Neoechinulin B and its analogues as potential entry inhibitors of influenza viruses, targeting viral hemagglutinin

Microbial lectins as a potential therapeutics for the prevention of certain human diseases

Lectins are protein or glycoprotein molecules with a specific ability to bind to carbohydrates. From viruses to mammals, they are found in various organisms and exhibit remarkable diverse structures and functions. They are significant contributors to defense mechanisms against microbial attacks in plants. They are also involved in functions such as controlling lymphocyte migration, regulating glycoprotein biosynthesis, cell-cell recognition, and embryonic development in animals. In addition, lectins serve as invaluable molecular tools in various biological and medical disciplines due to their reversible binding ability and enable the monitoring of cell membrane changes in physiological and pathological contexts. Microbial lectins, often referred to as adhesins, play an important role in microbial colonization, pathogenicity, and interactions among microorganisms. Viral lectins are located in the bilayered viral membrane, whereas bacterial lectins are found intracellularly and on the bacterial cell surface. Microfungal lectins are typically intracellular and have various functions in host-parasite interaction, and in fungal growth and morphogenesis. Although microbial lectin studies are less extensive than those of plants and animals, they provide insights into the infection mechanisms and potential interventions. Glycan specificity, essential functions in infectious diseases, and applications in the diagnosis and treatment of viral and bacterial infections are critical aspects of microbial lectin research. In this review, we will discuss the application and therapeutic potential of viral, bacterial and microfungal lectins.

Curcumin as a natural potential drug candidate against important zoonotic viruses and prions: A narrative review

Zoonotic diseases are major public health concerns and undeniable threats to human health. Among Zoonotic diseases, zoonotic viruses and prions are much more difficult to eradicate, as they result in higher infections and mortality rates. Several investigations have shown curcumin, the active ingredient of turmeric, to have wide spectrum properties such as anti-microbial, anti-vascular, anti-inflammatory, anti-tumor, anti-neoplastic, anti-oxidant, and immune system modulator properties. In the present study, we performed a comprehensive review of existing in silico, in vitro, and in vivo evidence on the antiviral (54 important zoonotic viruses) and anti-prion properties of curcumin and curcuminoids in PubMed, Google Scholar, Science Direct, Scopus, and Web of Science databases. Database searches yielded 13,380 results, out of which 216 studies were eligible according to inclusion criteria. Of 216 studies, 135 (62.5%), 24 (11.1%), and 19 (8.8%) were conducted on the effect of curcumin and curcuminoids against SARS-CoV-2, Influenza A virus, and dengue virus, respectively. This review suggests curcumin and curcuminoids as promising therapeutic agents against a wide range of viral zoonoses by targeting different proteins and signaling pathways.

Metabolomic profiling of Medicago sativa-derived fungal endophytes and evaluation of their biological activities

This study aimed to discover the potential of Medicago sativa-derived fungal endophytes as a prospective source of bioactive metabolites. In the present study, three different strains of fungal endophyte Aspergillus terreus were isolated from leaves L, roots T and stems St of Medicago sativa to explore their biological and chemical diversity. These isolated fungi were exposed to different fermentation conditions by adding various chemical elicitors to their solid fermentation media. According to LC-HRESIMS-based metabolomics and multivariate analysis, each chemical treatment had a different effect on the chemical profiles of the fungi. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) proposed several compounds with anticancer action against MCF-7 (a human breast cancer cell line) and MDA-MB-231 (a human epithelial breast cancer cell line).

Inhibition Effects and Mechanisms of Marine Compound Mycophenolic Acid Methyl Ester against Influenza A Virus

Influenza A virus (IAV) can cause infection and illness in a wide range of animals, including humans, poultry, and swine, and cause annual epidemics, resulting in thousands of deaths and millions of hospitalizations all over the world. Thus, there is an urgent need to develop novel anti-IAV drugs with high efficiency and low toxicity. In this study, the anti-IAV activity of a marine-derived compound mycophenolic acid methyl ester (MAE) was intensively investigated both in vitro and in vivo. The results showed that MAE inhibited the replication of different influenza A virus strains in vitro with low cytotoxicity. MAE can mainly block some steps of IAV infection post adsorption. MAE may also inhibit viral replication through activating the cellular Akt-mTOR-S6K pathway. Importantly, oral treatment of MAE can significantly ameliorate pneumonia symptoms and reduce pulmonary viral titers, as well as improving the survival rate of mice, and this was superior to the effect of oseltamivir. In summary, the marine compound MAE possesses anti-IAV effects both in vitro and in vivo, which merits further studies for its development into a novel anti-IAV drug in the future.

Antibacterial insights into alternariol and its derivative alternariol monomethyl ether produced by a marine fungus

Alternaria alternata FB1 is a marine fungus identified as a candidate for plastic degradation in our previous study. This fungus has been recently shown to produce secondary metabolites with significant antimicrobial activity against various pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and the notorious aquaculture pathogen Vibrio anguillarum. The antibacterial compounds were purified and identified as alternariol (AOH) and its derivative, alternariol monomethyl ether (AME). We found that AOH and AME primarily inhibited pathogenic bacteria (MRSA or V. anguillarum) by disordering cell division and some other key physiological and biochemical processes. We further demonstrated that AOH could effectively inhibit the unwinding activity of MRSA topoisomerases, which are closely related to cell division and are the potential action target of AOH. The antibacterial activities of AOH and AME were verified by using zebrafish as the in vivo model. Notably, AOH and AME did not significantly affect the viability of normal human liver cells at concentrations that effectively inhibited MRSA or V. anguillarum. Finally, we developed the genetic operation system of A. alternata FB1 and blocked the biosynthesis of AME by knocking out omtI (encoding an O-methyl transferase), which facilitated A. alternata FB1 to only produce AOH. The development of this system in the marine fungus will accelerate the discovery of novel natural products and further bioactivity study.IMPORTANCEMore and more scientific reports indicate that alternariol (AOH) and its derivative alternariol monomethyl ether (AME) exhibit antibacterial activities. However, limited exploration of their detailed antibacterial mechanisms has been performed. In the present study, the antibacterial mechanisms of AOH and AME produced by the marine fungus Alternaria alternata FB1 were disclosed in vitro and in vivo. Given their low toxicity on the normal human liver cell line under the concentrations exhibiting significant antibacterial activity against different pathogens, AOH and AME are proposed to be good candidates for developing promising antibiotics against methicillin-resistant Staphylococcus aureus and Vibrio anguillarum. We also succeeded in blocking the biosynthesis of AME, which facilitated us to easily obtain pure AOH. Moreover, based on our previous results, A. alternata FB1 was shown to enable polyethylene degradation.

