Roussoelins A and B: two phenols with antioxidant capacity from ascidian-derived fungus Roussoella siamensis SYSU-MS4723

Structure-Activity Relationships of Natural C-9-Methyl-Substituted 10-Membered Lactones and Their Semisynthetic Derivatives

Fungal 10-membered lactones (TMLs), such as stagonolide A, herbarumin I, pinolidoxin, and putaminoxin, are promising candidates for the development of nature-derived herbicides. The aim of this study was to analyze the structure-activity relationships (SAR) of C-9-methyl-substituted TMLs with a multitarget bioassay approach to reveal compounds with useful (phytotoxic, entomotoxic, antimicrobial) or undesirable (cytotoxic) bioactivities. A new TML, stagonolide L (1), along with five known compounds (stagonolides D (2) and E (3), curvulides A (4) and B1/B2 (5a,b), and pyrenolide C (6)), were purified from cultures of the phytopathogenic fungus Stagonospora cirsii, and five semisynthetic derivatives of 3 and 4 (7-11) were obtained. The absolute configuration of 4 was revised to 2Z, 4S, 5S, 6R, and 9R. The identity of 5a,b and stagonolide H is discussed. The phytotoxicity of compound 4, the entomotoxicity of 5a,b, and nonselective toxicity of compound 6 are demonstrated. The latter confirms the hypothesis that the α,β-unsaturated carbonyl group is associated with the high general toxicity of TML, regardless of its position in the ring and other substituents. The epoxide in compound 4 is important for phytotoxicity. The revealed SAR patterns will be useful for further rational design of TML-based herbicides including curvulide A analogs with a 4,5-epoxy group.

Shikimate-Derived Meroterpenoids from the Ascidian-Derived Fungus Amphichorda felina SYSU-MS7908 and Their Anti-Glioma Activity

Glioma is a clinically heterogeneous type of brain tumor with a poor prognosis. Current treatment approaches have limited effectiveness in treating glioma, highlighting the need for novel drugs. One approach is to explore marine natural products for their therapeutic potential. In this study, we isolated nine shikimate-derived diisoprenyl-cyclohexene/ane-type meroterpenoids (1-9), including four new ones, amphicordins A-D (1-4) from the ascidian-derived fungus Amphichorda felina SYSU-MS7908, and further semisynthesized four derivatives (10-13). Their structures were extensively characterized using 1D and 2D NMR, modified Mosher's method, HR-ESIMS, NMR and ECD calculations, and X-ray crystallography. Notably, amphicordin C (3) possesses a unique benzo[g]chromene (6/6/6) skeleton in this meroterpenoid family. In an anti-glioma assay, oxirapentyn A (7) effectively inhibited the proliferation, migration, and invasion of glioma cells and induced their apoptosis. Furthermore, an in silico analysis suggested that oxirapentyn A has the potential to penetrate the blood-brain barrier. These findings highlight the potential of oxirapentyn A as a candidate for the development of novel anti-glioma drugs.

Absolute configuration of cyclopropanes and the structural revision of pyrones from Marine-derived fungus Stagonospora sp. SYSU-MS7888

Two new cyclopropane derivatives (1-2) and seven undescribed α-pyrone derivatives (3-9), along with one known congener (10) were obtained from the marine fungus Stagonospora sp. SYSU-MS7888, which was isolated from the South China Sea. Their planar structures were established through extensive spectroscopic analyses including 1D and 2D NMR and HR-ESIMS. The absolute configurations were identified on basis of the quantum chemical calculations of ECD and NMR, as well as the modified Mosher's method. It's particularly noteworthy that the tetrasubstituted furopyrans, chenopodolans A-F, possessing phytotoxicity and zootoxicity, were structural misassignments. The structures of chenopodolans featuring with furopyran skeleton were revised as common trisubstituted α-pyrones by computational chemistry, NMR spectroscopic method, and empirical rule. Compounds 1, 2, 7, and 9 showed significant anti-inflammatory activity with IC₅₀ values ranging from 3.6 to 22.8 μM, which is better than the positive control indomethacin (IC₅₀ = 26.5 ± 1.13 μM). This discovery holds potential for the development of new anti-inflammatory agents.

Marine natural products

Covering: January to December 2021This review covers the literature published in 2021 for marine natural products (MNPs), with 736 citations (724 for the period January to December 2021) 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 (1425 in 416 papers for 2021), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. An analysis of the number of authors, their affiliations, domestic and international collection locations, focus of MNP studies, citation metrics and journal choices is discussed.

