Dibenzofurans from Lichens - A Pharmacological Overview.

Lichens are a symbiotic association between a fungus (mycobiont) and a green algae/- cyanobacterium (photobiont). Lichens are a source of secondary metabolites, most of them being exclusively for these species, among which dibenzofurans are found. Dibenzofurans are a small group (over 35 different identified compounds), being usnic acid the most studied. In the last 10 years, there has been a growing interest in the pharmacological activity of dibenzofurans. In this work, dibenzofurans isolated from lichens (alectosarmentin, condidymic acid, didymic acid, isousnic acid, isostrepsilic acid, usimines A-C and usnic acid) were reviewed, most of which showed antibacterial, antifungal, and cytotoxic activities. These findings provide future guidance for research on pharmacological activity of dibenzofurans.

Novel dibenzofuran and biphenyl phytoalexins from Sorbus pohuashanensis suspension cell and their antimicrobial activities.

Two novel sulfur-containing dibenzofurans, sorbusins A (1) and B (2), two unprecedented biphenyl glycosides, 2'-hydroxyaucuparin 2'-O-ɑ-L-rhamnoside (3) and noraucuparin 5-O-ɑ-L-rhamnoside (4), and four known analogues (5-8), were isolated from Sorbus pohuashanensis suspension cell induced by yeast extract. Their structures were elucidated based on spectroscopic analyses and quantum calculation of 13C NMR data. Structurally, compound 1 possessed a rare naturally occurring benzothiazole moiety and represents the first example of thiazole fused dibenzofuran. A plausible biosynthetic pathway for the sulfur-containing dibenzofurans is proposed. These dibenzofuran and biphenyl phytoalexins were evaluated for their antimicrobial activities against pathogenic fungi and drug-resistant bacteria. Compound 7 exhibited significant antibacterial activity against methicinllin-resistant Staphylococcus aureus with an MIC value of 3.13 µg/mL.

Three new dibenzofurans from Cydonia oblonga Mill.

Phytochemical investigation of Cydonia oblonga Mill. collected in Xinjiang province, China, led to the isolation and identification of three new dibenzofurans (1-3) along with one known compound (4). Their structures were elucidated based on HRESIMS, spectroscopic data (IR, UV, 1D, 2D NMR) and X-ray diffraction analysis.

Phenylpropanoid and dibenzofuran derivatives from Crataegus pinnatifida with antiproliferative activities on hepatoma cells.

Eleven aromatic compounds, including four pairs of undescribed phenylpropanoids and two undescribed dibenzofurans (1a/1b-4a/4b and 5-6), were isolated from the fruits of C. pinnatifida. Their structures were established by extensive spectroscopic analyses. Their relative and absolute configurations were determined by the assistance of quantum chemical calculations of NMR chemical shifts and electronic circular dichroism (ECD). All isolates were screened for the cytotoxicity against two human hepatoma cell lines, HepG2 and Hep3B. It was found that compound 7 exhibited noticeable cytotoxicity against both cells with the IC50 values of 12.24 (HepG2) and 24.90 (Hep3B) µM. Further Annexin VFITC/ PI staining assay suggested that 7 could induce apoptosis in a concentration-dependent manner to exert antiproliferative activities on hepatoma cells.

Dibenzofurans and Pseudodepsidones from the Lichen Stereocaulon paschale Collected in Northern Quebec.

Chemical investigation of the methanol extract of the lichen Stereocaulon paschale collected in Nunavik, Canada, led to the isolation and identification of two new dibenzofurans (1 and 3) and 11 known lichen metabolites. The structures of the new compounds were established by analysis of 1D and 2D NMR spectroscopic and high-resolution mass spectrometric data. Herein, the first isolation of ascomatic acid dibenzofuran derivatives (1-3) from a whole lichen organism is reported. In addition, some of the isolated metabolites showed antibacterial activity against the oral pathogens Porphyromonas gingivalis and Streptococcus mutans.

Dibenzofurans and derivatives from lichens and ascomycetes.

Covering: up to 2016.When looking for dibenzofuran in the biochemical databases, most papers and reviews deal with pollutants and polychlorinated dibenzofurans like dioxins. But dibenzofurans are also biosynthetized by a wide diversity of organisms in nature. Even if dibenzofurans from natural sources represent a small class of secondary metabolites, compared to flavonoids, xanthones or terpenoids, they are often endowed with interesting biological properties which have been recently described. This review provides an update on papers describing dibenzofurans from lichens, ascomycetes and cultured mycobionts. Other sources, such as basidiomycetes, myxomycetes or plants produce sporadically interesting dibenzofurans in terms of structures and activities.