Fluostatins C-E, novel members of the fluostatin family produced by Streptomyces strain Acta 1383

Divergent synthesis of 3,4-dihydro-2H-benzo[h]chromen-2-one and fluorenone derivatives from ortho-alkynylarylketones

Our research has led to the development of a divergent synthesis approach for the synthesis of 3,4-dihydro-2H-benzo[h]chromen-2-one 3 and fluorenone 9 derivatives using ortho-alkynylarylketones as common precursors. The synthesis of 3,4-dihydro-2H-benzo[h]chromen-2-ones 3 employed silver catalyzed ketonization to form polycarbonyl intermediates which underwent double intramolecular cyclization and decarboxylation to generate a lactone and a phenyl ring in a one-pot fashion. In addition, the same precursor could be used to prepare fluorenone derivatives 9 under acidic conditions. The reaction proceeded via the formation of indenone analogs, followed by the generation of the para-quinone methide intermediate and intramolecular cyclization to provide the corresponding products in good yields.

Biochemical and structural insights of multifunctional flavin-dependent monooxygenase FlsO1-catalyzed unexpected xanthone formation

Xanthone-containing natural products display diverse pharmacological properties. The biosynthetic mechanisms of the xanthone formation have not been well documented. Here we show that the flavoprotein monooxygenase FlsO1 in the biosynthesis of fluostatins not only functionally compensates for the monooxygenase FlsO2 in converting prejadomycin to dehydrorabelomycin, but also unexpectedly converts prejadomycin to xanthone-containing products by catalyzing three successive oxidations including hydroxylation, epoxidation and Baeyer-Villiger oxidation. We also provide biochemical evidence to support the physiological role of FlsO1 as the benzo[b]-fluorene C5-hydrolase by using nenestatin C as a substrate mimic. Finally, we resolve the crystal structure of FlsO1 in complex with the cofactor flavin adenine dinucleotide close to the “in” conformation to enable the construction of reactive substrate-docking models to understand the basis of a single enzyme-catalyzed multiple oxidations. This study highlights a mechanistic perspective for the enzymatic xanthone formation in actinomycetes and sets an example for the versatile functions of flavoproteins.

The biosynthesis of xanthones has not been well documented. Here, the authors report that monooxygenase FlsO1 catalyzes three successive oxidations – hydroxylation, epoxidation and Baeyer–Villiger oxidation—to form the xanthone scaffold in actinomycetes.

Flavin-enabled reductive and oxidative epoxide ring opening reactions

Epoxide ring opening reactions are common and important in both biological processes and synthetic applications and can be catalyzed in a non-redox manner by epoxide hydrolases or reductively by oxidoreductases. Here we report that fluostatins (FSTs), a family of atypical angucyclines with a benzofluorene core, can undergo nonenzyme-catalyzed epoxide ring opening reactions in the presence of flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (NADH). The 2,3-epoxide ring in FST C is shown to open reductively via a putative enol intermediate, or oxidatively via a peroxylated intermediate with molecular oxygen as the oxidant. These reactions lead to multiple products with different redox states that possess a single hydroxyl group at C-2, a 2,3-vicinal diol, a contracted five-membered A-ring, or an expanded seven-membered A-ring. Similar reactions also take place in both natural products and other organic compounds harboring an epoxide adjacent to a carbonyl group that is conjugated to an aromatic moiety. Our findings extend the repertoire of known flavin chemistry that may provide new and useful tools for organic synthesis.

Epoxide ring opening reactions are important in both biological processes and synthetic applications. Here, the authors show that flavin cofactors can catalyze reductive and oxidative epoxide ring opening reactions and propose the underlying mechanisms.

Streptomyces, Greek Habitats and Novel Pharmaceuticals: A Promising Challenge

Bacteria of the genus Streptomyces produce a very large number of secondary metabolites, many of which are of vital importance to modern medicine. There is great interest in the discovery of novel pharmaceutical compounds derived from strepomycetes, since novel antibiotics, anticancer and compounds for treating other conditions are urgently needed. Greece, as proven by recent research, possesses microbial reservoirs with a high diversity of Streptomyces populations, which provide a rich pool of strains with potential pharmaceutical value. This review examines the compounds of pharmaceutical interest that have been derived from Greek Streptomyces isolates. The compounds reported in the literature include antibiotics, antitumor compounds, biofilm inhibitors, antiparasitics, bacterial toxin production inhibitors and antioxidants. The streptomycete biodiversity of Greek environments remains relatively unexamined and is therefore a very promising resource for potential novel pharmaceuticals.

