Chemical investigations of secondary metabolites from selected fungi and from peanut seeds challenged by Aspergillus caelatus

Abstract

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 representing 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 described in this thesis led to the isolation and characterization of 20 compounds, seven of which were identified as being new. Many of the fungal metabolites encountered in this work showed antifungal, antimicrobial, and/or cytotoxic effects. vi TABLE OF CONTENTS LIST OF TABLES .

Chemical investigations of endophytic and fungicolous fungi

“…A complete set of NMR data are reported in the group member's thesis. 140 In examining the 1 H NMR spectrum of unrelated MYC-1906a metabolite 6.3 (Table 6. Even though a complete structure assignment could be made, compound 6.3…”