CJ-12,371 and CJ-12,372, two novel DNA gyrase inhibitors. Fermentation,isolation, structural elucidation and biological activities

Elucidation of Palmarumycin Spirobisnaphthalene Biosynthesis Reveals a Set of Previously Unrecognized Oxidases and Reductases

Spirobisnaphthalenes (SBNs) are a class of highly oxygenated, fungal bisnaphthalenes containing a unique spiroketal bridge, that displayed diverse bioactivities. Among the reported SBNs, palmarumycins are the major type, which are precursors for the other type of SBNs structurally. However, the biosynthesis of SBNs is unclear. In this study, we elucidated the biosynthesis of palmarumycins, using gene disruption, heterologous expression, and substrate feeding experiments. The biosynthetic gene cluster for palmarumycins was identified to be distant from the polyketide synthase gene cluster, and included two cytochrome P450s (PalA and PalB), and one short chain dehydrogenase/reductase (PalC) encoding genes as key structural genes. PalA is an unusual, multifunctional P450 that catalyzes the oxidative dimerization of 1,8-dihydroxynaphthalene to generate the spiroketal linkage and 2,3-epoxy group. Chemical synthesis of key intermediate and in vitro biochemical assays proved that the oxidative dimerization proceeded via a binaphthyl ether. PalB installs the C-5 hydroxy group, widely found in SBNs. PalC catalyzes 1-keto reduction, the reverse 1-dehydrogenation, and 2,3-epoxide reduction. Moreover, an FAD-dependent oxidoreductase, encoded by palD, which locates outside the cluster, functions as a 1-dehydrogenase. These results provided the first genetic and biochemical evidence for the biosynthesis of palmarumycin SBNs.

Isolation and Identification of Isocoumarin Derivatives With Specific Inhibitory Activity Against Wnt Pathway and Metabolome Characterization of Lasiodiplodia venezuelensis

The Wnt signaling pathway controls multiple events during embryonic development of multicellular animals and is carcinogenic when aberrantly activated in adults. Breast cancers are dependent on Wnt pathway overactivation mostly through dysregulation of pathway component protein expression, which necessitates the search for therapeutically relevant compounds targeting them. Highly diverse microorganisms as endophytes represent an underexplored field in the therapeutic natural products research. In the present work, the objective was to explore the chemical diversity and presence of selective Wnt inhibitors within a unique collection of fungi isolated as foliar endophytes from the long-lived tropical palm Astrocaryum sciophilum. The fungi were cultured, extracted with ethyl acetate, and screened for their effects on the Wnt pathway and cell proliferation. The endophytic strain Lasiodiplodia venezuelensis was prioritized for scaled-up fractionation based on its selective activity. Application of geometric transfer from analytical HPLC conditions to semi-preparative scale and use of dry load sample introduction enabled the isolation of 15 pure compounds in a single step. Among the molecules identified, five are original natural products described for the first time, and six are new to this species. An active fraction obtained by semi-preparative HPLC was re-purified by UHPLC-PDA using a 1.7 µm phenyl column. 75 injections of 8 µg were necessary to obtain sufficient amounts of each compound for structure elucidation and bioassays. Using this original approach, in addition to the two major compounds, a third minor compound identified as (R)-(-)-5-hydroxymellein (18) was obtained, which was found to be responsible for the significant Wnt inhibition activity recorded. Further studies of this compound and its structural analogs showed that only 18 acts in a highly specific manner, with no acute cytotoxicity. This compound is notably selective for upstream components of the Wnt pathway and is able to inhibit the proliferation of three triple negative breast cancer cell lines. In addition to the discovery of Wnt inhibitors of interest, this study contributes to better characterize the biosynthetic potential of L. venezuelensis.

Identification of spirobisnaphthalene derivatives with anti-tumor activities from the endophytic fungus Rhytidhysteron rufulum AS21B

The cultivation of the mangrove-derived fungus Rhytidhysteron rufulum AS21B in acidic condition changed its secondary metabolite profile. Investigation of the culture broth extract led to the isolation and identification of two new spirobisnaphthalenes (1 and 2) together with eleven known compounds (3-13) from the crude extract of the fungus grown under an acidic condition as well as six known compounds (4, 10, 14-17) were isolated from the crude extract of the fungus grown under a neutral condition. Their structures were elucidated on the basis of extensive spectroscopic data. The isolated compounds were evaluated for their cytotoxicity against two human cancer cell lines, Ramos lymphoma and drug resistant NSCLC H1975. Compounds 2 and 10 displayed the most promising anti-tumor activity against both cancer cell lines.

