Aromatic polyketides from a sponge-derived fungus Metarhizium anisopliae mxh-99 and their antitubercular activities

The potential of marine natural Products: Recent Advances in the discovery of Anti-Tuberculosis agents

Tuberculosis (TB) is an infectious airborne disease caused by Mycobacterium tuberculosis. Since the 1990 s, many countries have made significant progress in reducing the incidence of TB and associated mortality by improving health services and strengthening surveillance systems. Nevertheless, due to the emergence of multidrug-resistant TB (MDR-TB), alongside extensively drug-resistant TB (XDR-TB) and TB-HIV co-infection, TB remains one of the lead causes of death arising from infectious disease worldwide, especially in developing countries and disadvantaged populations. Marine natural products (MNPs) have received a large amount of attention in recent years as a source of pharmaceutical constituents and lead compounds, and are expected to offer significant resources and potential in the fields of drug development and biotechnology in the years to come. This review summarizes 169 marine natural products and their synthetic derivatives displaying anti-TB activity from 2013 to the present, including their structures, sources and functions. Partial synthetic information and structure-activity relationships (SARs) are also included.

UvHOS3-mediated histone deacetylation is essential for virulence and negatively regulates ustilaginoidin biosynthesis in Ustilaginoidea virens

Ustilaginoidea virens is the causal agent of rice false smut, which has recently become one of the most important rice diseases worldwide. Ustilaginoidins, a major type of mycotoxins produced in false smut balls, greatly deteriorates grain quality. Histone acetylation and deacetylation are involved in regulating secondary metabolism in fungi. However, little is yet known on the functions of histone deacetylases (HDACs) in virulence and mycotoxin biosynthesis in U. virens. Here, we characterized the functions of the HDAC UvHOS3 in U. virens. The ΔUvhos3 deletion mutant exhibited the phenotypes of retarded growth, increased mycelial branches and reduced conidiation and virulence. The ΔUvhos3 mutants were more sensitive to sorbitol, sodium dodecyl sulphate and oxidative stress/H2 O2 . ΔUvhos3 generated significantly more ustilaginoidins. RNA-Seq and metabolomics analyses also revealed that UvHOS3 is a key negative player in regulating secondary metabolism, especially mycotoxin biosynthesis. Notably, UvHOS3 mediates deacetylation of H3 and H4 at H3K9, H3K18, H3K27 and H4K8 residues. Chromatin immunoprecipitation assays indicated that UvHOS3 regulates mycotoxin biosynthesis, particularly for ustilaginoidin and sorbicillinoid production, by modulating the acetylation level of H3K18. Collectively, this study deepens the understanding of molecular mechanisms of the HDAC UvHOS3 in regulating virulence and mycotoxin biosynthesis in phytopathogenic fungi.

Advances in Natural Products from the Marine-Sponge-Associated Microorganisms with Antimicrobial Activity in the Last Decade

Microorganisms are the dominating source of food and nutrition for sponges and play an important role in sponge structure, chemical defense, excretion and evolution. In recent years, plentiful secondary metabolites with novel structures and specific activities have been identified from sponge-associated microorganisms. Additionally, as the phenomenon of the drug resistance of pathogenic bacteria is becoming more and more common, it is urgent to discover new antimicrobial agents. In this paper, we reviewed 270 secondary metabolites with potential antimicrobial activity against a variety of pathogenic strains reported in the literature from 2012 to 2022. Among them, 68.5% were derived from fungi, 23.3% originated from actinomycetes, 3.7% were obtained from other bacteria and 4.4% were discovered using the co-culture method. The structures of these compounds include terpenoids (13%), polyketides (51.9%), alkaloids (17.4%), peptides (11.5%), glucosides (3.3%), etc. Significantly, there are 124 new compounds and 146 known compounds, 55 of which have antifungal activity in addition to antipathogenic bacteria. This review will provide a theoretical basis for the further development of antimicrobial drugs.

