Fungi are well-known to produce a tremendous variety of bioactive secondary metabolites which play important roles as pharmaceuticals and agrochemicals. In contrast to random-screening approaches utilized in industry, our research applies ecology-based strategy to the selection of fungi for chemical studies. The research described here involves the chemical investigation of freshwater and fungicolous fungi as producers of novel metabolites with potential practical value. Freshwater fungi, as a distinctive ecological group, have only recently been studied in any depth, and remain underexplored in comparison with other fungal niche groups. Chemical studies of freshwater fungal isolates in our research group have led to the discovery of a variety of new bioactive metabolites, suggesting significant untapped potential among these organisms. Studies in this area described in this thesis led to the discovery of twenty-two new metabolites, many of which display significant antibacterial and/or antifungal activities. Some of these compounds possess novel structural features, such as new ring systems. Mycoparasitic and fungicolous fungi are those that colonize other fungi and could be viewed as potential producers of antifungal agents because of the negative effects they often exert on their hosts. Bioassay-guided fractionation of extracts from cultures of selected mycoparasitic and fungicolous fungal isolates afforded twenty-five new compounds representing diverse structural types. Most of these compounds display biological activity, with some showing antifungal and/or antiinsectan effects. The new secondary metabolites isolated during these studies represent a variety of different biosynthetic classes, including cyclic depsipeptides, nucleosides, polyketides, macrolides, terpenoids, and compounds with mixed biogenetic origin. Their structures were established by analysis of MS and NMR data, chemical degradation or derivatization reactions, and/or X-ray diffraction analysis data. Absolute configuration assignments were achieved by application of different strategies, such as Mosher's method, Marfey's method, or CD spectral analysis. Details of the isolation, structure elucidation, and biological activity of these new compounds are presented in this thesis.

Fungi have been an important source of many structurally diverse and biologically active secondary natural products. These secondary metabolites have found applications in pharmaceutical and agriculture industry. Fungi are estimated to be second only to insects in species diversity. It is estimated that there are at least 3.5 million species of fungi of which a less than 5% have so far been explored. Fungi are known to produce many secondary natural metabolites, however their role has still not been clearly understood. However it is possible that fungi which often thrive in competitive environments would experience evolutionary pressure to produce such metabolites for defensive or offensive functions. Our research focusses on isolation and structure elucidation of secondary metabolites from endophytic and mycoparasitic/fungicolous fungi. Mycoparasitic and fungicolous fungi are those that colonize other fungi, and could be potential sources of antifungal agents because of the negative effects exerted on their hosts due to this colonization. Endophytic fungi are those that colonize the inner tissues of plants in a symbiotic or a non-symbiotic manner. They may or may not be necessary for the growth, defense and survival of the host. They may protect the plants from attack by other pathogens by producing secondary metabolites that inhibit the growth of other pathogenic organisms. Many biologically active secondary metabolites have been isolated from various members of these two classes of fungi. During the course of this research fourteen new and several known compounds representing various biosynthetic classes including peptides, polyketides, terpenoids, and compounds with mixed biogenetic origins have been isolated and characterized using various tools such as NMR and MS. Details of the isolation, structure elucidation, and biological activity of these new compounds are presented in this thesis. Structure elucidation was performed mainly by analysis of various MS and NMR data, along with chemical derivatization reactions and/or X-ray diffraction analysis data. Absolute configuration assignments were made using, X-ray crystallography, and/or by ECD spectral analysis in combination with computational analysis.

Fungi continue to serve as valuable sources of a diverse variety of bioactive secondary metabolites, some of which have found applications as important pharmaceuticals and agrochemicals. Our research group employs an ecology-based strategy for the selection of fungi for chemical studies. The research described here involves chemical investigation of fungicolous and endophytic fungi that resulted in the isolation and identification of many new natural products, as well as some previously known metabolites. Mycoparasitic and fungicolous fungi are those that colonize other fungi, and are viewed as potential sources of antifungal agents because of the negative effects exerted on their hosts due to this colonization. Many antifungal compounds have been isolated by members of our research group from such fungi. Fractionation of the ethyl acetate extracts of cultures of thirteen fungal isolates, followed by characterization using various NMR and MS techniques, afforded fifteen new and twenty-six known compounds representing diverse structural classes. Some of these compounds showed antifungal and antiinsectan effects accounting for bioactivities originally observed for the crude extracts. Endophytic fungi are those that inhabit host plants asymptomatically and may or may not cause disease after some time. Studies show that in some cases they may be beneficial to the host plant by providing protection against various pathogens or by improving the resistance of the host in some way. Such advantages may be due, at least in part, to the production of bioactive secondary metabolites by these fungi. Chemical investigations of seven crop endophytes led to the isolation and characterization of eleven new and twenty-eight known compounds. Some of these fungal known fungal metabolites exhibited antifungal, antimicrobial, and/or antiinsectan effects, and may therefore provide insight into the potential protective roles of the corresponding crop endophytes against plant pathogens or insect pests. The fungal secondary metabolites isolated during the course of these studies represent a variety of biosynthetic classes, including peptides, polyketides, terpenoids, and compounds with mixed biogenetic origins. Details of the isolation, structure elucidation, and biological activity of these new compounds are presented in this thesis. Structure elucidation was performed mainly by analysis of various MS and NMR data, although chemical derivatization reactions and/or X-ray diffraction analysis data were employed in some instances. Absolute configuration assignments were made using Mosher's method, X-ray crystallography, and/or by ECD spectral analysis in combination with computational analysis. Details of the isolation, structure elucidation, and biological activity of these new compounds are presented in this thesis.