The potential of marine-derived piperazine alkaloids: Sources, structures and bioactivities

Marine-derived piperazine alkaloids (MDPAs) constitute a significant group of natural compounds known for their diverse structures and biological activities. Over the past five decades, substantial efforts have been devoted to isolating these alkaloids from marine sources and characterizing their chemical and bioactive profiles. To date, a total of 922 marine-derived piperazine alkaloids have been reported from various marine organisms. These compounds demonstrate a wide range of pharmacological properties, including cytotoxicity, antibacterial, antifungal, antiviral, and various other activities. Notably, among these activities, cytotoxicity emerges as the most prominent characteristic of marine-derived piperazine alkaloids. This review also summarizes the structure-activity relationship (SAR) studies associated with the cytotoxicity of these compounds. In summary, our objective is to provide an overview of the research progress concerning marine-derived piperazine alkaloids, with the aim of fostering their continued development and utilization.

Indole Diketopiperazine Alkaloids from the Marine Sediment-Derived Fungus Aspergillus chevalieri against Pancreatic Ductal Adenocarcinoma

A new prenylated indole diketopiperazine alkaloid, rubrumline P (1), was isolated along with six more analogues and characterized from the fermentation culture of a marine sediment-derived fungus, Aspergillus chevalieri, collected at a depth of 15 m near the lighthouse in Dahab, Red Sea, Egypt. In the current study, a bioassay-guided fractionation allowed for the identification of an active fraction displaying significant cytotoxic activity against the human pancreatic adenocarcinoma cell line PANC-1 from the EtOAc extract of the investigated fungus compared to the standard paclitaxel. The structures of the isolated compounds from the active fraction were established using 1D/2D NMR spectroscopy and mass spectrometry, together with comparisons with the literature. The absolute configuration of the obtained indole diketopiperazines was established based on single-crystal X-ray diffraction analyses of rubrumline I (2) and comparisons of optical rotations and NMR data, as well as on biogenetic considerations. Genome sequencing indicated the formation of prenyltransferases, which was subsequently confirmed by the isolation of mono-, di-, tri-, and tetraprenylated compounds. Compounds rubrumline P (1) and neoechinulin D (4) confirmed preferential cytotoxic activity against PANC-1 cancer cells with IC50 values of 25.8 and 23.4 µM, respectively. Although the underlying mechanism-of-action remains elusive in this study, cell cycle analysis indicated a slight increase in the sub-G1 peak after treatment with compounds 1 and 4.

Antiviral Effect of Ginsenosides rk1 against Influenza a Virus Infection by Targeting the Hemagglutinin 1-Mediated Virus Attachment

Influenza A virus (IAV) infections have been a serious hazard to public health everywhere. With the growing concern of drug-resistant IAV strains, there is an urgent need for novel anti-IAV medications, especially those with alternative mechanisms of action. Hemagglutinin (HA), an IAV glycoprotein, plays critical roles in the early stage of virus infection, including receptor binding and membrane fusion, making it a good target for developing anti-IAV drugs. Panax ginseng is a widely used herb in traditional medicine with extensive biological effects in various disease models, and its extract was reported to show protection in IAV-infected mice. However, the main effective anti-IAV constituents in panax ginseng remain unclear. Here, we report that ginsenoside rk1 (G-rk1) and G-rg5, out of the 23 screened ginsenosides, exhibit significant antiviral effects against 3 different IAV subtypes (H1N1, H5N1, and H3N2) in vitro. Mechanistically, G-rk1 blocked IAV binding to sialic acid in a hemagglutination inhibition (HAI) assay and an indirect ELISA assay; more importantly, we showed that G-rk1 interacted with HA1 in a dose-dependent manner in a surface plasmon resonance (SPR) analysis. Furthermore, G-rk1 treatment by intranasal inoculation effectively reduced the weight loss and mortality of mice challenged with a lethal dose of influenza virus A/Puerto Rico/8/34 (PR8). In conclusion, our findings reveal for the first time that G-rk1 possesses potent anti-IAV effects in vitro and in vivo. We have also identified and characterized with a direct binding assay a novel ginseng-derived IAV HA1 inhibitor for the first time, which could present potential approaches to prevent and treat IAV infections.

Inhibition of influenza A virus replication by a marine derived quinolone alkaloid targeting virus nucleoprotein

Owing to the emergence of drug resistance and high morbidity and mortality, the need for novel anti-influenza A virus (IAV) drugs with divergent targets is highly sought after. Herein, a novel quinolone alkaloid (QLA) derived from marine fungus was discovered with broad-spectrum anti-IAV activities with low toxicity. Distinct from current anti-IAV drugs, QLA may block virus replication and viral RNA (vRNA) export from the nucleus by targeting virus nucleoprotein (NP). QLA can block the binding of chromosome region maintenance 1 to nuclear export signal 3 of NP to inhibit the nuclear export of NP and vRNP. QLA may also affect vRNP assembly by interfering with the binding of NP to RNA rather than NP oligomerization. Arg305 and Phe488-Gly490 may be required for the interaction between QLA and NP, and the binding pocket around these amino acids may be a promising target for anti-IAV drugs. Importantly, oral administration of QLA can protect the mice against IAV-induced death and weight loss, superior to the effects of the clinical drug oseltamivir. In summary, the marine derived compound QLA has the potential to be developed into a novel anti-IAV agent targeting virus NP protein in the future.

Diprenylated cyclodipeptide production by changing the prenylation sequence of the nature’s synthetic machinery

Abstract

Ascomycetous fungi are often found in agricultural products and foods as contaminants. They produce hazardous mycotoxins for human and animals. On the other hand, the fungal metabolites including mycotoxins are important drug candidates and the enzymes involved in the biosynthesis of these compounds are valuable biocatalysts for production of designed compounds. One of the enzyme groups are members of the dimethylallyl tryptophan synthase superfamily, which mainly catalyze prenylations of tryptophan and tryptophan-containing cyclodipeptides (CDPs). Decoration of CDPs in the biosynthesis of multiple prenylated metabolites in nature is usually initiated by regiospecific C2-prenylation at the indole ring, followed by second and third ones as well as by other modifications. However, the strict substrate specificity can prohibit the further prenylation of unnatural C2-prenylated compounds. To overcome this, we firstly obtained C4-, C5-, C6-, and C7-prenylated cyclo-l-Trp-l-Pro. These products were then used as substrates for the promiscuous C2-prenyltransferase EchPT1, which normally uses the unprenylated CDPs as substrates. Four unnatural diprenylated cyclo-l-Trp-l-Pro including the unique unexpected N1,C6-diprenylated derivative with significant yields were obtained in this way. Our study provides an excellent example for increasing structural diversity by reprogramming the reaction orders of natural biosynthetic pathways. Furthermore, this is the first report that EchPT1 can also catalyze N1-prenylation at the indole ring.