Orchestrated Biosynthesis of the Secondary Metabolite Cocktails Enables the Producing Fungus to Combat Diverse Bacteria

Fungal secondary metabolites with antibiotic activities can promote fungal adaptation to diverse environments. Besides the global regulator, individual biosynthetic gene clusters (BGCs) usually contain a pathway-specific transcription factor for the tight regulation of fungal secondary metabolism. Here, we report the chemical biology mediated by a supercluster containing three BGCs in the entomopathogenic fungus Metarhiziumrobertsii. These clusters are jointly controlled by an embedded transcription factor that orchestrates the collective production of four classes of chemicals: ustilaginoidin, indigotide, pseurotin, and hydroxyl-ovalicin. The ustilaginoidin BGC is implicated as a late-acquired cluster in Metarhizium to produce both the bis-naphtho-γ-pyrones and the monomeric naphtho-γ-pyrone glycosides (i.e., indigotides). We found that the biosynthesis of indigotides additionally requires the functions of paired methylglucosylation genes located outside the supercluster. The pseurotin/ovalicin BGCs are blended and mesosyntenically conserved to the intertwined pseurotin/fumagillin BGCs of Aspergillus fumigatus. However, the former have lost a few genes, including a polyketide synthase gene responsible for the production of a pentaene chain used for assembly with ovalicin to form fumagillin, as observed in A. fumigatus. The collective production of chemical cocktails by this supercluster was dispensable for fungal virulence against insects and could enable the fungus to combat different bacteria better than the metabolite(s) produced by an individual BGC could. Thus, our results unveil a novel strategy employed by fungi to manage chemical ecology against diverse bacteria.

Elucidation of ustilaginoidin biosynthesis reveals a previously unrecognised class of ene-reductases

Ustilaginoidins are a type of mycotoxin featuring a dimeric naphtho-γ-pyrone skeleton, produced by the rice false smut pathogen Ustilaginoidea virens. Here we used gene disruption, heterologous expression in Aspergillus oryzae, feeding experiments, and in vitro experiments to fully elucidate the biosynthesis of ustilaginoidins. A new route to dimeric 2,3-unsaturated naphtho-γ-pyrones via dimerization of YWA1 (and 3-methyl YWA1) followed by dehydration was discovered. Intriguingly, the reduction of the 2,3-double bond of the pyrenone ring was catalyzed by a phospholipid methyltransferase-like enzyme (UsgR). The reductase was specific for reduction of monomeric, linear naphtho-γ-pyrenones, but not for the dimers. Atroposelective coupling of various monomers by the laccase (UsgL) led to diverse ustilaginoidins. Moreover, 3-epimerism of the 3-methyl-2,3-dihydro-naphtho-γ-pyrones adds additional complexity to the biosynthesis.

The 2,3-double bond reduction of the pyrenone ring in linear naphtho-γ-pyrenones was catalyzed by a phospholipid methyltransferase-like enzyme, namely UsgR, which is a previously unrecognised class of ene-reductases.

Marine Sponge-Associated Fungi as Potential Novel Bioactive Natural Product Sources for Drug Discovery: A Review

Marine sponge-associated fungi are promising sources of structurally interesting and bioactive secondary metabolites. Great plenty of natural products have been discovered from spongeassociated fungi in recent years. Here reviewed are 571 new compounds isolated from marine fungi associated with sponges in 2010-2018. These molecules comprised eight different structural classes, including alkaloids, polyketides, terpenoids, meroterpenoids, etc. Moreover, most of these compounds demonstrated profoundly biological activities, such as antimicrobial, antiviral, cytotoxic, etc. This review systematically summarized the structural diversity, biological function, and future potential of these novel bioactive natural products for drug discovery.

Ustilaginoidin D induces hepatotoxicity and behaviour aberrations in zebrafish larvae

Ustilaginoidins, a group of bis-naphtho-γ-pyrones, are one of the major mycotoxins produced by Ustilaginoidea virens. This group of bis-naphtho-γ-pyrone mycotoxins has been demonstrated to have antibacterial and immunological inhibitory activities and strong cytotoxicity to human oral epidermoid carcinoma. However, little is yet known about the toxicity of ustilaginoidins to animals or toxicity mechanisms. In this study, toxicity assays to zebrafish larvae show that ustilaginoidin D is highly toxic to zebrafish with an LC₅₀ of ∼7.50 μM. Ustilaginoidin D causes an obvious yolk sac absorption delay and liver damage in zebrafish, which is indicated by liver atrophy and the increased alanine and aspartate transaminase activities. Interestingly, different doses of ustilaginoidin D can alter zebrafish movement behavior in a distinct manner. Transcriptome analyses show that global gene expression profiling in zebrafish is significantly changed in response to ustilaginoidin D exposure. KEGG pathway analyses reveal that differentially expressed genes are enriched in the pathways related to lipid metabolism and hyperbilirubinemia, which are indicators of severe liver injury. Consistently, the expression of the marker genes for hepatotoxic responses is significantly induced by ustilaginoidin D. The findings indicate that ustilaginoidin D induces lipid metabolism disorders and hepatotoxicity in zebrafish larvae and poses a potential risk to food safety.

