Di-Isatropolone C, a Spontaneous Isatropolone C Dimer Derivative with Autophagy Activity.

Isatropolone C from Streptomyces sp. CPCC 204095 features a fused cyclopentadienone-tropolone-oxacyclohexadiene tricyclic moiety in its structure. Herein, we report an isatropolone C dimer derivative, di-isatropolone C, formed spontaneously from isatropolone C in methanol. Notably, the structure of di-isatropolone C resolved by NMR reveals a newly formed cyclopentane ring to associate the two isatropolone C monomers. The configurations of four chiral carbons, including a ketal one, in the cyclopentane ring are assigned using quantum NMR calculations and DP4+ probability. The plausible molecular mechanism for di-isatropolone C formation is proposed, in which complex dehydrogenative C-C bond coupling may have happened to connect the two isatropolone C monomers. Like isatropolone C, di-isatropolone C shows the biological activity of inducing autophagy in HepG2 cells.

Iterative Methylation Leads to 3-Methylchuangxinmycin Production in Actinoplanes tsinanensis CPCC 200056.

A new congener of chuangxinmycin (CM) was identified from Actinoplanes tsinanensis CPCC 200056. Its structure was determined as 3-methylchuangxinmycin (MCM) by 1D and 2D NMR. MCM could be generated in vivo from CM by heterologous expression of the vitamin B12-dependent radical SAM enzyme CxnA/A1 responsible for methylation of 3-demethylchuangxinmycin (DCM) in CM biosynthesis, indicating that CxnA/A1 could perform iterative methylation for MCM production. In vitro assays revealed significant activities of CM, DCM, and MCM against Mycobacterium tuberculosis H37Rv and clinically isolated isoniazid/rifampin-resistant M. tuberculosis, suggesting that CM and its derivatives may have potential for antituberculosis drug development.

Mining and characterization of the PKS-NRPS hybrid for epicoccamide A: a mannosylated tetramate derivative from Epicoccum sp. CPCC 400996.

BACKGROUND: Genomic analysis indicated that the genomes of ascomycetes might carry dozens of biosynthetic gene clusters (BGCs), yet many clusters have remained enigmatic. The ascomycete genus Epicoccum, belonging to the family Didymellaceae, is ubiquitous that colonizes different types of substrates and is associated with phyllosphere or decaying vegetation. Species of this genus are prolific producers of bioactive substances. The epicoccamides, as biosynthetically distinct mannosylated tetramate, were first isolated in 2003 from Epicoccum sp. In this study, using a combination of genome mining, chemical identification, genetic deletion, and bioinformatic analysis, we identified the required BGC epi responsible for epicoccamide A biosynthesis in Epicoccum sp. CPCC 400996. RESULTS: The unconventional biosynthetic gene cluster epi was obtained from an endophyte Epicoccum sp. CPCC 400996 through AntiSMASH-based genome mining. The cluster epi includes six putative open reading frames (epiA-epiF) altogether, in which the epiA encodes a tetramate-forming polyketide synthase and nonribosomal peptide synthetases (PKS-NRPS hybrid). Sequence alignments and bioinformatic analysis to other metabolic pathways of fungal tetramates, we proposed that the gene cluster epi could be involved in generating epicoccamides. Genetic knockout of epiA completely abolished the biosynthesis of epicoccamide A (1), thereby establishing the correlation between the BGC epi and biosynthesis of epicoccamide A. Bioinformatic adenylation domain signature analysis of EpiA and other fungal PKS-NRPSs (NRPs) indicated that the EpiA is L-alanine incorporating tetramates megasynthase. Furthermore, based on the molecular structures of epicoccamide A and deduced gene functions of the cluster epi, a hypothetic metabolic pathway for biosynthesizing compound 1 was proposed. The corresponding tetramates releasing during epicoccamide A biosynthesis was catalyzed through Dieckmann-type cyclization, in which the reductive (R) domain residing in terminal module of EpiA accomplished the conversion. These results unveiled the underlying mechanism of epicoccamides biosynthesis and these findings might provide opportunities for derivatization of epicoccamides or generation of new chemical entities. CONCLUSION: Genome mining and genetic inactivation experiments unveiled a previously uncharacterized PKS - NRPS hybrid-based BGC epi responsible for the generation of epicoccamide A (1) in endophyte Epicoccum sp. CPCC 400996. In addition, based on the gene cluster data, a hypothetical biosynthetic pathway of epicoccamide A was proposed.

