Phenolic polyketides from the marine alga-derived Streptomyces sp. OUCMDZ-3434

Natural Product-Derived Phytochemicals for Influenza A Virus (H1N1) Prevention and Treatment

Influenza A (H1N1) viruses are prone to antigenic mutations and are more variable than other influenza viruses. Therefore, they have caused continuous harm to human public health since the pandemic in 2009 and in recent times. Influenza A (H1N1) can be prevented and treated in various ways, such as direct inhibition of the virus and regulation of human immunity. Among antiviral drugs, the use of natural products in treating influenza has a long history, and natural medicine has been widely considered the focus of development programs for new, safe anti-influenza drugs. In this paper, we focus on influenza A (H1N1) and summarize the natural product-derived phytochemicals for influenza A virus (H1N1) prevention and treatment, including marine natural products, flavonoids, alkaloids, terpenoids and their derivatives, phenols and their derivatives, polysaccharides, and derivatives of natural products for prevention and treatment of influenza A (H1N1) virus. We further discuss the toxicity and antiviral mechanism against influenza A (H1N1) as well as the druggability of natural products. We hope that this review will facilitate the study of the role of natural products against influenza A (H1N1) activity and provide a promising alternative for further anti-influenza A drug development.

Metabolic Profiling, Antiviral Activity and the Microbiome of Some Mauritian Soft Corals

Soft corals, recognized as sessile marine invertebrates, rely mainly on chemical, rather than physical defense, by secreting intricate secondary metabolites with plausible pharmaceutical implication. Their ecological niche encompasses a diverse community of symbiotic microorganisms which potentially contribute to the biosynthesis of these bioactive metabolites. The emergence of new viruses and heightened viral resistance underscores the urgency to explore novel pharmacological reservoirs. Thus, marine organisms, notably soft corals and their symbionts, have drawn substantial attention. In this study, the chemical composition of four Mauritian soft corals: Sinularia polydactya, Cespitularia simplex, Lobophytum patulum, and Lobophytum crassum was investigated using LC-MS techniques. Concurrently, Illumina 16S metagenomic sequencing was used to identify the associated bacterial communities in the named soft corals. The presence of unique biologically important compounds and vast microbial communities found therein was further followed up to assess their antiviral effects against SARS-CoV-2 and HPV pseudovirus infection. Strikingly, among the studied soft corals, L. patulum displayed an expansive repertoire of unique metabolites alongside a heightened bacterial consort. Moreover, L. patulum extracts exerted some promising antiviral activity against SARS-CoV-2 and HPV pseudovirus infection, and our findings suggest that L. patulum may have the potential to serve as a therapeutic agent in the prevention of infectious diseases, thereby warranting further investigation.

Total Synthesis of (-)-5-Deoxyenterocin and Attempted Late-Stage Functionalization Reactions

The first total synthesis of (-)-5-deoxyenterocin has been accomplished starting from pentane-1,3,5-triol (16 steps in the longest linear sequence, 0.2 % overall yield). (-)-Menthone served as the source of chirality to distinguish the enantiotopic hydroxymethyl groups of the substrate. Key steps of the synthesis include two aldol reactions to either end of the C5 -skeleton, a diastereoselective hydroxylation reaction and a biomimetic twofold intramolecular aldol reaction as the final step. Although this step suffered from geometrical constraints and was low yielding (10 %), enough synthetic material could be secured to substantiate the relative and absolute configuration of the natural product. Additional experiments were directed toward a C-H functionalization at carbon atom C5. Despite the fact that several protocols could be successfully applied to (3aR)-(+)-sclareolide as model substrate, (-)-5-deoxyenterocin withstood any selective functionalization.

