Alternaria is a cosmopolitan fungal genus widely distributing in soil and organic matter. It includes saprophytic, endophytic and pathogenic species. At least 268 metabolites from Alternaria fungi have been reported in the past few decades. They mainly include nitrogen-containing metabolites, steroids, terpenoids, pyranones, quinones, and phenolics. This review aims to briefly summarize the structurally different metabolites produced by Alternaria fungi, as well as their occurrences, biological activities and functions. Some considerations related to synthesis, biosynthesis, production and applications of the metabolites from Alternaria fungi are also discussed.

Natural dibenzo-α-pyrones are an important group of metabolites derived from fungi, mycobionts, plants and animal feces. They exhibit a variety of biological activities such as toxicity on human and animals, phytotoxicity as well as cytotoxic, antioxidant, antiallergic, antimicrobial, antinematodal, and acetylcholinesterase inhibitory properties. Dibenzo-α-pyrones are biosynthesized via the polyketide pathway in microorganisms or metabolized from plant-derived ellagitannins and ellagic acid by intestinal bacteria. At least 53 dibenzo-α-pyrones have been reported in the past few decades. This mini-review aims to briefly summarize the occurrence, biosynthesis, biotransformation, as well as their biological activities and functions. Some considerations related to synthesis, production and applications of dibenzo-α-pyrones are also discussed.

The EtOAc extract of the liquid fermentation of Alternaria sp. Samif01, an endophytic fungus obtained from Salvia miltiorrhiza Bunge, showed antibacterial activity against several tested bacterial pathogens. Fractionation of this extract led to the isolation of seven dibenzo-α-pyrones (1-7), including one new compound, 2-acetoxy-2-epi-altenuene (1) and one new natural product, 3-epi-dihydroaltenuene A (2). 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 1 was determined by TDDFT-ECD computation. Altenuisol (5), 4-hydroxyalternariol-9-methyl ether (6), and alternariol (7) 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 2, 5 and 6 displayed promising antioxidant effects using DPPH and hydroxyl radical assays. The cytotoxicity of the isolated compounds was evaluated as well.

One bioactive compound, identified as alternariol 9-methyl ether, was isolated from the crude extract of the endophytic fungus Alternaria sp. Samif01 residing in the roots of Salvia miltiorrhiza Bunge. Alternariol 9-methyl ether was active against bacteria with minimum inhibitory concentration values ranging from 25 to 75 μg/mL and median inhibitory concentration (IC50) values ranging from 16.00 to 38.27 μg/mL. The IC50 value of alternariol 9-methyl ether against spore germination of Magnaporthe oryzae was 87.18 μg/mL. Alternariol 9-methyl ether also showed antinematodal activity against Bursaphelenchus xylophilus and Caenorhabditis elegans with IC50 values of 98.17 μg/mL and 74.62 μg/mL, respectively. This work is the first report on alternariol 9-methyl ether and its biological activities from the endophytic fungus Alternaria sp. Samif01 derived from S. miltiorrhiza Bunge. The results indicate the potential of Alternaria sp. Samif01 as a source of alternariol 9-methyl ether and also support that alternariol 9-methyl ether is a natural compound with high potential bioactivity against microorganisms.

A total of 57 endophytic fungal isolates were obtained from the roots of Salvia miltiorrhiza Bunge (Lamiaceae). Fourteen (14) distinct isolates were selected for further taxonomical identification by morphological traits and internal transcribed spacer (ITS) rRNA gene sequence analysis. Twelve (12) genera were identified among which Alternaria and Fusarium were dominants. Eight endophytic fungi (that is, Pleosporales sp. Samif02, Leptosphaeria sp. Samif03, Peyronellaea glomerata Samif04, Xylomelasma sp. Samif07, Bionectria ochroleuca Samif08, Sarocladium kiliense Samif11, Petriella setifera Samif13 and Cadophora sp. Samif14) were separated as the endophytic fungi from S. miltiorrhiza for the first time. Most of the fungal isolates were observed to have antibacterial activity that suggests antibacterial compounds mainly exist in mycelia. The ethyl acetate extracts of Alternaria sp. Samif01, Xylomelasma sp. Samif07, Fusarium redolens Samif09, Sarocladium kiliense Samif11 and Petriella setifera Samif13 were also observed to have antifungal activity. Among the isolates, Alternaria sp. Samif01 and Sarocladium kiliense Samif11 were found to have strong antibacterial and antifungal activities. The results indicate that there is a diversity of the endophytic fungi from S. miltiorrhiza, and these endophytic fungi could be an excellent resource for searching natural antimicrobial compounds.