Discovery of an Unexpected 1,4-Oxazepine-Linked seco-Fluostatin Heterodimer by Inactivation of the Oxidoreductase-Encoding Gene flsP

Fluostatins belong to the atypical angucyclinone aromatic polyketides featuring a distinctive tetracyclic benzo[a]fluorene skeleton. To understand the formation of the heavily oxidized A-ring in fluostatins, a flavin adenine dinucleotide-binding oxidoreductase-encoding gene flsP was inactivated, leading to the production of an unprecedented 1,4-oxazepine-linked seco-fluostatin heterodimer difluostatin I (7) and five new fluostatin-related derivatives, fluostatins T-X (8-12). Their structures were elucidated by mass spectrometry, nuclear magnetic resonance, X-ray diffraction analysis, and biosynthetic considerations. Difluostatin I (7) represents the first example with an A-ring-cleaved 3',4'-seco-fluostatin skeleton. The absolute configuration of fluostatin T (8) was determined by X-ray diffraction analysis. Fluostatin W (11) contains an uncommon isoxazolinone ring. These findings highlight the structural diversity of fluostatins.

Mutation of an atypical oxirane oxyanion hole improves regioselectivity of the α/β-fold epoxide hydrolase Alp1U

Epoxide hydrolases (EHs) have been characterized and engineered as biocatalysts that convert epoxides to valuable chiral vicinal diol precursors of drugs and bioactive compounds. Nonetheless, the regioselectivity control of the epoxide ring opening by EHs remains challenging. Alp1U is an α/β-fold EH that exhibits poor regioselectivity in the epoxide hydrolysis of fluostatin C (compound 1) and produces a pair of stereoisomers. Herein, we established the absolute configuration of the two stereoisomeric products and determined the crystal structure of Alp1U. A Trp-186/Trp-187/Tyr-247 oxirane oxygen hole was identified in Alp1U that replaced the canonical Tyr/Tyr pair in α/β-EHs. Mutation of residues in the atypical oxirane oxygen hole of Alp1U improved the regioselectivity for epoxide hydrolysis on 1. The single site Y247F mutation led to highly regioselective (98%) attack at C-3 of 1, whereas the double mutation W187F/Y247F resulted in regioselective (94%) nucleophilic attack at C-2. Furthermore, single-crystal X-ray structures of the two regioselective Alp1U variants in complex with 1 were determined. These findings allowed insights into the reaction details of Alp1U and provided a new approach for engineering regioselective epoxide hydrolases.

Enantioselective Epoxidation of 2,3-Disubstituted Naphthoquinones by a Side Chain Truncated Guanidine-Urea Bifunctional Organocatalyst

An organocatalytic enantioselective epoxidation of 2,3-disubstituted naphthoquinones with tert-butyl hydroperoxide as an oxidant was developed using a guanidine-urea bifunctional catalyst lacking C₂ symmetry, which was designed based upon the insights obtained from the DFT calculation model for our previous C₂ symmetric catalyst. The present organocatalytic reaction provides access to a variety of optically active naphthoquinone epoxides bearing aryl and methyl substituents at C2 and C3 in high yields with high enantioselectivities (up to 97:3 er).

S-Bridged Thioether and Structure-Diversified Angucyclinone Derivatives from the South China Sea-Derived Micromonospora echinospora SCSIO 04089

Angucyclinces belong to the class of aromatic polyketides and display a wide variety of structure diversity and pharmaceutical significance. Herein we report the isolation, structure elucidation, and bioactivity evaluation of structure-diversified angucyclinone derivatives and anthracene from the South China Sea-derived Micromonospora echinospora SCSIO 04089, including a thioether, gephysulfuromycin (1), two new benzo[b]phenanthridines, homophenanthroviridone (2) and homophenanthridonamide (3), a new benzo[b]fluorene, homostealthin D (4), a new naphtho[2,3-b]benzofuran, nenesfuran (5), a new naphthoquinone, WS-5995 D (6) and a new anthracene, nenesophanol (7), together with three known compounds (8-10). Their structures were elucidated by extensive spectroscopic analyses. The structures of 1-3 and 5-8 were confirmed by X-ray crystallographic analyses. Gephysulfuromycin (1) featured a rare single S-bridged 3,12a-epithiotetraphene skeleton. Homophenanthroviridone (2) was found to be cytotoxic to SF-268, MCF-7, and HepG2 cell lines with IC₅₀ values of 5.4 ± 0.4, 6.8 ± 0.3, and 1.4 ± 0.1 μM, respectively. Compound 2 was also active against Gram-positive bacteria with MIC (minimal inhibition concentration) values ranging 2-4 μg mL^-1.

