Xanthones and Oxepino[2, 3‐b]chromones from Three Endophytic Fungi

Abstract

Three new metabolites, microsphaeropsones A-C (1-3) with a unique oxepino[2,3-b]chromen-6-one (ring-enlarged xanthone) skeleton, were isolated from the endophytic fungus Microsphaeropsis species, co-occurring with their putative biogenetic anthraquinoide precursors citreorosein (4) and emodin (5). From another Microsphaeropsis species, large amounts of fusidienol A (8 a), smaller amounts of emodin (5), the known aromatic xanthones 9 a and 9 b, the new 3,4-dihydrofusidienol A (8 b), and the new aromatic xanthone 9 c were isolated. The endophyte Seimatosporium species produced a new aromatic xanthone, seimatoxanthone A (10), and 3,4-dihydroglobosuxanthone A (12), closely related to alpha-diversolonic ester (13) from Microdiplodia sp.. The structures were determined mainly by extensive 1D and 2D NMR experiments and supported by X-ray single-crystal analysis of 1 and the oxidation product 7. The absolute configurations of the microsphaeropsones A-C (1-3) were established by comparison of the electronic and vibrational circular dichroism (ECD and VCD) spectra of 1 with time-dependent DFT (TDDFT) and DFT calculations by using either the solid-state structures or DFT-optimized geometries as inputs. Preliminary studies indicated that 1, 2, and enone 7 showed antibacterial, fungicidal, and algicidal properties.

Oxepinochromenones, Furochromenone, and their Putative Precursors from the Endolichenic Fungus Coniochaeta sp.

“…Brocaenol A (7): 1 H, 13 C NMR and the MS data were consistent with literature values. 11 Microxanthone (8): 1 H, 13 C NMR and the MS data were consistent with literature values.…”

“…11 Microxanthone (8): 1 H, 13 C NMR and the MS data were consistent with literature values. 13 Moniliphenone (9): 1 H, 13 C NMR and the MS data were consistent with literature values. 19 Isosulochrin (10): 1 H, 13 C NMR and the MS data were consistent with literature values.…”

“…The 1 H and 13 C NMR spectra of 6 displayed resonances for the same xanthone skeleton as found in 8, 13 which was co-isolated in the current work. Comparison of the NMR data of 6 and 8 indicated that 6 differs from 8 by having different substituents at C-3, C-5, and C-6, respectively.…”

“…Analysis of its 1 H, 13 C, and HMQC NMR data (Table 1) revealed two exchangeable protons (δ H 4.30 and 12.19, respectively), two methyl groups including one O-methyl, two methines including one oxymethine, 10 olefinic/aromatic carbons (four of which are protonated), one carboxylic carbon (δ C 172.5), and one R, -unsaturated ketone carbon (δ C 182.3). The 1 H-1 H COSY NMR data showed the isolated spin-system of C-5-C-8 (including OH-7).…”

“…Conioxepinol Table 1; HMBC correlations (CDCl 3 , 400 MHz) H-2 f C-1, 4, 9a, 11; H-4 f C-2, 4a, 9a, 11; H-5 f C-6, 7, 10a, 12; H-6 f C-7, 10a; H-7 f C-5, 6, 8; H 3 -11 f C-2, 3, 4; H 3 -13 f C-12; OH-1 f C-1, 2, 3, 9a; HRESIMS m/z 357.0584 (calcd for C 16 13 C NMR (DMSO-d 6 , 100 MHz) δ 179.1 (C, C-9), 168.4 (C, C-12), 164.8 (C, C-6), 160.6 (C, C-1), 157.8 (C, C-10a), 155.3 (C, C-4a), 153.5 (C, C-3), 135.0 (C, C-8), 113.1 (CH, C-7), 108.8 (C, C-8a), 107.6 (CH, C-2), 106.4 (C, C-9a), 103.9 (CH, C-4), 103.3 (CH, C-5), 62.3 (CH 2 , C-11), 52.7 (CH 3 , C-13); HMBC data (DMSO-d 6 , 400 MHz) H-2 f C-1, 4, 9, 9a, 11; H-4 f C-2, 3, 9, 9a, 11; H-5 f C-6, 7, 8a, 9, 10a; H-7 f C-5, 6, 8a, 12; H 2 -11 f C-2, 3, 4; H 3 -13 f C-12; OH-1 f C-1, 2, 9a; HRESIMS m/z 339.0477 (calcd for C 16 H 12 O 7 Na, 339.0475).…”