A pyran-2-one and four meroterpenoids from Thapsia transtagana and their implication in the biosynthesis of transtaganolides

Four meroterpenoids (3a, 3b, 4 and 5), a prenylated pyran-2-one (2) along with the known compounds 7-O-geranylscopoletin (1), and thapsitranstagin (6) have been isolated from the roots of Thapsia transtagana. The presence of 1 and 2 supports the biogenetic hypothesis that transtaganolides, a group of bioactive metabolites, are meroterpenoids which come from an O-prenylated coumarin via successive pericyclic reactions.     

Hypoxia-inducible factor-1 and nuclear factor-kappaB inhibitory meroterpene analogues of bakuchiol, a constituent of the seeds of Psoralea corylifolia

Two new meroterpenoids, 12,13-dihydro-12,13-dihydroxybakuchiol (2) and (12'S)-bisbakuchiol C (3), were isolated from the seeds of Psoralea corylifolia L. (Fabaceae). The structures of 2 and 3 were elucidated by spectroscopic and chemical methods. Six meroterpenoids isolated from P. corylifolia and three semi-synthetic analogues were evaluated for HIF-1 and NF-kappaB inhibition, and O-methyl and O-ethylbakuchiols (6 and 7) inhibited HIF-1 and NF-kappaB activation without significantly decreasing the viability of the AGS and HeLa cells, respectively.     

Larvicidal effects of fungal Meroterpenoids in the control of Aedes aegypti L., the main vector of dengue and Yellow fever

The mosquito Aedes aegypti is an increasing problem of public health, being the vector responsible for dengue and Yellow Fever in tropical and subtropical regions. The aim of this work was to determine the potential larvicidal activity of a series of meroterpenoids, compounds 1-7, previously obtained fungal secondary metabolites from Penicillium sp., against the third-instar larvae of A. aegypti. The lethal concentrations (LC(50) and LC(90)) of 1-7 were evaluated 24 h after exposure. Dehydroaustin (4) was the most active meroterpenoid in the series, with an LC(50) value of 2.9 ppm, making it an attractive natural insecticide.     

Austalides V and W,new meroterpenoids from the fungus Aspergillus ustus and their antitumor activities

Two new austalide meroterpenoids, named austalides V and W (1 and 2), were isolated from the fungus Aspergillus ustus VKM F-4692. Their structures were elucidated by extensive spectroscopic analysis and by comparison with related known compounds. The main structural feature of both compounds is a tetrahydrofuranyl ring (G), a structural fragment, first found in austalides. Austalides V (1) and W (2) were able to inhibit the propagation of prostate and bladder cancer cells; this biologic activity is possibly related to the inhibition of a number of key pathways regulating cell growth and migration.     

Stachybotrychromenes A–C: novel cytotoxic meroterpenoids from <Emphasis Type="Italic">Stachybotrys</Emphasis> sp.

In the course of gaining new insights into the secondary metabolite profile of various Stachybotrys strains, in particular concerning triprenyl phenol-like compounds, so far, unknown metabolites with analogous structural features were discovered. Three novel meroterpenoids containing a chromene ring moiety, namely stachybotrychromenes A–C, were isolated from solid culture of the filamentous fungus Stachybotrys chartarum DSMZ 12880 (chemotype S). Their structures were elucidated by means of comprehensive spectroscopic analysis (1D and 2D NMR, ESI-HRMS, and CD) as well as by comparison with spectroscopic data of structural analogues described in literature. Stachybotrychromenes A and B exhibited moderate cytotoxic effects on HepG2 cells after 24 h with corresponding IC₅₀ values of 73.7 and 28.2 μM, respectively. Stachybotrychromene C showed no significant cytotoxic activity up to 100 μM. Moreover, it is noteworthy that stachybotrychromenes A–C are produced not only by S. chartarum chemotype S but also S. chartarum chemotype A and Stachybotrys chlorohalonata.     

