Azacoccones A − E, five new aza-epicoccone derivatives from Aspergillus flavipes

Unexpected Formation of 4-[(1-Carbamoyl-3-oxo-1,3-dihydro-2-benzofuran-1-yl)amino]benzoic Acid from 4-[(3-Amino-1-oxo-1H-2-benzopyran-4-yl)amino]benzoic Acid

With the aim of obtaining derivatives belonging to 2′,3′-diphenyl-3H-spiro[[2]benzofuran-1,4′-imidazole]-3,5′(3′H)-dione nucleus, we synthesized 4-[(3-amino-1-oxo-1H-2-benzopyran-4-yl)amino]benzoic acid (a 3,4-diaminoisocoumarine derivative), a known precursor of 4-[(1-carbamoyl-3-oxo-1,3-dihydro-2-benzofuran-1-yl)amino]benzoic acid (a phthalide–carboxamide-bearing system) by a novel methodology that we report here. The reaction conditions were optimized to afford the latter in 62% yield.

N-{2-[(3-Oxo-1,3-dihydro-2-benzofuran-1-yl)acetyl]phenyl}acetamide

With the aim of obtaining different derivatives belonging to the isoindolo[2,1-a]quinoline family, we have synthesized a novel N-{2-[(3-oxo-1,3-dihydro-2-benzofuran-1-yl)acetyl]phenyl}acetamide derivative by a Claisen–Smichdt-type condensation reaction in 75% yield.

Recent updates on the bioactive compounds of the marine-derived genus Aspergillus

The genus Aspergillus is widely distributed in terrestrial and marine environments. In the marine environment, several Aspergillus species have proved their potential to produce a plethora of secondary metabolites including polyketides, sterols, fatty acids, peptides, alkaloids, terpenoids and miscellaneous compounds, displaying a variety of pharmacological activities such as antimicrobial, cytotoxicity, anti-inflammatory and antioxidant activity. From the beginning of 2015 until December 2020, about 361 secondary metabolites were identified from different marine Aspergillus species. In our review, we highlight secondary metabolites from various marine-derived Aspergillus species reported between January 2015 and December 2020 along with their biological potential and structural aspects whenever applicable.

Biologically Significant and Recently Isolated Alkaloids from Endophytic Fungi

A selection of the established and recently characterized alkaloids from the exploration of plant- and some marine-associated endophytic fungi is reviewed, with reference to alkaloids of biological significance.

Azacoccones F-H, new flavipin-derived alkaloids from an endophytic fungus Epicoccum nigrum MK214079

Three new flavipin-derived alkaloids, azacoccones F-H (1-3), along with six known compounds (4-9) were isolated from the endophytic fungus Epicoccum nigrum MK214079 associated with leaves of Salix sp. The structures of the new compounds were established by analysis of their 1D/2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectroscopy (HRESIMS) data. The absolute configuration of azacoccones F-H (1-3) was determined by comparison of experimental electronic circular dichroism (ECD) data with reported ones and biogenetic considerations. Epicocconigrone A (4), epipyrone A (5), and epicoccolide B (6) exhibited moderate antibacterial activity against Staphylococcus aureus ATCC 29213 with minimal inhibitory concentration (MIC) values ranging from 25 to 50 μM. Furthermore, epipyrone A (5) and epicoccamide A (7) displayed mild antifungal activity against Ustilago maydis AB33 with MIC values of 1.6 and 1.8 mM, respectively. Epicorazine A (8) showed pronounced cytotoxicity against the L5178Y mouse lymphoma cell line with an IC₅₀ value of 1.3 μM.

Azacoccone E inhibits cancer cell growth by targeting 3-phosphoglycerate dehydrogenase

Serine plays critically important roles in tumorigenesis. Homo sapiens 3-phosphoglycerate dehydrogenase (PHGDH) catalyzes the first committed step for the synthesis of glucose-derived serine via the phosphoserine pathway and has been associated with a wide variety of cancers, including breast cancer, melanoma, colon cancer, glioma, nasopharyngeal carcinoma, cervical adenocarcinoma, etc. Azacoccone E, an aza-epicoccone derivative from the culture of Aspergillus flavipes, exhibited effective inhibitory activity against PHGDH in vitro. The microscale thermophoresis (MST) method and the cellular thermal shift assay (CETSA) confirmed that azacoccone E directly bound to PHGDH. And the cell-based experiments showed that this compound was selectively toxic to PHGDH-dependent cancer cells and could cause apoptosis. Further biochemical assays revealed that it was a noncompetitive inhibitor with respect to the substrate of 3-PG and exhibited a time-dependent inhibition. Furthermore, molecular docking demonstrated that azacoccone E coordinated in an allosteric site of PHGDH with low binding energy. Therefore, azacoccone E can be considered as a possible drug candidate targeting at PHGDH for treatment of cancers.

Parasubindoles A-G, Seven Eremophilanyl Indoles from the Whole Plant of Parasenecio albus

Parasubindoles A-G (1-7), seven eremophilanyl indoles with an unprecedented 12 H-cyclopentane[ b]naphthalenespiro-1,3'-indole skeleton, were isolated from the whole plant of Parasenecio albus. Their structures with absolute configurations were elucidated by spectroscopic methods, single-crystal X-ray diffraction, and ECD analyses. Plausible biosynthetic pathways of 1-7 were postulated.

Alkaloids with Immunosuppressive Activity from the Bark of Pausinystalia yohimbe

Ten new alkaloids (1-10), including two pairs of enantiomeric mixtures (5a,b and 6a,b), and 15 known analogues (11-25) were obtained from the bark of Pausinystalia yohimbe. The structures of 1-25 were established by spectroscopic methods, and the absolute configurations of compounds 1-10 were resolved by X-ray diffraction and ECD data analyses. The in vitro immunosuppressive activities of selected isolates were tested. Compounds 11 and 16 exhibited moderate inhibition with IC₅₀ values of 16.8 and 27.6 μM against ConA-induced T lymphocyte proliferation and 13.5 and 40.5 μM against LPS-induced B lymphocyte proliferation, respectively.