Key points

• Prenyltransferases as biocatalysts for unnatural substrates.

• Chemoenzymatic synthesis of designed molecules.

• A cyclodipeptide prenyltransferase as prenylating enzyme of already prenylated products.

Graphical Abstract

Antiviral Potential of Natural Resources against Influenza Virus Infections

Influenza is a severe contagious disease caused by influenza A and B viruses. The WHO estimates that annual outbreaks lead to 3-5 million severe infections of which approximately 10% lead to the death of the patient. While vaccination is the cornerstone of prevention, antiviral drugs represent the most important treatment option of acute infections. Only two classes of drugs are currently approved for the treatment of influenza in numerous countries: M2 channel blockers and neuraminidase inhibitors. In some countries, additional compounds such as the recently developed cap-dependent endonuclease inhibitor baloxavir marboxil or the polymerase inhibitor favipiravir are available. However, many of these compounds suffer from poor efficacy, if not applied early after infection. Furthermore, many influenza strains have developed resistances and lost susceptibility to these compounds. As a result, there is an urgent need to develop new anti-influenza drugs against a broad spectrum of subtypes. Natural products have made an important contribution to the development of new lead structures, particularly in the field of infectious diseases. Therefore, this article aims to review the research on the identification of novel lead structures isolated from natural resources suitable to treat influenza infections.

Efficient production of a cyclic dipeptide (cyclo-TA) using heterologous expression system of filamentous fungus Aspergillus oryzae

Background

Cyclic dipeptides are an important class of natural products owing to their structural diversity and biological activities. In fungi, the cyclo-ring system is formed through the condensation of two α-amino acids via non-ribosomal peptide synthetase (NRPS). However, there are few investigations on the functional identification of this enzyme. Additionally, information on how to increase the production of cyclic dipeptide molecules is relatively scarce.

Results

We isolated the Eurotium cristatum NWAFU-1 fungus from Jing-Wei Fu brick tea, whose fermentation metabolites contain echinulin-related cyclic dipeptide molecules. We cloned the cirC gene, encoding an NRPS, from E. Cristatum NWAFU-1 and transferred it into the heterologous host Aspergillus oryzae. This transformant produced a novel metabolite possessing an l-tryptophan-l-alanine cyclic dipeptide backbone (Cyclo-TA). Based on the results of heterologous expression and microsomal catalysis, CriC is the first NRPS characterized in fungi that catalyzes the formation of a cyclic dipeptide from l-tryptophan and l-alanine. After substrate feeding, the final yield reached 34 mg/L. In this study, we have characterized a novel NRPS and developed a new method for cyclic dipeptide production.

Conclusions

In this study we successfully expressed the E. Cristatum NWAFU-1 criC gene in A. oryzae to efficiently produce cyclic dipeptide compounds. Our findings indicate that the A. oryzae heterologous expression system constitutes an efficient method for the biosynthesis of fungal Cyclic dipeptides.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01872-8.

Antimicrobial Alkaloids from Marine-Derived Fungi as Drug Leads versus COVID-19 Infection: A Computational Approach to Explore their Anti-COVID-19 Activity and ADMET Properties

Therapeutic strategies based upon enzyme inhibition have recently gained higher attention in treating hazardous ailments. Herein, the potential use of seventy-two antimicrobial alkaloids isolated from marine-derived fungi to fight COVID-19 infection via inhibition of SARS-CoV-2 lethal virus was performed using in silico analyses. Molecular modelling was performed to assess their enzyme inhibitory potential on the main protease SARS-CoV-2 M^Pro, 3-chymotrypsin-like protease SARS-CoV-2 3CL^pro, and papain-like protease SARS-CoV-2 PL^pro using Discovery Studio 4.5. Validation of the docking experiments was done by determination of RMSD (root mean square deviation) after redocking the superimposition of the cocrystalized ligands. Results showed that gymnastatin Z (72) showed the best fitting score in SARS-CoV-2 M^Pro and SARS-CoV-2 3CL^pr active sites with ∆G equal −34.15 and −34.28 Kcal/mol, respectively. Meanwhile, scalusamide C (62) displayed the highest fitting within SARS-CoV-2 PL^pro active sites (∆G = −26.91 Kcal/mol) followed by eutypellazine M (57). ADMET/TOPKAT prediction displayed that eutypellazine M and scalusamide C showed better pharmacokinetic and pharmacodynamic properties. Gymnastatin Z is safer showing better toxicity criteria and higher rat oral LD₅₀ and rat chronic LOAEL (lowest observed adverse effect level). Chemometric analysis using principle component analysis (PCA) based on the binding energies observed for the compounds with respect to the three tested enzymes revealed the clustering of the compounds into different clusters. Eutypellazine M, scalusamide C, and gymnastatin Z appear in one cluster due to their closeness in activity. Thus, these compounds could serve as promising SARS-CoV-2 enzymes inhibitors that could help in alleviation of COVID-19 infection. Further investigations are recommended to confirm the results of molecular modelling.

Microbial Natural Products with Antiviral Activities, Including Anti-SARS-CoV-2: A Review

The SARS-CoV-2 virus, which caused the COVID-19 infection, was discovered two and a half years ago. It caused a global pandemic, resulting in millions of deaths and substantial damage to the worldwide economy. Currently, only a few vaccines and antiviral drugs are available to combat SARS-CoV-2. However, there has been an increase in virus-related research, including exploring new drugs and their repurposing. Since discovering penicillin, natural products, particularly those derived from microbes, have been viewed as an abundant source of lead compounds for drug discovery. These compounds treat bacterial, fungal, parasitic, and viral infections. This review incorporates evidence from the available research publications on isolated and identified natural products derived from microbes with anti-hepatitis, anti-herpes simplex, anti-HIV, anti-influenza, anti-respiratory syncytial virus, and anti-SARS-CoV-2 properties. About 131 compounds with in vitro antiviral activity and 1 compound with both in vitro and in vivo activity have been isolated from microorganisms, and the mechanism of action for some of these compounds has been described. Recent reports have shown that natural products produced by the microbes, such as aurasperone A, neochinulin A and B, and aspulvinone D, M, and R, have potent in vitro anti-SARS-CoV-2 activity, targeting the main protease (M^pro). In the near and distant future, these molecules could be used to develop antiviral drugs for treating infections and preventing the spread of disease.