Understand the Specific Regio- and Enantioselectivity of Fluostatin Conjugation in the Post-Biosynthesis

Fluostatins, benzofluorene-containing aromatic polyketides in the atypical angucycline family, conjugate into dimeric and even trimeric compounds in the post-biosynthesis. The formation of the C-C bond involves a non-enzymatic stereospecific coupling reaction. In this work, the unusual regio- and enantioselectivities were rationalized by density functional theory calculations with the M06-2X (SMD, water)/6-311 + G(d,p)//6-31G(d) method. These DFT calculations reproduce the lowest energy C1-(R)-C10'-(S) coupling pathway observed in a nonenzymatic reaction. Bonding of the reactive carbon atoms (C1 and C10') of the two reactant molecules maximizes the HOMO-LUMO interactions and Fukui function involving the highest occupied molecular orbital (HOMO) of nucleophile p-QM and lowest unoccupied molecular orbital (LUMO) of electrophile FST2- anion. In particular, the significant π-π stacking interactions of the low-energy pre-reaction state are retained in the lowest energy pathway for C-C coupling. The distortion/interaction-activation strain analysis indicates that the transition state (TScp-I) of the lowest energy pathway involves the highest stabilizing interactions and small distortion among all possible C-C coupling reactions. One of the two chiral centers generated in this step is lost upon aromatization of the phenol ring in the final difluostatin products. Thus, the π-π stacking interactions between the fluostatin 6-5-6 aromatic ring system play a critical role in the stereoselectivity of the nonenzymatic fluostatin conjugation.

Iodine-mediated synthesis of benzo[a]fluorenones from yne-enones

The chalcones derived from o-alkynylacetophenones and aromatic aldehydes (yne-enones) when heated under reflux with iodine in acetic acid gave a range of benzo[a]fluorenone derivatives in moderate to good yields. The transformation involves the formation of a vinyl indenone intermediate through regioselective alkyne hydration and intramolecular aldol condensation followed by electrocyclic ring closure and aromatization.

An iodine mediated synthesis of benzo[a]fluorenone derivatives from the chalcones derived from o-alkynylacetophenones and aromatic aldehydes is described.

The functional differentiation of the post-PKS tailoring oxygenases contributed to the chemical diversities of atypical angucyclines

Angucyclines are one of the largest families of aromatic polyketides with various chemical structures and bioactivities. Decades of studies have made it easy for us to depict the picture of their early biosynthetic pathways. Two families of oxygenases, the FAD-dependent oxygenases and the ring opening oxygenases, contribute to the formation of some unique skeletons of atypical angucyclines. The FAD-dependent oxygenases involved in the biosynthetic gene clusters of typical angucyclines catalyze two hydroxylation reactions at C-12 and C-12b of prejadomycin, while their homolog JadH in jadomycin gene cluster catalyze the C-12 hydroxylation and 4a,12b-dehydration reactions of prejadomycin, which leads to the production of dehydrorabelomycin, a common intermediate during the biosynthesis of atypical angucyclines. Ring opening oxygenases of a unique family of oxygenases catalyze the oxidative C—C bond cleavage reaction of dehydrorabelomycin, followed by different rearrangement reactions, resulting in the formation of the various chemical skeletons of atypical angucyclines. These results suggested that the functional differentiation of these oxygenases could apparently enrich the sources of aromatic polyketides with greater structure diversities.

Marine Bacterial Aromatic Polyketides From Host-Dependent Heterologous Expression and Fungal Mode of Cyclization

The structure diversity of type II polyketide synthases-derived bacterial aromatic polyketides is often enhanced by enzyme controlled or spontaneous cyclizations. Here we report the discovery of bacterial aromatic polyketides generated from 5 different cyclization modes and pathway crosstalk between the host and the heterologous fluostatin biosynthetic gene cluster derived from a marine bacterium. The discovery of new compound SEK43F (2) represents an unusual carbon skeleton resulting from a pathway crosstalk, in which a pyrrole-like moiety derived from the host Streptomyces albus J1074 is fused to an aromatic polyketide SEK43 generated from the heterologous fluostatin type II PKSs. The occurrence of a new congener, fluoquinone (3), highlights a bacterial aromatic polyketide that is exceptionally derived from a characteristic fungal F-mode first-ring cyclization. This study expands our knowledge on the power of bacterial type II PKSs in diversifying aromatic polyketides.