Expanding the Chemical Diversity of Secondary Metabolites Produced by Two Marine-Derived Enterocin- and Wailupemycin-Producing Streptomyces Strains

To expand the chemical diversity of secondary metabolites produced by two marine-derived enterocin- and wailupemycin-producing Streptomyces strains, OUCMDZ-3434 and OUCMDZ-2599, precursor feeding and solid fermentation strategies were used. Two new compounds, wailupemycins Q (1) and R (2), were isolated from the extracts of liquid and solid fermentation of OUCMDZ-3434. Furthermore, during the fermentation of OUCMDZ-3434, p-fluorobenzoic acid was added as the key biosynthetic precursor, which resulted in the isolation of eight new fluorinated enterocin and wailupemycin derivatives (3-10) and 10 previously reported analogues (11-20). From the solid fermentation extract of OUCMDZ-2599, a new sulfur-containing compound thiotetromycin B (21) and its known analogue thiotetromycin (22) were identified. Moreover, the solid fermentation strategy effectively activated the biosynthesis of siderophores (23-25) of strain OUCMDZ-2599. Compound 3 showed moderate antibacterial activity against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus subsp. aureus with MIC values of 4 μg/mL. Compounds 23-25 were significantly capable of binding Fe(III).

Design, synthesis, and biological evaluation of a series of new anthraquinone derivatives as anti-ZIKV agents

The major severe complications linked to Zika virus (ZIKV) cause the global public health problems, including microcephaly and other congenital abnormalities in newborns, and Guillain-Barré syndrome, meningoencephalitis, multi-organ failure in adults. However, neither approved vaccines nor drugs are available for ZIKV. In this study, we describe the design, synthesis and the anti-ZIKV activities of a series of anthraquinone analogs. Most of the newly synthesized compounds demonstrated moderate to excellent potency against ZIKV. Among all, compound 22, showed the most potent anti-ZIKV activity (EC₅₀ value from 1.33 μM to 5.72 μM) with low cytotoxicity (CC₅₀＞50 μM) in multiple cellular model. Importantly, 22 significantly improved the survival of ZIKV-infected mice (Ifnar1^-/-), alleviated ZIKV-associated pathological damages and suppressed the excessive inflammatory response and pyroptosis induced by ZIKV in vivo and in vitro. Furthermore, the molecular docking simulation analysis and the surface plasmon resonance results demonstrated the direct binding between 22 and ZIKV RdRp, and the mechanistic study revealed that 22 suppressed viral RNA synthesis by ZIKV NS5 in cells. Taken together, this study highlights that 22 may be a novel anti-ZIKV drug candidate and provides treatment options for ZIKV-associated diseases.

Natural Products and Biological Activity from Actinomycetes Associated with Marine Algae

Marine natural products have been recognized as the most promising source of bioactive substances for drug discovery research. This review illustrates the diversity of culturable actinobacteria associated with marine algae, their bioactivity and metabolites, and approaches to their isolation and determination of their biological properties. Furthermore, actinobacteria associated with marine algae are presented as a new subject for an extensive investigation to find novel and active natural products, which make them a potentially rich and innovative source for new drug development deserving more attention and exploration.

Aromatic Polyketides from the Mangrove-Derived Streptomyces sp. SCSIO 40069

A chemical investigation of Streptomyces sp. SCSIO 40069 resulted in the isolation of a series of aromatic polyketides with rare skeletons, including five new compounds RM18c-RM18g (1-5) and three known ones (6-8). Their structures and absolute configurations were determined by diverse methods, including HRMS and NMR spectra, chemical reaction, Snatzke's method, quantum mechanical-nuclear magnetic resonance (QM-NMR), and X-ray crystallographic analysis. Compounds 1, 2, 4b, and 8 displayed moderate or weak antibacterial activities.

Absolute Configuration of the Polyketide Natural Product (-)-Enterocin

The absolute configuration of the polyketide natural product (-)-enterocin was established by two independent approaches. In the first approach, synthetic enterocin with a defined configuration was compared to the natural product. While identical in all scalar properties, the compound displayed an opposite specific rotation and a different chiral HPLC retention time when compared with (-)-enterocin. In a second approach, the vibrational circular dichroism (VCD) of the natural product was measured and shown to be opposite to the calculated VCD of its enantiomer.