Dihydroisatropolone C from Streptomyces and Its Implication in Tropolone-Ring Construction for Isatropolone Biosynthesis.

Isatropolones/isarubrolones are actinomycete secondary metabolites featuring a tropolone-ring in their structures. From the isatropolone/isarubrolone producer Streptomyces sp. CPCC 204095, 7,12-dihydroisatropolone C (H2ITC) is discovered and identified as a mixture of two interchangeable diastereomers differing in the C-6 configuration. As a major metabolite in the mycelial growth period of Streptomyces sp. CPCC 204095, H2ITC can be oxidized spontaneously to isatropolone C (ITC), suggesting H2ITC is the physiological precursor of ITC. Characterization of H2ITC makes us propose dihydrotropolone-ring construction in the biosynthesis of isatropolones.

Mintaimycins, a Group of Novel Peptide Metabolites from Micromonospora sp. C-3509.

A group of peptide metabolites (1-4), designated as mintaimycins, were isolated from Micromonospora sp. C-3509. The planar structures of mintaimycins were determined by combination of mass spectrometry, 1D and 2D NMR spectroscopy, and the stereochemistry of mintaimycins were partially resolved by Marfey's or Mosher's method. Mintaimycins featured a central ß-methylphenylalanine or phenylalanine linked at its amino group with 5-methyl-2-hexenoic acid, and at its carboxyl group with 5-hydroxy-norleucine or leucine that combined a derivative of hexanoic acid or 4-methylpentanoic acid. Mintaimycin A1 (1), the principal component, was found to exhibit the biological activity of inducing pre-adipocyte differentiation of 3T3-L1 fibroblast cells at 10.0 µmol/L.

The Cytochrome P450 Catalyzing C-S Bond Formation in S-Heterocyclization of Chuangxinmycin Biosynthesis.

Microbial sulfur-containing secondary metabolites show various biological activities, but the C-S bond-forming in their biosynthetic metabolism has not been thoroughly understood. Here, we present genetic, biochemical and structural characterization of a cytochrome P450 monooxygenase CxnD exhibiting C-S bond forming activity in S-heterocyclization of chuangxinmycin biosynthesis. In vivo and in vitro analyses demonstrated that CxnD generated an indole-fused dihydrothiopyran skeleton from a L-Trp-derived thiol intermediate. Furthermore, X-ray crystal structure of CxnD in complex with a substrate analogue and structure-based mutagenesis revealed intimate details of the substrate binding mode. A radical mechanism initiated by abstraction of the imino hydrogen atom or an electron from indole group of the substrate was proposed for CxnD, which provided valuable insights into the molecular basis for the intra-molecular C(sp2 )-H thiolation by the P450 in chuangxinmycin biosynthesis.

Cytotoxic and Antibacterial Cervinomycins B1-4 from a Streptomyces Species.

AntiSMASH analysis of genome DNA of Streptomyces CPCC 204980, a soil isolate with potent antibacterial activity, revealed a gene cluster for polycyclic xanthones. A subsequent chemical study confirmed that the microorganism produced polycyclic xanthone cervinomycin A2 (1) and the new congeners cervinomycins B1-4 (2-5). The structures of 1-5 were determined by comprehensive analyses of MS and NMR data, which indicated that 2-5 featured a common dihydro-D ring in the polycyclic xanthone core moiety of their molecules. 2-5 are toxic to human cancer cells and active against Gram-positive bacteria.

Isarubrolones Containing a Pyridooxazinium Unit from Streptomyces as Autophagy Activators.

Isarubrolones are bioactive polycyclic tropoloalkaloids from Streptomyces. Three new isarubrolones (2-4), together with the known isarubrolone C (1) and isatropolones A (5) and C (6, 3( R)-hydroxyisatropolone A), were identified from Streptomyces sp. CPCC 204095. The structures of these compounds were determined using a combination of mass spectrometry, 1D and 2D NMR spectroscopy, and ECD. Compounds 3 and 4 feature a pyridooxazinium unit, which is rarely seen in natural products. Compound 6 could conjugate with amino acids or amines to expand the structural diversity of isarubrolones with a pentacyclic or hexacyclic core. Importantly, 1 and 3-6 were found to induce complete autophagy.

Genome-Guided Discovery of Pretilactam from Actinosynnema pretiosum ATCC 31565.