Molecular basis of dimer formation during the biosynthesis of benzofluorene-containing atypical angucyclines

Lomaiviticin A and difluostatin A are benzofluorene-containing aromatic polyketides in the atypical angucycline family. Although these dimeric compounds are potent antitumor agents, how nature constructs their complex structures remains poorly understood. Herein, we report the discovery of a number of fluostatin type dimeric aromatic polyketides with varied C−C and C−N coupling patterns. We also demonstrate that these dimers are not true secondary metabolites, but are instead derived from non-enzymatic deacylation of biosynthetic acyl fluostatins. The non-enzymatic deacylation proceeds via a transient quinone methide like intermediate which facilitates the subsequent C–C/C−N coupled dimerization. Characterization of this unusual property of acyl fluostatins explains how dimerization takes place, and suggests a strategy for the assembly of C–C and C–N coupled aromatic polyketide dimers. Additionally, a deacylase FlsH was identified which may help to prevent accumulation of toxic quinone methides by catalyzing hydrolysis of the acyl group.

Benzofluorene-containing angucyclines, bacterial natural compounds with potential use as therapeutics/antibiotics, occur as dimers. Here, the authors elucidated the dimerization mechanism which turned out to work spontaneously, without enzymatic catalysis.

Asymmetric Epoxidation of 1,4-Naphthoquinones Catalyzed by Guanidine-Urea Bifunctional Organocatalyst

An enantioselective nucleophilic epoxidation of 2-substituted 1,4-naphthoquinones in the presence of a newly developed guanidine-bisurea bifunctional organocatalyst with tert-butyl hydroperoxide (TBHP) as an oxidant is presented. 1,4-Naphthoquinones bearing substituents at C6, C7, and C2 were available for the reaction, and the corresponding epoxides were obtained with 88:12-95:5 er in 71-98% yields. DFT calculations indicated that substituents at C2 and C6 in the terminal Ar group of the catalyst 9k play a key role in controlling the stereochemical outcome.

Determinación de la actividad antimicrobiana e insecticida de extractos producidos por bacterias aisladas de suelo

Colombia es considerado uno de los países con mayor diversidad biológica, sin embargo, muy poca de esa diversidad ha sido explorada para identificar sustancias biológicamente activas. Los metabolitos secundarios bacterianos pueden presentar actividad frente a patógenos de plantas y animales y representan alternativas biotecnológicas para la industria. El objetivo de este estudio fue evaluar el potencial de diferentes cepas bacterianas aisladas de suelo, para producir sustancias biológicamente activas como antibacterianos, antifúngicos e insecticidas. Un total de 92 extractos metanólicos de metabolitos secundarios bacterianos fueron evaluados. La actividad antibacterial y antifúngica se evaluó mediante el ensayo de difusión en agar frente a diversas bacterias como Bacillus subtilis, Enterococcus faecalis, Escherichia coli y Staphylococcus aureus frente a diferentes hongos Alternaria sp., Colletotrichum sp., Fusarium sp., Pestalotia sp. y Verticillium sp. La actividad insecticida se evaluó determinando el efecto de los extractos sobre la mortalidad de larvas de Aedes aegypti (Diptera) y Spodoptera frugiperda (Lepidoptera). Se determinó que el 50% de los aislamientos bacterianos tuvieron algún tipo de actividad, aunque la mayor actividad biológica se detectó en los extractos producidos por bacterias del género Bacillus, identificados por medio de análisis del ADN ribosomal 16S y por caracterización bioquímica con API® 50 CHB, MicroLogTM y Biolog. Las especies del género Bacillus identificadas han sido caracterizadas como productoras de compuestos antimicrobianos de amplio espectro o de varios compuestos con diferentes actividades. La actividad biológica presentada por los extractos evidencian que los microorganismos terrestres y especialmente, las especies de Bacillus son productores prolíficos de diversas sustancias bioactivas.