Novel terpenoids of the fungus Aspergillus insuetus isolated from the Mediterranean sponge Psammocinia sp. collected along the coast of Israel

Three novel meroterpenoids, insuetolides A-C (1-3) and four drimane sesquiterpenes, the new (E)-6-(4'-hydroxy-2'-butenoyl)-strobilactone A (4) and the known 2α, 9α, 11-trihydroxy-6-oxodrim-7-ene (5), strobilactone A (6) and (E,E)-6-(6',7'-dihydroxy-2',4'-octadienoyl)-strobilactone A (7), were isolated from the EtOAc extract of the culture medium of the marine-derived fungus Aspergillus insuetus (OY-207), which was isolated from the Mediterranean sponge Psammocinia sp. The structures of the compounds were determined by spectroscopic methods. Insuetolides A-C reveal a new carbon skeleton derived from the cyclization of farnesyl and 3, 5-dimethylorsellinic acid. Compounds 1, 6, and 7 exhibited anti-fungal activity towards Neurospora crassa with MIC values of 140, 242, and 162 μM, respectively; and compounds 3, 4, and 7 exhibited mild cytotoxicity towards MOLT-4 human leukemia cells.     

Cytotoxic Meroterpenoids from the Fungus Alternaria sp. JJY‐32

Two new meroterpenoids, tricycloalternarenes X and Y, together with one known meroterpenoid, tricycloalternarene I, were isolated from the fungus Alternaria sp. JJY‐32. The structures including absolute configurations were established by the comprehensive spectroscopic data, electronic circular dichroism (ECD) spectral analyses, and biosynthesis consideration. Tricycloalternarene X showed cytotoxicity against the HL‐60 and HO8910 cells with IC₅₀ values of 7.54 and 20.32 μm .     

Biomimetic synthetic studies on meroterpenoids from the marine sponge Aka coralliphaga: Divergent total syntheses of siphonodictyal B,liphagal and corallidictyals A–D

The marine sponge Aka coralliphaga is a rich source of biologically active and structurally interesting meroterpenoids. Inspired by these natural products, we have used biosynthetic speculation to devise biomimetic syntheses of siphonodictyal B, liphagal and corallidictyals A–D from sclareolide. This work resulted in the development of new cascade reactions in the synthesis of liphagal, the reassignment of the structure of siphonodictyal B, and the realisation that corallidictyals A and B are possibly isolation artefacts.     

Identical ring cleavage products during anaerobic degradation of naphthalene, 2-methylnaphthalene, and tetralin indicate a new metabolic pathway

Anaerobic degradation of naphthalene, 2-methylnaphthalene, and tetralin (1,2,3,4-tetrahydronaphthalene) was investigated with a sulfate-reducing enrichment culture obtained from a contaminated aquifer. Degradation studies with tetralin revealed 5,6,7,8-tetrahydro-2-naphthoic acid as a major metabolite indicating activation by addition of a C(1) unit to tetralin, comparable to the formation of 2-naphthoic acid in anaerobic naphthalene degradation. The activation reaction was specific for the aromatic ring of tetralin; 1,2,3,4-tetrahydro-2-naphthoic acid was not detected. The reduced 2-naphthoic acid derivatives tetrahydro-, octahydro-, and decahydro-2-naphthoic acid were identified consistently in supernatants of cultures grown with either naphthalene, 2-methylnaphthalene, or tetralin. In addition, two common ring cleavage products were identified. Gas chromatography-mass spectrometry (GC-MS) and high-resolution GC-MS analyses revealed a compound with a cyclohexane ring and two carboxylic acid side chains as one of the first ring cleavage products. The elemental composition was C(11)H(16)O(4) (C(11)H(16)O(4)-diacid), indicating that all carbon atoms of the precursor 2-naphthoic acid structure were preserved in this ring cleavage product. According to the mass spectrum, the side chains could be either an acetic acid and a propenic acid, or a carboxy group and a butenic acid side chain. A further ring cleavage product was identified as 2-carboxycyclohexylacetic acid and was assumed to be formed by beta-oxidation of one of the side chains of the C(11)H(16)O(4)-diacid. Stable isotope-labeling growth experiments with either (13)C-labeled naphthalene, per-deuterated naphthalene-d(8), or a (13)C-bicarbonate-buffered medium showed that the ring cleavage products derived from the introduced carbon source naphthalene. The series of identified metabolites suggests that anaerobic degradation of naphthalenes proceeds via reduction of the aromatic ring system of 2-naphthoic acid to initiate ring cleavage in analogy to the benzoyl-coenzyme A pathway for monoaromatic hydrocarbons. Our findings provide strong indications that further degradation goes through saturated compounds with a cyclohexane ring structure and not through monoaromatic compounds. A metabolic pathway for anaerobic degradation of bicyclic aromatic hydrocarbons with 2-naphthoic acid as the central intermediate is proposed.     