Quinone derivatives isolated from the endolichenic fungus Phialocephala fortinii are Mdr1 modulators that combat azole resistance in Candida albicans

One of the main azole-resistance mechanisms in Candida pathogens is the upregulation of drug efflux pumps, which compromises the efficacy of azoles and results in treatment failure. The combination of azole-antifungal agents with efflux pump inhibitors represents a promising strategy to combat fungal infection. High-throughput screening of 150 extracts obtained from endolichenic fungal cultures led to the discovery that the extract of Phialocephala fortinii exhibits potent activity for the reversal of azole resistance. From P. fortinii cultures, a total of 15 quinone derivatives, comprising 11 new derivatives and 4 known compounds, were obtained. Among these compounds, palmarumycin P3 (3) and phialocephalarin B (8) specifically modulate the expression of MDR1 to inhibit the activity of drug efflux pumps and therefore reverse azole resistance. The present study revealed Mdr1 targeting as an alternative mechanism for the discovery of new agents to fight antifungal drug resistance.

Anteaglonialides A-F and Palmarumycins CE(1)-CE(3) from Anteaglonium sp. FL0768, a Fungal Endophyte of the Spikemoss Selaginella arenicola

Anteaglonialides A-F (1-6), bearing a spiro[6-(tetrahydro-7-furanyl)cyclohexane-1,2'-naphtho[1,8-de][1,3]-dioxin]-10-one skeleton, three new spirobisnaphthalenes, palmarumycins CE1-CE3 (7-9), nine known palmarumycin analogues, palmarumycins CP5 (10), CP4a (11), CP3 (12), CP17 (13), CP2 (14), and CP1 (15), CJ-12,371 (16), 4-O-methyl CJ-12,371 (17), and CP4 (18), together with a possible artifact, 4a(5)-anhydropalmarumycin CE2 (8a), and four known metabolites, O-methylherbarin (19), herbarin (20), herbaridine B (21), and hyalopyrone (22), were encountered in a cytotoxic extract of a potato dextrose agar culture of Anteaglonium sp. FL0768, an endophytic fungus of the sand spikemoss, Selaginella arenicola. The planar structures and relative configurations of the new metabolites 1-9 were elucidated by analysis of extensive spectroscopic data, and the absolute configuration of 1 was determined by the modified Mosher's ester method. Application of the modified Mosher's ester method combined with the NOESY data resulted in revision of the absolute configuration previously proposed for 10. Co-occurrence of 1-6 and 7-18 in this fungus led to the proposal that the anteagloniolides may be biogenetically derived from palmarumycins. Among the metabolites encountered, anteaglonialide F (6) and known palmarumycins CP3 (12) and CP1 (15) exhibited strong cytotoxic activity against the human Ewing's sarcoma cell line CHP-100, with IC50 values of 1.4, 0.5, and 1.6 μM, respectively.

Naphthoquinone spiroketals and organic extracts from the endophytic fungus Edenia gomezpompae as potential herbicides

From the fermentation mycelium of the endophytic fungus Edenia gomezpompae were obtained several phytotoxic compounds including two new members of the naphthoquinone spiroketal family, namely, palmarumycin EG1 (1) and preussomerin EG4 (4). In addition, preussomerins EG1-EG3 (7-9) and palmarumycins CP19 (2), CP17 (3), and CP2 (6), as well as ergosta-4,6,8(14),22-tetraen-3-one (5), were obtained. Compounds 2, 3, and 5 are new to this species. The structures of palmarumycins CP19 (2) and CP17 (3) were unambiguously determined by X-ray analysis. The isolates and mycelium organic extracts from four morphological variants of E. gomezpompae caused significant inhibition of seed germination, root elongation, and seedling respiration of Amaranthus hypochondriacus, Solanum lycopersicum, and Echinochloa crus-galli. The treatments also affected respiration on intact mitochondria isolated from spinach.

Spirobisnaphthalenes from the mangrove-derived fungus Rhytidhysteron sp. AS21B

Three new spirobisnaphthalenes (1-3) were isolated from the mangrove-derived fungus Rhytidhysteron sp., together with five known derivatives (4-8). The structures of the compounds were established on the basis of extensive spectroscopic data, and the relative configurations of their stereogenic carbons were determined by a single-crystal X-ray crystallographic analysis. Compounds 3-5 displayed cytotoxicity against both cancer cell lines, MCF-7 and CaSki, while 2 was active only on CaSKi cells.