Cladosporioles A and B, Two New Indole Derivatives from the Deep-Sea-Derived Fungus Cladosporium cladosporioides 170056

Two new (cladosporioles A and B, 1 and 2) and fourteen known (3-16) compounds were isolated from the deep-sea-derived fungus Cladosporium cladosporioides 170056. The relative structures of the new compounds were elucidated mainly by detailed analysis of their NMR and HR-ESI-MS spectroscopic data. Their absolute configurations were determined by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. All isolates were tested for antimicrobial activity against Vibrio parahaemolyticus. Compound 15 exhibited weak effect with the MIC value of 156.25 μg/mL.

2,5-Diketopiperazine Derivatives as Potential Anti-Influenza (H5N2) Agents: Synthesis, Biological Evaluation, and Molecular Docking Study

2,5-Diketopiperazine derivatives, consisting of benzylidene and alkylidene substituents at 3 and 6 positions, have been considered as a core structure for their antiviral activities. Herein, the novel N-substituted 2,5-Diketopiperazine derivatives were successfully prepared and their antiviral activities against influenza virus were evaluated by monitoring viral propagation in embryonated chicken eggs. It was found that (3Z,6Z)-3-benzylidene-6-(2-methyl propylidene)-4-substituted-2,5-Diketopiperazines (13b–d), (3Z,6E)-3-benzylidene-6-(2-methylpropyli dene)-1-(1-ethyl pyrrolidine)-2,5-Diketopiperazine (14c), and Lansai-C exhibited negative results in influenza virus propagation at a concentration of 25 µg/mL. Additionally, molecular docking study revealed that 13b–d and 14c bound in 430-cavity of neuraminidase from H5N2 avian influenza virus and the synthesized derivatives also strongly interacted with the key amino acid residues, including Arg371, Pro326, Ile427, and Thr439.

Chevalinulins A and B, Proangiogenic Alkaloids with a Spiro[bicyclo[2.2.2]octane-diketopiperazine] Skeleton from Deep-Sea Cold-Seep-Derived Fungus Aspergillus chevalieri CS-122

Chevalinulins A (1) and B (2), two indole diketopiperazine alkaloids containing an unprecedented spiro[bicyclo[2.2.2]octane-diketopiperazine] skeleton, together with a known analogue neoechinulin B (3), were isolated from the deep-sea cold-seep-derived fungus Aspergillus chevalieri CS-122. Their structures were determined by spectroscopic analysis, single-crystal X-ray diffraction, specific rotation (SR), and NMR calculations. Compounds 1 and 2 exhibited significant in vivo proangiogenic activity in transgenic zebrafish.

Neoechinulin A as a Promising SARS-CoV-2 Mpro Inhibitor: In Vitro and In Silico Study Showing the Ability of Simulations in Discerning Active from Inactive Enzyme Inhibitors

The COVID-19 pandemic and its continuing emerging variants emphasize the need to discover appropriate treatment, where vaccines alone have failed to show complete protection against the new variants of the virus. Therefore, treatment of the infected cases is critical. This paper discusses the bio-guided isolation of three indole diketopiperazine alkaloids, neoechinulin A (1), echinulin (2), and eurocristatine (3), from the Red Sea-derived Aspergillus fumigatus MR2012. Neoechinulin A (1) exhibited a potent inhibitory effect against SARS-CoV-2 Mpro with IC50 value of 0.47 μM, which is comparable to the reference standard GC376. Despite the structural similarity between the three compounds, only 1 showed a promising effect. The mechanism of inhibition is discussed in light of a series of extensive molecular docking, classical and steered molecular dynamics simulation experiments. This paper sheds light on indole diketopiperazine alkaloids as a potential structural motif against SARS-CoV-2 Mpro. Additionally, it highlights the potential of different molecular docking and molecular dynamics simulation approaches in the discrimination between active and inactive structurally related Mpro inhibitors.

Potential Antiviral Action of Alkaloids

Viral infections and outbreaks have become a major concern and are one of the main causes of morbidity and mortality worldwide. The development of successful antiviral therapeutics and vaccines remains a daunting challenge. The discovery of novel antiviral agents is a public health emergency, and extraordinary efforts are underway globally to identify safe and effective treatments for different viral diseases. Alkaloids are natural phytochemicals known for their biological activities, many of which have been intensively studied for their broad-spectrum of antiviral activities against different DNA and RNA viruses. The purpose of this review was to summarize the evidence supporting the efficacy of the antiviral activity of plant alkaloids at half-maximum effective concentration (EC₅₀) or half-maximum inhibitory concentration (IC₅₀) below 10 μM and describe the molecular sites most often targeted by natural alkaloids acting against different virus families. This review highlights that considering the devastating effects of virus pandemics on humans, plants, and animals, the development of high efficiency and low-toxicity antiviral drugs targeting these viruses need to be developed. Furthermore, it summarizes the current research status of alkaloids as the source of antiviral drug development, their structural characteristics, and antiviral targets. Overall, the influence of alkaloids at the molecular level suggests a high degree of specificity which means they could serve as potent and safe antiviral agents waiting for evaluation and exploitation.

Synthesis and Antiviral Activities of Neoechinulin B and Its Derivatives

We have previously reported that neoechinulin B (1a), a prenylated indole diketopiperazine alkaloid, shows antiviral activities against hepatitis C virus (HCV) via the inactivation of the liver X receptors (LXRs) and the resultant disruption of double-membrane vesicles. In this study, a two-step synthesis of the diketopiperazine scaffold of 1a was achieved by the base-induced coupling of 1,4-diacetyl-3-{[(tert-butyldimethylsilyl)oxy]methyl}piperazine-2,5-dione with aldehydes, followed by the treatment of the resultant coupling products with tetra-n-butylammonium fluoride. Compound 1a and its 16 derivatives 1b-q were prepared using this method. Furthermore, variecolorin H, a related alkaloid, was obtained by the acid treatment of 1a in MeOH. The antiviral evaluation of 1a and its derivatives revealed that 1a, 1c, 1d, 1h, 1j, 1l, and 1o exhibited both anti-HCV and anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) activities. The results of this study indicate that the exomethylene moiety on the diketopiperazine ring is important for the antiviral activities. The antiviral compounds can inhibit the production of HCV and SARS-CoV-2 by inactivating LXRs.

Natural Indole Alkaloids from Marine Fungi: Chemical Diversity and Biological Activities

The indole scaffold is one of the most important heterocyclic ring systems for pharmaceutical development, and serves as an active moiety in several clinical drugs. Fungi derived from marine origin are more liable to produce novel indole-containing natural products due to their extreme living environments. The indole alkaloids from marine fungi have drawn considerable attention for their unique chemical structures and significant biological activities. This review attempts to provide a summary of the structural diversity of marine fungal indole alkaloids including prenylated indoles, diketopiperazine indoles, bisindoles or trisindoles, quinazoline-containing indoles, indole-diterpenoids, and other indoles, as well as their known biological activities, mainly focusing on cytotoxic, kinase inhibitory, antiinflammatory, antimicrobial, anti-insecticidal, and brine shrimp lethal effects. A total of 306 indole alkaloids from marine fungi have been summarized, covering the references published from 1995 to early 2021, expecting to be beneficial for drug discovery in the future.

