Angucycline group antibiotics

Cloning and identification of saprolmycin biosynthetic gene cluster from Streptomyces sp. TK08046

Saprolmycins A-E are anti-Saprolegnia parasitica antibiotics. To identify the gene cluster for saprolmycin biosynthesis in Streptomyces sp. TK08046, polymerase chain reaction using aromatase and cyclase gene-specific primers was performed; the spr gene cluster, which codes for angucycline biosynthesis, was obtained from the strain. The cluster consists of 36 open reading frames, including minimal polyketide synthase, ketoreductase, aromatase, cyclase, oxygenase, and deoxy sugar biosynthetic genes, as defined by homology to the corresponding genes of the urdamycin, Sch-47554, and grincamycin biosynthetic gene clusters in Streptomyces fradiae, Streptomyces sp. SCC-2136, and Streptomyces lusitanus, respectively. To establish the function of the gene cluster, an expression cosmid vector containing all 36 open reading frames was introduced into Streptomyces lividans TK23. The transformant was confirmed to express the biosynthetic genes and produce saprolmycins by liquid chromatography-mass spectrometry analysis of the extract.

Fluorine-directed 1,2-trans glycosylation of rare sugars

To reconcile the urgent need to access well defined β-configured 2,6-di-deoxypyranose analogues for chemical biology, with the intrinsic α-selectivity of the native system, the directing role of fluorine at C2 has been explored. Localised partial charge inversion (C-H(δ+)→ C-F(δ-)) elicits a reversal of the substrate-based α-stereoselectivity, irrespective of the protecting group electronics.

C6 picoloyl protection: a remote stereodirecting group for 2-deoxy-β-glycoside formation

We reported a remote control glycosylation method using the picoloyl protecting group for 2-deoxy-β-glycosidic bond formation. The method is applicable to various 2-deoxythioglycosyl donors and the utility is illustrated by the synthesis of a deoxytrisaccharide component of landomycins.

Catalytic asymmetric reactions and synthesis of quinones

Organo- and metal–ligand catalysed asymmetric reactions of quinones lead to complex enantiopure compounds including quinones.

Design for carbon–carbon bond forming reactions under ambient conditions

The carbon–carbon (C–C) bond forms the ‘backbone’ of nearly every organic molecule, and lies at the heart of the chemical sciences! Let us explore designing of carbon–carbon frameworks at ambient conditions.

A comprehensive review of glycosylated bacterial natural products

A systematic analysis of all naturally-occurring glycosylated bacterial secondary metabolites reported in the scientific literature up through early 2013 is presented. This comprehensive analysis of 15 940 bacterial natural products revealed 3426 glycosides containing 344 distinct appended carbohydrates and highlights a range of unique opportunities for future biosynthetic study and glycodiversification efforts.

Angucyclines and Angucyclinones from Streptomyces sp. CB01913 Featuring C-Ring Cleavage and Expansion

Angucyclines and angucyclinones are aromatic polyketides with a tetracyclic benz[a]anthracene skeleton. The benz[a]anthracene scaffold is biosynthesized by type II polyketide synthases that catalyze the decarboxylative condensation of a short acyl-CoA starter and nine extender units. Angucyclines and angucyclinones, the largest group of polycyclic aromatic polyketides, achieve structural diversity via subsequent oxidation, ring cleavage, amino acid incorporation, and glycosylation. We here report the discovery of 14 angucyclinones and two angucyclines (1-16) from Streptomyces sp. CB01913, identifying 12 new compounds featuring various oxidations on rings A and C (1, 2, and 4), different sugar moieties attached to rings A and B (3 and 6), and C-ring cleavage (5 and 10-14) and expansion (8). These new structural features, highlighted by C-ring cleavage and expansion, enrich the structural diversity of angucyclines and angucyclinones. All compounds were tested for cytotoxicity and antibacterial activities, with 1, 5, 15, and 16 showing moderate activities against selected cancer cell lines or bacterial strains.

Monacyclinones, New Angucyclinone Metabolites Isolated from Streptomyces sp. M7_15 Associated with the Puerto Rican Sponge Scopalina ruetzleri

During an investigation of new actinomycete species from Caribbean sponges for novel bioactive natural products, frigocyclinone (1), dimethyldehydrorabelomycin (3) and six new angucyclinone derivatives were isolated from Streptomyces sp. strain M7_15 associated with the sponge Scopalina ruetzleri. Of these, monacyclinones A–B (4–5) contain the core ring structure of dehydrorabelomycin (2) with the aminodeoxysugar found in frigocyclinone (1). Monacyclinone C (6) is a hydroxylated variant of frigocyclinone (1) and monacyclinone D (7) is a Baeyer Villiger derivative of (6) which also exists as the open chain hydrolysis product monacyclinone E (8). Monacyclinone F (9) contains two unique epoxide rings attached to the angucyclinone moiety and an additional aminodeoxysugar attached through an angular oxygen bond. All structures were confirmed through spectral analyses. Activity against rhabdomycosarcoma cancer cells (SJCRH30) after 48 h of treatment was observed with frigocyclinone (1; EC₅₀ = 5.2 µM), monacyclinone C (6; 160 µM), monacyclinone E (8; 270 µM), and monacyclinone F (9; 0.73 µM). The strongest bioactivity against rhabdomycosarcoma cancer cells and gram-positive bacteria was exhibited by compound 9, suggesting that the extra aminodeoxysugar subunit is important for biological activity.