Metarhizium: jack of all trades, master of many

The genus Metarhizium and Pochonia chlamydosporia comprise a monophyletic clade of highly abundant globally distributed fungi that can transition between long-term beneficial associations with plants to transitory pathogenic associations with frequently encountered protozoans, nematodes or insects. Some very common 'specialist generalist' species are adapted to particular soil and plant ecologies, but can overpower a wide spectrum of insects with numerous enzymes and toxins that result from extensive gene duplications made possible by loss of meiosis and associated genome defence mechanisms. These species use parasexuality instead of sex to combine beneficial mutations from separate clonal individuals into one genome (Vicar of Bray dynamics). More weakly endophytic species which kill a narrow range of insects retain sexuality to facilitate host-pathogen coevolution (Red Queen dynamics). Metarhizium species can fit into numerous environments because they are very flexible at the genetic, physiological and ecological levels, providing tractable models to address how new mechanisms for econutritional heterogeneity, host switching and virulence are acquired and relate to diverse sexual life histories and speciation. Many new molecules and functions have been discovered that underpin Metarhizium associations, and have furthered our understanding of the crucial ecology of these fungi in multiple habitats.

Chemical Constituents from Endophytic Fungus Annulohypoxylon cf. stygium in Leaves of Anoectochilus roxburghii

The chemical investigation on endophytic fungus Annulohypoxylon cf. stygium in leaves of Anoectochilus roxburghii (Wall.) Lindl. has been performed. Sixteen compounds were isolated and their structures were identified as (-)-notoamide A, (-)-notoamide B, (+)-versicolamide B, notoamide C, notoamide D, stephacidin A, sterigmatocystin, dihydrosterigmatocystin, secosterigmatocystin, versiconol, averufanin, kipukasin D, kipukasin E, diorcinal, palmarumycin CP2 and (-)-(3R)-mellein methyl ether, respectively, by spectroscopic analysis and comparison with literature data. All the compounds were isolated from Annulohypoxylon genus for the first time. Sterigmatocystin and palmarumycin CP2 showed selective cytotoxic activities against HepG2, HeLa, MCF-7 and HT-29.

Biological and Chemical Diversity of Marine Sponge-Derived Microorganisms over the Last Two Decades from 1998 to 2017

Marine sponges are well known as rich sources of biologically natural products. Growing evidence indicates that sponges harbor a wealth of microorganisms in their bodies, which are likely to be the true producers of bioactive secondary metabolites. In order to promote the study of natural product chemistry and explore the relationship between microorganisms and their sponge hosts, in this review, we give a comprehensive overview of the structures, sources, and activities of the 774 new marine natural products from sponge-derived microorganisms described over the last two decades from 1998 to 2017.

Glycosylated Natural Products From Marine Microbes

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

New Naphtho-γ-Pyrones Isolated from Marine-Derived Fungus Penicillium sp. HK1-22 and Their Antimicrobial Activities

Three novel monomeric naphtho-γ-pyrones, peninaphones A–C (compounds 1–3), along with two known bis-naphtho-γ-pyrones (compounds 4 and 5) were isolated from mangrove rhizosphere soil-derived fungus Penicillium sp. HK1-22. The absolute configurations of compounds 1 and 2 were determined by electronic circular dichroism (ECD) spectra, and the structure of compound 3 was confirmed by single-crystal X-ray diffraction analysis. Compounds 4 and 5 are a pair of hindered rotation isomers. A hypothetical biosynthetic pathway for the isolated monomeric and dimeric naphtho-γ-pyrones is also discussed in this study. Compounds 1–3 showed antibacterial activity against Staphylococcus aureus (ATCC 43300, 33591, 29213, and 25923) with minimum inhibitory concentration (MIC) values in the range of 12.5–50 μg/mL. Compound 3 exhibited significant activity against the rice sheath blight pathogen Rhizoctonia solani.