Neoechinulins: Molecular, cellular, and functional attributes as promising therapeutics against cancer and other human diseases

Neoechinulins are fungal and plant-derived chemicals extracted from Microsporum sp., Eurotium rubrum, Aspergillus sp., etc. Two analogues of neoechinulin, i.e., A and B, exerted extensive pharmacological properties described in this review. Neoechinulin is an indole alkaloid and has a double bond between C8/C9, which tends to contribute to its cytoprotective nature. Neoechinulin A exhibits protection to PC12 cells against nitrosative stress via increasing NAD(P)H reserve capacity and decreasing cellular GSH levels. It also confers protection via rescuing PC12 cells from rotenone-induced stress by lowering LDH leakage. This compound has great positive potential against neurodegenerative diseases by inhibiting SIN-1 induced cell death in neuronal cells. Together with these, neoechinulin A tends to inhibit Aβ42-induced microglial activation and confers protection against neuroinflammation. Alongside, it also inhibits cervical cancer cells by caspase-dependent apoptosis and via upregulation of apoptosis inducing genes like Bax, it suppresses LPS-induced inflammation in RAW264.7 macrophages and acts as an antidepressant. Whereas, another analogue, Neoechinulin B tends to interfere with the cellular mechanism thereby, inhibiting the entry of influenza A virus and it targets Liver X receptor (LXR) and decreases the infection rate of Hepatitis C. The present review describes the pharmaceutical properties of neoechinulins with notes on their molecular, cellular, and functional basis and their therapeutic properties.

Antiviral fungal metabolites and some insights into their contribution to the current COVID-19 pandemic

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak, which started in late 2019, drove the scientific community to conduct innovative research to contain the spread of the pandemic and to care for those already affected. Since then, the search for new drugs that are effective against the virus has been strengthened. Featuring a relatively low cost of production under well-defined methods of cultivation, fungi have been providing a diversity of antiviral metabolites with unprecedented chemical structures. In this review, we present viral RNA infections highlighting SARS-CoV-2 morphogenesis and the infectious cycle, the targets of known antiviral drugs, and current developments in this area such as drug repurposing. We also explored the metabolic adaptability of fungi during fermentation to produce metabolites active against RNA viruses, along with their chemical structures, and mechanisms of action. Finally, the state of the art of research on SARS-CoV-2 inhibitors of fungal origin is reported, highlighting the metabolites selected by docking studies.

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.

Recent advances in the discovery of novel marine natural products and mycosporine-like amino acid UV-absorbing compounds

Abstract

Bioactive compounds from marine environments represent a rich source of bioproducts for potential use in medicine and biotechnology. To discover and identify novel marine natural products (MNPs), evaluating diverse biological activities is critical. Increased sensitivity and specificity of omics technologies, especially next-generation high-throughput sequencing combined with liquid chromatography-mass spectrometry and nuclear magnetic resonance, are speeding up the discovery of novel bioactive compounds. Mycosporine-like amino acids (MAAs) isolated from many marine microorganisms are among highly promising MNPs characterized by ultraviolet radiation (UV) absorbing capacities and are recognized as a potential source of ecologically friendly sunscreens. MAAs absorb damaging UV radiation with maximum absorption in the range of 310–360 nm, including both UVA and UVB ranges. MAAs are also characterized by other biological activities such as anti-oxidant, anti-cancer, and anti-inflammatory activities. The application of modern omics approaches promoted some recent developments in our understanding of MAAs’ functional significance and diversity. This review will summarize the various modern tools that could be applied during the identification and characterization of MNPs, including MAAs, to further their innovative applications.

Key points

• New omics technologies are speeding up the discovery of novel bio-products

• The vast diversity of bioactive capacities of marine natural products described

• Marine microorganisms as a source of environmentally friendly sunscreens

Structures and Biological Activities of Diketopiperazines from Marine Organisms: A Review

Diketopiperazines are potential structures with extensive biological functions, which have attracted much attention of natural product researchers for a long time. These compounds possess a stable six-membered ring, which is an important pharmacophore. The marine organisms have especially been proven to be a wide source for discovering diketopiperazine derivatives. In recent years, more and more interesting bioactive diketopiperazines had been found from various marine habitats. This review article is focused on the new 2,5-diketopiperazines derived from marine organisms (sponges and microorganisms) reported from the secondary half-year of 2014 to the first half of the year of 2021. We will comment their chemical structures, biological activities and sources. The objective is to assess the merit of these compounds for further study in the field of drug discovery.

Isolation, Structural Characterization and Antidiabetic Activity of New Diketopiperazine Alkaloids from Mangrove Endophytic Fungus Aspergillus sp. 16-5c

Six new DIKETOPIPERAZINE alkaloids aspergiamides A-F (1-6), together with ten known alkaloids (7-16), were isolated from the mangrove endophytic fungus Aspergillus sp. 16-5c. The structures of the new compounds were elucidated based on 1D/2D NMR spectroscopic and HR-ESIMS data analyses. The absolute configurations of aspergiamides A-F were established based on the experimental and calculated ECD data. All the compounds were evaluated for the antidiabetic activity against α-glucosidase and PTP1B enzyme. The bioassay results disclosed compounds 1 and 9 exhibited significant α-glucosidase inhibitory with IC₅₀ values of 18.2 and 7.6 μM, respectively; compounds 3, 10, 11, and 15 exhibited moderate α-glucosidase inhibition with IC₅₀ values ranging from 40.7 to 83.9 μM; while no compounds showed obvious PTP1B enzyme inhibition activity.

