Fungal indole diterpenes (IDTs) occupy a valuable region of bioactive natural product chemical space, displaying potent and selective inhibition of therapeutically important ion channels and with ...potential application in the treatment of glaucoma, cancer, and neurodegenerative diseases, as well as insecticides and antivirals. We have employed an integrated workflow of analytical scale chemical profiling using GNPS (Global Natural Products Social molecular networking) and cultivation profiling (also known as “MATRIX” miniaturized microbioreactor) to detect, prioritize, optimize the production, isolate, characterize, and identify a new series of indole diterpenes, noonindoles G–L (7–12), from an Australian marine-derived fungus, Aspergillus noonimiae CMB-M0339. The first reported examples of IDT glycosides, the molecular structures for 7–12, were assigned on the basis of detailed spectroscopic analysis and biosynthetic considerations.
Investigation of the secondary metabolites of Streptomyces virginiae CMB-CA091 isolated from the quartz-rich (tepui) soil of a cave in Venezuela yielded two new dimeric phenazine glycosides, ...tepuazines A and B (1 and 2); three new monomeric phenazine glycosides, tepuazines C–E (3–5); and a series of known analogues, baraphenazine G (6), phenazinolin D (7), izumiphenazine C (8), 4-methylaminobenzoyl-l-rhamnopyranoside (9), and 2-acetamidophenol (10). Structures were assigned to 1–10 on the basis of detailed spectroscopic analysis and biosynthetic considerations, with 1 and 2 featuring a rare 2-oxabicyclo3.3.1nonane-like ring C/D bridge shared with only a handful of known Streptomyces natural products. We propose a plausible convergent biosynthetic relationship linking all known members of this structure class that provides a rationale for the observed ring C/D configuration.
Further investigation into a fish gut-derived fungus
sp. CMB-F563, previously reported to produce the unprecedented Schiff base prolinimines A-B (
-
), revealed a new cryptic natural product,
...-amino-l-proline methyl ester (
)-only the second reported natural occurrence of an
-amino-proline, and the first from a microbial source. To enable these investigations, we developed a highly sensitive analytical derivitization methodology, using 2,4-dinitrobenzaldehyde (2,4-DNB) to cause a rapid in situ transformation of
to the Schiff base
, with the latter more readily detectable by UHPLC-DAD (400 nm) and HPLC-MS analyses. Moreover, we demonstrate that during cultivation
is retained in fungal mycelia, and it is only when solvent extraction disrupts mycelia that
is released to come in contact with the furans
-
(which are themselves produced by thermal transformation of carbohydrates during media autoclaving prior to fungal inoculation). Significantly, on contact,
undergoes a spontaneous condensation with
-
to yield the Schiff base prolinimines
-
, respectively. Observations made during this study prompted us to reflect on what it is to be a natural product (i.e.,
), versus an artifact (i.e.,
-
), versus a media component (i.e.,
-
).
The ethyl acetate extract of an ISP-2 agar cultivation of the wasp nest-associated fungus
sp. CMB-MD14 exhibited promising antibacterial activity against vancomycin-resistant enterococci (VRE), with ...a bioassay guided chemical investigation yielding the new meroterpene, oxandrastin A (
), the first andrastin-
metabolite with an extra oxygenation at C-2. A culture media optimisation strategy informed a scaled-up rice cultivation that yielded
, together with three new oxandrastins B-D (
-
), two known andrastins C (
) and F (
), and a new meroterpene of the austalide family, isoaustalide F (
). Structures of
-
were assigned based on detailed spectroscopic analysis and chemical interconversion. A GNPS molecular networking analysis of the rice cultivation extract detected the known austalides B (
), H (
), and H acid (
), tentatively identified based on molecular formulae and co-clustering with
. That the anti-VRE properties of the CMB-MD14 extract were exclusively attributed to
(IC
6.0 µM, MIC
13.9 µM), highlights the importance of the 2-OAc and 3-OAc moieties to the oxandrastin anti-VRE pharmacophore.
A library of fungi previously recovered from the gastrointestinal tract (GIT) of several fresh, commercially sourced Australian mullet fish was re-profiled for production of a rare class of ...phenylpropanoid piperazine alkaloids (chrysosporazines) using an integrated platform of; (i) miniaturized 24-well plate cultivation profiling (MATRIX), (ii) UPLC-DAD and UPLC-QTOF-MS/MS (GNPS) chemical profiling, and; (iii) precursor directed biosynthesis to manipulate in situ biosynthetic performance and outputs; to detect two new fungal producers of chrysosporazines. Chemical analysis of an optimized PDA solid phase cultivation of
sp. CMB-F661 yielded the new regioisomeric chrysosporazine T (
) and U (
), while precursor directed cultivation amplified production and yielded the very minor new natural products azachrysosporazine T1 (
) and U1 (
), and the new unnatural analogues neochrysosporazine R (
) and S (
). Likewise, chemical analysis of an optimized M1 solid phase cultivation of
sp. CMB-F455 lead to the GNPS detection of multiple chrysosporazines and brasiliamides, and the isolation and structure elucidation of chrysosporazine D (
) and brasiliamide A (
). Access to new chrysosporazine regioisomers facilitated structure activity relationship investigations to better define the chrysosporazine P-glycoprotein (P-gp) inhibitory pharmacophore, which is exceptionally potent at reversing doxorubrin resistance in P-gp over expressing colon carcinoma cells (SW600 Ad300).
