The production of reactive oxygen species by mitochondria is implicated in mitochondrial dysfunction associated with a range of diseases and ageing. In addition, reactive oxygen species produced by mitochondria are involved in redox signalling pathways that modulate a number of cell processes. Mitochondria targeted antioxidants comprised of an antioxidant moiety linked to a lipophilic triphenylphosphonium cation have recently been used to decrease oxidative damage to mitochondria and to investigate the involvement of mitochondrial reactive oxygen species in redox signalling. These lipophilic cations are selectively accumulated by mitochondria within cells due to the mitochondria membrane potential. This thesis presents the synthesis and characterization of mitochondria targeted membrane uncoupler, cyclic nitroxide and alkyl thionitrite derivatives, all of which had the potential to influence reactive oxygen species. The biological analysis of these compounds is also presented.
A triphenylphosphonium derivative of the membrane uncoupler 2,4-dinitrophenol (DNP) was anticipated to act as a self regulating protonophore. The DNP moiety would influence the scale of the membrane potential while the triphenylphosphonium cation would respond to the membrane potential. These two factors would combine so that as the membrane potential was dissipated by the uncoupler, the phosphonium cation would be released from the mitochondria and the effect of the uncoupler would thereby be nullified until the membrane potential had increased again. The compound was prepared by nitration of 3-(4-hydroxyphenyl)propyl triphenylphosphonium bromide. An untargeted derivative was also prepared by nitration of 3-(4-hydroxyphenyl)-1-propanol. Unfortunately, while this compound had appropriate acidity and lipophilicity to act as a membrane uncoupler, and did enter mitochondria in response to the membrane potential, it did not act as an uncoupler.
A chemically stable targeted cyclic nitroxide based on Tempol was prepared following literature procedure, although other synthetic routes were also trialled. This compound was shown to concentrate in mitochondria in response to the membrane potential, was reduced by ubiquinol of the coenzyme Q pool, acted as a superoxide dismutase mimetic, and protected membranes against lipid peroxidation.
A mitochondria targeted thionitrite or nitric oxide (NO) donor was anticipated to exhibit an effect on respiration at low oxygen concentrations as the released NO interacted with aspects of the respiratory chain. The alkyl thionitrites were synthesised from appropriate thiol precursors, several of which were prepared. Two targeted alkyl thionitrites were prepared with primary or tertiary carbon arrays next to the thionitrite functionality. Another targeted thionitrite, based on S-nitroso-N-acetylpenicillamine (SNAP), was also prepared. These compounds were difficult to characterise because of issues surrounding their stability. However, modified high resolution positive ion electrospray mass spectrometry in combination with HPLC and NMR was used to identify the compounds and to gauge the purity of the samples. Initial biological investigations verified that the primary alkylthionitrite derivative accumulated in mitochondria, released NO, and had an effect on respiration at low oxygen concentrations.
| Identifer | oai:union.ndltd.org:ADTP/217814 |
| Date | January 2008 |
| Creators | Blaikie, Frances H, n/a |
| Publisher | University of Otago. Department of Chemistry |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Frances H Blaikie |
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