Determination of the absolute configurations of the stereogenic centers of ustilaginoidins by studying the biosynthetic monomers from a gene knockout mutant of Villosiclava virens

Ustilaginoidins are a kind of mycotoxins with 9,9'-linked bis-naphtho-γ-pyrones structures produced by the rice false smut pathogen Villosiclava virens. These metabolites displayed a wide range of bioactivities, such as teratogenic, cytotoxic, phytotoxic, and antibacterial activities. So far 26 ustilaginoidins have been isolated from V. virens, among which 18 compounds contained stereogenic center(s), however, most of them were unknown for the absolute configurations, except that of ustilaginoidin D. In this study, the absolute structures of these ustilaginoidins were constructed for the first time by analysis of the biosynthetic monomers obtained from a gene knockout mutant (ΔUV_2091) of V. virens. The gene UV_2091 was predicted to encode an enzyme that dimerized the monomeric naphtho-γ-pyrones in V. virens. Knockout of this gene led to the accumulation of three monomers, namely hemiustilaginoidin F (1), epihemiustilaginoidin D (2), and hemiustilaginoidin D (3), but the production of ustilaginoidins was completely blocked. The structures of the monomers were deduced by spectroscopic analysis, in combination with TDDFT ECD calculations for determining the absolute configurations. These compounds were tested for their phytotoxic, cytotoxic, antibacterial, and antifungal activities. Compounds 1 and 3 showed inhibition against the radicle and plumule elongation of rice and lettuce seeds at the tested concentrations. Compound 1 was active against the tested five human cancer cells, with half maximal inhibitory concentrations (IC50s) of 13.2~37.3 μM. Compounds 1~3 inhibited the growth of the tested pathogenic bacteria with minimum inhibitory concentrations of 8~32 µg/mL, while compound 3 exhibited antifungal activity against Magnaporthe oryzae (IC50, 5.21 µg/mL). A comparison of these data with those of the ustilaginoidins provided insights into the structure-bioactivity relationships.

Marine natural products as potential anti-tubercular agents

Tuberculosis has been one of the greatest global health challenges of all time. Although the current first-line anti-tuberculosis (anti-TB) medicines used in the clinic have reduced mortality, multidrug-resistance and extensively drug-resistance forms of the disease have now spread worldwide and become a global problem. Even so, few new clinically approved drugs have emerged during the past 30 years. Highly biodiverse marine organisms have received considerable attention for drug discovery in the past couple of decades, and emerging TB drug resistance has motivated interest in assessing marine natural products (MNPs) in the treatment of this disease. So far, more than 170 compounds have been isolated from marine organisms with anti-TB properties, ten of which exhibit potent activity and have the potential for further development. This review systematically surveys MNPs with anti-TB activity and illustrates the impact of these compounds on drug discovery research against tuberculosis.

New Ustilaginoidins from Rice False Smut Balls Caused by Villosiclava virens and Their Phytotoxic and Cytotoxic Activities

Ustilaginoidins are a class of bis-naphtho-γ-pyrones, typically produced by Villosiclava virens, the pathogen of the rice false smut (RFS), which has been one of the most destructive rice fungal diseases. Previously, we found that ustilaginoidins identified from the culture of V. virens on rice medium were less polar than those reported from the RFS balls in general. In this study, we reinvestigated the high-performance liquid chromatography with diode array detection and high-resolution mass spectrometry (HPLC-DAD-HRMS) profile of the ethyl acetate (EtOAc) extract of the RFS balls and found several interesting peaks that correspond to new ustilaginoidins. As a result, eight new and polar congeners, named ustilaginoidins Q-T (1-4), 2,3-dihydroustilaginoidin T (5), and ustilaginoidins U-W (6-8), were isolated. In addition, 17 known ustilaginoidins, including ustilaginoidins K-N (9-12), ustilaginoidin P (13), ustilaginoidin E₁ (14), isochaetochromin B₂ (15), and ustilaginoidins A-J (16-25), were re-isolated. The structures of the new compounds were elucidated by comprehensive analysis of the spectroscopic data. Ustilaginoidins Q (1) and R (2) feature an uncommon 2-hydroxypropyl-substituted skeleton and biogenetically incorporate one more acetate unit than common ustilaginoidins. Ustilaginoidin W (8) is a rare formate-containing bis-naphtho-γ-pyrone. Ustilaginoidins R (2), U (6), B (17), and I (24) showed moderate inhibitory activities toward the radicle or germ elongation of rice seeds. Ustilaginoidins R (2), S (3), V (7), W (8), B (17), C (18), and H-J (23-25) were cytotoxic to the tested human cancer cell lines (HCT116, NCI-H1650, BGC823, Daoy, and HepG2), with IC₅₀ values in the range of 4.06-44.1 μM.