Secondary metabolites of fungi of the <Emphasis Type="Italic">Usti</Emphasis> section,genus <Emphasis Type="Italic">Aspergillus</Emphasis> and their application in chemosystematics

Secondary metabolites of 22 fungal strains (genus Aspergillus, section Usti) isolated at diverse geographic regions, including the Arctic permafrost deposits, were studied. The studied strains were found to synthesize a variety of biologically active compounds, structurally identified as drimane sesqueterpenoids, isoquinoline alkaloids (TMC-120 A?C, derivative 1), meroterpenoids (austalides О and J), and anthraquinone pigments (averufin, versicolorin C). Desferritriacetylfusigen production by A. calidoustus isolates is reported for the first time. The individual spectra of secondary metabolites were used for reidentification of 17 strains, of which 15 were identified as A. calidoustus and two, as A. pseudodeflectus.     

Meroterpenoids from the fruiting bodies of higher fungus Ganoderma resinaceum

Phytochemical investigation on the fruiting bodies of Ganoderma resinaceum led to the isolation of five new meroterpenoids, namely ganoresinains A–E (1–5), and four known analogues (6–9). The new compounds were identified by extensive analyses of spectroscopic data (NMR, MS, UV, and IR) and comparison with the literature data. Compound 1 and 6 were isolated as enantiomeric mixture, which were separated over analytical chiral HPLC chromatography. Compounds 6–9 were isolated from G. resinaceum for the first time.     

A genome-wide polyketide synthase deletion library uncovers novel genetic links to polyketides and meroterpenoids in Aspergillus nidulans

Fungi possess an advanced secondary metabolism that is regulated and coordinated in a complex manner depending on environmental challenges. To understand this complexity, a holistic approach is necessary. We initiated such an analysis in the important model fungus Aspergillus nidulans by systematically deleting all 32 individual genes encoding polyketide synthases. Wild-type and all mutant strains were challenged on different complex media to provoke induction of the secondary metabolism. Screening of the mutant library revealed direct genetic links to two austinol meroterpenoids and expanded the current understanding of the biosynthetic pathways leading to arugosins and violaceols. We expect that the library will be an important resource towards a systemic understanding of polyketide production in A. nidulans.     

Cloning, overexpression, and purification of novobiocic acid synthetase from Streptomyces spheroides NCIMB 11891

