Many fungi, lichens, and bacteria produce xanthones (derivatives of 9H-xanthen-9-one, “xanthone” from the Greek “xanthos”, for “yellow”) as secondary metabolites. Xanthones are typically polysubstituted and occur as either fully aromatized, dihydro-, tetrahydro-, or, more rarely, hexahydro-derivatives. This family of compounds appeals to medicinal chemists because of their pronounced biological activity within a notably broad spectrum of disease states, a result of their interaction with a correspondingly diverse range of target biomolecules. This has led to the description of xanthones as “privileged structures”.(1) Historically, the total synthesis of the natural products has mostly been limited to fully aromatized targets. Syntheses of the more challenging partially saturated xanthones have less frequently been reported, although the development in recent times of novel and reliable methods for the construction of the (polysubstituted) unsaturated xanthone core holds promise for future endeavors. In particular, the fascinating structural and biological properties of xanthone dimers and heterodimers may excite the synthetic or natural product chemist.

Xanthones from Fungi, Lichens, and Bacteria: The Natural Products and Their Synthesis

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.

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A comprehensive review of glycosylated bacterial natural products.

Xanthones from fungi, lichens, and bacteria : the natural products and their synthesis

This work assesses the current instrumentation, method development, and applications in countercurrent chromatography (CCC) and centrifugal partition chromatography (CPC), collectively referred to as countercurrent separation (CCS). The article provides a critical review of the CCS literature from 2007 since our last review (J. Nat. Prod. 2008, 71, 1489–1508), with a special emphasis on the applications of CCS in natural products research. The current state of CCS is reviewed in regard to three continuing topics (instrumentation, solvent system development, theory) and three new topics (optimization of parameters, workflow, bioactivity applications). The goals of this review are to deliver the necessary background with references for an up-to-date perspective of CCS, to point out its potential for the natural product scientist, and thereby to induce new applications in natural product chemistry, metabolome, and drug discovery research involving organisms from terrestrial and marine sources.

http://pubs.acs.org/doi/pdf/10.1021/np501065h

Countercurrent Separation of Natural Products: An Update.

The development of new drugs will certainly benefit from an ever improving knowledge of the living beings chemistry. However, identification of drugable molecules within the immense biodiversity of forests, soils or oceans still requires considerable investments in technical equipments, time and human resources. An important part of this process is the quick identification of known substances in order to concentrate the efforts on the discovery of new ones. A range of “dereplication” procedures are currently emerging to meet this challenge as key strategies to improve the performance of natural product screening programs. Initially defined in 1990 as “a process of quickly identifying known chemotypes”, dereplication is today a not so univocal concept and has evolved over the last years in different ways. The present review covers all dereplication-related sudies in natural product research from 1990 to 2014. Its writing brought to light five distinct dereplication workflows that can be characterized by the nature of starting materials, by the selected analytical technique, and above all by the final objective. Dereplication can be used as an untargeted workflow for the rapid identification of the major compounds whatever their chemical class in a single sample or for the acceleration of bioactivity-guided fractionation procedures. In other cases dereplication is fully integrated in metabolomic studies for the untargeted chemical profiling of natural extract collections or for the targeted identification of a predetermined class of metabolites. Finally a quite distinct dereplication approach mainly based on gene-sequence analyses is frequently used for the taxonomic identification of microbial strains.

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Dereplication strategies in natural product research: How many tools and methodologies behind the same concept?

Two new xanthone antibiotics, citreamicin delta (1) and epsilon (2), with potent activity against Gram-positive pathogens including multidrug-resistant Staphylococcus aureus (MDRSA) were discovered. Compounds 1 and 2 exhibited MIC values < 1 microg/mL versus a number of resistant strains. The compounds were obtained from EtOAc extracts of Streptomyces vinaceus and were purified by countercurrent chromatography and reversed-phase HPLC. Their structures were elucidated using primarily NMR and mass spectroscopy.

Citreamicins with potent gram-positive activity.

Resistance to currently available antibiotics has become a widely recognized crisis in the medical community. To address this, many companies and researchers are refocusing their attention towards natural products, which have an excellent track record of producing effective antibacterial drugs. The AMRI natural product library was screened for activity against multi-drug resistant Staphylococcus aureus (MDRSA). The active samples were counter screened for cytotoxicity against the human hepatocellular carcinoma HepG2 cell line to determine an in vitro therapeutic index (in vitro TI). Those samples with a high in vitro TI were selected for fractionation and dereplication. This led to the discovery of a new anthracycline structure. This metabolite, named mutactimycin E (1), exhibited moderate activity against several gram positive organisms. Here we report the isolation, structure elucidation and biological activities of this new compound.

