1,3-Cyclohexadien-1-Als: Synthesis, Reactivity and Bioactivities

In synthetic organic chemistry, there are very useful basic compounds known as building blocks. One of the main reactions wherein they are applied for the synthesis of complex molecules is the Diels-Alder cycloaddition. This reaction is between a diene and a dienophile. Among the most important dienes are the cyclic dienes, as they facilitate the reaction. This review considers the synthesis and reactivity of one of these dienes with special characteristics-it is cyclic and has an electron withdrawing group. This building block has been used for the synthesis of biologically active compounds and is present in natural compounds with interesting properties.

Fungal Diversity in Intertidal Mudflats and Abandoned Solar Salterns as a Source for Biological Resources

Intertidal zones are unique environments that are known to be ecological hot spots. In this study, sediments were collected from mudflats and decommissioned salterns on three islands in the Yellow Sea of South Korea. The diversity analysis targeted both isolates and unculturable fungi via Illumina sequencing, and the natural recovery of the abandoned salterns was assessed. The phylogeny and bioactivities of the fungal isolates were investigated. The community analysis showed that the abandoned saltern in Yongyudo has not recovered to a mudflat, while the other salterns have almost recovered. The results suggested that a period of more than 35 years may be required to return abandoned salterns to mudflats via natural restoration. Gigasporales sp. and Umbelopsis sp. were selected as the indicators of mudflats. Among the 53 isolates, 18 appeared to be candidate novel species, and 28 exhibited bioactivity. Phoma sp., Cladosporium sphaerospermum, Penicillium sp. and Pseudeurotium bakeri, and Aspergillus urmiensis showed antioxidant, tyrosinase inhibition, antifungal, and quorum-sensing inhibition activities, respectively, which has not been reported previously. This study provides reliable fungal diversity information for mudflats and abandoned salterns and shows that they are highly valuable for bioprospecting not only for novel microorganisms but also for novel bioactive compounds.

Safety of the fungal workhorses of industrial biotechnology: update on the mycotoxin and secondary metabolite potential of Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei

This review presents an update on the current knowledge of the secondary metabolite potential of the major fungal species used in industrial biotechnology, i.e., Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei. These species have a long history of safe use for enzyme production. Like most microorganisms that exist in a challenging environment in nature, these fungi can produce a large variety and number of secondary metabolites. Many of these compounds present several properties that make them attractive for different industrial and medical applications. A description of all known secondary metabolites produced by these species is presented here. Mycotoxins are a very limited group of secondary metabolites that can be produced by fungi and that pose health hazards in humans and other vertebrates when ingested in small amounts. Some mycotoxins are species-specific. Here, we present scientific basis for (1) the definition of mycotoxins including an update on their toxicity and (2) the clarity on misclassification of species and their mycotoxin potential reported in literature, e.g., A. oryzae has been wrongly reported as an aflatoxin producer, due to misclassification of Aspergillus flavus strains. It is therefore of paramount importance to accurately describe the mycotoxins that can potentially be produced by a fungal species that is to be used as a production organism and to ensure that production strains are not capable of producing mycotoxins during enzyme production. This review is intended as a reference paper for authorities, companies, and researchers dealing with secondary metabolite assessment, risk evaluation for food or feed enzyme production, or considerations on the use of these species as production hosts.

Antimycobacterial Natural Products from Endophytes of the Medicinal Plant Aralia nudicaulis

Antimycobacterial extracts of a Penicillium sp. (isolate HL4-159-41B) and a Coniothyrium sp. (isolate HL6-097-027B) isolated from the rhizomes of the Canadian medicinal plant Aralia nudicaulis were found to contain palitantin (1) and botrallin (2), craterellin C (3), mycosporulone (4), spiromassaritone (5), and massarigenin D (6) respectively. Bioassays against Mycobacterium tuberculosis H37Ra revealed that 1-4 possess moderate antimycobacterial activity.