Integration of high-content screening and untargeted metabolomics for comprehensive functional annotation of natural product libraries

Traditional natural products discovery using a combination of live/dead screening followed by iterative bioassay-guided fractionation affords no information about compound structure or mode of action until late in the discovery process. This leads to high rates of rediscovery and low probabilities of finding compounds with unique biological and/or chemical properties. By integrating image-based phenotypic screening in HeLa cells with high-resolution untargeted metabolomics analysis, we have developed a new platform, termed Compound Activity Mapping, that is capable of directly predicting the identities and modes of action of bioactive constituents for any complex natural product extract library. This new tool can be used to rapidly identify novel bioactive constituents and provide predictions of compound modes of action directly from primary screening data. This approach inverts the natural products discovery process from the existing "grind and find" model to a targeted, hypothesis-driven discovery model where the chemical features and biological function of bioactive metabolites are known early in the screening workflow, and lead compounds can be rationally selected based on biological and/or chemical novelty. We demonstrate the utility of the Compound Activity Mapping platform by combining 10,977 mass spectral features and 58,032 biological measurements from a library of 234 natural products extracts and integrating these two datasets to identify 13 clusters of fractions containing 11 known compound families and four new compounds. Using Compound Activity Mapping we discovered the quinocinnolinomycins, a new family of natural products with a unique carbon skeleton that cause endoplasmic reticulum stress.

Micromonospora fluostatini sp. nov., isolated from marine sediment

The novel actinomycete strain PWB-003T, which produced fluostatins B and C antibiotics, was isolated from nearshore sediment collected from Panwa Cape, Phuket Province, Thailand. Data from the present polyphasic study indicated that strain PWB-003T represented a member of the genus Micromonospora. It produced single spores on substrate mycelia and contained meso-diaminopimelic acid in the cell-wall peptidoglycan. Whole-cell hydrolysate contained ribose, xylose, arabinose, mannose and glucose. The predominant menaquinone was MK-10 (H4). Cellular fatty acids comprised C18 : 1ω9c, iso-C16 : 0, anteiso-C17 : 0, iso-C15 : 0 and iso-C17 : 0. On the basis of 16S rRNA gene sequence similarity analysis, the novel strain was closely related to Micromonospora eburnea LK2-10T (99.38 %), Micromonospora chaiyaphumensis MC5-1T (99.16 %), Micromonospora yangpuensis FXJ6.011T (98.97 %), Micromonospora echinaurantiaca DSM 43904T (98.97 %), Micromonospora pallida DSM 43817T (98.97 %), Micromonospora sagamiensis DSM 43912T and Micromonospora auratinigra JCM 12357T (both 98.97 %). The G+C content of the DNA was 74.5 mol%. DNA-DNA relatedness values among strain PWB-003T and related type strains ranged from 11.3 ± 1.3 to 38.8 ± 1.1 %. On the basis of these observations, strain PWB-003T could be distinguished from its closely related type strains and is considered to represent a novel species of the genus Micromonospora, for which the name Micromonospora fluostatini sp. nov. (type strain PWB-003T = JCM 30529T = PCU 341T = TISTR 2345T) is proposed.

Marine natural products

This review covers the literature published in 2012 for marine natural products, with 1035 citations (673 for the period January to December 2012) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1241 for 2012), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Streptomyces rochei ACTA1551, an indigenous Greek isolate studied as a potential biocontrol agent against Fusarium oxysporum f.sp. lycopersici

Many studies have shown that several Greek ecosystems inhabit very interesting bacteria with biotechnological properties. Therefore Streptomyces isolates from diverse Greek habitats were selected for their antifungal activity against the common phytopathogenic fungus Fusarium oxysporum. The isolate encoded ACTA1551, member of Streptomyces genus, could strongly suppress the fungal growth when examined in antagonistic bioassays in vitro. The isolate was found phylogenetically relative to Streptomyces rochei after analyzing its 16S rDNA sequence. The influence of different environmental conditions, such as medium composition, temperature, and pH on the expression of the antifungal activity was thoroughly examined. Streptomyces rochei ACTA1551 was able to protect tomato seeds from F. oxysporum infection in vivo while it was shown to promote the growth of tomato plants when the pathogen was absent. In an initial effort towards the elucidation of the biochemical and physiological nature of ACTA1551 antifungal activity, extracts from solid streptomycete cultures under antagonistic or/and not antagonistic conditions were concentrated and fractionated. The metabolites involved in the antagonistic action of the isolate showed to be more than one and produced independently of the presence of the pathogen. The above observations could support the application of Streptomyces rochei ACTA1551 as biocontrol agent against F. oxysporum.