Therapeutic Potential of Neoechinulins and Their Derivatives: An Overview of the Molecular Mechanisms Behind Pharmacological Activities

Neoechinulins are diketopiperazine type indole alkaloids that demonstrate radical scavenging, anti-inflammatory, antiviral, anti-neurodegenerative, neurotrophic factor-like, anticancer, pro-apoptotic, and anti-apoptotic properties. An array of neoechinulins such as neoechinulins A-E, isoechinulins A-C, cryptoechunilin have been isolated from various fungal sources like Aspergillus sp., Xylaria euglossa, Eurotium cristatum, Microsporum sp., etc. Besides, neoechinulin derivatives or stereoisomers were also obtained from diverse non-fungal sources viz. Tinospora sagittata, Opuntia dillenii, Cyrtomium fortunei, Cannabis sativa, and so on. The main purpose of this review is to provide update information on neoechinulins and their analogues about the molecular mechanisms of the pharmacological action and possible future research. The recent data from this review can be used to create a basis for the discovery of new neoechinulin-based drugs and their analogues in the near future. The online databases PubMed, Science and Google scholar were researched for the selection and collection of data from the available literature on neoechinulins, their natural sources and their pharmacological properties. The published books on this topic were also analysed. In vitro and in vivo assays have established the potential of neoechinulin A as a promising anticancer and anti-neuroinflammatory lead molecule. Neoechinulin B was also identified as a potential antiviral drug against hepatitis C virus. Toxicological and clinical trials are needed in the future to improve the phyto-pharmacological profile of neoquinolines. From the analysis of the literature, we found that neoechinulins and their derivatives have special biological potential. Although some modern pharmacological analyzes have highlighted the molecular mechanisms of action and some signalling pathways, the correlation between these phytoconstituents and pharmacological activities must be validated in the future by preclinical toxicological and clinical studies.

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.

Small Molecule Inhibitors of Influenza Virus Entry

Hemagglutinin (HA) plays a critical role during influenza virus receptor binding and subsequent membrane fusion process, thus HA has become a promising drug target. For the past several decades, we and other researchers have discovered a series of HA inhibitors mainly targeting its fusion machinery. In this review, we summarize the advances in HA-targeted development of small molecule inhibitors. Moreover, we discuss the structural basis and mode of action of these inhibitors, and speculate upon future directions toward more potent inhibitors of membrane fusion and potential anti-influenza drugs.

Alkylated Salicylaldehydes and Prenylated Indole Alkaloids from the Endolichenic Fungus Aspergillus chevalieri and Their Bioactivities

Sixteen metabolites, including seven C₇-alkylated salicylaldehyde derivatives (1-7) and nine prenylated indole alkaloids (8-16), three of which are new, namely, asperglaucins A and B (1 and 2) and neoechinulin F (8), were separated from the endolichenic fungus Aspergillus chevalieri SQ-8. Asperglaucin A (1) represents an unusual phthalide-like derivative with a benzo[c]thiophen-1(3H)-one scaffold. All compounds were assessed in vitro for antibacterial, antineuroinflammatory, and antioxidant activities. Notably, asperglaucins A and B exhibited potent antibacterial activities against two plant pathogens Pseudomonas syringae pv actinidae (Psa) and Bacillus cereus, with an MIC value of 6.25 μM; further SEM analyses illustrated that the possible bacteriostatic mechanisms for compounds 1 and 2 were to alter the external structure of B. cereus and Psa, and to cause the rupture or deformation of the cell membranes, respectively, and the results suggest that compounds 1 and 2 may serve as potential promising candidates for lead compounds of agrochemical bactericides. Furthermore, compounds 6 and 10 significantly inhibited nitric oxide production with an IC₅₀ value of ca. 12 μM, and the possible anti-inflammatory mechanisms involved were also studied by molecular docking. Finally, the tested phenolics 3-5 showed significant antioxidative effects. Thus, strain SQ-8 represents a novel resource of these bioactive metabolites to be utilized.

Marine endophytic fungi associated with Halopteris scoparia (Linnaeus) Sauvageau as producers of bioactive secondary metabolites with potential dermocosmetic application

Marine fungi and, particularly, endophytic species have been recognised as one of the most prolific sources of structurally new and diverse bioactive secondary metabolites with multiple biotechnological applications. Despite the increasing number of bioprospecting studies, very few have already evaluated the cosmeceutical potential of marine fungal compounds. Thus, this study focused on a frequent seaweed in the Portuguese coast, Halopteris scoparia, to identify the endophytic marine fungi associated with this host, and assess their ability to biosynthesise secondary metabolites with antioxidative, enzymatic inhibitory (hyaluronidase, collagenase, elastase and tyrosinase), anti-inflammatory, photoprotective, and antimicrobial (Cutibacterium acnes, Staphylococcus epidermidis and Malassezia furfur) activities. The results revealed eight fungal taxa included in the Ascomycota, and in the most representative taxonomic classes in marine ecosystems (Eurotiomycetes, Sordariomycetes and Dothideomycetes). These fungi were reported for the first time in Portugal and in association with H. scoparia, as far as it is known. The screening analyses showed that most of these endophytic fungi were producers of compounds with relevant biological activities, though those biosynthesised by Penicillium sect. Exilicaulis and Aspergillus chevalieri proved to be the most promising ones for being further exploited by dermocosmetic industry. The chemical analysis of the crude extract from an isolate of A. chevalieri revealed the presence of two bioactive compounds, echinulin and neoechinulin A, which might explain the high antioxidant and UV photoprotective capacities exhibited by the extract. These noteworthy results emphasised the importance of screening the secondary metabolites produced by these marine endophytic fungal strains for other potential bioactivities, and the relevance of investing more efforts in understanding the ecology of halo/osmotolerant fungi.

Comprehensive Overview on the Chemistry and Biological Activities of Selected Alkaloid Producing Marine-Derived Fungi as a Valuable Reservoir of Drug Entities

Marine-associated fungal strains act as a valuable reservoir of bioactive diverse secondary metabolites including alkaloids which are highly popular by their biological activities. This review highlighted the chemistry and biology of alkaloids isolated from twenty-six fungal genera associated with marine organisms and marine sea sediments. The selected fungi are from different marine sources without focusing on mangroves. The studied fungal genera comprises Acrostalagmus, Arthrinium, Chaetomium, Cladosporium, Coniothyrium, Curvularia, Dichotomomyces, Eurotium, Eutypella, Exophiala, Fusarium, Hypocrea, Microsphaeropsis, Microsporum, Neosartorya, Nigrospora, Paecilomyces, Penicillium, Pleosporales, Pseudallescheria, Scedosporium, Scopulariopsis, Stagonosporopsis, Thielavia, Westerdykella, and Xylariaceae. Around 347 alkaloid metabolites were isolated and identified via chromatographic and spectroscopic techniques comprising 1D and 2D NMR (one and two dimensional nuclear magnetic resonance) which were further confirmed using HR-MS (high resolution mass spectrometry) and Mosher reactions for additional ascertaining of the stereochemistry. About 150 alkaloids showed considerable effect with respect to the tested activities. Most of the reported bioactive alkaloids showed considerable biological activities mainly cytotoxic followed by antibacterial, antifungal, antiviral, antioxidant; however, a few showed anti-inflammatory and antifouling activities. However, the rest of the compounds showed weak or no activity toward the tested biological activities and required further investigations for additional biological activities. Thus, alkaloids isolated from marine-associated fungi can afford an endless source of new drug entities that could serve as leads for drug discovery combating many human ailments.