Organocatalytic asymmetric robinson annulation of alpha,beta-unsaturated aldehydes: applications to the total synthesis of (+)-palitantin

The highly enantioselective organocatalytic Robinson annulation of alpha,beta-unsaturated aldehydes was achieved, catalyzed by l-proline and trialkylamines and providing the formal [4 + 2] cycloaddition adducts. Additionally, in some examples in the catalysis with diarylpyrrolinol silyl ethers, the reactions afforded the [4 + 2] adducts with high enantioselectivity (>99.5% ee). The structure of the adduct, obtained from the reaction of 3-methylbut-2-enal and (E)-3-(2-nitrophenyl)acrylaldehyde, was confirmed by X-ray analysis. The absolute configurations of some [4 + 2] cycloadducts were investigated, and the methodology was applied in the synthesis of (+)-palitantin.

Production and fungitoxic activity of Sch 642305, a secondary metabolite of Penicillium canescens

Production of fungitoxic extrolites was evaluated in culture filtrates of several isolates belonging to Penicillium canescens and P. janczewskii that showed some extent of inhibitory activity against the plant pathogenic fungus Rhizoctonia solani. In addition to griseofulvin and dechlorogriseofulvin that are already known in these species, curvulinic acid, previously unreported in Penicillium, was produced by all isolates assayed. Another extrolite recently characterized from a P. verrucosum strain by the name of Sch 642305 was detected in 5 isolates of P. canescens only. The purified compound completely inhibited mycelial growth of isolates of Rhizoctonia solani and other plant pathogenic fungi in vitro. The role of this extrolite as a possible biochemical determinant of antagonism toward plant pathogenic fungi, and implications concerning chemotaxonomy are discussed.

Chemical response of Picea glehnii seed-epiphytic Penicillium species to Pythium vexans under in vitro competitive conditions for mycelial growth

The potential protection of Picea glehnii seedlings from damping-off by seed-epiphytic Penicillium species was investigated. We studied the chemical response of seed-epiphytic Penicillium species (Pen. cyaneum, Pen. damascenum, and Pen. implicatum) to Pythium vexans, a damping-off fungus, in vitro. Penicillium species were cultured singly or cocultured with Pyt. vexans for 14 or 18 d, and mycelial growth, pH of culture filtrate, antifungal activity of the culture filtrate against Pyt. vexans, and the amount of antifungal compound produced by each Penicillium species, were examined. The filtrate of both the single culture of Penicillium and the coculture of Penicillium and Pyt. vexans showed antifungal activity against Pyt. vexans. In a coculture with Pyt. vexans, Pen. cyaneum produced an antifungal compound (patulin) as in the single culture. Pen. damascenum cocultured with Pyt. vexans produced an antifungal compound (citrinin), as it did in the single culture and in larger amounts on day 10. Pen. implicatum produced two antifungal compounds, frequentin and palitantin, and the ratio of frequentin (with higher antifungal activity than palitantin) to palitantin was higher in the coculture with Pyt. vexans than in the single culture. Our results indicate that these Penicillium species have the ability to produce antifungal compounds and to keep anti-fungal activity under competitive condition with Pyt. vexans. The chemical response of these Penicillium species to Pyt. vexans may contribute to protect P. glehnii seedlings from damage by Pyt. vexans.

Organic acids and water-soluble phenolics produced by Paxillus sp. 60/92 together show antifungal activity against Pythium vexans under acidic culture conditions

Ectomycorrhizal fungi can produce antifungal compounds in vitro as well as in symbiosis with the host plant that can reduce root diseases. The objective of this study was to isolate antifungal compounds from culture filtrate of Paxillus sp. 60/92, which can form mycorrhizas with Picea glehnii seedlings. Culture filtrate of Paxillus sp. 60/92 showed antifungal activity against Pythium vexans at pH 3-4 but not at pH 5-10, although sterile MMN-b liquid medium (pH 3-10) did not show antifungal activity. Upon separation of antifungal compounds in the culture filtrate, antifungal activity was detected in the organic acid and water-soluble phenolics fractions adjusted to pH 3. Although antifungal activity of individual fractions was lower than that of the culture filtrate, a mixture of these fractions showed antifungal activity similar to that of the culture filtrate. Furthermore, antifungal activity of oxalic acid, which is known to be produced by Paxillus involutus, was increased by mixing with the water-soluble phenolic fraction. Our findings indicate that Paxillus sp. 60/92 produces organic acids and water-soluble phenolics that together show antifungal activity at pH 3-4 against P. vexans.