Cytotoxic and antibacterial angucycline- and prodigiosin-analogues from the deep-sea derived Streptomyces sp. SCSIO 11594

Two new C-glycoside angucyclines, marangucycline A (1) and marangucycline B (2), along with three known compounds, dehydroxyaquayamycin (3), undecylprodigiosin (4) and metacycloprodigiosin (5), have been identified as products of the deep-sea sediment strain Streptomyces sp. SCSIO 11594. New structures were elucidated on the basis of HRESIMS, 1D and 2D NMR analyses and comparisons to previously reported datasets. Compounds 2 and 4 displayed in vitro cytotoxicity against four cancer cell lines A594, CNE2, HepG2, MCF-7 superior to those obtained with cisplatin, the positive control. Notably, compound 2 bearing a keto-sugar displayed significant cytotoxicity against cancer cell lines with IC50 values ranging from 0.24 to 0.56 μM; An IC50 value of 3.67 μM was found when using non-cancerous hepatic cell line HL7702, demonstrating the cancer cell selectivity of 2. Compounds 1-3 were proved to have weak antibacterial activities against Enterococcus faecalis ATCC29212 with an MIC value of 64.0 μg/mL. Moreover, 3 displayed selective antibacterial activity against methicillin-resistant Staphylococcus epidermidis shhs-E1 with an MIC value of 16.0 μg/mL.

Dereplication strategies for targeted isolation of new antitrypanosomal actinosporins A and B from a marine sponge associated-Actinokineospora sp. EG49

High resolution Fourier transform mass spectrometry (HRFTMS) and nuclear magnetic resonance (NMR) spectroscopy were employed as complementary metabolomic tools to dereplicate the chemical profile of the new and antitrypanosomally active sponge-associated bacterium Actinokineospora sp. EG49 extract. Principal Component (PCA), hierarchical clustering (HCA), and orthogonal partial least square-discriminant analysis (OPLS-DA) were used to evaluate the HRFTMS and NMR data of crude extracts from four different fermentation approaches. Statistical analysis identified the best culture one-strain-many-compounds (OSMAC) condition and extraction procedure, which was used for the isolation of novel bioactive metabolites. As a result, two new O-glycosylated angucyclines, named actinosporins A (1) and B (2), were isolated from the broth culture of Actinokineospora sp. strain EG49, which was cultivated from the Red Sea sponge Spheciospongia vagabunda. The structures of actinosporins A and B were determined by 1D- and 2D-NMR techniques, as well as high resolution tandem mass spectrometry. Testing for antiparasitic properties showed that actinosporin A exhibited activity against Trypanosoma brucei brucei with an IC₅₀ value of 15 µM; however no activity was detected against Leishmania major and Plasmodium falciparum, therefore suggesting its selectivity against the parasite Trypanosoma brucei brucei; the causative agent of sleeping sickness.

Synthesis of a landomycinone skeleton via Masamune–Bergmann cyclization

In this report, a synthetic study of landomycinone via Masamune–Bergmann cyclization is described.

Intriguing properties of the angucycline antibiotic auricin and complex regulation of its biosynthesis

Streptomyces bacteria are major producers of bioactive natural products, including many antibiotics. We identified a gene cluster, aur1, in a large linear plasmid of Streptomyces aureofaciens CCM3239. The cluster is responsible for the production of a new angucycline polyketide antibiotic auricin. Several tailoring biosynthetic genes were scatted in rather distant aur1 flanking regions. Auricin was produced in a very narrow growth phase interval of several hours after entry into stationary phase, after which it was degraded to non-active metabolites because of its instability at the high pH values reached after the production stage. Strict transcriptional regulation of the auricin biosynthetic gene cluster has been demonstrated, including feed-forward and feedback control by auricin intermediates via several of the huge number of regulatory genes present in the aur1 cluster. The complex mechanism may ensure strict confinement of auricin production to a specific growth stage.