/pdf/mutactimycin-e-a-new-anthracycline-antibiotic-with-gram-3kdvhdpwgw.pdf

Mutactimycin E, a New Anthracycline Antibiotic with Gram-positive Activity

Three new antibiotics, neopyrrolomycins B (1), C (2), and D (3), with potent activity against Gram-positive pathogens were discovered. They exhibited MIC values < 1 microg/mL versus a number of resistant strains. The compounds were obtained from the ethyl acetate extracts of a Streptomyces sp. after purification by column chromatography and RP-HPLC. Their structures were elucidated using X-ray crystallography (1) and NMR spectroscopy (2 and 3).

Neopyrrolomycins with broad spectrum antibacterial activity.

The departure of many pharmaceutical companies from antibiotic research starting in the 1980s resulted in the absence of new antibiotics to combat the current crisis of increasing microbial resistance to currently available antibiotics. In an effort to address the increasing need for novel antibiotics, AMRI began a screening campaign to identify potent compounds from our natural product library. Natural products, particularly those produced by microbial fermentation, were the direct source or inspiration for almost all antibiotics used today and remain the richest source for new antibacterial compound series. AMRI’s extensive library consisting of over 280 000 samples was screened for activity against a multi-drug resistant strain of Staphylococcus aureus (ATCC 43 300, Rockville, MD, USA). The hits arising out of this assay were then tested against the human hepatocellular carcinoma cell line HepG2 to filter out those samples where activity was the result of general cytotoxicity and determine an in vitro therapeutic index (in vitro TI). Samples with a high in vitro TI were selected for fractionation and dereplication. The resulting subset of samples possessing selectivity for the bacterial target were then fractionated on an HPLC system employing UV, ELSD (evaporative light scattering) and MS detectors. The eluted fractions were collected into 96-well microtiter plates and submitted for bioassay. LC/MS data for the active fractions generated UV spectra and molecular weights, which were used to search internal and external databases.1 The analysis of the extract from strain 4731, which exhibited excellent activity against several Gram-positive organisms, resulted in the discovery of a new anthraquinone, which was closely related to the known antibiotic ericamycin.2,3 Here we report the isolation, structure elucidation and biological activities of 1. The Actinoplanes sp. strain 4731 was isolated from a soil sample collected from grassland near Nanton, in Alberta, Canada. The culture was isolated by a previously described capillary chemotaxis technique,4 using 0.18% mannitol as a chemo-attractant, spread-plating on water-yeast extract agar plates5 and incubating in the dark at 28 1C for 10 days. All colonies visible under a dissecting scope were transferred to and purified on starch casein agar plates. Pure cultures were macerated and stored in a 10% glycerol/5% lactose solution at 80 1C. Before fermentation, the culture was streaked from a cryovial onto starch casein agar to verify purity. Fresh culture macerate was prepared from these agar plates after 14 days and used to inoculate the fermentation. Strain 4731 was identified by sequencing of the 16S rRNA gene. Genomic DNA was isolated from a culture grown in tryptic soy broth for 7 days at 28 1C by a phenol:chloroform extraction method.6 The 16S rRNA gene was amplified using Taq polymerase (Promega, Madison, WI, USA) and the following two primer pairs: 27F, 50-AGA GTTTGATCMTGGCTCAG-30; 1115R, 50-AGGGTTGCGCTCGTTG-30; and 339F, 50-CTCCTACGGGAGGCAGCAG-30; 1429R, 50-TACGGYT ACCTTGTTACGACTT-30. An NCBI BLAST search of our consensus sequence showed the four closest matches (99% max identity) were all Actinoplanes strains. The fermentation procedure utilized was a two-step process, in which a suspension of culture macerate (mycelium and spores) was inoculated into 250-ml flasks containing 30 ml of a nutrient seed medium having the following composition per liter: 20 g D-glucose, 15 g Pharmamedia (ADM Traders Protein, Lubbock, TX, USA), 5 g yeast extract (Difco, Franklin Lakes, NJ, USA), 4 g CaCO3, 3 g (NH4)2SO4 and 0.03 g ZnSO4 7 H2O, adjusted to pH 6.5 before autoclaving. After inoculation, the flasks were incubated on a rotary shaker at 250 r.p.m. (20 0 throw) and 28 1C for 2 days. One milliliter aliquots of the seed culture were then used to inoculate one hundred 250-ml flasks containing 30 ml of a production medium with the following composition per liter: 30 g D-glucose, 10 g maltose, 20 g Quaker oatmeal and 4 g yeast extract, adjusted to pH 7.0 before autoclaving. Following inoculation, the production flasks were incubated on a rotary shaker at 250 r.p.m. and 28 1C for 8 days. The combined cultures (B3 l) were harvested by extracting with an equal volume of ethyl acetate resulting in a total extract volume

Chris Smith

Papers

Citreamicins with potent gram-positive activity.

Mutactimycin E, a New Anthracycline Antibiotic with Gram-positive Activity

Neopyrrolomycins with broad spectrum antibacterial activity.

5-Hydroxy ericamycin, a new anthraquinone with potent antimicrobial activity.