Dibenzo-α-pyrones from the endophytic fungus <i>Alternaria</i> sp. Samif01: isolation, structure elucidation, and their antibacterial and antioxidant activities

<p>The EtOAc extract of the liquid fermentation of <i>Alternaria</i> sp. Samif01, an endophytic fungus obtained from <i>Salvia miltiorrhiza</i> Bunge, showed antibacterial activity against several tested bacterial pathogens. Fractionation of this extract led to the isolation of seven dibenzo-α-pyrones (<b>1</b>–<b>7</b>), including one new compound, 2-acetoxy-2-<i>epi</i>-altenuene (<b>1</b>) and one new natural product, 3-<i>epi</i>-dihydroaltenuene A (<b>2</b>). The structures of the new metabolites were elucidated by comprehensive analysis of the spectroscopic data including (1D, 2D) NMR and HRESIMS, while the absolute configuration of <b>1</b> was determined by TDDFT–ECD computation. Altenuisol (<b>5</b>), 4-hydroxyalternariol-9-methyl ether (<b>6</b>), and alternariol (<b>7</b>) showed inhibitory activities against the tested bacteria with minimum inhibitory concentration values in the range of 86.7–364.7 μM. A preliminary structure–antibacterial activity relationship was discussed. In addition, compounds <b>2</b>, <b>5</b> and <b>6</b> displayed promising antioxidant effects using DPPH and hydroxyl radical assays. The cytotoxicity of the isolated compounds was evaluated as well.</p> <p>The endophytic fungus <i>Alternaria</i> sp. Samif01 isolated from <i>Salvia miltiorrhiza</i> Bunge produced seven bioactive dibenzo-α-pyrones, including one new compound (<b>1</b>), whose absolute configuration was determined by ECD calculation.</p

Bioactive Spirobisnaphthalenes from the Endophytic Fungus <i>Berkleasmium</i> sp.

Nine new spirobisnaphthalenes, palmarumycins B₁–B₉ (<b>1</b>–<b>9</b>), along with 13 known compounds (<b>10</b>–<b>22</b>), were isolated from cultures of the fungus <i>Berkleasmium</i> sp., an endophyte isolated from the medicinal plant <i>Dioscorea zingiberensis</i> C. H. Wright. The structures of the new compounds were elucidated by analysis of the 1D and 2D NMR and HRESIMS spectra and by comparison with known compounds. Compounds <b>7</b>–<b>9</b> contain an uncommon 2,3-dihydro-1<i>H</i>-inden-1-one unit. All isolated compounds were evaluated for their antibacterial activities against <i>Bacillus subtilis</i>, <i>Staphylococcus hemolyticus</i>, <i>Agrobacterium tumefaciens</i>, <i>Pseudomonas lachrymans</i>, <i>Ralstonia solanacearum,</i> and <i>Xanthomonas vesicatoria</i> and for their antifungal effects against the spore germination of <i>Magnaporthe oryzae</i>. Palmarumycin C₈ (<b>22</b>) exhibited the best antibacterial and antifungal effects. In addition, diepoxin δ (<b>11</b>) and palmarumycin C₈ (<b>22</b>) showed pronounced cytotoxic activities against five human cancer cell lines (HCT-8, Bel-7402, BGC-823, A 549, A 2780) with IC₅₀ values of 1.28–5.83 μM

Bioactive Dibenzo-α-pyrone Derivatives from the Endophytic Fungus <i>Rhizopycnis vagum</i> Nitaf22