In spite of significant shortcomings among existing clinical antifungal agents, the rate of development of new therapeutics has been sluggish, and the mortality rate caused by fungal diseases has remained almost unchanged. Natural products have provided useful templates for the development of several of the most important therapeutic antifungal agents. In particular, fungi have been rich sources of antifungal natural products, and many fungal species remain chemically underexplored. Our research program has focused on fungicolous and coprophilous fungal niche groups. These types of fungi often show antagonistic effects toward host or competitor fungi—a phenomenon hypothesized to be associated in part with the production of antifungal metabolites. Earlier results reported from our research program have shown that studies of such fungi can be effective approaches to the discovery of new bioactive natural products, including antifungal agents. During our continued efforts to discover new antifungal and antiinsectan natural products, diverse fungal metabolites were obtained from complex fermentation extracts by use of various chromatographic methods. In addition to previously known compounds and simple analogues thereof, structurally interesting new metabolites were encountered. Those isolated from fungicolous fungi include ten new caryophyllene-type sesquiterpenoids from a Pestalotiopsis sp., three of which contain previously undescribed ring systems or new skeletons. The remainder are oxidized analogues of punctaporonins. Seven new polyketide-derived metabolites were obtained from another Pestalotiopsis isolate, in this case, P. disseminata, and two unusual ring systems were identified. A distinctive biosynthetic pathway was proposed for these seven polyketides. Members of another class of polyketides (pyrenocines), which contain pyrone or thiopyran units, were encountered from Penicillium paxilli. One of the three new pyrenocine analogues obtained contains an adenine unit—a rare feature among fungal secondary metabolites. Chemical investigation of another Penicillium sp., P. lanosum, afforded a new fumiquinazoline analogue, as well as a compound previously described in a thesis of a member of our research group. In work described here, the original stereochemical assignment was revised, and the compound was renamed as lanosindole. Metabolites isolated from this fungicolous Penicillium isolate have amino acid origins in common, and two of them showed antiinsectan activity. Seven new polyketide alcohols were obtained from the coprophilous fungus Podospora appendiculata. Two of them contain a tetrahydropyran unit and three are acyclic, differentiating them from other known members of this class. Finally, funiculosin B, an antifungal metabolite of mixed biogenetic origin containing a rare tetrahydroxycyclopentanyl moiety, was isolated from a flower-colonizing isolate of Capnodium sp. The structures of the compounds described above were determined mainly by analysis of NMR and MS data. Synthetic modification, X-ray crystallographic analysis, and ECD data analysis in conjunction with molecular modeling were applied to their stereochemical assignments. The results described in this thesis indicate that fungicolous and coprophilous fungi are prolific producers of new natural products, some of which display activity in assays of medical and agricultural relevance. Although most of the new compounds described here were inactive against pathogenic fungi, the rich diversity of chemistry encountered suggests potential for this ecology-based approach in the discovery of new bioactive natural products.

