Search

Phenyl polyenes comprise a small family of bacterial natural products with broad and potent bioactivities, primarily found in actinobacteria. Here we report the discovery of five new phenyl polyene metabolites, maduraflavacins A-E ( 1 - 5 ), from a rare, marine-derived actinobacteria strain Actinomadura glauciflava NA03286. The structures of these natural products were determined by NMR spectroscopy, HRESIMS, LC-MS/MS, and chemical derivatization. All of these new maduraflavacins feature methyl substitutions at the polyene side chain, and maduraflavacins A-C ( 1 - 3 ) possessed a 1- N -β-d-glucosamine-(3 → 1)- O -β-d-glucopyranosyl-(3 → 1)- O -β-d-glucopyranosyl-(6 → 1)- O -β-d-glucopyranoside tetrasaccharide moiety via an amido linkage with a phenyl polyene skeleton. Compounds 1 and 2 showed weak antibacterial activities against the Gram-positive bacteria Staphylococcus aureus Sau 16339 and Micrococcus luteus , respectively.

Oxabornyl polyenes represent a unique group of polyketides characterized by a central polyene core flanked by a conserved oxabornyl moiety and a structurally diverse oxygen heterocyclic ring. They are widely distributed in fungi and possess a variety of biological activities. Due to the significant spatial separation between the two stereogenic ring systems, it is difficult to establish their overall relative configurations. Here, we isolated three oxabornyl polyenes, prugosenes A1-A3 ( 1 - 3 ), from Talaromyces sp. JNU18266-01. Although these compounds were first reported from Penicillium rugulosum , their overall relative and absolute configurations remained unassigned. By employing ozonolysis in combination with ECD calculations, we were able to establish their absolute configurations, and additionally obtained seven new chemical derivatives ( 4 - 10 ). Notably, through NMR data analysis and quantum chemical calculations, we achieved the structural revision of prugosene A2. Furthermore, prugosenes A1-A3 exhibited potent antiviral activity against the respiratory syncytial virus, with compound 1 displaying an IC 50 value of 6.3 μM. Our study thus provides a valuable reference for absolute configuration assignment of oxabornyl polyene compounds.

New approaches are still needed to fully explore the biosynthetic potential of microbes. We recently devised a melC reporter-guided fermentation media screening approach for targeted activation of cryptic gene clusters. Using this approach, we successfully activated the expression of the hcl gene cluster in Streptomyces sp. LZ35 and discovered a novel polyene macrolide hexacosalactone A ( 1 ).

This paper describes a seven-step synthesis of the proposed structure for chaunopyran A produced by cocultivation of a Chaunopycnis sp. and Trichoderma hamatum . This synthesis included a coupling of a diene sulfone and a tetrahydropyranyl aldehyde as a key step. The sign of the specific rotation value of the synthetic sample was opposite that of the natural product, suggesting that the absolute configuration of the natural product should be revised.

Exploration of unstable compounds is a rarely explored area of natural product research. We describe the integration of genomic and metabolomic analyses with bioassay-guided compound mining to effectively explore unstable bacillaenes. New bacillaene structures ( 2 , 4 , and 5 ) were identified from compound mixtures using the DANS-SVI ( d ifferential a nalysis of 2D N MR s pectrum- s ingle spectrum with v ariable i ntensities) method, which were further verified by the isolation of the pure compounds under strictly controlled conditions. Compound 1 exhibited antibacterial activity against multi-drug-resistant bacterial strains, while glycosylation decreased the activity of the bacillaene scaffold.

In our screening program for new biologically active secondary metabolites, a new strain, Nocardiopsis CG3 (DSM 106572), isolated from the saltpan of Kenadsa, was found to produce five new polyene macrolactams, the kenalactams A-E (1-5). Their structures were elucidated by spectral methods (NMR and HRESIMS), and the absolute configuration was derived by chemical derivatization (Mosher's method). Through a feeding experiment, alanine was proven to be the nitrogen-bearing starter unit involved in biosynthesis of the polyketide kenalactam A (1). Kenalactam E (5) was cytotoxic against human prostate cancer PC-3 cells with an IC 50 value of 2.1 μM.