Actinosynnema is a small but well-known genus of actinomycetes for production of ansamitocin, the payload component of antibody-drug conjugates against cancers. However, the secondary metabolite production profile of Actinosynnema pretiosum ATCC 31565, the most famous producer of ansamitocin, has never been fully explored. Our antiSMASH analysis of the genomic DNA of Actinosynnema pretiosum ATCC 31565 revealed a NRPS-PKS gene cluster for polyene macrolactam. The gene cluster is very similar to gene clusters for mirilactam and salinilactam, two 26-membered polyene macrolactams from Actinosynnema mirum and Salinispora tropica, respectively. Guided by this bioinformatics prediction, we characterized a novel 26-membered polyene macrolactam from Actinosynnema pretiosum ATCC 31565 and designated it pretilactam. The structure of pretilactam was elucidated by a comprehensive analysis of HRMS, 1D and 2D-NMR, with absolute configuration of chiral carbons predicted bioinformatically. Pretilactam features a dihydroxy tetrahydropyran moiety, and has a hexaene unit and a diene unit as its polyene system. A preliminary antibacterial assay indicated that pretilactam is inactive against Bacillus subtilis and Candida albicans.

Cytotoxic Dibohemamines D-F from a Streptomyces Species.

Three dimeric analogues of bohemamines, dibohemamines D-F (1-3), together with dibohemamine A (4), were isolated from Streptomyces sp. CPCC 200497. Their structures were solved using a combination of mass spectrometry, 1D and 2D NMR spectroscopy, and CD. Dibohemamines D and E were new dimeric analogues of bohemamines, and dibohemamine F was a known compound obtained previously by semisynthesis. Dibohemamine F displayed potent cytotoxicity against cancer cell lines A549 and HepG2 with IC50 values of 1.1 and 0.3 µM, respectively. Dibohemamines D and E showed moderate cytotoxicity against cancer cell lines A549 and HepG2.

Binding of a biosynthetic intermediate to AtrA modulates the production of lidamycin by Streptomyces globisporus.

The control of secondary production in streptomycetes involves the funneling of environmental and physiological signals to the cluster-situated (transcriptional) regulators (CSRs) of the biosynthetic genes. For some systems, the binding of biosynthetic products to the CSR has been shown to provide negative feedback. Here we show for the production of lidamycin (C-1027), a clinically relevant antitumor agent, by Streptomyces globisporus that negative feedback can extend to a point higher in the regulatory cascade. We show that the DNA-binding activity of the S. globisporus orthologue of AtrA, which was initially described as a transcriptional activator of actinorhodin biosynthesis in S. coelicolor, is inhibited by the binding of heptaene, a biosynthetic intermediate of lidamycin. Additional experiments described here show that S. globisporus AtrA binds in vivo as well as in vitro to the promoter region of the gene encoding SgcR1, one of the CSRs of lidamycin production. The feedback to the pleiotropic regulator AtrA is likely to provide a mechanism for coordinating the production of lidamycin with that of other secondary metabolites. The activity of AtrA is also regulated by actinorhodin. As AtrA is evolutionarily conserved, negative feedback of the type described here may be widespread within the streptomycetes.

[Identification of 3-demethylchuangxinmycin from Actinoplanes tsinanensis CPCC 200056].

Chuangxinmycin (CM) from Actinoplanes tsinanensis was an antibiotic discovered by Chinese scientists about 40 years ago. It contains a new heterocyclic system of indole fused with dihydrothiopyran, whose biosynthetic mechanism remains unclear. CM is used as an oral medicine in the treatment of bacterial infections in China. The simple structure makes CM as an attractive candidate of structure modification for improvement of antibacterial activity. Recently, we analyzed the secondary metabolites of Actinoplanes tsinanensis CPCC 200056, a CM producing strain, as a natural CM analogue. We discovered the first natural CM analogue 3-demethylchuangxinmycin (DCM) as a new natural product. Compared to CM, DCM exhibited a much weaker activity in the inhibition of the bacterial strains tested. The finding provides valuable information for the structure-activity relationship in the biosynthesis of CM.

6-Deoxy-13-hydroxy-8,11-dione-dihydrogranaticin B, an intermediate in granaticin biosynthesis, from Streptomyces sp. CPCC 200532.

