Marine natural products.

Metabolites from marine organisms have proven to be a rich source for the discovery of multiple potent bioactive molecules with diverse structures. In recent years, we initiated a program to investigate the diversity of the secondary metabolites from marine invertebrates and their symbiotic microorganisms collected from the South China Sea. In this review, representative cases are summarized focusing on molecular diversity, mining, and application of natural products from these marine organisms. To provide a comprehensive introduction to the field of marine natural products, we highlight typical molecules including their structures, chemical synthesis, bioactivities and mechanisms, structure–activity relationships as well as biogenesis. The mining of marine-derived microorganisms to produce novel secondary metabolites is also discussed through the OSMAC strategy and via partial chemical epigenetic modification. A broad prospectus has revealed a plethora of bioactive natural products with novel structures from marine organisms, especially from soft corals, gorgonians, sponges, and their symbiotic fungi and bacteria.

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Metabolites from marine invertebrates and their symbiotic microorganisms: molecular diversity discovery, mining, and application

Vibrational optical activity for structural characterization of natural products.

Marine natural products as potential anti-tubercular agents

Two separate commercial products of kratom [Mitragyna speciosa (Korth) Havil Rubiaceae] were used to generate reference standards of its indole and oxindole alkaloids While kratom has been studied for over a century, the characterization data in the literature for many of the alkaloids are either incomplete or inconsistent with modern standards As such, full 1H and 13C NMR spectra, along with HRESIMS and ECD data, are reported for alkaloids 1-19 Of these, four new alkaloids (7, 11, 17, and 18) were characterized using 2D NMR data, and the absolute configurations of 7, 17, and 18 were established by comparison of experimental and calculated ECD spectra The absolute configuration for the N(4)-oxide (11) was established by comparison of NMR and ECD spectra of its reduced product with those for compound 7 In total, 19 alkaloids were characterized, including the indole alkaloid mitragynine (1) and its diastereoisomers speciociliatine (2), speciogynine (3), and mitraciliatine (4); the indole alkaloid paynantheine (5) and its diastereoisomers isopaynantheine (6) and epiallo-isopaynantheine (7); the N(4)-oxides mitragynine-N(4)-oxide (8), speciociliatine-N(4)-oxide (9), isopaynantheine-N(4)-oxide (10), and epiallo-isopaynantheine-N(4)-oxide (11); the 9-hydroxylated oxindole alkaloids speciofoline (12), isorotundifoleine (13), and isospeciofoleine (14); and the 9-unsubstituted oxindoles corynoxine A (15), corynoxine B (16), 3-epirhynchophylline (17), 3-epicorynoxine B (18), and corynoxeine (19) With the ability to analyze the spectroscopic data of all of these compounds concomitantly, a decision tree was developed to differentiate these kratom alkaloids based on a few key chemical shifts in the 1H and/or 13C NMR spectra

The Chemistry of Kratom [Mitragyna speciosa]: Updated Characterization Data and Methods to Elucidate Indole and Oxindole Alkaloids.

Investigation of the marine-derived fungus Pleosporales sp. CF09-1 cultured in modified PDB medium led to the isolation of six new azaphilone derivatives, pleosporalones B and C (1 and 2) and pleosporalones E-H (4-7), and one known analogue (3). The absolute configurations of C-2' and C-3' in 3 were assigned by a vibrational circular dichroism method. The C-11 relative configurations for the pair of C-11 epimers (4 and 5) were established by comparing the magnitude of the computed 13C NMR chemical shifts (Δδcalcd) with the experimental 13C NMR values (Δδexp) for the epimers. Antiphytopathogenic and anti- Vibrio activities were evaluated for 1-7. Pleosporalone B (1) exhibited potent antifungal activities against the fungi Alternaria brassicicola and Fusarium oxysporum with the same MIC value of 1.6 μg/mL, which were stronger than the positive control ketoconazole among these compounds. Additionally, pleosporalone C (2) displayed significant activity against the fungus Botryosphaeria dothidea (MIC, 3.1 μg/mL). Compounds 6 and 7 displayed moderate anti- Vibrio activities against Vibrio anguillarum and Vibrio parahemolyticus, with MIC values of 13 and 6.3 μg/mL for 6 and 6.3 and 25 μg/mL for 7, respectively.

Absolute Configuration of Bioactive Azaphilones from the Marine-Derived Fungus Pleosporales sp. CF09-1.

Marine-derived fungi of the genera Aspergillus could produce novel compounds with significant bioactivities. Among these fungi, the strain Aspergillus flavus is notorious for its mutagenic mycotoxins production. However, some minor components with certain toxicities from A. flavus have not been specifically surveyed and might have potent biological activities. Our investigation of the marine-derived fungus Aspergillus flavus CF13-11 cultured in solid medium led to the isolation of four C-6′/C-7′ epimeric drimane sesquiterpene esters, asperienes A–D (1–4). Their absolute configurations were assigned by electronic circular dichroism (ECD) and Snatzke’s methods. This is the first time that two pairs of C-6′/C-7′ epimeric drimane sesquiterpene esters have successfully been separated. Aperienes A–D (1–4) displayed potent bioactivities towards four cell lines with the IC50 values ranging from 1.4 to 8.3 μM. Interestingly, compounds 1 and 4 exhibited lower toxicities than 2 and 3 toward normal GES-1 cells, indicating more potential for development as an antitumor agent in the future.

https://www.mdpi.com/1660-3397/17/10/550/pdf

Asperienes A-D, Bioactive Sesquiterpenes from the Marine-Derived Fungus Aspergillus flavus.

Marine-derived fungi are well known as rich sources of bioactive natural products. Growing evidences indicated that indole alkaloids, isolated from a variety of marine-derived fungi, have attracted considerable attention for their diverse, challenging structural complexity and promising bioactivities, and therefore, indole alkaloids have potential to be pharmaceutical lead compounds. Systemic compilation of the relevant literature. In this review, we demonstrated a comprehensive overview of 431 new indole alkaloids from 21 genera of marine-derived fungi with an emphasis on their structures and bioactivities, covering literatures published during 1982–2019.

https://link.springer.com/content/pdf/10.1007/s42995-020-00072-w.pdf

Yu-Fei Yue

Papers

Absolute Configuration of Bioactive Azaphilones from the Marine-Derived Fungus Pleosporales sp. CF09-1.

Asperienes A-D, Bioactive Sesquiterpenes from the Marine-Derived Fungus Aspergillus flavus.

Marine-derived fungi as a source of bioactive indole alkaloids with diversified structures