Brasiliquinones A, B and C, new benz[alpha]anthraquinone antibiotics from Nocardia brasiliensis. I. Producing strain, isolation and biological activities of the antibiotics

Asymmetric Total Synthesis of Brasiliquinones B and C via Oxidative Cyclization of a Hydroquinone-Silyl Enol Ether Hybrid

The asymmetric total synthesis of angucycline antibiotics (S)-brasiliquinones B and C was accomplished. The benz[a]anthraquinone core was constructed via oxidative cyclization of a hydroquinone-silyl enol ether hybrid. The resultant pentacyclic acetal was converted to the silyl enol ether, which was treated with Pd(II)/O₂ to afford brasiliquinone C, after multistep conversion including dehydrogenation, desilylation and deacetalization, and hydroquinone oxidation. The (S)-configuration of natural brasiliquinones was confirmed based on the stereochemical correlation with the synthetic products.

Identification and Mobilization of a Cryptic Antibiotic Biosynthesis Gene Locus from a Human-Pathogenic Nocardia Isolate

The genus Nocardia contains >50 human pathogenic species that cause a range of illnesses from skin and soft tissue infections to lung and brain infections. However, despite their membership in the most prominent family of secondary metabolite producers (the Actinomycetes), the ability of Nocardia species, especially those that cause human infections, to produce secondary metabolites has not been as well studied. Using genome mining, we have investigated cryptic secondary metabolite biosynthesis gene clusters from Nocardia species and identified a conserved locus within human pathogenic strains of Nocardia brasiliensis and Nocardia vulneris. Direct capture and heterologous expression in a Streptomyces host activated the biosynthetic locus, revealing it to be the source of the brasiliquinones, benz[a]anthraquinone antibiotics whose biosynthetic pathway has remained hidden for over two decades, until now. Our findings highlight these hitherto neglected human pathogenic Nocardia as a source of diverse and important natural products.

Bioactive molecules from Nocardia: diversity, bioactivities and biosynthesis

Nocardia spp. are catalase positive, aerobic, and non-motile Gram-positive filamentous bacteria. Many Nocarida spp. have been reported as unusual causes of diverse clinical diseases in both humans and animals. Therefore, they have been studied for a long time, primarily focusing on strain characterization, taxonomic classification of new isolates, and host pathophysiology. Currently, there are emerging interests in isolating bioactive molecules from diverse actinobacteria including Nocardia spp. and studying their biosynthetic mechanisms. In addition, these species possess significant metabolic capacity, which has been utilized for generating diverse functionalized bioactive molecules by whole cell biotransformation. This review summarizes the structural diversity and biological activities of compounds biosynthesized or biotransformed by Nocardia spp. Furthermore, the recent advances on biosynthetic mechanisms and genetic engineering approaches for enhanced production or structural/functional modification are presented.

Bioprospecting from cultivable bacterial communities of marine sediment and invertebrates from the underexplored Ubatuba region of Brazil

Shrimp fisheries along the Brazilian coast have significant environmental impact due to high by-catch rates (21 kg per kilogram of shrimp). Typically discarded, by-catch contains many invertebrates that may host a great variety of bacterial genera, some of which may produce bioactive natural products with biotechnological applications. Therefore, to utilize by-catch that is usually discarded we explored the biotechnological potential of culturable bacteria of two abundant by-catch invertebrate species, the snail Olivancillaria urceus and the sea star Luidia senegalensis. Sediment from the collection area was also investigated. Utilizing multiple isolation approaches, 134 isolates were obtained from the invertebrates and sediment. Small-subunit rRNA (16S) gene sequencing revealed that the isolates belonged to Proteobacteria, Firmicutes and Actinobacteria phyla and were distributed among 28 genera. Several genera known for their capacity to produce bioactive natural products (Micromonospora, Streptomyces, Serinicoccus and Verrucosispora) were retrieved from the invertebrate samples. To query the bacterial isolates for their ability to produce bioactive metabolites, all strains were fermented and fermentation extracts profiled by UP LC-HRMS and tested for antimicrobial activity. Four strains exhibited antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus warneri.

Anthraquinones and Derivatives from Marine-Derived Fungi: Structural Diversity and Selected Biological Activities

Anthraquinones and their derivatives constitute a large group of quinoid compounds with about 700 molecules described. They are widespread in fungi and their chemical diversity and biological activities recently attracted attention of industries in such fields as pharmaceuticals, clothes dyeing, and food colorants. Their positive and/or negative effect(s) due to the 9,10-anthracenedione structure and its substituents are still not clearly understood and their potential roles or effects on human health are today strongly discussed among scientists. As marine microorganisms recently appeared as producers of an astonishing variety of structurally unique secondary metabolites, they may represent a promising resource for identifying new candidates for therapeutic drugs or daily additives. Within this review, we investigate the present knowledge about the anthraquinones and derivatives listed to date from marine-derived filamentous fungi's productions. This overview highlights the molecules which have been identified in microorganisms for the first time. The structures and colors of the anthraquinoid compounds come along with the known roles of some molecules in the life of the organisms. Some specific biological activities are also described. This may help to open doors towards innovative natural substances.

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.