Novobiocic acid synthetase, a key enzyme in the biosynthesis of the antibiotic novobiocin, was cloned from the novobiocin producer Streptomyces spheroides NCIMB 11891. The enzyme is encoded by the gene novL, which codes for a protein of 527 amino acids with a calculated mass of 56,885 Da. The protein was overexpressed as a His(6) fusion protein in Escherichia coli and purified to apparent homogeneity by affinity chromatography and gel chromatography. The purified enzyme catalyzed the formation of an amide bond between 3-dimethylallyl-4-hydroxybenzoic acid (ring A of novobiocin) and 3-amino-4,7-dihydroxy-8-methyl coumarin (ring B of novobiocin) in an ATP-dependent reaction. NovL shows homology to the superfamily of adenylate-forming enzymes, and indeed the formation of an acyl adenylate from ring A and ATP was demonstrated by an ATP-PP(i) exchange assay. The purified enzyme exhibited both activation and transferase activity, i.e. it catalyzed both the activation of ring A as acyl adenylate and the subsequent transfer of the acyl group to the amino group of ring B. It is active as a monomer as determined by gel filtration chromatography. The reaction was specific for ATP as nucleotide triphosphate and dependent on the presence of Mg(2+) or Mn(2+). Apparent K(m) values for ring A and ring B were determined as 19 and 131 micrometer respectively. Of several analogues of ring A, only 3-geranyl-4-hydroxybenzoate and to a lesser extent 3-methyl-4-aminobenzoate were accepted as substrates.     

Phycobilins of cryptophycean algae. Structures of novel bilins with acryloyl substituents from phycoerythrin 566

Cryptomonad strain CBD phycoerythrin 566 carries four open-chain tetrapyrrole (bilin) prosthetic groups: three singly thioether-linked bilins at alpha-19, beta-82, and beta-158 and a bilin linked through two thioether bonds at beta-50,61 (amino acid sequence numbering from Wilbanks, S. M., Wedemayer, G.J., and Glazer, A.N. (1989) J. Biol. Chem. 264, 17860-17867). The structures of all four peptide-linked prosthetic groups were determined by 1H NMR spectroscopy. The bilin at beta-82 was identified as phycoerythrobilin (PEB), a common prosthetic group in cyanobacterial and red algal phycobiliproteins. The structures of the remaining bilins were novel. The bilin at alpha-19, designated Cys-bilin 618, differed from PEB in having additional double bonds between C-2 and C-3 of ring A and between C-12' and C-12", i.e. an acryloyl substituent at C-12 of ring C. The doubly linked bilin at beta-50,61 designated DiCys-bilin 584, differed from doubly linked PEB (Schoenleber, R.W., Lundell, D.J., Glazer, A.N., and Rapoport, H. (1984) J. Biol. Chem. 259, 5481-5484) in possessing an acryloyl substituent at C-12 of ring C in place of a propionyl substituent. Similarly, the bilin at beta-158, designated Cys-bilin 584, differed from singly-linked PEB in possessing an acryloyl substituent at C-12 of ring C in place of a propionyl substituent. The three novel cryptomonad bilins join heme d1 and chlorophylls c1, c2, and c3 as the only known porphyrin-derived natural products with acryloyl substituents.     

Effect of Covalent Dimer Conjugates of Angiotensin II on Receptor Affinity and Activity in Vitro

Abstract

Angiotensin II [1-8 or 2-8] analogues and [4–8] fragments were dimerized through the amino-or carboxy-terminal groups in order to try to increase their potency as reported for other hormones. The binding affinity to the angiotensin II receptor subtypes A (A II_A) and B (A II_B) was tested and compared to the potency in rabbit aortic ring. The [2–8] dimers coupled through the N-terminus show no significant change in potency in aortic ring. The [4–8] fragments coupled through the N-terminus are inactive in the ring. They have however a significantly increased affinity for the A II^A receptor, the specific function of which has not yet been reported. When angiotensin II analogues or fragments are coupled through the C-terminus, there was a significant drop in affinity and potency, confirming the importance of the free carboxyl group in position 8 for binding and activity. It is concluded that binding to the A II_B receptor correlates well with the effectiveness in aortic ring. However, in contrast to the beneficial effect reported for a large number of other hormones, dimerization of angiotensin II or its fragments is not accompanied by an increased biological activity in aortic ring.     