Discovery of a DNA Topoisomerase I Inhibitor Huanglongmycin N and Its Congeners from Streptomyces sp. CB09001

Huanglongmycin (HLM) congeners G-N (7-14) were isolated from Streptomyces sp. CB09001. Among them, 10-12 possesses a tricyclic scaffold with benzene-fused pyran/pyrone, confirmed by X-ray single crystal diffraction analysis of 12. The structure-activity relationship study of 1, 13, and 14 revealed not only the stronger cytotoxicity of 14 against tested cancer cells but also the critical role of the C-7 ethyl group of 14 in its binding to the DNA-topoisomerase I complex.

Ulvapyrone, a pyrone-linked benzochromene from sea lettuce Ulva lactuca Linnaeus (family Ulvaceae): newly described anti-inflammatory agent attenuates arachidonate 5-lipoxygenase

Green marine macroalgae, particularly Ulva lactuca, is an essential constituent of the cuisines in many Asian countries. The present work aims to separate a bioactive pyrone attached benzochromene analogue, named as ulvapyrone from the organic extract of U. lactuca, followed by its structural characterisation as 2-{(6a'-hydroxyethyl-4'-methyltetrahydro-2H-pyran-2'-one)-6'-yl}-4-methyl-7-ethylacetate-8-hydroxy-7, 8-dihydrobenzo [de]chromene. Ulvapyrone exhibited prospective inhibition property against arachidonate 5-lipoxygenase (IC₅₀ ∼1 mg mL^-1) comparable to that demonstrated by ibuprofen (IC₅₀ 0.9 mg mL^-1), which connoted its anti-inflammatory activity. The studied benzochromene exhibited promising antioxidant potential (IC₅₀ 0.5-0.6 mg mL^-1), which further reinforced its attenuation property against 5-lipoxygenase. Bioactivities of ulvapyrone were linearly correlated with electronic parameter (topological polar surface area ∼102) along with less binding energy (-8.22 kcal mol^-1) with the allosteric site of 5-lipoxygenase. In silico predictions of physicochemical parameters along with absorption, distribution, metabolism and excretion could recognise the acceptable oral bioavailability of ulvapyrone.

Microbial Metabolites: The Emerging Hotspot of Antiviral Compounds as Potential Candidates to Avert Viral Pandemic Alike COVID-19

The present global COVID-19 pandemic caused by the noble pleomorphic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has created a vulnerable situation in the global healthcare and economy. In this pandemic situation, researchers all around the world are trying their level best to find suitable therapeutics from various sources to combat against the SARS-CoV-2. To date, numerous bioactive compounds from different sources have been tested to control many viral diseases. However, microbial metabolites are advantageous for drug development over metabolites from other sources. We herein retrieved and reviewed literatures from PubMed, Scopus and Google relevant to antiviral microbial metabolites by searching with the keywords "antiviral microbial metabolites," "microbial metabolite against virus," "microorganism with antiviral activity," "antiviral medicine from microbial metabolite," "antiviral bacterial metabolites," "antiviral fungal metabolites," "antiviral metabolites from microscopic algae' and so on. For the same purpose, the keywords "microbial metabolites against COVID-19 and SARS-CoV-2" and "plant metabolites against COVID-19 and SARS-CoV-2" were used. Only the full text literatures available in English and pertinent to the topic have been included and those which are not available as full text in English and pertinent to antiviral or anti-SARS-CoV-2 activity were excluded. In this review, we have accumulated microbial metabolites that can be used as antiviral agents against a broad range of viruses including SARS-CoV-2. Based on this concept, we have included 330 antiviral microbial metabolites so far available to date in the data bases and were previously isolated from fungi, bacteria and microalgae. The microbial source, chemical nature, targeted viruses, mechanism of actions and IC50/EC50 values of these metabolites are discussed although mechanisms of actions of many of them are not yet elucidated. Among these antiviral microbial metabolites, some compounds might be very potential against many other viruses including coronaviruses. However, these potential microbial metabolites need further research to be developed as effective antiviral drugs. This paper may provide the scientific community with the possible secret of microbial metabolites that could be an effective source of novel antiviral drugs to fight against many viruses including SARS-CoV-2 as well as the future viral pandemics.