Bioactive Diphenyl Ethers and Isocoumarin Derivatives from a Gorgonian-Derived Fungus Phoma sp. (TA07-1)

Three new diphenyl ether derivatives-phomaethers A-C (1-3) and five known compounds-including a diphenyl ether analog, 2,3'-dihydroxy-4-methoxy-5',6-dimethyl diphenyl ether (4); and four isocoumarin derivatives, diaportinol (5), desmethyldiaportinol (6), citreoisocoumarinol (7), and citreoisocoumarin (8)-were isolated from a gorgonian-derived fungus Phoma sp. (TA07-1). Their structures were elucidated by extensive spectroscopic investigation. The absolute configurations of 1 and 2 were determined by acid hydrolysis reactions. It was the first report to discover the diphenyl glycoside derivatives from coral-derived fungi. Compounds 1, 3, and 4 showed selective strong antibacterial activity against five pathogenic bacteria with the minimum inhibiting concentration (MIC) values and minimum bactericidal concentration (MBC) values between 0.156 and 10.0 μM.

Naphthalimides Selectively Inhibit the Activity of Bacterial, Replicative DNA Ligases and Display Bactericidal Effects against Tubercle Bacilli

The DNA ligases, enzymes that seal breaks in the backbones of DNA, are essential for all organisms, however bacterial ligases essential for DNA replication use β-nicotinamide adenine dinucleotide as their co-factor, whereas those that are essential in eukaryotes and viruses use adenosine-5'-triphosphate. This fact leads to the conclusion that NAD⁺-dependent DNA ligases in bacteria could be targeted by their co-factor specific inhibitors. The development of novel alternative medical strategies, including new drugs, are a top priority focus areas for tuberculosis research due to an increase in the number of multi-drug resistant as well as totally drug resistant tubercle bacilli strains. Here, through the use of a virtual high-throughput screen and manual inspection of the top 200 records, 23 compounds were selected for in vitro studies. The selected compounds were evaluated in respect to their Mycobacterium tuberculosis NAD⁺ DNA ligase inhibitory effect by a newly developed assay based on Genetic Analyzer 3500 Sequencer. The most effective agents (e.g., pinafide, mitonafide) inhibited the activity of M. tuberculosis NAD⁺-dependent DNA ligase A at concentrations of 50 µM. At the same time, the ATP-dependent (phage) DNA LigT₄ was unaffected by the agents at concentrations up to 2 mM. The selected compounds appeared to also be active against actively growing tubercle bacilli in concentrations as low as 15 µM.

Main Ustilaginoidins and Their Distribution in Rice False Smut Balls

Rice false smut has become an increasingly serious fungal disease in rice (Oryza sativa L.) production worldwide. Ustilaginoidins are bis-naphtho-γ-pyrone mycotoxins previously isolated from the rice false smut balls (FSBs) infected by the pathogen Villosiclava virens in rice spikelets on panicles. To investigate the main ustilaginoidins and their distribution in rice FSBs, five main bis-naphtho-γ-pyrones, namely ustilaginoidins A (1), G (2), B (3), I (4) and C (5), were isolated and identified by NMR and high-resolution mass spectrometry as well as by comparison with the data in the literature. The rice FSBs at early, middle and late maturity stages were divided into their different parts and the contents of five main ustilaginoidins for each part were determined by HPLC analysis. The results revealed that the highest levels of ustilaginoidins were in late stage rice FSBs, followed by those at middle stage. Most ustilaginoidins, 96.4% of the total quantity, were distributed in the middle layer at early stage. However, ustilaginoidins were mainly distributed in the outer and middle layers at middle and late stages. Small amounts of ustilaginoidins A (1) and G (2) were found in the inner part of rice FSBs at each maturity stage. The contents of ustilaginoidins A (1) and G (2) without hydroxymethyl groups at C-2 and C-2’ of the γ-pyrone rings in rice FSBs were relatively high at early stage, while the contents of ustilaginoidins B (3), I (4), and C (5) with hydroxymethyl groups at C-2 or C-2’ were relatively high at late stage.