Fungi are rich sources of structurally diverse secondary metabolites, some of which possess biological activities of importance to medicine and agriculture. Research in our group focuses on application of ecological considerations to the selection of underexplored fungi for chemical analysis in search of new natural products with potentially important bioactivities. The work described in this thesis involved studies of members of two different fungal ecological groups, fungicolous and endophytic fungi. Fungicolous fungi colonize other fungi and are viewed as potential sources of antifungal agents due to the negative effects often exerted on the host organisms. Our prior studies of such fungi have proven them to be productive sources of new bioactive natural products. Fractionation of extracts produced from eleven fungicolous fungal isolates resulted in the isolation and identification of 24 different, structurally-diverse natural products, many of which were bioactive. Most of these were previously known, but six were new compounds, with one being a distinctive new peptaibol-type metabolite. Endophytic fungi colonize the inner tissues of host plants, often asymptomatically, and occur widely in most plant species. Some endophytes may benefit the host, possibly through production of protective secondary metabolites, but in most cases, their roles are not well understood. Stenocarpella maydis is a widely occurring fungal endophyte and pathogen of corn and is associated with diplodiosis (a neuromycotoxicosis) of cattle. Investigations of extracts of S. maydis and S. macrospora cultures led to the identification of seven compounds, including diplodiatoxin, diplosporin, chaetoglobosins K, L, M, and O, and (all-E) trideca-4,6,10,12-tetraene-2,8-diol, none of which were previously known from U.S. Stenocarpella isolates. Diplodiatoxin was detected as a major component of S. maydis-rotted maize grain, stalks, and stalk residues, and chaetoglobosin M was detected in extracts of naturally-diseased S. maydis-rotted maize seeds collected in the field. Chaetoglobosin K displayed potent antifungal and antiinsectan activity, while diplodiatoxin displayed phytotoxicity. Because of their well-known cytotoxic effects, we proposed that mixtures of chaetoglobosins are responsible, at least in part, for inducing diplodiosis in livestock. Our prior investigations of another common corn endophyte, Acremonium zeae, led to isolation of the pyrrocidines, which display potent antifungal and antibacterial activities against a range of corn pathogens. Further studies of these extracts led to the isolation and identification of three resorcylic acid lactone (RAL)-type compounds, one of which was new. These RAL's, did not exhibit antifungal activity, but demonstrated mild phytotoxicity to maize leaves in assays. They are also members of a compound class we have encountered among other endophytes that inhibit the heat shock protein Hsp90, and have been proposed to play a role in the colonization process. These chemical investigations provide further knowledge that may be useful in determining the roles that endophytes, in particular S. maydis and A. zeae, play in maize. The metabolites encountered during these investigations represented different biosynthetic pathways, and included polyketides, terpenoids, and compounds of mixed biogenetic origin. Structures were characterized by analysis of 1D and 2D NMR data, mass spectrometry, chemical degradation or derivatization reactions, and/or X-ray diffraction analysis. Absolute configuration assignments were determined using Mosher's method, Marfey's method, or chiral amino acid analysis methods.

Many years of study have revealed that fungi are excellent sources of novel bioactive secondary metabolites. Some of these secondary metabolites possess therapeutic qualities that improve the quality of life for millions of people. Such metabolites include well known classes such as the penicillins, cephalosporins, and statins, yet many fungi remain underexplored as sources of biologically active metabolites. The research described in this thesis employs an ecology-based approach to targeting fungi for chemical investigation, and describes studies of fungi from two niche groups, fungicolous/mycoparasitic and endophytic fungi, as possible sources of new secondary metabolites with biological activities. In a parallel project, the structures of bioactive compounds isolated from peanut seeds that had been subjected to fungal attack were elucidated in the pursuit of compounds with beneficial bioactivities. Mycoparasitic fungi are those that colonize other fungi by parasitizing the host, often leading to damage to the host fungus. Fungicolous fungi are those that colonize other fungi, but have not been proven to be true mycoparasites. The damage often caused by colonization of host fungi indicates that mycoparasitic and fungicolous fungi can produce antifungal compounds. Chemical investigations of such fungi described in this thesis afforded 37 compounds of various biosynthetic types, seven of which were new. Many of these compounds show antifungal, antimicrobial, and/or cytotoxic effects. Endophytic fungi live asymptomatically within plant tissues and in some cases may provide benefits to the host plant through the production of secondary metabolites. Chemical investigations of corn, wheat, and sorghum endophytes led to the isolation and characterization of 21 compounds, seven of which were new. Many of the endophyte metabolites encountered in this work showed antifungal, antimicrobial, and/or cytotoxic effects. The compounds isolated from peanut seeds were produced in response to fungal attack by an Aspergillus caelatus strain. All of these compounds were stilbene-derived phytoalexins, which are considered to be inducible chemical defenses whose production is elicited or enhanced upon microbial attack. Further studies of these newly identified compounds and their production could lead a a better understanding of how the plant defends itself. Such knowledge could enable researchers to manipulate this mechanism to obtain greater peanut resistance to invasion by pests. Additionally, the health benefits from related stilbene-derived compounds (e.g. resveratrol) from peanuts and other plants have been widely established. Knowledge about the presence of compounds of this type could add to the importance of peanut crop production. The compounds identified in this work were isolated using multiple chromatographic techniques, and the structures were established based on analysis of 1D and 2D NMR data combined with MS, chemical derivatizations, and/or optical measurement data. Absolute configuration assignments were achieved by application of Mosher's Method, CD spectral analysis, and/or chemical derivatizations. Details of the isolation, structure elucidation, and biological activity of these compounds are presented in this thesis.