New aminocoumarin antibiotics derived from 4-hydroxycinnamic acid are formed after heterologous expression of a modified clorobiocin biosynthetic gene cluster

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Streptomyces tunisiensis DSM 42037 mediated bioconversion of ferulic acid released from barley bran

Streptomyces tunisiensis DSM 42037 exhibited growth capacity on a minimum medium containing 1% barley bran. This peculiar strain released 83.5% of total ferulic acid present in barley bran after 5 days of incubation and the highest amount of released ferulic acid (19 mg/L) was observed on the 3rd day of incubation. The concentrated supernatant of S. tunisiensis also released ferulic acid from the parietal arabinoxylan complex of barley bran. This strain was able to convert the free ferulic acid into 4-vinyl guaiacol (14 mg/L) and acetovanillone (12 mg/L) at molar yield of 97% and 83% respectively. The biotransformation products were successively purified by preparative thin layer and silica gel column chromatography followed by HPLC and identified by ¹H nuclear magnetic resonance. Streptomyces tunisiensis DSM 42037 could have potential applications in the food, pharmaceutical and cosmetic industries thanks to its ability in biotransforming ferulic acid into 4-vinyl guaiacol and acetovanillone.

Identification of 4-diphenylamino 3-iodo coumarin as a potent inhibitor of DNA gyrase B of S. aureus

A necessity of therapeutics against antibiotic-resistant bacteria has led to a search for novel antibacterial compounds. The strategy to isolate compounds from non-microbial sources is the key to prevent antibiotic resistance. Here, we report isolation and characterization of an antibacterial coumarin derivative, 4-diphenylamino 3-iodo coumarin (4-DPA3IC) from a traditional drug formulation. The compound elicited high activity against MDR strains of S. aureus. Targets were identified through computational methods encompassing modules of Schrodinger 10.4. The 4-DPA3IC targeted S. aureus DNA gyrase enzyme B subunit. Amino acid residues and interactions involved here are totally different from those of novobiocin and clorobiocin. The validation was done by in vitro DNA gyrase supercoiling inhibition assay. This study proved 4-DPA3IC could potentially act against novobiocin and cholorbiocin resistant strains of S. aureus. Thus, the 4-DPA3IC is a unique inhibitor of bacterial DNA gyrase due to its plant origin as compared to other reported inhibitors.

Structural insights into simocyclinone as an antibiotic, effector ligand and substrate

Simocyclinones are antibiotics produced by Streptomyces and Kitasatospora species that inhibit the validated drug target DNA gyrase in a unique way, and they are thus of therapeutic interest. Structural approaches have revealed their mode of action, the inducible-efflux mechanism in the producing organism, and given insight into one step in their biosynthesis. The crystal structures of simocyclinones bound to their target (gyrase), the transcriptional repressor SimR and the biosynthetic enzyme SimC7 reveal fascinating insight into how molecular recognition is achieved with these three unrelated proteins.

RadH: A Versatile Halogenase for Integration into Synthetic Pathways

Flavin-dependent halogenases are useful enzymes for providing halogenated molecules with improved biological activity, or intermediates for synthetic derivatization. We demonstrate how the fungal halogenase RadH can be used to regioselectively halogenate a range of bioactive aromatic scaffolds. Site-directed mutagenesis of RadH was used to identify catalytic residues and provide insight into the mechanism of fungal halogenases. A high-throughput fluorescence screen was also developed, which enabled a RadH mutant to be evolved with improved properties. Finally we demonstrate how biosynthetic genes from fungi, bacteria, and plants can be combined to encode a new pathway to generate a novel chlorinated coumarin "non-natural" product in E. coli.

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.

Miniaturized Cultivation of Microbiota for Antimalarial Drug Discovery

The ongoing search for effective antiplasmodial agents remains essential in the fight against malaria worldwide. Emerging parasitic drug resistance places an urgent need to explore chemotherapies with novel structures and mechanisms of action. Natural products have historically provided effective antimalarial drug scaffolds. In an effort to search nature's chemical potential for antiplasmodial agents, unconventionally sourced organisms coupled with innovative cultivation techniques were utilized. Approximately 60,000 niche microbes from various habitats (slow-growing terrestrial fungi, Antarctic microbes, and mangrove endophytes) were cultivated on a small-scale, extracted, and used in high-throughput screening to determine antimalarial activity. About 1% of crude extracts were considered active and 6% partially active (≥ 67% inhibition at 5 and 50 μg/mL, respectively). Active extracts (685) were cultivated on a large-scale, fractionated, and screened for both antimalarial activity and cytotoxicity. High interest fractions (397) with an IC50 < 1.11 μg/mL were identified and subjected to chromatographic separation for compound characterization and dereplication. Identifying active compounds with nanomolar antimalarial activity coupled with a selectivity index tenfold higher was accomplished with two of the 52 compounds isolated. This microscale, high-throughput screening project for antiplasmodial agents is discussed in the context of current natural product drug discovery efforts.

Biological activities of novel gyrase inhibitors of the aminocoumarin class

Thirty-one aminocoumarin antibiotics derived from mutasynthesis experiments were investigated for their biological activities. Their inhibitory activities toward Escherichia coli DNA gyrase were determined in two different in vitro assays: an ATPase assay and a DNA supercoiling assay. The assays gave a similar rank order of the activities of the compounds tested, although the absolute 50% inhibitory concentrations (IC(50)s) obtained in each assay were different. To confirm that the compounds also acted as gyrase inhibitors in vivo, reporter gene assays were carried out with E. coli by using gyrA and sulA promoter fusions with the luxCDABE operon. A strong induction of both promoters was observed for those compounds that showed gyrase inhibitory activity in the biochemical assays. Compounds carrying analogs of the prenylated benzoyl moiety (ring A) of clorobiocin that were structurally very different showed high levels of activity both in the biochemical assay and in the reporter gene assay, indicating that the structure of this moiety can be varied considerably without a loss of affinity for bacterial gyrase. The experimentally determined IC(50)s were compared to the binding energies calculated in silico, which indicated that a shift of the pyrrole carboxylic acid moiety from the O-3'' to the O-2'' position of the deoxysugar moiety has a significant impact on the binding mode of the compounds. The aminocoumarin compounds were also investigated for their MICs against different bacterial pathogens. Several compounds showed high levels of activity against staphylococci, including a methicillin-resistant Staphylococcus aureus strain. However, they showed only poor activities against gram-negative strains.