Phomopsidone A, a novel depsidone metabolite from the mangrove endophytic fungus Phomopsis sp. A123
Graphical abstract
Introduction
A great number of compounds with novel structures and diverse bioactivities have been isolated and identified from marine-derived endophytic fungi in the past decades [1], [2]. During our ongoing search for chemical constituents produced by mangrove endophytic fungi, a novel pentacyclic depsidone, phomopsidone A (1), together with the known depsidone compound excelsione (2) [3] (i.e. phomopsidone [4]), and four known isobenzofuranones including 7-methoxy-6-methyl-3-oxo-1,3-dihydroisobenzofuran-4-carboxylic acid (3) [5], diaporthelactone (4) [6], 7-hydroxy-4,6-dimethy-3H-isobenzofuran-1-one (5) [7], and 7-methoxy-4,6-dimethyl-3H-isobenzofuran-1-one (6) [8] were obtained from the metabolites of the mangrove endophytic fungal strain Phomopsis sp. A123.
Phomopsis sp. A123 was isolated from the foliage of mangrove plant Kandelia candel (L.) Druce in 2003, which was previously known as the producer of cytotoxic deacetylmycoepoxydiene and mycoepoxydiene [9], [10]. Herein, we report the isolation and structural elucidation of phomopsidoneA (1). The cytotoxic activity, radical-scavenging activity against 2,2-diphenyl-1-picrylhydrazinyl (DPPH), and antimicrobial activity of compounds 1–6 were also described.
Section snippets
General procedures
UV spectra were recorded by UNICO single-beam 210A spectral photometer. The IR spectra were measured in KBr on a Nicolet FT-IR 360. NMR spectra were taken by a Bruker Avance III-600 NMR spectrometer with TMS as an internal standard, δ in ppm relative to Me4Si, and J in Hz. HRESI-MS data were acquired using BioTOFTM-Q mass spectrometer (Bruker). Column chromatography was performed with silica gel (200–300 mesh, Qingdao Marine Chemical, Inc., Qingdao, China), silica gel GF254 (Merck), Sephadex
Structure elucidation
Compound 1 was isolated as white powder. The molecular formula was determined to be C18H12O7 by HRESI-MS based on the protonated molecular ion ([M + H]+) at m/z 341.0630 (calc. 341.0656 for [C18H12O7 + H]+), indicating twelve degrees° of unsaturation. The detailed analysis of 1H and 13C NMR spectra clearly indicated the presence of a penta-substituted phenyl moiety. DEPT analysis indicated that compound 1 contains two methyl groups (δC 22.8, q; and 12.1, q). The down field chemical shift of C-8 (δC
Conclusion
During our continuing search for bioactive natural products from marine-derived endophytic fungi, a novel depsidone, phomopsidone A (1), together with excelsione (2) [3] (i.e. phomopsidone[4]), and four known isobenzofuranones (3–6) were isolated from the mangrove endophytic fungus Phomopsissp. A123. The bioactivity assays demonstrated that these compounds possess cytotoxic, antioxidant, and antifungal activities.
Structurally, phomopsidone A (1) belongs to depsidones, a group of secondary
Acknowledgment
This work was supported by the NSFC grants 90913024 and 31300075.
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These authors contributed equally.