Anti-L. donovani Activity in Macrophage/Amastigote Model of Palmarumycin CP18 and its Large Scale Production

Palmarumycin CP18, isolated from an extract of the fermentation broth and mycelium of the Panamanian endophytic fungus Edenia sp., was previously reported with strong and specific activity against Leishmania donovani. Here we report that when the same strain was cultured on different solid media – Harrold Agar, Leonian Agar, Potato dextrose Agar (PDA), Corn Meal Agar, Honey Peptone Agar, and eight vegetables (V8) Agar – in order to determine the optimal conditions for isolation of palmarumycin CP18, no signal for this compound was observed in any of the 1H NMR spectra of fractions obtained from these extracts. However, one extract, prepared from the fungal culture in PDA contained significant amounts of CJ-12,372, a possible biosynthetic precursor of palmarumycin CP18. Edenia sp. was cultivated on a large scale on PDA and CJ-12,372 was converted to palmarumycin CP18 by oxidation of its p-hydroquinone moiety with DDQ in dioxane. Palmarumycin CP18 showed anti-leishmanial activity against L. donovani in a macrophage/amastigote model, with IC50 values of 23.5 μM.

Preparative separation of spirobisnaphthalenes from endophytic fungus Berkleasmium sp. Dzf12 by high-speed counter-current chromatography

High-speed counter-current chromatography (HSCCC) was applied for the first time for the preparative separation of spirobisnaphthalenes from a crude extract of the endophytic fungus Berkleasmium sp. Dzf12, associated with the medicinal plant Dioscorea zingiberensis. Six spirobisnaphthalenes were successfully separated by HSCCC with a two-phase solvent system composed of n-hexane-chloroform-methanol-water (1.5:3.0:2.5:2.0, v/v). About 18.0 mg of diepoxin κ (1), 245.7 mg of palmarumycin C13 (2), 42.4 mg of palmarumycin C16 (3), 42.2 mg of palmarumycin C15 (4), 32.6 mg of diepoxin δ (5), and 22.3 mg of diepoxin γ (6) with purities of 56.82, 71.39, 76.57, 75.86, 91.01 and 82.48%, respectively, as determined by high-performance liquid chromatography (HPLC), were obtained from 500 mg of the crude extract in a one-step elution within 7 h of separation procedure by HSCCC. The purified spirobisnaphthalenes were further structurally characterized by means of physicochemical and spectrometric analysis.

Antibacterial spirobisnaphthalenes from the North American cup fungus Urnula craterium

Urnucratins A-C (1-3), which possess an unusual bisnaphthospiroether skeleton with one oxygen bridge and one C-C bridge and represent a new subclass of bisnaphthalenes, were isolated from the North American cup fungus Urnula craterium. Their structures, including absolute configurations, were determined by means of HRMS, NMR, and quantum chemical CD calculations. Urnucratin A (1) was found to be active against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and Streptococcus pyogenes with MIC values of 2, 1, and 0.5 μg/mL, respectively.

Conidiation color mutants of Aspergillus fumigatus are highly pathogenic to the heterologous insect host Galleria mellonella

The greater wax moth Galleria mellonella has been widely used as a heterologous host for a number of fungal pathogens including Candida albicans and Cryptococcus neoformans. A positive correlation in pathogenicity of these yeasts in this insect model and animal models has been observed. However, very few studies have evaluated the possibility of applying this heterologous insect model to investigate virulence traits of the filamentous fungal pathogen Aspergillus fumigatus, the leading cause of invasive aspergillosis. Here, we have examined the impact of mutations in genes involved in melanin biosynthesis on the pathogenicity of A. fumigatus in the G. mellonella model. Melanization in A. fumigatus confers bluish-grey color to conidia and is a known virulence factor in mammal models. Surprisingly, conidial color mutants in B5233 background that have deletions in the defined six-gene cluster required for DHN-melanin biosynthesis caused enhanced insect mortality compared to the parent strain. To further examine and confirm the relationship between melanization defects and enhanced virulence in the wax moth model, we performed random insertional mutagenesis in the Af293 genetic background to isolate mutants producing altered conidia colors. Strains producing conidia of previously identified colors and of novel colors were isolated. Interestingly, these color mutants displayed a higher level of pathogenicity in the insect model compared to the wild type. Although some of the more virulent color mutants showed increased resistance to hydrogen peroxide, overall phenotypic characterizations including secondary metabolite production, metalloproteinase activity, and germination rate did not reveal a general mechanism accountable for the enhanced virulence of these color mutants observed in the insect model. Our observations indicate instead, that exacerbated immune response of the wax moth induced by increased exposure of PAMPs (pathogen-associated molecular patterns) may cause self-damage that results in increased mortality of larvae infected with the color mutants. The current study underscores the limitations of using this insect model for inferring the pathogenic potential of A. fumigatus strains in mammals, but also points to the importance of understanding the innate immunity of the insect host in providing insights into the pathogenicity level of different fungal strains in this model. Additionally, our observations that melanization defective color mutants demonstrate increased virulence in the insect wax moth, suggest the potential of using melanization defective mutants of native insect fungal pathogens in the biological control of insect populations.

