists and turns, but the unexpected often led to new revelations and insights. Indeed, in our recent excursion into applications of synthetic organic chemistry to neuroscience, avoiding the more-traveled paths was richly rewarding.

A comprehensive review of glycosylated bacterial natural products

A systematic analysis of all naturally-occurring glycosylated bacterial secondary metabolites reported in the scientific literature up through early 2013 is presented. This comprehensive analysis of 15 940 bacterial natural products revealed 3426 glycosides containing 344 distinct appended carbohydrates and highlights a range of unique opportunities for future biosynthetic study and glycodiversification efforts.

Total Synthesis of the Aglycone of IB-00208

A total synthesis of the aglycone of IB-00208 was accomplished in 22 steps using a newly developed approach towards polycyclic 1,4-dioxygenated xanthones from benzocyclobutenones. The generality of this entry to xanthones was initially established on several model systems before it was successfully applied to the construction of the hexacyclic core of the natural product. A new and potentially general approach towards angularly-fused benzocyclobutenones using ring-closing metathesis (RCM) was also developed.

Naphthopyranones--isolation, bioactivity, biosynthesis and synthesis

The 1H-naphtho[2,3-c]pyran-1-one (naphthopyranone) moiety forms the structural framework of a group of secondary metabolites that have been isolated from a range of organisms including fungi, bacteria, lichen and plants. This review documents the known naturally occurring naphthopyranones - their isolation, biosynthesis and biological activity. A survey of methods reported for the synthesis of naphthopyranone natural products is presented.

Mining soil metagenomes to better understand the evolution of natural product structural diversity: pentangular polyphenols as a case study

Sequence-guided mining of metagenomic libraries provides a means of recovering specific natural product gene clusters of interest from the environment. In this study, we use ketosynthase gene (KS) PCR amplicon sequences (sequence tags) to explore the structural and biosynthetic diversities of pentangular polyphenols (PP). In phylogenetic analyses, eDNA-derived sequence tags often fall between closely related clades that are associated with gene clusters known to encode distinct chemotypes. We show that these common “intermediate” sequence tags are useful for guiding the discovery of not only novel bioactive metabolites but also collections of closely related gene clusters that can provide new insights into the evolution of natural product structural diversity. Gene clusters corresponding to two eDNA-derived KS_β sequence tags that reside between well-defined KS_β clades associated with the biosynthesis of (C24)-pradimicin and (C26)-xantholipin type metabolites were recovered from archived soil eDNA libraries. Heterologous expression of these gene clusters in Streptomyces albus led to the isolation of three new PPs (compounds 1–3). Calixanthomycin A (1) shows potent antiproliferative activity against HCT-116 cells, whereas arenimycins C (2) and D (3) display potent antibacterial activity. By comparing genotypes and chemotypes across all known PP gene clusters, we define four PP subfamilies, and also observe that the horizontal transfer of PP tailoring genes has likely been restricted to gene clusters that encode closely related chemical structures, suggesting that only a fraction of the “natural product-like” chemical space that can theoretically be encoded by these secondary metabolite tailoring genes has likely been sampled naturally.

Approaches to polycyclic 1,4-dioxygenated xanthones. Application to total synthesis of the aglycone of IB-00208

Hexacyclic xanthone natural products such as IB-00208 present a formidable challenge in organic synthesis. A new approach to polycyclic 1,4-dioxygenated xanthones from benzocyclobutenones has been developed and applied to the first total synthesis of the aglycone of IB-00208. The 22-step synthesis features an acetylide stitching process that joins an aryl aldehyde with an angularly fused benzocyclobutenone, which was prepared by a ring-closing metathesis reaction. The resulting acetylenic benzocyclobutenone diol underwent a Moore rearrangement to give an intermediate that was further elaborated to the aglycone of IB-00208 as a mixture of hydroquinone–quinone tautomers.