Bioactive Alkaloids from Genus Aspergillus: Mechanistic Interpretation of Their Antimicrobial and Potential SARS-CoV-2 Inhibitory Activity Using Molecular Modelling

Genus Aspergillus represents a widely spread genus of fungi that is highly popular for possessing potent medicinal potential comprising mainly antimicrobial, cytotoxic and antioxidant properties. They are highly attributed to its richness by alkaloids, terpenes, steroids and polyketons. This review aimed to comprehensively explore the diverse alkaloids isolated and identified from different species of genus Aspergillus that were found to be associated with different marine organisms regarding their chemistry and biology. Around 174 alkaloid metabolites were reported, 66 of which showed important biological activities with respect to the tested biological activities mainly comprising antiviral, antibacterial, antifungal, cytotoxic, antioxidant and antifouling activities. Besides, in silico studies on different microbial proteins comprising DNA-gyrase, topoisomerase IV, dihydrofolate reductase, transcriptional regulator TcaR (protein), and aminoglycoside nucleotidyl transferase were done for sixteen alkaloids that showed anti-infective potential for better mechanistic interpretation of their probable mode of action. The inhibitory potential of compounds vs. Angiotensin-Converting Enzyme 2 (ACE2) as an important therapeutic target combating COVID-19 infection and its complication was also examined using molecular docking. Fumigatoside E showed the best fitting within the active sites of all the examined proteins. Thus, Aspergillus species isolated from marine organisms could afford bioactive entities combating infectious diseases.

Marine-derived fungi as a source of bioactive indole alkaloids with diversified structures

Marine-derived fungi are well known as rich sources of bioactive natural products. Growing evidences indicated that indole alkaloids, isolated from a variety of marine-derived fungi, have attracted considerable attention for their diverse, challenging structural complexity and promising bioactivities, and therefore, indole alkaloids have potential to be pharmaceutical lead compounds. Systemic compilation of the relevant literature. In this review, we demonstrated a comprehensive overview of 431 new indole alkaloids from 21 genera of marine-derived fungi with an emphasis on their structures and bioactivities, covering literatures published during 1982-2019.

Prenylation and Dehydrogenation of a C2-Reversely Prenylated Diketopiperazine as a Branching Point in the Biosynthesis of Echinulin Family Alkaloids in Aspergillus ruber

The echinulin family alkaloids can be grouped into three series depending on the number of the exo double bonds adjacent to the diketopiperazine core structure. Heterologous expression of the putative echinulin biosynthetic gene cluster from Aspergillus ruber in Aspergillus nidulans led to accumulation of echinulin without a double bond and neoechinulin A with one double bond (Δ¹⁰) as major products. Their analogues with a different number of prenyl moieties were detected as minor products. Neoechinulin B and analogues with two double bonds (Δ^10,14) were not observed. Feeding experiments confirmed that the cytochrome P450 enzyme EchP450 only catalyzes the formation of the double bond between C10 and C11. Coincubation and substrate concentration dependent assays with the prenyltransferase EchPT2 revealed that the reversely C2-prenylated preechinulin without a double bond is a much better substrate than neoechinulin A. These results prove that preechinulin serves as a common substrate for the formation of echinulin by two regiospecific prenylation steps with EchPT2 or for EchP450 to introduce one double bond and subsequent prenylations with low regioselectivity.

Regioselective C5-H direct iodination of indoles

An efficient regioselective C5-H direct iodination of indoles is reported herein for the first time, which offers a general and practical access to the difficult C5 functionalization of indoles.

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.

Advances in the development of entry inhibitors for sialic-acid-targeting viruses

Over the past decades, several antiviral drugs have been developed to treat a range of infections. Yet the number of treatable viral infections is still limited, and resistance to current drug regimens is an ever-growing problem. Therefore, additional strategies are needed to provide a rapid cure for infected individuals. An interesting target for antiviral drugs is the process of viral attachment and entry into the cell. Although most viruses use distinct host receptors for attachment to the target cell, some viruses share receptors, of which sialic acids are a common example. This review aims to give an update on entry inhibitors for a range of sialic-acid-targeting viruses and provides insight into the prospects for those with broad-spectrum potential.

A new cytotoxic indole alkaloid from the fungus Penicillium polonicum TY12

A new dimeric monoterpene indole alkaloid polonidine A (1), along with five known compounds, cyclopenol (2), verrucosidin (3), fructigenine A (4), 3-O-methylviridicatin (5) and aurantiomides C (6), were isolated from Penicillium polonicum TY12. Their structures were established on the basis of extensive spectroscopic analyses. Compound 1 exhibited moderate cytotoxic activities and moderate antibacterial activity against Bacillus subtilis with MIC of 4.0 μg/mL.

Entry Inhibitors: Efficient Means to Block Viral Infection

The emerging and re-emerging viral infections are constant threats to human health and wellbeing. Several strategies have been explored to develop vaccines against these viral diseases. The main effort in the journey of development of vaccines is to neutralize the fusion protein using antibodies. However, significant efforts have been made in discovering peptides and small molecules that inhibit the fusion between virus and host cell, thereby inhibiting the entry of viruses. This class of inhibitors is called entry inhibitors, and they are extremely efficient in reducing viral infection as the entry of the virus is considered as the first step of infection. Nevertheless, these inhibitors are highly selective for a particular virus as antibody-based vaccines. The recent COVID-19 pandemic lets us ponder to shift our attention towards broad-spectrum antiviral agents from the so-called ‘one bug-one drug’ approach. This review discusses peptide and small molecule-based entry inhibitors against class I, II, and III viruses and sheds light on broad-spectrum antiviral agents.

C7-Prenylation of Tryptophan-Containing Cyclic Dipeptides by 7-Dimethylallyl Tryptophan Synthase Significantly Increases the Anticancer and Antimicrobial Activities

Prenylated natural products have interesting pharmacological properties and prenylation reactions play crucial roles in controlling the activities of biomolecules. They are difficult to synthesize chemically, but enzymatic synthesis production is a desirable pathway. Cyclic dipeptide prenyltransferase catalyzes the regioselective Friedel-Crafts alkylation of tryptophan-containing cyclic dipeptides. This class of enzymes, which belongs to the dimethylallyl tryptophan synthase superfamily, is known to be flexible to aromatic prenyl receptors, while mostly retaining its typical regioselectivity. In this study, seven tryptophan-containing cyclic dipeptides 1a-7a were converted to their C7-regularly prenylated derivatives 1b-7b in the presence of dimethylallyl diphosphate (DMAPP) by using the purified 7-dimethylallyl tryptophan synthase (7-DMATS) as catalyst. The HPLC analysis of the incubation mixture and the NMR analysis of the separated products showed that the stereochemical structure of the substrate had a great influence on their acceptance by 7-DMATS. Determination of the kinetic parameters proved that cyclo-l-Trp-Gly (1a) consisting of a tryptophanyl and glycine was accepted as the best substrate with a KM value of 169.7 μM and a turnover number of 0.1307 s-1. Furthermore, docking studies simulated the prenyl transfer reaction of 7-DMATS and it could be concluded that the highest affinity between 7-DMATS and 1a. Preliminary results have been clearly shown that prenylation at C7 led to a significant increase of the anticancer and antimicrobial activities of the prenylated derivatives 1b-7b in all the activity test experiment, especially the prenylated product 4b.