Biomimetic Total Synthesis of Enterocin

The first chemical total synthesis of the highly oxygenated polyketide enterocin has been accomplished. The key step of the synthesis was a late‐stage biomimetic reaction cascade involving two intramolecular aldol reactions in which each step proceeded in 52 % yield (averaged) and which established four of the seven stereogenic centers. The pivotal precursor for the cascade reaction was assembled from three readily available building blocks. A chiral dithioacetal with two stereogenic centers originating from L‐arabinose represented the core fragment to both ends of which the other building blocks were attached by aldol reactions. The remaining stereogenic center was installed by Davis oxygenation immediately prior to the key step.

Isolation and characterization of marine sponge-associated Streptomyces sp. NMF6 strain producing secondary metabolite(s) possessing antimicrobial, antioxidant, anticancer, and antiviral activities

Background

Actinomycetes associated with marine sponge represent a promising source of bioactive compounds. Herein, we report the isolation, identification, and bioactivity evaluation of Streptomyces sp. NMF6 associated with the marine sponge Diacarnus ardoukobae.

Results

Results showed that the strain belonged to the genus Streptomyces, and it was designated as Streptomyces sp. NMF6 with the GenBank accession number MW015111. Ethyl acetate (EtOAc) extract of the strain NMF6 demonstrated a promising antimicrobial activity against Staphylococcus aureus, Enterococcus faecalis, Vibrio damsela, and Candida albicans and a strong antioxidant activity, which were confirmed by DPPH, ferric-reducing power, and phosphomolybdenum assays; results are expressed as ascorbic acid equivalents. NMF6 extract also demonstrated cytotoxicity against breast cancer cell line (MCF-7), hepatocellular carcinoma cell line (Hep-G2), and human colon carcinoma cell line (HCT-116); the selectivity index values were < 2. The extract showed promising antiviral activity against HSV-1, CoxB4, and hepatitis A viruses at concentrations that were nontoxic to the host cells, with the selectivity index values being 13.25, 9.42, and 8.25, respectively. GC-MS analysis of the extract showed the presence of 20 compounds, with bis(2-ethylhexyl) phthalate being the major component (48%).

Conclusions

Our study indicates that the marine sponge–associated Streptomyces sp. NMF6 strain is a potential source of bioactive compounds that could be developed into therapeutic agents.

Marine Natural Products as a Source of Drug Leads against Respiratory Viruses: Structural and Bioactive Diversity

Respiratory viruses, including influenza virus, respiratory syncytial virus, coronavirus, etc., have seriously threatened the human health. For example, the outbreak of severe acute respiratory syndrome coronavirus, SARS, affected a large number of countries around the world. Marine organisms, which could produce secondary metabolites with novel structures and abundant biological activities, are an important source for seeking effective drugs against respiratory viruses. This report reviews marine natural products with activities against respiratory viruses, the emphasis of which was put on structures and antiviral activities of these natural products. This review has described 167 marinederived secondary metabolites with activities against respiratory viruses published from 1981 to 2019. Altogether 102 references are cited in this review article.

Aromatic Polyketides and Hydroxamate Siderophores from a Marine-Algae-Derived Streptomyces Species

Four new aromatic polyketides, wailupemycins M-P (1-4), and two new hydroxamate siderophores, streptamides A (5) and B (6), together with the previously reported nocardamine (7), were isolated from the marine-algae-derived Streptomyces sp. OUCMDZ-3434. Wailupemycins M-P (1-4), possessing an α-pyrone moiety, were isolated from the extract of a liquid fermentation, and the siderophores (5-7) were isolated from the extract of a solid fermentation. Their structures were assigned based on detailed spectroscopic analysis and quantum chemical calculations. Compounds 5-7 were capable of binding Fe(III). Compound 5 can form a tighter Fe(III) complex than that of deferoxamine B mesylate (DFB).