Novonestmycins A and B, two new 32-membered bioactive macrolides from Streptomyces phytohabitans HBERC-20821

Two new 32-membered macrolide compounds, named Novonestmycins A (1) and B (2), were isolated from the soil strain Streptomyces phytohabitans HBERC-20821. Their structures were elucidated by using spectroscopic methods, including 1D, 2D-NMR and MS spectrometry. The two compounds showed strong activities against the phytophathogenic fungi Corynespora cassiicola, Rhizoctonia solani and Septoria nodorum, with MIC values of 0.78, 0.39 and 0.78 μg ml(-1), respectively. In addition, the two compounds exhibited potent inhibitory activities against four different human tumor cell lines as well as one 5-FU-resistant human hepatocellular carcinoma cell line, with IC50 of 0.15-0.48 μg ml(-1) and 0.24-1.34 μg ml(-1), respectively.

Functional diversity of Nocardia in metabolism

Bacteria affiliated in the genus Nocardia are aerobic and Gram-positive actinomycetes that are widely found in aquatic and terrestrial habitats. As occasional pathogens, several of them cause infection diseases called 'nocardiosis' affecting lungs, central nervous system, cutaneous tissues and others. In addition, members of the genus Nocardia exhibit an enormous metabolic versatility. On one side, many secondary metabolites have been isolated from members of this genus that exhibit various biological activities such as antimicrobial, antitumor, antioxidative and immunosuppressive activities. On the other side, many species are capable of degrading or converting aliphatic and aromatic toxic hydrocarbons, natural or synthetic polymers, and other widespread environmental pollutants. Because of these valuable properties and the application potential, Nocardia species have attracted much interest in academia and industry in recent years. A solid basis of genetic tools including a set of shuttle vectors and an efficient electroporation method for further genetic and metabolic engineering studies has been established to conduct efficient research. Associated with the increasing data of nocardial genome sequences, the functional diversity of Nocardia will be much faster and better understood.

Angucyclines: Biosynthesis, mode-of-action, new natural products, and synthesis

Covering: 1997 to 2010. The angucycline group is the largest group of type II PKS-engineered natural products, rich in biological activities and chemical scaffolds. This stimulated synthetic creativity and biosynthetic inquisitiveness. The synthetic studies used five different strategies, involving Diels-Alder reactions, nucleophilic additions, electrophilic additions, transition-metal mediated cross-couplings and intramolecular cyclizations to generate the angucycline frames. Biosynthetic studies were particularly intriguing when unusual framework rearrangements by post-PKS tailoring oxidoreductases occurred, or when unusual glycosylation reactions were involved in decorating the benz[a]anthracene-derived cores. This review follows our previous reviews, which were published in 1992 and 1997, and covers new angucycline group antibiotics published between 1997 and 2010. However, in contrast to the previous reviews, the main focus of this article is on new synthetic approaches and biosynthetic investigations, most of which were published between 1997 and 2010, but go beyond, e.g. for some biosyntheses all the way back to the 1980s, to provide the necessary context of information.

Fujianmycin C, A Bioactive Angucyclinone from a Marine Derived Streptomyces sp. B6219 [1]

From a marine-derived streptomycete, a new bioactive angucyclinone, fujianmycin C (1), has been isolated along with five known, metabolites fujianmycins A (2) and B (3), ochromycinone (4), ochromycinone methyl ether (5), and tetrangulol methyl ether (6). The structure elucidation of fujianmycin C (1) was performed by detailed analysis of data such as 1H, 13C, 1H,1H COSY, HSQC, HMBC and NOESY spectra. Fujianmycin C (1) exhibited antibacterial activity against Streptomyces viridochromogenes (Tü57).

Microbial transformation of amino- and hydroxyanthraquinones by Beauveria bassiana ATCC 7159

Microbial biotransformation of four amino- and hydroxyanthraquinones catalyzed by Beauveria bassiana ATCC 7159 has been studied. Incubation of 1,2-diaminoanthraquinone (1) with B. bassiana ATCC 7159 afforded 1-amino-2-(4'-O-methyl-2beta-N-D-glucopyranosylamino)anthraquinone (5) in a hitherto unprecedented biotransformation involving N-glycosylation of an amine. Biotransformation of 1-aminoanthraquinone (2) yielded 1-amino-2-(4'-O-methyl-2beta-O-D-glucopyranosyloxy)anthraquinone (6) as a result of microbial hydroxylation of C-2 followed by 4'-O-methyl-glucosylation of the newly introduced hydroxyl group. 1,8-Dihydroxyanthraquinone (3) and 1,2-dihydroxyanthraquinone (4) afforded 8-hydroxy-1-(4'-O-methyl-1beta-O-D-glucopyranosyloxy)anthraquinone (7) and 1-hydroxy-2-(4'-O-methyl-2beta-O-D-glucopyranosyloxy)anthraquinone (8), respectively, resulting from 4'-O-methyl-glucosylation of the existing hydroxyl groups of the substrates. The efficiency of these conversions suggests that microbial biotransformation reactions offer an attractive alternative to chemical 4'-O-methyl-glucosylation of amino- and hydroxyanthraquinones.

Alternative sources of biologically active substances

The majority of antibiotics and substances with diverse biological activity used in medicine are produced by actinomycetes, nonfilamentous bacteria and fungi. Other microorganisms, such as myxobacteria, pseudomonads, nocardias, basidiomycetes, marine microorganisms, enterobacteria, halobacteria, hyperthermophiles etc. are investigated for new biologically active metabolites.