Recent Advances in Isolation, Synthesis and Biological Evaluation of Terrein

Phytotoxic and Antimicrobial Terrein Derivatives and Butenolides Isolated from the Endophytic Fungus Aspergillus terreus HT5

Two new terrein derivatives, aspergilethers A and B (1 and 2), two known analogues (3 and 4), and three known butenolides (5-7) were isolated from the endophyte Aspergillus terreus HT5. Their structures were determined by spectroscopic analysis and ECD and NMR calculations. Interestingly, 1 and 2 had unpresented medium aliphatic side chains in terrein derivatives, with different absolute configurations at C-7, which was very scarce. (+)-Terrein (3) exhibited potent postemergence phytotoxicity toward Amaranthaceae, Portulacaceae, and Fabaceae, with MIC values of 250-1000 μg/mL. Transcriptome analysis and qRT-PCR suggested that (+)-terrein induced the transcriptional expression of aging-related genes to accelerate organ senescence and stimulated plant detoxification response. The conjugated system between keto carbonyl and double bonds in the cyclopentenone ring and side chain, and the configurations of C-2 and C-3, played critical roles in the phytotoxicity of terrein derivatives. Meanwhile, 3 was first reported to display moderate antioomycetes activity toward Phytophthora nicotiana.

Secondary metabolites from Aspergillus terreus F6-3, a marine fungus associated with Johnius belengerii

Two new terrein derivatives asperterreinones A-B (1-2), one new octahydrocoumarin derivative (±)-asperterreinin A (6), along with seventeen known compounds, were isolated from Aspergillus terreus F6-3, a marine fungus associated with Johnius belengerii. The structures of 1, 2, and 6 were established on the basis of 1D and 2D NMR, mass spectroscopy, comparative electronic circular dichroism (ECD) spectra analysis, density functional theory calculation of 13C NMR, and DP4+ probability analysis. Among all the isolates, eurylene (7), a constituent of the Malaysian medicinal plant Eurycoma longifolia, was obtained from a microbial source for first time. In the in vitro bioassay, 11 and 13 showed potent inhibitory activity against the Escherichia coli β-glucuronidase (EcGUS) with IC50 values of 27.75 ± 0.73 and 17.73 ± 0.81 μM, respectively. It was the first time that questinol (11) and (±)-aspertertone B (13) were reported as potent EcGUS inhibitors.

Photoclick reaction for rapid and simple fluorescence detection of itaconic acid and its derivatives in fungal cultures

Itaconic acid (IA) and its derivatives produced by fungi have significant potential as industrial feedstocks. We recently developed a method for the detection of these compounds based on their terminal C-C double bonds. However, the presence of reducing agents, such as glucose and other fungal metabolites, leads to undesirable side reactions, and consequently, deteriorates the detection specificity. Therefore, we developed a fluorescence detection method for IA and its derivatives underpinned by a photoclick reaction. The photoclick reaction between conjugated IA and 5-(4-methoxyphenyl)-2-phenyl-2H-tetrazole under UV irradiation affords a fluorescent product. No fluorescence was detected when succinic acid was subjected to the reaction, indicating that a terminal C-C double bond is required to induce fluorescence. Optimal reaction conditions were determined to be a combination of 80% final dimethyl sulfoxide concentration, 30-s UV irradiation, and a pH of 2. Two weeks after the reaction at 4 °C, 89.0% of the initial intensity was retained, indicating that the reaction product was relatively stable. Glucose and kojic acid did not induce fluorescence after the reaction, indicating that these reducing agents did not affect fluorescence. IA was detected in a culture of Aspergillus terreus, and its quantification using the photoclick reaction was in agreement with the results obtained using high-performance liquid chromatography analysis. Interestingly, the IA derivative avenaciolide present in submillimolar quantities was also detectable in a culture of Aspergillus avenaceus using this method. The established method will enable the development of high-throughput screening methods to identify fungi that produce IA and its derivatives.

A Focused Review of the Pharmacological Potentials of Terrein as an Anticancer Agent

Terrein is one of the most important biomolecules of fungal origin being studied from a medicinal perspective. Secondary metabolites are the intermediate products produced during the metabolism of organisms for a large number of functions, for example, defense and communication signals. From the outset, terrein has largely been studied as an anticancer secondary biomolecule. Aspergillus terreus is the only fungal source of some valuable drugs and mycotoxins. From the beginning, a few species of Aspergillus were known to be viable chemical factories. Terrein is a potent biological molecule present in the fungus that is responsible for its medicinal and agricultural values. Numerous evaluations conducted on terrein showed it to have marked biological activities (antimicrobial, antiproliferative, anti-oxidative, and others). To date, terrein has emerged as a very attractive therapeutic regimen against cancer due to its dual targeting nature; tumor angiogenesis and cell proliferation. This focused review provides details of the therapeutic value of terrein and its modes of action as an anticancer agent. Besides this, terrein has other marked bioactivities and manifold uses in the field of medicine, which have also been discussed here.

Aspergillus co-cultures: A recent insight into their secondary metabolites and microbial interactions

There is an urgent need for novel antibiotics to combat emerging resistant microbial strains. One of the most pressing resources is Aspergillus microbial cocultures. The genome of Aspergillus species comprises a far larger number of novel gene clusters than previously expected, and novel strategies and approaches are essential to exploit this potential source of new drugs and pharmacological agents. This is the first review consulting recent developments and chemical diversity of Aspergillus cocultures and highlighting its untapped richness. The analyzed data revealed that cocultivation of several Aspergillus species with other microorganisms, including bacteria, plants, and fungi, is a source of novel bioactive natural products. Various vital chemical skeleton leads were newly produced or augmented in Aspergillus cocultures, among which were taxol, cytochalasans, notamides, pentapeptides, silibinin, and allianthrones. The possibility of mycotoxin production or complete elimination in cocultivations was detected, which pave the way for better decontamination strategies. Most cocultures revealed a remarkable improvement in their antimicrobial or cytotoxic behavior due to their produced chemical patterns; for instance, weldone and asperterrin whose antitumor and antibacterial activities, respectively, were superior. Microbial cocultivation elicited the upregulation or production of specific metabolites whose importance and significance are yet to be revealed. With more than 155 compounds isolated from Aspergillus cocultures in the last 10 years, showing overproduction, reduction, or complete suppression under the optimized coculture circumstances, this study filled a gap for medicinal chemists searching for new lead sources or bioactive molecules as anticancer agents or antimicrobials.

Reactive Azlactone Intermediate Drives Fungal Secondary Metabolite Cross-Pathway Generation

Pathogenic fungi of Aspergillus section Fumigati are known to produce various secondary metabolites. A reported isolation of a compound with an atypical carbon skeleton called fumimycin from A. fumisynnematus prompted us to examine a related fungus, A. lentulus, for production of similar products. Here we report the isolation of fumimycin and a related new racemic compound we named lentofuranine. Detailed analyses revealed that both compounds were assembled by a nonenzymatic condensation of a polyketide intermediate from the terrein biosynthetic pathway and a highly reactive azlactone intermediate produced by an unrelated nonribosomal peptide synthetase carrying a terminal condensation-like domain. While highly reactive azlactone is commonly used in chemical synthesis, its production by a conventional non-metalloenzyme and employment as a biosynthetic pathway intermediate is unprecedented. The observed unusual carbon skeleton formation is likely due to the reactivity of azlactone. Our finding provides another example of a chemical principle being aptly exploited by a biological system.