Antileishmanial constituents of the Panamanian endophytic fungus Edenia sp

Bioassay-directed fractionation of extracts from the fermentation broth and mycelium of the fungus Edenia sp. led tothe isolation of five antileishmanial compounds, preussomerin EG1 (1), palmarumycin CP2 (2), palmarumycin CP17 (3), palmarumycin CP18 (4), and CJ-12,371 (5). Compounds 3 and 4 are new natural products, and this is only the second report of compound 1. The structures of compounds 1-5 were established by spectroscopic analyses (HRMS and NMR). All metabolites caused significant inhibition of the growth of Leishmania donoVani in the amastigote form, with IC50 values of 0.12, 3.93, 1.34, 0.62, and 8.40 microM, respectively. Compounds 1-5 were inactive when tested against Plasmodium falciparum or Trypanasoma cruzi at a concentration of 10 microg/mL, indicating that they have selective activity against Leishmania parasites. Compounds 1-5 showed weak cytotoxicity to Vero cells (IC50 of 9, 162, 174, 152, and 150 microM, respectively); however, the therapeutic window of these compounds is quite significant with 75, 41, 130, 245, and 18 times (respectively) more antileishmanial activity than cytotoxicity.

Naphthoquinone spiroketal with allelochemical activity from the newly discovered endophytic fungus Edenia gomezpompae

Chemical investigation of the mycelium of Edenia gomezpompae, a newly discovered endophytic fungus isolated from the leaves of Callicarpa acuminata (Verbenaceae) collected from the ecological reserve El Eden, Quintana Roo, Mexico, resulted in the isolation of four naphthoquinone spiroketals, including three new compounds and palmarumycin CP2 (4). We elucidated the structures of the metabolites by extensive NMR spectroscopy studies, including DEPT, COSY, NOESY, HSQC, HMBC, and chiroptical methods. The trivial names proposed for these compounds are preussomerin EG1 (1), preussomerin EG2 (2) and preussomerin EG3 (3). In addition, the X-ray data for 4 were obtained. The bioactivity of the mycelial organic extracts and the pure compounds was tested against three endophytic fungi (Colletotrichum sp., Phomopsis sp., and Guignardia manguifera) isolated from the same plant species (C. acuminata, Verbenaceae) and against four economically important phytopathogenic microorganisms (two fungoid oomycetes, Phythophtora capsici and Phythophtora parasitica, and the fungi Fusarium oxysporum and Alternaria solani). Spiroketals 1-3 displayed significant growth inhibition against all the phytopathogens. IC50 values for the four phytopathogens were from 20 to 170 microg/ml. Palmarumycin CP2 (4) was not bioactive against any of the fungi tested. Compound 1 showed the strongest bioactivity. The acetylated derivatives of preussomerin EG1 (1), 1a and 1b, were obtained and their biological activity was tested on endophytes and phytopathogens. Preussomerin EG1 1, 1a and 1b exhibited significant bioactivity against all microorganisms tested with the exception of Alternaria solani. This is the first report of allelochemicals with antifungal activity from the newly discovered endophytic fungus E. gomezpompae.

Aspergillus fumigatus conidial pigment and cAMP signal transduction: significance for virulence

The conidial pigment of Aspergillus fumigatus contains 1,8-dihydroxynaphthalene (DHN)-like pentaketide melanin. It plays a major role in the protection of the fungus against immune effector cells; for example, it is able to scavenge reactive oxygen species generated by alveolar macrophages and neutrophiles. The polyketide synthase PKSP (ALB1) is a key-enzyme of the biosynthesis pathway; its structural gene is part of a gene cluster. Furthermore, the presence of a functional pksP (albl) gene in A. fumigatus conidia is associated with an inhibition of phagolysosome fusion in human monocyte-derived macrophages. Moreover, the analysis of mutants that are defective in elements of the cAMP signaling pathway found that they are almost avirulent in an optimized low dose murine inhalation model. Taken together, our results indicate that the cAMP/PKA signal transduction pathway is required for A. fumigatus pathogenicity. In addition, we showed that the expression of the pksP gene is, at least in part, controlled by the cAMP/ PKA signal transduction pathway. Currently, we hypothesize that pentaketide melanin is important for defence against ROS. However, besides its contribution to the biosynthesis of DHN-like melanin, PKSP also appears to be involved in the formation of another compound which is immunosuppressive.