The suicide inactivation of ox liver short-chain acyl-CoA dehydrogenase by propionyl-CoA. Formation of an FAD adduct.

R-Phycoerythrin contains two covalently bound bilin prosthetic groups, phycoerythrobilin and phycourobilin. The two chromophore types were separated as their peptide-bound derivatives by subjecting tryptic digests of R-phycoerythrin to adsorption chromatography on Sephadex G-25. The structure and apoprotein linkages of the bound phycoerythrobilin were found to be identical with those previously reported for this phycobilin [Killilea, O'Carra & Murphy (1980) Biochem. J. 187, 311-320]. Phycourobilin is a tetrapyrrole, containing no oxo bridges and has the same order of side chains as IX alpha bilins. The chromophore is linked to the peptide through two and possibly three of its pyrrole rings. One linkage possibly consists of an ester bond between the hydroxy group of a serine residue and the propionic acid side chain of one of the inner rings. The second linkage is a labile thioether bond between a cysteine residue and the C2 side chain of pyrrole ring A. The third linkage is a stable thioether bond between a cysteine residue and the alpha-carbon atom of the C2 side chain of pyrrole ring D. Ring D is unsaturated and is attached to ring C through a saturated carbon bridge. Rings B and C have a conjugated system of five bonds, as found in other urobilinoid pigments. Ring A is attached to ring B via a saturated carbon bridge. Both of the alpha-positions of ring A are in the reduced state, but the ring does contain an unsaturated centre (probably a double bond between the beta-carbon and the ring nitrogen atom). The presence of this double bond and its isomerization into the bridge position between rings A and B would explain the extension of the conjugated system of phycourobilin to that of a phycoerythrobilinoid/rhodenoid pigment in acid or alkali.     

SEPH, a Cdc7p orthologue from Aspergillus nidulans, functions upstream of actin ring formation during cytokinesis

In the filamentous fungus, Aspergillus nidulans, multiple rounds of nuclear division occur before cytokinesis, allowing an unambiguous identification of genes required specifically for cytokinesis. As in animal cells, both an intact microtubule cytoskeleton and progression through mitosis are required for actin ring formation and contraction. The sepH gene from A. nidulans was discovered in a screen for temperature-sensitive cytokinesis mutants. Sequence analysis showed that SEPH is 42% identical to the serine-threonine kinase Cdc7p from fission yeast. Signalling through the Septation Initiation Network (SIN), which includes Cdc7p and the GTPase Spg1p, is emerging as a primary regulatory pathway used by fission yeast to control cytokinesis. A similar group of proteins comprise the Mitotic Exit Network (MEN) in budding yeast. This is the first direct evidence for the existence of a functional SIN-MEN pathway outside budding and fission yeast. In addition to SEPH, potential homologues were also identified in other fungi and plants but not in animal cells. Deletion of sepH resulted in a viable strain that failed to septate at any temperature. Interestingly, quantitative analysis of the actin cytoskeleton revealed that sepH is required for construction of the actin ring. Therefore, SEPH is distinct from its counterpart in fission yeast, in which SIN components operate downstream of actin ring formation and are necessary for ring contraction and later events of septation. We conclude that A. nidulans has components of a SIN-MEN pathway, one of which, SEPH, is required for early events during cytokinesis.     

Isolation, crystallization, crystal structure analysis and refinement of B-phycoerythrin from the red alga Porphyridium sordidum at 2.2 A resolution.