Despite numerous efforts to discover novel bioactive products from microorganisms, previously reported compounds are repetitively reisolated. A new polyketide glycoside, gordonic acid (1), isolated from the mixed culture of two Gram-positive bacteria, Gordonia sp. KMC005 and Streptomyces tendae KMC006, is reported. The structure of 1 was characterized as an acyclic polyene polyketide substituted with a β-d-digitoxopyranose through NMR, HR-ESI-QTOF-MS, IR, and UV spectral data. The stereochemistry for 1 was determined by Mosher's method followed by 2D NOESY analysis and by NMR chemical shift calculations supported by DP4 analysis. Gordonic acid (1) showed weak activity against Micrococcus luteus and Enterococcus hirae.

Marine algae from the genus Karlodinium are known to be involved in fish-killing events worldwide. Here we report for the first time the chemistry and bioactivity of a natural product from the newly described mixotrophic dinoflagellate Karlodinium armiger. Our work describes the isolation and structural characterization of a new polyhydroxy-polyene named karmitoxin. The structure elucidation work was facilitated by use of 13 C enrichment and high-field 2D NMR spectroscopy, where 1 H- 13 C long-range correlations turned out to be very informative. Karmitoxin is structurally related to amphidinols and karlotoxins; however it differs by containing the longest carbon-carbon backbone discovered for this class of compounds, as well as a primary amino group. Karmitoxin showed potent nanomolar cytotoxic activity in an RTgill-W1 cell assay as well as rapid immobilization and eventual mortality of the copepod Acartia tonsa, a natural grazer of K. armiger.

Co-cultivation of Chaunopycnis sp. (CMB-MF028) and Trichoderma hamatum (CMB-MF030), fungal strains co-isolated from the inner tissue of an intertidal rock platform mollusc (Siphonaria sp), resulted in transcriptional activation of a rare class of 2-alkenyl-tetrahydropyran, chaunopyran A (7), and biotransformation and deactivation of the antifungal pyridoxatin (1), to methyl-pyridoxatin (8). This study illustrates the complexity of offensive and counter-offensive molecular defenses encountered during fungal co-cultivation, and the opportunities for activating new, otherwise transcriptionally silent secondary metabolites.

Three new cyclohexene amine derivatives, daryamides D-F (1-3), a new arylamine derivative, carpatamide D (4), and a new ornithine lactamization derivative, ornilactam A (5), were isolated from the marine-derived Streptomyces strain SNE-011. Their structures, including absolute configurations, were elucidated on the basis of spectroscopic analysis and chemical methods. The carpatamide skeleton could be considered as the biosynthetic precursor of the daryamides.

Bioassay-guided fractionation of the organic extracts of a Bacillus amyloliquefaciens strain (AP183) led to the discovery of a new macrocyclic polyene antibiotic, bacillusin A (1). Its structure was assigned by interpretation of NMR and MS spectroscopic data as a novel macrodiolide composed of dimeric 4-hydroxy-2-methoxy-6-alkenylbenzoic acid lactones with conjugated pentaene-hexahydroxy polyketide chains. Compound 1 showed potent antibacterial activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium with minimum inhibitory concentrations in a range of 0.6 to 1.2 μg/mL. The biosynthetic significance of this unique class of antibiotic compounds is briefly discussed.

Salternamides A-D (1-4), the first secondary metabolites discovered from saltern-derived actinomycetes, were isolated from a halophilic Streptomyces strain isolated from a saltern on Shinui Island in the Republic of Korea. The planar structures of the salternamides, which are new members of the manumycin family, were elucidated by a combination of spectroscopic analyses. The absolute configurations of the salternamides were determined by chemical and spectroscopic methods, including the modified Mosher's method, J-based configuration analysis, and circular dichroism spectroscopy. Salternamide A (1), which is the first chlorinated compound in the manumycin family, exhibited potent cytotoxicity against a human colon cancer cell line (HCT116) and a gastric cancer cell line (SNU638) with submicromolar IC50 values. Salternamides A and D were also determined to be weak Na(+)/K(+) ATPase inhibitors.