Convergent de novo synthesis of vineomycinone B2 methyl ester

An efficient de novo synthesis of vineomycinone B2 methyl ester has been achieved. The longest linear route required only 14 steps from achiral commercially available starting materials (4.0% overall yield). The key transformations included the de novo asymmetric synthesis of two key fragments, which were joined by a convergent late stage Suzuki's glycosylation for the construction of the aryl β-C-glycoside. A subsequent BBr3 one-pot debenzylation, demethylation and air oxidation provided vineomycinone B2 methyl ester.

Warkmycin, a novel angucycline antibiotic produced by Streptomyces sp. Acta 2930*

A novel angucycline-type antibiotic, warkmycin, was isolated from the culture filtrate of Streptomyces strain Acta 2930. Its chemical structure was elucidated by HR-MS, one-dimensional and 2D NMR experiments. The compound inhibits the growth of Gram-positive bacteria and shows a strong antiproliferative activity against mouse fibroblast cell line NIH-3T3 and human cancer cell lines HepG2 and HT29.

Langkocyclines: novel angucycline antibiotics from Streptomyces sp. Acta 3034(*)

Langkocyclines A1-A3 and B1 and B2, five new angucycline antibiotics produced by Streptomyces sp. Acta 3034, were detected in the course of our HPLC-diode array screening. The producing strain was isolated from the rhizospheric soil of a Clitorea sp. collected from Burau Bay, Langkawi, Malaysia, and was characterized by morphological, physiological and chemotaxonomic features in addition to 16S ribosomal RNA gene sequence information. Strain Acta 3034 is closely related to Streptomyces psammoticus NBRC 13971(T) and Streptomyces lanatus NBRC 12787(T). Langkocyclines consist of an angular tetracyclic benz[a]anthracene skeleton and hydrolyzable O-glycosidic sugar moieties. The yellow-colored A-type langkocyclines differ in their aglycon from the blue-lilac-colored B-type langkocyclines. The A-type langkocycline aglycon is identical to that of aquayamycin and urdamycin A. The chemical structures of the langkocyclines were elucidated by HR-MS, 1D and 2D NMR experiments. They are biologically active against Gram-positive bacteria and exhibit a moderate antiproliferative activity against various human tumor cell lines.

Saccharosporones A, B and C, cytotoxic antimalarial angucyclinones from Saccharopolyspora sp. BCC 21906

Three new angucyclinones, saccharosporones A, B and C, together with (+)-ochromycinone, (+)-rubiginone B2, tetrangulol methyl ether and fujianmycin A, were obtained from fermentation of the terrestrial actinomycete of the genus Saccharopolyspora BCC 21906 isolated from a soil collected in Chanthaburi Province, Thailand. Structures of the new compounds and their relative configurations were assigned by NMR spectral data interpretation. Saccharosporones A and B exhibited antimalarial activity against Plasmodium falciparum K1 with IC50 values of 4.1 and 3.9 μM. Both metabolites also possessed cytotoxic activities against cancer cell lines (KB, MCF-7 and NCI-H187) and nonmalignant Vero cell, while saccharosporone C only showed cytotoxic activity against NCI-H187.

Purification and identification of bioactive angucyclinones from Streptomyces matensis BG5, isolated from the rhizosphere of Rosa indica L

A newly isolated strain Streptomyces sp. BG5 was investigated for the production of bioactive compounds. The strain exhibited broad-spectrum activity against an array of nine test organisms including gram-positive bacteria, gram-negative bacteria, and fungal and microalgal pathogens, along with a moderate cytotoxic response (28.9% mortality) in a microwell cytotoxicity assay against the brine shrimp Artimia salina. The morphological, physiological, and biochemical characterization of the Streptomyces sp. BG5 strongly suggested it to be a member of the genus Streptomyces. The nucleotide sequence of 16S rRNA gene (1433 pb) of the Streptomyces sp. BG5 (Gene bank accession number EU301836) exhibited high similarity (98%) with Streptomyces matensis. The large-scale fermentation of Streptomyces sp. BG5 and subsequent extraction, isolation, and purification of the crude extract afforded three pure compounds. The structures of these compounds were identified as ochromycinone (1a), emycin D (2), and 1-acetyl-β-carbolin (3), based on nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and by comparison with reference data from the literature.

Angucyclines from an insect-derived actinobacterium Amycolatopsis sp. HCa1 and their cytotoxic activity

One new angucyclinone derivative, amycomycin A (1), and one new angucycline, amycomycin B (2), along with 5 known compounds (3-7), were isolated from an actinobacterium Amycolatopsis sp. HCa1 associated with the grasshopper, Oxya chinensis. Their structures were elucidated on the basis of spectroscopic methods, including extensive NMR spectra. Compounds 1-7 were tested in vitro for their cytotoxic effects on five cell lines including human gastric adenocarcinoma cell line (BGC823), human hepatocarcinoma cell line (HepG2), human melanoma cell line (A375), human oral squamous carcinoma cell line (KB), and ghost cell line (Ghost-R5X4). Cell viability assays showed that compound 7 was active in four cell lines with IC(50) values less than 18.0 μM except in KB showing no activity up to 100 μM.

