Thesis (Phd (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / Dissertation presented for
the degree of
Doctor of Philosophy
(Chemistry)
at
Stellenbosch University. / ENGLISH ABSTRACT: The human pathogen Staphylococcus aureus is a major cause of hospital-, and more recently,
community-acquired infections. The rate at which this organism is acquiring resistance to
antibiotics is increasing while the development of new antibiotics is slowing down. There is
therefore a desperate need for new antistaphylococcal agents, and in particular ones with novel
mechanisms of action that can be used to circumvent established resistance pathways. Unlike
humans, S. aureus employs the essential cofactor coenzyme A (CoA) as its major low molecular
weight thiol. Together, CoA and the enzyme CoA disulfide reductase (CoADR) are responsible for
maintaining the internal redox homeostasis in this organism, and disruption of this balance (or
reduction of CoA levels) may therefore be potential mechanisms by which new antistaphylococcal
agents may act. In this study we set out to achieve this by direct inhibition of CoADR, and by
inhibition of one or more of the CoA biosynthetic enzymes.
For the inhibition of CoADR CoA analogues containing Michael acceptors were designed and
prepared by employing a chemo-enzymatic approach. This strategy involved the chemical
synthesis of pantothenamides containing α,β-unsaturated ester, ketone and sulfone moieties as
Michael acceptors, followed by their biotransformation into the corresponding CoA analogues by
three CoA biosynthetic enzymes. The compounds prepared in this manner all inhibited CoADR
potently. A full kinetic evaluation of the inhibition by these compounds suggested that these
compounds act by alkylation of the single active site cysteine of CoADR in an irreversible fashion.
In this study we also set out to determine the mechanism of action of the antistaphylococcal
compound CJ-15,801, which is structurally similar to pantothenic acid, the biosynthetic precursor of
CoA. Due to this similarity we proposed that the antibiotic properties of CJ-15,801 are based on the
inhibition of enzymes involved in CoA biosynthesis and metabolism. Our investigations confirmed
that the second enzyme of the CoA pathway, phosphopantothenoylcysteine synthetase (PPCS),
acts as the main target of CJ-15,801. These studies were followed by an investigation into
alternative synthetic methodologies for the preparation of CJ-15,801 and its analogues. As a result
an established Pd-catalyzed coupling reaction was modified and applied in the third known total
synthesis of CJ-15,801, as well as of several of its analogues. This protocol has several
advantages over its predecessors, most importantly its suitability for preparing these compounds
on large (up to one gram) scale. / AFRIKAANSE OPSOMMING: Die menslike patogeen Staphylococcus aureus is 'n wesenlike oorsaak van hospitaal- en meer
onlangs gemeenskap-verworwe infeksies. Terwyl die tempo waarteen hierdie organisme
weerstandbiedig teenoor antibiotika raak toeneem, neem die ontwikkeling van nuwe antibiotiese
middels af. Dit is dus van kardinale belang dat nuwe antistafilokokale middels ontwikkel word, en
meer spesifiek antibiotika met 'n nuwe meganisme van aksie wat gebruik kan word om huidige
weerstandbiedende padweë te ontwyk. In teenstelling met mense, gebruik S. aureus die
essensiele kofaktor koënsiem A (KoA) as sy vernaamste lae molekulere gewig tiol. Die ensiem
KoA disulfied reduktase (KoADR) en KoA is saam verantwoordelik om die interne redoks
homeostase in hierdie organisme te handhaaf, en ontwrigting van die balans (of vermindering van
KoA vlakke) kan dus potensieel 'n meganisme van aksie wees waardeur nuwe antistafilokokale
middels kan optree. In hierdie studie het ons gepoog om dit te bewerkstellig deur KoADR direk te
inhibeer, asook deur inhibisie van een of meer van die KoA biosintetiese ensieme.
Vir die inhibisie van KoADR is KoA-analoë wat Michael-akseptor groepe bevat ontwerp en berei
deur van 'n chemo-ensiematiese benadering gebruik te maak. Met hierdie strategie is
pantoteenamiede gesintetiseer wat α,β-onversadigde ester, ketoon en vinielsulfoon funksionaliteite
as Michael-akseptore bevat, gevolg deur biotransformasie na die ooreenstemmende KoA-analoë
met behulp van drie CoA biosintetiese ensieme. Die verbindings gesintetiseer met hierdie metode
het almal KoADR potent geinhibeer. 'n Omvattende kinetiese evaluasie het voorgestel dat al
hierdie verbindings funksioneer deur alkielering van die enkele aktiewe setel sisteïen van KoADR
op 'n onomkeerbare wyse.
In die studie het ons ook gepoog om die meganisme van aksie van die antistafilokokale verbinding
CJ-15,801 te bepaal. Hierdie verbinding is struktureel soortgelyk aan pantoteensuur, die
biosintetiese voorganer van KoA. As gevolg van hierdie ooreenkomste het ons voorgestel dat die
antibiotiese aktiwiteit van CJ-15,801 die gevolg is van die inhibisie van een of meer van die
ensieme wat verantwoordelik is vir KoA biosintese en metabolisme. Ons ondersoeke het bevestig
dat die tweede ensiem in die KoA biosintetiese padweg, naamlik
fosfopantotenoïelsisteïensintetase, die hoofteiken van CJ-15,801 is. Hierdie studies is gevolg deur
die ondersoek van alternatiewe metodologieë vir die sintese van CJ-15,801 en analoë daarvan. 'n
Gevestigde Pd-gekataliseerde koppelings reaksie was gevolglik gemodifiseer en toegepas om
slegs die derde totale sintese van CJ-15,801 te bewerkstelling, asook die sintese van verskeie
analoë daarvan. Hierdie protokol hou verskeie voordele in vergelyking met sy voorgangers,
waarvan die mees belangrikste die bereiding van hierdie verbindings op groot (tot een gram) skaal
is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5464 |
| Date | 12 1900 |
| Creators | Van der Westhuyzen, Renier |
| Contributors | Strauss, Erick, University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
Page generated in 0.0024 seconds