Molecules derived from the extremes of life: a decade later

Covering: Early 2008 until the end of 2019Microorganisms which survive (extreme-tolerant) or even prefer (extremophilic) living at the limits of pH, temperature, salinity and pressure found on earth have proven to be a rich source of novel structures. In this update we summarise the wide variety of new molecules which have been isolated from extremophilic and extreme-tolerant microorganisms since our original 2009 review, highlighting the range of bioactivities these molecules have been reported to possess.

Chemoreactive-Inspired Discovery of Influenza A Virus Dual Inhibitor to Block Hemagglutinin-Mediated Adsorption and Membrane Fusion

Owing to the emergence of drug resistance and high morbidity and mortality, the need for novel anti-influenza A virus (IAV) drugs with divergent targets is highly sought after. Herein, we reveal the discovery of an anti-IAV agent as a dual inhibitor to block hemagglutinin-mediated adsorption and membrane fusion using a chemoreactive ortho-quinone methide (o-QM) equivalent. Based on the o-QM equivalent nonenzymatically multipotent behavior, we created a series of clavatol-derived pseudo-natural products and found that penindolone (PND), a new diclavatol indole adduct, exhibited potent and broad-spectrum anti-IAV activities with low risk of inducing drug resistance. Distinct from current anti-IAV drugs, PND possesses a novel scaffold and is the first IAV inhibitor targeting both HA1 and HA2 subunits of virus hemagglutinin to dually block the IAV adsorption and membrane fusion process. More importantly, intranasal and oral administration of PND can protect mice against IAV-induced death and weight loss, superior to the effects of the clinical drug oseltamivir. Thus, the use of chemoreactive intermediates could expand our understanding of chemical diversity and aid in the development of anti-IAV drugs with novel targets.

Repurposing Papaverine as an Antiviral Agent against Influenza Viruses and Paramyxoviruses

Influenza viruses are highly infectious and are the leading cause of human respiratory diseases and may trigger severe epidemics and occasional pandemics. Although antiviral drugs against influenza viruses have been developed, there is an urgent need to design new strategies to develop influenza virus inhibitors due to the increasing resistance of viruses toward currently available drugs. In this study, we examined the antiviral activity of natural compounds against the following influenza virus strains: A/WSN/33 (H1N1), A/Udorn/72 (H3N2), and B/Lee/40. Papaverine (a nonnarcotic alkaloid that has been used for the treatment of heart disease, impotency, and psychosis) was found to be an effective inhibitor of multiple strains of influenza virus. Kinetic studies demonstrated that papaverine inhibited influenza virus infection at a late stage in the virus life cycle. An alteration in influenza virus morphology and viral ribonucleoprotein (vRNP) localization was observed as an effect of papaverine treatment. Papaverine is a well-known phosphodiesterase inhibitor and also modifies the mitogen-activated protein kinase (MAPK) pathway by downregulating the phosphorylation of MEK and extracellular signal-regulated kinase (ERK). Thus, the modulation of host cell signaling pathways by papaverine may be associated with the nuclear retention of vRNPs and the reduction of influenza virus titers. Interestingly, papaverine also inhibited paramyxoviruses parainfluenza virus 5 (PIV5), human parainfluenza virus 3 (HPIV3), and respiratory syncytial virus (RSV) infections. We propose that papaverine can be a potential candidate to be used as an antiviral agent against a broad range of influenza viruses and paramyxoviruses.IMPORTANCE Influenza viruses are important human pathogens that are the causative agents of epidemics and pandemics. Despite the availability of an annual vaccine, a large number of cases occur every year globally. Here, we report that papaverine, a vasodilator, shows inhibitory action against various strains of influenza virus as well as the paramyxoviruses PIV5, HPIV3, and RSV. A significant effect of papaverine on the influenza virus morphology was observed. Papaverine treatment of influenza-virus-infected cells resulted in the inhibition of virus at a later time in the virus life cycle through the suppression of nuclear export of vRNP and also interfered with the host cellular cAMP and MEK/ERK cascade pathways. This study explores the use of papaverine as an effective inhibitor of both influenza viruses as well as paramyxoviruses.

Biologically Active Echinulin-Related Indolediketopiperazines from the Marine Sediment-Derived Fungus Aspergillus niveoglaucus

Seven known echinulin-related indolediketopiperazine alkaloids (1–7) were isolated from the Vietnamese sediment-derived fungus Aspergillus niveoglaucus. Using chiral HPLC, the enantiomers of cryptoechinuline B (1) were isolated as individual compounds for the first time. (+)-Cryptoechinuline B (1a) exhibited neuroprotective activity in 6-OHDA-, paraquat-, and rotenone-induced in vitro models of Parkinson’s disease. (−)-Cryptoechinuline B (1b) and neoechinulin C (5) protected the neuronal cells against paraquat-induced damage in a Parkinson’s disease model. Neoechinulin B (4) exhibited cytoprotective activity in a rotenone-induced model, and neoechinulin (7) showed activity in the 6-OHDA-induced model.

Marine Pharmacology in 2014-2015: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis, Antiviral, and Anthelmintic Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The systematic review of the marine pharmacology literature from 2014 to 2015 was completed in a manner consistent with the 1998-2013 reviews of this series. Research in marine pharmacology during 2014-2015, which was reported by investigators in 43 countries, described novel findings on the preclinical pharmacology of 301 marine compounds. These observations included antibacterial, antifungal, antiprotozoal, antituberculosis, antiviral, and anthelmintic pharmacological activities for 133 marine natural products, 85 marine compounds with antidiabetic, and anti-inflammatory activities, as well as those that affected the immune and nervous system, and 83 marine compounds that displayed miscellaneous mechanisms of action, and may probably contribute to novel pharmacological classes upon further research. Thus, in 2014-2015, the preclinical marine natural product pharmacology pipeline provided novel pharmacology as well as new lead compounds for the clinical marine pharmaceutical pipeline, and thus continued to contribute to ongoing global research for alternative therapeutic approaches to many disease categories.