Six new dibenzo-α-pyrones, rhizopycnolides A (<b>1</b>) and B (<b>2</b>) and rhizopycnins A–D (<b>3</b>–<b>6</b>), together with eight known congeners (<b>7</b>–<b>14</b>), were isolated from the endophytic fungus <i>Rhizopycnis vagum</i> Nitaf22 obtained from <i>Nicotiana tabacum</i>. The structures of the new compounds were unambiguously elucidated using NMR, HRESIMS, TDDFT ECD calculation, and X-ray crystallography data. Rhizopycnolides A (<b>1</b>) and B (<b>2</b>) feature an uncommon γ-butyrolactone-fused dibenzo-α-pyrone tetracyclic skeleton (6/6/6/5), while rhizopycnin B (<b>4</b>) was the first amino group containing dibenzo-α-pyrone. Rhizopycnolides A (<b>1</b>) and B (<b>2</b>) are proposed to be biosynthesized from polyketide and tricarboxylic acid cycle pathways. The isolated compounds were tested for their antibacterial, antifungal, and cytotoxic activities. Among them, rhizopycnolide A (<b>1</b>), rhizopycnins C (<b>5</b>) and D (<b>6</b>), TMC-264 (<b>8</b>), penicilliumolide D (<b>11</b>), and alternariol (<b>12</b>) were active against the tested pathogenic bacteria <i>Agrobacterium tumefaciens</i>, <i>Bacillus subtilis</i>, <i>Pseudomonas lachrymans</i>, <i>Ralstonia solanacearum</i>, <i>Staphylococcus hemolyticus</i>, and <i>Xanthomonas vesicatoria</i> with MIC values in the range 25–100 μg/mL. Rhizopycnin D (<b>6</b>) and TMC-264 (<b>8</b>) strongly inhibited the spore germination of <i>Magnaporthe oryzae</i> with IC₅₀ values of 9.9 and 12.0 μg/mL, respectively. TMC-264 (<b>8</b>) showed potent cytotoxicity against five human cancer cell lines (HCT-116, HepG2, BGC-823, NCI-H1650, and A2780) with IC₅₀ values of 3.2–7.8 μM

Bioactive Dibenzo-α-pyrone Derivatives from the Endophytic Fungus <i>Rhizopycnis vagum</i> Nitaf22

Six new dibenzo-α-pyrones, rhizopycnolides A (<b>1</b>) and B (<b>2</b>) and rhizopycnins A–D (<b>3</b>–<b>6</b>), together with eight known congeners (<b>7</b>–<b>14</b>), were isolated from the endophytic fungus <i>Rhizopycnis vagum</i> Nitaf22 obtained from <i>Nicotiana tabacum</i>. The structures of the new compounds were unambiguously elucidated using NMR, HRESIMS, TDDFT ECD calculation, and X-ray crystallography data. Rhizopycnolides A (<b>1</b>) and B (<b>2</b>) feature an uncommon γ-butyrolactone-fused dibenzo-α-pyrone tetracyclic skeleton (6/6/6/5), while rhizopycnin B (<b>4</b>) was the first amino group containing dibenzo-α-pyrone. Rhizopycnolides A (<b>1</b>) and B (<b>2</b>) are proposed to be biosynthesized from polyketide and tricarboxylic acid cycle pathways. The isolated compounds were tested for their antibacterial, antifungal, and cytotoxic activities. Among them, rhizopycnolide A (<b>1</b>), rhizopycnins C (<b>5</b>) and D (<b>6</b>), TMC-264 (<b>8</b>), penicilliumolide D (<b>11</b>), and alternariol (<b>12</b>) were active against the tested pathogenic bacteria <i>Agrobacterium tumefaciens</i>, <i>Bacillus subtilis</i>, <i>Pseudomonas lachrymans</i>, <i>Ralstonia solanacearum</i>, <i>Staphylococcus hemolyticus</i>, and <i>Xanthomonas vesicatoria</i> with MIC values in the range 25–100 μg/mL. Rhizopycnin D (<b>6</b>) and TMC-264 (<b>8</b>) strongly inhibited the spore germination of <i>Magnaporthe oryzae</i> with IC₅₀ values of 9.9 and 12.0 μg/mL, respectively. TMC-264 (<b>8</b>) showed potent cytotoxicity against five human cancer cell lines (HCT-116, HepG2, BGC-823, NCI-H1650, and A2780) with IC₅₀ values of 3.2–7.8 μM