Marine cyanobacteria are prolific producers of structurally intriguing and biologically important secondary metabolites, many of which are of mixed NRPS/PKS biosynthetic origins, and have a broad range of biological activity, including ion channel modulation, cancer cell toxicity, anti-parasitic, anti-bacterial, anti- inflammatory, brine shrimp toxicity, and molluscicidal. Presently, there is one clinically approved drug that is an analog of the cyanobacterial natural product, dolastatin 10, while there are several agents in clinical trial, including soblidotin and synthadotin, which are analogs of dolastatin 15 and 10, respectively. Additionally, others are currently undergoing preclinical evaluation as anti-cancer agents, including apratoxin F, curacin A, desmethoxymajusculamide C (DMMC) and somacystinamide. The primary research objective of the research herein was to isolate and elucidate the structures of biologically active secondary metabolites from tropical marine cyanobacteria. In total, fifteen novel compounds from either Oscillatoria or Moorea were isolated and characterized. These include thirteen highly modified peptides (veraguamides A-C and H-L, precarriebowmide, tasiamides C-E, and lyngbyabellin N) and two alkyl amides (parguerene and mooreamide). The planar structure elucidation of each of these metabolites involved the use of 2D NMR spectroscopy and mass spectrometry techniques, including a mass spectrometry based dereplication algorithm to deduce the planar structure of several of the modified peptides. Absolute stereochemical analysis involved many techniques, such as Marfey's analysis, semi-synthesis, ³J coupling constant analysis, circular dichroism, ¹³C NMR comparisions, NOE correlations, and chiral GCMS analysis. Many of these compounds were biologically evaluated with veraguamide A and lyngbyabellin N exhibiting cancer cell cytotoxicity [IC₅₀ = 141 nM (H-460) and IC₅₀ = 40.9 (HCT-116), respectively], and mooreamide exhibiting cannabinoid receptor binding activity (Ki = 0.47 [mu]M). A secondary research objective has been the structure-activity relationship (SAR) study to investigate the active pharmacophore in the lyngbyamide family of compounds, which consist of a cyclopropyl fatty acid (tail) and an amide head group. In total, 50 analogs were synythesized, designed to probe the importance of several structural characteristics of the lyngbyamides. These compounds were tested in a wide array of biological assays, and a subset were found to possess strong activity in the stabilization of cathepsin L-mediated proteolysis, brine shrimp toxicity, and surface tension suppression

While quinones are essential for respiratory microorganisms, their importance for microbes that rely on fermentation metabolism is not understood. This gap in knowledge hinders our understanding of anaerobic microbial habitats, such in mammalian digestive tracts and fermented foods. We show that Lactiplantibacillus plantarum, a model fermentative lactic acid bacteria species abundant in human, animal, and insect microbiomes and fermented foods, uses multiple exogenous, environmental quinones as electron shuttles for a hybrid metabolism involving EET. Interestingly, quinones both stimulate this metabolism as well as cause oxidative stress when extracellular electron acceptors are absent. We also found that quinone-producing, lactic acid bacteria species commonly enriched together with L. plantarum in food fermentations accelerate L. plantarum growth and medium acidification through a mainly quinone- and EET-dependent mechanism. Thus, our work provides evidence of quinone cross-feeding as a key ecological feature of anaerobic microbial habitats.

Genome sequencing of microorganisms has revealed a greatly increased capacity for natural products biosynthesis than was previously recognized from compound isolation efforts alone. Hence, new methods are needed for the discovery and description of this hidden secondary metabolite potential. Here we show that provision of heavy nitrogen ¹⁵N-nitrate to marine cyanobacterial cultures followed by single-filament MALDI analysis over a period of days was highly effective in identifying a new natural product with an exceptionally high nitrogen content. The compound, named cryptomaldamide, was subsequently isolated using MS to guide the purification process, and its structure determined by 2D NMR and other spectroscopic and chromatographic methods. Bioinformatic analysis of the draft genome sequence identified a 28.7 kB gene cluster that putatively encodes for cryptomaldamide biosynthesis. Notably, an amidinotransferase is proposed to initiate the biosynthetic process by transferring an amidino group from arginine to serine to produce the first residue to be incorporated by the hybrid NRPS-PKS pathway. The maldiisotopic approach presented here is thus demonstrated to provide an orthogonal method by which to discover novel chemical diversity from Nature.

Natural products and their derivatives continue to be wellsprings of nascent therapeutic potential. However, many laboratories have limited resources for biological evaluation, leaving their previously isolated or synthesized compounds largely or completely untested. To address this issue, the Canvass library of natural products was assembled, in collaboration with academic and industry researchers, for quantitative high-throughput screening (qHTS) across a diverse set of cell-based and biochemical assays. Characterization of the library in terms of physicochemical properties, structural diversity, and similarity to compounds in publicly available libraries indicates that the Canvass library contains many structural elements in common with approved drugs. The assay data generated were analyzed using a variety of quality control metrics, and the resultant assay profiles were explored using statistical methods, such as clustering and compound promiscuity analyses. Individual compounds were then sorted by structural class and activity profiles. Differential behavior based on these classifications, as well as noteworthy activities, are outlined herein. One such highlight is the activity of (-)-2(S)-cathafoline, which was found to stabilize calcium levels in the endoplasmic reticulum. The workflow described here illustrates a pilot effort to broadly survey the biological potential of natural products by utilizing the power of automation and high-throughput screening.