James B. Gloer

Isolation, Structure Elucidation, and Biomimetic Total Synthesis of Versicolamide B, and the Isolation of Antipodal (−)-Stephacidin A and (+)-Notoamide B from Aspergillus versicolor NRRL 35600†

Prenylated indole alkaloids containing, the bicyclo[2.2.2]diazaoctane ring system as a structural core, now number more than thirty-eight family members. These natural substances, produced by various genera of fungi, in particular Aspergillus sp. and Penicillium spp., among others, exhibit a range of interesting structural and stereochemical features. Significantly, a myriad of biological activities are displayed by members of this family including insecticidal, anti-tumor, anthelmintic, calmodulin inhibitory, and anti-bacterial activities. Structurally, these substances arise from the oxidative condensation of one or two isoprene units, tryptophan and another cyclic amino acid residue, such as proline, β-methylproline or pipecolic acid. With respect to the relative stereochemistry within the core bicyclo[2.2.2]diazaoctane ring system, all of the known members of the paraherquamides (e.g., 1, 2)/stephacidins (e.g., 3, 4)/asperparalines and notoamides (e.g., 5, 6) have been shown to possess the syn-stereochemistry, while only the brevianamides (9, 10) have been shown to possess the anti-relative configuration (Schemes 1 and ​and2).2). The syn-/anti-relationship refers to the relative stereochemistry between the C-19 stereogenic center (sclerotiamide numbering) and the cyclic amino acid residue (proline, β-methylproline, or pipecolic acid; Scheme 2). This reveals that in the oxidative cyclization process(es) to construct this core ring system biosynthetically, both faces of the isoprene-derived dienophile participate in the ring-forming process. However, until now, this stereochemical divergence was cleanly separated between the brevianamides and all other members of this growing family of natural products. Herein, we describe the isolation, structure elucidation, and confirmatory biomimetic total synthesis of the first member of the paraherquamide-stephacidin family to possess the rare anti-relative stereochemistry within the bicyclo[2.2.2]diazaoctane ring system. We propose the new name versicolamide B for this natural product (8), a minor metabolite of Aspergillus versicolor NRRL 35600, Based on CD spectra, we have assigned the absolute configuration to this compound, and have concluded that it possesses the ent-configuration with respect to the bicyclo[2.2.2]diazaoctane core. Surprisingly and as striking, we have also isolated (−)-stephacidin A and (+)-notoamide B from Aspergillus versicolor NRRL 35600 and conclude that these substances are produced as the corresponding antipodes to the structures that have been previously described for these natural products. The provocative biogenetic implications of these stereochemical findings are discussed herein.

A protective endophyte of maize: Acremonium zeae antibiotics inhibitory to Aspergillus flavus and Fusarium verticillioides

The maize endophyte Acremonium zeae is antagonistic to kernel rotting and mycotoxin producing fungi Aspergillus flavus and Fusarium verticillioides in cultural tests for antagonism, and interferes with A. flavus infection and aflatoxin contamination of preharvest maize kernels. Chemical studies of an organic extract from maize kernel fermentations of Acremonium zeae (NRRL 13540), which displayed significant antifungal activity against Aspergillus flavus and F. verticillioides, revealed that the metabolites accounting for this activity were two newly reported antibiotics pyrrocidines A and B. Pyrrocidines were detected in fermentation extracts for 12 NRRL cultures of Acremonium zeae isolated from maize kernels harvested in Illinois (4/4 cultures), North Carolina (5/5), Georgia (1/2) and unrecorded locations within the USA (2/2). Pyrrocidine B was detected by LCMSMS in whole symptomatic maize kernels removed at harvest from ears of a commercial hybrid that were wound-inoculated in the milk stage with A. zeae (NRRL 13540) or (NRRL 13541). The pyrrocidines were first reported from the fermentation broth of an unidentified filamentous fungus LL-Cyan426, isolated from a mixed Douglas Fir hardwood forest on Crane Island Preserve, Washington, in 1993. Pyrrocidine A exhibited potent activity against most Gram-positive bacteria, including drug-resistant strains, and was also active against the yeast Candida albicans. In an evaluation of cultural antagonism between 13 isolates of A. zeae in pairings with A. flavus (NRRL 6541) and F. verticillioides (NRRL 25457), A. zeae (NRRL 6415) and (NRRL 34556) produced the strongest reaction, inhibiting both organisms at a distance while continuing to grow through the resulting clear zone at an unchanged rate. Maximum colony diameters for A. zeae (NRRL 6415) and (NRRL 13540), on potato dextrose agar after 14 d, were attained within the range of 25-30 degrees C, with less growth recorded at 15 degrees and 37.5 degrees and no growth at 5 degrees. Potential interactions between A. zeae and other maize endophytes are considered and the significance of these interactions relative to the aflatoxin and fumonisin contamination of preharvest maize is presented. This is the first report of natural products from Acremonium zeae.

Halogenated Organic Molecules of Rhodomelaceae Origin: Chemistry and Biology

Natural Science Foundation of China [30530080]; Ministry of Science and Technology of China [2007AA09Z403]; Department of Science and Technology of Shandong Province [2006GG2205023]

ANTIINSECTAN ALKALOIDS : SHEARININES A-C AND A NEW PAXILLINE DERIVATIVE FROM THE ASCOSTROMATA OF EUPENICILLIUM SHEARII

Abstract Four new antiinsectan indole alkaloids ( 1–4 ) have been isolated from organic extracts of the sclerotioid ascostromata of Eupenicillium shearii (NRRL 3324). These extracts also afforded five known, related metabolites ( 5–9 ). The structures of the new compounds were determined through analysis of 1 H NMR, 13 C NMR, HMQC, and HMBC experiments. Compounds 1–9 were isolated from fractions displaying activity in dietary assays against the corn earworm Helicoverpa zea and the dried-fruit beetle Carpophilus hemipterus , and most of the compounds show potent activity in these assays. Shearinine A ( 1 ) also exhibited activity in a topical assay against H. zea , and shearinine B ( 2 ) caused significant mortality in a leaf disk assay against the fall armyworm Spodoptera frugiperda .