Isolation and Identification of Tyrosinase Inhibitors from Marine Algae Enteromorpha sp

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The extract of marine green algae Enteromorpha sp. was evaluated in vitro for inhibitory activity against mushroom tyrosinase enzyme. The principle active agents i.e. coumarin; 4-hydroxycoumarin (1) and two sterols; ergosta-5,7,22-trien-3β-ol (2) & ergosterol peroxide (3) were isolated for the first time, from a crude methanol extract of Enteromorpha sp. showing anti-tyrosinase activity. Their structures were elucidated by IR, extensive NMR spectroscopy, LC-ESI-MS, Single crystal X-ray diffraction techniques. Thus, Enteromorpha sp. can be an alternative edible anti-tyrosinase agent.

Antiviral potential of natural products from marine microbes

Humans have been suffered from viral infections over the centuries, such as influenza, HSV, and HIV, which have killed millions of people worldwide. However, the availability of effective treatments for infectious diseases remains limited until now, as most of the viral pathogens resisted to many medical treatments. Marine microbes are currently one of the most copious sources of pharmacologically active natural products, which have constantly provided promising antivirus agents. To date, a large number of marine microbial secondary metabolites with antiviral activities have been widely reported. In this review, we have summarized the potential antivirus compounds from marine microorganisms over the last decade. In addition, the structures, bioactivities, and origins of these compounds were discussed as well.

Recent progresses in marine microbial-derived antiviral natural products

Viruses have always been a class of pathogenic microorganisms that threaten the health and safety of human life worldwide. However, for a long time, the treatment of viral infections has been slow to develop, and only a few antiviral drugs have been using clinically. Compared with these from terrestrial environments, marine-derived microorganisms can produce active substances with more novel structures and unique functions. From 2015 to 2019, 89 antiviral compounds of 8 structural classes have been isolated from marine microorganisms, of which 35 exhibit anti-H1N1 activity. This review surveys systematically marine microbial-derived natural products with antiviral activity and illustrates the impact of these compounds on antiviral drug discovery research.

From Ocean to Medicine: Pharmaceutical Applications of Metabolites from Marine Bacteria

Oceans cover seventy percent of the planet's surface and besides being an immense reservoir of biological life, they serve as vital sources for human sustenance, tourism, transport and commerce. Yet, it is estimated by the National Oceanic and Atmospheric Administration (NOAA) that eighty percent of the oceans remain unexplored. The untapped biological resources present in oceans may be fundamental in solving several of the world's public health crises of the 21st century, which span from the rise of antibiotic resistance in bacteria, pathogenic fungi and parasites, to the rise of cancer incidence and viral infection outbreaks. In this review, health risks as well as how marine bacterial derived natural products may be tools to fight them will be discussed. Moreover, an overview will be made of the research pipeline of novel molecules, from identification of bioactive bacterial crude extracts to the isolation and chemical characterization of the molecules within the framework of the One Health approach. This review highlights information that has been published since 2014, showing the current relevance of marine bacteria for the discovery of novel natural products.

Exploring Natural Product Artifacts: The Polyketide Enterocin Warms to a Ballet of Isomers

The polyketide enterocin is responsive to environmental stimuli, where mild heating promotes an equilibrium mixture of the isomeric acetals enterocins B and C, which subsequently undergo pseudo-chair-boat inversion to enterocin D. When exposed to aqueous base, enterocin is converted to the isomeric Michael acceptor enterocin F. These studies demonstrate that knowledge of environmental stimuli and associated artifacts is critical to understanding the chemical and ecological properties of enterocins and other classes of natural products.

Marine Actinomycetes-derived Natural Products

Actinomycetes is an abundant resource for discovering a large number of lead compounds, which play an important role in microbial drug discovery. Compared to terrestrial microorganisms, marine actinomycetes have unique metabolic pathways because of their special living environment, which has the potential to produce a variety of bioactive substances. In this paper, secondary metabolites isolated from marine actinomycetes are reviewed (2013-2018), most of which exhibited cytotoxic, antibacterial, and antiviral biological activities.