Bioactive Monoterpenes and Polyketides from the Ascidian-Derived Fungus Diaporthe sp. SYSU-MS4722

There has been a tremendous increase in the rate of new terpenoids from marine-derived fungi being discovered, while new monoterpenes were rarely isolated from marine-derived fungi in the past two decades. Three new monoterpenes, diaporterpenes A–C (1–3), and one new α-pyrones, diaporpyrone A (6), along with nine known polyketides 4, 5, and 7–13 were isolated from the ascidian-derived fungus Diaporthe sp. SYSU-MS4722. Their planar structures were elucidated based on extensive spectroscopic analyses (1D and 2D NMR and HR-ESIMS). The absolute configurations of 1 and 3 were identified by an X-ray crystallographic diffraction experiment using Cu-Ka radiation, and those of compound 2 were assigned by calculating NMR chemical shifts and ECD spectra. It afforded an example of natural epimers with different physical properties, especially crystallization, due to the difference in intermolecular hydrogen bonding. Compounds 9, 10, and 13 showed moderate total antioxidant capacity (0.82 of 9; 0.70 of 10; 0.48 of 13) with Trolox (total antioxidant capacity: 1.0) as a positive control, and compounds 5 and 7 showed anti-inflammatory activity with IC₅₀ values of 35.4 and 40.8 µM, respectively (positive control indomethacin: IC₅₀ = 35.8 µM).

Two New Picoline-Derived Meroterpenoids with Anti-Acetylcholinesterase Activity from Ascidian-Derived Fungus Amphichorda felina

Amphichoterpenoids D (1) and E (2), two new picoline-derived meroterpenoids with a rare 6/6/6 tricyclic pyrano[3,2-c]pyridinyl-γ-pyranone scaffold, were isolated from the ascidian-derived fungus Amphichorda felina SYSU-MS7908. Their structures, including the absolute configurations, were established by extensive spectroscopic methods (1D and 2D NMR and high-resolution mass spectrometry) and ECD calculations. Compounds 1 and 2 showed anti-acetylcholinesterase (anti-AChE) activities with IC₅₀ values of 12.5 μM and 11.6 μM, respectively. The binding interactions between 1, 2, and AChE were investigated using molecular docking analyses.

Genome Mining of α-Pyrone Natural Products from Ascidian-Derived Fungus Amphichordafelina SYSU-MS7908

Culturing ascidian-derived fungus Amphichorda felina SYSU-MS7908 under standard laboratory conditions mainly yielded meroterpenoid, and nonribosomal peptide-type natural products. We sequenced the genome of Amphichorda felina SYSU-MS7908 and found 56 biosynthetic gene clusters (BGCs) after bioinformatics analysis, suggesting that the majority of those BGCSs are silent. Here we report our genome mining effort on one cryptic BGC by heterologous expression in Aspergillus oryzae NSAR1, and the identification of two new α-pyrone derivatives, amphichopyrone A (1) and B (2), along with a known compound, udagawanone A (3). Anti-inflammatory activities were performed, and amphichopyrone A (1) and B (2) displayed potent anti-inflammatory activity by inhibiting nitric oxide (NO) production in RAW264.7 cells with IC₅₀ values 18.09 ± 4.83 and 7.18 ± 0.93 μM, respectively.

Mono- and Dimeric Xanthones with Anti-Glioma and Anti-Inflammatory Activities from the Ascidian-Derived Fungus Diaporthe sp. SYSU-MS4722

Seven new xanthones, diaporthones A-G (1-7), together with 13 known analogues, including five mono- (8-14) and six dimeric xanthones (15-20), were obtained from the ascidian-derived fungus Diaporthe sp. SYSU-MS4722. Their planar structures were established by extensive spectroscopic analyses, including 1D and 2D NMR and high-resolution mass spectrometry (HR-ESIMS). The absolute configurations of 1-7 were clearly identified by X-ray crystallographic analysis and calculation of the ECD Spectra. Compounds 15-20 showed significant anti-inflammatory activity with IC50 values between 6.3 and 8.0 μM. In addition, dimeric xanthones (15-20) showed selective cytotoxicity against T98G cell lines with IC50 values ranging from 19.5 to 78.0 μM.

Absolute configuration of polypropionate derivatives: Decempyrones A-J and their MptpA inhibition and anti-inflammatory activities

Under guidance of ¹H NMR, ten new polypropionate derivatives, decempyrones A-J (1-10) along with two known analogues (11 and 12), were isolated from the marine-derived fungusFusarium decemcellulare SYSU-MS6716. The planar structures were elucidated on the basis of extensive spectroscopic analyses (1D and 2D NMR, and HR-ESIMS). The absolute configuration of the chiral centers in the side chain is a major obstacle for the structure identification of natural polypropionate derivatives. Herein, the J-based configurational analysis (JBCA), chemical degradation, geminal proton rule, and the modified Mosher's method were adopted to fix their absolute configurations in the side chain. Compounds 3 and 10 exhibited potent anti-inflammatory activity by inhibiting the production of NO in RAW264.7 cells activated by lipopolysaccharide with IC₅₀values 22.4 ± 1.8 and 21.7 ± 1.1 μM. In addition, compounds 3 and 10 displayed MptpA inhibitory activity with an IC₅₀ value of 19.2 ± 0.9 and 33.1 ± 2.9 µM. Structure-activity relationships of the polypropionate derivatives were discussed.