Rifamycin Biosynthetic Congeners: Isolation and Total Synthesis of Rifsaliniketal and Total Synthesis of Salinisporamycin and Saliniketals A and B

Total Synthesis of the Proposed Structure of Neaumycin B

The total synthesis of the proposed structure of anti-glioblastoma natural product neaumycin B was achieved in 22 steps (longest linear sequence). The synthesis features HCl-mediated [6,6]-spiroketalization, a combination of Krische iridium-catalyzed crotylation, Marshall palladium-catalyzed propargylation, Fürstner nickel-catalyzed regio- and enantioselective vicinal monoprotected diol formation, Brown crotylation and asymmetric halide-aldehyde cycloaddition, so as to establish the challenging contiguous stereocenters.

Rifamycin-Related Polyketides from a Marine-Derived Bacterium Salinispora arenicola and Their Cytotoxic Activity

Eight rifamycin-related polyketides were isolated from the culture broth of a marine-derived bacterium Salinispora arenicola, including five known (2-5 and 8) and three new derivatives (1, 6, and 7). The structures of the new compounds were determined by means of spectroscopic methods (HRESIMS and 1D, 2D NMR) and a comparison of their experimental data with those previously reported in the literature. The isolated compounds were evaluated for their cytotoxicity against one normal, six solid, and seven blood cancer cell lines and 1 showed moderate activity against all the tested cell lines with GI50 values ranging from 2.36 to 9.96 µM.

Beyond the approved: target sites and inhibitors of bacterial RNA polymerase from bacteria and fungi

Covering: 2016 to 2022RNA polymerase (RNAP) is the central enzyme in bacterial gene expression representing an attractive and validated target for antibiotics. Two well-known and clinically approved classes of natural product RNAP inhibitors are the rifamycins and the fidaxomycins. Rifampicin (Rif), a semi-synthetic derivative of rifamycin, plays a crucial role as a first line antibiotic in the treatment of tuberculosis and a broad range of bacterial infections. However, more and more pathogens such as Mycobacterium tuberculosis develop resistance, not only against Rif and other RNAP inhibitors. To overcome this problem, novel RNAP inhibitors exhibiting different target sites are urgently needed. This review includes recent developments published between 2016 and today. Particular focus is placed on novel findings concerning already known bacterial RNAP inhibitors, the characterization and development of new compounds isolated from bacteria and fungi, and providing brief insights into promising new synthetic compounds.

The one-pot synthesis of amidonapthoquinones from aminonaphthoquinones

Described here is a one-pot method of synthesizing amidonaphthoquinones from the corresponding aminonaphthoquinones. The scope of amides that can be synthesized using this methodology is relatively broad and the yield of product is higher than the traditional methods of synthesizing these substrates.

Photoelectrocyclization Reactions of Amidonaphthoquinones

Readily available acrylamide naphthoquinones can be converted into the corresponding aza-anthraquinones using 6π-photoelectrocyclization reactions. Not only do these reactions not proceed thermally but, as demonstrated here, they can also be used to generate a range of aza-anthraquinone and aza-tetracycline derivatives including the natural products griffithazanone A and marcanine A. Several of the aza-anthraquinones generated in this work showed antibacterial activity.

Antibacterial Salinaphthoquinones from a Strain of the Bacterium Salinispora arenicola Recovered from the Marine Sediments of St. Peter and St. Paul Archipelago, Brazil

Salinaphthoquinones A-E (1-5) were isolated from a marine Salininispora arenicola strain, recovered from sediments of the St. Peter and St. Paul Archipelago, Brazil. The structures of the compounds were elucidated using a combination of spectroscopic (NMR, IR, HRESIMS) data, including single-crystal X-ray diffraction analysis. A plausible biosynthetic pathway for 1-5 is proposed. Compounds 1 to 4 displayed moderate activity against Staphylococcus aureus and Enterococcus faecalis with MIC values of 125 to 16 μg/mL.

Marine Rare Actinomycetes: A Promising Source of Structurally Diverse and Unique Novel Natural Products

Rare actinomycetes are prolific in the marine environment; however, knowledge about their diversity, distribution and biochemistry is limited. Marine rare actinomycetes represent a rather untapped source of chemically diverse secondary metabolites and novel bioactive compounds. In this review, we aim to summarize the present knowledge on the isolation, diversity, distribution and natural product discovery of marine rare actinomycetes reported from mid-2013 to 2017. A total of 97 new species, representing 9 novel genera and belonging to 27 families of marine rare actinomycetes have been reported, with the highest numbers of novel isolates from the families Pseudonocardiaceae, Demequinaceae, Micromonosporaceae and Nocardioidaceae. Additionally, this study reviewed 167 new bioactive compounds produced by 58 different rare actinomycete species representing 24 genera. Most of the compounds produced by the marine rare actinomycetes present antibacterial, antifungal, antiparasitic, anticancer or antimalarial activities. The highest numbers of natural products were derived from the genera Nocardiopsis, Micromonospora, Salinispora and Pseudonocardia. Members of the genus Micromonospora were revealed to be the richest source of chemically diverse and unique bioactive natural products.

Marine natural products

Covering: 2016. Previous review: Nat. Prod. Rep., 2017, 34, 235-294This review covers the literature published in 2016 for marine natural products (MNPs), with 757 citations (643 for the period January to December 2016) 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 (1277 in 432 papers for 2016), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included.

Aryne-based strategy in the total synthesis of naturally occurring polycyclic compounds

This review has outlined the strategies and tactics of using arynes in the total syntheses of polycyclic natural products.

Living GenoChemetics by hyphenating synthetic biology and synthetic chemistry in vivo

Marrying synthetic biology with synthetic chemistry provides a powerful approach toward natural product diversification, combining the best of both worlds: expediency and synthetic capability of biogenic pathways and chemical diversity enabled by organic synthesis. Biosynthetic pathway engineering can be employed to insert a chemically orthogonal tag into a complex natural scaffold affording the possibility of site-selective modification without employing protecting group strategies. Here we show that, by installing a sufficiently reactive handle (e.g., a C–Br bond) and developing compatible mild aqueous chemistries, synchronous biosynthesis of the tagged metabolite and its subsequent chemical modification in living culture can be achieved. This approach can potentially enable many new applications: for example, assay of directed evolution of enzymes catalyzing halo-metabolite biosynthesis in living cells or generating and following the fate of tagged metabolites and biomolecules in living systems. We report synthetic biological access to new-to-nature bromo-metabolites and the concomitant biorthogonal cross-coupling of halo-metabolites in living cultures.

Coupling synthetic biology and chemical reactions in cells is a challenging task. The authors engineer bacteria capable of generating bromo-metabolites, develop a mild Suzuki-Miyaura cross-coupling reaction compatible with cell growth and carry out the cross-coupling chemistry in live cell cultures.