Cytotoxic Indolyl Diketopiperazines from the Aspergillus sp. GZWMJZ-258, Endophytic with the Medicinal and Edible Plant Garcinia multiflora

Two new indolyl diketopiperazines, gartryprostatins A and B (1 and 2), with an unusual 2,3-furan-fused pyrano[2,3-g]pyrrolo[1″,2″:4',5']pyrazino[1',2':1,5]pyrrolo[2,3-b]indole nucleus, along with a new naturally occurring compound (gartryprostatin C, 3) were isolated from the solid culture of Aspergillus sp. GZWMJZ-258, an endophyte from Garcinia multiflora (Guttiferae). The structures of compounds 1-3 were determined by nuclear magnetic resonance, mass spectrometry, Marfey's analysis of amino acids, and chemical calculation. Compounds 1-3 displayed selective inhibition on human FLT3-ITD mutant AML cell line, MV4-11, with IC₅₀ values of 7.2, 10.0, and 0.22 μM, respectively.

Secondary Metabolites with α-Glucosidase Inhibitory Activity from the Mangrove Fungus Mycosphaerella sp. SYSU-DZG01

Four new metabolites, asperchalasine I (1), dibefurin B (2) and two epicoccine derivatives (3 and 4), together with seven known compounds (5-11) were isolated from a mangrove fungus Mycosphaerella sp. SYSU-DZG01. The structures of compounds 1-4 were established from extensive spectroscopic data and HRESIMS analysis. The absolute configuration of 1 was deduced by comparison of ECD data with that of a known structure. The stereostructures of 2-4 were further confirmed by single-crystal X-ray diffraction. Compounds 1, 8 and 9 exhibited significant α-glucosidase inhibitory activity with IC₅₀ values of 17.1, 26.7 and 15.7 μM, respectively. Compounds 1, 4, 6 and 8 showed antioxidant activity by scavenging DPPH· with EC₅₀ values ranging from 16.3 to 85.8 μM.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

Diketopiperazine and Diphenylether Derivatives from Marine Algae-Derived Aspergillus versicolor OUCMDZ-2738 by Epigenetic Activation

A chemical-epigenetic method was used to enhance the chemodiversity of a marine algicolous fungus. Apart from thirteen known compounds, (+)-brevianamide R ((+)-3), (‒)-brevianamide R ((‒)-3), (+)-brevianamide Q ((+)-4), (‒)-brevianamide Q ((‒)-4), brevianamide V ((+)-5), brevianamide W ((‒)-5), brevianamide K (6), diorcinol B (7), diorcinol C (8), diorcinol E (9), diorcinol J (10), diorcinol (11), 4-methoxycarbonyldiorcinol (12), two new compounds, (+)- and (‒)-brevianamide X ((+)- and (‒)- 2)), as well as a new naturally occurring one, 3-[6-(2-methylpropyl)-2-oxo-1H-pyrazin-3-yl]propanamide (1), were isolated from chemical-epigenetic cultures of Aspergillus versicolor OUCMDZ-2738 with 10 µM vorinostat (SAHA). Compared to cultures in the same medium without SAHA, compounds 1–4, 8, 9, 11, and 12 were solely observed under SAHA condition. The structures of these compounds were elucidated based on spectroscopic analysis, specific rotation analysis, ECD, and X-ray crystallographic analysis. (±)-3, (±)-4, and (±)-5 were further resolved into the corresponding optically pure enantiomers and their absolute configurations were determined for the first time. Compounds 11 and 12 showed selective antibacterial against Pseudomonas aeruginosa with a minimum inhibitory concentration (MIC) of 17.4 and 13.9 μM, respectively. Compound 10 exhibited better α-glucosidase inhibitory activity than the assay control acarbose with IC₅₀ values of 117.3 and 255.3 μM, respectively.

New α-Pyridones with Quorum-Sensing Inhibitory Activity from Diversity-Enhanced Extracts of a Streptomyces sp. Derived from Marine Algae

Four new α-pyrones (1-4) and eight known analogues (5-12) were identified from the secondary metabolites of Streptomyces sp. OUCMDZ-3436 derived from the marine green algae Enteromorpha prolifera. Seven new α-pyridones (14-20) were constructed by diversity-oriented synthesis, which has been an effective approach to expanding the chemical space of natural-product-like compounds. Compounds 16, 17, 19, and 20 were found to have inhibitory effect on the gene expression controlled by quorum sensing in Pseudomonas aeruginosa QSIS-lasI.