New polyenic antibiotics active against gram-positive and -negative bacteria. II. Screening of antibiotic producers and taxonomical properties of Gluconobacter sp. W-315

Optimizing the Synthesis Strategy of the Chlorinated Chain Characteristic to the Enacyloxin Series Using Models

In this paper are presented the results of the preliminary studies conducted on two model substrates that allowed the testing of various strategies and set the proper conditions that thereafter culminated in the synthesis of the C1-C23 chain of enacyloxin-IIa and its congeners. Innovative strategic options were explored on each model allowing the stereochemical control of the following two elements: (a) the 2E, 4E, 6E, 8E, and 10Z chlorinated undecapentaenoic chain, thanks to Z-selective Kaneda's alkyne allylchlorination and an E-selective Pd/Cu allene-alkyne coupling and (b) the unusual syn-anti -OH/-Cl/-OCONH2 C17-C19 triad, thanks to a highly diastereoselective Mukaiyama aldol reaction.

Enantioselective Synthesis of the 1,3-Dienyl-5-Alkyl-6-Oxy Motif: Method Development and Total Synthesis

The 1,3-dienyl-5-alkyl-6-oxy motif is widely found in various types of bioactive natural products. However, present synthesis is mainly non-asymmetric which relied upon different olefination or transition metal-catalyzed cross-coupling reactions using enantioenriched precursors. Herein, based upon a newly developed enantioselective α-alkylation of conjugated polyenoic acids, a variety of 1,3-dienyl-5-alkyl-6-oxy motif (with E-configured internal olefin) was generated as the corresponding α-adducts in a highly enantioselective and diastereoselective manner. Utilizing 1,3-dienyl-5-alkyl-6-oxy motif as key intermediates, we further demonstrated their synthetic potential by expedient total syntheses of three types of natural products (glutarimide antibiotics, α-pyrone polyketides and Lupin alkaloids) within 4-7 steps.

Advancements in Enacyloxins Total Synthesis: Access to the Chlorinated Polyunsaturated Chain Peculiar to this Promising Family of Antibiotics

The first synthesis of the protected chain specific to the enacyloxin antibiotic family is reported. The noticeable features are (a) the construction of the chlorinated undecapentaenoic moiety implementing the sequence Tsuji's alkyne syn allyl-chlorination, E-selective Pd/Cu-catalyzed allene-alkyne coupling, Horner-Wadsworth-Emmons olefination, dehydration; (b) control of the C18 chlorinated stereogenic center by organo-catalyzed aldehyde α-chlorination; and (c) the assemblage of this aldehyde with the C1-C16 ketone using a highly diastereoselective Mukaiyama aldol.

Aerial warfare: An inducible production of volatile bioactive metabolites in a novel species of Scytinostroma sp

Antimicrobial volatile organic compounds (VOCs) may provide fungi an advantage over other competing microorganisms. As these defensive metabolites are often produced in response to microbial competitors, they are easily overlooked in axenic cultures. We used media supplemented with spent medium from Candida albicans to induce the expression of a broad-spectrum antimicrobial response in a previously uncharacterised white-rot fungus, Scytinostroma sp. Crude extractions of Scytinostroma sp. metabolites were found to be cytotoxic to fibroblast cells and antimicrobial to filamentous fungi, yeasts and Gram-positive bacteria. Volatile antimicrobial activity was observed for Scytinostroma sp. cultures and metabolite extracts using antimicrobial assays in bi-compartmentalised plates. Culture headspace analysis using solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) revealed a pronounced shift in Scytinostroma sp. VOCs when cultured on media supplemented with C. albicans spent medium. We observed a significant increase in the levels of 45 identified VOCs, including 7 metabolites with reported antimicrobial activity. Using preparative HPLC combined with GC-MS, we determined that isovelleral is likely to be the main broad-spectrum antimicrobial metabolite produced by Scytinostroma sp. Isovelleral is a sesquiterpene dialdehyde with both antibiotic and antifeedant properties, previously detected in fruit bodies of other Basidiomycetes.

Metabolomic Comparison and Assessment of Co-cultivation and a Heat-Killed Inducer Strategy in Activation of Cryptic Biosynthetic Pathways

Co-cultivation has been used as a promising tool to turn on or up-regulate cryptic biosynthetic pathways for microbial natural product discovery. Recently, a modified culturing strategy similar to co-cultivation was investigated, where heat-killed inducer cultures were supplemented to the culture medium of producer fermentations to induce cryptic pathways. In the present study, the repeatability and effectiveness of both methods in turning on cryptic biosynthetic pathways were unbiasedly assessed using UHPLC-HRESIMS-based metabolomics analysis. Both induction methods had good repeatability, and they resulted in very different induced metabolites from the tested producers. Co-cultivation generated more induced mass features than the heat-killed inducer cultures, while both methods resulted in the induction of mass features not observed using the other induction method. As examples, pathways leading to two new natural products, N-carbamoyl-2-hydroxy-3-methoxybenzamide (1) and carbazoquinocin G (5), were induced and up-regulated through co-culturing a producer Streptomyces sp. RKND-216 with inducers Alteromonas sp. RKMC-009 and M. smegmatis ATCC 120515, respectively.

Biosynthesis of polyketides by trans-AT polyketide synthases

This review discusses the biosynthesis of natural products that are generated bytrans-AT polyketide synthases, a family of catalytically versatile enzymes that represents one of the major group of proteins involved in the production of bioactive polyketides.

Metabolite induction via microorganism co-culture: a potential way to enhance chemical diversity for drug discovery

Microorganisms have a long track record as important sources of novel bioactive natural products, particularly in the field of drug discovery. While microbes have been shown to biosynthesize a wide array of molecules, recent advances in genome sequencing have revealed that such organisms have the potential to yield even more structurally diverse secondary metabolites. Thus, many microbial gene clusters may be silent under standard laboratory growth conditions. In the last ten years, several methods have been developed to aid in the activation of these cryptic biosynthetic pathways. In addition to the techniques that demand prior knowledge of the genome sequences of the studied microorganisms, several genome sequence-independent tools have been developed. One of these approaches is microorganism co-culture, involving the cultivation of two or more microorganisms in the same confined environment. Microorganism co-culture is inspired by the natural microbe communities that are omnipresent in nature. Within these communities, microbes interact through signaling or defense molecules. Such compounds, produced dynamically, are of potential interest as new leads for drug discovery. Microorganism co-culture can be achieved in either solid or liquid media and has recently been used increasingly extensively to study natural interactions and discover new bioactive metabolites. Because of the complexity of microbial extracts, advanced analytical methods (e.g., mass spectrometry methods and metabolomics) are key for the successful detection and identification of co-culture-induced metabolites. This review focuses on co-culture studies that aim to increase the diversity of metabolites obtained from microbes. The various strategies are summarized with a special emphasis on the multiple methods of performing co-culture experiments. The analytical approaches for studying these interaction phenomena are discussed, and the chemical diversity and biological activity observed among the induced metabolites are described.

Future potential for anti-infectives from bacteria - how to exploit biodiversity and genomic potential

The early stages of antibiotic development include the identification of novel hit compounds. Since actinomycetes and myxobacteria are still the most important natural sources of active metabolites, we provide an overview on these producers and discuss three of the most promising approaches toward finding novel anti-infectives from microorganisms. These are defined as the use of biodiversity to find novel producers, the variation of culture conditions and induction of silent genes, and the exploitation of the genomic potential of producers via "genome mining". Challenges that exist beyond compound discovery are outlined in the last section.