A new granaticin analogue and its hydrolysis product were isolated from Streptomyces sp. CPCC 200532. Their structures were determined to be 6-deoxy-13-hydroxy-8,11-dione-dihydrogranaticins B (1) and A (2), respectively, by detailed analysis of spectroscopic data. Compound 1 was regarded as an intermediate in granaticin biosynthesis, as it was bioconvertable to granaticin B. Compared to granaticin B, 1 showed similar cytotoxicity against cancer cell line HCT116, but decreased cytotoxicity against cancer cell lines A549, HeLa, and HepG2. Compound 2 displayed lower cytotoxicity than 1 against all four cancer cell lines tested.

Aromatic acid derivatives from the lateral roots of Aconitum carmichaelii.

Seven new aromatic acid derivatives (1-7), together with five known analogs, were isolated from the lateral roots of Aconitum carmichaelii. Structures of the new compounds were determined by spectroscopic and chemical methods as 4-methyl ( - )-(R)-hydroxyeucomate (1), 4-butyl ( - )-(R)-hydroxyeucomate (2), 4-butyl-1-methyl (+)-(R)-2-O-(4'-hydroxy-3'-methoxybenzoyl)malate (3), 1-butyl-4-methyl (+)-(R)-2-O-(4'-hydroxy-3'-methoxybenzoyl)malate (4), dimethyl (+)-(R)-2-O-(4'-hydroxy-3'-methoxybenzoyl)malate (5), dimethyl (+)-(R)-2-O-(4'-hydroxybenzoyl)malate (6), and methyl ( ± )-3-(4'-hydroxy-3'-methoxyphenyl)-3-sulfopropionate (7), respectively. Compounds 1 and 2 are 2-benzylmalates (eucomate derivatives), 3-6 belong to 2-O-benzoylmalates, and 7 is a rare phenylpropionate containing a sulfonic acid group. The absolute configurations of eucomate derivatives were confirmed by X-ray crystallographic analysis of 4-methyl eucomate (11).

19-[(1'S,4'R)-4'-Hydroxy-1'-methoxy-2'-oxopentyl]geldanamycin, a natural geldanamycin analogue from Streptomyces hygroscopicus 17997.

A novel natural geldanamycin analogue was discovered in Streptomyces hygroscopicus 17997. Its 4,5-dihydro form was also identified in the gdmP gene disruption mutant of Streptomyces hygroscopicus 17997. The structures of the two compounds were determined to be 19-[(1'S,4'R)-4'-hydroxy-1'-methoxy-2'-oxopentyl]geldanamycin (1) and 19-[(1'S,4'R)-4'-hydroxy-1'-methoxy-2'-oxopentyl]-4,5-dihydrogeldanamycin (2), respectively, by extensive spectroscopic data analysis, including 2D NMR, modified Mosher's method, and electronic circular dichroism. Compared to geldanamycin, 1 and 2 showed increased water solubility and decreased cytotoxicity against HepG2 cells.

Diterpenoid alkaloids from the lateral root of Aconitum carmichaelii.

Twenty-six new diterpenoid alkaloids, 1-26 (1-4: hetisan-type C(20)-diterpenoid alkaloids; 5-26: aconitane C(19)-diterpenoid alkaloids), and two known analogues, hypaconitine 27 and benzoylmesaconine 28, have been isolated from a water extract of the lateral root of Aconitum carmichaelii. Compounds 7 and 8 are rare examples of conformational isomers obtained from the same material. The conformation and conformational transformation of ring A in the C(19)-diterpenoid alkaloids are discussed on the basis of NMR data analysis in combination with single-crystal X-ray crystallography of 6 and 27 by anomalous scattering of Cu Kα radiation. In preliminary analgesic and toxicity assays, the isomer with ring A in the chair conformation (8 or 27) was found to be more active than that with ring A in the boat conformation (7 or 27a). In addition, 15, 16, and 19 showed neuroprotective activity.

Alkaloids from the root of Isatis indigotica.