Screening for microtubule-disrupting antifungal agents by using a mitotic-arrest mutant of Aspergillus nidulans and novel action of phenylalanine derivatives accompanying tubulin loss

The microtubule, which is one of the major targets of anthelmintics, anticancer drugs, and fungicides, is composed mainly of alpha- and beta-tubulins. We focused on a unique characteristic of an Aspergillus nidulans benA33 mutant to screen for microtubule-disrupting antifungal agents. This mutant, which has a beta-tubulin with a mutation of a single amino acid, undergoes mitotic arrest due to the formation of hyperstable microtubules at 37 degrees C. The heat sensitivity of the mutant is remedied by some antimicrotubule agents. We found that an agar plate assay with the mutant was able to distinguish three types of microtubule inhibitors. The growth recovery zones of the mutant were formed around paper disks containing microtubule inhibitors, including four benzimidazoles, ansamitocin P-3, griseofulvin, and rhizoxin, on the agar plate at 37 degrees C. Nocodazole, thiabendazole, and griseofulvin reversed the mitotic arrest of the mutant and promoted its hyphal growth. Ansamitocin P-3 and rhizoxin showed growth recovery zones around the growth-inhibitory zones. Benomyl and carbendazim also reversed mitotic arrest but produced weaker growth recovery than the aforementioned drugs. Other microtubule inhibitors, such as colchicine, Colcemid, paclitaxel, podophyllotoxin, TN-16, vinblastine, and vincristine, as well as some cytoskeletal inhibitors tested, did not show such activity. In our screening, we newly identified two mycotoxins, citrinin and patulin, two sesquiterpene dialdehydes, polygodial and warburganal, and four phenylalanine derivatives, arphamenine A, L-2,5-dihydrophenylalanine (DHPA), N-tosyl-L-phenylalanine chloromethylketone, and N-carbobenzoxy-L-phenylalanine chloromethyl ketone. In a wild-type strain of A. nidulans, DHPA caused selective losses of microtubules, as determined by fluorescence microscopy, and of both alpha- and beta-tubulins, as determined by Western blot analysis. This screening method involving the benA33 mutant of A. nidulans is useful, convenient, and highly selective. The phenylalanine derivatives tested are of a novel type of microtubule-disrupting antifungal agents, producing an accompanying loss of tubulins, and are different from well-known tubulin inhibitors affecting the assembly of tubulin dimers into microtubules.

Penicillium fungi from Picea glehnii seeds protect the seedlings from damping-off

•  In a coinoculation test of seed-epiphytic Penicillium species and pathogenic Pythium vexans to Picea glehnii seedlings, the number of surviving seedlings which were inoculated with P. vexans 5 d after preinoculation with Penicillium damascenum PGS-O7 increased compared with those inoculated with P. vexans alone. •  The phytotoxicity of antifungal compounds to P. glehnii seeds and seedlings was assessed in growth experiments. Production of these compounds was quantitatively analysed in the rhizosphere of the host seedlings using chromatography techniques. •  Dense mycelial growth of P. damascenum was observed microscopically around the roots of the inoculated seedlings. Furthermore, the antifungal and phytotoxic compound citrinin produced by P. damascenum was detected as a component released around the roots of the normally growing fungus-inoculated seedlings. •  We propose two possible mechanisms for the protection of P. glehnii seedlings by P. damascenum from P. vexans; first, chemical protection by an antibiotic agent, citrinin produced by P. damascenum, and second, the occupation of the space around the P. glehnii roots by the P. damascenum mycelia.