A stereaceous basidiomycete was investigated with regard to its capacity to produce yellow pigments after physical injury of the mycelium. Two pigments were isolated from mycelial extracts, and their structures were elucidated by ESIMS and one- and two-dimensional NMR methods. The structures were identified as the previously undescribed polyenes (3Z,5E,7E,9E,11E,13Z,15E,17E)-18-methyl-19-oxoicosa-3,5,7,9,11,13,15,17-octaenoic acid (1) and (3E,5Z,7E,9E,11E,13E,15Z,17E,19E)-20-methyl-21-oxodocosa-3,5,7,9,11,13,15,17,19-nonaenoic acid (2). Stable-isotope feeding with [1-(13)C]acetate and l-[methyl-(13)C]methionine demonstrated a polyketide backbone and that the introduction of the sole methyl branch is most likely S-adenosyl-l-methionine-dependent. Dose-dependent inhibition of Drosophila melanogaster larval development was observed with both polyenes in concentrations between 12.5 and 100 μM. GI50 values for 1 and 2 against HUVEC (K-562 cells) were 71.6 and 17.4 μM (15.4 and 1.1 μM), respectively, whereas CC50 values for HeLa cells were virtually identical (44.1 and 45.1 μM).

Two new marine cyanobacterial natural products, parguerene (1) and precarriebowmide (2), were isolated from a collection of Moorea producens obtained from La Parguera, Puerto Rico. The planar structures of both were deduced by 2D NMR spectroscopy and mass spectrometry. Parguerene is a modified acyl amide with some structural similarity to the bacterial metabolite stipiamide (3), whereas precarriebowmide is a lipopeptide and represents a minor modification compared to two other known metabolites, carriebowmide (4) and carriebowmide sulfone (5). The identification of 2 led to an investigation into whether carriebowmide and carriebowmide sulfone were true secondary metabolites or isolation artifacts.

Fostriecin (FST, 1) is a natural product with promising antitumor activity produced by Streptomyces pulveraceus. Its antitumor activity is associated with the selective inhibition of protein phosphatase activities. The biosynthetic gene cluster for FST has recently been cloned and sequenced. To better understand the post-polyketide synthase (PKS) modification steps in the biosynthetic pathway of FST, we constructed and characterized three post-PKS modification gene mutants of fosG, fosK, and fosM by knockout inactivation in S. pulveraceus. As a result, we determined that a fosK-encoded cytochrome P450 monooxygenase is responsible for C-18 hydroxylation, formation of an unsaturated lactone is dependent upon FosM, and the fosG gene product is involved in hydroxylation at C-4 after the action of FosM to yield PD 113,271 from FST. The accumulated analogues from the ΔfosK and ΔfosM mutant strains possessed a malonyl ester moiety that suggested that all the post-PKS modification steps in FST biosynthesis occur with the polyketide chain bearing a malonyl ester at the C-3 position, with formation of the unsaturated six-membered lactone as the last step in FST biosynthesis.

Bahamaolides A and B (1 and 2), two new 36-membered macrocyclic lactones, were isolated from the culture of the marine actinomycete Streptomyces sp. derived from a sediment sample collected at North Cat Cay in the Bahamas. The planar structures of 1 and 2, bearing a hexaenone and nine consecutive skipped hydroxy groups, were determined by 1D and 2D NMR, mass, IR, and UV spectra. The absolute configurations of the bahamaolides were established by combined multistep chemical reactions and spectroscopic analysis. Bahamaolide A displayed significant inhibitory activity against Candida albicans isocitrate lyase and antifungal activity against various pathogenic fungi.

Three polyenylpyrone metabolites, pyridinopyrones A to C (1-3), have been isolated from the culture broth of a marine-derived Streptomyces sp., strain CNQ-301. The structures of the pyridinopyrones were assigned on the basis of chemical modification and combined spectroscopic methods, focusing on interpretation of 1D and 2D NMR data. Pyridinopyrones B and C (2, 3), examined as an inseparable mixture of methyl positional isomers, were ultimately defined by hydrogenation and NMR analysis of a saturated derivative. The biosynthesis of these metabolites was defined by the incorporation of stable isotope-labeled precursors, revealing that the biosynthetic starter unit is nicotinic acid, while the polyene chain and pendant methyl groups are acetate- and methionine-derived, respectively.