Biological Activity of Peanut (Arachis hypogaea) Phytoalexins and Selected Natural and Synthetic Stilbenoids

The peanut plant (Arachis hypogaea L.), when infected by a microbial pathogen, is capable of producing stilbene-derived compounds that are considered antifungal phytoalexins. In addition, the potential health benefits of other stilbenoids from peanuts, including resveratrol and pterostilbene, have been acknowledged by several investigators. Despite considerable progress in peanut research, relatively little is known about the biological activity of the stilbenoid phytoalexins. This study investigated the activities of some of these compounds in a broad spectrum of biological assays. Since peanut stilbenoids appear to play roles in plant defense mechanisms, they were evaluated for their effects on economically important plant pathogenic fungi of the genera Colletotrichum, Botrytis, Fusarium, and Phomopsis. We further investigated these peanut phytoalexins, together with some related natural and synthetic stilbenoids (a total of 24 compounds) in a panel of bioassays to determine their anti-inflammatory, cytotoxic, and antioxidant activities in mammalian cells. Several of these compounds were also evaluated as mammalian opioid receptor competitive antagonists. Assays for adult mosquito and larvae toxicity were also performed. The results of these studies reveal that peanut stilbenoids, as well as related natural and synthetic stilbene derivatives, display a diverse range of biological activities.

Sclerotial metabolites of Aspergillus Flavus toxic to a detritivorous maize insect (Carpophilus Hemipterus, Nitidulidae)

The fungal sclerotium represents an important survival structure in the life cycle of many fungi, including Aspergillus flavus . Purified sclerotial metabolites from a non-aflatoxigenic strain of A. flavus (NRRL 6541) showed substantial antifeedant activity against Carpophilus hemipterus (Nitidulidae). This insect is known to encounter A. flavus sclerotia that form naturally in both standing and downed maize ears. The most abundant active component was dihydroxyaflavinine, but one novel analogue of dihydroxyaflavinine and a third unrelated metabolite, compound ‘1’ were also found to deter Carpophilus feeding when incorporated into a pinto bean diet at 100 p.p.m. d.w. Naturally occurring levels of each of these metabolites were found to be higher than 100 p.p.m. in A. flavus sclerotia. Arthropod predation is recognized as a selective force that has shaped the chemical defence systems of A. flavus and other sclerotium-producing fungi.

Chaetochalasin A: A New Bioactive Metabolite from Chaetomium Brasiliense

Abstract Chaetochalasin A ( 1 ), a new bioactive fungal metabolite with a previously undescribed ring system, has been isolated from an EtOAc extract of Chaetomium brasiliense (NRRL 22999). The structure of 1 was determined by NMR experiments and single-crystal X-ray diffraction analysis.

Product-to-Parent Reversion of Trenbolone: Unrecognized Risks for Endocrine Disruption

Return of the Steroid Trace levels of organic contaminants enter aquatic ecosystems from a variety of sources, including runoff of from agricultural lands. When these compounds and their metabolites break down, it is generally assumed that they become inert and pose less ecological risk. Qu et al. (p. 347, published online 26 September) tracked the sunlight-mediated transformation of metabolites of trenbolone acetate (TBA)—a common growth-promoting steroid given to beef cattle—across a number of conditions in the laboratory and in the field. When the degradation products were exposed to dark conditions following photodegradation, they surprisingly reverted back to TBA metabolites, including analog steroidal compounds similar to TBA with unknown biological effects. Phototransformation of growth steroid metabolites is readily reversible in aquatic environments. Trenbolone acetate (TBA) is a high-value steroidal growth promoter often administered to beef cattle, whose metabolites are potent endocrine-disrupting compounds. We performed laboratory and field phototransformation experiments to assess the fate of TBA metabolites and their photoproducts. Unexpectedly, we observed that the rapid photohydration of TBA metabolites is reversible under conditions representative of those in surface waters (pH 7, 25°C). This product-to-parent reversion mechanism results in diurnal cycling and substantial regeneration of TBA metabolites at rates that are strongly temperature- and pH-dependent. Photoproducts can also react to produce structural analogs of TBA metabolites. These reactions also occur in structurally similar steroids, including human pharmaceuticals, which suggests that predictive fate models and regulatory risk assessment paradigms must account for transformation products of high-risk environmental contaminants such as endocrine-disrupting steroids.

New Stilbenoids from Peanut (Arachis hypogaea) Seeds Challenged by an Aspergillus caelatus Strain

Four new stilbene derivatives, termed arahypins, have been isolated from peanut seeds challenged by an Aspergillus caelatus strain, along with two known stilbenoids that have not been previously reported in peanuts. The structures of these new putative phytoalexins were determined by analysis of NMR, MS, and UV data. Together with other known peanut stilbenoids that were also produced in the challenged seeds, these new compounds may play a defensive role against invasive fungi.

Leporin A: an antiinsectan N-alkoxypyridone from the sclerotia of Aspergillus leporis

Abstract Leporin A (5), an antiinsectan N-methoxy-2-pyridone, was isolated from the sclerotia of Aspergillus leporis. The structure was determined through analysis of various 1D- and 2D-NMR experiments. Two previously reported aflavinine derivatives (3 and 4) were also isolated from this source.