Investigations of secondary metabolites from fungi: isolation, structure elucidation, and semi-synthetic studies

Peramuna, Peramunu

Investigations of secondary metabolites from fungi: isolation, structure elucidation, and semi-synthetic studies

dc.contributor.advisor	Cichewicz, Robert
dc.contributor.author	Peramuna, Peramunu
dc.contributor.committeeMember	Acar, Handan
dc.contributor.committeeMember	White, Robert
dc.contributor.committeeMember	McCall, Laura-Isobel
dc.date.accessioned	2022-12-20T15:26:28Z
dc.date.available	2022-12-20T15:26:28Z
dc.date.issued	2022-12-16
dc.date.manuscript	2022
dc.description.abstract	Trichomoniasis, caused by Trichomonas vaginalis remains a worldwide threat, afflicting an astonishing 3.9% of the world’s population. This parasite is recognized as a cause of vaginitis and can result in serious health consequences including infertility, premature delivery, and neonatal death. Currently nitroimidazoles (metronidazole and tinidazole) has been the treatment of choice for decades. However, nitroimidazole resistance has been detected up to 9.6% of clinical T. vaginalis isolates, which makes the spread of drug resistance a realistic concern. Mycoplasma genitalium is a sexually transmitted pathogenic bacterium that resides in the genitourinary tract in humans. It has been implicated in urogenital infections of both men and women, which include preterm birth, cervicitis and more importantly recognized as an independent etiologic agent of acute and persistent male NGU (non-gonococcal urethritis). The rapidly increasing resistance to the recommended first and second line antibiotics (macrolides and quinolones) has necessitated the need to explore novel drug targets in this pathogen. Our previous studies based on identifying fungal derived bioactive natural products against T. vaginalis led to the discovery of decalin-linked tetramic acid containing metabolites. Interestingly, this series of tetramic acids also exhibits potent activity against M. genitalium. An exploratory structure-activity study of phomasetin (1) was undertaken to identify the structural features that drive the bioactivity. Further, tetramic acid of 1 and pyrrolocin A (2) was derivatized using ‘click’ chemistry to modify the bioactivity. The semisynthetic analogues of 1 and 2 hold promise to improve treatment options against T. vaginalis and M. genitalium through the creation of compounds that exhibit improved activity and selectivity. The other approach to explore novel drug targets in M. genitalium includes identifying bioactive natural products from fungi. To address this, we have screened samples from a fungal natural product extract library assembled through the University of Oklahoma Citizen Science Soil Collection Program. Analysis of one of the bioactive extracts using bioassay guided fractionation led to the purification of the compound PF-1140 along with a new and several other known pyridones. The N-hydroxy pyridones are generally regarded as siderophores with high binding affinity for iron (III) under physiological conditions. Results from UV-vis absorption spectroscopy-based titration experiments revealed that PF-1140 is capable of undergoing complexation with several metals including Fe3+, Co2+, Ni2+ and Cu2+. The results suggest that metal chelation may play an important role in the potent inhibition of M. genitalium survival through disruption of metal homeostasis. Chromosome segregation is an essential cellular process that has a potential to yield numerous targets for drug development. This pathway is presently under-utilized partially due to the difficulties in the development of robust reporter assays suitable for high throughput screening. In bacteria, chromosome segregation is mediated by two partially redundant systems, condensins and ParAB. These two systems are synthetically lethal in Pseudomonas aeruginosa, giving rise to a straightforward screening assay based on cell viability. Using this assay, we screened a library of fungal extracts for potential inhibitors of the ParAB pathway as judged by their enhanced activity on condensin-deficient cells. We found such activity in extracts of Humicola variabilis and fractionated it to several novel [sterigmatocystin NPDG 1, sterigmatocystin NPDG 2, sterigmatocystin NPDG 3, sterigmatocystin NPDG 4 and sterigmatocystin NPDG 5] and two known analogues including sterigmatocystin (6) and deoxysterigmatocystin (7). The analog sterigmatocystin NPDG 1 induced defects in chromosome segregation which manifested themselves as increased frequencies of anucleate cells in drug-treated cells and a delay in cell division. Overproduction of Par A and Par B altered the susceptibility of bacteria to sterigmatocystin, indicating that the drug directly interacts with the proteins. Sterigmatocystin analogs varied in their potency revealing the importance of the terminal benzoic ring of the molecule, and the structural basis for this variability was suggested by molecular docking studies. The data describe the first known inhibitor of ParAB and expand the known spectrum of activities of sterigmatocystin to include bacterial chromosome segregation.	en_US
dc.identifier.uri	https://shareok.org/handle/11244/336970
dc.language	en_US	en_US
dc.subject	fungal natural products	en_US
dc.subject	isolation and structure elucidation	en_US
dc.subject	semi-synthetic studies	en_US
dc.thesis.degree	Ph.D.	en_US
dc.title	Investigations of secondary metabolites from fungi: isolation, structure elucidation, and semi-synthetic studies	en_US
ou.group	Dodge Family College of Arts and Sciences::Department of Chemistry and Biochemistry	en_US
shareok.orcid	0000-0002-9372-1370	en_US