Natural product based inhibitors of the thioredoxin–thioredoxin reductase system

Spiroketal naphthodecalins are readily assembled by Barton's base mediated Ullmann binaphthyl ether coupling, Dakin reactions and hypervalent iodine spirocyclization. The core structures can be further diversified by enone addition and Stille coupling reactions. Nanomolar inhibitors for the Trx/TrxR redox control system were prepared by this approach and compared to series of natural product isolates. Cytotoxicity in MCF-7 cell assays ranged from an IC50 of 1.6 to >100 microM.

Biosynthesis of fungal melanins and their importance for human pathogenic fungi

For more than 40 years fungi have been known to produce pigments known as melanins. Predominantly these have been dihydroxyphenylalanine (DOPA)-melanin and dihydroxynaphthalene (DHN)-melanin. The biochemical and genetical analysis of the biosynthesis pathways have led to the identification of the genes and corresponding enzymes of the pathways. Only recently have both these types of melanin been linked to virulence in some human pathogenic and phytopathogenic fungi. The absence of melanin in human pathogenic and phytopathogenic fungi often leads to a decrease in virulence. In phytopathogenic fungi such as Magnaporthe grisea and Colletotrichum lagenarium, besides other possible functions in pathogenicity, DHN-melanin plays an essential role in generating turgor for plant appressoria to penetrate plant leaves. While the function of melanin in human pathogenic fungi such as Cryptococcus neoformans, Wangiella dermatitidis, Sporothrix schenckii, and Aspergillus fumigatus is less well defined, its role in protecting fungal cells has clearly been shown. Specifically, the ability of both DOPA- and DHN-melanins to quench free radicals is thought to be an important factor in virulence. In addition, in several fungi the production of fungal virulence factors, such as melanin, has been linked to a cAMP-dependent signaling pathway. Many of the components involved in the signaling pathway have been identified.

Unified route to the palmarumycin and preussomerin natural products. Enantioselective synthesis of (-)-preussomerin G

The total syntheses of eight members of the palmarumycin family have been achieved, with identification of the absolute stereochemistry for three of these natural products. In addition, the ras-farnesyl transferase inhibitor (-)-preussomerin G has been synthesized, achieving the first enantioselective route for accessing this family of natural products. Highlights of the synthetic work include an asymmetric epoxidation of a cyclic enone in excellent yield and enantiomeric excess and a potentially biomimetic oxidative spirocyclization for the introduction of the bis-spiroketal array unique to the preussomerin natural products.

Synthesis of cis- and trans-5,8-dihydroxy-5,6,7,8-tetrahydro-1,4-naphthoquinone

Cis- and trans-5,8-dihydroxy-5,6,7,8-tetrahydro-1,4-naphthoquinone (1a, 1b) were for the first time synthesized from 5,8-dihydroxy-1,4-naphthoquinone (naphthazazine) (6) as a starting material and racemic triol (3) was first synthesized from 7. The configuration of 1a was determined by X-ray analysis.

UV mutagenesis and enzyme inhibitors as tools to elucidate the late biosynthesis of the spirobisnaphthalenes

The metabolite pattern of UV mutants of the spirobisnaphthalene producing fungus F-24'707 by TLC and HPLC analysis has been investigated. Mutants with differences in colony morphology or colour compared to the parent strain were isolated. Cultivation in shaking flasks and P flasks showed differences in the metabolite pattern of some of the strains. Furthermore, enzyme inhibitors were used to block the spirobisnaphthalene biosynthesis of the parent strain at different steps. Feeding of precursors and intermediates of cladospirone bisepoxide (15) led to a two-fold increase of the production of 15. From these data and preceding biosynthetic studies we deduced a general pathway for the biosynthesis of all spirobisnaphthalenes of the fungus F-24'707. This enables us to present the hypothesis that all bisnaphthalenes described so far are produced using a common pathway with only a few intermediates as central branching points.

Total syntheses of (+/-)-preussomerins G and I

[formula: see text] Preussomerins G and I (2 and 3) have been synthesized for the first time. The key reaction in the synthesis is a possibly biomimetic tautomerization reaction depicted in Scheme 3 and the foregoing graphic. The driving force for this interesting rearrangement is primarily derived from the increase in resonance energy associated with converting a naphthalene ring into two isolated benzene rings.