A new polyene pigment, mycenaaurin A (1), was isolated from fruiting bodies of Mycena aurantiomarginata. Mycenaaurin A consists of a tridecaketide that is flanked by two amino acid moieties. These are likely to be derived biosynthetically from S-adenosylmethionine. The tridecaketide itself contains an alpha-pyrone, a conjugated hexaene, and an isolated alkenyl moiety. The structure of the new pigment was established by 2D NMR spectroscopic methods and APCIMS. The absolute configuration of the four stereogenic centers was determined by degradation of 1 by ozonolysis and GC-MS comparison of the resulting fragments, after appropriate derivatization, with authentic synthetic samples. Mycenaaurin A (1) might act as a constitutive defense compound, since it exhibits antibacterial activity against the gram-positive bacterium Bacillus pumilus.

The karlotoxins are a family of amphidinol-like compounds that play roles in avoiding predation and in prey capture for the toxic dinoflagellate Karlodinium veneficum. The first member of the toxin group to be reported was KmTx 1 (1), and here we report an additional five new members of this family (3-7) from the same strain. Of these additional compounds, KmTx 3 (3) differs from KmTx 1 (1) in having one less methylene group in the saturated portion of its lipophilic arm. In addition, 64-E-chloro-KmTx 3 (4) and 10-O-sulfo-KmTx 3 (5) were identified. Likewise, 65-E-chloro-KmTx 1 (6) and 10-O-sulfo-KmTx 1 (7) were also isolated. Comparison of the hemolytic activities of the newly isolated compounds to that of KmTx 1 shows that potency correlates positively with the length of the lipophilic arm and is disrupted by sulfonation of the polyol arm.

Eight new polyacetylenes (1-8) and six known polyacetylenes were isolated from the entire parts of Bupleurum longiradiatum, a poisonous plant. The structures of the new compounds were determined by spectroscopic data interpretation. The absolute configuration of the known compound bupleurotoxin (9) was established by the modified Mosher's method. All isolates were also tested for their cytotoxicity against a human leukemia cell line (HL-60).

The chlorinated polyene aurantoic acid (1) and the 4-methylene sterol dehydroconicasterol (2) were isolated from the Indonesian sponge Theonella swinhoei, and their structures were elucidated by interpretation of spectroscopic data. Aurantoic acid is a unique member in the class of naturally occurring conjugated polyene derivatives, while dehydroconicasterol is the likely biogenetic precursor of the major Theonella 4-methylene sterols.

Three new pentaketides, aspinotriols A ( 1) and B ( 3) and aspinonediol ( 5), were isolated together with two known compounds, aspinonene ( 7) and dihydroaspyrone ( 9), from the marine fungus Aspergillus ostianus strain 01F313, which was collected in Pohnpei and cultured with bromine-modified artificial seawater. The structures of the new compounds were determined by spectroscopic analyses including 1D and 2D NMR. Although 1 and 3 are diastereomers, they show nearly superimposable (1)H and (13)C NMR spectra. The absolute configurations of compounds 1, 3, 5, and 9 were elucidated by the modified Mosher's method.

Etnangien (1), a new macrolide antibiotic active against Gram-positive bacteria, was isolated from the culture broth of the myxobacterium Sorangium cellulosum, strains So ce750 and So ce1045. Spectroscopic structure elucidation of 1 revealed a complex macrocyclic lactone bearing a modified C21 carboxylic acid side chain. The latter contains two allylic hydroxyl groups and an all-E hexaene unit, which provides the characteristic UV chromophore of 1. Initial studies toward the mechanism of action showed that bacterial and viral nucleic acid polymerases are inhibited by etnangien (1).

Addition of NaCl to the solid-phase fermentation of an Australian isolate of Gymnoascus reessii resulted in enhanced production of chloropolyenylpyrroles, while the addition of NaBr suppressed chloropolyenylpyrrole production in favor of bromo and dechloro analogues. Access to a wider selection of polyenylpyrroles provided scope for SAR comparisons on this rare class of cytotoxic natural products, with the bromo- and dechloropolyenylpyrroles displaying significantly reduced cytotoxicity. These results suggest that the chloro substituent is a critical element in the pharmacophore for this rare class of natural product.