Greek indigenous streptomycetes as biocontrol agents against the soil-borne fungal plant pathogen Rhizoctonia solani

AIMS

To examine the biocontrol potential of multiactive Greek indigenous Streptomyces isolates carrying antifungal activity against Rhizoctonia solani that causes damping-off symptoms on beans.

METHODS AND RESULTS

A total of 605 Streptomyces isolates originated from 12 diverse Greek habitats were screened for antifungal activity against R. solani DSM843. Almost one-third of the isolates proved to be antagonistic against the fungus. From the above isolates, six were selected due to their higher antifungal activity, identified by analysing their 16S rRNA gene sequence and studied further. The obtained data showed the following: firstly, the isolates ACTA1383 and ACTA1557 exhibited the highest antagonistic activity, and therefore, they were selected for in vivo experiments using bean seeds as target; secondly, in solid and liquid culture experiments under optimum antagonistic conditions, the medium extracts from the isolates OL80, ACTA1523, ACTA1551 and ACTA1522 suppressed the growth of the fungal mycelium, while extracts from ACTA 1383 and ACTA1557 did not show any activity.

CONCLUSIONS

These results corresponded important indications for the utility of two Greek indigenous Streptomyces isolates (ACTA1557 and ACTA1383) for the protection of the bean crops from R. solani damping-off symptoms, while four of them (isolates OL80, ACTA1523, ACTA1551 and ACTA1522) seem to be promising producers of antifungal metabolites.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study on the biocontrol of R. solani using multiactive Streptomyces isolates originated from ecophysiologically special Greek habitats. Our study provides basic information to further explore managing strategies to control this critical disease.

Fluostatins I-K from the South China Sea-derived micromonospora rosaria SCSIO N160

The strain SCSIO N160 was isolated from a South China Sea sediment sample and was characterized as a Micromonospora rosaria species on the basis of its 16S rRNA gene sequence. Three new fluostatins, I-K (1-3), were isolated from the culture of M. rosaria SCSIO N160, together with six known compounds, fluostatins C-F (4-7), rabelomycin (8), and phenanthroviridone (9). The structure of fluostatin D (5) was confirmed by an X-ray crystallographic study. The absolute configuration of 1 and 3 was assigned by electronic circular dichroism calculations. Compounds 8 and 9 exhibited good antimicrobial activities against Staphylococcus aureus ATCC 29213 with MIC values of 1.0 and 0.25 μg/mL, respectively. Compound 9 also exhibited significant in vitro cytotoxic activities toward SF-268 (IC50 0.09 μM) and MCF-7 (IC50 0.17 μM).

Streptomyces synnematoformans sp. nov., a novel actinomycete isolated from a sand dune soil in Egypt

A polyphasic taxonomic study was undertaken to establish the status of a novel actinomycete, strain S155(T), isolated from a sand dune soil in Egypt. The organism formed characteristic synnemata-like structures and exhibited chemical and morphological features consistent with its classification in the genus Streptomyces. An almost-complete 16S rRNA gene sequence of the isolate was compared with corresponding sequences of representative streptomycetes. The 16S rRNA gene sequence data supported the assignment of the strain to the genus Streptomyces and showed that it formed a distinct phyletic line; the organism was most similar to the type strains of Streptomyces ruber (97.0 %), Streptomyces rubiginosus (97.0 %), Streptomyces roseiscleroticus (96.9 %) and Streptomyces thermoalcalitolerans (97.1 %). It was readily distinguished from the type strains of these species using a combination of phenotypic properties. On the basis of these results, strain S155(T) (=CGMCC 4.2055(T) =DSM 41902(T)) is proposed as the type strain of the novel species Streptomyces synnematoformans sp. nov.

Total Synthesis of Isoprekinamycin: Structural Evidence for Enhanced Diazonium Ion Character and Growth Inhibitory Activity toward Cancer Cells

The structurally novel diazobenzo[a]fluorene antibiotic isoprekinamycin (IPK) has been synthesized for the first time employing a Suzuki coupling of a brominated AB ring synthon with a boronate ester representing the D ring, followed by anionic cyclization and appropriate functional group manipulations. The first indication that the diazobenzo[a]fluorene system exhibits in vitro anticancer activity is provided and X-ray crystallographic evidence for enhancement of diazonium ion character as a consequence of intramolecular H-bonding is described.