The light-harvesting pigment-protein complex B-phycoerythrin from the red alga Porphyridium sordidum has been isolated and crystallized. B-Phycoerythrin consists of three different subunits forming an (alpha beta)6 gamma aggregate. The three-dimensional structure of the (alpha beta)6 hexamer was solved by Patterson search techniques using the molecular model of C-phycocyanin from Fremyella diplosiphon. The asymmetric unit of the crystal cell (space group P3, with a = b = 111.2 A, c = 59.9 A, alpha = beta = 90 degrees, gamma = 120 degrees) contains two (alpha beta) monomers related by a local dyad. Three asymmetric units are arranged around the crystallographic 3-fold axis building an (alpha beta)6 hexamer, as in C-phycocyanin. The crystal structure has been refined by energy-restrained crystallographic refinement and model building. The conventional R-factor of the final model was 18.9% with data to 2.2 A resolution. The molecular structures of the alpha and beta-subunits resemble those of C-phycocyanin. Major changes in comparison to phycocyanin are caused by deletion or insertion of segments involved in protein-chromophore interactions. The singly linked phycoerythrobilin chromophores alpha-84, alpha-140a, beta-84 and beta-155 are each covalently bound to a cysteine by ring A. The doubly linked chromophore beta-50/beta-61 is attached at cysteine beta-50 through ring A and at cysteine beta-61 through ring D. B-Phycoerythrin contains additionally a 30 kDa gamma-subunit, which is presumably located in the central cavity of the hexamer. It is disordered, as a consequence of crystal and local symmetry averaging.     

Structural defects in the regulatory particle-core particle interface of the proteasome induce a novel proteasome stress response

Proteasomes consist of a 19-subunit regulatory particle (RP) and 28-subunit core particle (CP), an α(7)β(7)β(7)α(7) structure. The RP recognizes substrates and translocates them into the CP for degradation. At the RP-CP interface, a heterohexameric Rpt ring joins to a heteroheptameric CP α ring. Rpt C termini insert individually into the α ring pockets to form a salt bridge with a pocket lysine residue. We report that substitutions of α pocket lysine residues produce an unexpected block to CP assembly, arising from a late stage defect in β ring assembly. Substitutions α5(K66A) and α6(K62A) resulted in abundant incorporation of immature CP β subunits, associated with a complete β ring, into proteasome holoenzymes. Incorporation of immature CP into the proteasome depended on a proteasome-associated protein, Ecm29. Using ump1 mutants, we identified Ecm29 as a potent negative regulator of RP assembly and confirmed our previous findings that proper RP assembly requires the CP. Ecm29 was enriched on proteasomes of pocket lysine mutants, as well as those of rpt4-Δ1 and rpt6-Δ1 mutants, in which the C-terminal residue, thought to contact the pocket lysine, is deleted. In both rpt6-Δ1 and α6(K62A) proteasomes, Ecm29 suppressed opening of the CP substrate translocation channel, which is gated through interactions between Rpt C termini and the α pockets. The ubiquitin ligase Hul5 was recruited to these proteasomes together with Ecm29. Proteasome remodeling through the addition of Ecm29 and Hul5 suggests a new layer of the proteasome stress response and may be a common response to structurally aberrant proteasomes or deficient proteasome function.     

The influence of intercalator structure on DNA binding strength: the importance of side chain orientation

A naphthothiophene intercalator with a cationic side chain linked to the ring through an ester group (1E) has been shown to bind to DNA almost an order of magnitude more strongly than a similar compound with the side chain linked to the ring through an amide group (1A) (W.D. Wilson, et al., Biophys. Chem. 24, 101-109 (1986]. X-ray crystallographic analysis of these two compounds indicates that both the ester and amide groups are essentially planar but that the amide is twisted approximately 30 degrees out of the aromatic plane of the naphthothiophene while the ester and ring system are co-planar. Proton NMR studies of the DNA complexes of these two compounds indicate that the naphthothiophene ring is intercalated in both 1A and 1E but that the protons of the ring system near the side chain interact with DNA base pairs at the binding site significantly better in 1E than in 1A. The protons next to the ester group on the side chain of 1E are also shifted upfield significantly more on addition of DNA than those of 1A. The large planar area of 1E, thus, allows greater stacking, complex geometry optimization, and dipolar interactions of the ester group with DNA base pairs at the binding site to account for the larger binding constant of this compound relative to 1A.