Arixanthomycins A-C: Phylogeny-guided discovery of biologically active eDNA-derived pentangular polyphenols

Soil microbiomes are a rich source of uncharacterized natural product biosynthetic gene clusters. Here we use short conserved biosynthetic gene sequences (natural product sequence tags) amplified from soil microbiomes as phylogenetic markers to correlate genotype to chemotype and target the discovery of novel bioactive pentangular polyphenols from the environment. The heterologous expression of an environmental DNA-derived gene cluster (the ARX cluster), whose ketosynthase beta (KS_β) sequence tag was phylogenetically distinct from any known KS_β sequence, led to the discovery of the arixanthomycins. Arixanthomycin A (1) exhibits potent antiproliferative activity against human cancer cell lines.

Butremycin, the 3-hydroxyl derivative of ikarugamycin and a protonated aromatic tautomer of 5'-methylthioinosine from a Ghanaian Micromonospora sp. K310

A new actinomycete strain Micromonospora sp. K310 was isolated from Ghanaian mangrove river sediment. Spectroscopy-guided fractionation led to the isolation of two new compounds from the fermentation culture. One of the compounds is butremycin (2) which is the (3-hydroxyl) derivative of the known Streptomyces metabolite ikarugamycin (1) and the other compound is a protonated aromatic tautomer of 5′-methylthioinosine (MTI) (3). Both new compounds were characterized by 1D, 2D NMR and MS data. Butremycin (2) displayed weak antibacterial activity against Gram-positive S. aureus ATCC 25923, the Gram-negative E. coli ATCC 25922 and a panel of clinical isolates of methicillin-resistant S. aureus (MRSA) strains while 3 did not show any antibacterial activity against these microbes.

Pharmaceutically active secondary metabolites of marine actinobacteria

Marine actinobacteria are one of the most efficient groups of secondary metabolite producers and are very important from an industrial point of view. Many representatives of the order Actinomycetales are prolific producers of thousands of biologically active secondary metabolites. Actinobacteria from terrestrial sources have been studied and screened since the 1950s, for many important antibiotics, anticancer, antitumor and immunosuppressive agents. However, frequent rediscovery of the same compounds from the terrestrial actinobacteria has made them less attractive for screening programs in the recent years. At the same time, actinobacteria isolated from the marine environment have currently received considerable attention due to the structural diversity and unique biological activities of their secondary metabolites. They are efficient producers of new secondary metabolites that show a range of biological activities including antibacterial, antifungal, anticancer, antitumor, cytotoxic, cytostatic, anti-inflammatory, anti-parasitic, anti-malaria, antiviral, antioxidant, anti-angiogenesis, etc. In this review, an evaluation is made on the current status of research on marine actinobacteria yielding pharmaceutically active secondary metabolites. Bioactive compounds from marine actinobacteria possess distinct chemical structures that may form the basis for synthesis of new drugs that could be used to combat resistant pathogens. With the increasing advancement in science and technology, there would be a greater demand for new bioactive compounds synthesized by actinobacteria from various marine sources in future.

General and expedient synthesis of 1,4-dioxygenated xanthones

A facile entry to 1,4-dioxygenated xanthones having a variety of substitution patterns and substituents was developed that features a novel application of the Moore cyclization using substrates that were readily assembled in a highly convergent fashion by an acetylide stitching process. The practical utility of the methodology was demonstrated by an efficient synthesis of a naturally occurring xanthone and correction of the structure of dulcisxanthone C.

Isolation of the lysolipin gene cluster of Streptomyces tendae Tü 4042

Streptomyces tendae Tü 4042 produces the aromatic polyketide antibiotic lysolipin. Lysolipin has strong antibacterial activity against a variety of multidrug-resistant pathogens. The complete lysolipin biosynthetic gene cluster was isolated and fully sequenced. Within a 42-kb genomic region, 42 genes were identified that code for a type II polyketide synthase (llpF, E, and D), cyclases (llpCI-CIII), methyltransferases (llpMI-MVI), a halogenase (llpH), an amidotransferase (llpA), a ferredoxin (llpK), a transporter (llpN) and regulatory proteins (llpRI-RV). In addition, 15 genes encoding enzymes involved in redox modifications of the polyketide precursor molecule (llpOI-OVIII, ZI-ZIV, U, L, and S) were present in the lysolipin biosynthetic gene cluster. With this high number of oxidoreductases, lysolipin is among the most highly modified aromatic polyketides known to date. The heterologous expression of the cluster in Streptomyces albus led to lysolipin production with a yield comparable to that of wild-type, indicating that all biosynthetic genes were successfully cloned.