Marine natural products

This review covers the literature published in 2013 for marine natural products (MNPs), with 982 citations (644 for the period January to December 2013) 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 (1163 for 2013), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Antibacterial and antifungal compounds from marine fungi

This paper reviews 116 new compounds with antifungal or antibacterial activities as well as 169 other known antimicrobial compounds, with a specific focus on January 2010 through March 2015. Furthermore, the phylogeny of the fungi producing these antibacterial or antifungal compounds was analyzed. The new methods used to isolate marine fungi that possess antibacterial or antifungal activities as well as the relationship between structure and activity are shown in this review.

Bioactive bis-naphtho-γ-pyrones from rice false Smut pathogen Ustilaginoidea virens

Ustilaginoidins were bis-naphtho-γ-pyrones mycotoxins possessing an aR configuration of the chiral axis previously reported from the false smut balls of rice infected by the fungal pathogen Ustilaginoidea virens. To investigate the chemical diversity of these metabolites and their bioactivities, we fermented this fungus on solid rice media, which afforded the isolation of 13 ustilaginoidins, including seven new compounds, namely ustilaginoidins K-P, 1-6, and E1, 7, together with the known ustilaginoidins A, 8, D, 9, E, 10, F, 11, and G, 12, and isochaetochromin B2, 13. The structures of the new compounds were elucidated by using (1D, 2D) NMR, high-resolution mass spectrometry, UV, and circular dichroism, as well as by comparison with the literature data. A plausible biosynthesis pathway was proposed for these dimeric polyketides. The isolated compounds were evaluated for their antibacterial, cytotoxic, and radicle elongation inhibitory activities. Ustilaginoidins K, 1 and L, 2 showed cytotoxic activities on the A2780 human ovarian cancer cell line with IC50 values of 4.18 and 7.26 μM, respectively. Ustilaginoidins N, 4, D, 9, E, 10, and G, 12 were active against the tested pathogenic bacteria with MIC values in the range of 16-64 μg/mL. Ustilaginoidins O, 5, E, 10, and F, 11, and isochaetochromin B2, 13 displayed moderate inhibitory activity on the radicle elongation of rice seeds.

Bis-naphtho-γ-pyrones from fungi and their bioactivities

Bis-naphtho-γ-pyrones are an important group of aromatic polyketides derived from fungi. They have a variety of biological activities including cytotoxic, antitumor, antimicrobial, tyrosine kinase and HIV-1 integrase inhibition properties, demonstrating their potential applications in medicine and agriculture. At least 59 bis-naphtho-γ-pyrones from fungi have been reported in the past few decades. This mini-review aims to briefly summarize their occurrence, biosynthesis, and structure, as well as their biological activities. Some considerations regarding to synthesis, production, and medicinal and agricultural applications of bis-naphtho-γ-pyrones are also discussed.

Cladosins A-E, hybrid polyketides from a deep-sea-derived fungus, Cladosporium sphaerospermum

Five new fungal hybrid polyketides, cladosins A-D (1-4), that contain a novel linear 6(3)-enamino-8,10-dihydroxy-tetraketide (1 and 2) or 6-enamino-7(8)-en-10-ol (3 and 4) moiety, as well as the biogenetically related cladosin E (5), were isolated from the deep-sea-derived fungus Cladosporium sphaerospermum 2005-01-E3. Their structures (1-5) were elucidated through a combination of spectroscopic data, chemical conversion, and both Mosher's and Marfey's methods for stereochemical assignment. A plausible biogenetic pathway to 1-5 is proposed. Cladosin C (3) possesses mild anti-influenza A H1N1 virus activity.