Seventeen new alkaloids (1-17) and 14 known analogues have been isolated from an aqueous extract of the root of Isatis indigotica. The structures and absolute configurations of these compounds were determined by extensive spectroscopic data analysis, including 2D NMR, single-crystal X-ray crystallography using anomalous scattering of Cu Kα radiation, and electronic circular dichroism spectra calculations based on the quantum-mechanical time-dependent density functional theory. Compounds 1, 2, and 3 are the first examples of natural products with unique linkages between a molecule of 2-(4-methoxy-1H-indol-3-yl)acetonitrile and 2-(1H-indol-3-yl)acetonitrile, 2-(4-methoxy-1H-indol-3-yl)acetonitrile, and 4-hydroxyphenylethane, respectively. Compounds (-)-4 and (+)-4 represent the first natural products with the pyrrolo[2,3-b]indolo[5,5a,6-b,a]quinazoline skeleton. Some structural assignments for the new alkaloids suggest that the assignments made for certain previously reported alkaloids require revision. Compounds 1-3 and arvelexin (18) show antiviral activity against the influenza virus A/Hanfang/359/95 (H3N2), with IC(50) values of 3.70-12.35 µM, and 17 inhibits Coxsackie virus B3 replication with an IC(50) of 6.87 µM.

[Chemical constituents from aqueous extract of Gastrodia elata].

Two new compounds (1 and 2), together with twenty-one known compounds (3-23), were isolated by a combination of various chromatographic techniques including column chromatography over macroporous resin, MCI gel, silica gel, and Sephadex LH-20 and reversed-phase HPLC. Their structures were identified by spectroscopic data analysis as 4-hydroxy-3-(4-hydroxybenzyl) benzyl methyl ether (1), 4-( methoxymethyl) phenyl-1-O-beta-D-glucopyranoside (2), hibicutaiwanin (3), 4-(4-hydroxybenzyl)-2-methoxyphenol (4), 4,4'-methylenebis(2-methoxyphenol) (5), L-phenyllactic acid (6) ,4-hydroxy-3-methoxybenzyl ethol ether (7), p-hydroxylbenzyl alcohol (8), p-hydroxylbenzyl methyl ether (9), p-hydroxylbenzyl ethyl ether (10), p-hydroxybenzaldehyde (11), p-hydroxybenzoic acid (12), p-hydroxybenzoic acid (13), gastrodin (14), 4-(ethoxymethyl) phenyl-1-O-beta-D-glucopyranoside (15), 4-(beta-D-glucopyranosyloxy) benzaldehyde (16), p-methylphenyl-1-O-beta-D-glucopyranoside (17 ), methyl-O-beta-D-glucopyranoside (18), 5-hydroxymethl-furan aldehyde (19), parishin (20), parishin B (21), parishin C (22), and diosgenin (23). The 13C-NMR data of compound 4 was first reported.

[Lignans from Sinocalamus affinis].

Fifteen compounds were isolated from the stem (with skin removed) of Sinocalamus affinis by a combination of various chromatographic techniques including silica gel, macroporous adsorbent resin, Sephadex LH-20, and preparative HPLC. Their structures were elucidated by spectroscopic data as ( + )-(1S, 2R)-1, 2-bis (4-hydroxy- 3-methoxyphenyl)-1, 3-propanediol (1), threo-guaiacylglycerol-beta-O-4'-coniferyl ether(2), erythro-guaiacylglycerol-beta-O-4'-coniferyl ether(3), ( + )-(7S, 8R, 8'R)-5'-methoxylariciresinol(4), ( + )-(7S, 8R, 8'R)-5, 5'-dimethoxylariciresinol (5), ( +/- )-glaberide I (6), ( - )-syringaresinol (7), ( - )-medioresinol(8), ( - )-(8R, 8R')-4, 4'-dihydroxy-3, 3', 5, 5'-tetramethoxyligna-9, 9'-diol(9), ( - )-secoisolariciresinol-9, 9'-acetonide (10), and ( + )-lyoniresinol (11); a new natural product 2, 6-dimethoxypyran4-one (12), and beta-sitosterol, 4-hydroxycinnamic acid, and 2, 6-dimethoxy-p-benzoquinone. These compounds were isolated from the genus Sinocalamus for the first time, compound 10 should be an artifact.

Isatropolone/isarubrolone Cm from Streptomyces with biological activity of inducing incomplete autophagy.

Isatropolones/isarubrolones are Streptomyces secondary metabolites featuring a tropolone ring in the pentacyclic scaffolds of these molecules. They are able to induce complete autophagy in human HepG2 cells. Here, methyl isatropolones (1-2) and isarubrolone (3) are identified from Streptomyces CPCC 204095. They all have a methyl tropolone ring in the pentacyclic scaffold of these molecules resolved by MS and NMR spectra. Biological activity assay indicates that isatropolone Cm (1) and isarubrolone Cm (3) induce incomplete autophagy in human HepG2 cells.