Saquayamycins G-K, cytotoxic angucyclines from Streptomyces sp. Including two analogues bearing the aminosugar rednose

Streptomyces sp. KY40-1, a strain isolated from the Kentucky Appalachian foothills, is the producer of moromycins A (18) and B (19). Further investigations of this strain led to the isolation and structure elucidation of the five new saquayamycins G-K (1-5), along with known compounds. Two of the new compounds bear the unusual aminosugar rednose, which was found here for the first time in angucyclines. The different attachment positions of this aminosugar in these two compounds indicate a high acceptor substrate flexibility of the responsible glycosyl transferase or alternatively the involvement of multiple glycosyl transferases. The cytotoxic activity of the isolated compounds was determined using human prostate cancer (PC-3) and non-small-cell lung cancer (H460) cell lines. Cell viability assays showed that saquayamycins J (4), K (5), A (7), and B (8) were most active in PC3 cells, with saquayamycin B (8) showing the highest activity (GI(50) = 0.0075 μM). The aminosugar-containing saquayamycins H (2) and saquayamycin B (8) showed the highest activity against H460 cells, with a GI(50) of 3.3 and 3.9 μM, respectively. The results presented here provide more insights into the structure-activity relationship of saquayamycins with respect to the nature, number, and linkage of sugar residues.

Elucidation of post-PKS tailoring steps involved in landomycin biosynthesis

The functional roles of all proposed enzymes involved in the post-PKS redox reactions of the biosynthesis of various landomycin aglycones were thoroughly studied, both in vivo and in vitro. The results revealed that LanM2 acts as a dehydratase and is responsible for concomitant release of the last PKS-tethered intermediate to yield prejadomycin (10). Prejadomycin (10) was confirmed to be a general pathway intermediate of the biosynthesis. Oxygenase LanE and the reductase LanV are sufficient to convert 10 into 11-deoxylandomycinone (5) in the presence of NADH. LanZ4 is a reductase providing reduced flavin (FMNH) co-factor to the partner enzyme LanZ5, which controls all remaining steps. LanZ5, a bifunctional oxygenase-dehydratase, is a key enzyme directing landomycin biosynthesis. It catalyzes hydroxylation at the 11-position preferentially only after the first glycosylation step, and requires the presence of LanZ4. In the absence of such a glycosylation, LanZ5 catalyzes C5,6-dehydration, leading to the production of anhydrolandomycinone (8) or tetrangulol (9). The overall results provided a revised pathway for the biosynthesis of the four aglycones that are found in various congeners of the landomycin group.

Cascade assembly of the benzo[a]anthraquinone ring system common to the angucycline antibiotics

A benzo[a]anthraquinone ring system, common to a group of angucycline antibiotics, has been prepared by a unique cascade of reactions. The reaction sequence was initiated by a Suzuki-Miyaura cross-coupling between a bromoquinone and vinyl boronic anhdyride. The reaction product is proposed to undergo a 6π-electron cyclization triggered by reductive activation of the quinone. The reaction process is proposed to be autocatalytic.

Kiamycin, a unique cytotoxic angucyclinone derivative from a marine Streptomyces sp

Kiamycin (1), a new angucyclinone derivative possessing an 1,12-epoxybenz[a]anthracene ring system, was isolated from the marine Streptomyces sp. strain M268 along with the known compounds 8-O-methyltetrangomycin (3) and 8-O-methylrabelomycin (4). Their structures were elucidated by detailed spectroscopic analysis and comparison with literature data. The new angucyclinone derivative showed inhibitory activities against the human cell lines HL-60 (leukemia), A549 (lung adenocarcinoma), and BEL-7402 (hepatoma) with inhibition rates of 68.2%, 55.9%, and 31.7%, respectively, at 100 µM. It appears to have potential as an anticancer agent with selective activity.

Cytotoxic angucycline class glycosides from the deep sea actinomycete Streptomyces lusitanus SCSIO LR32

Five new C-glycoside angucyclines, named grincamycins B-F (1-5), and a known angucycline antibiotic, grincamycin (6), were isolated from Streptomyces lusitanus SCSIO LR32, an actinomycete of deep sea origin. The structures of these compounds were elucidated on the basis of extensive spectroscopic analyses, including MS and 1D and 2D NMR experiments. All compounds except grincamycin F (5) exhibited in vitro cytotoxicities against the human cancer cell lines HepG2, SW-1990, HeLa, NCI-H460, and MCF-7 and the mouse melanoma cell line B16, with IC₅₀ values ranging from 1.1 to 31 μM.