A long-chain polyhydroxy polyene amide, zooxanthellamide D (ZAD-D, 1, C54H83NO19), was isolated from a cultured marine dinoflagellate of the genus Symbiodinium. ZAD-D (1) is a polyhydroxy amide consisting of a C22-acid part and a C32-amine part and furnishes three tetrahydropyran rings and six isolated butadiene chromophores. The relative stereochemistry of the tetrahydropyran ring systems was elucidated by NMR techniques. This metabolite showed moderate cytotoxicity against two human tumor cell lines. A phylogenetic tree of Symbiodinium has been updated and compared with the structures of the hitherto isolated polyols of Symbiodinium, zooxanthellatoxins and zooxanthellamides, providing a promising chemotaxonomic perspective for the classification of this morphologically indistinguishable dinoflagellate.

Three polyene antibiotics, mediomycins A (1), B (2), and clethramycin (3), were isolated from Streptomyces mediocidicus ATCC23936. Their structures were elucidated through extensive NMR study coupled with chemical reactions and MS/MS fragmentation analysis. All three compounds are linear polyenes consisting of a conjugated oxo-triene group and a hexaene moiety. Compounds 1 and 2 are new polyenes. All three compounds demonstrated a broad spectrum of antifungal activity in vitro.

In the course of our continuing search for new antitumor-antibiotics from marine-derived actinomycete bacteria, four new cytotoxic compounds, designated as daryamides A (1), B (2), and C (3) and (2E,4E)-7-methylocta-2,4-dienoic acid amide (4), were isolated from the culture broth of a marine-derived Streptomyces strain CNQ-085. The structures of these new compounds were assigned by detailed interpretation of spectroscopic data. The relative configuration of 1 was determined by comprehensive NMR analysis, while the absolute configuration of 1 was determined as 4S,5R using the modified Mosher method. The daryamides show weak to moderate cytotoxic activity against the human colon carcinoma cell line HCT-116 and very weak antifungal activities against Candida albicans.

Analysis of the genome of Streptomyces aizunensis NRRL B-11277 indicated its potential to produce a compound of novel and highly predictable structure. The structure was predicted with sufficient accuracy to allow straightforward detection of the specific metabolite in HPLC profiles of fermentation extracts and hence to guide the isolation. The spectroscopic work was reduced to a confirmation of structure rather than a first principle determination. The compound, ECO-02301 (1), demonstrated potent antifungal activity. This work exemplifies not only the discovery of novel antibiotics from well-characterized organisms but also the utility of genomics as a further tool, complementary to spectroscopy, to enable rapid determination of complex structures.

In our screening of marine Streptomycetes for bioactive principles, two novel antitumor antibiotics designated as chinikomycins A (2a) and B (2b) were isolated together with manumycin A (1), and their structures were elucidated by a detailed interpretation of their spectra. Chinikomycins A (2a) and B (2b) are chlorine-containing aromatized manumycin derivatives of the type 64-pABA-2 with an unusual para orientation of the side chains. They exhibited antitumor activity against different human cancer cell lines, but were inactive in antiviral, antimicrobial, and phytotoxicity tests.

Reinvestigation of the production of the unusual polyene carboxylic acid serpentene (1a) from Streptomycessp. Tü 3851 revealed the presence of additional polyene carboxylic acids. The methyl esters of the new all-trans serpentene (2) and four new dicarboxylic acids (3-6) were isolated after methylation of the isolated polyene fraction. The dicarboxylic acids might result from omega- and beta-oxidation of the parent compounds 1 and 2.

During the course of our screening program designed to discover novel anticancer and anti-infective agents from marine microorganisms, a strain of Streptomyces aureoverticillatus (NPS001583) isolated from a marine sediment was found to produce a novel macrocyclic lactam with cytotoxicity against various tumor cell lines. Using extensive MS, UV, and NMR spectral analyses, the structure has been established as compound 1, aureoverticillactam, a 22-atom macrocyclic lactam incorporating both triene and tetraene conjugated olefins.

Labelling experiments with 13C-labelled precursors demonstrated that the majority of the macrolide ring of rapamycin is formed from six acetate and seven propionate units. A two-carbon unit in the ring was not labelled by acetate, propionate, glycine, or methionine. Methionine and glycine did, however, label the three methoxy groups of rapamycin to a high degree. Results from the incorporation experiments demonstrated that there were errors in the published 13C-nmr spectral assignments for rapamycin; these have now been corrected.