Antitumor compounds from marine actinomycetes

Chemotherapy is one of the main treatments used to combat cancer. A great number of antitumor compounds are natural products or their derivatives, mainly produced by microorganisms. In particular, actinomycetes are the producers of a large number of natural products with different biological activities, including antitumor properties. These antitumor compounds belong to several structural classes such as anthracyclines, enediynes, indolocarbazoles, isoprenoides, macrolides, non-ribosomal peptides and others, and they exert antitumor activity by inducing apoptosis through DNA cleavage mediated by topoisomerase I or II inhibition, mitochondria permeabilization, inhibition of key enzymes involved in signal transduction like proteases, or cellular metabolism and in some cases by inhibiting tumor-induced angiogenesis. Marine organisms have attracted special attention in the last years for their ability to produce interesting pharmacological lead compounds.

Ethyl 2-amino-4-(3-chloro-phen-yl)-5,10-dioxo-5,10-dihydro-4H-benzo[g]chromene-3-carboxyl-ate

The title mol­ecule, C₂₂H₁₆ClNO₅, was obtained by the reaction of (E)-ethyl 3-(3-chloro­phen­yl)-2-cyano­acrylate and 2-hydroxy­naphthalene-1,4-dione catalysed by triethylamine in ethanol. In the crystal structure, the chlorobenzene ring makes a dihedral angle of 88.63 (4)° with the fused ring system. The six-membered ring formed by an intra­molecular N—H⋯O hydrogen bond is almost planar. The crystal packing is stabilized by N—H⋯O hydrogen bonds.

Marine pharmacology in 2003–2004: Anti-tumour and cytotoxic compounds

During 2003 and 2004, marine pharmacology research directed towards the discovery and development of novel anti-tumour agents was published in 163 peer-reviewed articles. The purpose of this review is to present a structured assessment of the anti-tumour and cytotoxic properties of 150 marine natural products, many of which are novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids and peptides. The organisms yielding these bioactive marine compounds include invertebrate animals, algae, fungi and bacteria. Anti-tumour pharmacological studies were conducted with 31 structurally defined marine natural products in a number of experimental and clinical models that further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines was reported for 119 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy is the fact that marine anti-cancer research was sustained by a global collaborative effort, involving researchers from Australia, Austria, Canada, China, Egypt, France, Germany, Italy, Japan, Mexico, the Netherlands, New Zealand, Papua New Guinea, the Philippines, South Africa, South Korea, Spain, Switzerland, Taiwan, Thailand and the United States of America (USA). Finally, this 2003-2004 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine anti-tumour agents continued at the same pace as during 1998-2002.

Discovery of novel metabolites from marine actinomycetes

Recent findings from culture-dependent and culture-independent methods have demonstrated that indigenous marine actinomycetes exist in the oceans and are widely distributed in different marine ecosystems. There is tremendous diversity and novelty among the marine actinomycetes present in marine environments. Progress has been made to isolate novel actinomycetes from samples collected at different marine environments and habitats. These marine actinomycetes produce different types of new secondary metabolites. Many of these metabolites possess biological activities and have the potential to be developed as therapeutic agents. Marine actinomycetes are a prolific but underexploited source for the discovery of novel secondary metabolites.

Actinophages as indicators of actinomycete taxa in marine environments

It is necessary to continue to screen for new metabolites and evaluate the potential of less known and new bacterial taxa so that new and improved compounds for future use against drug-resistant bacteria or for chemical modification may be developed. There has been considerable interest in the detection and identification of marine microorganisms since they have been reported to produce bioactive compounds ranging from antitumour to antibacterial and antiviral agents. In this study, an improved technique that involves the exploitation of marine actinophages as indicators of the marine actinomycete taxa and uses marine bacteriophages as tools to reduce the numbers of common marine bacteria, which impedes the growth of rare actinomycetes on isolation plates, has been applied. This technique reduced the numbers of colony forming units of unwanted bacteria on isolation plates and hence increased the chances of detecting novel marine actinomycete genera for isolation and subsequent screening for antiviral activity.

Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (656 for 2003), together with their relevant biological activities, source organisms and country or origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product.