Methods in Microbial Biodiscovery Salim, Angela A; Khalil, Zeinab G; Elbanna, Ahmed H ...
Marine drugs,
09/2021, Letnik:
19, Številka:
9
Journal Article
Recenzirano
Odprti dostop
This review presents an account of the microbial biodiscovery methodology developed and applied in our laboratory at The University of Queensland, Institute for Molecular Bioscience, with examples ...drawn from our experiences studying natural products produced by Australian marine-derived (and terrestrial) fungi and bacteria.
Cultivation profiling followed by chemical analysis of Streptomyces lincolnensis yielded four new isomeric bianthracenes, lincolnenins A–D (1–4), with relative stereostructures assigned on the basis ...of detailed spectroscopic analysis. Lincolnenins A (1) and B (2) exhibit restricted rotation about alternate bianthracene 9–9′ and 9–8′ bridges, respectively, and exist as single atropisomers, whereas C (3) and D (4) are thermally interconvertible atropisomers sharing a common 8–8′ bianthracene bridge. Absolute configurations were assigned to 1–4 on the basis of diagnostic ROESY correlations and ECD calculations, whereas acid-mediated dehydration of 1 led to formation and revision of the absolute configuration of the biosynthetically related known Streptomyces antibiotic, setomimycin (5). Lincolnenin A (1) exhibited significant bactericidal activity against multiple susceptible and drug-resistant Gram-positive pathogens (MIC99 < 2.0 μM), including Mycobacterium tuberculosis H37Ra (MIC99 = 0.9 μM).
Subjecting the Australian marine-derived fungus Aspergillus noonimiae CMB-M0339 to cultivation profiling using an innovative miniaturized 24-well plate format (MATRIX) enabled access to new examples ...of the rare class of 2,6-diketopiperazines, noonazines A–C (1–3), along with the known analogue coelomycin (4), as well as a new azaphilone, noonaphilone A (5). Structures were assigned to 1–5 on the basis of a detailed spectroscopic analysis, and in the case of 1–2, an X-ray crystallographic analysis. Plausible biosynthetic pathways are proposed for 1–4, involving oxidative Schiff base coupling/dimerization of a putative Phe precursor. Of note, 2 incorporates a rare meta-Tyr motif, typically only reported in a limited array of Streptomyces metabolites. Similarly, a plausible biosynthetic pathway is proposed for 5, highlighting a single point for stereo-divergence that allows for the biosynthesis of alternate antipodes, for example, the 7R noonaphilone A (5) versus the 7S deflectin 1a (6).
Chiral, dimeric natural products containing complex structures and interesting biological properties have inspired chemists and biologists for decades. A seven-step total synthesis of the axially ...chiral, dimeric tetrahydroxanthone natural product rugulotrosin A is described. The synthesis employs a one-pot Suzuki coupling/dimerization to generate the requisite 2,2'-biaryl linkage. Highly selective point-to-axial chirality transfer was achieved using palladium catalysis with achiral phosphine ligands. Single X-ray crystal diffraction data were obtained to confirm both the atropisomeric configuration and absolute stereochemistry of rugulotrosin A. Computational studies are described to rationalize the atropselectivity observed in the key dimerization step. Comparison of the crude fungal extract with synthetic rugulotrosin A and its atropisomer verified that nature generates a single atropisomer of the natural product.
An inter-kingdom beach warfare between a Streptomyces sp. and Aspergillus sp. co-isolated from shallow water beach sand, collected off Heron Island, Queensland, Australia, saw the bacteriostatic ...Aspergillus metabolite cyclo-(L-Phe-trans-4-hydroxy-L-Pro) (3) stimulate the Streptomyces to produce nitric oxide (NO), which in turn mediated transcriptional activation of a silent biosynthetic gene cluster (BGC) for fungistatic heronapyrrole B (1). Structure activity relationship studies, coupled with the use of NO synthase inhibitors, donors and scavangers, and both genomic and transcriptomic analyses, confirmed the extraordinary chemical cue specificity of 3, and its NO-mediated mechanism of transcriptional action. Our findings reveal the importance of inter-kingdom (fungal-bacterial) chemical communication in the regulation of silent BGCs coding for chemical defenses. We propose that the detection and characterisation of NO mediated transcriptional activation (NOMETA) of silent chemical defences in the environment, may inspire broader application in the field of microbial biodiscovery.
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